3D Geomechanical Modeling of Shale Formations and its Application in Borehole Stabilization
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AbstractThe issue of borehole instability as seen in shale formation drilling is a major problem currently facing the industry. In recent years, deep exploration and more intensive development of hard and brittle shale gas reservoirs has shown that borehole instability is a widely occurring issue present in this type of strata. Because of the high frequency of catastrophic failures that accompany drilling in shale, this is an important technical problem to be solved. Furthermore, as a result of the recent shale gas revolution in North America, there has been a focus on integrated innovations and the development of multi-disciplinary fields and multiple technologies related to exploitation of this resource. As part of this ongoing multi-disciplinary approach, the advanced development concept known as geological engineering integration has been put forward. Rooted in the study of geodynamics and aimed at the problem of borehole instability in shale formations, this study explores and develops concepts related to geomechanics, including well location optimization, well trajectory optimization, pre-drilling formation pressure prediction and well wall stability prediction techniques. The meticulous modeling of 3D geomechanics is of great significance to the study of regional borehole stability in a shale formation. Therefore, a geomechanical modeling method for shale formations and its field application in Indonesia's Oilfield A is demonstrated in this thesis. As part of this modeling, a detailed study on the physical, chemical, and mechanical properties of shale in Oilfield A is carried out by laboratory mineral analysis, electron microscopy, cation exchange capacity and rock mechanics parameters. These experimental results form the cornerstone of the 3D geomechanical modeling of Indonesia's Oilfield A. Leveraging the Petrel software platform, the 3D geomechanical modeling method and principles of a shale formation are introduced in detail. Through a series of core tests, well logging data and seismic inversion data, the mechanical parameters of Oilfield A are described in depth, and the spatial distributions of important parameters such as 3D elastic modulus, 3D Poisson’s ratio and 3D pore pressure in this oilfield are established. 3D geomechanical models of heterogeneity, porosity and elastoplastic features are also established. Using the finite element method, the 3D stress distributions and 3D safe density windows of Oilfield A are also calculated. By establishing a 3D fine geomechanical model, various attributes are extracted along the borehole trajectory of well A-10, and a prediction of borehole stability is carried out. The drilling fluid density windows and well depth structure are also recommended, indicating the type and approximate depth of possible downhole complications. The numerical results of the minimum in-situ stress present in Indonesia's Oilfield A are calibrated by LOT (leaking of test) data. Importantly, the relative errors that exist between LOT data and the minimum in-situ stress are small, and the maximum relative error is only 0.02. The drilling period of well A-10 is 28 days. Compared with the average drilling period of 55 days in Oilfield A, the drilling period is shortened by 49 days as a result of the modeling studied. Importantly, no complex accidents occur in the drilling process. Through direct or indirect validations of all established 3D pore pressure, collapse pressure, rupture pressure, in situ-stress and other models, both a confident geomechanical model and a density window model are finally determined. The results show that the geomechanical model can accurately reflect the magnitude and heterogeneity of in-situ stress in a shale formation and can effectively solve the problem of regional borehole stability found in this formation.
CitationDeng, L. (2021). 3D Geomechanical Modeling of Shale Formations and its Application in Borehole Stabilization (Unpublished master's thesis). University of Calgary, Calgary, AB.
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