Infill drilling lessons leart in the past 20 years

8/10/2019 Infill drilling lessons leart in the past 20 years

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Infill drilling-lessons learnt in the past 20 yearsBlock 1, Forum 5 paper

Infill drilling-lessons learnt in the past 20 yearsLinhua Guan, Texas A&M UniversityYuqi Du, New Mexico TechZhiming Wang, Chevron

Abstract:

It has been known that infill drilling can improve the recovery of hydrocarbon by acceleratingthe hydrocarbon productions because most reservoirs in the real world are not homogeneous.With the increasing demand for energy and higher oil and gas prices, more and more fields allover the world are undergoing infill drilling. This paper describes the development of infilldrilling in the petroleum industry and summarizes what petroleum engineers have learnt in thepast 20 years about infill drilling. Various field examples are discussed on the successfulnessand failure of the infill drilling campaigns in the industry. The results of our study indicate thatwhen the reservoirs become more heterogeneous, the infill drilling works better.

Introduction

The importance of enhanced oil recovery technology (EOR) cannot be overemphasized,especially in the context of a mature petroleum province or a country, such as the U.S., withdeclining domestic production and increasing imports. The decline of domestic production andincreasing of petroleum imports reminds us of our increasing dependence on foreignpetroleum supplies. Combined with the fact that the probability of finding new discoveries iscontinually decreasing reinforces the need for EOR oil recovery technology.

The significance of EOR lies in the promise it holds for increasing the expected productionfrom existing oil fields. In mature petroleum provinces, such as the onshore US in general,growth of reserves in existing oil fields typically contributes more to the industrys continuedviability than the discovery of new fields. In other words, in thoroughly explored provinces,

better technology, more accurate reservoir characterization, and more effective productionfrom known fields typically add new reserves faster than exploration for new fields.

It has been known that infill drilling can improve the recovery of hydrocarbon by acceleratingthe hydrocarbon productions because most reservoirs in the real world are nothomogeneous.

1-7Driscoll

1and Gould et al.

.2, 4summarized the various factors that contribute

to increased recovery after infill drilling in 1980s:

Improved areal sweep

Areal heterogeneity

Improved vertical sweep

Lateral pay connectivity

Recovery of wedge-edge oil

Reduced economic limits

Recently, with the increasing demand for energy and favourable oil and gas prices, more andmore fields all over the world are undergoing infill drilling. The advances in reservoirmanagement provide a much clear picture of hydrocarbon distribution in the reservoirs whichhelps petroleum engineers to plan highly effective well profiles and the advanced imagingtechnologies allow the hydrocarbon field operators to select the best locations for infill drillingto optimize well placement.

In the past 20+ years, many infill drilling projects have been put into production and lots ofvaluable experiences have been gained on infill drilling. Therefore, the purpose of this paperis to present lessons learned and best practices on infill drilling from published literatures andprovides a concise compendium to the current understanding of current industry infill drillingpractice.

opyright World Petroleum Congress all rights reserved


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At the same time, this paper will discuss two recent developed fast techniques which canrapidly determine the infill drilling potentials in mature, tight hydrocarbon basins and presentlessons learned on the application guidelines for those two fast methods to help independentoperators develop operational and design strategies for current and future infill drillingprojects.

The scope of this paper is the update of Gould4and Wus

5reviews on lessons learned of infill

drilling in the petroleum industry. Consequently, all the infill drilling cases appear in openliterature before 1989 are not included in this paper. It should be noted that most of thereviewed field studies are from SPE and only some of the papers have been peer reviewed.

Recent Infill Drilling Field Experience

Infill drilling of additional wells after initial development (primary and/or secondary) played animportant role in improving the oil and gas recovery in the tight hydrocarbon reservoirs.

6

Generally speaking, the reservoir heterogeneity and layer continuity can be changed by thewell spacing. The infill drilling wells reduce the well spacing of the hydrocarbon fields and thenenhance the well connectivity. Wu, et al.

7reported the results of their study to determine the

impact of infill drilling on the waterflood recovery in West Texas carbonate reservoir in 1989.Their study shows a certain degree of correlation between the waterflood recovery and well

spacing.

During the literature search, we found dozens of papers on field infill drilling projects since1989. Table 1 summarizes some of the typical infill drilling projects reviewed in our study infield name order, includes comments on reservoir type, rock type, initial well spacing, as wellas lessons learned from each case and case reference.

If the infill drilling projects are classified by field environment, the results will be that theonshore fields are the majority. It seems that the infill drilling is not widely used in the offshorereservoirs as a viable improved hydrocarbon recovery method which might be caused by theunique characteristics of the offshore environments.

Table 1- Summary of Reviewed Infill Drilling Projects

Field name Reservoir type Rock type Initialwellspacing

Lessons Learned References

BarrowIsland Field

Australiaoffshore oil field

Highly complexsandstones

40-acre Field productionsignificantly increased.

29

BombayHigh

Offshore field inIndia

Highlyheterogeneouscarbonate

N/A Re-entry and clamp-oninfill wells improved fieldrecovery.

32

EastCanton

Onshore oil fieldin Ohio

Low-permeabilitysands

40-acre Infill wells increaserecovery factor from11% to 13%.

