The Application of Geo-Microbial Hydrocarbon Detection in Deepwater Lithologic Play Exploration in Central Canyon, Qiongdongnan Basin, Northern South China Sea

Abstract

The central canyon is a deepwater channel-levee system developed in parallel to the slope across Qiongdongnan basin(QDNB). Previous exploration has discovered a gas reservoir in the central canyon system(CCS) of Lingshui sag, indicating that the study area has good oil and gas prospect. A detailed interpretation of the latest seismic data resulted in the discovery of a number of traps. However the complex structure and lithology distribution in the research area made it difficult to identify reservoirs and the geo-fluid properties. An effective hydrocarbon detection method is urgently required in the area to make exploration breakthrough. Geo-Microbial Hydrocarbon Detection (GMHD) technology is a maturing and economically effective method for petroleum exploration, which is developed upon a significant but underutilized geological principle that hydrocarbon microseepage is present vertically above buried oil and gas reservoir. It combined a quantitative biological method with a qualitative geochemical method to make reliable detection and interpretation of hydrocarbon microseepage. GMHD technology could be applied to forecast the existence, distribution and properties of hydrocarbon accumulations (or “sweet spots”) in depths. Lithologic traps A and B, identified by 3D seismic survey with a depth of approximately 1500 m under water, were prospective CCS channel lithologic traps of tertiary Huangliu Formation. In 2014 GMHD survey project, 140 surface sediment samples were collected in regular grid spaced at 700m covering an area of 60 km². Additional 40 sediment samples were collected at an existing gas well in adjacent region for analog purpose. GMHD survey identified three positive microbial anomalies respectively above the existing gas well, trap A and B. Post GMHD survey wildcat wells drilling in positive anomalies in trap A and B has encountered commercial gas flows. It is further proved by well testing results that the gas discovery in Trap A and B is the first major petroleum exploration breakthrough of China State-Own Company proprietary blocks. It is also proved that GMHD technology is sensitive and effective in detecting hydrocarbon bearing potential in lithologic traps of deepwater area. The application of GMHD technology can significantly reduce exploration and drilling costs.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015