MUD CIRCULATION & TREATING EQUIPMENT

MUD SYSTEM OVERVIEW

Overview

The rig uses many pieces of equipment to circulate and treat or condition the mud.

Mud Tanks

Mud circulation begins here, in the mud tanks, sometimes called pits. Crew members prepare the mud in these tanks and make it ready for circulation

Mud Pumps

The heart of the circulating system is the mud pump. Often, rigs have two pumps, one primary pump and one for back up. Or, if hole conditions required, the driller can compound or combine the two pumps to circulate large volumes of mud. In fact, on deep wells, the rig may have three or four compound pumps. The powerful pump, or pumps, pick up mud from the mud tanks and send it to the drill string and bit. The pump moves the mud into the discharge line, up to standpipe and into the rotary hose.

Standpipe & Rotary Hose

The standpipe takes the mud about half way of the mast. The rotary hose is attached to the standpipe. The rotary hose is strong, flexible hose that moves with the swivel as it goes up and down in the mast. From the rotary hose, the pump moves mud through the swivel and then down the kelly and drill string. On rigs with a top drive, the mud moves through a passage in the top drive and then into the drill string.

Bit & Annulus

The pump moves the mud down the drill string to the bit. At the bit, the mud jets out of the openings or nozzles in the bit. The jets of mud move cuttings away from the bit. Mud then continues up the annulus, carrying the cuttings with it.

Return Line, Shaker & Mud tanks

From the annulus, the mud with the cuttings in it goes through the return line, sometimes called the Flow Line, to the shale shaker. The shale shaker removes the cuttings from the mud. The mud then falls into the mud tanks, where the mud pump can pick it up and continue the circulation process.

[TOOL BOX]: Arrange this circulating equipment in proper order, place the mouse around the component, click and hold on it and move it to its proper position. The mud pump is in position, what comes next?

MUD STORAGE, TANKS & RESERVE PIT

Overview:

Mud is made up at the rig location. Most rigs have several steel mud tanks. Mud and additives are mixed and held in the tanks. Some land rigs also have a reserve pit dug out of the ground. Mud tanks are also called mud pits, a carrier over from the days of earthen pits, mud tank is the preferred term. The rig does not necessarily use all the mud tanks at once, although it does use several. The active tanks hold mud the pump actively circulates.

Mud House

Often, mud components come to the rig in sacks. Normally, the crew stores the sacks in a special compartment called the mud house or sack room. The house or room keeps the sacks dry and allows them to be stored with care.

Bulk Tank

These silo-like tanks are bulk tanks or P-tanks. They hold mud additives like barite and bentonite. Crew members use some additives in such large quantities that suppliers load them into the bulk tanks to save time and money. Bulk tanks usually have their own hopper or pneumatic system for transferring the additives to the mud system.

Active Tank

The pump takes the mud out of the active mud tanks and circulates it through the system. Crew members connect the mud tanks with the piping and manifold. The number of active mud tanks depends on the amount of mud needed to keep the hole full, and the volume required on the surface to keep the mud in good condition for circulating.

Sand Trap

The sand trap is the tank directly below the shale shaker. The shale shaker removes most of the cuttings from the mud, but some are so small the shaker cannot trap them. These fall into the sand trap. The sand trap is the first settling tank. Crew members have to clean it regularly to remove the built-up solids.

Settling Tanks

Some small or old rigs may have two or more settling tanks in the tank system. They allow solids in the mud to settle out, but settling tanks do not do a very good job as compared with newer generation solids-removal equipment. So, today, most rigs use a dessander and desilter.

Reserve Tanks

Reserve tank is not a part of the active mud tank system, instead, the crew uses them to hold excess mud, or they may use them to mix a different type of mud in the pump’s currently circulating. They may also store heavy mud for emergency well control operations.

Slug Tank

A slug tank is a relatively small separate tank, or it may be a small separate part of a larger tank. The crew uses the slug tank to mix a slug. A slug is a small amount of heavy mud that is pumped down the string. Crew members may also use the slug tank to mix a small amount of mud for a special purpose. For example, the driller may need place or spot a small quantity of high viscosity mud, also called a pill, at some point down hole.

Suction Tank

The suction tank is where the mud pump picks up mud ready to circulate down hole. Mud in the suction tank should be clean, free of solids & gas, and be properly formulated or conditioned.

Chemical Tank

Crew members use the chemical tank to make special chemicals, such as caustic, that they will put into the active mud tanks.

Reserve Pit

On some land rigs, the rig owner digs a large pit next to the rig. This pit is called the reserve pit. The crew puts waste mud and run-off from the rig site in the reserve pit. In an emergency, they can also use it as a place to put more mud than the tanks can hold. Often, the rig operator lines the reserve pit with a thick plastic sheet to prevent liquids from leaching into the soil. And if the rig is on a migratory bird fly way, the operator covers it with a netting to keep the waterfowl from landing in it. Land rigs drilling in environmentally sensitive areas will not have a reserve pit. Instead, waste & run-off of a hole to an approved waste disposal area.

[TOOL BOX]: Here is your chance to be the driller’s assistant and carry out task to keep the mud system operating properly. For each task the driller gives you, click the location where the task will be carried out. When you select the right location, you’ll get your next instructions. See if you can carry out all five tasks before the timer runs out. Click “begin” when you’re ready to start.

MUD PUMPS

Over View

Powerful mud pumps pick up mud from the suction tank, and circulate the mud down hole, out the bit, and back to the surface. Although rigs usually have two mud pumps, and some times three of four, normally they use only one at a time. The others are mainly used as back up in case one fails. Sometimes however, the rig crew may compound the pumps. That is, they may use two, three or four pumps at the same time to move large volumes of mud when required. Rigs use one of two types of mud pumps: triplex pumps or duplex plumps. Triplex pumps have three pistons that move back & forth in liners; Duplex pumps have two pistons that move back & forth in liners. Triplex has many advantages: they weigh 30% less than a duplex of equal horsepower or kilowatts; the lighter-weighted parts are easier to handle, and therefore easier to maintain. The other advantages include: they cost less to operate, their fluid end is more accessible, and they discharge mud more smoothly, that is the triplex’s output does not surge as much as duplex. One of the most important advantages of triplex over duplex pumps is that they can move large volumes of mud at the higher pressure required for modern deep hole drilling. Triplex pumps are gradually phasing out duplex units.

