SUMMARYThe Monte Carlo method is used to generate parent stochastic discrete fracture network, from which a series of fractured rock samples of different sizes and orientations are extracted. The fracture network combined with a regular grid forms composite element mesh of the fractured rock sample, in which each composite element is composed of sub-elements incised by fracture segments. The composite element method (CEM) for the seepage is implemented to obtain the nodal hydraulic potential as well as the seepage flow rates through the fractured rock samples. The application of CEM enables a large quantity of stochastic tests for the fractured rock samples because the pre-process is facilitated greatly. By changing the sizes and orientations of the samples, the analysis of the seepage characteristics is realized to evaluate the variation of the permeability components, the existence of the permeability tensor and the representative element volume. The feasibility and effectiveness are illustrated in a numerical example.
Two-phase flow in shale gas reservoirs is caused by water flowback after multi-stage fractured, this paper presents a two-phase pressure transient analysis model of multi-stage fractured horizontal well in shale gas reservoirs. With the new mathematics model, the two-phase flow characteristics and well testing analysis for early production period can be described.
The two-phase flow model is established by material balance law, Langmuir isotherm law and Fick diffusion law. Accurate solution to this flow model is obtained by source function theory, Laplace transform, three-dimensional eigenvalue method and orthogonal transformation. According to the solution, bilogarithmic type curve of the two-phase flow model is illustrated, the pressure transient performance under the effects of hydraulic fractures and shale gas reservoir properties are discussed.
It is found that there are seven different flow regimes which have been identified on the type curve of two-phase flow model, initial gas-water saturation, storage ratio and fractured stages have deeply impacted the type curve; absorption index, skin factor and interporosity flow coefficient have lower influence to the curve shape. According to the research results and field data of Lower Paleozoic shale in China, improved well testing analysis and dynamic monitoring have been provided. The research of this paper can make optimization design for the parameters selection of drilling and hydrofracture in shale gas reservoir.
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