BAKER HUGHES INCORPORATED
`Exhibit 1006
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`Page 1 of 6
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`Fluid pressure exists in a reservoir for the same reason that pressure exists
`at the bottom of the ocean. Imagine a swimmer in a large swimming pool
`who decides to see whether he or she can touch bottom. Everything is go-
`ing well except that the swimmer’s ears begin to hurt. The deeper the dive,
`the more the ears hurt. The reason for the pain is that the pressure of the
`water is pressing against the eardrums. The deeper the swimmer goes, the
`greater the pressure.
`Just as water creates pressure in a swimming pool, fluids in a reservoir
`create pressure. When the reservoir has a connection to the surface (fig.
`1.38), usually the only pressure in it is the pressure caused by fluid in and
`above it. As long as this connection to the surface exists, rocks that overlie
`a reservoir do not create any extra pressure in the reservoir. Even though
`their weight bears down on the formation, fluids can rise to the surface and
`escape. Imagine again the swimming pool full of water. Dump a huge load
`of rocks into it. The rocks do not increase the water pressure; instead the
`water sloshes over the sides.
`
`ll reservoir fluids are under pressure. The weight of the fluid itself
`creates a normal pressure. Abnormal pressure occurs when the weight
`of the formations on top of the reservoir is added to the fluid pressure.
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`Normal Pressure
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`.
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`I
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`The same thing happens in a reservoir. Unlike a swimming pool,
`however, a reservoir’s connection to the surface is usually circuitous. It may
`outcrop at the surface many miles away, or it may be connected to the surface
`through other porous beds that overlie it. In most cases, though, as long as
`the reservoir has some outlet to the surface, the pressure in it is caused only
`by the fluids and is considered to be normal pressure.
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`SURFACE
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`10-PPG
`DRILLING-FLUID
`COLUMN
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`-
`'.
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`HFERMEABLE
`FORMATION
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`10,000 FT
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`0.52 PSI/FT
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`MUD
`PRESSURE
`5,200 PSI
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`FORMATION
`PRESSURE
`4.050 PSI
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`MUD SHEATH
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`Figure Q8 When the petroleum reservoir has a connection to the surface, the
`Pressure is considered normal.
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`Petroleum Geology
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`23
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`Page 2 of 6
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` T
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`Once the kelly is made up tightly to the joint, the driller picks them
`up and moves them from the mousehole to the rotary table. The crew stabs
`the bottom of the new joint of pipe into the top of the joint of pipe coming
`out of the borehole and again uses the kelly spinner to make up the joints.
`With the new joint made up, they pull the slips, and the driller lowers the
`pipe until the bit nears the bottom. Then he or she starts the pumps, begins
`rotation, applies weight to the bit, and drills another 40 feet ("I 2 metres) or so
`of hole, depending on the length of the kel ly. Th_e crew repeats this p rncess
`each time the kelly is drilled down.
`When the rig uses a top drive, the crew follows essentially the same
`procedures to make up the drill string, often making up two, three, or four
`joints at a time instead of one. The multiple made-up joints, called a stand,
`sit in a rack on the rig floor to the side of the mast or derrick.
`Eventually, at a depth that could range from hundreds of feet (metres)
`to a few thousand feet (metres), drilling comes to a temporary halt, and the
`crew pulls the drill stem from the hole. This first part of the hole is known as
`the surface hole. Even though the formation that contains the hydrocarbons
`may lie many thousands of feet (metres) below this point, the toolpusher
`stops drilling temporarily to take steps to protect and seal. off the forn1a|:ions
`close to the surface. For example, drilling mud could contaminate zones
`containing fresh water that nearby towns use for drinking. To protect such
`zones, the crew runs special pipe called casing into the hole and cements it
`in place.
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`Tripping Out
`The first step in running casing is to pull the drill stem and the bit out of the
`hole. Pulling the drill stem and the bit out of the hole in order to run cas-
`ing, change bits, or perform some other operation in the horelmle is called
`tripping em’.
`To trip nut, the driller stops rotation and circulation. Then, using con~
`trols on the drawworks, he or she raises the d rill stern off the hot to m of the
`hole until the topjoint of drill pipe clears the rotary table and holds it there.
