The Sedimentary Characteristics And Favorable Sandbody Prediction Of Guantao Formation In Qingxi Area Of Dongying Depression

With the improvement of domestic oil and gas exploration,more and more researchers begin to search for unconformity obstructed oil and gas reservoirs.The unconformity contact between the the Guantao Formation and the lower Shahejie Formation in the Qingxi area may provide conditions for formation of oil and gas reservoir.This thesis established a depositional model of the Guantao Formation in Qingxi area through the analysis of stratigraphic contrast,unconformity surface identification,over-stripping line location characterization,provenance analysis and sedimentary facies characteristics in the study area.Favorable sand bodies were predicted.Presently,the Guantao Formation in Qingxi area has a low degree of development.the marker layer and unified stratigraphic contrast division of the study area are still lacking.Therefore,under the guidance of sedimentology theory,this study used well logging,mud logging,seismic data and other data to identify the landmark layer in the study area.According to the principle of cycle comparison and hierarchical control,the stratum of Guantao Formation in Qingxi area was compared and divided.Finally,the Guantao component was divided into 5 sand layer groups,5 of which were further divided into 4 small layers.The identification of the unconformity in the study area largely relied on the logging curve and changes in lithology.The unconformity three-layer structure in the study area was identified,and the depths of the unconformity in key wells were determined.The identification of the position of the over-stripping line has always been challenging in the identification of stratigraphic oil and gas reservoirs.This reflects that there is an error between the pinch point on the seismic profile and the actual over-stripping point.In this study,the error correction formula was used to reasonably extrapolate the position of the over-stripping wire in the study area.The location of the stratum over-stripping in the study area was clarified.The direction of the provenance system in the study area affects the orientation and distribution of the sand body.By observing the paleo-geomorphic features and the seismic profile reflection characteristics of the study area,the thesis found that the study area was controlled by two major provenance systems.In general,the Qingtuozi Uplift affects the distribution and scope of the sand bodies in a wider and larger area.The Chenjiazhuang Uplift has a more obvious impact on the sand bodies in the 3rd and 4th layers of the 5th sand group of the Guantao Formation.After analyzing the lithology,logging,and seismic data of the Guantao Formation in the Qingxi area,an identification table of lithologic facies markers,logging facies markers,and seismic facies markers in the study area was established.The main fluvial facies developed in the Guantao Formation in the Qingxi area were identified.Alluvial fans formed at the bottom of the Guantao Formation near the Qingtuozi Uplift and Chenjiazhuang Uplift.A plan view of the sedimentary facies of the study area was drawn.Based on the above-mentioned research results,the evolution of sedimentary models in the study area was established.The lower part of Guantao Formation in Qingxi area was divided into three evolution stages,namely the development stage of alluvial fans,the contraction stage of alluvial fans,and the disappearance stage of alluvial fans.The prediction of favorable sand bodies was based on the established sedimentary evolution model,sedimentary facies,provenance direction,sand body thickness and area,and oil-bearing properties.The 3 and 4 layers of the 5 sand group in the Yong123 well area,the 5 sand group4 in the Yong 63 area and the 5 sand group 2 in the Qing 7 well area have favorable sand bodies,which was suggested as the focus in the next stage exploration.