Review on the progress for physical simulation for gas reservoirs co-production in multi-pressure system

The gas reservoirs co-production in multi-pressure system is one of the important measures to improve the development efficiency of the superposed gas-bearing systems. However, the co-production effect is not ideal due to the special reservoir forming background. The mechanism of co-production and high-efficient development of the multi-pressure system has become an key scientific problem, which restricts the efficient exploration and development of superposed gas-bearing systems. This paper focuses on the gas reservoirs co-production in multi-pressure system, and divides the physical simulation types of co-production into two separate fields: coalbed methane and non coalbed methane. It clarifies the current research status of gas reservoirs co-production in multi-pressure system from the aspects of device functions and characteristics, understanding of co-production, and existing problems. Firstly, the large-scale physical simulation test device can effectively eliminate or weaken the problems of homogeneous single-type reservoir samples, single monitoring data means and single stress loading form caused by paralleling multiple core grippers to build the physical simulation model. The development direction of the physical simulation for co-production in multi-pressure system should be to achieve true three-dimensional heterogeneous complex in-situ stress state of large-scale heterogeneous multi-type reservoir samples. The characteristics of fluid pressure transmission between adjacent reservoirs, the inter-layer crossflow, the multi-phase natural gas symbiosis should be considered. On this basis, the sensitivity of co-production of multi-pressure system to reservoir physical properties was deeply summarized. The differences in inter-layer pressure difference, permeability, effective stress, water saturation and other factors may induce the fluid interference and reservoir gas production damage, and optimizing co-production style may be a way to reduce the fluid interference and reservoir gas production damage. In totally, the next research should focus on exploring the influence of the coupling effect of low porosity and low permeability, gas water two-phase flow, multiphase gas symbiosis and coexistence of multiple types of reservoirs on the dynamic evolution law of reservoir-wellbore flow field induced by co-production fluid interference, clarifying the reservoir damage and its mechanism of different phase fluid intrusions on the reservoir, and revealing the coupling flow characteristics of inter-layer crossflow and wellbore pipe flow considering the fluid interference effect.