An Experimental Investigation of the Conductivity of Unpropped Fractures in Shales
- Weiwei Wu (The University of Texas at Austin) | Pratik Kakkar (The University of Texas at Austin) | Junhao Zhou (The University of Texas at Austin) | Rodney Russell (The University of Texas at Austin) | Mukul M. Sharma (The University of Texas at Austin)
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- Society of Petroleum Engineers
- SPE Hydraulic Fracturing Technology Conference and Exhibition, 24–26 January, The Woodlands, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2017. Society of Petroleum Engineers
- 1.6.9 Coring, Fishing, 1.6 Drilling Operations, 2.4 Hydraulic Fracturing, 2.6 Acidizing, 2.5.2 Fracturing Materials (Fluids, Proppant), 3 Production and Well Operations, 2 Well completion, 5.8.2 Shale Gas
- fracture conductivity, unpropped fracture, fluid-shale interaction, shale, water-based fluid
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There is a great deal of evidence that shows that hydraulic fracturing creates a large surface area of induced unpropped (IU) fractures, that are too small to accommodate commonly used proppants and subsequently close during production (Sharma and Manchanda 2015). Due to their enormous surface area, IU fractures can play an important role in hydrocarbon production if they are allowed to remain open during production. Therefore, the conductivity of these IU fractures under different conditions of stress and when exposed to different fracturing fluids is of great importance.
In this study, core-scale IU fractures were created with preserved shale samples from the Eagle Ford and Utica shales. Samples with different mineralogies were selected to represent a broad cross-section of representative samples. Great care was taken to ensure that the shale samples were preserved since we had observed that shale desiccation results in large changes in mechanical properties. The fracture conductivities of unpropped fractures created in each of the shale samples was measured as a function of closure stress using nitrogen or brine. The unpropped fractures were exposed to several water-based fracturing fluids including neutral brine, alkaline brine (pH 11-12) and acidic brine (pH < 1), with or without clay stabilizers. The effects of fluid type, pH, clay stabilizers, shale mineralogy and cyclic stress on IU fracture conductivities were investigated. Batch tests were also performed to study the change of mechanical properties and fines production caused by fluid-shale interaction.
Unpropped fractures demonstrated conductivities that were 3 to 4 orders magnitude lower than propped fractures, and were more susceptible to closure stress. Exposure to water-based fracturing fluids decreased the unpropped conductivity by one order of magnitude. The primary mechanism for the decrease was shale softening caused by exchange of water and ions between the native fluid of shale and the exposed fracturing fluid. Shale softening was observed in exposure to all brines tested, regardless of their pH. In addition to shale softening, fines generation also contributed to the reduction of unpropped conductivity when shales were exposed to alkaline or acidic brine. Amine-based clay stabilizers improved the unpropped conductivity by reducing the amount of clay-based fines. However, they were not as effective at stabilizing non-clay fines. Shale mineralogy affected the unpropped conductivities in two ways: it controlled the mechanical properties of the native preserved shale, and also impacted the fluid-shale interactions. A clear correlation was observed between mineralogy and stress dependence. Clay-rich samples showed the most stress sensitivity in the presence of water or brine at neutral pH, whereas the calcite-rich samples showed less stress sensitivity. High clay content also resulted in lower restored conductivity after cyclic stress. Mechanical properties of shale such as hardness and Young's modulus, before and after fluid exposure, strongly correlated with the mineralogy of shales. Unpropped conductivity was more sensitive to cyclic stress than propped conductivities, and it dropped by 80% after one cycle of closure stress between 300 and 4000 psi of closure stress. It is clearly shown that water-based fracturing fluids are able to impact conductivities of IU fractures in shales significantly, and these impacts need to be taken into account in the selection of fracturing fluids.
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Alotaibi, M., Nasralla, R. A. and Nasr-El-Din, H. A. 2010. Wettability Challenges in Carbonate Reservoirs. Presented at Society of Petroleum Engineers Improved Oil Recovery Conference, Tulsa, 24-28 April. SPE-129972-MS. http://dx.doi.org./10.2118/129972-MS.
