Controlling Factors of Dissolution Pores in Zeolite Cements of Permian Clastic Rocks in Northwest of Junggar Basin

Abstract Zeolite cement dissolution pores, buried at a depth of over 3600 meters, are found well developed in clastic rocks of Permian in northwest of Junggar basin. Studying the controlling factors of zeolite cement dissolution pores have important meaning to predict the distribution of favorable reservoirs in deep oil and gas exploration of Permian. A comprehensive research method of thin slice analysis of 800 pieces of castings from 60 wells, core observation, scanning electron microscopy, and clay mineral analysis was adopted. It is believed that the dissolution pores of zeolite cements are mainly controlled by zeolite distribution, the scale and range of inorganic and organic acids. Firstly, different zeolite cement types appear a regular pattern that control dissolution pore types and their distribution scope. The study area are well developed three types zeolite cements: heulandite, analcite and laumontite. The heulandite cements are developed in basin edge, showing a belt-like distribution, and then the analcite distribution area. laumontite cements are distributed in basin central. Horizontally in basin edge, reservoir pore type is primary intergranular pore, and followed by analcite dissolution pore. In central basin, the major pore type is laumonitite dissolution pore, and followed by primary intergranular pore. No heulandite dissolution pores are found in study area. Secondly, analcite dissolution pores, formed by inorganic acid and distributed in basin edge, are controlled by the scale of stratigraphic unconformities and faults. Laumonitite dissolution pores, formed by organic acid and developed in central basin, are controlled by the scope of source rock. Thirdly, it is proposed that the meddle-belt of basin is the favorable zone for Permian reservoirs because it is located fan delta front where the laumontite cement is developed, close to the source rock, and in the updip direction of the three stages of organic acid migration. It is considered that central basin has favorable conditions to form laumontite dissolution pores, and pointed out that this zone is a favorable zone for the development of deep reservoirs in the Permian.