Fluid dynamic response characteristics of CBM coproduction reservoir in MSGBS

In order to study the dynamic response characteristics of reservoir fluid during Coalbed Methane (CBM) coproduction in Multi-layer Superimposed Gas Bearing System (MSGBS),using the physical simulation test device of CBM coproduction in MSGBS with independent intellectual property rights,the coproduction tests with interlayer pressure difference of 0.2,0.4 and 0.6 MPa were carried out respectively,and the dynamic response characteristics of reservoir fluid during coproduction were analyzed. The results show that：the reservoir pressure evolution has the characteristics of phased change,and the reservoir pressure change curve can be divided into sudden drop type,shielding type and backflow type. At the initial stage of coproduction,there will be interlayer interference,which makes the fluid migration show the characteristics of centrifugal flow,indicating that the reverse flow of CBM occurs. During coproduction,different energy bodies are connected in the wellbore,and the energy dynamic balance state between coal reservoir systems was destroyed,which makes the fluid transfer from high-energy gas bearing system to low-energy gas bearing system,so that the fluid migration is restrained or shielded. With the increase of fluid energy difference between gas bearing systems,the fluid of high-energy system flows back into lower energy potential system. The interlayer pressure difference increases,the interlayer interference phenomenon is significant,the compatibility of coproduction becomes worse,the amplitude of reservoir pressure rise increases,the centrifugal flow range of reservoir flow field increases,and the reservoir damage area increases. When the interlayer pressure difference increases from 0.2 MPa to 0.4 MPa and 0.6 MPa respectively,the CBM backflow increases from 0.42 L to 3.73 L and 7.97 L respectively,and the cumulative flow of coproduction decreases from 218.74 L to 208.61 L and 192.21 L.