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The most common methods of predicting a gas/water two-phase relative permeability include experimental measurement, theoretical simulation, and numerical calculation. The experimental method is relatively accurate but time-consuming and laborious. The method of theoretical modeling involves a complicated solving process, and the range of application of the numerical calculation method is comparatively narrow. In this work, based on the least square support vector machine (LSSVM) combined with the gray optimization algorithm (GWO), the prediction model (GWO-LSSVM) of the gas/water phase permeability is established. The model was validated by the gas-water two-phase relative permeability data obtained by a non-steady-state method from a gas reservoir under high pressure/high temperature (133–152.5°C, 50.3–55 MPa) conditions. The irreducible water saturation (Swc), absolute permeability (K), porosity (j), and gas saturation (Sg) have been set as the input parameters. The water phase relative permeability (Krw) and the gas phase relative permeability (Krg) have been set as output variables. The training data of water phase and gas phase relative permeability were 147 and 141, respectively. The prediction data were 32 and 58, respectively. The results show that the absolute relative deviation (AARD) of Krw for the presented GWO-LSSVM model is 3.69%, while that of Krg is 2.92%, showing that the model can accurately predict the gas-water relative permeability at high temperature and high pressure. The method provides a new and effective instrument for estimating the gaswater two-phase relative permeability parameters in the development of gas reservoirs. [ABSTRACT FROM AUTHOR]

Performing stress‐sensitivity evaluation on a high‐temperature and high‐pressure gas reservoir is essential for correctly understanding the characteristics of physical property changes and reasonably designing the development scheme of a reservoir under stratum conditions. By focusing on six core samples with different physical properties in a gas field in the Yingqiong Basin, stress‐sensitivity experiments have been conducted along with mercury intrusion porosimetry and X‐ray diffraction measurements to study the relationship among porosity, permeability, and effective stress at a temperature of 140°C and effective stress ranging from 2 MPa to 70 MPa. Our results showed that the stress‐sensitivity curve characterized by three‐stage segmentation is primarily affected by average pore radius and mineral composition but has no direct relation with porosity and permeability. Meanwhile, the stress sensitivity of permeability is mainly related to the average pore throat radius and mineral composition of core specimen. The smaller the pore throat radius and the higher the clay content, the stronger the stress sensitivity of permeability. Under high‐temperature and high‐pressure conditions, the stress sensitivities of permeability and porosity can be characterized by power functions although the stress sensitivity of permeability is about 2–11 times higher than that of porosity. [ABSTRACT FROM AUTHOR]

Interest in tight gas reservoirs (TGR) has quickly spread worldwide. Most researches on the permeability stress-sensitivity of tight gas reservoirs mainly concentrated on experimental approach, physical modeling or pressure behavior analysis, while transient production rate performance does not attract much attention. This study developed a dual-porosity model of a horizontal well in fractured tight gas reservoirs considering the stress-sensitivity effect. The solution methods include variable substitution, perturbation technique, Laplace transformation, Sturm-Liouville eigenvalue theory, orthogonal transformation and numerical inversion. The results showed that the production rate decreases with the increasing of permeability modulus and the derivative curve will be warped up during the whole system late radial flow stage. The influences of other parameters are also analyzed. The work undertaken here has both theoretical and practical significance in predicting production performance and evaluating underground fluid transport in such formations. [ABSTRACT FROM AUTHOR]

Transient rate decline analysis (TRDA) is an important analysis in modern reservoir engineering and applications. Most studies have focused on the threshold pressure gradient (TPG) of low permeability reservoirs and have placed an emphasis on the transient pressure response or steady productivity, whereas transient production decline has not been a focus. This paper presents a transient production decline analysis model of a horizontal well in low permeability gas reservoirs considering the threshold pressure gradient. An accurate solution is determined by employing the Laplace transformation, Sturm-Liouville eigenvalue method, and orthogonal transformation. The bi-logarithmic type curves of dimensionless production and the derivative are plotted by the Stehfest numerical inversion method. Five different flow regimes were recognized, and the effects of the influencing factors, such as the threshold pressure gradient, wellbore storage coefficient, skin factor, horizontal section length, and formation thickness, are discussed. This research contributes to the understanding of transient flow behavior and provides the theoretical basis for efficiently exploiting low permeability reservoirs. [ABSTRACT FROM AUTHOR]

After multistage fracturing, the flowback of fracturing fluid will cause two-phase flow through hydraulic fractures in shale gas reservoirs. With the consideration of two-phase flow and desorbed gas transient diffusion in shale gas reservoirs, a two-phase transient flow model of multistage fractured horizontal well in shale gas reservoirs was created. Accurate solution to this flow model is obtained by the use of source function theory, Laplace transform, three-dimensional eigenvalue method, and orthogonal transformation. According to the model’s solution, the bilogarithmic type curves of the two-phase model are illustrated, and the production decline performance under the effects of hydraulic fractures and shale gas reservoir properties are discussed. The result obtained in this paper has important significance to understand pressure response characteristics and production decline law of two-phase flow in shale gas reservoirs. Moreover, it provides the theoretical basis for exploiting this reservoir efficiently. [ABSTRACT FROM AUTHOR]

Abstract: Observational procedures are used to develop liquid loading models associated with gas production. The performance of various critical liquid-removal flow rate models are compared and critiqued by examining model outputs. Critical liquid-removal flow rates calculated by different models are found to vary considerably. Using the balance relationship between total surface free energy of liquid droplets and turbulent kinetic energy of gas flow, we developed a new model that considers the influence of droplet diameter on critical liquid-removal flow rate of gas wells. Model reliability is verified by comparing model results with gas well production data from four gas reservoirs in China. [Copyright &y& Elsevier]