27

F-pad Oil field inPrudhoe Bay

Heterogeneoussandstone

80-acre Infill wells increased oilrecovery of 2.1 MMSTB

19

GullfaksField

Norway offshoreoil field

Highlyheterogeneousreservoirs

N/A Through tubing infilldrilling increasedGullfaks oil recovery.

28

Hugoton Onshore gasfield in USA

Shallow marinecarbonate

640-acre

The 659 infill wells havenot added GIP.

8-10,20-21

Leonardian-RestrictedPlatform

Oil field inPermian Basin

Highly Complexcarbonate

80-acre Infill wells developedpotential reserves.

14

Moxa Arch Gas field inWyoming

Highlyheterogeneoussands

640-acre

Infill drilling on 160 acrewould increase reservesby 68%.

17

Niger Delta Giant oil field inNigeria

Poorly connectsands

N/A Infill drilling, stimulationand gas-lift improvedfield recovery.

16



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North Kadi Oil field in NorthCambay Basin,India

Fluvial depositsands

N/A 33% infill wells achived1.7% additionl reserves.

35

North Rlley Oil field inTexas

Stratifieddolomite

80-acre Continuity is the majorfactor to the success ofinfill drilling.

12

Ozona Onshore gas

field in Texas

Complex

turbidite sands

320-

acre

Infill wells greatly

increase Ozonareserves.

24-25

Seventy-sixWest

Oil field inTexas

Highly complexsandstones

N/A Estimated 6 MMSTB ofremaining oil can bedeveloped by infill wells.

13

Tapis Field Offshore oil fieldin South ChinaSea

Highlyheterogeneoussandstone

N/A Integration studyincreased reserves by30%.

18

WassonSan AndresField

Onshore field inTexas

Dolomites 80-acre Infill wells and patternreconfiguration added14.2 MMSTB reserve.

30

Successful Infill Drilling ExperienceIt is well known that internal reservoir heterogeneity can created significant fluid flowanisotropy, which can trap the remaining mobile oil in the compartments poorly contacted bythe current well spacing and in zones inefficiently swept of waterflooding or gasflooding.Therefore, it is not surprised to find (Table 1) that infill drilling has been successful in bothsandstone and carbonate reservoirs.

Holtz, et al.14

reported that Leonardian Restricted Platform Carbonate reservoirs exhibitabnormally low recovery efficiencies. Cumulative production from those mature PermianBasin reservoirs is only 17 percent of the STOOIP, less than half the average efficiency ofother carbonate reservoirs in the Permian Basin. Later, it was found that this poor recoveryefficiency is directly related to high degrees of vertical and lateral facies heterogeneity causedby high-frequency, cyclic sedimentation in low-energy carbonate platform environments.

Because of their geologic complexity, the Leonardian Restricted Platform Carbonatereservoirs have the potential of 683 MMSTB for reserve growth. Their study indicated that theultimate recovery efficiency of the above reservoirs can nearly triples when reservoirdevelopment changes from 80-acre primary recovery to 10-acre secondary recovery.

It seems that the success potential of infill drilling is directly related to reservoir heterogeneity.Holtz, et al.

15have demonstrated that in their further studies in the Permian Basin. Normal

carbonate reservoirs in Permian Basin exhibit an average recovery efficiency of about 35percent. However, those reservoirs producing from rocks deposited in restricted platformsettings are associated with even lower efficiencies, exhibit average efficiencies of less than20 percent, reflecting the high degree of heterogeneity in these rocks. Because of their lowrecovery efficiencies and high degree of heterogeneity, these reservoirs are ideal candidatesfor studies of the potential for reserve growth.

The Moxa Arch Frontier Formation in Wyoming is very heterogeneous with permeabilitiesranging from 0,001 mD to more that 0.1 mD. The productive sand thicknesses vary from lessthan 10 ft to over 70 ft. Effective drainage areas range from over 640 acres to less than 100acres. Cipolla and Kyte

17concluded that infill drilling on 160 acre spacing within a portion of

the Moxa Arch field would increase reserves by 68% when compared to reserves for 320 acrespacing based on their study.

Extensive infill drilling has been practiced in the West Texas carbonate reservoirs as amethod of modifying waterflood patterns and increasing pay continuity.

37The Seventy-six

West Field13

is one of nearly 300 south Texas fields with similar depositional, structural, andproduction characteristics. Therefore, the infill drilling success of Seventy-Six West field canbe expected from other south Texas fields.



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Integration - The Key to the Success of Infill Drilling Projects

The integration study of sequence stratigraphy, log analysis, 3D seismic, reservoir simulation,and drilling has increased Tapis Field reserves by 30% through rig workover, infill drilling fromexisting platforms and installation of a new satellite platform.

18 The Tapis field experience

further demonstrates the value of integration for mature fields.

Yeager, et al.

26

conducted an integration study to determine the infill drilling potential for aportion of the Bakersville Field in Coshocton County, Ohio. Their result indicated that theexisting wells are effectively recovering the gas in place. Therefore, potential infill locationsoffsetting highly productive Beekmantown completions are likely to encounter reservoirpressures significantly lower than the original 3,100 psia. Based on the results of their study,the Bakersville operator decided not to drill proposed infill wells, thereby eliminatingunnecessary capital expenditures.

