Characteristics And Controlling Factors Of Weathering Crust Karst Reservoirs In

The Regional tectonic position of Central sichuan basin belongs to the middle gently fold belt and the south of low plait shortcomings. It is a large,wide distribution and thickness area,the oil and gas resources should be very rich. But at present,as influented by many factors,the reservoir exploration degree is low, which brought many difficulties for the oil and gas exploration.This thesis take the theory of tectonic geology, reservoir geology, logging geology as the guide, close in combination with regional geological material, existing seismic exploration achievements, drilling, logging and core data,through investigated8field geological profile field, analysis the weathering crust in central sichuan leikoupo formation. The results show that:different areas (profile) in the central sichuan of the weathering crust located in different layer, weathering crust thickness developed in field and underground is more uniform, about60m. Karst breccia usually develop on the top of weathering karst. The weathering identification marks are obvious both in the field observation and logging, but the seismic identification marks are not obvious, which has not been establishd. In the reservoir, dolostone and breccia dolostone have the best reservoir performance, followed by gray dolostone, dolomite qualitative limestone, limestone and the muddy limestone, muddy dolostone is the worst. The reservoir space type is mainly Intragranular dissolution pores and dissolution pores between the particles and intergranular dissolution pores,in which the dissolution pores are most. Fractures develop in some portion, mainly of them are structure fractures, the dissolution pores and fractures are often filled or half filled. The reservoir’s Property are low hole-(especially) low permeability. In the region, the weathering karst reservoir developed most in Longgang area, Moxi and Yuanba take the second place. In the layer,the greastest development of reseavoir is T2l43, Followed by T3l1、 Tal2、T2l3、T2I41, relatively poorer are T2l42and T2l2. By analysis and study of the formation conditions of weathering karst reservoir, we find that the top surface of leikoupo formation don’t have objective conditions to develop large karst (large fracture hole) conditions, weathering karst reservoir are not developed over all. Comprehensive analysis of the develop factors of the weathering crust reservoir,as the different of solubility and dissolution in each lithologies,the difference of porosity and permeability in the matrix,so in normal circumstance,the ancient weathering crust has a higher development degree in dolomite distribution area. Karstmore develop more in three geomorphic units of Dissolved Gaoping melting mound, dissolved Ping. The fracture affect the reservoir by promote of karstification,improve the permeability,increse the capacity,but the fracture has a limited extent to resevoir. Overall, the study area mainly affected by lithology (layer) control in the region, followed by paleogeomorphology, local place influenced by the crack,each of the weight coefficient is0.42,0.32and0.26.