A new device to bypass lower pressure formations in well cementing job

Abstract

In cased and perforation completion method widely applied in oil and gas wells, it is difficult to avoid the cementing slurry damage to the lower pore pressure formations. This paper presents a new type of down-hole device, consisting of a packer and valve on each side, to isolate the target interval. Several devices can be connected to the casing strings as necessary and are able to make the cementing slurry bypass such formations. The internal pressure resistance was tested and the pressure loss was calculated when the slurry, at a flow rate of 1.5 m3/min, flowing through it. The surface experiment results show that the device can bear 28 MPa without any leakage. Through calculation, the extra pressure loss when normal cementing slurry flows each such device is only about 2.2 MPa, which can satisfy the field requirements. In casing completion operations, multiple devices can be connected to the casing string at the corresponding intervals. Pressuring the liquid in the casing, the pins at the end of the string will be cut off, allowing cement slurry to circulate and bypass such target sections. Two successful field cases applied in coal bed methane wells proved its feasibility. This technology will be able to provide a new promising completion method to avoid cementing slurry damage to formations with lower pore pressure intervals in oil, gas or coal-bed methane wells.