Mathematical and Experimental Simulation of Hydraulic Fracturing in Shallow Coal Seams

Abass, Hazim; Hedayati, S.; Kim, C.M.

doi:10.2118/23452-ms

Cited by 12 publications

(10 citation statements)

References 5 publications

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“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] et al 1 investigated how well the fractures are contained in coal during a stimulation treatment. In this study, 12 vertical wells were drilled, completed, and subsequently evaluated via mining excavation.…”

Section: Literature Reviewmentioning

confidence: 99%

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Lessons Learned From Modeling Hydraulic Fracture Treatments in Coals Using a Fully Functional Three Dimensional Fracture Model in a San Juan Basin Project

Ramurthy¹,

Lyons²

2007

Proceedings of Rocky Mountain Oil &Amp; Gas Technology Symposium

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fax 01-972-952-9435. AbstractThe two main objectives of using a hydraulic fracture model in coals are: (a) optimization of job design and placement, and (b) post-fracture diagnostics. Though certain limitations still exist, hydraulic fracture modeling in coals has undergone major advancements in the past decade. Pseudo or lumped three-dimensional (3-D) models have usually been employed to try and meet the objectives mentioned above. The effectiveness of using such models in coals has been very limited. Fully functional 3-D models are currently available in the industry and can be used to obtain better estimates of the fracture dimensions. This paper shows that a grid-oriented fully functional 3-D fracture simulator with shear decoupling can be especially useful in coals for post-fracture diagnostics if sufficient input data can be fixed from logs and Diagnostic Fracture Injection Tests (DFIT).When problems occurred with placement of fracture treatments, especially in the upper Fruitland coals of a San Juan basin project, instead of experimenting with various ideas arbitrarily, technical evaluation using DFIT data and fracture modeling with a grid-oriented, fully functional 3-D fracture simulator, was used to pin-point the issues and address them accordingly. This paper will discuss the deficiencies of using 2-D and pseudo-3-D fracture models in coals and also will discuss the lessons learned from using a grid-oriented, fully functional 3-D fracture simulator in this project along with the successful implementation of the results developed from the modeling work. Literature ReviewOver the last 25 years, numerous papers have been published regarding hydraulic fracturing and modeling in coals. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] et al. 1 investigated how well the fractures are contained in coal during a stimulation treatment. In this study, 12 vertical wells were drilled, completed, and subsequently evaluated via mining excavation. The treatment designs were adjusted using the information gathered from excavation. Layne, et al. 2 through their U.S. Department of Energy (DOE) work wanted to advance the hydraulic fracturing techniques in coals by improving the understanding of fracturing treatments using mineback observations. They used five fracture models that were developed under contract to the DOE to analyze the mineback observations. Jones, et al. 3 evaluated 130 fracturing treatments in their study. They observed high treating pressures during fracture treatments in Black Warrior basin and attributed the following as possible causes: (a) high pore pressure buildup due to fluid leakoff, (b) multiple fracture propagation, and (c) fracture-tip plugging by coal fines. They modified a pseudo-3-D model to replicate a fracture tipscreenout caused by coalfines plugging within the pad. Jones, et al. 4 presented another paper addressing the unusual treating pressures observed during hydraulic fracture treatments in coal. As part of that work, they presented methodologies to design fractur...

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Section: Literature Reviewmentioning

confidence: 99%

“…Abass, et al 10 conducted laboratory experiments on unconfined coal samples to simulate fracture treatments of coal seams. The authors observed creation of multiple fractures and high leakoff associated with multiple fractures from such tests.…”

Section: Literature Reviewmentioning

confidence: 99%

Lessons Learned From Modeling Hydraulic Fracture Treatments in Coals Using a Fully Functional Three Dimensional Fracture Model in a San Juan Basin Project

Ramurthy¹,

Lyons²

2007

Proceedings of Rocky Mountain Oil &Amp; Gas Technology Symposium

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“…18 gave the best fit to the data of Abass et al 5 and showed the most reasonable behavior. Figure 4 illustrates the quality of the fit.…”

