Fracture Acidizing: What Role Does Formation Softening Play in Production Response?
- Hisham A. Nasr-El-Din (Texas A&M University) | Saad M. Al-Driweesh (Saudi Aramco) | Arthur S. Metcalf (BJ Services Company) | John B. Chesson (BJ Services Intl. Thailand Ltd.)
- Document ID
- Society of Petroleum Engineers
- SPE Production & Operations
- Publication Date
- May 2008
- Document Type
- Journal Paper
- 184 - 191
- 2008. Society of Petroleum Engineers
- 5.8.7 Carbonate Reservoir, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 2.5.2 Fracturing Materials (Fluids, Proppant), 3.2.4 Acidising, 1.14 Casing and Cementing, 2.4.3 Sand/Solids Control, 2.2.2 Perforating, 3 Production and Well Operations, 1.8 Formation Damage, 4.1.2 Separation and Treating, 2 Well Completion, 4.2.3 Materials and Corrosion
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Fracture acidizing of carbonates has yielded increases in production in many areas of the world, but depending on rock strength and reservoir closure pressure, this response may be lower than expected. Also, as a result of rock strength and closure pressure, production may decline at a higher rate than following a proppant fracture treatment.
Laboratory results are presented describing the effect of various acid systems on the strength reduction of limestone -nd dolomite-formation rock samples. Formation samples were dry or saturated with 2-wt% potassium chloride brine before testing. Samples were exposed to neat, emulsified, gelled, and crosslinked 15-wt% hydrochloric acids (HCls) and each exhibited a differing effect on rock-strength reduction. In addition, production responses are presented and compared with regard to the type of acid system used for stimulation.
On the basis of the results obtained, acid-system choices made a significant difference in the degree of rock softening of carbonates. Emulsified acid caused the least softening effect on limestone and dolomite cores. Softening effects were greater on limestone than on dolomite rocks. Production responses from emulsified-acid treatments were best.
The Khuff is a deep gas carbonate made up of sequences of limestone and dolomite sections. Acid fracturing has been used to increase gas production from this reservoir (Rahim et al. 2002; Bartko et al. 2003).
Since 1999, acid fracturing of the Khuff formation has proved to be successful in obtaining required high gas rate. In the beginning, the acid-fracturing program consisted of pumping a viscous pad (high-temperature-crosslinked borate gel) followed by 28-wt% in-situ-gelled acid and then by an acid stage of regular 28-wt% HCl, pumped below the fracture closure pressure. Typically, the total acid volume ranged from 500 to 2,000 gal/ft. Over the next few years, introduction of emulsified acids (Nasr-El-Din et al. 2001), in-situ-gelled acids (Yeager and Shuchart 1997; Taylor and Nasr-El-Din 2003; Nasr-El-Din et al. 2002a), HCl/formic (Nasr-El-Din et al. 2002b; 2006b), and viscoelastic surfactant-based fluid system (Nasr-El-Din et al. 2006a) has contributed to optimizing the acid-fracturing treatments. In all cases, extensive analyses of flowback samples were conducted to determine the reactive efficiencies of the fluids used.
The most recent work evaluated stimulation of the Khuff in light of pumping rate, acid volume, and acid system and compared these to the lithology (Bartko et al. 2003). Of significance was that increasing treatment pumping rate resulted in wells with better initial production responses. The work showed that the emulsified-acid system outperformed the other acid systems being used on all types of lithology, using a PI/kh basis. In addition, neither the emulsified-acid system nor the in-situ-crosslinked acid system was affected by lithology variances.
The productivity of some of the treated wells declined with time. One of the potential reasons for this decline is softening of reservoir rock following acid-fracturing treatments. The objectives of the present study are to: assess the effect of various acid systems on rock embedment stress (RES), examine the impact of the lithology of rock softening, and compare rock softening and field results obtained with various acid systems.
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ASTM E10-1. 2001. Standard Test Method for Brinell Hardness ofMetallic Materials. West Conshohocken, Pennsylvania: ASTM International, 10February.
Bartko, K.M., Nasr-El-Din, H.A., Rahim, Z., and Al-Muntasheri, G.A. 2003. Acid Fracturing of a Gas CarbonateReservoir: The Impact of Acid Type and Lithology on Fracture Half Length andWidth. Paper SPE 84130 presented at the SPE Annual Technical Conference andExhibition, Denver, 5-8 October. doi: 10.2118/84130-MS
Beg, M.S., Kunak, A.O., Gong, M., Zhu, D., and Hill, A.D. 1998. A Systematic Experimental Study ofAcid Fracture Conductivity. SPEPF 13 (4): 267-271.SPE-52402-PA doi: 10.2118/52402-PA
Cook, C.C. and Brekke, K. 2004. Productivity Preservation ThroughHydraulic Propped Fractures in the Eldfisk North Sea Chalk Field.SPEREE 7 (2): 105-114. SPE-88031-PA doi: 10.2118/88031-PA
Economides, M.J., Hill, A.D., and Ehlig-Economides, C. 1993. PetroleumProduction Systems. Upper Saddle River, New Jersey: Prentice Hall, 412.
