Practice and Lessons Learned for the Development of Naturally Fractured Carbonate Gas Reservoir in Weiyuan Gas Field of Sichuan Basin, China

摘要

Dengying gas reservoir in Weiyuan Gas Field is classified as a fractured dolomite gas reservoir with extreme low matrix permeability and bottom water. The ultimate gas recovery is only 37% in the wake of 50 years’ exploitation. By integrating core analysis, well logging interpretation and dynamic performance analysis, we investigate the key factors affecting gas recovery. Firstly, fractures are the main pathway both for gas to flow into the wellbore and water to invade into the gas reservoir. Secondly, the great amount of water produced from gas wells boosts liquid loading and therefore increases the additional pressure loss in the borehole dramatically. Thirdly, the trapped gas, isolated in the matrix from intermittent production after watered-out owing to non-uniform water flow through the fractures, could not be recovered. For this reason, some imperative measures should be taken to improve the gas recovery. On the one hand, a reasonable flow rate of the gas well should be optimized for preventing from water invasion and extending water- free production period. On the other hand, dewatering is a practical method to extend the life span of the producing well and to improve the gas recovery.