| The carbonate crack-cavity reservoirs of Ordovician Yingshan Formation in Lungu 7 well block has undergone multiple tectonic movements and long-term karst reformation.The reservoir has strong heterogeneity.The type,filling degree and distribution of crack-cavity are very complex.This paper studies the characteristics and main controlling factors of crack-cavity reservoirs of Yingshan Formation in Lungu 7 well block,analyzes the favorable distribution blocks of karst crack-cavity,and provides a degree of guidance and suggestions for the following exploration and development of oil and gas in Lungu 7 well block.Based on the investigation of palaeokarst in the Ordovician wild similar outcrops in Tarim Basin,this study observed and described cores and thin section of the study block,and divided the storage space of the carbonate reservoir of Yingshan Formation into three types: cavity,pore and crack.According to the type and combination relationship of storage space,karst crackcavity reservoirs are divided into three types: cavernous reservoirs,crackd reservoirs and crackpore reservoirs.Using cores,drilling,FMI electrical imaging logging data to compare with conventional logging curves,to establish a set of conventional logging identification modes which is suitable for crack-cavity reservoirs in Lungu 7 well block.Based on the depth-domain seismic data of the study block,using the cavity development section identified by single well as the sample of training and judgment test,characterize the development of solution cavity by multi-attributes fusion(attribute extraction and optimization→attribute volume and sample point preprocessing → multi-attribute correlation analysis → principal component analysis →fusion seismic attributes establishment),and the matching degree is as high as 86% after backjudgment.Using the method of combining wells and seismic data to describe and analyze the distribution characteristics of the reservoir,and discuss the main controlling factors those affect the development of the reservoir.Then analyze the favorable distribution block of karst crackcavity reservoirs.The study found that the filling degree of the cracks-cavity in the study block is relatively high,63% of the cracks are fully filled,the filling is mainly calcareous mud,most of the solution cavities are semi-filled,and the filling is mainly mechanical sediments.Cavernous reservoir is the most developed in the block,the second is crack-pore reservoir,and crackd reservoir is the worst.On the vertical,the crack-cavity reservoirs have obvious zonation.The storage space of crack-cavity reservoirs in the epikarst zone is dominated by low-angle cracks and solution cavities.The karstification is strong and the reservoirs are well developed,mainly cavernous reservoirs.The seepage karst zone is dominated by high-angle cracks and solution cavities.The development of solution cavity relys mainly on faults,mainly crack-cavity reservoirs which are poorly developed.The reservoirs in the runoff karst zone are basically underdeveloped,mainly low-angle or horizontal cracks,and the corrosion expansion of cracks is not obvious,and isolated dark rivers are occasionally observed.The rivers are developed,has horizontal spread to a certain extent,and the scale is small.On the plane,the distribution of epikarst zone reservoirs has obvious regionalization,mainly in the central and western regions of the study block.The development of seepage karst zone reservoirs is mostly related to faults,and solution cavity are often distributed in the shape of "String bead" near the fault zone.According to analysis,in the study block,the main controlling factors that affecting the development of crack-cavity reservoirs are faults,paleo-geomorphology,paleo-climate,lithology,etc.The favorable distribution block of crack-cavity reservoirs is the block where karst residual hills are developed and close to faults in the karst hill depression geomorphic block in the central and western part of the study block. |
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