`Then, the rotary helpers set the slips around the drill pipe to suspend it in
`the hole. Next, using the tongs, the rotary helpers break the kelly out of the
`drill string and put it into the rathoie (fig. 4.45). Since they leave the kelly
`bushing, the swivel, and the rotary hose on the kelly when placing it in the
`rathole, the area above the rotary where the top of the d.r'1l.| string protrudes
`from the hole is clear. Only the traveling block hangs above the drill pipe
`suspendecl in the hole.
`Attached to the traveling block are a set of d.rill pipe lifting devices
`called elcmto.rs. The elevators usually remain attached to the traveling block
`at all times and swing downward into position when the crew removes the
`swivel from the hook. Elevators are clamps that can latch onto the. tool joints
`of the drill. pipe (fig. 4.46). The crew latches the elevators around the drill
`pipe, and the driller‘ raises the traveling block to pull the pipe upwaI‘L'l.
`When the third joint of pipe clears the rotary table, the rotary helpers 591
`the slips and use the tongs to break out the pipe. The pipe is usually IL‘-
`moved from the hole in stands of three joints. The crew guides the stand
`to the rack on the rig floor.
`Once the bolztorn of the stand of pipe is set down on the. rig flout‘.
`the derriekhand goes into action. Standing on a small platform called the
`munlce_1;burm.i that is about 90 feet (metres) high in the mast or derrick,
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`108
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`FUNDAMENTALS or PETROLEUM
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`WELL
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`STIMULATION
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`Several powerful, truck-
`Figure 5.26
`mounted pumps are arranged at the
`well site for a fracturing job.
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`162
`
`he term well stimulation encompasses several techniques used to en-
`large old channels or to create new ones in the producing formation.
`Since oil usually exists in the pores of sandstone or the cracks of limestone
`formations, enlarging or creating new channels causes the oil or gas to move
`more readily to a well. Sometimes the problem is low permeability. In this
`case, the well will be stimulated immediately after completion. In other cases,
`the natural permeability of the rock may be adequate, but the formation
`near the wellbore may be damaged in a way that restricts the flow channels
`in porous rock. Formation damage can occur during drilling, completion,
`workover, production, or injection.
`There are three ways to do this. The first and oldest method is to use
`explosive fracturing. During the 1930s, acid stimulation, or acidizing, became
`commercially available. Hydraulicfracturing, the third stimulation method,
`was introduced in 1948.
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`Explosives
`As early as the 1860s, crews exploded nitroglycerin inside wells to improve
`their productivity. They simply lowered a nitro charge into the open hole
`on a conductor line and detonated it to fracture the formation. Nitro shooting
`became fairly routine until the advent of acidizing and hydraulic fracturing.
`For a time in the 1960s, lease operators experimented with nuclear explosives
`in a limited number of gas wells. While this method increased production
`somewhat, the cost was prohibitive.
`Oil companies are still interested in explosive techniques because
`certain kinds of tight forniatinns do not respond readily to either acidizing
`u r hydrauliu: fracturing. .Reset-rrcli continues today to find other techniques
`that miglit increase pmcluction, but currently fracturing and acidizing are
`the most effective well stimulation methods.
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`Hydraulic Fracturing
`Hydraulic fracturing is all about P113!"-iSl.1|'L’. Several powerful pumps (fig.
`5.26) inject a liquid, the fracturing fluid, into the well at a fast rate. The fluid
`develops a high pressure that actually splits, or fractures, the rock. To
`visualize this, imagine splitting a log with an axe. The axe head is a wedge.
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`FUNDAMENTALS or PETROLEUM
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`A wedge first cuts a tiny crack in the log that the force of the blow enlarges
`into a wider cut until the log splits. In fracturing, the fluid acts as a wedge
`and its high pressure is the force that pushes it into the rock. Hydraulic
`fracturing splits the rock instead of the casing because the casing is stronger
`than the rock.
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`Hydraulic fracturing improves the productivity of a well by either
`creating new fractures that act as flow channels or extending existing flow
`channels farther into the formation. Fracturing is a usual part of completion,
`and refracturing to restore productivity of an old well is a regular procedure.
`Workover people commonly shorten the word fracturing tofrac, as in frac job
`and frac unit. Hydraulic fracturing works well in sandstone reservoirs.
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`Proppants
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`During early experimental work, engineers discovered that a hydraulically
`formed fracture tends to heal, or lose its fluid—carrying capacity, after the part-
`ing pressure is released unless the fracture is propped open in some manner.