Akrad, O. M., Miskimins, J. L., and Prasad, M. 2011. The Effects of Fracturing Fluids on Shale Rock Mechanical Properties and Proppant Embedment. Presented at the SPE Annual Technical Conference and Exhibition, Denver, Colorado, 30 October-2 November. SPE-146658-MS. http://dx.doi.org/10.2118/146658-MS.
ASTM E10-15a. 2015. Standard Test Method for Brinell Hardness of Metallic Materials, ASTM International, West Conshohocken, PA. http://dx.doi.org/10.1520/E0010-15A.
Auradou, H., Drazer, G., Hulin, J.P. and Koplik, J. 2005. Permeability anisotropy induced by the shear displacement of rough fracture walls. Water Resources Research, 41(9). http://dx.doi.org/10.1029/2005wr003938.
Beg, M.S., Kunak, A.O., Gong, M., Zhu, D., and Hill, A.D. 1998. A Systematic Experimental Study of Acid Fracture Conductivity. SPE Production & Facilities. 13(4): 267-271. SPE-52402-PA doi: 10.2118/52402-PA.
Chen, L., Zhang, G., Wang, L., Wu, W. and Ge, J. 2014. Zeta potential of limestone in a large range of salinity. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 450: 1-8. http://dx.doi.org/10.1016/j.colsurfa.2014.03.006.
Chenevert, M.E. and Amanullah, M. 2001. Shale Preservation and Testing Techniques for Borehole-Stability Studies. SPE Drill & Compl 16(3): 146-149. SPE-73191-PA. http://dx.doi.org/10.2118/73191-PA.
Chipperfield, S. 2006. After-Closure Analysis to Identify Naturally Fractured Reservoirs. SPE Form Eval 9 (1):50-60. SPE-90002-PA. http://dx.doi.org/10.2118/90002-PA.
Deng, J., Mou, J., Hill, A. D., and Zhu, D. 2012. A New Correlation of Acid-Fracture Conductivity Subject to Closure Stress. SPE Prod & Oper 27(02):158-169. SPE-140402-PA. http://dx.doi.org/10.2118/140402-PA.
Fan, L., Thompson, J.W., and Robinson, J.R. 2010. Understanding Gas Production Mechanism and Effectiveness of Well Stimulation in the Haynesville Shale Through Reservoir Simulation. Presented at the Canadian Unconventional Resources and International Petroleum Conference, Calgary, Alberta, Canada, 19-21 October. SPE-136696-MS. http://dx.doi.org/10.2118/136696-MS.
Fredd, C.N., McConnell, S.B., Boney, C.L. and England, K.W. 2001. Experimental study of fracture conductivity for water-fracturing and conventional fracturing applications. SPE J, 6(03); 288-298.SPE-74138-PA. http://dx.doi.org/10.2118/74138-PA.
Gangi, A.F. 1978. Variation of whole and fractured porous rock permeability with confining pressure. In International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts 15(5):249-257. http://dx.doi.org/10.1016/0148-9062(79)90824-6.
Gong, M., Lacote, S. and Hill, A.D. 1999. New Model of Acid-Fracture Conductivity Based on Deformation of Surface Asperities. SPE J. 4(3): 206-214. SPE-57017-PA. http://dx.doi.org/10.2118/57017-PA.
Grieser, B., Wheaton, R., Magness, B., Blauch, M. and Loghry, R. 2007. Surface Reactive Fluid´s Effect on Shale. Presented at the SPE Production and Operations Symposium, Oklahoma City, Oklahoma, USA, 31 March-1 April. SPE-106815-MS. http://dx.doi.org/10.2118/106815-MS.
Gross, M., Fischer, M., Engelder, T. and GreenField, R. 1995. Factors controlling joint spacing in interbedded sedimentary rocks; integrating numerical models with field observations from the Monterey Formation, USA. In: Ameen, M.S. (Ed.). Fractography. Geological Society Special Publication, Geological Society, London: 215-233. http://dx.doi.org/10.1144/GSL.SP.1995.092.01.12.
