ChapterVI Water Flood Design_ Surveillance [Compatibility Mode]

CHAPTER VI Surveillance, and Evaluation Ibrahim Kocabas UAEU, Al Ain

Design involves both technical and economical considerations. As a whole including reservoir, design and economic aspects any design should contain the following relevant information.

Waterflood Design Design Elements are: • (R (Res eser ervo voir ir de desc scri ript ptio ion) n) Re Rese serv rvoi oirr eva evalu luat atio ion n and and eve opment o a conceptua reservo r mo e • Selection of po potential flooding plans • • • • •

Foreca Fore casst of of rec reco over ery y ov over er the pro roje ject ct lif ifee Preliminar facilities desi n Esti Es tima mati tion on of ca capi pita tall ex expe pend ndit itur ures es an and d fu futu ture re operating expenses Cond ndu uct dec eciisio ion n an anal aly ysi siss an and eco econo nom mic evaluations en y var a es a may cause uncer a n y

Waterflood Design The above design elements should be executed in the followin hases of desi n and o eration: I. Broad conceptual design II. Evaluation of th the reservoir III.. Dev III Develo elopi ping ng pre prefer ferred red alt altern ernati atives ves . pera ng, mon or ng an eva ua ng waterflood

e

These phases will be detailed in the following

I. Broad conceptual design This part contains two substeps : 1. Id Iden enti tify fy bu busi sine ness ss op oppo port rtun unit itie ies: s: The waterflood objective objective is to enhance enhance and/or accelerate the recovery an max m ze pro . en e mo va ons cou e: • Declining reserves • Replacing or in increasing reserves • Performance under primary depletion • Su Succ cces essf sful ul wa wate terf rflo lood od in th thee sam samee or or sim simil ilar ar re rese serv rvoi oirs rs 2. Perfo Perform rm a quic quick k feas feasibi ibility lity stu study dy on the att attrac ractiv tivene eness ss of the project.

II.

Evaluation of the reservoir

Reservoir Evaluation consists of three steps: . o ect ng an eva uat ng t e n ormat on for reservoir study and asset development p ann ng 2. Rev Review iewing ing col collec lected ted inf inform ormati ation on for a equacy to ena e us construct development alternatives for a detailed stu y. 3. Des Descri cribin bing g the the fur furthe therr test testing ing nee needs ds

II. Evaluation of the reservoir (step 1) 1. Collecting data for reservoir r eservoir evaluation:

• Data on Field information; • Ph sical descri tion o the reservoir • Areal and vertical extent of producing ormation, A and h • I Iso sopa pach ch ma maps ps of gr gros osss and and net net sa sand nd • Cor orrrel elat atio ion n o la ers an and d ot othe herr zo zon nes • Surrounding environment, any information on ad acent la ers and a ui ers

II.

Evaluation of the reservoir (step 1) .

•

Geologic data ,

internal boundaries such as faults or other im er erme meab able le bo boun unda dari ries es)) 3. Re Rese serv rvoi oirr char charac acte teri rist stic icss (engineering (engineering data) data) • Areal Areal permeability permeability and porosity variation and hence (Pay quality and continuity; zonation and natural fracture heterogeneities; heterogeneities; Fracture

•

Vertical variation of permeability permeability with thickness and zone

II.

Evaluation of the reservoir (step 1)

Collecting data for reservoir evaluation (cont.):

4. Unusual completions 5. Pr Prim imar ary y prod produc ucttio ion n his histo torry • Primary producing mechanism • Primary recovery data and remaining reserves • Pressure distribution in the reservoir • Existence of gas caps and aquifers 6. Pr Prod oduc ucti tion on equ equip ipme ment nt ins insta tall lled ed 7. Wel elll co comp mple leti tion on da data ta

II.

Eval Ev alua uati tion on of the re rese serv rvoi oirr st ste e 1

Collecting data for reservoir evaluation cont. :

• Distribution of of Re Resources • Trapped gas saturation from solution gas drive • Vertical variation of saturation as a result of ravit se re ation • Presence of mobile connate water • Areas alread water looded b natural drive

II.