Rushing and Blasingame33

presented the results of the Clear Fork carbonate in the TXLSouth Unit Field in the Ector County, Texas, using an integrated approach. The primaryevaluation tool was decline type curve analysis and well performance analysis wascomplemented with petrophysical and geological studies, each representing differentreservoir scales. Based on their study results, Rushing and Blasingame identified the bestfield areas for future infill drilling. At the same time, the integrated study is also the key to thesuccess of the infill drilling optimization of the naturally fractured tight-gas MesaverdeSandstone reservoirs in San Juan Basin.

31Therefore; it is the recommended method for

future infill drilling projects.

Unsuccessful Infill Drilling Experience

The Hugoton gas field in the largest gas field in the Lower 48 states and several hundredsinfill wells have been drilled since the Kansas Hugoton infill drilling program started in 1987.

8

Since then, many researcher have analyzed the performance of the Hugoton infill drillingprogram.

McCoy, et al.8-10

compared the 659 Kansas Hugoton infill well performances and companionoriginal wells using official deliverability tests and production history data and they concludedthat the results from those infill drilling wells have not found any additional gas-in-place. At thesame time, they presented the pitfalls in the used of official deliverability and wellhead shut-inpressure difference between infill wells and companion original wells to indicate additionalgas-in-place.

The further published Hugoton infill drilling studies20-21

also supported the fact that theHugoton infill wells and original wells are in pressure communication and the pressuredifference between each set of original and infill wells is caused by the pressure gradient inthe high permeability layer(s) between the two wells. The original wells already have drainedsignificant volumes of gas from the high permeable productive layers in the area of new infillwells. Therefore, trapped or bypassed gas does not exist due to low areal heterogeneity ofthe Hugoton field.

Xue, et al.22

compared the waterflood infill drilling and CO2 flood in the Monahans unit andJohnson J.L. AB unit and they found that with waterflood infill drilling at 10-acre spacing, therecovery factor can be as high as 30%. However, the economic analysis indicates thatwaterflood on a 10-acre well spacing is less profitable when compared to CO2 flood.Moreover, it is rarely reported that infill drilling practice has been applied to the fields whosecurrent well spacing is less than 10-acre even for the low-permeability hydrocarbon fields.

Vertical Infill Wells vs. Deviated/Horizontal Infill Wells

Tewari, et al.32

demonstrated that the sidetracking of problematic wells was a viable option inthe offshore Bombay High field for production of bypassed oil since it could reduce the wellinventories and saved valuable slot on the offshore platform. The results of their Bombay fieldstudy indicated that limited success of workover jobs, poor cementation, bad wellboreconditions, and early water breakthrough are the main reason to make infill wells susceptibleto channelling behind casing and cross flow between the layers. Based on their study, Tewari,

et al. concluded that the drilling of infill wells through clamp-on is a cost-effective technique for



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incremental oil recovery in the highly heterogeneous and multilayered carbonate field likeBombay High.

Horizontal wells are usually drilled as development wells to recover incremental oil and toaccelerate oil from certain locations such as poorly floodable and drainable oil. Bower

23

reported a case in Canada that the estimated potential incremental oil reserve can be as highas 2.8 billion barrels due to horizontal infill wells.

Historic production and well performance data from Yibal field34

indicated that the later drilledhorizontal wells are comparable vertical wells on oil rates except the early drilled horizontalwells. But, the later drilled horizontal wells have much higher water cut which made themuneconomical. A further study suggests that the only parts of the perforated intervalscontribute to the fluid flow in the horizontal wells and it is confirmed by the recent productionlogging.

A study on the 12,000 horizontal wells drilled in different regions of Western CanadianSedimentary Basin in 2004 indicated that the horizontal wells, in general, have beeneconomically, especially for the wells in tight gas heavy oil reservoirs, in a variety of reservoirsetting in Western Canadian Sedimentary Basins.

36However, this study also revealed that

about one out of three horizontal wells in Western Canada are not profitable. Therefore, itmay be prudent in many situations to drill vertical wells rather than horizontal infill wells due tovarious reservoir uncertainty and risks, although horizontal wells may offer many advantages.

Blanket vs. Targeted Infill Drilling

Operators have historically used blanket infill drilling technique to drill infill wells in largehydrocarbon basins. In this method, wells are drilled on uniform well patterns and spacing,therefore, reservoir quality is not considered. Obviously, it is not the optimum developmentstrategy.

Yadavalli, et al.11

evaluated the waterflood infill drilling performance in the study area of theJohnson J.L.AB unit in Ector County, West Texas. The economic evaluation for blanket andtargeted infill drilling scenarios indicated that the targeted infill drilling scenario resulted in ahigher recovery and better economic return than the blanket infill drilling scenario. Moreover,they found that the optimum infill drilling pattern did not need to be a regular pattern.

Generally speaking, targeted infill drilling techniques can optimize a hydrocarbon fielddevelopment by maximizing economic returns and reducing capital expenditures. However,targeted infill drilling methods often require a complete reservoir evaluation to identify areas ofthe field with best quality rock and largest volume of remained hydrocarbon in place which willmake it uneconomical for some large hydrocarbon fields.

In the following sections, we will discuss two recent developed targeted infill drillingtechniques that do not need a complete reservoir evaluation to determine infill drillingpotentials in large tight gas basins.

