Seismic Characterization And Reservoir Prediction Of The Fracture Wall Of Maokou Formation In Jiulongshan Area

The Jiulongshan ground structure is a large NE-trending dome-shaped anticline anticline,which is an inherited tectonic uplift with structural traps from the surface to the Earthly Sinian.The Jiulongshan structure has the characteristics of large structure,high uplift,good preservation conditions,long-term production in the vertical direction,and abundant drilling.The source rocks of the Cambrian,Permian and Triassic Xujiahe Formations in the Jiulongshan area are abundant.The deep faults extend far in the lateral direction,and there are many longitudinal and vertical cut layers,often causing one or more hydrocarbon source layers or paleo-oil.The reservoirs are connected with the reservoir traps,forming good hydrocarbon migration conditions and providing abundant hydrocarbon sources for the accumulation.The Lower Permian of the Jiulongshan area includes two major reservoir systems: the Qixia Formation and the Maokou Formation.When the predecessors in this area studied the reservoirs of the Maokou Formation in Jiulongshan,the main controlling factors,reservoir response characteristics and distribution characteristics of the reservoirs were unknown.This paper mainly analyzes the main controlling factors and scale of the fracture cavity system through comprehensive analysis of lithology,thickness and curvature,and uses the forward modeling to identify the corresponding seismic model of the reservoir,and predicts the distribution of the fracture-disintegrating fracture system in three-dimensional space.The prediction of the reservoir and the optimization of the favorable targets.The results and conclusions obtained from the study of the Lower Permian in the Jiulongshan area are:(1)The Jiulongshan structure Maokou Formation is located in the favorable sedimentary facies belt of the Taichung Formation in Taichung.The reservoir rock types are mainly composed of bright-grained limestone and thin layer dolomite.The reservoirs of Maokou Formation are mainly intergranular pores,intercrystalline pores and micro-cracks,which belong to the fracture-cavity reservoir.(2)The large-scale fault zone is the basis of the development of the fracture-cavity system.In addition,the paleo-geomorphology of the south-central part of the Jiulongshan area is relatively low after the deposition of the Maokou Formation,forming a dissolution slope,which cooperates with the fault development and provides favorable formation for the fracturecavity.The geological conditions also jointly control the development and distribution of the fracture cavity.The deep faults formed in the Caledonian period are connected with the paleo-weathering crust,and the hydrothermal fluid continues to vertically and laterally dissolve the Maokou Formation along the fault,forming a fracture cavity and improving the reservoir properties of the Maokou Formation.After the cover layer is sealed,a fracture hole body is formed;(3)The results show that the geophysical response characteristics of the isolated cavernous reservoirs in the Maokou Formation are characterized by bead-like pull-up and amplitude attenuation.The geophysical response of the Maokou Formation fracture-cavity reservoir is the top boundary of the Maokou Formation.The characteristics of the same phase axis "twisted intermittent,pull down";(4)Using the curvature body to complete the three-dimensional engraving of the fracture system of the Maokou Formation;the comprehensive structure and the development of the fracture system of the Maokou Formation are divided into three types of favorable zones(fracture hole system),which indicates that the top boundary of the Maokou Formation is distorted.Intermittent,pull-down features,low-impact features on the inversion profile,abnormalities in body curvature,coherence,and fracture development.The second-class(fracture hole system)time-offset profile is characterized by distortion,discontinuity,and pull-down of the top-end axis of the Maokou Formation.The impedance profile is relatively high impedance and the slot system characteristics are slightly worse.The features are not very obvious on the curvature profile,and there is no abnormality on the coherence profile.On the time-shifted profile of the three types of wells(isolated caves),the in-phase axis is pulled up and the amplitude is weakened.It exhibits low impedance on the impedance profile.The body curvature is abnormal on the profile,and the plane is represented by a circular anomaly,and there is no abnormality on the coherent section.