Triplex Pump

In a triplex pump, the pistons discharge mud only when they move forward in the liner. Then when they move back, they draw in mud on the same side of the piston. Because of this, they’re also called “single-acting”. Single-acting triplex pumps pump mud at relatively high speeds. Input horsepower ranges from 220 to 2200 (from 164-1641 KW); large pumps can pump over 1100 gallons per minute (over 4000 liters per minute). Some big pumps have a maximum rated working pressure of over 7000 psi (over 50000KPa) with 5 inch (137 mm) liners.

Triplex Pump Operation

Here’s a schematic of a triplex pump. It has 3 pistons, each moving in its own liner. It also has 3 intake valves and 3 discharge valves. It also has a pulsation dampener in the discharge line. Look at the piston at left, it has just completed pushing mud out of the liner and through the open discharge valve. The piston is at its maximum point of forward travel; the other two pistons are at the other positions in their travel, also pumping mud. But right now, concentrate on the left one to understand how the pump works.

The left piston has completed its back stroke, drawing in mud through the open intake valve. As the piston moved back, it lifted the intake valve off its seat and drew mud in, a strong spring holds the discharge valve closed. The left piston has moved forward, pushing mud out through the now open discharge valve, a strong spring holds the intake valve closed. The left piston has completed its forward stroke, the full length of the liner, completely discharging the mud from it. All three pistons work together to keep a continuous flow of mud coming into and out of the pump. Crew member can change the liners and pistons, not only can they replace worn-out ones, but they can also install different sizes. Generally they use large liners and pistons when the pump needs to move large volumes of mud at relatively low pressure; they use small liners and pistons when the pump needs to move smaller volumes of mud at relatively high pressure.

[TOOL BOX]: You can control the position of the piston with your mouse to see how the triplex pump operates at any given point in this cycle.

Duplex Pump

In a duplex pump, the pistons discharge mud on one side of the piston and at the same time, taking in mud on the other side. Notice the top piston and liner. As the piston moves forward, it discharges mud on one side as it draws in mud on the other. Then, as it moves back, it discharges mud on the opposite side and draws in mud on the side where it earlier discharged. Duplex pumps are therefore double-acting. Double-acting pumps move more mud on a single stroke than a triplex, however, because they’re double acting, they have a seal around the piston rod. The seal keeps them from moving as fast as triplex. Input horsepower ranges from 190 to 1790 (or from 142-1335KW). The largest pump’s max. rated working pressure is about 5000psi (almost 35000KPa) with 6 inch (152 mm) liners.

[TOOL BOX]: Triplex and duplex pumps are called reciprocating pumps because of the back & forth motion of their pistons. Use your mouse to move this duplex pump’s piston back & forth so you can study the pump’s operation.

Pump Components

A mud pump has a Fluid End, Power End and Intake & Discharge Valves. The fluid end of the pump contains the pistons with liners, which take in and discharge the fluid or mud. The pump’s pistons draw in mud from the intake valves and push mud out through the discharge valves. The power end houses the large crankshaft & gear assembly that moves the piston assemblies in the fluid end. Pumps are powered by a pump motor. Large modern DC electric rigs use powerful electric motors to drive the pump. Mechanical rigs use chain drives or power bands (belts) from the rig’s engines and compound to drive the pump.

Bladder-type Pulsation Dampener

A pulsation dampener connected to the mud discharge line smooth out surges created by the pistons as they discharge mud. This is a standard bladder-type dampener. The bladder in the dampener body separates pressurized nitrogen gas above from mud below. The bladder is made from synthetic rubber and is flexible. When mud discharge pressure presses against the bottom of the bladder, nitrogen pressure above the bladder resists it. This resistance smoothes out the surges of the mud leaving the pump.

[TOOL BOX]: Here is a pump without a pulsation dampener. See the surges or pulses of high pressure mud leaving the pump. These surges can cause vibrations and damage or wear equipment. Add the pulsation dampener to see the difference it makes. Using your mouse, click on the pulsation dampener and drag it into place.

Non-bladder Type Pulsation Dampener

Here is the latest type of pulsation dampener. It does not have a bladder. It is a sphere about four ft (1.2 m) in diameter. It is built into the mud pump’s discharge line. The large chamber is full of mud. It has no moving parts, so it does not need maintenance. The mud in the large volume’s sphere absorbs the surge of the mud leaving the pump.

Suction Dampener

A suction dampener smoothes out the flow of the mud coming into the pump. Crew members mount it on a triplex mud pump’s suction line. Inside the steel chamber is an air-charged rubber bladder of diaphragm. The crew charges the bladder about 10-15 psi (50-100KPa). The suction dampener absorbs surges in the mud pump’s suction line caused by the fast moving pump pistons. The pistons constantly start and stop the mud’s flow through the pump. At the other end of the suction line, a charging pump sends a smooth flow of mud to the pump’s intake. When the smooth flow meets the surging flow, the impact is absorbed by the dampener.

Discharge Line Relief Valve

Workers always install a discharge pressure relief valve. They install it on the pump’s discharge side in or near the discharge line. If for some reason, too much pressure builds up in the discharge line, perhaps the drill bit or annulus gets plugged, the relief valve opens. The open valve protects the mud pump and system against damage from overpressure.

Suction Line Relief Valve

Some rig owners install a suction line relief valve. They install it on top of the suction line, near the suction dampener. They mount it on top, so it won’t clog up with mud when the system shut down. A suction relief valve protects the charging pump and the suction line dampener. A suction relief valve usually has a 2 inch (50 mm) seat opening. The installer normally adjusts it to a 70 psi (500KPa) reliving pressure. If both of the suction and discharge valves failed on the same side of the pump, a high back flow or a pressure surge would occur. The high backflow could damage the charging pump or the suction line dampener.

Pump Discharge Line

The discharge line is a high pressure line through which the pump moves mud. From the discharge line, the mud goes through the standpipe, and rotary hose, to the drill string equipment.

