Effect of Acid Spending on Etching and Acid-Fracture Conductivity
- Maysam Pournik (University of Oklahoma) | Lingling Li (Texas A&M University) | Bradley T. Smith (Texas A&M University) | Hisham A. Nasr-El-Din (Texas A&M University)
- Document ID
- Society of Petroleum Engineers
- SPE Production & Operations
- Publication Date
- February 2013
- Document Type
- Journal Paper
- 46 - 54
- 2013. Society of Petroleum Engineers
- 3.2.4 Acidising, 4.1.2 Separation and Treating
- 3 in the last 30 days
- 1,345 since 2007
- Show more detail
- View rights & permissions
|SPE Member Price:||USD 5.00|
|SPE Non-Member Price:||USD 35.00|
In acid fracturing, while the near-wellbore area of the fracture receives live, unspent acid, sections of the fracture farther down the length receive partially spent acid because of the acid's reaction with the rock. As a result, there is a distribution of acid concentration along the fracture length. However, almost all experimental studies on acid-fracture conductivity have been conducted with live acid, which is representative of what occurs near the wellbore.
An experimental study was conducted to investigate the effect of spent acids on the resulting fracture conductivity in a laboratory facility designed to perform acid-fracture-conductivity characterization. Gelled HCl acid systems with different degrees of acid spending were used to etch fractured cores under identical treatment conditions, which were set to mimic field conditions. Detailed etched surface characterization, fluid analysis, and conductivity measurements were performed on acid-etched fracture faces.
Experimental results show that the amount of rock dissolved and the actual etching pattern depend highly on acid concentration. While there was less fracture-face etching with more spent acid systems, the etching pattern also changed with acid spending, which sometimes offset the additional etched volume of unspent acid. As a result, the retained conductivity was generally higher for more spent acid, and the decline in conductivity with closure stress was more subtle with the spent acid, probably because of less weakening of the fracture face.
While there have been many developments in enhancing the etched length of acid-fractured wells, a major reason for the lack of long etched fractures is acid spending along the fracture. In order to understand the etched fracture profile, there is a need to realize how the degree of acid spending limits etching and affects the resulting fracture conductivity. On the basis of the newly discovered effect of acid spending on conductivity, acid-etched length and conductivity can be predicted more accurately and acid-fracture treatments better designed.
|File Size||1 MB||Number of Pages||9|
Ben-Naceur, K. and Economides, M.J. 1988. The Effectiveness ofAcid Fractures and Their Production Behavior. Presented at the SPE EasternRegional Meeting, Charleston, West Virginia, USA, 1-4 November. SPE-18536-MS.http://dx.doi.org/10.2118/18536-MS.
Conway, M.W., Asadi, M., Penny, G.S. et al. 1999. A ComparativeStudy of Straight/Gelled/Emulsified Hydrochloric Acid Diffusivity CoefficientUsing Diaphragm Cell and Rotating Disk. Presented at the SPE Annual TechnicalConference and Exhibition, Houston, 3-6 October. SPE-56532-MS. http://dx.doi.org/10.2118/56532-MS.
Crowe, C.W., Hutchinson, B.H., and Trittipo, B.L. 1989. FluidLoss Control: The Key to Successful Acid Fracturing. SPE Prod Eng 4 (2): 215-220. SPE-16883-PA. http://dx.doi.org/10.2118/16883-PA.
de Rozières, J., Chang, F.F., and Sullivan, R.B. 1994.Measuring Diffusion Coefficients in Acid Fracturing Fluids and TheirApplication to Gelled and Emulsified Acids. Presented at the SPE AnnualTechnical Conference and Exhibition, New Orleans, 25-28 September.SPE-28552-MS. http://dx.doi.org/10.2118/28552-MS.
Fredrickson, S.E. 1986. Stimulating Carbonate Formations Usinga Closed Fracture Acidizing Technique. Presented at the SPE East Texas RegionalMeeting, Tyler, Texas, USA, 21-22 April. SPE-14654-MS. http://dx.doi.org/10.2118/14654-MS.
Gomaa, A.M. and Nasr-El-Din, H.A. 2010. New Insights Into theViscosity of Polymer-Based In-Situ Gelled Acids. SPE Prod & Oper 25 (3): 367-375. SPE-121728-PA. http://dx.doi.org/10.2118/121728-PA.
