中上扬子地区下志留统龙马溪组有机质碳化区预测

确定有机质碳化区分布范围和排除页岩气勘探高风险区是中国南方海相页岩气选区和勘探评价面临的重要任务。以大量钻井、露头资料为基础,对中上扬子地区下志留统龙马溪组开展了有机质碳化区识别与预测,编制龙马溪组有机质碳化区分布工业化图件,初步获得四点成果和认识:①提出海相页岩有机质碳化判识标准,其中测井电阻率"细脖子型"响应特征与页岩有机质石墨化具有唯一相关性,是判断高过成熟海相页岩有机质碳化的金标准。②中上扬子地区龙马溪组有机质碳化分布具有一定规律性,主要分布于川东-鄂西、鄂西北部、川南西部和长宁构造东侧4个探区,总面积超过35 000 km^2。③在川东-鄂西和川南西部2个探区,龙马溪组有机质碳化呈连片分布趋势,面积较大,显示弱-严重碳化特征。④在鄂西北部和长宁构造东侧2个探区,有机质碳化区面积相对较小,分别显示严重碳化和弱碳化特征。综合认为,上述4个碳化区为龙马溪组页岩气勘探禁区,也是页岩气资源评价和战略选区面临的高风险区。

Prediction of organic matter carbonization zones for Lower Silurian Longmaxi Formation in Middle-Upper Yangtze region

It is a significant task for selecting and evaluating of marine shale gas areas in South China to determine the distribution range of organic matter carbonization belts and exclude the high risk zones of shale gas exploration. Based on a large number of drilling and outcrop data,this study has carried out the identification and prediction of the organic matter carbonation areas for Longmaxi Formation of Lower Silurian in the middle and upper Yangtze regions,and compiled the industrial maps of the distribution of the organic matter carbonation areas in Longmaxi Formation,as well as preliminarily obtained four achievements and understandings. Firstly,the criteria for identification of organic matter carbonation in high-over mature marine shales were put forward,in which the response characteristic of thin neck type from the logging resistivity is exclusively correlated with the carbonization of organic matter in shales. Therefore,it is a perfect standard for judging organic matter carbonization of high-over mature marine shales,reliable to apply this method and criterion. Secondly,the distribution of organic matter carbonation for Longmaxi Formation in the middle and upper Yangtze region has certain regularity,indicating that carbonation points are mainly distributed in four exploration areas,i.e. East SichuanWest Hubei,Northwest Hubei,the west of South Sichuan and the east of Changning structure,covering an area of more than 35 000 km^2.Thirdly,the organic matter carbonation of Longmaxi Formation shows a trend of continuous distribution in Eastern Sichuan-Western Hubei and west of southern Sichuan,with characteristics of a widespread area as well as weak-severe carbonation. Finally,regions of organic matter carbonation are relatively small,showing the characteristics of serious and weak carbonation in northwestern Hubei and the eastern Changning structure,respectively. Consequently,these four carbonation areas are restricted zones for the shale gas exploration of Longmaxi Formation,and high-risk belts for the shale gas resource evaluation and strategically selected areas.