This article was downloaded by: [Vadim Ahmetgareev] On: 18 March 2015, At: 12:27 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Click for updates Petroleum Science and Technology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/lpet20 Analysis of Low Salinity Waterflooding in Bastrykskoye Field V. Ahmetgareev a , A. Zeinijahromi b , A. Badalyan b , R. Khisamov a & P. Bedrikovetsky b a TATNIPINEFT Research Centre, Bugulma, Tatarstan, Russia b Australian School of Petroleum, The University of Adelaide, Adelaide, Australia Published online: 16 Mar 2015. To cite this article: V. Ahmetgareev, A. Zeinijahromi, A. Badalyan, R. Khisamov & P. Bedrikovetsky (2015) Analysis of Low Salinity Waterflooding in Bastrykskoye Field, Petroleum Science and Technology, 33:5, 561-570, DOI: 10.1080/10916466.2014.997390 To link to this article: http://dx.doi.org/10.1080/10916466.2014.997390 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &
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This article was downloaded by: [Vadim Ahmetgareev]On: 18 March 2015, At: 12:27Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Click for updates
Petroleum Science and TechnologyPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/lpet20
Analysis of Low Salinity Waterflooding inBastrykskoye FieldV. Ahmetgareeva, A. Zeinijahromib, A. Badalyanb, R. Khisamova & P.Bedrikovetskyb
a TATNIPINEFT Research Centre, Bugulma, Tatarstan, Russiab Australian School of Petroleum, The University of Adelaide,Adelaide, AustraliaPublished online: 16 Mar 2015.
To cite this article: V. Ahmetgareev, A. Zeinijahromi, A. Badalyan, R. Khisamov & P. Bedrikovetsky(2015) Analysis of Low Salinity Waterflooding in Bastrykskoye Field, Petroleum Science andTechnology, 33:5, 561-570, DOI: 10.1080/10916466.2014.997390
To link to this article: http://dx.doi.org/10.1080/10916466.2014.997390
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the“Content”) contained in the publications on our platform. However, Taylor & Francis,our agents, and our licensors make no representations or warranties whatsoever as tothe accuracy, completeness, or suitability for any purpose of the Content. Any opinionsand views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor & Francis. The accuracy of the Contentshould not be relied upon and should be independently verified with primary sourcesof information. Taylor and Francis shall not be liable for any losses, actions, claims,proceedings, demands, costs, expenses, damages, and other liabilities whatsoever orhowsoever caused arising directly or indirectly in connection with, in relation to or arisingout of the use of the Content.
This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &
Analysis of Low Salinity Waterflooding in Bastrykskoye Field
V. Ahmetgareev,1 A. Zeinijahromi,2 A. Badalyan,2 R. Khisamov,1 and P. Bedrikovetsky2
1TATNIPINEFT Research Centre, Bugulma, Tatarstan, Russia2Australian School of Petroleum, The University of Adelaide, Adelaide, Australia
Low salinity waterflooding is presently one of the most promising enhanced oil recovery (EOR) methods.Wettability alteration and residual oil decrease are the most important EOR mechanisms of low salinitywaterflooding. However, the mobility control EOR due to fines migration, induced by low salinity water,and the consequent flux diversion is also an important feature of the smart waterflooding. We analyzethe limited available field data from 10 years of low salinity water injection in Bastrykskoye field.The mathematical model for fines-assisted waterflooding is used for history matching resulting in goodagreement between the field and modeling data. The model is used to compare recovery factor fortwo scenarios of low salinity water injection and formation (normal) water injection. Low incrementalrecovery and low decrease in the amount of produced water during the development of Bastrykskoye fieldis explained by the production of significant amount of the reservoir water before the commencement oflow salinity water injection.
Keywords: field data, low salinity waterflood, fines-assisted waterflooding, history matching, finesmigration
1. INTRODUCTION
Low salinity waterflooding is a recently developed enhanced oil recovery (EOR) technique thatimproves mostly microscopic displacement efficiency by alternating the rock wettability, makingit more water wet. The detailed analysis of microscopic physics mechanisms of low salinity wa-terflooding can be found in reviews by Morrow and Buckley (2011) and Sheng (2014). Recentstudies of low salinity waterflooding have largely focused on the effects of water compositions onwettability, capillary pressure, relative permeability, and residual oil saturation (Tang and Morrow,1999; Berg et al., 2010). Morrow and Buckley suggest also that the formation of lamellae andemulsions, stabilized by fines, their migration, and straining, may result in mobility control anddeep reservoir flow diversion. Tang and Morrow (1999) and Fogden et al. (2011) suggested anothermechanism of oil-wet and mixed-wet fines detachment by advancing water-oil capillary menisci; theresulting straining may also decrease the water relative permeability and increase oil recovery. Theseeffects appear to be separate phenomena from the fines lifted by low salinity water and plugging ofwater-filled pores, but may occur simultaneously with fines migration. Hussain et al. (2013) aimedto confirm the above effects of the water phase permeability reduction during high and low salinitywaterflooding in oil-saturated rock. It was concluded that the water-wet particles have been removed
Address correspondence to A. Zeinijahromi, The University of Adelaide, Adelaide, Australia. E-mail: [email protected]
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lpet.
