Abstract
Based on both macroscopic and microscopic characteristics of cores from Lower Jurassic Da’anzhai Member in north central Sichuan Basin, and combined with physical property data, a detail study has been conducted, which includes reservoir characteristics such as lithologic characters, physical properties, and reservoir space types, and control factors of reservoir development. The study suggests that, there are two typical kinds of reservoirs: crystalline shell limestone and argillaceous shell limestone. The reservoirs properties are poor with ultra-low porosity and low permeability, which can be significantly improved by fractures. Reservoir space type is pore-fracture, mainly constitutive of the micro-fractures accompanied by dissolved pores. The reservoir development is controlled by sedimentation, diagenesis and tectogenesis together. Shell beach and lacustrine slop are the favorable facies for reservoir development. Dissolution is the primary constructive diagenesis to improve reservoir porosity and permeability. Structural fractures are necessary for reservoir effectiveness and high production.
Highlights
Due to the limited distribution and quantity, lacustrine carbonate reservoir didn’t arouse attentions from petroleum geologists at first
Strata of Da’anzhai member, which located in Upper Ziliujing Formation of Lower Jurassic, are mainly dark gray, black shale with shell limestone and argillaceous shell limestone interbeds
The reservoir development is controlled by sedimentation, diagenesis and tectogenesis together
Summary
Due to the limited distribution and quantity, lacustrine carbonate reservoir didn’t arouse attentions from petroleum geologists at first. As more lacustrine carbonate hydrocarbon reservoirs had been discovered in China and abroad, relevant researches have been further conducted. According to the third round of petroleum resources assessment of China, hydrocarbon resources from lacustrine carbonate reservoirs are approximately 45×108t, which suggest a considerable exploration potential. Jurassic Da’anzhai member in Sichuan Basin is a typical lacustrine carbonate hydrocarbon bearing formation [1]. For north central Sichuan Basin, the exploration degree is relatively low and pertinent researches are just beginning in recent years [5, 6]. In this area, hydrocarbon shows are active and reservoirs are widespread, but the oil and gas productions are low. The author hopes that through this study of lacustrine carbonate reservoir characteristics and control factors of Da’anzhai
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