Well Performance Evaluation In Tight Gas Reservoirs

China is very rich in gas resources, including a huge amount of tight sandstone gasresources. Because of its occurrence in the low porosity and low permeability of tightsandstone, it is difficult to develop effectively using conventional exploration anddevelopment technologies.Under the conditions of current technology and development ability, tight gasreservoir development mainly relies on conventional technologies. There are no setsof development technologies for tight gas reservoirs of their own characteristics. Now,production analysis of tight gas reservoirs is using some conventional analysismethods, such as the Arps rate-time decline analysis method, material balance methodand the RTA analysis methods. The permeation mechanism and the developmentfeature of tight sandstone gas reservoirs are different from conventional gas reservoir.Moreover we don’t have clear understanding of the permeation mechanism as well asuncertainty of physical characteristics of tight gas reservoirs. All of those lead to largeerrors of the evaluation of tight sandstone gas reservoirs if using conventionalproduction analysis methods.In this paper, we summarize issues of the tight gas reservoir development andreservoir features, then study the permeation mechanism of the tight gas reservoirs,including the slippage effect, the relationship between the capillary pressure andpermeability, stress sensitivity and non-linear flow characteristics. We alsosummarize the characteristics of the current tight gas reservoir developmenttechniques.We identify the challenges and common pitfalls of production analysis andprovide guidelines for the analysis of production data. We provide a comprehensiveworkflow which consists of model-based production analysis complemented bytraditional decline curve analysis and flowing material balance method to estimatereserves in tight gas reservoirs. Example of the analysis of production data of tight gasreservoir is given.Base on the Arps rate-time decline relations, we develop a new rate-time relation which called power-low exponential decline model to model production behaviorbased on the diagnosis of rate-time data in tight gas reservoirs. For tight gas reservoirs,production data often shows a long term of transient flow, and even not occursintended to pseudosteady state flow (boundary dominate flow). The power-lawexponential decline model can be well fitted to the entire production history,including transient flow, transition flow, boundary dominate flow.