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from the rock by moving low salinity water, resulting in decrease in relative permeability for wa-ter and in increase in fractional flow for oil. The conclusions agree with the above mechanismsproposed by Sarkar and Sharma (1990). In order to separate these effects, the injections leadingto fines lifting and permeability decline are called in the current work the fines-assisted water-flooding.
The available literature on laboratory studies and mathematical modeling of low salinity wa-terflooding highly exceeds that on field trials. Several limited field applications show significantrecovery of residual oil (Seccombe et al., 2010). However, the North Sea pilot, where the screeningcriteria for low salinity waterflood have been met, did not exhibit an incremental recovery (Skret-tingland et al., 2010). The lack of information on real field applications of smart waterflooding is aserious restriction for large scale application of the technology in oil industry.
2. DESCRIPTION OF LOW SALINITY WATERFLOODING IN THE FIELD
Map of the Bastrykskoye field is shown in Figure 1. Purple circles correspond to 18 injectors double-color circles correspond to 36 producers. The circle sizes are proportional to accumulated injectionand liquid volume produced. Bastrykskoye field consists of two isolated sandstone reservoirs withalmost no hydrodynamic interaction between. Average thickness of the upper Tula layer is 4 m,thickness of the impermeable clay layer in between is 6 m and the lower Bobrik thickness is 10 m.Figure 2 shows three cross sections that are shown in the map in Figure 1. Lower Bobrik layerhas lower permeability than upper Tula layer. Pressure depletion started in 1982 followed by lowsalinity water injection started in 1988. Figure 3 shows that the significant amount of water hasalready been produced at the moment of waterflood commencement in 1988. Field mean water cutreached the value 0.48 on January 1, 2014. The injectors are located below water-oil contact. Partialpressure maintenance with oil and water production occurred during 1982–1988. Full pressuremaintenance occurred during low salinity water injection during 1988–2014. Figure 1 shows oilsaturation averaged over the production thickness. The saturation field is obtained from 3 days’reservoir simulation after matching the production and injection history up to January 1, 2014.Water cut in production wells gradually decreases from the position of initial oil-water contact up tothe central part of the anticlinal field. One can also see that oil saturation increases from peripheralareas, where the injectors are located, towards the central part of the field.
The main properties of fluids and rocks are given in Table 1. The initial pressure is above thebubble point pressure; there is no initial gas cap. The primary energy for the primary productionis provided by adjacent aquifer. Table 2 shows the formation and injected water compositions,respectively. Extremely high formation water salinity is defined by sodium chlorite concentrationthat highly exceeds those for other salts, while magnesium and calcium salts dominate in injectedwater. Thus, intensive ion exchange is expected during the displacement of formation water byinjected water.
Permeability distribution of different layers can be seen in three cross sections in Figure 2.The positions of three cross-sections are shown in Figure 1. The reservoir has minor-to-averageheterogeneity. The multiple horizontal sub-layers are combined into two layers. The upper Tulalayer has high permeability. However, the lateral correlation of sublayers is lower than that in thelower Bobrik layer.
Water injection into aquifers yields better sweep and displacement than that in the oil zone, as thedisplacement of oil by water is going on by the plane moving upwards water-oil contact. Slope ofthe peripheral zones near the initial water-oil contact also increases the recovery during bottom-upwaterflooding, as gravity decelerates water and accelerates the oil. This explains high displacementefficiency (see Table 1).
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FIGURE 1 Well placing in Bastrykskoye field with map of oil saturation.
3. RESERVOIR SIMULATION
The mathematical model for low-salinity waterflooding, where the incremental recovery is causedby the capillary phenomena and wettability alteration with the consequent decrease in residual oilsaturation is similar to that of the chemical EOR (Lake, 1989). The basic equations include massbalances for oil, water and some ions. The equations for equilibrium ion exchange and sorption onclays give the ion sorption isotherms. The relative phase permeability and capillary pressure areion-concentration-dependent.
