IR18 Improved Oil Recovery Technique for Mishrif Carbonate Reservoirs in NR and WQ Fields in Iraq

Second EAGE Workshop on Iraq

15 - 18 September 2013 Dead sea, Jordan

IR18Improved Oil Recovery Technique for MishrifCarbonate Reservoirs in NR and WQ Fields in IraqA.M.R. Awadeesian* (South Iraq Oil Company), K. Al Obaidi (ShellTechnology Centre) & S. Chatterjee (Shell Technology Centre Bangalore)

SUMMARYThe Mishrif carbonate reservoirs in the North-Rumaila and West-Qurna oil fields are impressivelycharacterized by successive-TMF-buildups. These buildups are ranked into 3-specific-reservoir-facies-performance groups, reflecting multiple-vertical-stacking pattern (RFP3-to-RFP1). A Pre-mature water-breakthrough; is seriously expected to be created mostly by RFP1 type, with vast increase in the water-oil-ratio versus continuous decrease in the oil recovery, when these carbonates treated with usual water-oil-displacement technique.To improve oil recovery for Mishrif carbonate reservoirs by overcoming the above expected problems: amodified water-flooding technique is lab-organized and settled by (micro-booster-displacement)methodology; on tens of standard-size-plugs, characterized by multi-TMFs / differential poro-permbuildups, taken from the investigated good-recovery cored intervals in the representative oil-wells fromboth fields. Suitable economic/soluble polymer with surface active agents were used, and polymerized-alkaline-surfactant-water,PAS-water flooding technique; is performed. A decrease of (10 to 15%) in water-oil-ratio; is successfully achieved after water-breakthrough by successive injections of the preparedcontrolling agent of (crudeoil-in-wateremulsion) type. An analogy scheme by facies/pore-analogy-systemhas achieved for the Majnoon domain, and RFP3-to-RFP2 / limited-RFP1 buildup is more matched, withregular / non-constrained petro-link, and limited oil-bypassing zones. The 1st and 2nd stages of thepresented water-oil displacement-technique; is of special request for Majnoon carbonates reservoirsdevelopment.



Introduction

The Mishrif carbonate reservoirs in the North-Rumaila and West-Qurna oil fields are impressively characterized by successive-TMF-buildups. The TMFbuildup is mainly recognized by composite-lithofacies/multi-pore system of various pore-throat-sorting (PTS)-grades. These buildups are ranked into 3-specific-reservoir-facies-performance groups, reflecting multiple-vertical-stacking pattern (RFP3-to-RFP1). A Pre-mature water-breakthrough; is seriously expected to be created mostly by RFP1 type, with vast increase in the water-oil-ratio versus continuous decrease in the oil recovery, when these carbonates treated with usual water-oil-displacement technique. To improve oil recovery for Mishrif carbonate reservoirs by overcoming the above expected problems: a modified water-flooding technique is lab-organized and settled by (micro-booster-displacement) methodology; on tens of standard-size-plugs, characterized by multi-TMFs / differential poro-perm buildups, taken from the investigated good-recovery cored intervals in the representative oil-wells from both fields. The lab-experiments were carried-out under reservoir conditions of pressure and temperature (2250 psi, 85-90 degree celsius) respectively. Suitable economic/soluble polymer with surface active agents were used, and polymerized-alkaline-surfactant-water,PAS-water flooding technique; is performed. The water-breakthrough has created by [0.15 to 0.25 pore volumes fluid injected (Vpi) ] with (18 – 30%) improved oil recovery. A decrease of (10 to 15%) in water-oil-ratio; is successfully achieved after water-breakthrough by successive injections of the prepared controlling agent of (crudeoil-in-wateremulsion) type, designed within pore volumes fluid-injected of (0.3 - 0.5, 0.65 - 0.85, 0.85 - 1.1 Vpi). The technique insures; good residual-oil-mobility by (65%), obviously improved ultimateoil recovery by (85–90%) @ the terminal-stage(6.5 Vpi). On the absence of SCAL analysis for Mishrif in Majnoon field; an analogy scheme by facies/pore-analogy-system has achieved for the Majnoon domain, and RFP3-to-RFP2 / limited-RFP1 buildup is more matched, with regular / non-constrained petro-link, and limited oil-bypassing zones. The 1st and 2nd stages of the presented water-oil displacement-technique; is of special request for Majnoon carbonates reservoirs development.

Case Study

The Mishrif carbonate reservoirs in the North-Rumaila and West-Qurna oil fields, are impressively characterized by successive-TMF-buildups. The TMF buildup is mainly recognized by composite-lithofacies / multi-pore system of various grades of pore-throat-sorting (PTS). These build-ups are ranked into 3-specific-reservoir-facies performance groups, reflecting multiple-vertical-stacking pattern in (RFP3-to-RFP1) progression. The Rock-Static-Phase is specifically carried-out for studying the Rock-Facies / Pore-Geometry Characterization by; analyzing hundreds rock-thin-sections, with RCAL+SCAL lab-experiments achieved on tens of conventional core plug-sized samples, progressed in three stages of work; as in the following scheme: Rock-Facies/Pore-Geometry Characterization: 1: MIT: Facies&TMFsInvestigationTechnique. 2: Facies/PetrophysicalClassification: Rock Pore Volume (Vp) , Phi% , Ka (mD). 3: Rock Capillarity System: + Pore-Size Determination and Distribution. + Effective-Porosity Determination. + Pore-Throat-Sorting (PTS) Calculation. + Swirr Determination. The methodologies used are mainly based on Amyx, J.W. 1960, Jennings, J. R. 1987 and Razoian, A. M. 2002 2008. Reservoir Facies Performance Group One (RFP1) The rock-fabric / pore-geometry system classified under this group of reservoir facies performance is exclusively represent heterogeneous rock-fabric/pore-network structure. The group characteristically covered from the grain-dominated bioclastic packstone (floatstone)-facies RF4-type to coated-grain