Fast Methods for Determining Infill Drilling PotentialsThe recommended way to determine infill-drilling potential in a reservoir is to conduct acomplete reservoir evaluation involving geological, geophysical, and reservoir analyses andinterpretations. While it is accurate, this approach can be prohibitively time-consuming andexpensive for some large hydrocarbon fields.

As a matter of fact, it is almost economically impossible for operators to conduct a completereservoir evaluation when they are dealing with a large, mature tight hydrocarbon field whichhas hundreds or even thousands of developing wells. It is not uncommon for a company tohave hundreds or even thousands of infill candidates to choose from in the tight hydrocarbonfields. Therefore, for some large, low-permeability hydrocarbon basins with large data setsand complex geology, the cost and time requirements of a conventional reservoir evaluationstudy are not acceptable.

At the same time, the low-permeability wells are usually being produced not by major oilcompanies, for the most part, by small independent operators. Research is the key to the



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survival of those low-permeability wells; however, those small independent producers do nothave the means to conduct their own research. Faced with the daunting task of trying todetermine where to drill several hundred infill wells in a tight hydrocarbon reservoir, manyoperators have to rely on very simple analyses to select infill locations. This sometimesresults in wells being drilled in the wrong locations, and even worse, after seeing less-than-expected infill performance, many operators will simply give up on infill drilling and this may

be missing significant opportunities.

Moving Window TechniqueIn the early 1990s, U.S. Department of Energy has released the Infill Drilling Predictive Model(IDPM) for infill drilling of waterflood projects. This model can use a minimum amount ofreservoir and geologic description to determine if an existing waterflood project would benefitfrom infill drilling.

12However, the IDPM requires knowledge of two important heterogeneity

elements which are not easily or often measured in actual fields. The two heterogeneityelements are pay continuity and permeability variation among layers.

As an alternative approach to conducting detailed studies, various authors have usedempirical or statistical analyses to model variable well performance.

37-45In particular; McCain

et al.40

used a statistical, moving-window method to determine infill potential in a complex,low-permeability gas reservoir. Later, Voneiff and Cipolla

41further developed the moving

window technique and apply it for rapid assessment of infill and re-completion potential in theOzona field.

Methodology

The moving window method is a rigorous, model-based analysis method. It is based on acombination of the material balance equation and the pseudo-steady state flow equation,simplified by assuming that many properties are constant within an individual moving domain.The result is a linear regression equation that is applied within each window.

46

The moving window technique is a set of empirically derived approximations and comparisonsthat attempt to mimic what a reservoir engineer does when faced with a single infill locationevaluation. It can quickly evaluate the infill drilling potentials within weeks even withthousands of wells. The primary advantages of the technique are its speed and reliance upon

well location and production data only.

Figure 1 shows the diagram of the moving window method and it consists of a multitude oflocal analyses, each in an areal window centered on an existing well. The regressioncoefficients for each window are determined by regressing parameters for the wells withineach window. The windows are limited in size, e.g., 3000 acres, and generally contain 5 to 20wells. If the number of wells in a window is less than a minimum value, e.g., 3-5, a regional orglobal regression is used instead of a local regression.

Figure 1. Diagram of the fast method showing how the window moves across area. The smallblue circles are the well locations and big circles are the moving domains.

47



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Once the regression equation coefficients are determined for each window, performance canbe estimated for infill wells by substituting the appropriate values for candidate infill wellconditions. The result of this analysis is a prediction of BY for a new infill well offsetting eachexisting well. The primary advantages of the moving domain technique are its speed and itsreliance upon only well location and production data. It is routinely used to conduct infillscreening studies of projects consisting of 1000s of wells and can be used to evaluate an

entire basin in a few man-days.

Applications

The Ozona Field is located in Crockett County in Southwest Texas and it contains two majorproducing sands with about 1,800 wells.

41-42These sands are complex turbidite deposits

characterized by lenticular gas-bearing members at depths of 6,000 to 7,500 ft withpermeability from less than 0.001 mD to over 0.10 mD. The development of this field beganin 1960s on 320-acre well spacing, with subsequent infill drilling on 160 and 80-acre spacing.Later, the 40-acre spacing was granted for the majority of the field in 1995.

The production and geological studies of the Ozona Field24-25, 41-42

show limited sandcontinuity among wells and large variety in sand qualities over short distances. Therefore,well interference was not expected in the majority of the field. The large number of existing

wells and the compartmentalized nature of the sands precluded detailed reservoir analysis todetermine the infill drilling potential in the Ozona field.

Voneiff, et al.41

applied the moving window technique first to determine the infill drillingpotentials in the Ozona field. The results of their study identified 1,246 infill candidatesrepresenting 18 billion m

3of additional reserves in the field. Using this method, not only were

they able to quantify the number of infill wells and infill reserves, but they were also able toidentify the location of the infill wells in a short time frame.

Beside the applications in the Ozone field, the moving window technique also has beensuccessfully applied to Cotton Valley in east Texas,

40Milk River formation in Western Canada

Basin,43-44

Mesaverde formation in the San Juan Basin,44

Morrow formation in PermianBasin,

44and Austin Chalk

45to quantify infill drilling potentials.

DiscussionGuan, et al.

