Sains Malaysiana 44(10)(2015): 1377–1388

A Finite Element Model to Predict Wellbore Fracture Pressure with Acid Damage

(Model Unsur Terhingga untuk Meramalkan Retak Tekanan Telaga Gerudi dengan Kerosakan Asid)

FANHUI-ZENG*, JIANCHUN-GUO & YUXUAN-LIU

State Key Laboratory of Oil and Gas Geology and Exploration, Southwest Petroleum University, 610500 Chengdu, P.R. China

Diserahkan: 13 Jun 2013/Diterima: 4 Ogos 2015

ABSTRACT

Hydraulic fracturing becomes more difficult when confronted with a formation of high fracturing pressure. In such formations, acidizing before the main fracturing treatment provide a method to reduce fracture pressure. The aim of this paper was to investigate the evolution of fracture pressure in a wellbore with acidizing. Five experiments were conducted to study the mechanisms of acid damage on reservoir minerals and cementing materials properties. Consequently, a mathematical model to predict fracture pressure with acidizing has been established and verified by field data. The analysis results showed that it is possible to reduce fracture pressure with decreased rock strength and fracture critical stress intensity factor by means of acid damage. Acid damage destroys the crystal structure of mineral particles, breaks the crystalline layers in cementing materials, increases rock porosity and reduces the rock strength. In addition, as the acid concentration, formation temperature and acid treatment time increased, it was useful to reduce fracture pressure in the wellbore. Using the proposed model, we were able to select the optimal acid damage construction parameters to reduce fracture pressure.

Keywords: Acid damage; fracture pressure; hydraulic fracture; mechanisms of acid damage; prediction model

ABSTRAK

Keretakan hidraulik menjadi sukar apabila berhadapan dengan pembentukan tekanan keretakan tinggi. Dalam pembentukan itu, pengasidan sebelum rawatan keretakan utama merupakan suatu kaedah bagi mengurangkan tekanan retak. Tujuan kajian ini adalah untuk mengkaji evolusi tekanan retak dalam telaga gerudi dengan pengasidan. Lima kajian telah dijalankan untuk mengkaji mekanisme kerosakan asid dalam tangki mineral dan sifat bahan penyimenan. Oleh yang demikian, model matematik untuk meramalkan tekanan retak dengan pengasidan telah dibangun dan dibuktikan melalui data lapangan. Keputusan analisis menunjukkan bahawa tekanan retak dapat dikurangkan dengan mengurangkan kekuatan batu dan faktor keamatan tekanan kritikal retak melalui kerosakan asid. Kerosakan asid memusnahkan struktur kristal zarah mineral, memecahkan lapisan kristal dalam bahan penyimenan, meningkatkan keliangan batu dan mengurangkan kekuatan batu. Sebagai tambahan, semasa kepekatan asid, suhu pembentukan dan tempoh rawatan asid meningkat, adalah disarankan tekanan retak dikurangkan dalam telaga gerudi. Berdasarkan model yang dicadangkan, kami dapat memilih parameter penghasilan kerosakan asid yang optimum untuk mengurangkan tekanan retak.

Kata kunci: Kerosakan asid; mekanisme kerosakan asid; model ramalan; retak hidraulik; tekanan retak

RUJUKAN

Anderson, R.A., Ingram, D.S. & Zanier, A.M. 1973. Determining fracture pressure gradients from well logs. Journal of Petroleum Technology 25: 1259-1268.

Asadpourea, A., Mohammadib, S. & Vafaia, A. 2006. Modeling crack in orthotropic media using a coupled finite element and partition of unity methods. Finite Elements in Analysis and Design 42: 1165-1175.

Atkinson, B.K. 1979. A fracture mechanics study of subcritical tensile cracking of quartz in wet environments. Pure and Applied Geophysics 117: 1011-1024.

Colback, P.S.B. & Wild, B.L. 1965. The influence of moisture content on the compressive strength of rock. Proceedings of the 3rd Canadian Rock Mechanics Symposium. pp. 65-83.

Chen, Z.X., Mian, C. & Yan, J. 1997. Determination of rock fracture toughness with hydraulic fracturing method. Chinese Journal of Rock Mechanics and Engineering 16: 59-62.

Ding, W.X. & Feng, X.T. 2005. Study on chemical damage effect and quantitative analysis method of meso-structure of limestone. Chinese Journal of Rock Mechanics and Engineering 24: 1283-1288.