Collecting data for reservoir evaluation (cont.):

•

oc , u an roc u proper es (engineering data) • e a ve permea y or e reservo r roc • Gravity, FVF and viscosity as function of rese eservo rvo r pr press essur uree • Capillary pressure data The reservoir evaluation should lead to development

II. Evaluation of the reservoir (step 2) 2. Review data and based on the established conceptual model decide (or Estimate);

(This part is the major decision making part of reservoir engineering aspects of waterflooding.)

• • • • •

Possible flood patterns Injection and production rates Timing of of the pr project oject and anticipated recovery over project life Identify variables that may cause uncertainty in the technical analysis

II.


3. Describe further testing needs; we can no ave enoug con ence n s ep 2, the we should specify the need for ) • p o e es • Interwell tracer study e erm na on o res ua o s r u on • Injectivity tests , deserves special attention and pilot tests will be

tests will be dealt in surveillance part.

Eval alua uati tion on of th the e re rese serv rvo oir st ste e 3 : II. Ev Pilot project design considerations

acquiring the data needed to provide a performance. For a pilot the purpose is to conditions. conditi ons. We should keep in mind that our successful expansion of the project to filed performance of the pilot.

A pilot test is:

• • • • • • • •

A simu mula lati tion on of th thee la larger fi fiel eld d ef effor ortt A lace to make our mistakes before the et too costl A pla lace ce to wor work k th the bug bugss of of th the equ equiipm pmen entt A pl plac acee to to dev devel elop op th thee con contr trol olss and and da data ta ne need eded ed to insure the success of the project A pl plac acee to to put put ou ourr bes bestt eng engin inee eeri ring ng ta tale lent nt to th thee tes testt and and o ra ra n o ers A place for intensive planning A pl plac acee for for fi find ndin ing g eve every ry pr prob oble lem m ima imagi gina nabl blee wit with h their attendant delays

(step 3) : Pilot project design considerations A pilot test is not: • A sho hort rt te terrm mo mone ney y mak makin ing g pr prop opo osi sittio ion n • o a e s mu a on • A gr grea eatt pl plac acee to to dem demo ons nstr trat atee th theeor ory y in in ac on

III. II I. Dev evel elo op pref prefer erre red d alte altern rna ati tive vess Detailed description of the technical and economic aspects o t e water oo es gn s ou conta n information on the attractiveness of each item

a. Reservoir En ineerin Part

• Is reservoir descri tion results ade uate and promising for implementing the waterflood?

III. Develo

referred alternatives

• At Attr trac acttiv iveene nesss of of Po Poss ssiibl blee flo flood od pa patt tter erns ns o Peripheral flood o Aquifer in injection o Central flood o a ern oo ng

• Pattern co configuration

III. Develo


• Esti Estima mati tion on of in inje ject ctio ion n an and d pr prod oduc ucti tion on ra rate tess o Information from injectivity tests o Empirical co correlations o Local ex experience • An Anti tici cipa pate ted d rec recov over ery y ove overr the the pr proj ojec ectt li life o Material ba balance me methods o Empirical co correlations o Analytical models o Reservoir simulators

III. Develo


• Identify variables that may cause u ce ce y e ec c ys s • Original oil in place wee e c e cy • Injection rates Based on the results of each item of the , implemented. The next step is monitoring .

V.

Operate, monitor an and evaluate waterflood

Monitoring and evaluation includes : • Mo Moni nito tori ring ng re rese serv rvoi oirr, well wellss and and faci facili liti ties es pe perf rfor orma manc ncee • Mo Modi dify fy “l “liv ivin ing” g” re rese serv rvoi oirr mod model el as ad addi diti tion onal al da data ta ar aree • • •

Evalua Eval uate te pe perf rfor orma manc ncee an and d re revi vise se th thee ea earl rlie ierr pl plan an an and d strategies based upon actual performance en y new oppor un es or expans on Pla lan n a st stra rate tegy gy for te term rmin inat atin ing g th thee ope opera rati tion on

Following are details of some important items it ems in waterflood

VI.2 Waterflood Surveillance and monitoring project is a well-planned and well-executed . program should be designed for each field fields. The basic elements of all surveillance

VI.2 VI.2

Waterfl Wat erflood ood Surv Surveill eillance ance and mon monito itorin ring g

1. Fir First st elem element ent is that that in gene general ral thr three ee majo majorr included incl uded in any water waterflood flood surve surveillan illance ce , injection/production well conditions and . 2. Th Thee oth other er el elem emen entt is re reco cord rd 3. The fina finall eleme element nt cons consist istss of cons conside iderat ration ionss

VI.2 Waterflood Surveillance and monitoring e surve ance an mon or ng program may be divided into two general type of activities name y, measuremen an es ng ac v es. en e measure quan es are emp oye n a number of surveillance techniques for e e o ev u o eme em o purposes.

