| Dianqianbei Depression is a reformed residual region. Based on the results of regional geological survey and drills in the gas-bearing shale zones in the northern part of it, it is shown that the excellent marine black shale is more than 50m thick in net thickness respectively in lower Silurian Longmaxi and lower Cambrian Niutitang Formations. The shale evaluation factors for both formations in this area, including the shale thickness, buried depth, gas content, mineral composition, organic geochemical indices, mechanical and physical properties, etc., are rather similar in correlation with those in the commercial shale gas fields in America. It means that these shale formations are favorable for hydrocarbon accumulation and can be the prospecting targets. Effected by late intense tectonic activities, the lower Paleozoic marine shale would be seriously influenced by some adverse factors such as heavy fracturing, regional cap-rock erosion and
atmospheric freshwater leaching but the gas concentration in the shale would increase with increasing TOC content and
well-getting preservation. It is suggested that as integrated evaluation and selection of plays for exploration, six "qualita鄄tive and quantitative principles" (QQP) should be taken into account. The preservation condition should be the key one of factors. It is proposed that the plays for exploration targets are the Longmaxi and Niutitang gas-bearing shale in Yiliang-Junlian-Xuyong area, and Niutitang gas-bearing shale in Hezhang-Zhenxiong area. |
