A differential pressure casing gas recovery device for pumping wells

The Changqing Ansai oilfield is a low-permeability oilfield in a hilly and gully region, with low well productivity and high produced gas-oil ratio in the low–medium water cut stage. In order to recover casing gas from producing wells with casing pressure lower than back pressure and large elevation differences between wells and stations, and reduce back pressure of well groups in winter, a differential pressure casing gas recovery device was developed for pumping wells. This device connects the casing gas line and the flow line through the casing check valve and the tubing check valve, respectively, forming a three-way structure at the wellhead to be capable of differential pressure-driven gas collection, invaded gas collection and constant-pressure gas collection. When the difference between casing pressure and back pressure is less than the fluctuation amplitude of the wellhead tubing pressure, the differential pressure gas collection is enabled. When the casing pressure is lower than the back pressure of the well group, the invaded gas collection is achieved, as the pressure drop of up-dip pipelines reduces with the increasing gas velocity. When the casing pressure is continuously above the back pressure, the constant pressure gas collection is performed. Field application results show that this device can recover more than 260 m³/day of casing gas per well and reduce back pressure by 0.6 MPa in winter. The presented device delivers a remarkable performance of gas collection and back pressure reduction.