VI.2 Waterflood Surveillance and monitoring activities is observation of the items that needs .

tests for diagnosis of problems commonly , application of a well planned and well .

VI.2 VI.2 an

Part 1: Measurement Waterf Wat erfloo lood d Su Surve rveill illanc ance e (Part

es ng

Table 1 lists the items that should normally be included in the . Table 1. Listing Lis ting of waterflood project items needing surveillance

Reservoir

Wells

Facilities/Operations

Pressure

Perforations

Water quality

Rates

Fluid entry/exit

Injection facilities

Volumes

Cement integrity

Production facilities

Cuts

Downhole equipment

Pipelines

Fluid samples

Surface equipment

Monitoring equipment

VI.2.1

Reservoir Surveillance (Part 1: Measurement and

testing)

The following items require constant monitoring in reservoir surveillance eservo eser vo r pr pres essur suree, week y recor ng o bottom bot tomhol holee pre pressu ssure re reado readouts uts in in submer submersib sibly ly pum pumped ped . headers, injection wellheads, producing well flow liness and fresh sour line source-wa ce-water ter in ecti ection on headers headers Injection and production rates, ( daily recording of them)

VI.2.1

Reservoir Surveillance (Part 1: Measurement

and testing)

Fluid volumes, (daily recording of oil water and gas volumes includes data from producing wells, water supply wells, fresh water injection into producers fro salt control, injection wells, and saltwater dispsal wells) WOR/GOR’s ( daily recording of them)

VI.2.1

Reservoir Surveillance (Part 1: Measurement

and testing)

Fluid samples ( weekly recording of producing well water we g ts an eve s n t er gas p ase o producing wells. Quarterly analysis of injection water . chemical analysis of all injected and produced water. Howeve How everr, s eci ecial al rob roblem lemss att attrib ribute uted d to H2 H2S S corrosion, oxygen corrosion, inorganic scales and organic debris such as bacteria, paraffin and oil in water reverse emulsions can necessitate more frequent analysis of the produced or injected water.)

VI.2.2 Well surveillance (Part 1: Measurement and testing)

For well surveillance ; there are four types of wells requiring surveillance: production, injection, water supply and water disposal. Of these production and injection wells require the most attention.


program of selected well tests to be conducted . depend depen d on surfa surface/do ce/downhole wnhole equipm equipment, ent, well , injected fluids the stage of the waterflood , description.


Key items for well surveillance are • flui uid d ent entrry int into o or or exi exitt fro from m tar targe gett zon zones es,, • cem emen ent/ t/co com mpl plet etio ion n in inte tegr griity ty,, an and d • mec echa hani nica call eq equi uipm pmen entt, bot both h do down wnho hole le and surface.

VI.2.3 Facilities and operations surveillance ( Part 1: Measurement and testing)

In general the ingredients common to most operations needing surveillance regarding facilities and operations are • injection/production facilities, • fluid tr transmission li lines, • field monitoring equipment and, • most important, wa water quality.

VI.2.3 Facilities and operations surveillance ( Part 1: Measurement and testing)

most damaging conditions that arise in . water quality are (1) geochemical analyses analyses of the waters waters involved involved and the description of suspended solids, (2) membrane filter tests tests to describe plugging plugging effects effects o e suspen e so s an (3) flow tests to study study the effects effects of the injected water

VI.3 VI.3

Waterflood Waterflo od Su Surve rveill illanc ance e(Part (Part II. Special

a. Well testing Program

n mportant ey to t e success u app cat on an surveillan surve illance ce of water waterflood flood is a detail detailed, ed, accurat accuratee e n t on o u ow pat s. F u ow distribution is governed by reservoir properties, we con t ons an operat ng pract ces. we planned and well executed well testing program can prov e or con rm reservo r we con t on information that cannot be adequately obtained y ot er means.

