Productivity evaluation method for offshore abnormal HTHP gas reservoirs

The development of gas reservoirs is, in a way, affected by stress sensitivity of the reservoirs. With the increasing of sensitivity, the productivity follows obvious decline tendency. At present, stress sensitivity is less considered when the deliverability of highly deviated wells in offshore HTHP (high temperature/high pressure) gas reservoirs is studied. In offshore gas fields, production wells are mostly highly deviated wells due to the restriction of production platforms, and the deliverability is aslo significantly affected by the pseudo-skin coefficient induced by the well deviation. A steady-state deliverability equation of highly deviated wells, which takes stress sensitivity and high-velocity non-Darcy effect into consideration comprehensively, was developed based on the basic theories of seepage mechanics. Then, a field case study was conducted on a HTHP gas reservoir of CNOOC to verify the reliability of the deliverability equation. It is concluded that at the early development stage of HTHP gas reservoirs, it is necessary to reduce gas production rate as much as possible to keep the reservoir pressure and avoid fast productivity decline.