(bioclastic) grainstone (rudstone)-facies RF5-type,& transit-facies to Bioclastic (peloidal)-grainstone-facies RF106-type. The related pore-complex is: intergranular/leached-intergranular, separate-vugs, and well-interconnected solution-enlarged-voids, as well as; solution micro-channels pore-system. The rock-pore system is particularly characterized by variable continuity pore-passageways. The total porosity and absolute permeability ranges (15 – 25%) and (188 – 3540mD) respectively.

Figure 1 Reservoir Facies Group 1.

Reservoir Facies Performance Groups Two & Three RFP 2 & RFP 3 The mud to grain-dominated bioclastic wackestone facies, mud to grain-dominated bioclastic packstone (floatstone), and Rudistid bafflestone facies; are mainly characterizing these two performance groups. The rock-texture/pore-geometry buildup is basically separate and distinguishes the group’s specification. The total porosities vary between (19 – 28%), and the absolute permeability between (45 to 283mD).



Figure 2 Reservoir Facies Group 2.



Figure 3 Reservoir Facies Group 3. Rock-Dynamic-Phase Pre-mature water-breakthrough; is seriously expected to be created mostly by RFP1 type, with vast increase in the water-oilratio versus continuous decrease in the oil recovery, when these carbonates treated with usual water-oil-displacement technique. To improve oil recovery for Mishrif carbonate reservoirs by overcoming the above expected problems, a modified water flooding technique is organized in Lab-methodology and settled by (micro-booster-displacement) on tens of standard-sized-plugs, characterized by multi-TMFs / differential poro-perm buildups, taken from the investigated good-recovery. The lab-experiments were carried-out under reservoir conditions of pressure and temperature (2250 psi , 85-90°C) respectively. Suitable economic / soluble polymer with surface active agents were used, and polymerized-alkaline-surfactant-water, itemized as PAS-water flooding technique; is performed. The water-breakthrough has created by [0.15 - 0.25 pore volumes fluid injected (Vpi)] with (18 – 30%) improved oil recovery. A decrease of (10 to 15%) in the water-oil-ratio; is successfully achieved after water-breakthrough by successive injections of the prepared controlling agent of (crude oil-in-water emulsion) has designed within pore volumes fluid-injected of (0.3 - 0.5, 0.65 - 0.85 and 0.85 - 1.1 Vpi). The technique insures; a good residual-oil-mobility by (65%), obviously improved ultimate oil recovery by (85 – 90%) at the terminal-stage (6.5 Vpi). On the absence of SCAL analysis for Mishrif in Majnoon field; an analogy scheme by facies / pore-system has achieved for the Majnoon domain, and RFP3-to-RFP2 / limited-RFP1 buildup is more matched, with regular / non-constrained petro-link, and limited oil-bypassing zones; by incomplete TMFs. The 1st and 2nd stages of the presented water-oil-displacement-technique; is of special request for Majnoon carbonates reservoirs development.



Section 1 KL (mD), Ko (mD), Swi % & Soi % measurements, have completed for (22% brine)-saturated-core-plug-samples. Preparation and Treatment of Fluids: 1: Filtration of river-waters (Garmat Ali River, The 3 rd River ) by (10 micron) & (5-micron), and Chlorine-treated. 2: Clay-Stabilizer , Polyachrylamide. 3: Corrosion-Inhibitor, Oxygen-Scavenger. 4: Preparation of Alkali-Surf-Sol: With Suitable Range. 5: (HEC)-Polymer: By Preferable Processing. Section 2 In order to insure technical warranty for suitable usage of the prepared reservoir-heterogeneity controlling agent (oil-in-water emulsion); in injection into high permeability rock-plug sample; the following experiment under reservoir conditions has carried out; and the subsequent steps achieved: 1. The large differential pressure per unit distance occurs at the injection site (the injection well at the field scale). 2. Anomalous flow with varying pressure attained during the injection. 3. Fluid flow reduction created by emulsion-flow under: low differential pressure deep into the reservoir. 4. Accordingly fluid-permeability decrease; high permo-facies stability.

Figure 4 Section 2 crude oil-in-water Emulsion Injection.



Figure 5 Section 3 crude oil-in-water Emulsion Injection.



Figure 6 Section 4 Wettability Adjustment.



Figure 7 Emulsion Injection.



Figure 8 IOR vs. Conventional Technology for Mishrif.

Conclusion

The paper describes techniques to improve the oil recovery in Mishrif giant carbonate reservoir. Case study performed on core plugs proved that high permeability rock types acted as thief zones resulted in poor water injection performance. Better performance was achieved when suitable economic soluble polymer with surface active agents was used, and polymerized-alkaline-surfactant-water, itemized as PAS-water flooding technique; is performed. Results showed reduction in residual oil saturation in Mishrif carbonate core plugs. Also, a decrease of 10 to 15% in the water-oil-ratio is successfully achieved after water-breakthrough by successive injections of the prepared controlling agent of crude oil-in-water emulsion.

IR18 Improved Oil Recovery Technique for Mishrif Carbonate Reservoirs in NR and WQ Fields in Iraq

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