Section 11 Equipment

7/30/2019 Section 11 Equipment

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Hydraulic FracturingSection 11 Equipment

Page 11.1 Rev 0

11. Equipment

11.1 Hors epow er Requirements

Working out horsepower requirements is a relatively easy thing to do, provided you know theexpected treating pressure and slurry rate:-

HHP =STPx Slurry Rate

40.8......................................................... (11.1)

where STPis in psi and Slurry Rate is in bpm. The 40.8 is simply a conversion factor for theunits (in the SI system, pumping power in kW is directly equal to pressure (Pa) multipliedby rate (m

3/sec)). This formula will tell you how many pumps of what size you need on

location. Remember to have at least 20% excess horsepower on location and - as a minimum- mobilise at least one spare pump. This excess capacity is required in case of pump failure orhigher than expected treating pressures.

It is also worthwhile looking at the set of curves supplied with each pump called pumpcurves. These curves show the maximum rate and pressure that the pump can run at in eachgear. Correctly speaking, these curves are showing maximum torque from the engine.Remember that it is quite possible to be limited by torque, rather than by horsepower. In sucha situation, the pump may not be able to run at a given rate and pressure, even though it iswithin the pumps rated horsepower. Remember also that the reduction ratios between theengine and transmission, and between the transmission and the pump, will affect the finaltorque available. In reality, pump curves are in fact pump-transmission-engine curves.

If a treatment is going to be close to the maximum power for a given pumping unit, it isrecommended that the pump curves be consulted in order to confirm that the pump canactually do the treatment.

11.2 Flow Lin es

This section is intended as a guideline only. Full details on requirements for high andlow pressure flow lines can be found in the BJ Services Standard Practices Manual,and it is recommend that this should be consulted before any rig-up is designed.

Suction Hoses

It is essential that sufficient suction hoses be used between the tanks and the blender. Theonly force available to move the fluid to the blender is the suction of the inlet pump andhydrostatic pressure from a difference in fluid levels. This is not much. In order to ensure thatthe suction pump receives fluid at sufficient rate, a simple rule applies;

One 4 diameter 10 suction hose will carry up to 10 bpm of gel

If 20 bpm is required, then two hoses will be needed, and so on. In addition, longer hoses willcarry less rate. For instance, 20 of 4 diameter hose will only carry half as much rate, i.e. 5bpm. So if 20 bpm were required from tanks which were 20 away, 4 x 4 flow lines would berequired.

From this it is easy to see why the blender is usually placed as close as possible to the fractanks, and why the frac tanks are often manifolded together with 8 (or larger) diameter lines.

Also consider the comparative diameter of manifolds and suctions hoses. For instance:-


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An 8 manifold has a flow are of 50.26 sq inches. This corresponds to the same flow area as4 x 4 inch hoses (50.24 sq inches). Therefore, there is little point in building an 8 manifoldand then using only 3 suction hoses.

High Pressure Flow Lines

When pumping abrasive fluids such as a frac gel with proppant down a high pressuretreating line, there is a limit to how fast it is advisable to pump. Above this pump rate, seals onchiksans, swivels and hammer unions start to wash out. It is generally accepted in theindustry that the velocity of the frac fluid should not exceed 40 ft sec

-1. Therefore:-

Qmax= 2.33 d2

........................................................................... (11.2)

where Qmax is the maximum flow rate down any single high pressure line, in bpm, and dis theinside diameter of the line, in inches.

Important Points

1. The actual inside diameter of high pressure flow lines is often significantly less thanthe nominal diameter. Equation 11.2 should be used with the actual diameter. This isillustrated in Figure 11.2a.

2. HP flexible lines, such as Coflexip hoses, have separate guidelines. For these, followthe manufacturers instructions.

Figure 11.2a Chart Showing Fluid Velocity against Fluid Rate for Various Nominal Diameters ofFigure 1502 High Pressure Iron.

11.3 High Pressur e Pumps

Most high pressure pumps used in hydraulic fracturing are of the triplex variety, althoughsome services companies have been known to use quintuplex pumps. Triplex means that

there are three pistons acting to pump the fluid. These pistons are driven by a rotatingcrankshaft, as illustrated in Figure 11.3a.

