Rate Decline Analysis for Limited-Entry Well in Abnormally High-Pressured Composite Naturally Fractured Gas Reservoirs

Abstract

Most naturally fractured gas reservoirs in China exhibit strongly heterogeneous, abnormally high-pressured and, stress-sensitive behaviors. In this work, a semianalytical solution is developed to study the production performance for limited-entry well in composite naturally fractured formations. The pressure-dependent porosity and permeability, anisotropy and limited-entry characteristics are taken into consideration. Furthermore, conventional Warren-Root model is amended to accommodate for permeability anisotropy. Laplace and finite Fourier cosine transforms are used to solve the diffusivity equations. The model is verified on the basis of previous literature’s results and data of a field example from Moxi gas field in Southwest China. Through the parameters sensitivity analysis, the effects of prevailing factors on production performance are investigated. Results indicate that a large inner region radius and high mobility ratio can improve gas production rate in the early stage, while they also lead to a drastic decline of production rate in the late stage. Large permeability stress-dependent coefficient and low penetrated interval both have a negative impact on production rate. With its high efficiency and simplicity, this proposed approach can serve as a convenient tool to evaluate the behavior of partially penetrated production well in abnormally high-pressured composite naturally fractured gas reservoirs.

Dewatering Optimization of Coal Seam Gas Production Wells: A Review and Future Perspectives

“…A high dewatering rate will result in a significant rise in the effective stress at the near-wellbore area and cause the reduction of cleat aperture and permeability, a phenomenon called the stress-sensitivity permeability, ,− as described by the curve from P i to P rb in Figure . This is detrimental to the dewatering efficiency and the pressure propagation, leading to a low production rate and small drainage radius. ,, If the stress concentration around the wellbore is excessive, it can lead to permanent (i.e., irrecoverable) permeability damage, resulting in long-term loss to the gas well productivity. ,,− An example of the impact of stress sensitivity during CSG production was presented by Yang et al via a numerical simulation. Their results show that (i) the existence of stress sensitivity can reduce the pressure funnel radius and decrease the production rate evidently, as presented in Figure , and (ii) increasing the dewatering rate is not always beneficial to gas production.…”