川西拗陷须五段非常规气形成条件分析

随着对非常规气蔵的研究方法和开采手段的升级,使页岩气得以开发。川西拗陷须五段常规的思维是把它作为烃源岩来认识的,运用非常规页岩气的研究理念和方法,针对川西拗陷两条野外剖面(莲花剖面、万家坪剖面)及6口取心井(XYHF-1井,XYHF-2井,X503井,FG5井,GH2井,MY1井)的岩心观察、取样分析测试,以分析川西拗陷须五段具有形成非常规气蔵的条件,并用3种不同的表征方法(激光共聚焦法、高压压汞法、氮气吸附法)对须五段内不同类型的岩石进行孔隙度、渗透率及其连通性时行表征,结果表明:细砂岩中不同类型孔隙的孔隙度为0.41%～6.65%,平均总孔隙度为2.14%;泥(页)岩的孔隙度为1.51%～5.99%,总孔隙度为2.70%。微米CT扫描发现须五段上亚段细砂岩的连通性好于下亚段,中亚段以粉砂岩为主,孔隙连通性差,有机质含量低;泥(页)岩的孔隙连通性也差,孔隙发育依附于有机质的发育,泥(页)岩样品的有机碳含量主要分布在0.5%～3%之间。综合评价认为马井-邡、崇州-郫县、新场-丰谷等地区成蔵条件较好,为I类地区,是川西坳陷须五段页岩气的目标区域。

ANALYSIS OF FORMING CONDITIONS OF UNCONVENTIONAL GAS OF THE Xu 5 MEMBER IN THE WEST SICHUAN DEPRESSION

Through measurement of 2 field cross sections(Lianhua section and Wanjiaping section),observation of cores from 8 drilling wells and analysis of samples,combined with the research concept and method of unconventional shale gas,the formation of unconventional gas reservoir of the Xu 5 Member in the west Sichuan depression is studied.Three characterization methods(Laser confocal method,high pressure mercury injection method and nitrogen adsorption method) are used to characterize the porosity,permeability and connectivity of different rocks in the Xu 5 Member.It shows that the porosity in the fine gained sandstone is 0.41%~6.65%(average 2.14%) and the porosity in the mudstone and shale is 1.51%~5.99% with average of 2.70%.Micron CT scan reveals that the connectivity of fine grained sandstone in the upper section of Xu 5 Member is better than that in the lower section.The lithology of the middle section is mainly composed of siltstone with poorly developed connectivity and low content of organics.Pore connectivity of the mudstone and shale is poor and the development of pore relays on the occurrence of organics.Carbon isotopic analysis indicates that the unconventional gas occurs as adsorbed gas state and the adsorption capacity of shale decreases as the temperature increases,while desorption rate is positively correlated with temperature.The organic carbon content of shaly source rock is in the range of 0.5%~3%.Comprehensive evaluation shows that the Majin-Sifang area,Chongzhou-Pixian area and Xinchang-Fenggu area possess favorable reservoir forming conditions and are the exploration targets of shale gas.