`Proppan ts, or propping agents, hold the fractures open. Sand, nutshells, and
`beads of aluminum, glass, and plastic may be used as proppants (fig. 5.27).
`Spacer materials are used between the particles of the proppant to ensure
`its optimum distribution.
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`Figure 5.27
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`Sand is one proppant used to hold fractures open.
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`Fracturing Fluid
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`The fracturing fluid may be either oil based or water based. In reality, the
`fluid is nearly always brine because it is safe, available, and cheap. Some
`fracturing fluids are gels, which suspend the proppants better. Polymer addi-
`tives reduce friction between the fluid and the walls of the tubing. Although
`this may not sound as if it would be a factor, any slowing of the fluid due to
`friction requires larger pumps to keep the injection rate high enough. Finally,
`additives reduce fluid loss into the formation.
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`Production
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`163
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`Acidizing
`In acid stimulation, or acidizing, an acid reacts chemically with the rock to
`dissolve it (fig. 5.28). As in hydraulic fracturing, this enlarges existing flow
`channels and opens new ones to the wellbore. Well servicing crews stimulate
`both new and old wells with acid. Reservoir rocks most commonly acidized
`are limestone (calcium carbonate) and dolomite (a mixture of calcium and
`magnesium carbonates), or carbonate reservoirs.
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`Types of Acids
`Acids that are strong enough to dissolve rock are often strong enough to eat away
`the metal of the pipes and equipment in the well. Acidizing, therefore, always
`involves a compromise between acid strength and additives to prevent damage
`to the equipment. Oilfield acids must create reaction products that are soluble;
`otherwise, solids would precipitate and plug the pore spaces just opened up.
`Since acidizing uses large volumes of acid, it must be fairly inexpensive.
`Workers on acidizing jobs must be trained to handle the acids they
`use, many of which have dangerous fumes and can burn the skin. Acidizing
`contractors choose the type of acid based on the formation and the condi-
`tions in the well. The choices include hydrochloric, hydrofluoric, acetic, and
`formic acids.
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`Additives
`/mliiitiires are used with oilfield acids for many reasons, but one of the most
`important is to prevent or delay corrosion——that is, to inhibit the acid from
`attacking the steel tithing or casing in the well. A .‘a‘IttjiICt'£l'tIi', or surface ac-
`tive agent, is another type of additive. It is mixed in small amounts with an
`acid to make it easier to pump the mixture into the rod: formation and to
`prevent spent acid and oil from forming emu lsions. An minister: is a thick
`mixture like inayonnaisc.
`Other common additives are serntesteritig agents, which prevent the
`precipitation of ferric iron during acidizing, and rmtislmtge agents, which
`prevent an acid from reacting with certain types of crude and forming an
`insoluble sludge that blocks channels or reduces permeability.
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`Types of Acidizing Treatments
`There are two basic kinds of acid stimulation treatments: acid fracturing
`and matrix acidizing.
`Ac-£rifra::tu-i'ii:g, or_,Fracti.i.re ricidizing, is similar to hydraulic fracturing, with
`acid as the fluid. Acid fracturing does not require proppants, however, because
`it does not just Force the rock apart, but also eats it away. It is the more widely
`used treatment for well :;t1'rnuIation with acid. Since most limestone and dolomite
`formations have very low permeabilities, injecting acid into these formations,
`even at a moderate pumping rate, usually results in fracturing.
`Mm‘r'ix ricidizirrg can be subdivided into two types. The first is welltmre
`cteriirrrp, or wrtiiiorc soak. In wellbore soak, the crew fills up the weilbore with acid
`without any pressure and allows it to react merely by soaking. It is a relatively
`slow process because little acid actually comes i.n contact with the forrnation.
`The second matrix acidizing method is a low—pressure treatment that does not
`fracture the formation, but allows the acid to work through the natural pores (fig.
`5.29). This second process is what people in the oil patch are usually referring to
`when they speak of matrix acidizing. Operators generally use matrix acidizing
`when the formation is damaged or when a water zone or gas cap is nearby and
`fracturing might result in excessive water or gas production.
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`FUNDAMENTALS or PETROLEUM
`Page 6 of 6
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`Figure 5.28 Acid enlarges existing
`channels or makes new ones.
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`Figure 5.29 Acid is injected down the
`tubing and into the formation through
`perforations to remove formation damage
`without fracturing the formation.
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`164