46have systematically evaluated the accuracy of the moving window technique

and they concluded that this technique can accurately predict infill well performance for agroup of infill candidates, often to within 10%. However, predicted infill potential for individualwells can be off by more than +/-50%. The method can predict average infill well performancereasonably well even when well productivity has decreased significantly due to depletion. Atthe same time, the accuracy of predicted infill well performance, for either individual wells orthe average of a group of wells, decreases as heterogeneity increases. Moreover, theaccuracy of predicted average infill well performance increases as the number of wells in theproject increases.

Guan, et al.47-48

also found that larger errors usually occur in sparsely drilled regions of thereservoir. When the number of wells in a particular window is inadequate, the moving domain

technique defaults to a regional or global correlation, instead of a local correlation. A regionalor global correlation obviously will not predict local performance as accurately as a localcorrelation. At the same time, the fast method is based on analysis of well locations andproduction data; thus, if no wells are drilled in local regions of high permeability, the fastmethod will not be able to predict higher infill performance for the particular area.

It appears that the fast method performs well in predicting the average infill well performancefor a group of wells. So we should examine the infill-drilling program for groups of wells whenwe use this technology to evaluate infill-drilling potential. When we use this technology, wecan divide a basin or field into smaller areas and predict the distributions of infill performanceas a group for the smaller areas, rather than individual wells.

Based on the previous studies results we suggest using this fast method as an infill-screeningtool in the tight-gas basins consisting of thousands of wells. In this case, it is almost

impossible to conduct conventional reservoir studies while the moving domain technique canbe used to evaluate an entire basin in a matter of man-days. The result of this technique cantell petroleum engineers what areas need to put more efforts in further studies.



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Rapid Inversion Method

Another approach for infill and recompletion candidate well selection, rapid inversion method,has been recently developed by Gao and McVay

49at Texas A&M University. It uses reservoir

simulation combined with automatic history matching. In this method, a reservoir simulatorserves as the forward model, which calculates well production responses from reservoirdescription data. Then, sensitivity coefficients are calculated internally and used in the

inversion of history production data to estimate the permeability field. Finally, based on theestimated permeability field and forward model, the expected performances of potential infillwells are determined.

Methodology

This rapid inversion method uses Modified Generalized Pulse-Spectrum Technique (MGPST)to calculate sensitivity coefficients. The MGPST was first proposed by Chu et al.

50by using

the basic ideas of Tang et al.51

and it produces the sensitivity coefficients in one simulationrun. However, the linear system to be solved depends on the number of wells as opposed tothe number of parameters. Since the number of wells is usually much less than the number ofgrid blocks, therefore, the MGPST is very efficient.

Since the rapid inversion method is simulation-based, all the data required to initialize a

reservoir simulator (e.g. reservoir property distributions, PVT properties, reservoir pressure)are required to apply the method. However, since the goal of this method is rapid,approximate estimation of infill potential, this approach does not conduct a detailed reservoircharacterization study. Instead, in an initial application, it simply uses whatever data areavailable. For example, reservoir property maps are used if they are available; otherwise, themodel is initialized with uniform average values.

This use of reservoir simulation inversion technology in Gao and McVays method differs fromtypical application of reservoir simulation in the scale of application. Since the goal of thismethod is to determine infill or recompletion potential over large areas and for large numberof wells, often at scales exceeding individual reservoirs, the large-scale, coarse-resolutionpermeability fields are determined rather than small-scale, fine-resolution property fields usedin conventional studies of individual reservoirs. Another difference of this proposed inversion

approach from conventional reservoir study is that instead of producing at historical rates andmatching on pressure, this approach produces wells in the simulation at estimated flowingbottom-hole pressure and match on production data. This is because the method primarilyrelies on readily available well location and production data.

This rapid inversion method uses Modified Generalized Pulse-Spectrum Technique (MGPST)to calculate sensitivity coefficients. The MGPST was first proposed by Chu et al.

50by using

the basic ideas of Tang et al.51

and it produces the sensitivity coefficients in one simulationrun. In MGPST, the linear system to be solved depends on the number of wells as opposed tothe number of parameters such as Gradient Simulator method

49. Therefore, for large field

case with large number of parameters, the MGPST is more efficient.

Application

The rapid inversion method has been applied in an actual production data from the 9-township area from a large gas basin in the North America.49The study field is a shallow gasreservoir with approximately 42 years of production history and there are approximately 201wells with production through 1/31/2004.

Using the estimated permeability distribution obtained by history matching production datathrough 12/31/2000, reservoir performance was forecasted through 1/31/2004. There were 49new wells that began production during this 3-year period. Figures 2 shows field-widepredicted performance for infill wells, those wells first produced after 2001 and close toexisting wells.



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0

2

4

6

8

10

12

14

16

18

20

2001 2002 2003 2004 2005

Decimal year

FieldCumulativeProduction,

Bcf

cal

obs

Figure 2. Predicted field cumulative production for 34 infill wells.

49

The results in the above field case application showed that in areas with existing wells withsufficient production data to quantify reservoir quality, the proposed method can accuratelypredict the production potential of groups of infill wells.

Discussion

It is shows in their paper49

apparent that performance was predicted more accurately for infillwells than step-out wells. This is because the infill wells benefit from the more accuratepermeability distribution resulting from the production influence of nearby existing wells.

