Technical system and achievements of rolling exploration in large and medium-sized deep-water gas fields: a case study of marginal gas field A in central canyon of Qiongdongnan Basin

A complete technical system of gas field rolling exploration such as target search, evaluation and drilling was introduced to promote the development of the deep-water marginal gas field A in the central canyon of the Qiongdongnan Basin. In addition to the traditional target search technology of oil and gas potential in the zone, a target search technology of evaluation process was proposed for the marginal gas field A. A total of five potential oil and gas blocks were searched, and the structure A4 was selected for oil and gas target evaluation. The main controlling factors of hydrocarbon accumulation in the structure A4 were studied from two aspects: trap interpretation and implementation, and trap hydrocarbon detection. The predicted dominant gas-bearing areas in the central part of structure A4 have favorable gas-bearing information characteristics such as strong amplitude attributes, low density, low velocity, low P-wave impedance, and low P-wave and S-wave velocity ratios. They were generally classified as class Ⅲ AVO anomaly, which can upgrade the HL_0 gas group to control natural gas geological reserves. The rolling exploration well A4-1 was drilled, encountering a gas layer of over 20 m in the Huangliu Formation, and a suspicious gas layer of nearly 10 m in the second member of Yinggehai Formation. The proven geological reserves of natural gas were nearly 3 billion cubic meters, and the drilling effect was good. The application of rolling exploration research in the deep-water marginal gas field A not only effectively promotes the subsequent rolling exploration activities of the marginal gas field A, but also confirms that rolling exploration is also applicable to deep-water oil and gas exploration.