Velocity ChartFigure 1502 HP Iron

0

20

40

60

80

100

120

0 10 20 30 40 50 60

Fluid Rate, bpm

Fluid

Velocity,

ftsec

-1

1.5"

2"

3"

4"

40 ft sec-1

Max Velocity for Abrasive Fluid


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Figures 11.3b and 11.3c show what happens whilst the pump is operating. Figure 11.3bshows the suction or inlet stroke of the cycle. As the plunger moves back towards the powerend, fluid is pushed through the suction valve by the blender. The spring acting to close thisvalve requires between 30 to 40 psi just to lift it up, so the blender must provide a boostpressure significantly greater than this in order to quickly fill the fluid end.

Figure 11.3c shows the power or discharge stroke. As the plunger moves away from thepower end, the increased pressure in the fluid end causes the suction valve to close, andonce this pressure is high enough, the discharge valve to open.

Figure 11.3a Schematic Diagram of a Generic Frac Pump

Figure 11.3b Generic Frac Pump, Suction Stroke

Power End Fluid End

Discharge Valve

Plunger

Suction Valve


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Figure 11.3c Generic Frac Pump, Discharge Stroke

Frac pumps are usually powered by diesel engines, although some have been built withelectric motors and even gas turbines. For diesel powered units (which includes all of BJsfrac pumpers), there will be a transmission and a drive shaft in between the pump and theengine. The transmission allows the pump operator to select which gear the pump is in. Lowgear is for high pressure/low rate, whilst high gear is for low pressure/high rate. Thetransmission usually includes a torque converter, which amplifies the torque coming from theengine, for a corresponding drop in rpms. The pump curves supplied with each pump will tellthe operator what the maximum rate and pressure is for each gear. These curves include theengine/transmission gear ratio, which is the ratio for the torque converter. For instance a 2:1

engine transmission gear ration means that the torque converterreduces the input rpms by afactor of, and increases the input toque by a factor of 2

Also included on most pumpers is a lock-up device. This is a mechanism that allows slipbetween the engine and the transmission. In the event of the pump stalling, this can preventserious damage to the transmission and engine. In order to make this device lock up (whichmeans that there is no slip in the lock up device), the engine needs to be turning at areasonable rate (usually 1700 to 1800 rpm). Below this speed, the torque converter is notlocked up. The pump is still working, but there is slippage between the engine andtransmission. It is possible to run a pumper out of lock up, but the engine will quickly overheatif this is maintained for too long.

Figure 11.3d Skid mounted 16V 92T pumpunit (700 HHP). Skid splits into two parts.

Figure 11.3e Two views of a trailer-mountedGorilla pump unit (2700 HHP)


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Frac pumpers come in a variety of sizes, ranging from 350 HHP to 2700 HHP. Bigger pumpsare more cost effective for big treatments, but are very expensive and can be difficult to move

on roads and onto location. Smaller pumps may require more operators, more maintenance(per horsepower maintenance per pump unit is not significantly effected by size) and takeup more space on location. Figures 11.3d to 11.3g illustrate some of BJs fleet of fracpumpers.

11.4 Intensifiers

Intensifiers are devices that are used for pumping frac treatments for extended periods at highpressure and rate. They reply on conventional frac pumps for to power them, and work on theprinciple that at constant power, high rate and low pressure is the same as low rate and highpressure.

At the power fluid end of the intensifier, the frac pumps supply power fluid at high rate and(relatively) low pressure. This acts to displace a large diameter piston down the power end. Atthe other end of this piston is a smaller diameter piston, which is mounted inside thedownhole fluid end. This acts to pump the frac fluid at high pressure and (relatively) low rate,as illustrated in Figure 11.4a.

Suction Stroke Hydraulic fluid is forced behind the power fluid piston to force the pistonback. This allows the downhole fluid end to fill with frac fluid from the blender.

Power Stroke The pressure on the hydraulic fluid is released. At the same time, the inletvalve from the frac pumps is opened, allowing the power end to fill with power fluid. Thisforces the piston down the power fluid end. At the other side of the intensifier, the frac fluid is

forced out of the downhole fluid end at high pressure.

