The Evaluation Of Chang7Shale Gas Reservoir Characteristics Of Yanchang Formation In Zhenyuan And Jingchuan Area, Ordos Basin

ZhenYuan and JingChuan area is located in the south of the TianHuan sag,which locates in the Ordos Basin. The exploration place is2515.683km2. inZhenYuan and JingChuan.The southeast of the study area is generally high and thenorthwest is low in the YanChang formation. The width extent of the structure issmall, the largest one is in300m～500m. The top structure of the Chang7performsmonocline, which dips to northwest, the change of structures is relatively subdued,but the uplifted width extent in the southeast of the structure is large and had threenose structures on the uplift.During the early time of Chang7, the Lake played a role of quickly constructedsettlement, which made Lake Invasion reach its peak, water level quickly raise, andthe Lake Bank line significantly extend inside and outside, water covered area up toabove10×10~2km~2, and water was obviously deepened, half deep-deep lakedistributed in the north of YanChi, DingBian, WuQi, ZhiDan, YongNing, east ofHuanXian, QingYang, ZhengNing, ZhiLuo, LuoChuan and wide area of east ofLuoChuan. In JinSuoGuan and YiJun also has half deep-deep lake, the thickness wasabout70m～120m with ash black and deep grey shale. It formed the mainly stabledistribution shale source rocks in the basin, which named “ZhangJiaTan shale”. Inthe study area, the “ZhangJiaTan shale” of Chang7formation is also in thewidespread development. Shale is distributed throughout the study area, particularlyalong the KaiBian town-ZhenYuan County, ZhongYuan town-NanChuan town andShangXiao town-YuDu town-HongHe town deposition with the thick shale.According to the sedimentary facies, regional structural features, core materials,organic chemical experiments and log dates, we get a conclusion with the search results from the predecessors that the Chang7shale is distributed in the whole areaof the ZhenYuan and JingChuan, the thickness ranges from54.0m～118.0m, andburied depth ranges from1597.0m～2359.5m, the thickness of well logginginterpretation of organic-rich shale ranges from15.3m～94.7m. In the ZhenYuanCounty-KaiBian town-PingQuan town-NanChuan town region and HongHetown-TunZi town-SuoLuo town-DangYuan town region have more than50m-wideregional development organic-rich shale.In the Chang7organic-rich shale of the ZhenYuan and JingChuan area,abundance of organic matter of the underground experiment measured samples rangeis0.71%～14.0%, an average of2.75%.Abundance of organic matter of logginginterpretation study area ranges from0.57%～38.0%, average rate is6.02%. Thetype of the kerogen is ⅡA-Ⅲ, which is the mixture of most rotting mud,then thehumic. The type of shale gas of the purpose layer in the study area is the cause ofpyrolysis-original source of associated gas. The clay minerals of the organic-richshale in the Chang7formation mostly are illite and chlorite, kaolinite andmontmorillonite content which is less. The contents of illite is about40%, chlorite isabout20%, quartz is above20%, feldspar is about10%, kaolinite, montmorillonite,pyrite, calcite and dolomite occupy10%of the remaining. Intergranular-milipore,intercrystal-milipore, dissolved-milipore and milipore inner organic are the mainspace of storage-infiltrate in the Chang7formation shale reservoir.Intergranular-milipore and intercrystal-milipore are the main storage-infiltrate spacein the study layer, and with above70%destination in the reservoir. The diameter ofthe intergranular-milipore and milipore inner organic is respectively close to5μmand4μm. The aperture of the remaining two types of storage-percolation space isbetween1.5μm～2.0μm. The porosity of the Chang7with rich organic shale isillustrated by the underground observation model, and the shale reservoir pore size isin0.83%～1.39%, the average size is1.08%. Linear relationship is obvious betweenporosity and gas saturation. According to the evaluation criteria on favorable shalegas from SINOPEC, a forecast is made that the Change7shale reservoir is favorable.We find the area-ZhenYuan County-KaiBian town-PingQuan town-NanChuan townlocates in the north of the study area, and the area-HongHe town-HH2-HH55lies inthe middle-east of the study area. The two areas are large favorable areas in the sixfavorable areas, the remaining four area is generally small.