Diversion and Cleanup Studies of Viscoelastic Surfactant-Based Self-Diverting Acid
- Bernhard R. Lungwitz (Schlumberger) | Christopher N. Fredd (Schlumberger) | Mark Edward Brady (Schlumberger) | Matthew Jack Miller (Schlumberger) | Syed Afaq Ali (Chevron ETC) | Kelly N. Hughes (Chevron Corp.)
- Document ID
- Society of Petroleum Engineers
- SPE Production & Operations
- Publication Date
- February 2007
- Document Type
- Journal Paper
- 121 - 127
- 2007. Society of Petroleum Engineers
- 4.3.4 Scale, 4.1.2 Separation and Treating, 5.8.7 Carbonate Reservoir, 3 Production and Well Operations, 2.4.6 Frac and Pack, 2 Well Completion, 2.2.3 Fluid Loss Control, 5.1 Reservoir Characterisation, 5.5 Reservoir Simulation, 3.2.4 Acidising, 1.8 Formation Damage, 1.6.9 Coring, Fishing, 2.5.2 Fracturing Materials (Fluids, Proppant), 1.10 Drilling Equipment
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A self-diverting-acid based on viscoelastic surfactant (SDVA) has been successfully used recently on numerous stimulation treatments of carbonate formations in various fields.
The decrease of acid concentration during the spending process viscosifies the fluid through the transformation from spherical micelles to an entangled wormlike micellar structure while penetrating the carbonate rock. The highly viscous fluid acts as a temporary barrier and diverts the fluid into the remaining lower-permeability treating zones. After treatment, the SDVA barrier breaks when contacted either by formation hydrocarbons or pre- and postflush fluids. Quantifying diversion, fluid efficiency, and cleanup are important factors for successful candidate selection and job design. Laboratory tests defining these key factors are presented in this paper.
This paper demonstrates the diverting ability of the acid as a function of permeability, characterized by introducing the concept of maximum pressure ratio (dP max /dP 0) supported by core-flow and acid conductivity tests using limestone and dolomite cores. Results demonstrate high dP max /dP 0 in high-permeability cores and low dP max /dP 0 in low-permeability cores. Retained permeability measurements are presented that assess the level of cleanup. Flow-initiation experiments of spent acid systems with gas and brine were performed to illustrate the cleanup behavior of SDVA in comparison to gelled acid systems under conditions encountered in gas and oil wells. The results indicate that SDVA systems clean up easily and that SDVA provides higher regained permeability than conventional gelled acid systems.
The purpose of matrix stimulation in limestone and dolomite reservoirs is the formation of wormholes, which can bypass the damaged areas and increase the effective wellbore area. When acid enters the formation with the highest injectivity it creates highly conductive flow channels, called wormholes, by dissolving the carbonate-containing minerals. Consequently, the injectivity will be further increased. The other zones are left untreated by the acid. To overcome this problem, a diverting agent is used. Mechanical diverters such as ball sealers, degradable ball sealers, rock salt, and benzoic acid flakes are used alone or in conjunction with chemical diverters based on foams or polymeric gels (Williams et al. 1979; Economides and Nolte 1989). These materials can work effectively only in a narrow permeability contrast and may result in residual damage (Lynn and Nasr-El-Din 2001). These characteristics are highly undesirable, particularly in low-pressure gas wells, and in long vertical and horizontal sections.
Polymer-based systems such as in-situ crosslinked gelled acids (XLGA) have been used in the field as self-diverting fluids. These systems rely on a pH-triggered increase of viscosity during the acid spending process. Essentially, the pH change activates a metallic reagent that crosslinks the polymer chains, and the resulting viscosity increase causes a higher flow resistance (Mukherjee and Gudney 1993; Saxon et al. 1997). Further increase of the pH deactivates the metallic crosslinker and breaks the fluid down to the original linear gel with dissociated polymer chains. However, because of the nature of the long polymer chains, potential damage of the formation may occur (Lynn and Nasr-El-Din 2001).
