中国页岩气地质和地球化学研究的若干问题

Some essential geological and geochemical issues about shale gas research in China

近年来,中国页岩气研究和工业化生产获得极大发展,丰富了中国天然气地质学理论和增加了国内天然气生产供应。今后页岩气在中国天然气工业中要上更大台阶,研究解决以下4个地质和地球化学问题意义重大:①中国要突破当前单一的经济页岩气层组。美国已在29个盆地发现至少30套经济页岩气层组,但中国仅有一个盆地(四川盆地)发现1套经济页岩气层组(五峰组-龙马溪组),需要突破当前单一层组。②经济页岩气层组的RO区间值及气田的RO段值。中国经济页岩气层组的RO区间值为3.31%,气田的RO段值为2.34%,两值均较小;美国的气层组RO区间值为4.1%,气田RO段值为3.5%,两值均较大。美国一些腐泥型页岩气田发现在RO值为1.0%~1.3%的生油窗高阶段内,中国要注意处于该段值中的页岩气田勘探;同时要开辟煤系泥页岩气勘探。③气田的持续高产期。世界首个商业化开发的页岩气大气田(Barnett)实际生产显示,年产量达100×108m3的高产期预测约为20年。中国页岩气田开发尚处在建产阶段。④断裂在页岩气保存与开发中的作用。断裂对页岩气的富集与否具双重性。美国页岩气盆地构造稳定而断裂较少,而中国页岩气盆地构造活跃且断裂发育。总体上断裂对中国页岩气弊大于利,断裂使连续分布的五峰组-龙马溪组碎块化,限制了气田面积。

Recently,shale gas research and industrial production in China have been greatly developed,which has enriched the theory of natural gas geology in China and increased the supply of domestic natural gas production.In the future,shale gas will obtain great achievements among the developments of natural gas industry in China.The following four geological and geochemical issues about the exploration and research of shale gas has great significance:(1)China has to break through the single economic shale gas formation.The United States found at least 30 sets of economic shale gas formations in 29 basins.To date,only one basin in China(Sichuan Basin)has found one set of economic shale gas formation(Wufeng-Longmaxi formations).(2)Interval ROvalue of the economic shale gas formations and segment ROvalue of the gas fields.The interval ROvalues are3.31%for the economic shale gas formation in China and 4.1%for that in USA;the segment ROvalues are2.34%for the gas fields in China and 3.5%for that in USA.The former values are small and the latter values are big.A number of shale gas fields derived from sapropelic sources in the United States were found in the oil generation window with ROof 1.0%-1.3%.So shale gas exploration in China also needs to pay attention to this stage.At the same time,attentions should be paid to the exploration of shale gas derived from humic sources.(3)The continuous high-yield period of gas field.The world’s first commercially developed shale gas field(Barnett)shows a high-yield forecast of 100×108 m3 per year of about 20 years.Development of shale gas field in China is still in the construction stage.(4)The role of fracture in shale gas preservation and development.The fault has dual effect on the enrichment of shale gas.In the United States,tectonic in the shale gas basin is stable and faults are few,while in China structures in the shale gas basin are active and faults are developed.Therefore,faults have more harm than good to the shale gas in China,which caused the fragmentation of the continuously distributed Wufeng-Longmaxi formations,limiting the area of gas field.