Lo, K.K. and Dean, R.H. 1989. Modeling of Acid Fracturing.SPE Prod Eng 4 (2): 194-200. SPE-17110-PA. http://dx.doi.org/10.2118/17110-PA.
Lund, K., Fogler, H.S., McCune, C.C. et al. 1975. Acidization-II. The Dissolution of Calcite in Hydrochloric Acid. Chem. Eng. Sci. 30 (8): 825-835. http://dx.doi.org/10.1016/0009-2509(75)80047-9.
Mumallah, N.A. 1991. Factors Influencing the Reaction Rate ofHydrochloric Acid and Carbonate Rock. Presented at the SPE InternationalSymposium on Oilfield Chemistry, Anaheim, California, USA, 20-22 February.SPE-21036-MS. http://dx.doi.org/10.2118/21036-MS.
Mumallah, N.A. 1997. Effective HCl Diffusion Coefficients FromCorrelations of HCl-Limestone Reactions. Presented at the SPE ProductionOperations Symposium, Oklahoma City, Oklahoma, USA, 9-11 March. SPE-37458-MS.http://dx.doi.org/10.2118/37458-MS.
Navarrete, R.C., Miller, M.J., and Gordon, J.E. 1998. Laboratory andTheoretical Studies for Optimization of Acid Fracture Stimulation. Presented atthe SPE Permian Basin Oil and Gas Recovery Conference, Midland, Texas, USA,23-26 March. SPE-39776-MS. http://dx.doi.org/10.2118/39776-MS.
Nierode, D.E. and Kruk, K.F. 1973. An Evaluation of Acid FluidLoss Additives Retarded Acids, and Acidized Fracture Conductivity. Presented atthe Fall Meeting of the Society of Petroleum Engineers of AIME, Las Vegas,Nevada, USA, 30 September-3 October. SPE-4549-MS. http://dx.doi.org/10.2118/4549-MS.
Nierode, D.E. and Williams, B.B. 1971. Characteristics of AcidReaction in Limestone Formations. SPE J. 11 (4): 406-418.SPE-3101-PA. http://dx.doi.org/10.2118/3101-PA.
Nieto, C.M., Pournik, M., and Hill, A.D. 2008. The Texture ofAcidized Fracture Surfaces: Implications for Acid Fracture Conductivity. SPEProd & Oper 23 (3): 343-352. SPE-102167-PA. http://dx.doi.org/10.2118/102167-PA.
Novotny, E.J. 1977. Prediction of Stimulation From AcidFracturing Treatments Using Finite Fracture Conductivity. J Pet Technol 29 (9): 1186-1194. SPE-6123-PA. http://dx.doi.org/10.2118/6123-PA.
Pournik, M. 2008. Laboratory-scale fracture conductivitycreated by acid etching. PhD dissertation, Texas A&M University,College Station, Texas (December 2008).
Pournik, M., Nasr-El-Din, H.A., and Mahmoud, M.A. 2011. A NovelApplication of Closed-Fracture Acidizing. SPE Prod & Oper 26 (1): 18-29. SPE-124874-PA. http://dx.doi.org/10.2118/124874-PA.
Pursell, D.A., Holditch, S.A., and Blakeley, D. 1988.Laboratory Investigation of Inertial Flow in High-Strength Fracture Proppants.Presented at the SPE Annual Technical Conference and Exhibition, Houston, 2-5October. SPE-18319-MS. http://dx.doi.org/10.2118/18319-MS.
Ren, S.-Q. and Xiong, H.-J. 1989. Temperature and Common IonEffects on Effective Acid Penetration in a Fracture. SPE Prod Eng 4 (3): 221-225. SPE-14852-PA. http://dx.doi.org/10.2118/14852-PA.
Schechter, R.S. 1992. Oil Well Stimulation. EnglewoodCliffs, New Jersey: Prentice-Hall.
Settari, A. 1993. Modeling of Acid-Fracturing Treatments.SPE Prod & Fac 8 (1): 30-38. SPE-21870-PA. http://dx.doi.org/10.2118/21870-PA.
Williams, B.B. and Nierode, D.E. 1972. Design of AcidFracturing Treatments. J Pet Technol 24 (4): 849-859.SPE-3720-PA. http://dx.doi.org/10.2118/3720-PA.