One important parameter for each intensifier is the intensification ratio. This is equal toD

2/d

2(see Figure 11.4a). This defines by how much the intensifier converts high rate-low

pressure into low rate-high pressure. For instance, with an intensification ratio of 2.5, the fluidpressure going downhole, will be 2.5 times the power fluid pressure, whilst the fluid rate goingdown hole will be 2.5 times less than the power fluid rate.

Figure 11.4b shows how the intensifier is rigged up with the other equipment, whilst Figure11.4c and d show intensifiers on location.

Figure 11.3f Body-load Kodiak pump unit(2200 HHP)

Figure 11.3g Skid-mounted 1300 HHPpump unit


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Fig 11.4a Schematic diagram of a generic intensifier

Fig 11.4b Schematic diagram of the intensifier hook-up.

SUCTION

STROKE

POWERSTROKE

D

d

TO POWER

FLUID UNIT

HYDRAULIC

FLUID IN

HYDRAULIC

FLUID OUT

OPEN

CLOSED

OPEN

CLOSED

FROM FRAC

PUMPS

FROM

BLENDER

TO WELL

BLENDER

FRAC PUMP

FRAC PUMP

FRAC PUMP

RESERVOIR

COOLERBOOSTPUMP

POWER FLUID UNIT

INTENSIFIER

TOWELL


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Fig 11.4c Intensifier worksite. Each intensifier (A) is hooked up to three frac pumpers (B),which are pumping the power fluid. Power fluid is handled by the power fluid unit (C). Intensifiers

are rigged into a manifold (D). Note that whilst there are three intensifiers and 9 power fluidpumpers on location, there are also an additional two frac pumpers (E) rigged up to the

downhole line to provide extra horsepower.

Fig 11.4d Detail of an intensifier. In the foreground, on the RHS, is the downhole fluid end. Inthe background, on the LHS, is the power end, complete with high pressure iron rigging it to the

frac pumpers.

A

BC

DE


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11.5 Blending Equipment

The blender is the heart of the fracturing operation. Although modern blending equipment isoften highly automated, the blender operator (or Blender Tender) still retains one of the mostcritical positions on any location. Figure 11.5a shows a generic schematic diagram of a fracblender.

Figure 11.5a Generic flow diagram for a frac blender. Note that on a blender fitted with aCondor tub (such as BJs Cyclone blenders), the functions of the blender tub and the discharge

pump are combined.

The blender performs the following functions:-

i) Pre-gelling tanks.ii) Blending liquid and dry additives on the fly.iii) Blending proppant on the fly.iv) Providing supercharge for the high pressure pumps.v) Metering and recording a variety of job critical parameters.

Figures 11.5b to 11.5e show some of BJs fleet of frac blenders.

LIQUID ADDITIVE TANKSDRYADD.BIN

PROPPANT SILO

SUCTIONPUMP

DISCHARGEPUMP

SUCTIONMAN

IFOLD

DISCHARGEMA

NIFOLD

BLENDERTUB

RECIRCULATION LINE

FROM

FRACT

ANKS

TO

HIGHPRESSU

REPUMPS

RADIOACTIVEDENSIMETER

SLURRY SIDEFLOW METER

CLEAN SIDEFLOW METER

TO

FRACTANKS

LA METERINGPUMPS

Figure 11.5b 125D Frac blender, capable of 125bpm and 35,000 lbs/min proppant rate

Figure 11.5c Body-load mounted Cyclone IIblender, capable of 25 bpm


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When pumping a treatment the frac spread can be set up to either gel the frac tanks before

the treatment - so that all the fluids are prepared beforehand or to mix the gel on the fly.

Treatments with Pre-Gelled Tanks

When carrying out a treatment with tanks that are pre-gelled, considerable time and effort hasbeen invested into gelling a number of frac tanks filled with water. During this process, theblender will be used to circulate the tanks (via the suction manifold, suction pump, blendertub, discharge pump and recirculation line see Figure 11.5a), whilst adding the necessaryingredients to produce the required gel.

