Abstract:

The Kelasu ultra-deep gas field in the Kuqa depression of the Tarim Basin is challenged by severe water invasion, leading to rapid decline in production. Through analysis on surface seismic data and imaging logging data, the distribution patterns of faults and fractures were determined. Combining with the production performance of the gas field, three types of water invasion were identified in the Kelasu ultra-deep gas field: fault-communicated edge or bottom water, non-uniform water invasion along fractures, and occluded water invasion due to locally incomplete displacement. The former two types are dominant in the gas field. The three types differ significantly in characteristics and influence range. On one hand, the ability to communicate with edge or bottom water along the trend of second-order faults and vertically is strong, but water invasion perpendicular to the trend of faults has a minor, localized impact. On the other hand, fractures are oriented and distributed regularly, showing a feature of “zones generally and belts locally”. The differences in the internal connectivity of the gas reservoir, the order and the speed of water invasion in the gas reservoir are the external manifestations of the division and zonation of fractures, which have a global effect on water invasion in the gas reservoir. Considering the water invasion characteristics and development status of the gas field, strategies were proposed to optimize well pattern according to spatial distribution of fractures, and to strengthen researches on two supporting gas production technologies: chemical water plugging and gas injection to alleviate water lock.

Key words: Tarim Basin, Kuqa depression, Kelasu, ultra-deep gas field, fracture, water invasion characteristic, stable production strategy