Mud Conditioning

Over View:

The shale shaker mechanically takes out the large cuttings from the mud. It does not, however, remove very fine cuttings and other small solid particles. These solids can be fine sand particles and other very fine materials, often called “silt”. Good drilling practice requires removing these undesirable solids. If not removed, the solids can increase the weight of the mud more than required, reduce the bit’s penetration rate and significantly increase the rate of wear on circulating equipment. The rig uses mechanical solids-removing equipment, such as hydrocyclones and centrifuges to remove the fine solids. Sometimes the hole penetrates a formation that has small amount of gas. This gas gets into the mud, becomes entrained in it and must be removed before the pump re-circulates the mud back down hole. A degasser removes entrained gas from the mud.

Shale Shaker

The shale shaker has rapidly vibrating screens. The mud and cuttings from the return line fall onto it. The vibrating screens catch the larger cuttings. These cuttings fall into the reserve pit, the sea, or other container for disposal. The liquid mud goes into the sand trap, which is a special mud tank. Shale shakers look simple, in fact, though, manufacturers carefully design them to make the screens vibrate in a very-controlled way.

Degasser

Sometimes, the crew sends mud through a vacuum degasser. The degasser removes gas from the mud. If the gas were not removed, it could make the mud too light, not dense enough. As a result, the well could kick, formation fluids could enter the well bore and have to be controlled to prevent a blowout. Another problem, if the driller recirculates gas-cut mud, the gas could cause the mud pump to gas-lock. Gas-locked pumps pump gas and mud instead of just mud, which is highly inefficient. So to remove gas, crew members use a degasser.

Vacuum Degasser Operation

In a vacuum degasser, mud with gas in it enters at the top and spills out over special baffle plates, a spreader. Spreading out of the mud presents a large surface area for the gas to break out. Also the vacuum pump creates a vacuum, pressure lower than the surround atmosphere inside the degasser. This vacuum makes it very easy for the gas to escape from the spread-up mud. The removed gas leaves through a vent, which sends the gas a safe distance away from the rig. The gas-free mud falls to the bottom and goes back into the mud tank’s down stream from the degasser.

Hydrocyclone

A hydrocyclone system consists of several cones. Mud enters through a side opening at the large end of each cone. It swirls around inside the cone. This centrifugal force or cyclone motion throws the larger particles to the side of the cone. There the particles move to the bottom of the cone and drop out. Clean mud goes out the outlet at the top. A desander has large cones, it removes particles as small as about 40 microns. A micron is one millionth of a meter, which is very small. A desilter has smaller cones than a desander. Disilters remove particles down to about 20 microns. A mud cleaner has steel smaller cones, it removes particles down to bout 7 microns. Since barite, the desirable solid, which gives weight to the mud, is also about 7 microns, screens are included on mud cleaners to retrieve the barite so that it can be returned to mud system.

Hydrocyclone Operation

Inside the cone, mud enters from the side and spirals down. This movement flings the solids to the side. The spiraling action creates a vortex in the center, somewhat like a tornado. It is an area of lower pressure, so the vortex sucks the liquid mud up through the center and out through the top of the cone. Meanwhile, the solids slide down the side and out of the bottom of the cone. The smaller the cone, the smaller is the particle it can remove, but more cones are needed to handle a given volume of mud.

Centrifuge

A centrifuge spins mud at high speed. This creates centrifugal force. Centrifugal force throws the particles to the side of the centrifuge, where they’re removed. A centrifuge removes particles as small as 2-5 microns, which includes barite. Sometimes, crew members run a centrifuge at a specific speed to remove barite so the rig can use it again on a next tool. Occasionally, the rig owner runs two centrifuges, the first removes the barite, and the second the finer particles. Crew members then re-add the barite to the mud system.

Agitator

Crew members mount agitators on one or more of the tanks. Agitators stir the mud in the tanks to keep solids from settling and to maintain uniform mud properties. One popular agitator is the paddle-type, an electric motor rotates paddle to stir the mud.

Pit Volume Totalizer

A Pit Volume Totalizer, or PVT, alerts the driller to changing the level of mud in the tanks. A float in each tank rises or falls if the mud level rises or falls. For example, if the level rises, the rising floats send a signal to a recorder and to a digital panel on the rig floor. The panel alerts the driller of the rise. This device is called a pit volume totalizer, or PVT, because it measures the gain or fall in each of the tanks or pits, totals the gain or fall and sends this information to the driller on the rig floor. If the mud level in the tanks fall, the PVT also alerts the driller. This float in a mud tank is part of a pit volume totalizer. Usually, crew members install a float in each active tank. The floats rise or fall with the mud level in the active tanks. Mud level in the tanks is vital information. If the mud level rises, it often means that the well has kicked, formation fluids have entered the hole and forced mud out. The kick fluids replace mud in the hole and cause the mud level in the tanks to rise. On the other hand, if mud begins going into a formation, if mud is lost to the formation, the mud tank level drops. Lost circulation can also be a serious problem. The decrease in height of mud in the hole could lead to a kick, because hydrostatic pressure is reduced. Also drilling without mud returning to the surface is like drilling blind, no communication between the bottom of the hole and the surface exists.

Centrifugal Pump

The mud system normally has several centrifugal pumps. A centrifugal pump puts out relatively low pressure but it can move a large volume of mud. Crew members therefore use them in several ways. One job a centrifugal pump often does is supercharge the mud intake of the main mud pump. The small pump takes the mud from a suction tank, moves it through a line connected to the main pump suction line and keeps the suction line full of mud at all times. If the system does not use a charging pump, the force of gravity alone feeds the pump’s suction line. Sometimes, gravity cannot keep the pump’s intake completely full of mud. The pump’s pistons suck in the mud so fast that gravity cannot keep the suction line full of mud. The crew also uses a centrifugal pump to make some mud components.

Hopper

A hopper is like a big funnel. Crew members put sacks of mud material into it. They do not, however, use the hopper to mix caustic soda. The hopper can blow dry caustic back into the face of the worker mixing it. In addition to being dangerous, adding caustic through the hopper can flocculate the mud, cause it to clog up.
[TOOL BOX]: It takes special personal protective equipment to handle caustic soda. When working with caustic, one must wear goggles, a face shield, rubber gauntlets, safety boots, coveralls, and a hard hat. Caustic soda should be mixed using the chemical tank, not the hopper.