Advantages of Pre-Gelling Tanksi) Intense quality control can be carried out on the gel, prior to each tank being

accepted. If necessary, a tank or poor quality gel can be rejected, disposed off andthen re-blended.

ii) Fewer additives need to be mixed on the fly.iii) No need for an LFC Hydration Unit

Disadvantages of Pre-Gelling Tanksi) Considerable time can be taken up by blending the gel.ii) Gel properties cannot be varied on the fly.iii) Approximately 5% of the gel will be wasted as tank bottoms.iv) Bactericide must be blended with the gel to prevent sulphate-reducing bacteria from

breaking down the gel.

Mixing Gel on the Fly

Mixing the frac gel on the fly requires less pre-job preparation, but involves the use of moreequipment and the extra cost of the LFC or XLFC (Liquid Frac Concentrate see Section 5).LFC is an oil-based slurry of the polymer, usually mixed so that there is 4 lbs of polymer pergallon of slurry. The LFC is added to the water on the fly, allowing the gel to be prepared as itis needed. This requires an LFC hydration unit (see Figure 11.5e). This piece of equipmentconsists of an LFC storage tank, an metered LFC additive pump (usually progressing cavitytype), a hydration tank and a boost pump. Water is supplied to the LFC hydration unit, whichmeters in the LFC at a controlled ratio, to provide the required gel strength. The hydratingLFC/water mix passes into the hydration tank, which is large enough so that the gel spends 3to 4 minutes in there, before it is transferred to the blender by the boost pump. This 3 to 4minute hydration time allows the polymer time to hydrate. Some LFC Hydration units are

supplied with a QC system consisting of a viscometer and a pH probe to provide real timegel QC information.

Figure 11.5d Skid mounted Cyclone blender Figure 11.5e LFC hydration unit


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Advantages of Mixing on the Flyi) No wasted gel. Only the amount of gel required is blended, so that there is no

wastage from tank bottoms or if the treatment ends prematurely.ii) Gel properties may be varied on the fly.iii) Less time and effort required for job preparation.

iv) No need to use a bactericide.

Disadvantages of Pre-Gelling Tanksi) Extra cost of using LFC, rather than dry powder.ii) Extra cost of LFC Hydration Unit.iii) Loss of gel properties if the LFC Hydration Unit has an equipment problem.

11.6 Propp ant Storage and Handling

Proppant has to be stored on location, ready for use. It has to be kept clean and dry, andmust be delivered to the blender smoothly and quickly. Figure 11.6a shows frac sand beingdelivered to the hopper of a blender:-

Figure 11.6a Frac sand beingdelivered from a Sand King to thehopper of a blender. Note thatthere are two blenders in thispicture one is on standby as abackup in case of equipmentfailure.

There are two main methods for ensuring the smooth flow of proppant from the storage bin tothe blender. The first method is to use a gravity feed system, which relies on the proppantbeing stored in a bin which is higher than the blender hopper. A gate valve is used to controlthe sand rate. This can be done with either large vertically mounted bins (Figure 11.6b) orfrom a dump truck (Figure 11.6c):-

Figure 11.6b Verticallymounted, gravity feedproppant bins

Figure 11.6c Trailer mounted sand dumper


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The second method is to use a conveyor system to move the proppant from the bin ordumper, to the blender hopper. This method is typically used on larger frac jobs, as there isusually insufficient space around the blender hopper for all the bins to be positioned. Usually,BJs first option for storing large volumes of proppant is the Sand King, as shown in Figure11.6d:-

Figure 11.6d BJ Services Sand King

The Sand King is designed to be hauled to location empty, and then filled up with proppant.BJ has two models, one with 250,000 lbs capacity and one with 400,000 lbs capacity. Theproppant is held in several separate bins along the length of the Sand King. During thetreatment, gates positioned at the bottom of the hoppers are opened to allow proppant tofall onto a conveyor. This conveyor runs along the bottom of the entire length of the SandKing, and will transport the proppant to the blender hopper. When a very large treatment isplanned, such that several Sand Kings have to be used, a separate Sand Belt Conveyor isused, as shown in Figure 11.6e:-

Figure 11.6e Sand Belt Conveyor

This device allow several Sand Kings to be placed on either side of the belt, each one feedingonto the main belts of the Sand Belt Conveyor. This, in turn, feed the proppant to the blenderhopper.

