Combined Microbial Geochemical Exploration (MGCE) and “4G” Exploration Model Predict Oil and Gas Occurrences in Deep Water of South China Sea

Abstract

The area of deep water in South China Sea, where the next Chinese giant oil field could be found in a few years later, is the most attractive play in China. In order to improve the drilling success rate and reduce the drilling risk and cost, Microbial Geochemical Exploration (MGCE) and “4G” exploration model were applied to hydrocarbon detection of two potential traps in Baiyun Sag of Pearl River Mouth Basin. Microbial Geochemical Exploration (MGCE), which is based on the presence of hydrocarbon microseeps above buried oil and gas reservoir, combined a quantitative biological method with a qualitative geochemical method to make reliable detection and interpretation of hydrocarbon microseepage. “4G” exploration model, which integrates geology, geophysics, geochemistry and geo-microbiology information, could greatly improve the sensitivity, accuracy and reliability of hydrocarbon detection of potential traps. Trap A, identified by 3-D seismic survey with a depth of approximately 2000 m under water, was a prospective sandstone stratigraphic trap of Neogene Zhujiang Formation. 110 MGCE samples were collected from a regular grid spaced 700m by 1000m covering an area of 55 km². For analog, additional samples were collected at existing wells, known to be dry wells or producers of oil and gas in adjacent region. Two positive microbial anomalies were observed in the northern half of the area sampled (average 334). Wildcat well drilling in one positive anomaly in the northern region has encountered oil in economic quantities. As a result of the application of MGCE and “4G” Exploration Model, the seismic survey and potential drilling costs were reduced significantly. Structural trap B was an anticline developing on the palaeohigh and became complicated by faults. According to the AVO inversion and amplitude property anomaly, oil company believed there would be a gas reservoir in Neogene Zhujiang Formation and Zhuhai Formation at trap B. But at their favorable area, Microbial Value presented low and background (average 5) by the application of MGCE, and then the carbon dioxide gas was drilled. If they accepted our proposal, the oil company could have saved $40 million on drilling expenses. So, we believed that MGCE could be sensitive and effective in non hydrocarbon gas reservoir identification.

AAPG Datapages/Search and Discovery Article #90194 © 2014 International Conference & Exhibition, Istanbul, Turkey, September 14-17, 2014