Section: Stress-5train Modelingmentioning

confidence: 69%

“…5 presented more blatant examples of nonlinearity with their tests on unconfined coal samples, shown in Fig. 1.…”

Section: Introductionmentioning

confidence: 97%

Hydraulic Fracture Modeling in Formations Exhibiting Stress-Dependent Mechanical Properties

Poulsen¹,

Abass²

1993

Proceedings of SPE Annual Technical Conference and Exhibition

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Although most fracturing treatment design models assume that the behavior of the formation being fractured can be approximated by linear elastic theory, many formations, particularly unconventional ones such as coalbeds and poorly consolidated sandstones, exhibit sufficiently nonlinear behavior to invalidate this assumption. Methods are developed and presented for generalizing fracture design models and net fracturing pressure analysis to consider nonlinear stress-strain behavior.

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“…Competent rocks are well cemented, while coalbeds contains natural cleats (Jones et al, 1986;Abass et al, 1991;Laubach et al, 1998). Cleats are fractures and normally have no shear offset.…”

Section: Structure Of Coal Bedsmentioning

confidence: 99%

Complexity of Minifrac Tests and Implications for in-Situ Horizontal Stresses in Coalbed Methane Reservoirs

Fang

Khaksar

2011

All Days

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U.S.A., Minifrac tests are used to obtain key parameters of reservoirs for geomechanical modeling and hydraulic fracture treatment design. An ideal minifrac test can clearly indicate the leak-off pressure, fracture propagation pressure, shut-in pressure and fracture closure pressure. Repeated minifrac tests in the same interval provide additional value by verifying the fracture parameters with similar results. However, minifrac tests of two wells conducted in a coal seam in a coalbed methane (CBM) reservoir in China showed unconventional results -the fracture profile is less distinguishable for the fracture behaviors, and the subsequent test cycles in each well exhibited higher pressures than the precursors.A close examination of the test results with laboratory experiments and field microseismic monitoring results indicates that the discrepancies in pressure responses are correlated to the constitution of the coal seam. The coal seam contains many cleats, and the minifrac tests in most cases had opened these cleats instead of initiating new fractures. Opening a cleat whose plane is in line with the maximum horizontal stress orientation requires the least pressure but could be inhibited by connecting cleats with any other orientation that needs higher pressure to open or slide, which could lead to opening more cleats from different sites towards different directions. Eventually, multiple zigzag hydraulic fracture paths instead of a single planar fracture would be induced. The zigzag paths and simultaneously opening of multiple fracture paths will cause a stress increase in their vicinity, resulting in higher treating pressures for further advances. This implies that the magnitude of minimum horizontal stress S hmin shall be the least magnitude seen amongst the leak-off and fracture closure pressures of all tests, 0.0143 MPa/m for the case study.A conceptual model has been put forward to reveal the hydraulic fracturing in coalbeds. The mechanisms possibily contributing to the high treating pressure in hydraulically fracturing coalbeds have been explained from the geomechanics point of view, including poroelastic effects, fracture tortuosity effects and multiple fracture opening effects. This paper describes how the physical coal seam model reacts to fluid injection, which assists understanding the nature of minifrac tests and avoids the misinterpretation of the results. The approach can further help to quantify accurately the minimum horizontal stress magnitude from the complex minifrac tests, and hence contributes considerably to accurate geomechanical modelling and fracture treatment design for any CBM reservoirs.

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Mathematical and Experimental Simulation of Hydraulic Fracturing in Shallow Coal Seams

Cited by 12 publications

References 5 publications

Lessons Learned From Modeling Hydraulic Fracture Treatments in Coals Using a Fully Functional Three Dimensional Fracture Model in a San Juan Basin Project

Lessons Learned From Modeling Hydraulic Fracture Treatments in Coals Using a Fully Functional Three Dimensional Fracture Model in a San Juan Basin Project

Hydraulic Fracture Modeling in Formations Exhibiting Stress-Dependent Mechanical Properties

Complexity of Minifrac Tests and Implications for in-Situ Horizontal Stresses in Coalbed Methane Reservoirs

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