Study On The Relationship Between Reservoir-forming Structure Combination And Oil-Gas Reservoir Distribution In Alaer-Zhahaquan Area Of Qaidam Basin

The Alaer-Zhahaquan area in the Qaidam Basin is a hot spot for oil and gas exploration and development.A number of industrial oil and gas fields have been discovered,including Yuexi Oilfield,Yuejin No.2 East High Oilfield,Yuedong Oilfield,Yuejin No.4 Oilfield and Zhahaquan Oil Field.The predecessors have conducted a lot of research on the structure of the Alar-Zhahaquan area,but the concave-uplift combination structure?emphasizing the planar combination of the low and high parts of the structure?and the fault-rock combination structure?including fault plane structure,plane fault-rock combination structure,fault and two-sided rock formation combination,fault activity,fault disconnection rock layer position and fault-gap's maintenance?are closely related to oil and gas accumulation,But there are few studies on concave-uplift combined structures and the fault-rock combination structure.In this paper,based on high-quality seismic data,combined with logging core data,the concave-uplift combined structure of the T₄ seismic reflection layer?bottom of the upper segment of the Xiaganchaigou Formation?in the Alar-Zahaquan area is divided and compared with the N₂²-Q?Shangyoushashan Formation to Qigequan Formation?concave-uplift combination structure.The fault-rock combination structure of six faults was studied.It also analyzes the relationship between the concave-uplift combination structure,fault-rock combination structure and the discovered oil and gas reservoirs,and obtains the following knowledges:?1?The current concave-uplift combination structure of the T₄ reflection layer?bottom of the upper section of the Xiaganchaigou Formation?in the Alaer-Zhahaquan area is in the form of a side concave and a side uplift.During N₂²-Q?Shangyoushashan Formation to Qigequan Formation?,the ancient concave-uplift combination structure is a point-concave side uplift type,and the scope of the ancient concave-uplift combination structure is larger than that of the current concave-uplift combination structure.?2?Identify the relevant faults in the Alaer fault zone?Alaer fault,No.7 fault,No.8 fault,Yuedong fault,reverse fault,Zhahaquan fault?through the 2D and 3D seismic data of the Alaer-Zhahaquan area.And draw the fault-rock combination structure map of each fault,and the fault-plane structure,plane fault-rock combination structure,fault and two-sided rock formation combination,fault activity,fault disconnection rock layer position and fault-gap's maintenance have been studied.Among them,the faults related to the Alar fault are all along the slope fault,and the combined fault-rock formation structures are all reverse-trending half-valley and half-ridge.The Alar fault,the Yuedong fault,the No.8 fault and the No.7 fault during and after the main oil generation period?N₂²-Q?are highly active and are continuous active faults.?3?The tight reservoir?N₁¹?of the upper Ganchaigou Formation in the Zhahaquan is located at the valley line of the current concave-uplift combination structure in the T₄ seismic reflection layer?bottom of the upper section of the Xiaganchaigou Formation?,which in the ancient concave-uplift combination is between the valley line and the ridge line.The reservoirs in Yuexi Oilfield,Yuejin No.2 East High Oilfield,Yuedong Oilfield,and Yuejin No.4 Oilfield are valley-like combinations,and the source rock layers and faults are ridge-like combinations.Yuexi Oilfield,Yuejin No.2 East High Oilfield,Yuedong Oilfield and Yuejin No.4 Oilfield are all located at the high structural parts of the fault,and Zhahaquan Oilfield is located at the low structural parts of the fault?Yuedong Fault?.?4?Based on the predecessors'main achievements and understanding on the control of source rock formations related to the concave-uplift combination structure and fault-rock layer combination structure on the formation of oil and gas reservoirs,and the relationship between the oil and gas reservoirs and related concave-uplift structures and fault-rock formation structures has been found in the study area.It is preliminarily believed that the formation of the Zhahaquan?N₁¹?tight reservoir is mainly related to the ancient concave-uplift structure,and the current concave-uplift combination structure has limited influence on it.The formation of Yuexi Oilfield,Yuejin No.2Donggaodian Oilfield,Yuedong Oilfield and Yuejin No.4 Oilfield is mainly related to the fault-rock formation structure,the migration of oil and gas along the fault to the higher part of the fault and from the fault to the valley formation which have important impacts.?5?There are still favorable reservoir forming conditions between the ridge and valley lines of the current concave-uplift structure and the range between ridge and valley lines of the ancient concave-uplift structure which is recommended to strengthen research and exploration,and its location is roughly the ancient concave-uplift combination's valley line where the place is east of the YueDong fault.