The Petroleum Charging Conditions Of The Cretaceous Qingshuihe Formation In The Yongjin Area

Yongjin area is located in the center of Junggar Basin,which is a favorable area for oil and gas exploration.At present,great discoveries have been made in oil and gas exploration in Jurassic interval.With the deepening of exploration and development and the discovery of a large number of cretaceous reservoirs around the abdomen,Cretaceous interval has become an important replacement target for oil and gas exploration.The Cretaceous Qingshuihe Formation in the Yongjin has shallow burial and good physical properties,and oil and gas have been found in some Wells,showing good prospects for oil and gas exploration,and becoming an important target horizon for further oil and gas exploration.As far as the current research is concerned,sand body distribution and oil source and transport system are the most important core contents in the hydrocarbon accumulation conditions of Cretaceous interval in the Yongjin area.In this paper,the sequence division,sedimentary characteristics,sand body distribution,and fracture system of the Cretaceous Qingshuihe Formation in the Yongjin area are studied in detail with comprehensive logging data and seismic data.Regional priming was carried out in the sequence division and compared with other strata in the abdomen to ensure the consistency and accuracy of sequence division.Under the guidance of high-resolution sequence stratigraphy,sequence interfaces in the Yongjin area are accurately identified by using seismic reflection data,well log combination,mudstone acoustic time difference,sand/mud ratio analysis quantitative analysis,log data principal component analysis,wavelet analysis and other methods.A sequence division scheme is established and divided into two tertiary sequences.It is believed that it underwent the sedimentary process of early water inflow,middle water outflow and late water inflow.On the basis of sequence framework and sedimentary background,the deltaic front subfacies and shore-shallow lake subfacies are identified through typical sedimentary facies markers such as lithologic characteristics,grain size analysis and sedimentary structure.Based on the seismic properties and physical properties of the subaqueous distributary channel sand bodies in the delta front of the lower region,it is found that the sand bodies at the bottom of the Qingshuihe Formation are in good physical conditions under the influence of unconformity and are potential favorable reservoirs.The favorable key reservoir-forming conditions of the Cretaceous Qingshuihe Formation in the Yongjin area include rich source rock conditions,good reservoir-cap assemblage and transport system composed of unconformity and oil-source fault.The Tibetan model is established through systematic analysis.It is suggested that the northern part of Yongjin area is a favorable reservoir-forming region based on the favorable hydrocarbon supply path,trap development location,fault distribution and unconformity clay layer thickness.