Recently, a new polymer-free self-diverting acid system was developed with a fluid stability in temperatures greater than 300°F (Taylor et al. 2003; Chang et al. 2001). The fluid system has been applied successfully in both matrix (Al-Mutawa et al. 2001) and acid-fracturing (Al-Muhareb et al. 2003; Artola et al. 2004) treatments. It causes rapid viscosity development throughout the spending process. The reduction in acid concentration, together with the simultaneous release of ions in solution, promotes the transformation from spherical micelles into worm-like micelles, resulting in increased viscosity of the fluid. The highly viscous fluid subsequently diverts the remaining acid treatment fluid into zones of lower injectivity by reducing the acid loss into wormholes, resulting in an improved zonal coverage of the treatment interval. Diversion tests using multiple parallel cores with varying permeabilities showed effective stimulation in all cores (Taylor et al. 2003; Chang et al. 2001).
This paper presents new data providing further insight into the understanding of the unique properties of this SDVA based on laboratory studies. Specifically described are the chemical and physical properties of the SDVA fluid, including cleanup efficiency that is relevant to low-pressure reservoirs.
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Al-Muhareb, M., Nasr-El-Din, H., Samuel,E., Marcinew, R., and Samuel, M. 2003. Acid Fracturing of Power WaterInjectors: A New Field Application Using Polymer-Free Fluids. Paper SPE82210 presented at the SPE European Formation Damage Conference, The Hague, TheNetherlands, 13-14 May. DOI:http://www.spe.org/elibrary/servlet/spepreview?id=82210-MS.
Al-Mutawa, M,. Al-Anzi, E., Ravula, C.,Al Jalahmah, F., Jemmali, M., Samuel, E., and Samuel, M. 2003. Zero-Damaging Stimulation andDiversion Fluid: Field Cases From the Carbonate Formations in NorthKuwait. SPEPF 20 (2): 94-105. SPE-80225-PA. DOI:http://www.spe.org/elibrary/servlet/spepreview?id=80225-PA.
Artola, P., Alvarado, O., Huidobro, E.,and Salmorán, A. 2004. Non-Damaging ViscoelasticSurfactant-Based Fluids Used for Acid Fracturing Treatments in Veracruz Basin,Mexico. Paper SPE 86489 presented at the SPE International Symposium andExhibition on Formation Damage Control, Lafayette, Louisiana, 18-20 February.DOI: http://www.spe.org/elibrary/servlet/spepreview ?id=86489-MS.
Chang, F., Qi, Q., and Frenier, W. 2001.A Novel Self-Diverting AcidDeveloped for Matrix Stimulation of Carbonate Reservoirs. Paper SPE 65033presented at the SPE International Symposium on Oilfield Chemistry, Houston,13-16 February. DOI: http://www.spe.org/elibrary/servlet/spepreview?id=65033-MS.
Clark, H.B., Pike, M.T., and Rengel, G.L.1982. Water Soluble FluorochemicalSurfactant Well Stimulation Additives. JPT 34 (7): 1565-1569.SPE-9008-PA. DOI: http://www.se.org/elibrary/ servlet/spe previe w?id= 9008-PA.
Conway, M.W., Asadi, M., Penny, G.S., andChang, F. 1999. A ComparativeStudy of Straight/Gelled/Emulsified Hydrochloric Acid DiffusivityCoefficient UsingDiaphragm Cell and Rotating Disk. Paper SPE 56532presented at the SPE Annual Technical Conference and Exhibition, Houston, 3-6October. DOI: http://www.spe.org/elibrary/servlet/spepreview?id=56532-MS.
Crowe, C.W., Hutchinson, B.H., andTrittipo, B.L. 1989. Fluid-Loss Control: The Key toSuccessful Acid Fracturing. SPEPE 4 (2): 215-220;Trans., AIME, 1287. SPE-16883-PA. DOI:http://www.spe.org/elibrary/servlet/spepreview?id=16883-PA.
Economides, M. and Nolte, K. 1989.Reservoir Stimulation, second edition. Englewood Cliffs,New Jersey: Prentice-Hall Inc.
Fredd, C.N. 2000. Advances inUnderstanding and Predicting Wormhole Formation. Reservoir Stimulation,3rd Edition, Eds. K. Nolte and M. Economides. West Sussex, England, JohnWiley and Sons Ltd.
