Detailed assessement of a single-combination oil-gas accumulation zone in a mature exploration basin, China

As some basins or blocks in China, especially matured and gas fields, have already entered the mature or highly mature stage in exploration, the old traditional assessment method that treats “complex horizons” as a whole part can not meet the high resolution and precision requirements for detailed exploration in these areas. By comparing oil-gas evaluation systems at home and abroad and considering the evaluation method for “play” abroad, a single-combination assessment method for oil and gas accumulations in high matured exploration basins were put forward. The new method, composed of geological evaluation, resources estimation and target selection, focuses on conducting a division of the assessment horizon based on a combination of a regional/sub-regional seal and its corresponding reservoirs and hydrocarbon-supplying area, confirms the test results of drilled wells and the distribution of known reservoirs, and depicts boundaries of every key geological element. Finally, these preliminary maps of key elements are overlapped to figure out the scope and type of favorable exploration targets, hydrocarbon-supplying system, channel types, charge capacities, and the most favorable prospective traps. Detailed exploration practices in Qikou depression, Bohai Bay Basin, show this evaluation method works well.