Jet Hopper

A crew member opens the sack of material at the top of the hopper and feeds the material into the funnel. At the same time, a jet of mud from a centrifugal pump goes through a nozzle at the bottom of the funnel. This jet creates suction. The suction pulls the material into the mud stream and thoroughly mixes it.

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INTRODUCTION TO DRILLING FLUIDS

OVERVIEW

Drilling fluid or drilling mud as many people call it is a vitality in a rotary drilling process. The term “drilling fluid” includes air, gas, water and mud. “Mud” refers to the liquid that contains solids and water or oil. The mud is made up with clay and other additives that give it desirable properties.

MUD TYPES

Water Based Mud

Often, water is the base of drilling mud. Water makes up the liquid part or phase of a water-based mud. Crew members put clay and special additives into the water to make a mud with the properties needed to do its job well. For example, clays give it thickness or viscosity. The water in the mud may be fresh water, sea water or concentrated brine (salt water). The one used depends on its availability and whether it gives the mud the needed properties to drill the hole efficiently.

Oil Mud

At times, down hole drilling conditions require the crew to add oil to the mud, or in some cases, crew members use oil instead of water as the base of the mud. This is called oil-based mud. Oil based mud has many advantages. It can stabilize the formation and reduce downhole drilling problems. However, it is harder for the crew to work with because it can create slippery conditions and environmental precautions must be used. From an environmental standpoint, mud with oil is more difficult to handle because the oil clings to the drill cuttings. The oil must be cleaned off the cuttings before they’re disposed of.

Drilling with Air

Sometimes drilling fluid is dry air or natural gas. Here, dry air is coming out of the rig’s Blooey Line, carrying very fine drilled cuttings. Air drilling uses very large air compressors instead of mud pumps. Drilling with air or gas can prevent formation damage and can overcome severe lost circulation problems. And it allows the bit to drill very fast. Down hole conditions have to be just right for air or gas to be usable. For example, the bit cannot drill through formations containing large amounts of water. The water mixes with the cuttings and the air or gas and clogs up the hole.

Foam Drilling

If small amounts of water are present in the formations being drilled, special equipment can inject a foam agent into the air stream. The foam helps separate the cuttings and remove water from a hole.

Aerated Drilling

In some cases, the rig operator may use aerated mud, which like foam drilling, helps prevent clogging of the well bore. Aerated drilling uses both mud and air pumped into the standpipe at the same time.

DRILLING FLUID FUNCTION

Overview

When circulated down the drill string and up the hole, drilling mud serves many functions. For example, mud cleans the hole, cools and lubricates the bit & the drill string, lifts cuttings to the surface, carries information about formations being drilled, stabilizes the well bore, controls formation pressure and suspends cuttings when pumping stops.

Cleaning the Hole

One function of mud is to clean the hole. A clean hole allows the bit to drill into uncut formation rock. Here is an example of what can happen when cuttings are not moved off bottom. Mud jets out of the bit and moves cuttings away from the bottom of the hole. The mud then carries the cuttings up the annulus and to the surface for disposal.

Cooling / Lubrication

Heat is encountered down hole. Deep formations can be very hot and friction from rotating drilling components generates a lot of heat. High temperatures increase drill string and bit wear. Drilling fluid helps to reduce the temperature in the drill string down hole while drilling. In addition, drilling fluid provides lubrication to the drill string and bit that helps prevent wear.

Protecting Wellbore Walls

Mud stabilizes the hole, keeps it from caving in. As mud moves up the hole, it usually flows by permeable formations. Permeable formations although allow the fluid to flow, when the mud is next to a permeable formation, pressure forces the liquid part of the mud, the filtrate, into tiny openings or pore spaces in the formation. This leaves behind a thin sheet of solid particles, known as mud cake. These solids plaster the side of the hole, much like the plaster on the wall of a building. The wall cake helps keep the well from caving in.

Controlling Formation Pressure

The column of mud in the well creates pressure down hole, called hydrostatic pressure. The hydrostatic pressure of the mud column offsets formation pressure. Mud is the first line of defence in well control. As long as the hole is full of mud, that is the right weight, the well cannot kick and perhaps blowout. A kick is the entry of formation fluids into the well bore. The kick forces drilling mud out of the hole. If crew members fail to control a kick, a blowout can occur. A blowout is the uncontrolled flow of drilling mud and formation fluids out of the hole.

Obtaining Downhole Information

Mud is also used to obtain information about formations down hole. Mud loggers, by examining cuttings at the surface, can gather important information about the formation being drilled and the conditions down hole.

MUD PROPERTIES & ADDITIVES

Bentonite

In water, or oil based drilling mud, crew members usually add clay, called bentonite, or similar mineral. Bentonite swells in water, therefore thickens the mud, gives viscosity, to help clean the cuttings from the hole and provide other desirable properties.

[TOOL BOX]: Viscous fluids are more resistant to flow. Honey is a good example of a viscous fluid, pure water is not viscous.

Barite

Barite is a heavy mineral. The crew adds barite to mud to make it heavy or dense. Barite is over four times heavier than water. Dense mud exerts more pressure than light mud. Weighted mud controls formation pressure. This is called “Primary Well Control”.

[TOOL BOX]: Primary well control is using the density or weight of the drill fluid to provide sufficient pressure to prevent the influx of formation fluid into the well bore. If sufficient mud pressure is not used while drilling, the pressurized formation fluid forces the mud up the well bore where it blows out of control. When the hole is full of mud that weighs the right amount, the pressure of the mud equalizes the pressure of the formation, so formation fluids can’t enter the well bore.

PH

The control of many mud properties depends on its PH. The PH of mud is a measure of its acidity or alkalinity. The PH scale runs from 0 to 14. If the mud is neutral, neither acidic nor alkaline, it has a PH of 7. Mud with a PH below 7 is acidic, a PH above 7 shows that the mud is alkaline. Most drilling muds require a high PH, at least 9, or higher.

Prompt quiz: We’ve said that most drilling mud should have a PH of 9 or greater. Will the mud be called acidic or alkaline?