Eaton, B.A. 1969. Fracture gradient prediction and its application in oilfield operations. SPE Journal of Petroleum Technology 21(10): 1353-1360.

Feng, X.T., Chen, S. & Li, S. 2001. Effects of water chemistry on micro cracking and compressive strength of granite. International Journal of Rock Mechanics & Mining Sciences 38: 557-568.

Fogler, H.S. 1975. Acidization II-the kinetics of the dissolution of sodium and postassium feldspar in HF/HCl acid mixtures. Chemical Engineering Science 30: 1325-1322.

Freiman, S.W. 1984. Effects of chemical environments on slow crack growth in glasses and ceramics. Journal of Geophysical Research 89: 4072-4076.

Haimson, B. & Fairhurst, C. 1967. Initiation and extension of hydraulic fractures in rocks. Old SPE Journal 7: 310-318.

Hawkins, A.B. & McConnell, B.J. 1992. Sensitivity of sandstone strength and deformability to changes in moisture content. Quarterly Journal of Engineering Geology 25: 115-130.

Higgs, N. 1981. Mechanical Properties of Ultrafine Quartz, Chlorite, Bentonite in Environments of the Upper Crust. Ph.D. dissertation, Texas A & M University, College Station, TX. (Unpublished).

Hill, A.D. 1981. Theoretical and experimental studies of sandstone acidizing. SPEJ 21: 30-42.

Hoshino, K. 1974. Effect of porosity on the strength of the classic sedimentary rocks. Proceedings, Congress of the International Society for Rock Mechanics. Advances in Rock Mechanics, Reports of Current Research, Part A. U. S. Committee on Rock Mechanics, National Academy of Sciences, Washington, D.C. 2: 511-516.

Hossain, M.M., Rahman, M.K. & Sheik, S.R. 1999. A comprehensive monograph for hydraulic fracture initiation from deviated wellbores under arbitrary stress regimes. SPE Asia Pacific Oil and Gas Conference and Exhibition, 20-22 April, Jakarta, Indonesia.

Huang, R.Z. & Xu, J.J. 1986. A new method to predict fracture pressure. Oil Drilling & Production Technology 3: 1-14.

Hu, Y., Zhao, J., Zeng, Q., Xu, S. & Xie, H. 2003. Finite element method to calculate fracturing pressure of perforated well hydrofrac. Natural Gas Industry 23: 58-59.

Kline, W.E. & Fogler, H.S. 1981. Dissolution kinetics: The nature of the particle attack of layered silicates in HF. Chemical Engineering Science 36: 871-879.

Kronenberg, A.K. 1994. Hydrogen speciation and chemical weakening of quartz. In Silica: Physical Behavior, Geochemistry and Materials Applications, edited by Heaney, P.J., Prewitt, C.T. & Gibbs, G.V. Mineralogical Society of America 29: 123-176.

Lemaitre, J. 1972. Evaluation of dissipation and damage in metals submitted to dynamic loading, mechanical behavior of materials. Proceedings of the First International Conference, Kyoto, Japan. pp. 540-549.

Niemeijer, A.R. & Lloyd, G.E. 2010. The nature and importance of phyllonite development in crustal-scale fault cores: An example from the Median Tectonic Line, Japan. Journal of Structural Geology 28: 220-235

Rajesh, K.N. & Rao, B.N. 2010. Two-dimensional analysis of anisotropic crack problems using coupled mesh less and fractal finite element method. International Journal of Fracture 164: 285-318.

Sibson, R.H. 1977. Fault rocks and fault mechanisms. Journal of the Geological Society of London 133: 140-213.

Stephen, R.D. 1982. Prediction of fracture pressures for wildcat wells. Journal of Petroleum Technology 34: 863-872.

Tang, L.S., Peng, C.Z. & Si, J.W. 2002. Testing study on effects of chemical action on crack propagation in rock. Chinese Journal of Rock Mechanics and Engineering 6: 822-827.

Wiederhorn, S.M. & Johnson, H. 1973. Effect of electrolyte pH on crack propagation in glass. Journal of the American Ceramic Society 56: 192-197.

William, E., Kline, H. & Scott, F. 1981. Dissolution of silicate minerals by hydrofluoric acid. Industrial & Engineering Chemistry Fundamentals 20: 155-161.

*Pengarang untuk surat-menyurat, email: zengfanhui023024@126.com