Gu, M., Kulkarni, P., Rafiee, M., Ivarrud, E. and Mohanty, K. 2015. Optimum Fracture Conductivity for Naturally Fractured Shale and Tight Reservoirs. SPE Prod & Oper. (In press; posted October 2015). SPE-171648-PA. http://dx.doi.org/10.2118/171648-PA.
Gupta, J.K., Zielonka, M.G., Albert, R.A., El-Rabaa, A.M., Burnham, H.A. and Choi, N.H. 2012. Integrated Methodology for Optimizing Development of Unconventional Gas Resources. Presented at the SPE Hydraulic Fracturing Technology Conference, The Woodlands, Texas, 6-8 February. SPE-152224-MS. http://dx.doi.org/10.2118/152224-MS.
Janse, T., Zhu, D. and Hill, A.D. 2015. The effect of Rock Mechanical Properties on Fracture Conductivity for Shale Formations. Presented at SPE Hydraulic Fracturing Technology Conference, The Woodlands, Texas, USA, 3-5 February. SPE-173347-MS. http://dx.doi.org/10.2118/173347-MS.
Jung, C.M., Zhou, J., Chenevert, M.E. and Sharma, M.M. 2013, The impact of shale preservation on the petrophysical properties of organic-rich shales. Presented at SPE Annual Technical Conference and Exhibition, New Orleans, Louisiana, 30 September-2 October. SPE-166419-MS. http://dx.doi.org/10.2118/166419-MS.
Kamali, A. and Pournik, M. 2016. Fracture closure and conductivity decline modeling-Application in unpropped and acid etched fractures. Journal of Unconventional Oil and Gas Resources, 14:44-55. http://dx.doi.org/10.1016/j.juogr.2016.02.001.
Kamenov, A., Zhu, D., Hill, A. D. and Zhang, J. 2013. Laboratory Measurement of Hydraulic Fracture Conductivities in the Barnett Shale. Presented at the SPE Hydraulic Fracturing Technology Conference, The Woodlands, Texas, 4-6 February. SPE-163839-MS. http://dx.doi.org/10.2118/163839-MS.
Kumar, V., Sondergeld, C., and Rai, C. 2012. Nano to Macro Mechanical Characterization of Shale. Presented at SPE Annual Technical Conference and Exhibition, San Antonio, 8-10 October. SPE-159804-MS http://doi.org/10.2118/159804-MS.
Lee, H.S. and Cho, T.F. 2002. Hydraulic characteristics of rough fractures in linear flow under normal and shear load. Rock Mechanics and Rock Engineering, 35(4): 299-318. http://dx.doi.org/10.1007/s00603-002-0028-y.
Leone, J.A. and Scott, E.M. 1987, January. Characterization and control of formation damage during waterflooding of a high-clay-content reservoir. SPE Res Eng, 3(04): 1279-1286. SPE-16234-PA. http://dx.doi.org/10.2118/16234-PA
Manchanda, R., and Sharma, M.M. 2013. Time-Delayed Fracturing: A New Strategy in Multi-Stage, Multi-Well Pad Fracturing. Presented at the SPE Annual Technical Conference and Exhibition, New Orleans, Louisiana, 30 September - 2 October. SPE-166489-MS. http://dx.doi.org/10.2118/166489-MS.
Manchanda, R., Sharma, M.M. and Holzhauser, S. 2014. Time-Dependent Fracture-Interference Effects in Pad Wells. SPE Prod & Oper, 29(04): 274-287. SPE-164534-PA. http://dx.doi.org/10.2118/164534-PA.
Mayerhofer, M.J., Lolon, E.P. and Warpinski, N.R. 2010. What is Stimulated Reservoir Volume? SPE Prod and Oper, 25(1): 16-18. SPE-119890-PA. http://dx.doi.org/10.2118/119890-PA.