Caustic Soda

Because mud needs to have a high PH, another common mud additive is Caustic Soda or Sodium Hydroxide. Caustic soda is often called “caustic”. Crew members add caustic soda to the mud to control PH. Caustic soda increases the PH value, it makes the mud more alkaline. In general, caustics are the most dangerous chemicals that you’ll handle on the rig. High strength solutions can seriously burn your skin. Be very careful when handling it to avoid injury, wear the proper personal protective equipment, also remember to always add caustic soda to water, never add water to caustic soda. If you do, the caustic soda will boil up, splatter and cover you with a burning chemical.

Gelled Mud

When drilling stops, say let the crew make a connection (add a joint of drill pipe to the string), the driller normally stops pumping mud. When pumping stops, the mud stops moving. At rest, mud gels, that is it becomes a semi-solid like gelatin. Gelled mud suspends the cuttings. Gelling keeps the cuttings from falling down hole and piling up around the bit. The ability of a gel to keep the cuttings suspended is measured by its gel strength. When the driller starts the pump and resumes mud’s circulation, the mud’s gel strength reduces, which allows the drilling fluid to flow easier.

MUD TESTS

Overview

We’ve just covered a few key points about mud additives and the properties that mud should have to allow a successful drilling. On the rig, it is important for crew members to constantly monitor and maintain these properties. An important member of the drilling team is the mud engineer. The mud engineer runs tests on the drilling fluid. The mud engineer’s job is to monitor and maintain the mud’s properties to the specifications of the well operator. He may also recommend changes to improve drilling, such as adding more caustic soda to increase the mud’s PH. In this section, we will learn about tools that’re used to monitor mud properties.

Mud Balance

The density, or weight per unit volume of the drilling mud determines how much hydrostatic pressure the mud column exerts on the formation. It is therefore important to know the mud’s density at all times. To determine mud density, the mud engineer or helper uses a mud balance. The person weighing the mud puts a small amount of mud in the mud container at left on the balance. He then slides the adjustable counterweight to the right or left until the arm balances on the fork room. The person then reads the mud density at the point on the arm next to the counterweight. In many areas, mud density is read in pounds per gallon but can also be reported in pounds per cubic foot, milligrams per liter, and other units. Mud density is usually called mud weight by the rig crew.

[TOOL BOX]: Calculate the density of mud by adjusting the counterweight on the mud balance. Click on the correct density when you’ve finished.

Marsh Funnel

The viscosity of the mud is thickness or resistance to flow, is also an important factor. The mud’s viscosity determines how well it can carry cuttings up the hole. One measure of a mud’s viscosity is its funnel viscosity. That is how many seconds does it take exactly one quart of mud to flow out of a special funnel called a Marsh Funnel. A Marsh Funnel has a hole in the bottom that’s the standard size. The mud engineer or helper pours one quart of mud into the funnel and records the time that it takes to run out into a pitcher or beaker. In this example, one quart of mud flows out of the funnel and into the beaker in 35 sec, so this mud has a funnel viscosity of 35 sec. A less viscous or thinner mud would flow through the funnel faster; a more viscous or thicker mud would flow through the funnel slower.

Rotational Viscometer

This device also measures mud’s viscosity. It is a more scientific viscosity measure than the Marsh Funnel. A Fann V-G Meter measures the mud’s viscosity in centipoises. A centipoise is a unit of measure for viscosity, just as an inch is a unit of measure for length. The Fann V-G Meter works by spinning a rotor or bob in a sample of mud at two different speeds. In addition, a Fann V-G Meter is used to determine a mud’s yield point, which is a measure of the mud’s resistance to flow. Combined with a timer, the Meter also measures the mud’s gel strength. Gel strength is the mud’s ability to temporarily solidify or gel when it’s not flowing.

[TOOL BOX]: Here’s a mud with high gel strength. Click the button labeled “lower gel strength” to see what would happen if the gel strength wasn’t this high.

Filter Press

This is a Filter Press. Inside the white container is a piece of porous paper called filter paper. Also inside the container is a mud sample. The mud engineer puts the mud sample under 100 pounds per square inch of pressure for 30 minutes. The pressure forces the liquid part of the mud, the filtrate, through the filter paper and into the graduated cylinder. By measuring the amount of the filtrate, the mud engineer can get an indication of the amount of filtrate that will be lost to down hole formations and the amount of solids or wall cake build up on the wall of the hole.

Chloride Test

Mud engineers may run other drilling mud tests. One common test is for salt or chloride in the mud filtrate. By adding Potassium Chromate and other chemicals, the engineer can determine if the hole has penetrated a salt formation. It can also determine whether salt water has entered the well bore, which may be a sign of a kick.

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BASIC BOP EQUIPMENT

PRESSURE CONTROL

Overview:

Fluids in the formation are under pressure. When drilled, this pressure can escape to the surface if it is not controlled. Normally drilling mud offsets formation pressure, that is the weight or pressure of the drilling mud keeps fluid in the formation from coming to the surface. For several reasons however, the mud weight can become lighter than it’s necessary to offset the pressure in the formation. When this situation occurs, formation fluids enter the hole. When formation fluids enter the hole, this is called a “kick”. A blowout preventer stack is used to keep formation fluids from coming to the surface. These are called “BOP”s. By closing a valve in this equipment, the rig crew can seal off the hole. Sealing the hole prevents more formation fluids from entering the hole. With the well sealed or shut in, the well is under control. Rig crews use a surface BOP system on land rigs, jack-up rigs, submersible rigs and platform rigs. They use a subsea BOP system on offshore floating rigs, like semi-submersibles and drill ships.

[TOOL BOX]: Why do you suppose subsea BOP system are used on semi-submersibles and drill ships? Blowout prevention equipment is very large and very heavy. Semi-submersibles and drill ships are dynamic, that is they float and thus move with wind & waves while in working mode. On floating rigs, it is not practical to mount the BOP stack on top of the long riser pipe. The BOP stack is much too heavy for the relatively thin and flexible walls of the riser pipe. Also because the riser walls are relatively thin, they cannot withstand the high pressures that could develop inside the riser when the well’s shut in on a kick. So the rig crew mounts the BOP stack on the well head at the see floor and makes up the riser on top of the stack.

Blowout

A blow out is dangerous. Formation fluids like gas and oil blow to the surface and burn. Blow outs can injure or kill, destroy the rig, and harm the environment. Rig crews there for trained and work hard to prevent blowouts. Usually they’re successful, so blowouts are rare. But when they happen, they are spectacular and thus often make news.