Since the method is based primarily on well locations and production data for a rapidscreening evaluation, predictions for individual well locations can possess significant error,particularly for step-out wells or in areas without sufficient production data. Predictions forstep-out wells or in areas with insufficient production can be improved only by including othertypes of data, e.g. seismic data.

Conclusions

This paper reviewed the infill drilling experiences as it is found in the open literature andsummarized what petroleum engineers have learned during the past 20 + years on field infilldrilling projects. Both onshore and offshore infill drilling projects have been included in thispaper. Various success and failure infill drilling cases are presented, which will help operatorsto develop operational and design strategies for current and future infill drilling projects.

This paper also discussed two recently developed fast methods, moving window techniqueand rapid inversion method, to determine infill drilling potentials in large, mature, tighthydrocarbon basins. Both methods are primarily based only on the well locations andproduction data, which are widely available in the field, and both can accurately predict infillpotentials for groups of infill candidates.

References1. Driscoll, V.J., Recovery Optimization Through Infill Drilling Concepts, Analysis, and Field Results,

paper SPE 4977 presented at the 49thAnnual Meeting of the Society of Petroleum Engineers of

AIME, Houston, TX, October 6-9, 1974.2. Gould, T.L., and Munoz, M.A., An Analysis of Infill Drilling, paper SPE 11021 presented at the 57

th

Annual Fall Technical Conference and Exhibition of the Society of Petroleum Engineers of AIME,

New Orleans, Louisiana, September 26-29, 1982.



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3. Barber, A.H., George, C.J., Stiles, L.H., and Thompson, B.B., Infill Drilling to Increase Reserves Actual Experience in Nine Fields in Texas, Okalahoma, and Illinois, paper SPE 11023, JPT, August,1983.

4. Gould, T.L., Sam Sarem, A.M., Infill Drilling for Incremental Recovery, paper SPE 18941, JPT, March1989.

5. Wu, C.H., Laughlin, B.A., and Jardon, M., Infill Drilling Enhances Waterflooding Recovery, paper SPE17286, JPT, October 1989.

6. Thakur, G.C. and Satter, A.,Integrated Waterflood Asset Management, PennWell, 1998.7. Wu, C.H., et al.,An Evaluation of Waterflood Infill Drilling in West Texas Clearfork and San Andres

Carbonate Reserves, SPE paper 19783 presented at the 1989 SPE Annual Technical Conferenceand Exhibition, San Antonio, 8-11 October.

8. McCoy, T.F., Fetkovich, M.J., Needham, R.B., and Reese, D.E., Analysis of Kansas Hugoton InfillDrilling, paper SPE 20756 presented at the 65

thSPE Annual Technical Conference and Exhibition

held in New Orleans, Louisiana, September 23-26, 1990.9. McCoy, T.F., Fetkovich, M.J., Needham, R.B., and Reese, D.E., Analysis of Kansas Hugoton Infill

Drilling Program, paper SPE 20779, JPT, June 1992.10. Fetkovich, M.J., Ebbs, D.J., and Voelker, J.J., Mutiwell, Multilayer Model to Evaluate Infill Drilling

Potential in the Okalahoma Hugoton Field, paper SPE 20778, SPE Reservoir Engineering, August1994.

11. Yadavalli, S.K., Brimhall, R.M., and Wu, C.H., Case History of Waterflood Infill Drilling in theJohnson J.L. AB Unit, paper SPE 21817 presented at the Rock Mountain Regional Meeting and

Low-Permeability Reservoirs Symposium held in Denver, Colorado, Aril 15-17, 1991.12. Fuller, S.M., Sarem, A.M., and Gould, T.L., Screening Waterfloods for Infill Drilling Opportunities,

paper SPE 22333 presented at the SPE International Meeting on Petroleum Engineering held inBeijing, China, 24-27 March 1992.

13. Hamilton, D.S., Reservoir Heterogeneity at Seventy-Six West Field, Texas: An Opportunity forIncreased Oil Recovery From Barrier/Strandplain Reservoirs of the Jackson-Yegua Trend byGeological Targeted Infill Drilling, paper SPE 22672 presented at the 66

thAnnual Technical

Conference and Exhibition of the Society of Petroleum Engineers held in Dallas, TX, October 6-9,1991.

14. Holtz, M.H., Ruppel, S.C., and Hocott, C., Analysis of Reserve Growth Potential in Leonardian-Restricted Platform Carbonate reservoirs, Permian Basin: An Integrated Approach, paper SPE 22900presented at the 66

thAnnual Technical Conference and Exhibition of the Society of Petroleum

Engineers held in Dallas, TX, October 6-9, 1991.15. Tyler, N., Galloway, W. E., Garrett, C. M., Jr,, and Ewing, T. E., Oil Accumulation, Production

Characteristics, and Targets for Additional Recovery in Major Oil Reservoirs of Texas, 1984, TheUniversity of Texas at Austin, Bureau of Economic Geology Geological Circular 84-2, p. 29.