Fredd, C.N. and Fogler, H.S. 1998.Influence of Transport and Reaction on Wormhole Formation in PorousMedia. AIChE J. 44 (9): 1933-1949. DOI: http://dx.doi.org/10.1002/aic.690440902.
Fredd, C.N. and Fogler, H.S. 1999. Optimum Conditions for WormholeFormation in Carbonate Porous Media: Influence of Transport and Reaction.SPEJ 4 (3): 196-205. SPE-56995-PA. DOI:http://www.spe.org/elibrary/servlet/spepreview?id=56995-PA.
Fredd, C.N. and Miller, M.J 2000. Validation of Carbonate MatrixStimulation Model. Paper SPE 58713 presented at the SPE InternationalSymposium on Formation Damage Control, Lafayette, Louisiana, 23-24 February.DOI: http://www.spe .org/elibrary/ servlet/spepreview?id=58713-MS.
Hall, B.E. 1975. The Effect of Mutual Solvents onAdsorption in Sandstone Acidizing. JPT 27 (12):1439-1442.SPE-5377-PA. DOI: http://www.spe.org/elibrary/servlet/spepreview=?id=5377-PA.
Hinkel, J.J., Brown, J.E., Gadiyar, B.R.,and Beyer, E. 2003. NewEnvironmentally Friendly Surfactant Enhances Well Cleanup. Paper SPE82214 presented at the SPE Formation Damage Conference, The Hague, TheNetherlands, 13-14 May. DOI:http://www.spe.org/elibrary/servlet/spepreview?id=82214-MS.
Lynn, J.D. and Nasr-El-Din, H.A. 2001. A Core-Based Comparison of theReaction Characteristics of Emulsified and In-Situ Gelled Acids inLow-Permeability, High-Temperature, Gas-Bearing Carbonates. Paper SPE 65386presented at the SPE International Symposium on Oilfield Chemistry, Houston,13-16 February. DOI:http://www.spe.org/elibrary/servlet/spepreview?id=65386-MS.
Mukherjee, H. and Gudney, G. 1993.Extension of Acid FracturePenetration by Drastic Fluid Loss Control. JPT 45 (2):102-105. SPE-25395-PA. DOI: http://www.spe.org/elibrary/servlet/spepre viewid=25395-PA.
Navarette, R.C., Holms, B.A., McConnell,S.B., and Linton, D.E. 1998. Emulsified Acid Enhances WellProduction in High-Temperature Carbonate Formations. Paper SPE 50612presented at the SPE European Petroleum Conference, The Hague, The Netherlands,20-22 October. DOI:http://www.spe.org/elibrary/servlet/spepreview?id=50612-MS.
Rosen, M. and Dahanayake, M. 2000.Industrial Utilization of Surfactants: Principles and Practice,San Diego, California: American Oil Chemists Soc.
Saxon, A., Chariag, B., and Rahman, M.1997. An Effective MatrixDiversion Technique for Carbonate Formations. Paper SPE 37734 presented atthe Middle East Oil Show, Bahrain, 15-18 March. DOI:http://www.spe.org/elibrary/servlet/spepreview?id=37734-MS.
Taylor, D. et al. 2003. Viscoelastic Surfactant-BasedSelf-Diverting Acid for Enhanced Stimulation in Carbonate Reservoirs. PaperSPE 82263 presented at the SPE European Formation Damage Conference, The Hague,The Netherlands, 13-14 May. DOI:http://www.spe.org/elibrary/servlet/spepreview?id=82263-MS.
Walser, D.W. and Lopez, E. 2002.Improvements in In-Situ Cross-Linked Acid Systems For Stimulation Diversion inLong Carbonate Sections. Paper presented at Southwestern Petroleum ShortCourse.
Wang, Y., Hill A.D., and Schechter, R.S.1993. The Optimum Injection Ratefor Matrix Acidizing of Carbonate Formations. Paper SPE 26578 presented atthe SPE Annual Technical Conference and Exhibition, Houston, 3-6 October. DOI:http://www. spe.org/elibrary/servlet/spepreview?id=26578-MS.
Williams, B.B., Gidley, J.L., andSchechter, R.S. Acidizing Fundamentals, 1stedition. New York: Society of Petroleum Engineers of AIME.