Taking a Kick

A kick is the entry of formation fluids into the well bore while drilling. A kick occurs when the pressure exerted by the drilling mud is less than the pressure in the formation that the drill string is penetrating. The mud that circulates down the drill string and up the hole is the first line of defence against kicks. Drilling mud creates additional pressure as it circulates. The mud pressure keeps formation pressure from entering the well bore. On the rig, they say mud keeps the well from kicking. Sometimes however, crew members may accidentally allow the mud level or mud weight in the hole to drop, this drop in weight or level can happen for several reasons.

For example, the crew may fail to keep the hole full of mud when they pull the pipe out of it, or they may pull the pipe too fast, which can lower the bottom hole pressure. When the mud level or mud weight drops, the pressure exerted on the formation decreases. If either happens, formation fluids can enter the hole. If they do, the well takes a kick. In other words, when the formation pressure exceeds the weight of the mud column, then the well can kick.

[TOOL BOX]: Liquids and gases exert a force against the container. That is the liquid or gas pushes against the wall of the container. If we measure the amount of push or force being exerted on each unit of area on the container, we have the pressure of liquid or gas. So pressure is defined as Force per Unit Area. Common units that are used to measure pressure are Pounds per Square Inch and Kilopascals. This gauge shows the down hole pressure of the mud column; this gauge shows the reservoir pressure. Change the pressure of the mud column and see what happens. To keep a kick from becoming a blowout, the rig crew uses blowout prevention equipment.

BLOWOUT PREVENTERS

Basic Concepts

The blowout preventer—BOP stack, consists of several large valves stacked on top of each other. These large valves are called blowout preventers. Manufacturers rate BOP stacks to work against pressure as low as two thousand pounds per square inch or 2000 psi, and as high as 15000psi, that’s about 14000 Kilopascals to over 100000 Kilopascals. Rigs usually have two kinds of preventers. On top is annular preventer. It’s called an annular preventer because it’s around the top of the wellbore in a shape of a ring or an annulus. Below the annular preventer are ram preventers. The shown of valves in ram preventers close by forcing or ramming themselves together.
The choke line is a line through which well fluids flow to the choke manifold when the preventers are closed. Even though the preventers shut in the well, the crew must have a way to remove or circulate the kick and mud out of the well.

When the BOP shut in the well, mud & formation fluids exert through the choke line to the choke manifold. The manifold is made up of special piping and valves. The most important valve is the choke. The choke is a valve that has an adjustable opening. Crew members circulate the kick through the choke to keep back pressure on the well. Keeping the right amount of back pressure prevents more kick fluids from entering the well. At the same time, they can get the kick out of the well and put in heavier mud to kill the well. That is regain control of it. The well fluids leave the choke manifold and usually to a mud gas separator. A mud gas separator separates the mud from the gas in the kick. The clean mud goes back to the tanks; the gas is flared or burned at a safe distance away.

BOP Operation

When the well takes a kick and the BOP is open, well fluids force mud to flow up the well bore and into the BOP stack. When the driller closes the annular BOP, flow stops. Usually, drillers close the annular BOP first. The closed annular BOP diverts the flow of the choke line, which goes to the choke manifold. The driller can open a valve on the choke line and safely circulate the kick out of the well through the choke manifold.

[TOOL BOX]: Here is an annular preventer, click on it to see how it works. An annular BOP closes on drill pipe, drill collars or any shape of tubular in the well. It can also close an open hole, a hole with no tubulars in it at all. It’s usually the first preventer used to close in the well. Here are four types of Ram-Preventers: Pipe Rams, Blind Rams, Blind-Shear Rams and Variable Bore Rams (VBR Ram). Click on each one to see how the rams work.

Pipe Rams

Pipe rams are used when there is drill pipe in the BOP stack. The pipe rams fit around the pipe, closing off the annulars. Pipe rams back up the annular preventer. That is then it’s likely at the end the annular BOP failed, crew members could shut the pipe rams to seal the well. Also some pipe ram preventers are used to hang off or suspend the drill string and some subsea BOPs.

Blind Rams

Blind rams are designed to seal an open hole. If the annular BOP fails and there’s no pipe in the hole, the crew could seal the hole by closing the blind rams.

Blind-Shear Rams

Blind-shear rams are designed with blades that cut through the drill pipe and then seal the open hole. They’re used in extremely emergencies, like when an offshore floating rig has to move off a well that they’re drilling because of a hurricane or other such emergency. Blind shear rams allow them to cut the pipe, seal the hole and then move the rig a safe distance away.

VBR Ram

Variable Bore Rams or VBR are special pipe rams that can close over a range of pipe sizes such as 5 inch diameter to 3 inch diameter.

BASIC BOP EQUIPMENT

Overview

Here are the major parts of a land, jack-up, platform or submersible rig’s blowout prevention equipment: the blowout preventer or BOP stack, the driller’s BOP control panel, the BOP operating unit accumulator, the choke manifold, the choke control panel, the mud gas separator, the flare line & flare pit, the trip tank and drill string valves.

[TOOL BOX]: Prompt quiz: You’ve just learned the names of the equipment used in well control operations. Let’s see how well you can identify the equipment. Using the mouse, drag the labels to their correct locations. When you’ve completed this exercise, click the “accept” button.

Driller’s BOP Control

From this BOP control panel, the driller opens and closes or controls the blow out preventers and the line to the choke manifold. Rig builders usually place the control panel on the rig floor, close to the driller’s position. Lever and switches allow the driller to quickly open and close the preventers and other valves in the system.

Accumulator

The accumulator bottles store or accumulate hydraulic fluid under very high pressure, up to 3000 psi, over 20000 KPa. This high pressure fluid ensures that the preventers close very fast. The BOP operating unit accumulator is installed some distance from the rig floor.

Hydraulic Lines

When the driller activates the BOP operating unit, it pumps the hydraulic fluid through the high pressure pipes of lines into the BOP stack. The hydraulic pressure opens or closes the preventers.

Operating Lever on Accumulator

Usually, the driller operates the accumulator from a control panel on the rig floor. In an emergency however, crew members can operate the BOPs by using the control valves on the accumulator itself.