16. Ofoh, E.P., Geological Heterogeneity in the Niger Delta: A Case for Additional Recovery Through aCombined Effort of Geologically Targeted infill Drilling, Stimulation, and Gas-Lift Installation, paperSPE 24745 presented at the 67

thAnnual Technical Conference and Exhibition of the Society of

Petroleum Engineers held in Washington, DC, October 4-7, 1992.17. Cipolla, C.L., and Kyte, D.G., Infill Drilling in the Moxa Arch: A Case History of the Frontier

Formation, paper SPE 24909 presented at the 67th

Annual Technical Conference and Exhibition ofthe Society of Petroleum Engineers held in Washington, DC, October 4-7, 1992.

18. Abdullah, M.A.Y., and Olsen, B.S., Tapis- New Opportunities from a Maturing Field, paper SPE54339 presented at the 1999 SPE Asia Pacific Oil and Gas Conference and Exhibition held inJakarta, Indonesia, 20-22 April 1999.

19. Shirzadi, S.G. and Lawal, A.S., Multidisciplinary Approach for Targeting New Wells in the PrudhoeBay Field, paper SPE 26093 presented at the Western Regional Meeting held in Anchorage, Alaska,26-28 May 1993.

20. McCoy, et al., Analysis of Kansas Hugoton Infill Drilling: Part III 1993 Update and Infill Well CaseHistories, paper SPE 26189 presented at the SPE Gas Technology Symposium held in Calgary,Alberta, Canada, 28-30 June 1993.

21. Ryan, T.C., Oberst, R.J., and Hansen, C.D.: Analysis of Infill Drilling in Kansas Hugoton, paper SPE27921 presented at the SPE Mid-Continent Gas Symposium held in Amarillo, Texas, 22-24 May1994.

22. Xue, G., Mallk, Z.A., Wu, C.H., and Mamora, D.D.: A Comparative Technical and Economic Analysisof Waterflood Infill Drilling and CO2 flood in West Texas Carbonate Reservoirs, paper SPE 27642presented at the 1994 SPE Permian Basin Oil and Gas Recovery Conference held in Midland, Texas,16-18 March, 1994.

23. Bowers, B., Bielecky, J., Drummond, K, Ku, J., and Wall, B., Impact of Horizontal Drilling on WesternCanadian Supply of Conventional Crude Oil, paper No 95-98 presented at the 46

thAnnual Technical

Meeting of Petroleum Society of CIM, May 14-17, 1995.24. Cipolla, C.L., and Wood, M.C.: A Statistical Approach to Infill-Drilling Studies: Case History of the

Ozona Canyon Sands, paper SPE 35628, SPE Reservoir Engineering, August 1996.



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25. Cipolla, C.L., and Mayerhofer, M.: Infill Drilling & Reserve Growth Determination in Lenticular TightGas Sands, paper SPE 36735 presented at the SPE Annual Technical Conference & Exhibition heldin Denver, Colorado, 7-9 October 1996.

26. Yeager, D.L., Frantz, Jr., J.J., Moody, M.A., and Neese, M.A.: Evaluation of Infill Drilling Potential ofthe Beekmantown Formation, Bakersville Field, Coshocton County, Ohio, paper SPE 37335presented at the 1996 SPE Eastern Regional Meeting held in Columbus, Ohio, 23-25 October 1996.

27. Wozinak, D.A., Wing, J.L., and Schrider, L.A.: Infill Reserve Growth Resulting From Gas Huff-n-Puff

and Infill Drilling A Case History, paper SPE 39214 presented at the 1997 SPE Eastern RegionalMeeting held in Lexington, Kentucky, 22-24 October 1997.

28. Vikane, E., Samsonsen, B., and Lorentzen, K.E., Through Tubing Infill Drilling as a Method forIncreased Oil Recovery on the Gullfaks Field, paper SPE 39358 presented at the 1998 IADC/SPEDrilling Conference held in Dallas, Texas, 3-6 March 1998.

29. Allard, D.N., Hillyer, M.G., Gerbacia, W.E., and Rychener, L.M., Empirical Risk Assessment of InfillDrilling Location, Barrow Island, Australia, paper SPE 56816 presented at the 1999 SPE AnnualTechnical Conference and Exhibition held in Houston, Texas, 3-6 October 1999.

30. Thai, B.N., et al., Denver Unit Infill Drilling and Pattern Reconfiguration Program, paper SPE 59548presented at the 2000 SPE Permian Basin Oil and Gas Recovery Conference held n Midland, Texas21-23 March 2000.

31. Al-Hadrami, H.K., and Teufel, L.W., Influence of Permeability Anisotropy and ReservoirHeterogeneity on Optimization of Infill Drilling in Naturally Fractured Tight-Gas Mesaverde SandstoneReservoirs, San Juan Basin, paper SPE 60295 presented at the 2000 SPE Rocky Mountain

Regional/Low Permeability Reservoirs Symposium in Denver, CO, 12-15 March 2000.32. Tewari, R.D., Mittal, A.K., and Patra, S.K., An Overview of Re-Entry and Clamp-on Infill Drilling for

Incremental Recovery in Offshore Field, paper SPE 64438 presented at the SPE Asia Pacific Oil andGas Conference and Exhibition held in Brisbane, Australia, 16-18 October 2000.