If the incremental oil recovery is caused by lifting of attached fines, their migration and strain-ing in thin pore throats, the model is similar to those of mobility control EOR. In the presentstudy the comparison between the fines-assisted and normal waterflooding is performed for thefield conditions. Therefore, the mathematical model for low salinity waterflood with changing rel-ative phase permeability and accounting for fines mobilization and straining, yielding permeability
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FIGURE 2 Permeability of Tula and Bobrik layers in three cross sections of the field: (a) cross section position I;(b) cross section II; (c) position of the cross section III; (d) scale for permeability in mD, with perforation intervalsin red.
reduction in water swept areas, is used (see Zeinijahromi et al., 2013). The basic equations aremapped on the system of equations for polymer flooding, allowing modeling of the above pro-cesses with low salinity water injection using polymer option of black-oil model. Here we applythe reservoir simulation software Tempest (Roxar, Houston, TX) for modeling of low salinityand normal waterflooding. The tracer option in Tempest is equivalent to polymer option with-out adsorption, where relative permeability depends on tracer (salt) concentration, which fits tothe previously mentioned model for low salinity waterflooding. The tuning parameters are pseudo(at the reservoir scale) phase permeability for oil and formation water, and the reduction factorto obtain the phase permeability for low salinity water from the phase permeability for normalwater.
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FIGURE 3 History matching of Low Sal Waterflooding: accumulated oil production, accumulated water produc-tion, and accumulated water injection.
TABLE 1Properties of Rocks and Fluids in Bastrykskoye Field
Layer
Characteristic Tula Bobrik
Reservoir top depth, m −916.8 −927Reservoir type porous porousFormation thickness, m 24.4 10.3Net pay thickness, m 2.1 3.6Relative thickness of sandstone layers 0.81 0.62Initial oil saturation 0.83 0.86Reservoir temperature, ◦С 25 25Initial reservoir pressure, MPa 11.4 11.6Bubble point pressure, MPa 1.15 4GOR, m3/ton 6.07 14.2Oil density under reservoir conditions, kg/m3 848.8 851.5Oil density under surface conditions, kg/m3 864.7 878.3Oil viscosity under reservoir conditions, mPa·sec 12.6 6.83Formation volume factor 1.03 1.064Water density under reservoir conditions, kg/m3 1171.5 1171.5Water viscosity under reservoir conditions, mPa·sec 1.75 1.75Specific-productivity index, m3/(day·MPa·m) 3.11 3.11Displacement efficiency obtained from corefloods 0.652 0.663
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TABLE 2Composition of Formation and Injected Water in Bastrykskoye Field
Figure 3 presents the production and injection history along with the modeling data.The coreflood results presented in laboratory studies by Zeinijahromi et al. (2014) and Hussain
et al. (2013) show that changing formation water to injected fresh water yields significant decreasein relative permeability for water under residual oil saturation krwor while residual oil saturation,connate water saturation and relative permeability for oil under connate water are almost the same.
The fivefold decrease of krwor (reduction factor) that is used in this study is the same as thatobtained in laboratory studies by Zeinijahromi et al. (2014) and Hussain et al. (2013).
Let us describe the tuning procedure. The Corey form of pseudo relative permeability for eachof two reservoirs is assumed. The pseudo relative permeability kr depends on saturation (s) andsalinity (γ ): krj = krj(s,γ ), j = W,O. Following the coreflood results, it is assumed that pseudorelative permeability for oil is independent of salinity. Residual oil saturation and power for oil arealso independent of salinity. The value of end point relative permeability krwor for injected salinity(γ = 0) is assumed to be five times lower than that for formation water (γ = 1).
The Corey parameters are obtained by tuning the curves of cumulative oil and water production.The form of tuned pseudo relative permeability is shown in Figure 4a for Tula layer and in Figure4b for Bobrik layer.
The obtained Corey parameters for oil-formation water are shown in the tables below Figures4a and 4b. The Corey powers are lower than one. It determines the convex forms of pseudo phasepermeability, which is typical for those as obtained at the reservoir scale.
Figure 3 exhibits a good match between the field history and the modeling data after the historymatching.
4. COMPARISON BETWEEN NORMAL AND LOW SALINITY WATERFLOODS
Incremental recovery with low salinity waterflooding is achieved by changing the injected watercomposition if compared with the formation water. During the injection of formation water, whichin reality does not happen in industry, no ionic exchange or fines detachment due to alterationof electrostatic force occur. Therefore, we define formation water injection as a basic waterfloodoption, which is referred to as normal waterflooding. All options of water injection with differentcomposition are compared with the normal waterflooding.