Choke Manifold / Chokes

Here is a choke manifold. Flow gets to it from the BOP stack via a choke line. The manifold usually has two or more special valves that called chokes. Usually well flow goes through only one of the chokes, the others are back ups or used under special conditions.

Choke Operation

By adjusting the size of the opening in the choke, making the opening larger or smaller, the driller adjust the amount of the flow through the choke. The smaller the opening, the less flow; the larger the opening, the more flow. The less flow, the more back pressure on the well; the more flow, the less back pressure on the well. This adjustment of back pressure keeps the pressure on the bottom of the hole constant so that no more kick fluids can enter the well.

Choke Control Panel

The driller or another crew member uses the choke control panel to adjust the size of the choke’s opening as kick fluids flow through it. By watching the pressure on the drill pipe and casing, and by keeping the mud pump at constant speed, the choke operator can adjust the choke to keep the pressure on the bottom of the hole constant. The choke operator must keep the bottom hole pressure constant to successfully control and circulate a kick out of the hole.

Mud-Gas Separator

Often, kick fluids and mud from choke manifold go through a line to a mud gas separator. Frequently, formation gas is the main part of a kick. However, kick fluids may also contain water, oil, or combination of these fluids. In any case, the mud gas separator removes the gas from the mud. With the gas removed, the pump circulates gas-free mud into the mud tanks and back down the hole. The separated gas goes to a flare line.

Separator Operation

In the separator, mud with gas in it from choke manifold enters the top and falls over several baffle plates. The gas breaks out of the mud as it falls over the baffle plates and goes into the flare line. The gas-free mud falls to the bottom outlet where it goes to the mud tanks for circulation down hole.

Flare Line & Flare Pit

The flare line conducts gas from the mud gas separator to a flare pit on land rigs. The gas is burned or flared at the flare pit. Notice that the flare line outlet is a good distance away from the rig floor, so even while gas is flaring, the crew can still safely work on the rig floor.
Offshore, where there is no flare pit, the flare line conducts the gas over the side of the rig. The line runs over the water, a safe distance away from the rig.

Trip Tank

A trip tank is a special mud tank. It is used when they pull drill string from the hole, for example, to change out a dull bit. They also use the trip tank when they run drill string back into the hole. Pulling the drill string and running it back in is called a “trip”, which is why they call the small tank a “trip tank”. They use it to keep accurate track of how much mud the drill string displaces in the hole.

Trip Tank Operation

When the crew pulls drill string from the hole, the mud level in the hole drops. If they let the mud level drop too far, it won’t exert enough pressure to keep formation fluids from entering the hole. So, as the crew pulls pipe, they continually circulate fluid from the trip tank to replace the drill string and keep the hole full. They also watch for unusual changes, and may make sure that the volume of mud they put in exactly replaces the volume occupied by the drill string. Since the volumes are small, the level of mud in the trip tank is calibrated in small increments, such as stands of pipe, or barrels or liters of mud, or both. If the volume they put in is less than the volume occupied by the drill string they removed, then it’s likely that formation fluids have entered the hole. For example, let’s say the crew pulls one stand of drill pipe. In this instance, the stand displaces .7 barrels or 111 liters. There for, they should pump .7 barrels or 111 liters of mud to replace the stand. The mud level in the trip tank should sure drop .7 barrels or 111 liters. If the level in the tank shows less, then formation fluids have entered the hole and the crew must take steps to control the well.

SUBSEA BOP EQUIPMENT

Overview

Subsea BOP equipment is similar to a surface stack. There are, however, some very important differences. This section discusses these differences.
Subsea stacks attach to the wellhead on the sea floor. Meanwhile, the rig floats on the water, hundreds or thousands of ft or meters above. Major parts include: the Subsea BOP stack, this is a lot like a surface BOP stack; other parts are different, however. Here’s the flexible or ball joint.
The marine riser with a choke line and a kill line, guide lines, the telescopic joint with riser tensioners, the hose bundle, and two control pods. The driller controls the subsea BOP valves from electric BOP control panel on the rig. The subsea hose bundle carries the control signals and hydraulic fluid from the rig down to the control pod and selected subsea BOP valves.

Marine Riser System

Marine riser pipe is special pipe and fittings. It seals between the top of the subsea BOP stack and the drilling equipment located on the floating rig. Crew members run the drill string into the hole inside the riser pipe. The riser pipe also conducts drilling fluid up to the rig. Manufacturers attach two smaller pipes called the choke and kill lines to the outside. Crew members use them to control the well during a kick or special operations. Guide lines guide and help position equipment such as the BOP stack to ocean floor. The flexible joint cuts down on bending stresses on the riser pipe and BOP. The telescopic joint compensates for the vertical motion of the floating rig.

Riser & Guideline Tensioner

Crew members also attach the riser tensioning system to it. Riser tensioner lines support the long riser pipe. The riser and guide line tensioners put constant tension on the riser pipe and guide lines. This tension suspends the riser pipe. It also compensates what the movement of the rig caused by wave action. Riser tensioner systems usually range in capacity from over 300,000 to almost 1,000,000 pounds (that is 135,000 to over 450,000 kg) with 50 ft or 15 meters of wire line travel. They utilize up to 12 compression loaded tensioners that use air pressure for compensation.

DRILL STRING VALVES & IBOPS

Overview

Drill string valves stop fluids from flowing up to drill string. Often, if the well kicks with the bit off bottom, formation fluids flow up the annulus, and up the drill string. Crew members close the drill string valves to stop the flow in the string. If the kelly is made up, they can close the upper or lower kelly cock. If the kelly is not made up, then they can install a full opening safety valve on the top of the drill string.

An inside blowout preventer or IBOP is a one-way valve, a check valve they can install in the drill string. One side of the IBOP is a float valve that is sometimes made up in the drill string near the bit. It prevents back flow up the drill string. Another type of IBOP is the Drop-in valve or DIV. It’s dropped into the drill string and falls to a special landing sub that’s usually located near the top drill collar and drill stem. It allows the driller to pump mud down the string. But the check valve won’t allow influx fluid to flow up the string.
Another type of the inside BOP is the Heavy Duty Check Valve or Gray Type Valve after one company that makes it. It’s a plunger check valve that the crew stab it in the drill pipe at the surface. It’s usually used during stripping operations. Stripping is when the cerw lowers the pipe in the hole while the BOPs are closed & under pressure.

