Physical simulation of dynamic accumulation of fault-controlled gas reservoirs and its implications: a case study of typical gas reservoirs in northwestern part of Qaidam Basin

Abstract

The dynamic physical simulation of natural gas accumulation process is one of the important means to reveal the mechanism of natural gas migration and accumulation and to summarize its distribution law. However, due to the characteristics of natural gas itself including "easy to leak, difficult to move and difficult to observe" have become holdbacks for the physical simulation of natural gas migration and accumulation. In order to reveal the migration and accumulation mechanisms of fault-controlled gas reservoirs, and to summarize the formation sequence and distribution pattern of gas reservoirs, typical reservoirs in Dongping, Mahai and Nanbaxian areas in the northwestern part of Tarim Basin were taken as examples to establish a geological evolution model for each reservoir. Aiming at the problems of gas reservoir simulation, an adjustable simulation device for gas migration and accumulation was designed, which could realize the dynamic process of structural change and clarify the phenomenon of gas charging and migration, and the formation process of typical gas reservoirs such as Dongping, and Mahai-Nanbaxian, etc. was successfully simulated. It is clear that the fault not only acts as a channel for gas migration and power transmission, but also controls the evolution sequence and distribution pattern. The formation and evolution sequence models of two different types of natural gas reservoirs, named "late accumulation" and "long-term accumulation", were proposed, the mechanism of natural gas migration and accumulation driven by "fault transmission and high pressure" was revealed, and the vertical preservation sequence featured by "co-existence of natural gas in both deep and shallow formations, and the deeper formations are more favorable for preservation" was concluded. A new concept of natural gas exploration was put forward that "if there are shallow gas reservoirs, there must be deep ones", and we can find natural gas from shallow to deep formations.

Keywords

• fault-controlled gas reservoir
• natural gas accumulation
• physical simulation
• qaidam basin