McClure, M.W. 2014. The Potential Effect of Network Complexity on Recovery of Injected Fluid Following Hydraulic Fracturing. Presented at the SPE Unconventional Resources Conference, The Woodlands, Texas, USA, 1-3 April. SPE-168991-MS. http://dx.doi.org/10.2118/168991-MS.
Montemagno, C.D. and Pyrak-Nolte, L.J. 1999. Fracture network versus single fractures: measurement of fracture geometry with X-ray tomography. Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy, 24(7):575-579. http://dx.doi.org/10.1016/s1464-1895(99)00082-4.
Nierode, D. and Kruk, K. 1973. An Evaluation of Acid Fluid Loss Additives Retarded Acids and Acidized Fracture Conductivity. Presented at Fall Meeting of the Society of Petroleum Engineers of AIME, Las Vegas, Nevada, 30 September-3 October. SPE-4549-MS. http://dx.doi.org/10.2118/4549-MS.
Oliver, W.C. and Pharr, G.M. 2004. Measurement of hardness and elastic modulus by instrumented indentation: Advances in understanding and refinements to methodology. Journal of materials research, 19(01): 3-20. http://dx.doi.org/10.1557/jmr.2004.0002.
Ouchi, H., Agrawal, S., Foster, J.T. and Sharma, M.M. 2017. Effect of Small Scale Heterogeneity on the Growth of Hydraulic Fractures. Presented at the SPE Hydraulic Fracturing Technology Conference, The Woodlands, Texas, 24-26 January. SPE- 184873-MS. http://dx.doi.org10.2118/184873-MS.
Palisch, T., Duenckel, R., Bazan, L., Heidt, H.J., and Turk, G. 2007. Determining Realistic Fracture Conductivity and Understanding Its Impact on Well Performance--Theory and Field Examples. Presented at the SPE Hydraulic Fracturing Technology Conference, College Station, Texas, USA, 29-31 January. SPE-106301-MS. http://dx.doi.org/10.2118/106301-MS.
Pedlow, J. and Sharma, M. 2014. Changes in shale fracture conductivity due to interactions with water-based fluids. Presented at the SPE Hydraulic Fracturing Technology Conference, Woodlands, TX, 4 - 6 Feb. SPE 168586-MS. http://dx.doi.org/10.2118/168586-MS.
Potocki, D. J. 2012. Understanding Induced Fracture Complexity in Different Geological Settings Using DFIT Net Fracture Pressure. Presented at the SPE Canadian Unconventional Resources Conference, Calgary, 30 October-1 November. SPE-162814-MS. http://dx.doi.org/10.2118/162814-MS.
Pyrak-Nolte, L.J. and Morris, J.P. 2000. Single fractures under normal stress: The relation between fracture specific stiffness and fluid flow. International Journal of Rock Mechanics and Mining Sciences, 37(1): 245-262. http://dx.doi.org/10.1016/s1365-1609(99)00104-5.
Rowe, H., Hughes, N. and Robinson, K. 2012. The Quantification and Application of Handheld Energy-Dispersive X-ray Fluorescence in Mudrock Chemostratigraphy and Geochemistry. Chem. Geol., 324: 122-131. http://dx.doi.org/10.1016/j.chemgeo.2011.12.023.
Ruffet, C., Fery, J.J. and Onaisi, A. 1998. Acid Fracturing Treatment: A Surface-Topography Analysis of Acid-Etched Fractures to Determine Residual Conductivity. SPE J., 3(2): 155-162. SPE-38175-PA. http://dx.doi.org/10.2118/38175-PA.
Sharma, M.M. and Manchanda, R. 2015. The Role of Induced Un-propped (IU) Fractures in Unconventional Oil and Gas Wells. Presented at SPE Annual Technical Conference and Exhibition Houston, Texas, 28-30 September. SPE-174946-MS. http://dx.doi.org/10.2118/174946-MS.