Upper / Lower Kelly Cocks

An upper kelly cock is located above the kelly. The upper kelly cock normally surves as a back up to the lower kelly cock. If the lower kelly cock failed, crew members will use a special operating wrench to close the upper kelly cock. The closed upper kelly cock prevents further flow, it protects the equipment above the kelly from high pressure flow. Usually crew members close the lower kelly cock if a kick puts risk on the equipment above the kelly. They make it up at the bottom of the kelly. A crew member uses a special operating wrench to close it. The crew can also close the lower kelly cock to keep mud from falling out of the kelly when they break out the kelly to make a connection. A cock is another name for a valve. Cock is short for weathercock, which is English term for valve.

Full-Opening Safety Valve

Here is a full-opening safety valve. If the kelly is not made up in the drill string and flow occurs. Crew members can insert the safety valve in the drill string. This procedure is called “stabbing”. A full-opening valve has as large an inside opening as possible. When fully open, flow from the frill pipe passes through the valve with no additional restriction. This relatively large opening allows the crew to stab the valve against pressure coming out of the drill string.

Safety Valve Usage

The crew picks up the safety valve by its lifting handles. They make sure it’s fully open and stab it into the drill pipe. Then they screw it into the pipe. Finally they use a special operating wrench to close the valve and shut off flow. Driller should make sure the rig has the right crossover subs at hand on the rig floor. Crew members should be able to make up the safety valves and any drilling string member coming out of the rotary. For example, if a drill collar is in the rotary, the safety valve’s threads may not match the drill collar’s threads. They will need the right crossover sub to make it work.

[TOOL BOX]: This well is taking a kick. To shut it in, choose one of the two valves you see here: a one-way safety valve and a full-opening safety valve. Click on the valve you wan to use. Hold your mouse button down and drag the valve to drill pipe… Good choice! The full-opening safety valve is the correct valve to use in this situation. It can be stabbed on the drill pipe while it’s open and then close to shut in the drill string. You’re not done yet though, the annulus hasn’t been sealed, so the well is still not fully secured. Click on the correct preventer on this BOP stack that should be closed first. That’s right! The annular preventer is closed first. Good job! You’ve successfully closed in this well.

Float Valves

Float valves also prevent flow up the drill string. Crew members place a float valve in a sub, a special drill string fitting, just above the bit. One type allows mud to be pumped down but shut against upward flow. Under normal conditions, pump pressure moves drilling mud through the open one-way valve, and influx of formation fluids from below causes the float valve to close. This prevents further flow up the drill string.

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Metode Seismik Untuk Pendeteksian Reservoir Minyak dan Gas Bumi dengan Metode AVO (Amplitude Versus Off-Set)

1. Pendahuluan 
Selain mampu memetakan dimensi suatu perangkap minyak dan gas bumi, metode seismik mampu memetakan variasi sifat fisik batuan dengan pendekatan kecepatan penjalarannya. Dengan berkembangnya teknologi akuisisi dan pengolahan data, memungkinkan sinyal refleksi dan transmisi dapat direkam dan diproses secara akurat, sehingga informasi yang dibawanya sangat membantu dalam penafsiran sifat fisik batuan bawah permukaan. Dalam tulisan ini akan dikaji beberapa masalah yang berkaitan dengan pendeteksian reservoir minyak dan gas bumi dengan mengkaji perilaku sinyal refleksi dari reservoir batuan karbonat dan batuan pasir. Metode yang digunakan adalah metode AVO (Amplitude Versus Off-Set), yang dikembangkan oleh Aki Richard1), Hilterman2), dan Shuey3) dan lain-lain.

Pada tulisan ini pengkajian terutama dilakukan pada batuan karbonat, oleh karena kebanyakan penelitian dilakukan pada reservoir batuan pasir, seperti dilakukan oleh Ostrander 4), Fatti dkk.5), Rutherford dan William 6) dan lainnya. Untuk memahami sifat
fisik reservoir, akan diuji metode Damp Approximation Inverse (DAI), sebelum diterapkan pada data riil.

2. Metode AVO Untuk Pendeteksian Reservoir Minyak dan Gas Bumi dengan Metode AVO
Prinsip dasar metode AVO (Amplitude Versus Off-Set) adalah adanya perubahan koefisien refleksi terhadap sudut datang atau jarak (off-set) antara sumber gangguan dan penerima. Pengamatan data dilapangan menunjukkan bahwa amplitudo sinyal terpantul tidak selalu berkurang terhadap jarak pengukuran, karena koefisien refleksi selain dipengaruhi kontras sifat dan jenis batuan, juga sangat dipengaruhi jenis, kandungan fluida dalam batuan. Sesuai dengan uji data dan pemodelan dalam studi ini pendekatan Shuey3) akan digunakan, dimana koefisien refleksi dirumuskan sebagai :


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Pola Aliran dan Variabel Aliran Fluida Dua Fasa Dalam Pipa

Pada keadaan sebenarnya di lapangan, fluida reservoir yang diproduksi melalui sumur dapat terdiri dari campuran cairan dan gas. Pada persamaan kehilangan tekanan aliran dalam pipa, salah satu parameter yang digunakan adalah densitas. Untuk kondisi dua fasa (gas dan airan) maka densitas yang digunakan adalah campuran antara densitas gas dan densitas cairan. Demikian juga halnya untuk viskositas dan sifat-sifat fisik fluida lainnya. Perbedaan densitas yang besar antara gas dan cairan menyebabkan gas dapat bergerak labih cepat dibandingkan cairan. Hal ini menyebabkan perbandingan gas dan cairan pada suatu kondisi tertentu menjadi sulit untuk ditentukan.

1. Pola Aliran Fluida Dua Fasa dalam Pipa

Gas dan cairan yang mengalir secara serentak dalam pipa, akan membentuk distribusi fasa gas dan fasa cair, yang berbagai ragam bentuknya, sesuai dengan jumlah fasa gas dan cair yang mengalir. Distribusi fasa gas dan cair tersebut dalam perbandingan tertentu membentuk pola aliran tertentu pula. Bentuk pola aliran tersebut tergantung pada:


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