Natural Gas Accumulations In The Liuquan-Caojiawu Play Of The Langgu Depression

More than half of natural gas reserves in Langgu depression is from Liuquan-Caojiawu play, but in recent years, the progress of natural gas exploration in Liuquan-Caojiawu play is slow, the main reason is that the key accumulation elements is still ambiguous. In order to solve these problems, also to promote the natural gas development, this paper analyzes the natural gas accumulation of above area. According to the sedimentary and structural characteristics of Langgu depression, a source rock evaluation system is establish, and the evaluation result is that the effective source rock is in mid and lower Es3. On the basis of the natural gas geochemical characteristics, three kinds of natural gas are identified including biogas, low mature gas and biogenetic-low mature maxed gas. Based on above, the oil and gas accumulations characteristics of the four tertiary structures are analyzed. Three kinds of natural gas distribute on the Liuquannan anticline, biogas on the west wing, biogenetic-low mature gas on the east wing and the low-mature gas on the central part. The fault section characteristics of normal pressure and formation water show that two migration systems control the oil and gas distribution. The validity of reservoir-caprock assemblage is evaluated by well logging dates. The result is that the best assemblage is in mid Es3, which is favour of the oil and gas accumulation and conservation. Through the analysis of the typical oil and gas pool, three gas accumulation models of different kinds of gas are generalized. There are two type models of biogas accumulation i.e. secondary-buried source rock biogas accumulation model and oil-biodegraded gas accumulation model. Suitable environment fit for methane bacteria is an essential condition to biogas accumulation. Under generation and top accumulation model of low mature gas is controlled by source rock, reservoir and cap-rock assemblage and migration pathway. Biogas and low mature gas mixing accumulation model is always controlled by faults. According to the source rock, reservoir and cap-rock assemblage, pathway and hydrologic condition,this paper evaluates the different blocks of studied area,also predicts that the central and southern part of west wing and the shallow layer of Hupoying structure are the favorable exploration targets.