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FIGURE 4 Pseudo relative permeability.
Figure 5a shows the comparison for water cut and recovery factor between the normal and lowsalinity waterflooding. The incremental recovery factor due to injection of low salinity water is1.1% only. Injection of low salinity water results in reduction of amount of produced water by 1.7%only.
A comparative study is performed for a five-spot pattern in a two layer cake reservoir with similarheterogeneity to Bastrykskoye field as described in Zeinijahromi et al. (2013). The results of lowsalinity water injection in two-layer 5-spot pattern with size 200 × 200 m during 1,400 days (fouryears) are presented in Figure 5b. The layer properties, including pseudo phase permeability are thesame as that in Tula and Bobrik layers (Figure 4). Low salinity of injected water causes fivefolddecrease in relative permeability for water. The incremental recovery factor is 8.7% that agreeswith the results reported in Zeinijahromi et al. (2013). A higher incremental recovery obtainedfrom five-spot pattern if compared with injection into WOC in Bastrykskoye field is majorly due tocommencement of low salinity water injection from start of production.
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FIGURE 5 Comparison between injections of low salinity and high salinity waters for (a) conditions of Bastryk-skoye field, (b) two-layer cake reservoir (with Bastrykskoye field’s characteristics).
5. SUMMARY AND DISCUSSIONS
The objective of the present work is preliminary analysis of low salinity waterflooding in theBastrykskoye oil field and its comparison with the normal waterflooding. It is assumed that lowsalinity waterflooding causes fines migration and induced permeability damage in the swept areas,resulting in deep reservoir flux diversion.
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The tuned pseudo relative permeability has typical convex form, which is typical for up scaledrelative permeabilities at the reservoir length scale. The fivefold decrease of relative permeabilityfor water due to salinity decrease is typical for sandstone reservoir cores (see Hussein et al.,2013).
The tuned reservoir model shows very little recovery increment and small reduction in producedwater for low salinity fines-assisted waterflooding if compared with injection of formation water.However, these effects for injection into five-spot pattern are significant. The previously mentionedphenomena must be explained.
Significant amount of water has been produced before the injection in Bastrykskoye field (i.e., theinjected water displaces the oil under high water saturation). The water cut map shows that the sweepby the low salinity water is minimal due to water injection into the aquifer, almost no low salinitywater was produced (Figure 1). The central part of the reservoir is poorly swept by the injectedwater. Oil is directly displaced by high salinity formation water, injected water lags significantlybehind. The main reason has been previously mentioned as to why the incremental recovery factorwith low salinity waterflooding is not high.
Sweep efficiency for water injection into aquifer is higher than that with the injection into oil zone.The discussed fines-assisted low salinity waterflood mostly affects the sweep, which is already high.This is another reason why low salinity fines-assisted waterflood does not exhibit high incrementalrecovery in the case under consideration.
However, the model for low salinity waterflood accounts for fines migration and consequentdecrease of relative permeability for water (i.e., the effects of wettability change and residual oil sat-uration decreasing) are ignored. Accounting for decrease in relative permeability for oil and decreasein oil residual can bring additional incremental recovery if compared with the normal waterflooding.This study is supposed to be performed after the laboratory coreflooding and determining the relativephase permeability for formation and injected waters.
Both effects of sweep and of better displacement coefficient can affect only the boundary wells.The central part of the reservoir will be affected at the later stage, when the boundary wells arewatered out and abandoned, and central wells will produce injected water.
The problem whether in general the incremental recovery with low salinity waterflood in bothchemical EOR and mobility-improvement modes during the injection into aquifer is low, may be asubject of additional investigation.
Only very limited information from the field is available; hence, significant amount of addi-tional investigations (coreflooding, SEM, XRD) must be performed for detailed analysis of theBastrykskoye field case.
Despite some studies reported alternation of oil properties during low salinity water injection(Lager et al., 2008); no information of alterations of oil properties has been reported during LS waterinjection and oil production in Basrtykskoye field.
6. CONCLUSIONS
Oil and water production data for low salinity waterflooding in Bastrykskoye oilfield can be matchedby the fines-assisted-waterflood model (tracer model in Roxar) with high accuracy.
Low salinity water injection under the conditions of Bastrykskoye field results in low incre-mental recovery and low decrease in the produced water if compared with waterflooding byformation water under fivefold decrease in relative permeability for water due to induced finesmigration.
The phenomenon is explained by high flooding of the reservoir before commencement of lowsalinity water injection, by high salinity water. Another explanation is low salinity water injectioninto aquifer causes lower incremental recovery than that with the injection into oil-zone.
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