Sharma, M.M. and Yortsos, Y.C. 1987. Fines migration in porous media. AIChE Journal, 33(10):1654-1662. http://dx.doi.org/10.1002/aic.690331009.
Soliman, M.Y., Miranda, C., and Wang, H.M. 2010. Application of After-Closure Analysis to a Dual-Porosity Formation, to CBM, and to a Fractured Horizontal Well. SPE Prod & Oper, 25(4): 472-483. SPE-124135-PA. http://dx.doi.org/10.2118/124135-PA.
Tsang, Y.W. and Tsang, C.F. 1987. Channel model of flow through fractured media. Water Resources Research, 23(3): 467-479. http://dx.doi.org/10.1029/wr023i003p00467.
Tripathi, D. and Pournik, M. 2014. Effect of Acid on Productivity of Fractured Shale Reservoirs. Presented at SPE/AAPG/SEG Unconventional Resources Technology Conference, Denver, Colorado, USA, 25-27 August. SPE-2014-1922960-MS. http://dx.doi.org/10.15530/urtec-2014-1922960.
Vaidya, R. N. and Fogler, H. S. 1992. Fines Migration and Formation Damage: Influence of pH and Ion Exchange. SPE Prod Eng, 7(4): 325-330. SPE-19413-PA. http://dx.doi.org/10.2118/19413-PA.
Wang, L. and Cardenas, M.B. 2016. Development of an empirical model relating permeability and specific stiffness for rough fractures from numerical deformation experiments. Journal of Geophysical Research: Solid Earth, 121(7): 4977-4989. http://dx.doi.org/10.1002/2016jb013004.
Watanabe, N., Ishibashi, T., Hirano, N., Ohsaki, Y., Tsuchiya, Y., Tamagawa, T., Okabe, H. and Tsuchiya, N. 2011. Precise 3D numerical modeling of fracture flow coupled with X-ray computed tomography for reservoir core samples. SPE J, 16(03): 683-691. SPE-146643-PA. http://dx.doi.org/10.2118/146643-PA.
Wu, W. and Sharma, M.M. 2016. Acid Fracturing Shales: Effect of Dilute Acid on Properties and Pore Structure of Shale. SPE Prod & Oper. (In press; posted April 2016). SPE-173390-PA. http://dx.doi.org/10.2118/173390-PA.
Wu, W. and Sharma, M.M. 2017. A Model for the Conductivity and Compliance of Unpropped Fractures. Presented at the SPE Hydraulic Fracturing Technology Conference, The Woodlands, Texas, 24-26 January. SPE- 184852-MS. http://dx.doi.org10.2118/184852-MS.
Yasuhara, H., Polak, A., Mitani, Y., Grader, A.S., Halleck, P.M. and Elsworth, D. 2006. Evolution of fracture permeability through fluid-rock reaction under hydrothermal conditions. Earth and Planetary Science Letters, 244(1): 186-200. http://dx.doi.org/10.1016/j.epsl.2006.01.046.
Zhang, J., Al-Bazali, T., Chenevert, M., Sharma, M. M., Clark, D., Benaissa, S. and Ong, S. 2006. Compressive strength and acoustic properties changes in shale with exposure to water-based fluids. Presented at the 41st U.S. Symposium on Rock Mechanics (USRMS), Golden, Colorado, 17-21 June. ARMA-06-900.
Zhang, J., Zhu, D., and Hill, A. D. 2015. Water-Induced Damage to Propped-Fracture Conductivity in Shale Formations. SPE Prod & Oper, 31(02):147-156. SPE-173346-PA. http://dx.doi.org/10.2118/173346-PA.
Zoback, M. D., Kohli, A., Das, I. and Mcclure, M.W. 2012. The Importance of Slow Slip on Faults During Hydraulic Fracturing Stimulation of Shale Gas Reservoirs. Presented at the SPE Americas Unconventional Resources Conference, Pittsburgh, Pennsylvania, 5-7 June. SPE-155476-MS. http://dx.doi.org/10.2118/155476-MS.