(Part II. Special testing) a. e test ng rogram

n water oo ng certa n reservo r an or we conditions can results in anomalous distribution of flood operations. If fluid flow distribution distributionss can be ascertained then corrective measures can be undertaken as needed. The corrective measures can include injection and/or production well rate adjustment, well shut in, intermittent well operations, well conversions, injection profile modificati modification on and .

(Part II. Special testing) a. e test ng rogram

during dur ing wat waterf erfloo loodin ding g thu thuss can be cau caused sed by operating conditions. Reservoir characteristics include variations in , , pinchouts, lenses, fractures and active .

(Part II. Special testing) a. Well testing Program

Well and operating conditions leading to conditions, unbalanced injection production , . Regardless of the cause, unequal directional recognized, quantified and corrected. pressure transient testing and profile surveys

on

6.3.2. Project surveillance techniques based e mon or ng proce ures are

• Productivity index and inflow performance plots coupled with well-test well-t est plots of water cut and oil rates Productivity index plots (barrels per day per psia ps ia dr draw awdo down wn vs ti time me ) an and d in infl flow ow pe perf rfor orma manc ncee plots ( well opera operating ting press pressure ure vs tota totall reservoi reservoirr withdrawal rate) depend on the proper measurement of oil rate, formation water rate, well operating pressure and current reservoir pressure.

6.3.2. Project surveillance techniques based on the monitoring procedures are

Continuous plots of watercut, oil rate and productivity index facilitate detection of wellbore impairment, improve ability to measure the effectiveness of wellbore stimulations, and improve ability to determine the impact of high volume lift installations. Inflow performance plots are used to optimize the design of high volume lift installations.


• Reservoir withdrawal calculations Reservoir withdrawal calculations are made on at least a monthly basis to determine any changes in reservoir voidage. Reservoir withdrawal calculation calculationss are mportant ur ng a p ases o water oo operation.


For instance calculations during fill up time are important to maintain sufficient injection to production ratio. The injection rate should exceed the pro uc on ra e y a ac or o ree o our. This ratio allows for a reasonable fill up time usually . is achieved all pay is opened in all wells and fluid withdrawal rate is increased. During this period reservoir withdrawal rate calculations are maintained to ensure that injection rates equal reservoir fluid rates.


BHP transient test analysis

Pressure transient test analysis is used to determine Skin factors, kh product, p averages of water and oil banks and so on.


• Inject Injectivit ivity y plo plots ts with with profi profile le surve survey y compar sons Injectivity plots (barrels injected per day per psi differen differential tial n ec on pressure coup es w n ec on pro e p o s are use to detect injection well problems and injection well responses to stimulation, fracture treatment, and profile modification attempts.

coupled with chemical and transient pressure analysis can indicate indic ate injec injectivity tivity prob problems lems asso associate ciated d with calc calcium ium car ona e sca e, ac er a, oxygen corros on pro uc s an o carryover.


p rogram m • Geochemical progra Geoche Geoc hemi mica call ro ra ram m us uses es al alll th thee mo moni nito tori rin n procedures but special emphasis is placed on the chemical analyses of produced and injected water, well to well injection tracers, produced water salinity from all producers, H2S concentratio concentration n in produced gas o carryover concen ra on n pro uce wa er.

6.3.2. Project surveillance techniques

All five of these primary surveillance techniques, 1. 2. 3. 4. 5.

Produc Prod ucti tivi vity ty inde index x and and inflo inflow w perfo perform rman ance ce plo plots ts,, Rese Re serv rvoi oirr wit withd hdra rawa wall calc calcul ulat atio ions ns, BHP tr tran ansi sien entt te test ana naly lysi siss, In ectivit lots with rofile surve com arisons and Geoc Ge oche hemi mica call prog progra ram m incl includ udin ing g trace tracerr ana analy lysi siss

enables us to carry enables carry out syste systemati maticc well workov workovers ers on pro uc ng an n ect on we s. so ase on t e results of these techniques, frequently applied produce favorable results in injection wells, roduci rod ucin n wel wells ls and fie field ld rod roduct uctio ion n lev levels els..

V. Operate, monitor an and evaluate waterflood ( ctual Examples of Evaluation) Evaluation)

In many eng neer ng organ zat ons t e water oo performance of a project is predicted only once at t e t me t e pro ect s p anne . T s s rea y unfortunate. The real pay-off in terms of ncrease recovery, ncrease pro ta ty, an increased knowledge comes from a comparison o t e pre cte per ormance o a reservo r w t the way it is actually behaving.

