A wellbore stability analysis model with chemical-mechanical coupling for shale gas reservoirs

Ma, Tianshou; Chen, Ping

doi:10.1016/j.jngse.2015.05.028

Cited by 103 publications

(44 citation statements)

References 64 publications

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“…These values mainly represent gas shale reservoirs (suitable for hydraulic fracturing due to their brittleness) and were chosen to be within the reported ranges from the corresponding references. Studies have shown that hydro-mechanical properties of near-wellbore shales are influenced by the presence of natural and hydraulically generated fractures (Liang et al 2014;Song et al 2014), and the exposure of rock to drilling mud (Ma and Chen 2015). However, these effects are not considered in this paper.…”

Section: Resultsmentioning

confidence: 97%

Elastic–Brittle–Plastic Behaviour of Shale Reservoirs and Its Implications on Fracture Permeability Variation: An Analytical Approach

et al. 2018

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Shale gas has recently gained significant attention as one of the most important unconventional gas resources. Shales are fine-grained rocks formed from the compaction of silt-and clay-sized particles and are characterised by their fissured texture and very low permeability. Gas exists in an adsorbed state on the surface of the organic content of the rock and is freely available within the primary and secondary porosity. Geomechanical studies have indicated that, depending on the clay content of the rock, shales can exhibit a brittle failure mechanism. Brittle failure leads to the reduced strength of the plastic zone around a wellbore, which can potentially result in wellbore instability problems. Desorption of gas during production can cause shrinkage of the organic content of the rock. This becomes more important when considering the use of shales for CO 2 sequestration purposes, where CO 2 adsorption-induced swelling can play an important role. These phenomena lead to changes in the stress state within the rock mass, which then influence the permeability of the reservoir. Thus, rigorous simulation of material failure within coupled hydro-mechanical analyses is needed to achieve a more systematic and accurate representation of the wellbore. Despite numerous modelling efforts related to permeability, an adequate representation of the geomechanical behaviour of shale and its impact on permeability and gas production has not been achieved. In order to achieve this aim, novel coupled poro-elastoplastic analytical solutions are developed in this paper which take into account the sorption-induced swelling and the brittle failure mechanism. These models employ linear elasticity and a Mohr-Coulomb failure criterion in a plane-strain condition with boundary conditions corresponding to both open-hole and cased-hole completions. The post-failure brittle behaviour of the rock is defined using residual strength parameters and a non-associated flow rule. Swelling and shrinkage are considered to be elastic and are defined using a Langmuir-like curve, which is directly related to the reservoir pressure. The models are used to evaluate the stress distribution and the induced change in permeability within a reservoir. Results show that development of a plastic zone near the wellbore can significantly impact fracture permeability and gas production. The capabilities and limitations of the models are discussed and potential future developments related to modelling of permeability in brittle shales under elastoplastic deformations are identified.

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Section: Resultsmentioning

confidence: 97%

Elastic–Brittle–Plastic Behaviour of Shale Reservoirs and Its Implications on Fracture Permeability Variation: An Analytical Approach

et al. 2018

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“…In order to be against this increase of deviatoric stress, an object of higher drilling fluid density should be designed. For this case, based on the formation condition and rock mechanical properties by CTC testing, the drilling fluid density designed by the method from Ma et al [25] and Ma and Chen [26] must be larger than 1.017 g/cm 3 to avoid wellbore collapse ( Figure 15). In real scenarios, the decrease of drilling fluid density was much faster than expected.…”

