Study On Sedimentary Microfacies Of Lower Urhe Formation Of Permian In Mahu 1 Well Area

The Permian Lower Urhe Formation in Well Block Mahu 1 is an important oil-bearing series discovered in the southern slope of Mahu concavity in recent years,the sedimentary model of the southern slope of the Mahu concavity was used during the initial exploration period.With the continuous deepening of development in recent years,a growing number of phenomena are difficult to explain simple sedimentary models,especially in terms of sedimentary facies types.Owing to the lack of detailed classification of sedimentary microfacies for the Lower Urhe Formation in the Mahu 1well block by predecessors,it is urgent to carry out detailed description of sedimentary microfacies.Provide theoretical system guidance for the development of oil and gas fields in the Permian Lower Urhe Formation in the Mahu 1 well block.This study mainly includes the following four points of understanding:（1）Based on the original stratification,the study area is divided into three sub layers,namely,P₂w₁、P₂w₂ and P₂w₃,by using the marker layer method,sedimentary cycle method,and so on.Based on the distribution of heavy minerals and the contour map of sand to ground ratio and gravel to ground ratio of each small layer,the provenance analysis is conducted for the target layer,and it is determined that the provenance mainly comes from the northwest direction.（2）Obtain data through core observation,well logging data analysis,and establish a lithology chart,conduct petrographic analysis of the Lower Urhe Formation in the Mahu1 well area,the lithofacies types of the target strata in the study area are conglomerate,pebbly sandstone,medium fine sandstone,siltstone and mudstone.（3）Based on facies indicators such as lithofacies,sedimentary structure,and mudstone color,the type of sedimentary facies in the study area is analyzed and determined to be fan delta facies.Three subfacies and nine microfacies are identified,mainly developing fan channel,underwater distributary channel,debris flow microfacies,and debris flow microfacies.The study area is identified as a fan delta sedimentary system.（4）Based on the single well sedimentary facies histogram and well connected sedimentary facies profile,a study on the planar sedimentary facies of the Lower Urhe Formation in the Mahu 1 well area was carried out.It was determined that the lake level in the study area was continuously rising from P₂w₁ to P₂w3,and the provenance was continuously retreating,presenting a regression pattern as a whole.（5）Based on the well testing data and the planar distribution of sedimentary microfacies,the relationship between oil sedimentary microfacies and oil and gas resources in the Lower Urhe Formation in the Mahu 1 well block is clarified.It is determined that the distribution of oil and gas in the study area is obviously controlled by sedimentary microfacies.