During the treatment, it is important that the proppant system can produce a smooth,uninterupted flow of proppant to the blender, often at quite high rates. It must also be able tokeep the proppant dry, as wet proppant can cause the blenders proppant screws to seize up.


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11.7 Treatment Monito ring

On a modern frac spread, almost every parameter can be measured, displayed and recorded.The place at which this data is displayed and recorded is the Treatment Monitoring Centre,which is usually either a van or a container, as illustrated in Figures 11.7a and 11.7b, below:-

Figure 11.7a External view of BJs Stimulation Van 1800

Figure 11.7b External view of a Treatment Monitoring Container

The fracturing treatment will be controlled from this facility. The Frac Supervisor, the FracEngineer and the Company Man can sit in relative comfort and quiet, making treatment-critical decisions, based on the data that is being collected and displayed.

Figure 11.7c Two internal views of a Treatment Monitoring Van


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Most modern treatment monitoring facilities also include the capability to transmit thetreatment data real time back to a specially set up remote data monitoring computer. This canbe located either in BJs office or in the customers. With this facility, Engineers no longerhave to waste productive time on location or travelling to and from the location. This isespecially significant offshore, where the costs of mobilising personnel can be significant.With the remote data transmission, the Engineers get the same data displayed via similar

software (typically JobMaster or FracRT), with only a second or two delay. Typically, there isalso a voice link so that the on-site Engineer can discuss various items or pass oninstructions.

One other feature of most treatment monitoring containers or vans is a field lab. This will be acompact QC/QA facility, designed to ensure the quality of the fluids and proppants. On largerfrac spreads this may even be a separate piece of equipment. Sometimes these are fittedwith a fluid rheology and pH flow loop, allowing real time viscosity and pH data to bedisplayed and recorded.

11.8 The Wellhead Isolation Tool

The Wellhead Isolation Tool (WIT), often referred to as a Tree Saver, is a device that allowstreatments to be pumped at a STP higher than the maximum pressure rating of the wellhead.This allows treatments to be pumped at much higher rates than would normally be possible.The WIT does this by completely isolating the wellhead from the treating fluid, as illustrated infigures 11.8a, b and c.

The tool is used in the following manner:-

Prior to the treatment, the WIT operator obtains data for the type and size of wellhead topflange connection, the distance from the top flange to the tubing hanger, the tubing sizeand the tubing weight. This allows the WIT operator to assemble the stinger and sealassembly to match the wellhead.

The wellhead master valve is closed, and any pressure between the master valve and thetop flange is bleed off.

The WIT is assembled to the top flange, as illustrated in figure 11.8a. Some WIT are fittedwith a master valve above the stinger (below the Tee section), whilst others requireadditional valves to be fitted (as illustrated).

The WIT operator applies hydraulic pressure to the lower connection on the mastercylinder, to ensure that the tool is fully extended, or stung out of the wellhead.

The valves at the top of the WIT are closed.

The wellhead master valve is opened and the WIT is exposed to wellhead pressure.

The tool is stroked down by pumping hydraulic fluid into the top connection on the mastercylinder.

The stinger and the seal assembly are sized so that the seal assembly stings into the topof the tubing, at the point when the stinger is fully stroked into the well.

The upper section of the WIT and the master cylinder are clamped together, so thathydraulic pressure is no longer required to keep the tool stung into the tubing.

The WIT tool can be extremely useful, as it can be operated on a live well. This theneliminates the need killing the well and replacing the wellhead.

Use of the WIT on a live well is a very specialised process, requiring a trained operator. Thetool can be very dangerous if not assembled or operated correctly.

The WIT is generally available in two main sizes, big and small. The small size is used forstinging into most tubing sizes, from 2-3/8 up to 4 or larger. The large sized tool is used forstinging directly into casing, with no tubing in the well.


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Figure 11.8a Generic Wellhead Isolation Tool rigged up to wellhead. The WIT is connected tothe wellhead via the wellheads top flange. At this point the wellhead master valve is closed,

maintaining control of the well, and allowing the frac lines and WIT to be pressure tested.

