Fracture pressure prediction for layered formations with anisotropic rock strengths

Ma, Tianshou; Wu, Bisheng; Fu, Jianhong; Zhang, Qiangui; Chen, Ping

doi:10.1016/j.jngse.2017.01.002

Cited by 53 publications

(27 citation statements)

References 29 publications

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“…The reason why we ignored the influence of the anisotropic modulus can be concluded as follows: (1) The anisotropy of the tensile strength usually outclasses the modulus for anisotropic rocks with weak or medium anisotropy [12], for instance, the anisotropic degree of modulus is 1.14-1.61 for Taiwan argillite, while its anisotropic degree of tensile strength is~11.17 [20]; the anisotropic degree of modulus is~1.34 for Mosel slate, while its anisotropic degree of tensile strength is~3.69 [45]; the anisotropic degree of modulus is~1.29 for Longmaxi shale, while its anisotropic degree of tensile strength is~1.90 [47]. (2) The closed-form elastic solution of stress distribution on the Brazilian disc for an anisotropic medium is difficult to obtain, and it is also very complex to apply in the determination of Brazilian disc failure.…”

Section: Discussionmentioning

confidence: 99%

“…The formulas of the anisotropic tensile strength are less developed, due to the difficulty of experimental validation [11,12,20,21]. Hobbs investigated the variation of the tensile strength of the laminated rock using Griffith crack theory [62], Nova and Zaninetti proposed an anisotropic tensile failure criterion for schistose rock [63], and Lee and Pietruszczak proposed the tensile equivalent of the SPW theory and a novel 3-D tensile failure function for transversely isotropic rocks [21].…”

Section: Modeling Of "Bts" Under Tensile Failure Modesmentioning

confidence: 99%

“…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]. To present the anisotropic degree of "BtS" for different rocks, Figure 1 compares the maximum and minimum "BtS" for various anisotropic rocks.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Discussionmentioning

confidence: 99%

Section: Modeling Of "Bts" Under Tensile Failure Modesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Brazilian Tensile Strength of Anisotropic Rocks: Review and New Insights

Peng

Zhu

et al. 2018

Energies

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“…For example, the thermoelastic stress change is significant near the wellbore; it may change the fracture initiation and path during hydraulic fracturing [10][11][12]. The mathematical models can be mainly classified into two types, that is, analytical and numerical.…”

Section: Introductionmentioning

confidence: 99%

An Approximate Solution for Predicting the Heat Extraction and Preventing Heat Loss from a Closed-Loop Geothermal Reservoir

Feng

et al. 2017

Geofluids

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Approximate solutions are found for a mathematical model developed to predict the heat extraction from a closed-loop geothermal system which consists of two vertical wells (one for injection and the other for production) and one horizontal well which connects the two vertical wells. Based on the feature of slow heat conduction in rock formation, the fluid flow in the well is divided into three stages, that is, in the injection, horizontal, and production wells. The output temperature of each stage is regarded as the input of the next stage. The results from the present model are compared with those obtained from numerical simulator TOUGH2 and show first-order agreement with a temperature difference less than 4 ∘ C for the case where the fluid circulated for 2.74 years. In the end, a parametric study shows that (1) the injection rate plays dominant role in affecting the output performance, (2) higher injection temperature produces larger output temperature but decreases the total heat extracted given a specific time, (3) the output performance of geothermal reservoir is insensitive to fluid viscosity, and (4) there exists a critical point that indicates if the fluid releases heat into or absorbs heat from the surrounding formation.

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“…Wellbore stability is affected by a variety of factors, such as mechanical impact as a result of drillstring vibration during drilling [6], formation material properties [7,8] and change in loading boundary conditions. Especially, with the exploration and development of unconventional energy resources such as shale gas/oil and geothermal energy, wells are being drilled deeper and at orientations with respect to the stress field that result in higher stress concentrations around the well.…”

Section: Introductionmentioning

confidence: 99%

A Transient Analytical Model for Predicting Wellbore/Reservoir Temperature and Stresses during Drilling with Fluid Circulation

Liu

Zhang

et al. 2017

Energies

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Accurate characterization of heat transfer in a wellbore during drilling, which includes fluid circulation, is important for wellbore stability analysis. In this work, a pseudo-3D model is developed to simultaneously calculate the heat exchange between the flowing fluid and the surrounding media (drill pipe and rock formation) and the in-plane thermoelastic stresses. The cold drilling fluid descends through the drill pipe at constant injection rates and returns to the ground surface via the annulus. The fluid circulation will decrease the wellbore bottom temperature and reduce the near-wellbore high compressive stress, potentially leading to tensile fracturing of the well. The governing equations for the coupled heat transfer stress problem are formulated to ensure that the most important parameters are taken into account. The wellbore is subject to a non-hydrostatic in situ far-field stress field. In modeling heat exchange between fluid and surrounding media, the heat transfer coefficients are dependent on fluid properties and flow behavior. Analytical solutions in the Laplace space are obtained for the temperatures of the fluid in both the drill pipe and annulus and for the temperature and stress changes in the formation. The numerical results in the time domain are obtained by using an efficient inversion approach. In particular, the near-well stresses are compared for the cases with fixed and time-dependent cooling wellbore conditions. This comparison indicates that the using a fixed temperature wellbore conditions may over-estimate or under-estimate the bottom-hole stress change, potentially leading to wellbore stability problems.

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Fracture pressure prediction for layered formations with anisotropic rock strengths

Cited by 53 publications

References 29 publications

Brazilian Tensile Strength of Anisotropic Rocks: Review and New Insights

Brazilian Tensile Strength of Anisotropic Rocks: Review and New Insights

An Approximate Solution for Predicting the Heat Extraction and Preventing Heat Loss from a Closed-Loop Geothermal Reservoir

A Transient Analytical Model for Predicting Wellbore/Reservoir Temperature and Stresses during Drilling with Fluid Circulation

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