Reaction of Gelled Acids With Calcite
- Hisham A. Nasr-El-Din (Texas A&M University) | Abdullah M. Al-Mohammed (Saudi Aramco) | Ali Al-Aamri (Saudi Aramco) | Omar A. Al-Fuwaires (Saudi Aramco)
- Document ID
- Society of Petroleum Engineers
- SPE Production & Operations
- Publication Date
- August 2008
- Document Type
- Journal Paper
- 353 - 361
- 2008. Society of Petroleum Engineers
- 3.2.4 Acidising, 4.1.2 Separation and Treating, 2.5.2 Fracturing Materials (Fluids, Proppant), 5.8.7 Carbonate Reservoir, 2.2.3 Fluid Loss Control, 4.2.3 Materials and Corrosion, 1.8 Formation Damage
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Hydrochloric (HCl) acid is used to stimulate carbonate formations in both matrix and fracturing treatments. However, the reaction rate of the acid with calcite is fast. In addition, the viscosity of regular HCl solutions is relatively low. Acid-soluble polymers are usually added to the acid to increase its viscosity, which is needed to enhance acid diversion during matrix acidizing and reduce acid leakoff rate during acid fracturing. Gelled acids are extensively used in matrix and acid-fracturing treatments performed in carbonate formations. However, a few studies examined the impact of these polymers on the reaction of HCl acids with calcite.
This paper uses a rotating disk instrument to measure the dissolution rate of calcite by use of gelled acids. Measurements were conducted over a temperature range of 25 to 65°C, a pressure of 1,000 psi, and rotational speeds of 100 to 1,000 rpm. Acid formulations that are typically used in the field were examined. Polymer concentration was varied from 0.5 to 2 wt%. The apparent viscosity of the gelled acid was measured with a Brookfield viscometer. Measurements were done for the same solutions tested with the rotating disk instrument. The temperature was varied from 25 to 100°C, while the pressure was maintained at 300 psi. The shear rate was varied from 57 to 1,700 s-1.
Evidence of reverse and toroidal flows was noted for the first time by examining the etching patterns of the reacted disks. The etching pattern on the surface of the disk depended, among other factors, on the disk rotational speed and polymer concentration.
There was a significant increase in the apparent viscosity of gelled acids and a major decrease in the dissolution rate as the polymer concentration was increased from 0.5 to 1.5 wt%. The reaction of gelled acids with calcite was controlled by a surface reaction at 25°C, and by mass transfer at 65°C. Temperature increased the dissolution rate of calcite at all conditions examined. It did also reduce the viscosity of the gelled acid, which affected the way the acid reacted with calcite.
Carbonate reservoirs are heterogeneous, with large variations in rock permeability. Stimulation fluids, in matrix acidizing, will flow through the path of the least resistance where the permeability is high or the damage (skin) is low. There is a need for proper fluid diversion to enhance the outcome of matrix acid treatments. One way to enhance diversion is to increase the viscosity of the acid (Woo et al. 1999). High viscosity is also needed in acid-fracturing treatments to achieve deep acid penetration and longer fractures (Deysarkar et al. 1984).
Gelled (Pabley et al. 1982; Johnson et al. 1988; Crowe et al. 1989; Nasr-El-Din et al. 2002a) and in-situ gelled acids (Mukherjee and Cudney 1993; Magee et al. 1997; Yeager and Schuchart 1997; Buijse et al. 2000; Saxon et al. 2000; Taylor and Nasr-El-Din 2003) have been used to increase the viscosity of the acid on the surface or in the formation. An acid-soluble polymer is typically added to the injected acid to increase its viscosity on the surface. A suitable polymer, a crosslinker, and a breaker are added to the acid to form a gel in the formation over a certain pH range. To overcome some of the concerns raised about polymer-based acids, visco-elastic surfactants (Nasr-El-Din et al. 2006) were introduced to replace high-molecular-weight polymers, which are thought to cause formation damage (Lynn and Nasr-El-Din 2001).
Similar to other acid additives, polymers can affect the way the acid reacts with the rock. Several authors reported that the addition of polymers to the acid decreased the dissolution rate of rock by the acid (Taylor et al. 2004a) and the diffusivity of H+ (Hansford and Litt 1968; Mishra and Singh 1978; de Rozieres et al. 1994). There are several ways that polymers can affect the reaction of the acid with the rock. The polymer will increase the viscosity of the acid, which will reduce the diffusion rate of H+ from the bulk solution to the surface of the rock. Polymer molecules can adsorb on the rock surface and form a barrier that reduces acid reaction with the rock. Finally, polymers can change the flow pattern close to surface of the rock, and therefore, affect the way the acid reacts with the rock.
The present study uses the rotating-disk instrument to examine the reaction of gelled acids with calcite. This instrument has been extensively used to investigate the reaction of acids and chelating agents (Newtonian fluids) with carbonate rocks (Boomer et al. 1972; Lund et al. 1975; Anderson 1991; Fredd and Fogler 1998a, 1998b, 1998c; Conway et al. 1999; Gautelier et al. 1999; Alkattan et al. 1998, 2002; Frenier and Hill 2002; Taylor et al. 2004b, 2006; Lungwitz et al. 2007). It has been also used to study mass and heat transfer into non-Newtonian fluids (Hansford and Litt 1968; Mishra and Singh 1978; de Rozieres et al. 1994).