V. O erate, monitor and evaluate waterflood ( Actual Examples of Evaluation)

The following are three examples (borrowed from Craig) of some of the more common differences diff erences one observes between actual and predicted performance and what a study of these differences differences can tell us about how to improve our waterflooding operations.

V. Operate, monitor an and evaluate waterflood (Ex.1 Ex.1))

Example data shows a plot of WOR versus recovery.


Previous figure shows a plot of WOR versus recovery. The smooth curve is that which was predicted at the outset of the project. The jagged curve is that actually observed. We see that water breakthrough has come earlier than predicted and in addition it seems to be rising generally at a faster rate than we predicted. predicted. What could could be the causes of these differences?


First the reserv reservoir oir may may be more nonuni nonuniform form than expected. That is in in moving moving from from the injection to producing well the injected water is contacting less of the reservoir and recovering less oil than we predicted. Perhaps the injected water is bypassing the oil by moving through a gas cap or an aquifer of formation fractures. Injectivity profiles together with knowledge about the reservoir itself could help us tell whether we have a gas cap or aquifer bypassing.

V.

Operate, monitor an and evaluate waterflood x.

Loo ng at t e ocat on o we s exper enc ng the higher than expected WOR may tell us w et er t ere are any reservo r sca e fractures through which the water is mov ng. not er poss ty s t at t e n t a gas saturation is higher than expected so t at as ca y t ere s ess o poss e to recover by waterflooding.


Rev ew ng t e pro uct on story o t e reservoir reser voir prior to waterf waterfloodi looding ng migh mightt give give us a c ue as to w et er t s s a poss e explanation. Another possibility is that the o sp acement e c ency s ower t an expect exp ecteded- per perhap hapss due to selec selectio tion n of a non representat ve set o re at ve permea ty characteristics.


the various factors that went into the determine the real cause for the difference difference in . for the difference, difference, that is bypassing of the probably be remedied by injection well .

V. O erate, monitor and evaluate waterflood (Ex.1 Ex.1))

If on the other hand the reservoir is more non uniform than expected or has a higher initial gas saturation , a comparison of actual and predicted performance might allow us to make a more realistic prediction for the future waterflood recovery.


shows better than expected!

V. Operate, monitor an and evaluate waterflood (Ex.2)

The previous figure shows the actual performance is more favorable than that which we predicted. It’s true that we rather infrequently find this but a reservoir engineer should attempt to determine the reason for this diff difference erence also. Perhaps the reservoir is less heterogeneous than expected, or perh pe rhap apss the the cros crossf sflo low w of inj injec ecte ted d wate waterr betw betwee een n the dif different ferent zones or or layers layers in the the reservoir reservoir has caused improved sweep.

V. O erate, monitor and evaluate waterflood (Ex.2)

This may be an indication that the waterflood recovery from this project will be higher than that originally anticipated. In any event the reason for this difference is important.


predicted oil producing rate from a . prediction had indicated an increased oil after showing an initial increase, has tended trend.


V. Operate, monitor an and evaluate waterflood (Ex.3)

Some ossible reasons for this are that the water injection rate is lower than expected or perhaps the roducin wells are becomin lu ed b paraffin paraf fin or scale or may need lar larger ger pumps to maintain a reduced fl fluid le level. This t e of of performance also could be caused by a portion of th thee in in ec ectted wa wate terr ent enter erin in a thi thief ef zo zone ne or even by the existence of a higher initial gas sattur sa uraati tio on th than an ex ec ectted ed..

V. Operate, monitor an and evaluate waterflood (conclusion of examples) examples )

A conti continuous nuous evaluat evaluation ion of waterflo waterflood od perfo performanc rmancee can accomplish several things. It can provide a basis for injection and production well workov wor kovers ers and thus thus for high higher er rates rates and and increased daily income. The evaluation can lead to a modification of the flooding pattern and thus a higher recovery than might be ultimately obtained with the present pattern.

V. Operate, monitor an and evaluate waterflood (conclusion of examples) examples )

The comparis comparision ion of actual actual and predicted predicted waterfl waterflood ood per ormance can a so y e an mprove est mate o t e actual reservoir heterogeneity. It can al the least lead to a . Thus to ac Thus achi hiev evee ma maxi ximu mum m re reco cove verr th thee ro ec ectt must be well and continuously engineered. Next are two special topics to be covered if time permits :

VI.