Gong, M., Lacote, S., and Hill, A.D. 1999. New Method of Acid FractureConductivity Based on Deformation of Surface Asperities. SPEJ4 (3): 206-214. SPE-57017-PA doi: 10.2118/57017-PA
Melendez, M.G., Pournik, M., Zhu, D., and Hill, A.D. 2007. The Effects of Acid Contact Time andthe Resulting Weakening of the Rock Surfaces on Acid-Fracture Conductivity.Paper SPE 107772 presented at the SPE European Formation Damage Conference,Scheveningen, The Netherlands, 30 May-1 June. doi: 10.2118/107772-MS
Nasr-El-Din, H.A. Al-Driweesh, S., Bartko, K., Al-Ghadban, H., Ramanathan,V., Kelkar, S., and Samuel, M. 2006a. Acid Fracturing of Deep Gas WellsUsing a Surfactant-Based Acid: Long-Term Effects on Gas Production Rate.Paper SPE 102469 presented at the SPE Annual Technical Conference andExhibition, San Antonio, Texas, 24-27 September. doi: 10.2118/102469-MS
Nasr-El-Din, H.A., Al-Driweesh, S., Sierra, L., van Domelen, M., and Welton,T. 2006b. Long-Term ComparativeEvaluation of HCl/Formic Acid System Used To Stimulate Carbonate Formations atSevere Conditions in Saudi Arabia. Paper SPE 103978 presented at the SPEFirst International Oil Conference and Exhibition, Cancún, Mexico, 31 August -2September. doi: 10.2118/103978-MS
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 a Gelled Acid. Paper 75501 presented at theSPE Gas Technology Symposium, Calgary, 30 April-2 May. doi:10.2118/77501-MS
Nasr-El-Din, H.A., Al-Mutairi, S.H., Al-Malki, M., Metcalf, S., and Wallace,W. 2002b. Stimulation of Deep Gas Wells Using HCl/Formic Acid System: LabStudies and Field Application. Paper CIM2002/289 Petroleum Society's CanadianInternational Petroleum Conference, Calgary, 11-13 June.
Nasr-El-Din, H.A., Solares, J.R., Al-Mutairi, S.H., and Mahoney, M.D. 2001.Field Application of EmulsifiedAcid-Based System to Stimulate Deep, Sour Gas Reservoirs in Saudi Arabia.Paper SPE 71693 presented at the SPE Annual Technical Conference andExhibition, New Orleans, 30 September-3 October. doi: 10.2118/71693-MS
Navarrete, R.C., Miller, M.J., and Gordon, J.E. 1998. Laboratory and Theoretical Studiesfor Acid Fracture Stimulation Optimization. Paper SPE 39776 presented atthe SPE Permian Basin Oil and Gas Recovery Conference, Midland, Texas, 23-26March. doi: 10.2118/39776-MS
Nierode, D.E. and Kruk, K.F. 1973. An Evaluation of Acid Fluid LossAdditives, Retarded Acids and Acidized Fracture Conductivity. Paper SPE4549 presented at the Annual Meeting of the Society of Petroleum Engineers ofAIME, Las Vegas, Nevada, 30 September-3 October. doi: 10.2118/4549-MS
Novotny, E.J. 1977. Predictionof Stimulation from Acid Fracturing Treatments Using Finite FractureConductivity. JPT 29 (9): 1186-1194; Trans., AIME,263. SPE-6123-PA doi: 10.2118/6123-PA
Rahim, Z., Bartko, K.M., and Al-Qahtani, M.Y. 2002. Hydraulic Fracturing Case Historiesin the Carbonate and Sandstone Reservoirs of Khuff and Pre-Khuff Formations,Ghawar Field, Saudi Arabia. Paper SPE 77677 presented at the SPE AnnualTechnical Conference and Exhibition, San Antonio, Texas, 29 September-2October. doi: 10.2118/77677-MS
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
Yeager, V. and Shuchart, C. 1997. In Situ Gels Improve Formation Acidizing.Oil & Gas J. 95 (3): 70.