Figures 11.8b (left) and 11.8c (right) Once the WIT has been connected to the wellhead andpressure tested (Fig 11.8a), the next stage is to close the valves of the frac lines (not shown

note that some WITs have their own master valves) and open the master valve on the wellhead.One the wellhead is open, the stringer is stroked down into the top of the tubing by pumping

hydraulic fluid into the master cylinder.

Stinger

Frac Lines

Master Valve

Tubing Hanger

Seal Assembly

Master Cylinder

Hydraulic Lines

Wellhead

Wellhead

Isolation Tool

Top Flange

Bottom Flange

Hydraulically-Operated

Plug Valve


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11.9 The Frac Spread How it Fits Together

Figure 11.8a Schematic diagram of a frac spread

Figure 11.8a illustrates how all the various components of the frac spread fit together. All fracspreads will basically look like this, although the size and number of components may vary.Some treatments will not use an LFC hydration unit, as the gel will be batch mixed prior to thetreatment. Some treatments may use intensifiers, whilst some treatments (batch fracs, orLiquid Proppant fracs) may not have separate proppant handling equipment.

However, the basic process is the same, no matter what kind of treatment is being performed.Fluid (usually water) is moved from the storage tanks and is usually blended with gellingagents to increase its viscosity. It is then blended with the proppant and pumped down thewell.

Figures 11.8b to 11.8f, below, show some typical frac spreads:-

Low Pressure Lines

High Pressure Lines

Control/Data Cables

Frac Pumps

Frac Pumps

AnnulusPump

Blender

L

FCHydration

Fluid Tanks

Proppant

TreatmentMonitoring


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Figure 11.8b Large scale treatment, carried out on several low permeability zonessimultaneously. Note the number of Sand Kings and frac tanks on location, as well as the use oftwo blenders (one for backup in case of equipment failure). This frac spread features a separatemobile field lab (bottom left) and a third blender, just for gelling up the tanks and for pumpingfluid from the tanks that are located a significant distance from the blender (located just above

the bottom left hand row of frac tanks).

Figure 11.8c The MV Boss, a Gulf of Mexico frac boat, designed primarily for high permeability,frac and pack treatments. Moving from the aft end of the boat forward, the equipment is asfollows; Coflexip reel, solvent tanks, 5 frac pumps (the aft two have a mezzanine deck fitted

above them), two vertical proppant bins (square white tanks), and fluid storage tanks (roundwhite tanks). The blender is hidden behind the proppant bins and fluid tanks.


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Figure 11.8d Skin Bypass Frac spread, using the batch frac method. The two frac pumps arepositioned opposite each other, just below the wireline mast (the small read and yellow derrick).A third pump (with BJ painted on its roof) is being used as an annulus pump. The two vertical

stainless steel tanks on the RHS are for fluid storage. The two batch mixers (each with two roundbatch tanks - the blue batch mixer is 2 x 50 bbls, whilst the red one is 2 x 40 bbls), used to batch

mix the proppant into the gel, are located at the bottom of the picture

Figure 11.8e Coiled tubing frac spread. The wellhead is positioned directly below the CTinjector (center of picture), with the reel on the RHS. On the LHS are two nitrogen tankers. The

main part of the frac spread is positioned behind the injector, with the sand dump truck beingthe most prominent feature.


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Figure 11.8f The MV Thanh Lon g. This was a boat put together for a single fracturing treatment,for a customer operating offshore Vietnam. The aft deck holds the following equipment:- 4 x 1300HHP frac pumps, Cyclone II blender, 2 x 1200 cu ft proppant bins, treatment monitoring container

c/w field lab, 4 x 165 bbls tanks and a 100 bbl vertical tank.

References

Standard Practices Manual, BJ Services, January 2001

Corporate Safety Standards and Procedures Manual, BJ Services, January 2001

Equipment and Technology Catalogue, BJ Services, 1990 onwards

Bradley, H.B. (Ed): Petroleum Engineers Handbook, SPE, Richardson, Texas (1987)

Economides, M.J., and Nolte, K.G.: Reservoir Stimulation, Schlumberger EducationalServices, 1987.

Gidley, J.L., et al: Recent Advances in Hydraulic Fracturing, Monograph Series Vol 12, SPE,Richardson, Texas (1989).

Documents

Section 11 Equipment