Sedimentary Facies And Favorable Block Prediction In Chang4+5₁Member Of Yanchang Formation，Baibao Area

Based on integrating the previous research results and through the analysis of thecores，well logging and laboratory data，the author had deeply studied the provenancecharacteristics，sedimentary microfacies and physical property of chang4+51Memberof Yanchang Formation in Baibao area by comprehensively utilizing many theoriesand means，such as sedimentology，oil and gas geology，reservoir geology and logtheories，and provided a base for the searching of favorable block.Combined the methods of regional stratigraphic key layers，sedimentary cyclicalcontrol，stratigraphic thickness similarity and connecting-well section correlation，more than70wells of the study area have been divided and correlated，and6connecting-well in the area have been established，the chang4+51Member ofYanchang Formation are divided into chang4+511sub-Member and chang4+512sub-Member. The deposition thickness of the chang4+5Member is extraordinarysteady and with less alternation，the thickness of the chang4+511sub-Member is about18to24m，the thickness of the chang4+512sub-Member is about20to26m.Based on the analysis of the petrology，light and heavy minerals，palaeocurrentdirection，invariable element，trace element，rare earth element，the author had makea comprehensive and systematic study of the source direction and provenanceproperty of Yanchang Formation in Baibao area，the results indicate that there arethree provenance of the study area，the well field “Yuan139-Wu40-Wu207-Bai412”belongs to the typeI， the source supply is northeast trending； the area“Pingzhuang-Zhaizishan-Huachi-Wujiao”belongs to the typeII，sediments are lackand most is mud shale；there is a III provenance in the mixed area between typeI andtypeII.The Baibao area is located in the south-central part of the Ordos Basin. Throughthe analysis of drilling core， electrofacies, single well sedimentary andconnecting-well section sedimentary，it is thought that the main subfacies in studyarea is delta front，and fewer area exit predelta-shallow lake facies，the subfacies canFurther divided into8types microfacies，including underwater distributary channeland mouth bar. The underwater distributary channel is northeast-southwest trend，andthe sand body with a good communication. Based on the analysis of the casting thin slice and the scanning electron microscopeof the sandstone core in target stratum，and the results showed that the rock type ismainly arkose and lithic arkose，target stratum pore types as follow：primaryintergranular pore，feldspar dissolved pore，lithic dissolved pore and intercrystal pore，it also includes a little dissolution intergranular pores and micro cracks. The reservoirphysical properties of the target stratum are very poor，the porosity is between3.4%to20.1%，and average porosity is13.5%；the permeability is between0.003mD to32.4mD，and average permeability is1.74mD.When the sedimentary microfacies，lithology，reservoir space and reservoir physicalproperties in target stratum have been cleared，it can be concluded that reservoirphysical properties are mainly controlled by diagenesis ands edimentary facies andmicrofacies，the important diagenesis is compaction，pressure solution， some kindsof cementation，dissolution and tectonic disruption. At last，the favorable block hasbeen predicted in terms of the relation between sedimentary microfacies and reservoirphysical properties，reservoir lithology and sandstone strata thickness ratio.