33. Rusing, J.A., and Blasingame, T.A., Reservoir Characterization and Infill Drilling Study of a Low-Permeability Carbonate: An Evaluation of Blanket Versus Targeted Infill Drilling Strategies, paperSPE 84282 presented at the SPE Annual Technical Conference and Exhibition held in Denver,Colorado, 5-8 October 2003.

34. Mijnssen, F.C.J., et al., Maximizing Yibals Remaining Value, paper SPE 84939, SPE ReservoirEvaluation & Engineering, August 2003.

35. Ghosh, B.N., Sarkar, S.D., Lohiya, J.P., and Das, T,K., Improved Oil Recovery by Infill Drilling in aMature Field, A Success Story, paper SPE 89368 presented that the 2004 SPE/DOC FourteenSymposium on Improved Oil Recovery held in Tulsa, Oklahoma, 16-21 April 2004.

36. Singhal, A.K., and Selwyn, J., Some Lessons on Application of Horizontal Wells from the WesternCanadian Experience, paper SPE 89372 presented at the 2004 SPE/DOC Fourteen Symposium onImproved Oil Recovery held in Tulsa, Oklahoma, 16-21 April 2004.

37. French, R.L., Brimhall, R.M., and Wu, C.H., A Statistical and Economic Analysis of IncrementalWaterflood Infill Drilling Recoveries in West Texas Carbonate Reservoirs, paper SPE 22624presented at the 1991 SPE Annual Technical Conference and Exhibition, Dallas, 6-9 October.

38. Wu, C.H., Lu, G.F., Gillespie, W., and Yen, J., Statistical and Fuzzy Infill Drilling Models forCarbonate Reservoirs, paper SPE 37728 presented at the 1997 SPE Middle East Oil Show &Conference, Bahrain, 15-18 March.

39. Soto, B.R., Wu, C.H, and Buleba, A.M., Infill Drilling Recovery Models for Carbonate Reservoirs AMultiple Statistical, Non-Parametric Regression, and Neural Network Approach, paper SPE 57458presented at the 1999 SPE Eastern Regional Conference and Exhibition, Charleston, West Virginia,21-22 October.

40. McCain, W.D. Jr., Voneiff, G.W., Hunt, E.R., and Semmelbeck, M.E., A Tight Gas Field Study:Carthage (Cotton Valley) Field, paper SPE 26141 presented at the 1993 SPE Gas TechnologySymposium, Calgary, 28-30 June.

41. Voneiff, G.W. and Cipolla, C., A New Approach to Large-Scale Infill Evaluations Applied to theOzona (Canyon) Gas Field, paper SPE 35203 presented at the 1996 SPE Permian Oil and GasRecovery Conference, Midland, Texas, 27-29 March.

42. Cipolla, C. L., and Wood, M.C., A Statistical Approach to Infill-Drilling Studies: Case History of theOzona Canyon Sands, SPE Reservoir Engineering, August 1996, p196-202.

43. Hudson, J.W., Jochen, J.E., and Jochen, V.A., Practical Technique to Identify Infill Potential in Low-Permeability Gas Reservoirs Applied to the Milk River Formation in Canada, paper SPE 59779presented at the 2000 SPE/CERI Gas Symposium, Calgary, 3-5 April.

44. Hudson, J.W., Jochen, J.E., and Spivey, J.P., Practical Methods to High-Grade Infill OpportunitiesApplied to the Mesaverde, Morrow, and Cotton Valley Formations, paper SPE 68598 presented at the2001 SPE Hydrocarbon Economics and Evaluation Symposium, Dallas, 2-3 April 2001.

45. Kyte, D.G. and Meehan, D.N., Horizontal Spacing, Depletion, and Infill Potential in the Austin Chalk,paper SPE 36721 presented at the 1996 SPE Annual Technical Conference and Exhibition, Denver,CO, October 6-9.

46. Guan, L., McVay, D. A., Jensen, J. L., and Voneiff, G. W., Evaluation of a Statistical Infill CandidateSelection Technique, SPE paper 75718 presented at the 2002 SPE Gas Technology Symposium,Galgary, Alberta, April 30-May 2.



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47. Guan, L., McVay, D. A., and Jensen, J. L., Parameter Sensitivity Study of a Statistical Technique forFast Infill Evaluation of Tight Gas Reservoirs, CIPC paper 2004-163 presented at 2004 CanadianInternational Petroleum Conference, Calgary, June 8-10.

48. Guan, L., McVay, D. A., and Jensen, J. L. and Voneiff, G. W., Evaluation of a Statistical Method forAssessing Production Potential in Mature, Low-Permeability Gas Reservoirs, Journal of EnergyResources Technology, 126(3), 2004.

49. Gao, H., and McVay, D.A., Gas Infill Well Selection Using Rapid Inversion Methods, paper SPE

presented at the 2004 SPE Annual Technical Conference and Exhibition held in Houston, TX, 26-29September.

50. Chu, L., Reynolds, A.C. and Oliver, D.S., Computation of Sensitivity Coefficients for Conditioning thePermeability Field to Well-test Pressure data, In Situ(1995) 19, 179.

51. Tang, Y. N. and Chen, Y.M.., Generalized Pulse-Spectrum Technique for 2-D and 2-Phase HistoryMatching,Applied Numerical Mathematics(1989) Vol. 5, 529-539.

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Infill drilling lessons leart in the past 20 years