The reaction between acid and rock is a three-step process that involves the following:
- Transport of the H+ from the bulk solution to the rock surface
- Reaction at the surface
- Transfer of the reaction products away from the surface
The slowest step controls the overall reaction rate (de Rozieres et al. 1994).
The objectives of the present study are to (1) examine the effect of polymer concentration and disk rotational speed on the etching pattern on the surface of the rock; (2) assess the effect of polymer concentration, temperature, and disk rotational speed on the dissolution rate of calcite by use of gelled acids; and (3) determine the relationship between the apparent viscosity of gelled acids and the dissolution rate of calcite rock.
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Alkattan, M., Oelkers, E., Dandurand, J., and Schott, J. 1998. An experimental study ofcalcite and limestone dissolution rates as a function of pH from -1 to 3 andtemperature from 25 to 80°C. Chemical Geology 151 (1-4):199-214. doi:10.1016/S0009-2541(98)00080-1.
Alkattan, M., Oelkers, E., Dandurand, J., and Schott, J. 2002. An experimental study ofcalcite dissolution rates at acidic conditions and 25°C in the presence ofNaPO3 and MgCl2. Chemical Geology 190 (1-4):291-302. doi:10.1016/S0009-2541(02)00121-3.
Anderson, M.S. 1991. Reactivityof San Andres Dolomite. SPEPE 6 (2): 227-232. SPE-20115-PAdoi: 10.2118/20115-PA
Boomer, D.R., McCune, C.C., and Fogler, H.S. 1972. Rotating disk apparatus for reactionrate studies in corrosive liquid environments. Review of ScientificInstruments 43 (2): 225-229. doi:10.1063/1.1685599.
Buijse, M., Maier, R., Casero, A., and Fornasari, S. 2000. SuccessfulHigh-Pressure/High-Temperature Acidizing With In-Situ Crosslinked AcidDiversion. Paper SPE 58804 presented at the SPE International Symposium onFormation Damage Control, Lafayette, Louisiana, USA, 23-24 February. doi:10.2118/58804-MS
Conway, M.W., Asadi, M., Penny, G.S., and Chang, F. 1999. A Comparative Study ofStraight/Gelled/Emulsified Hydrochloric Acid Diffusivity Coefficient UsingDiaphragm Cell and Rotating Disk. Paper SPE 56532 presented at the SPEAnnual Technical Conference and Exhibition, Houston, 3-6 October. doi:10.2118/56532-MS
Crowe, C.W., Hutchinson, B.H., and Trittipo, B.L. 1989. Fluid-Loss Control: The Key toSuccessful Acid Fracturing. SPEPE 4 (2): 215-220;Trans., AIME, 287. SPE-16883-PA doi: 10.2118/16883-PA
de Rozieres, J., Chang, F.F., and Sullivan, R.B. 1994. Measuring Diffusion Coefficients inAcid Fracturing Fluids and Their Application to Gelled and EmulsifiedAcids. Paper SPE 28552 presented at the SPE Annual Technical Conference andExhibition, New Orleans, 25-28 September. doi: 10.2118/28552-MS
Deysarkar, A.K., Dawson, J.C., Sedillo, L.P., and Knoll-Davis, S. 1984.Crosslinked Acid Gel. J. Cdn. Pet. Tech. (January-February): 26-32.
Fredd, C.N. and Fogler, H.S. 1998a. Alternative Stimulation Fluids andtheir Impact on Carbonate Acidizing. SPEJ 3 (1): 34-41.SPE-31074-PA doi: 10.2118/31074-PA
Fredd, C.N. and Fogler, H.S. 1998b. The kinetics of calcitedissolution in acetic acid solutions. Chem. Eng. Sci. 53(22): 3863-3874. doi:10.1016/S0009-2509(98)00192-4.
Fredd, C.N. and Fogler, H.S. 1998c. The influence of chelatingagents on the kinetics of calcite dissolution. Journal of Colloid andInterface Science 204 (1): 187-197. doi:10.1006/jcis.1998.5535.
Frenier, W.W. and Hill, D.G. 2002. Effect of Acidizing Additives onFormation Permeability During Matrix Treatments. Paper SPE 73705 presentedat the SPE International Symposium and Exhibition on Formation Damage Control,Lafayette, Louisiana, USA, 20-21 February. doi: 10.2118/73705-MS
Gautelier, M., Oelkers, E., and Schott, J. 1999. An experimental study ofdolomite dissolution rates as a function of pH from -0.5 and temperature from25 to 80°C. Chemical Geology 157 (1-2): 13-26.doi:10.1016/S0009-2541(98)00193-4.
Hansford, G.S. and Litt, M. 1968. Mass transport from arotating disk into power-law liquids. Chem. Eng. Sci. 23 (8):849-864. doi:10.1016/0009-2509(68)80020-X.
