An improved method for predicting CO2 minimum miscibility pressure based on artificial neural network

A new semi-analytical flow model for multi-branch well testing in natural gas hydrates

Due to high energy density, clean combustion products and abundant resources, natural gas hydrates (NGHs) have been regarded as an important clean energy source with the potential for large-scale development and utilization. However, pilot tests in NGHs show that their production rates are far below commercial needs. Multilateral well technology may lead to a solution to this problem because it can dramatically expand the drainage area of production wells. This paper presents the practical rate transient analysis for multilateral horizontal wells in NGHs. In developing solution to the diffusivity equation of multilateral horizontal wells in NGHs, the superposition principle and reciprocity are applied. We wrote the governing equation in cylindrical coordinates to describe the NGH flow process. We used the moving boundaries and dissociation coefficients to model the solid-to-gas transition process in hydrates. To obtain solutions for flow in hydrate reservoirs, we used Laplace transforms and the Stehfest numerical inversion method. Superposition principle and Gaussian elimination are applied to obtain the desired solution for multilateral horizontal wells. We validated our proposed model with a commercial numerical simulator. By performing sensitivity analyses, effects on production behavior of the number of branches, dissociation coefficient, radius of the region with dissociated hydrate, and dispersion ratio are determined. A synthetic case study is conducted to show the typical production behaviors.

Complex fracture networks generated by fracturing treatments and the gas–water flow have intensified the well interference in shale gas reservoirs. In this paper, a high-precision numerical model is developed to capture the effects of well interference and gas–water flow on pressure transient behaviors of multi-horizontal-well pads. The unstructured Voronoi grid approach is employed to discretize the physical model. The model's accuracy is verified through published analytical solutions. The findings reveal that a multi-horizontal-well pad in shale gas reservoirs can exhibit up to ten distinct flow regimes. An increase in residual water saturation reduces the water flow ability and leads to an earlier commencement of the gas–water flow regime. Once the formation water becomes flowable, higher water saturation delays the initiation of all flow regimes. The well interference regime exhibits characteristics of the linear flow due to the increased well spacing. As fracture propagation leads to the well communication, the effect of fracture half-length on pressure transient behaviors becomes negligible. The case study from the Fuling shale gas reservoir demonstrates that the proposed model achieves a satisfactory fit to the actual pressure data and the pressure transient behaviors manifest a typical boundary-dominated flow regime.