Section: A Field Case Of the Well Collapse Problem During The Processmentioning

confidence: 99%

Mechanical Behavior and Permeability Evolution of Reconstituted Coal Samples under Various Unloading Confining Pressures—Implications for Wellbore Stability Analysis

et al. 2017

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Low pressure, low permeability, and low saturation of Chinese coal-bed methane (CBM) reservoirs make underbalanced drilling (UBD) widely used for mining CBM in China. In this study, mechanical behavior and permeability of coal rock were investigated under different degrees of unloading confining pressure (UCP)-reloading axial stress (RAS) by a triaxial experimental apparatus. These tests revealed that: (1) peak deviatoric stress of coal rock in UCP-RAS is lower than that in a conventional triaxial compression (CTC) test, and the peak deviatoric stress linearly relates the degree of unloading confining pressure. The deformation modulus of coal in UCP-RAS is lower than that in CTC, while the lateral expansion ratio is larger than that in CTC; (2) higher UCP leads to a faster increase of permeability during RAS until the failure of coal; (3) the cohesion and internal friction angle tested by UCP-RAS are lower by 4.57% and 15.18% than those tested by CTC. In addition, a field case (Zhaozhuang well, Qinshui Basin, China) of a well collapse problem validates the higher probability of wellbore collapse due to the increase of equivalent collapse fluid density, which is calculated by using coal rock parameters tested by UCP-RAS rather than by CTC.

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“…Most anisotropic rocks, such as shale, mudstone, sandstone, slate, gneiss, schist, coal, and marl, present anisotropic mechanical behavior, and these anisotropic rocks usually play an important role in rock engineering. Gas shale has received increasing attention recently, and its mechanical behavior (compressive, shear, tensile and fracture behavior) plays an important role in shale gas extraction [5][6][7][8]. The mechanical behavior is concerned with wellbore collapse and leakage in the process of drilling, and hydraulic fracturing during the process of exploitation [9][10][11][12].…”

Section: Introductionmentioning

confidence: 99%

Brazilian Tensile Strength of Anisotropic Rocks: Review and New Insights

Peng

Zhu

et al. 2018

Energies

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Strength anisotropy is one of the most distinct features of anisotropic rocks, and it also normally reveals strong anisotropy in Brazilian test Strength ("BtS"). Theoretical research on the "BtS" of anisotropic rocks is seldom performed, and in particular some significant factors, such as the anisotropic tensile strength of anisotropic rocks, the initial Brazilian disc fracture points, and the stress distribution on the Brazilian disc, are often ignored. The aim of the present paper is to review the state of the art in the experimental studies on the "BtS" of anisotropic rocks since the pioneering work was introduced in 1964, and to propose a novel theoretical method to underpin the failure mechanisms and predict the "BtS" of anisotropic rocks under Brazilian test conditions. The experimental data of Longmaxi Shale-I and Jixi Coal were utilized to verify the proposed method. The results show the predicted "BtS" results show strong agreement with experimental data, the maximum error is only~6.55% for Longmaxi Shale-I and~7.50% for Jixi Coal, and the simulated failure patterns of the Longmaxi Shale-I are also consistent with the test results. For the Longmaxi Shale-I, the Brazilian disc experiences tensile failure of the intact rock when 0 • ≤ β w ≤ 24 • , shear failure along the weakness planes when 24 • ≤ β w ≤ 76 • , and tensile failure along the weakness planes when 76 • ≤ β w ≤ 90 • . For the Jixi Coal, the Brazilian disc experiences tensile failure when 0 • ≤ β w ≤ 23 • or 76 • ≤ β w ≤ 90 • , shear failure along the butt cleats when 23 • ≤ β w ≤ 32 • , and shear failure along the face cleats when 32 • ≤ β w ≤ 76 • . The proposed method can not only be used to predict the "BtS" and underpin the failure mechanisms of anisotropic rocks containing a single group of weakness planes, but can also be generalized for fractured rocks containing multi-groups of weakness planes.

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A wellbore stability analysis model with chemical-mechanical coupling for shale gas reservoirs

Cited by 103 publications

References 64 publications

Elastic–Brittle–Plastic Behaviour of Shale Reservoirs and Its Implications on Fracture Permeability Variation: An Analytical Approach

Elastic–Brittle–Plastic Behaviour of Shale Reservoirs and Its Implications on Fracture Permeability Variation: An Analytical Approach

Mechanical Behavior and Permeability Evolution of Reconstituted Coal Samples under Various Unloading Confining Pressures—Implications for Wellbore Stability Analysis

Brazilian Tensile Strength of Anisotropic Rocks: Review and New Insights

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