Production prediction method of horizontal wells in tight gas reservoirs considering threshold pressure gradient and stress sensitivity

Semi-analytical modeling of transient pressure behaviour for a fractured vertical well with hydraulic/natural fracture networks by considering stress-sensitive effect

Tight gas reservoir (TGR) plays an important role in unconventional oil and gas resources. The existing seepage models for TGR rarely consider the effects of heterogeneity, stress-sensitivity, and the unsteady fluid exchange between matrix and fracture. Heterogeneity is common for tight gas reservoir which should be carefully considered in geological model. The stress-sensitivity effect of fracture is an important factor influencing the transient flow behavior of TGR. Ultra-low porosity and permeability cause the unsteady flow between matrix and fractures systems. So this paper introduced a mathematical model for the horizontal well in a dual-porosity composite tight gas reservoir with considering the stress-sensitivity effect and unsteady flow between matrix and fractures systems. Some mathematical methods including the finite Fourier cosine transform, perturbation technique, Laplace transform, superposition principle, Stehfest numerical inversion algorithm are used to solve the nonlinear partial differential equation. Different flow regimes are divided based on pressure transient analysis curves. The sensitivity analysis of related parameters is studied according to pressure transient analysis and rate transient analysis curves. The presented model and obtained results in this paper give better understanding on pressure and rate transient behaviors of composite TGR. Cited as :  Zhao, K., Du, P. Performance of horizontal wells in composite tight gas reservoirs considering stress sensitivity. Advances in Geo-Energy Research, 2019, 3(3): 287-303, doi: 10.26804/ager.2019.03.07

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Performance of horizontal wells in composite tight gas reservoirs considering stress sensitivity

A general analytical method for transient flow rate with the stress-sensitive effect

Underground gas storage (UGS) of CH4 and H2 is an economical and reliable solution for large-scale energy storage. Cyclic gas injection-withdrawal of UGS can induce periodical stress perturbation in reservoirs, which may significantly influence the permeability of the reservoir. Understanding the effect of cyclic stress on the permeability evolution in reservoirs is important for optimizing the injection-withdrawal strategy. Therefore, the alterations of rock mechanical properties, permeability and its stress sensitivity of a sandstone sample from UGS under cyclic stress were obtained by experiments. Results indicated that the stress-strain curves of the sandstone under cyclic stress was not coincided and formed a hysteresis loop, and with the increasing cycles, the hysteresis loop transformed from sparse to dense. With the increase of cycles, the elastic modulus (E) in the sandstone first increased, then decreased slightly, and finally almost remained constant, while the Poisson's ratio (v) increased at early cycles and then nearly remain unchanged. The evolution of permeability of sandstone can be separated into three stages: rapid decline stage (1-10th cycles), slight decline stage (10-30th cycles), and almost stable and unchanged stage (30-50th cycles), which shows good consistent with the deformation behaviors of sandstone. Correspondingly, the change of compressibility coefficient in the sandstone can also be divided into three stages, including the rapid decline stage (1-10th cycles), slight increase stage (10-30th cycles) and slow decline stage (30-50th cycles), which shows an opposite variation trend with the rock mechanical properties in sandstone. For a certain cyclic stress loading-unloading, the permeability and compression coefficient in the sandstone at minimum stress were larger than those at maximum stress. The irreversible permeability loss rate of the sandstone showed good consistent with the changes of stress sensitivity coefficient caused by cyclic stress. 

Experimental study on the permeability variation of sandstone at cyclic stress: Implication for underground gas storage

Horizontal well transient rate decline analysis in low permeability gas reservoirs employing an orthogonal transformation method

Most researches of the threshold pressure gradient in tight gas reservoirs are experimental and mainly focus on the transient pressure response, without paying much attention to the transient rate decline. This paper establishes a dual-porosity rate transient decline model for the horizontal well with consideration of the threshold pressure gradient, which represents the non-Darcy flow in a fracture system. The solution is obtained by employing the Laplace transform and the orthogonal transform. The bi-logarithmic type curves of the dimensionless production rate and derivative are plotted by the Stehfest numerical inversion method. Seven different flow regimes are identified and the effects of the influence factors such as the threshold pressure gradient, the elastic storativity ratio, and the cross flow coefficient are discussed. The presented research could interpret the production behavior more accurately and effectively for tight gas reservoirs.

Dual-porosity model of rate transient analysis for horizontal well in tight gas reservoirs with consideration of threshold pressure gradient

Characteristics of transient production rate performance of horizontal well in fractured tight gas reservoirs with stress-sensitivity effect

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Horizontal well transient rate decline analysis in low permeability gas reservoirs employing an orthogonal transformation method

Dual-porosity model of rate transient analysis for horizontal well in tight gas reservoirs with consideration of threshold pressure gradient

Characteristics of transient production rate performance of horizontal well in fractured tight gas reservoirs with stress-sensitivity effect