Johnson, D.E., Fox, K.B., Burns, L.D., and O'Mara, E.M. 1988. Carbonate Production Decline RatesAre Reduced through Improvements in Gelled Acid Technology. Paper SPE 17297presented at the Permian Basin Oil and Gas Recovery Conference, Midland, Texas,USA, 10-11 March. doi: 10.2118/17297-MS
Lund, K., Fogler, H.S., McCune, C.C., Ault, J.W. 1975. Acidization—II. Thedissolution of calcite in hydrochloric acid. Chem. Eng. Sci.30 (8): 825-835. doi:10.1016/0009-2509(75)80047-9.
Lungwitz, B., Fredd, C., Brady, M., Miller, M., Ali, S., and Hughes, K.2007. Diversion and CleanupStudies of Viscoelastic Surfactant-Based Self-Diverting Acid. SPEPO22 (1): 121-127. SPE-86504-PA doi: 10.2118/86504-PA
Lynn, J.D. and Nasr-El-Din, H.A. 2001. A Core-Based Comparison of theReaction Characteristics of Emulsified and In-Situ Gelled Acids in LowPermeability, High Temperature, Gas Bearing Carbonates. Paper SPE 65386presented at the SPE International Symposium on Oilfield Chemistry, Houston,13-16 February. doi: 10.2118/65386-MS
Magee, J., Buijse, M.A., and Pongratz, R. 1997. Method for Effective Fluid DiversionWhen Performing a Matrix Acid Stimulation in Carbonate Formations. PaperSPE 37736 presented at the Middle East Oil Show, Bahrain, 17-20 March. doi:10.2118/37736-MS
Mishra, P. and Singh, P.C. 1978. Mass transfer fromrotating disk to non-Newtonian fluids. Chem. Eng. Sci. 33(11): 1463-1470. doi:10.1016/0009-2509(78)85195-1.
Mukherjee, H. and Cudney, G. 1993. Extension of Acid FracturePenetration by Drastic Fluid-Loss Control. JPT 45 (2):102-105. SPE-25395-PA doi: 10.2118/25395-PA
Nasr-El-Din, H.A., Al-Habib, N.S., Al-Mumen, A.A., Jemmali, M., and Samuel,M. 2006. A New EffectiveStimulation Treatment for Long Horizontal Wells Drilled in CarbonateReservoirs. SPEPO 21 (3): 330-338. SPE-86516-PA doi:10.2118/86516-PA
Nasr-El-Din, H.A., Al-Mutairi, S.H., Al-Jari, M., Metcalf, A.S., andWalters, W. 2002a. Stimulation ofa Deep Sour Gas Reservoir Using Gelled Acid. Paper SPE 75501 presented atthe SPE Gas Technology Symposium, Calgary, 30 April-2 May. doi:10.2118/75501-MS
Nasr-El-Din, H.A., Taylor, K.C., and Al-Hajji, H.H. 2002b. Propagation of Cross-linkers Used inIn-Situ Gelled Acids in Carbonate Formations. Paper SPE 75257 presented atthe SPE/DOE Improved Oil Recovery Symposium, Tulsa, 13-17 April. doi:10.2118/75257-MS
Pabley, A.S., Ewing, B.C., and Callaway, R.E. 1982. Performance of CrosslinkedHydrochloric Acid in the Rocky Mountain Region. Paper SPE 10877 presentedat the Rocky Mountain Regional Meeting, Billings, Montana, USA, 19-21 May. doi:10.2118/10877-MS
Saxon, A., Chariag, B., and Abdel Rahman, M.R. 2000. An Effective Matrix DiversionTechnique for Carbonate Reservoirs. SPEDC 15 (1): 57-62.SPE-62173-PA doi: 10.2118/62173-PA
Taylor, K.C. and Nasr-El-Din, H.A. 2003. Laboratory Evaluation of In-SituGelled Acids for Carbonate Reservoirs. SPEJ 8 (4): 426-434.SPE-87331-PA doi: 10.2118/87331-PA
Taylor, K.C., Al-Ghamdi, A., and Nasr-El-Din, H.A. 2004a. Effect of Additives on the AcidDissolution Rates of Calcium and Magnesium Carbonates. SPEPF19 (3): 122-127. SPE-80256-PA doi: 10.2118/80256-PA
Taylor, K.C., Al-Ghamdi, A., and Nasr-El-Din, H.A. 2004b. Measurement ofAcid Reaction Rates of a Deep Dolomitic Gas Reservoir. J. Cdn. Pet.Tech. 43 (10): 49.
Taylor, K.C., Nasr-El-Din, H.A., and Mehta, S. 2006. Anomalous Acid Reaction Rates inCarbonate Reservoir Rocks. SPEJ 11 (4): 488-496. SPE-89417-PAdoi: 10.2118/89417-PA
Woo, G.T., Lopez, H., Metcalf, A.S., and Boles, J. 1999. A New Gelling System for AcidFracturing. Paper SPE 52169 presented at the SPE Mid-Continent OperationsSymposium, Oklahoma City, Oklahoma, USA, 28-31 March. doi: 10.2118/52169-MS
Yeager, V. and Shuchart, C. 1997. In-Situ Gels Improve Formation Acidizing.Oil and Gas Journal 95 (3): 70-72.