Wh waterfloods fail ?

After discussing the design, surveillance and ev u o oo s m y e o e o o out some common reasons of why waterfloods . Sometimes actual field performance does not several reasons. Even before this failure issue result of average and exceptional waterfloods.

VI.


Water aterflood floodss can fail fail primarily primarily due to: oo swee e c e cy o Ver erti tica call perm permea eabi bili lity ty var varia iati tion onss caus causin ing g earl early y o Frac Fractu ture ress an and d dir direc ecti tion onal al pe perm rmea eabi bili lity ty o Fl Flui uid d di dist stri ribu buti tion on in th thic ick k re rese serv rvoi oirs rs wi with th ve verr high vertic vertical al permeabil permeability ity underru underruns ns the oil oil o Vis isco cous us fi fing nger erin ing g an and d un unfa favo vora rabl blee mo mobi bili lity ty ratio o Unbalanced injectivity

VI.


Waterfloods can also fail due to: : • Unexpected expenses o Extensive remedial work o Equ pment a ure an un er es gn o producing and injection equipment

•

ers o In Init itia iall oil oil sa satu tura rati tion onss too too sm smal alll to to for form m an oi oill o Oil re resaturation of ga gas ca cap

VII. Int Interw erwell ell tra tracer cerss tes testin ting g

Tracer tests deserve special attention for their role in Geochemical surveillance, identifying primary reasons reaso ns why why waterflo waterfloods ods fail and and reservo reservoir ir characterization and will be treated in the following .

Interwell trac Interwell tracers ers are are used used to to track track inject injection ion fluid from injection wells to production wells. T e pro uce tracer t m ng an concentrat on can be used to deduce reservoir properties as t ey re ate to pre erent a ow pat s. e use of tracers to obtain some relevant information s summar ze as:

VII. Interwell tracers testing

be achieved by selective injection of tracer . injected in only one zone and is observed in different dif ferent zone then the shale separating wells)


Characterization of faults ( the absence of the tracer roduction at an off offset set roducer ma be as a result of a fault between the injector and roducer. Fi . E8 Not otee: ALL Fi ures in in Tracer Section Secti on are are borrowed from Waterfl Waterflood ood Asset Managemen Managementt book G. Takhur Takhur and coauthor

The flow along the fault zones are so high than t e transverse rect on t us ear y tracer breakthrough may be detected at a producer near t e au t.



Volumetric sweep efficiency at breakthrough The volumetric sweep efficiency eff iciency at breakthrough is a measure of the seriousness of channeling because the amount of fluid injected towards a producer at the time of breakthrough provides some qualitative information on the volume of the high permeability channel. (see Fig. E1 E11). 1).


Breakthrough Eff Efficiency iciency


Delineation of flow barriers(Any type of flow restriction such as low permeability region between an injector and producer pair will reduce the movement of tracer to the producer.(See Fig. E9)


Delineation of flow barriers


Directional flow trends t rends On the other hand if localized fractures are present in the reservoir earl tracer breakthrou h ma occur. Preferential flow paths can be ascertained by monitorin tracer breakthrou h times at neighboring production wells in different dire di rect ctiion onss fro rom m th thee in ec ecttor or.. Se Seee Fi . E1 E10 0


Directional flow trends (cont):Breakthrough times are combined with pressure drops between wells to calculate the transmissibility. If preferential flow directions are present sweep efficiency could be improved by adjusting the pattern and/or flow rates. (See Fig. E10)


Directional flow trends


Pattern balancing ( Pattern balancing is mportant n max m z ng t e sweep e c ency and ultimate recovery from a waterflood.

The relative amount of tracer recovered at eac we prov e an est mate o ow muc o the injected fluid flows towards each producer. g.


Pattern balancing


Identification of problem injectors ( problem ec o s c e e e y gg g e injected fluid at each injector with a diff different erent ce . As shown in Fig.E.13. early breakthrough at a

injector.


Identification of problem injectors


(Water production at a well can be due to . injected fluid can be detected by tagging this .

ChapterVI Water Flood Design_ Surveillance [Compatibility Mode]

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