The Differences In Storage Spaces And Occurrence Ways Of Shale Gas And Oil

From 1895, the world’s oil industry has gone through nearly 160 years, which also experienced three stages of development:primary oil recovery, secondary oil recovery and enhanced water injection oil production. With the growing global energy for demand, rising oil prices and the advancement of science and technology, prompting people begin to pay close attention to shale gas and oil resources exploration which was considered to hydrocarbon source rock and caprock in traditional oil and gas exploration. Research also shows that shale gas and oil resources is very large, about 4 times of conventional oil resources, which also greatly extended the life of oil industry. With the successful exploration of shale gas and oil in North American, the world’s energy pattern has been gradually changed, at the same time shale gas and oil also caused a strong impact on the world oil price system.Shale oil and gas resources is also very rich in China, learn from the successful experience of foreign shale gas exploration and development and combine with the actual geological conditions in our country, we get success in shale gas exploration in Jiulaodong and Longmaxi Formation in Southern Sichuan Basin, and have found three main shale gas production areas in China. The successful development of shale gas resources in the world makes people begin to pay more attention to anther resource which is much more valuable-shale oil. Jiyang Depression is one of main fault basins in Eastern China, which developed thick lacustrine shale deposition, and the maturity of shale is moderate, and is in the stage of large number of oil source, which is an ideal goal of shale oil exploration. Taking well log and logging data, analysis test data and scanning electron microscopy(SEM) of Weiyuan, Changning and Jiaoshiba area into consideration, we studied the types of shale gas reservoir space and occurrence ways, at the same time we defined the influence factors of shale gas reservoir space development and the occurrence ways of shale gas. On this basis, combined with previous related studies of shale oil and the existing test and analysis data of typical well in Jiyang Depression, we get a study about the reservoir spaces and occurrence mode of shale oil and made its influence factors clearly.Researches suggest that shale gas reservoir spaces are mainly intergranular pore, organic matter pore, intercrystal pore, secondary dissolution pore and fracture, meanwhile fractures can be divided into structural fractures, interlayer lamellation seam, clay minerals transformation and organic matter evolution seam. Primary intergranular pore is mainly controlled by diagenesis and mineral composition, the higher the siliceous mineral content, the more development of primary intergranular pore and its aperture is much more bigger, the greater the diagenesis, the less intergranular pore development. Organic pores’development is mainly affected by organic matter abundance, organic matter maturity and types. The higher the organic matter content and organic matter maturity, the more development of organic pores, and have a significant linear correlation. In the study area, organic matter content in mud shale is very high, and mainly distribute between 1%-3%, beside that organic matter maturity is also very high, reaching 2.58%. Organic matter pores develop very well, and can be a main type of shale gas reservoir. Intergranular pore development is mainly influenced by diagenesis, the stronger the diagenesis, the more development of clay minerals intergranular pores, and manly distributed in thin seam shape. Secondary dissolution pores’development is mainly affected by unstable mineral. Structural fractures are influenced by mineral composition, the strength of structure function and its period of time and diagenesis, the higher of brittleness mineral content, the greater intensity of tectonic activities, the more period of time, the stronger the diagenesis, the more development of tectonic fracture. Since the early Paleozoic, the study area was influenced by multiphase tectonic movements, this also resulted in the development of structural fractures. But most of the fractures are filled by calcite and mainly developed at the bottom of Longmaxi Formation. Interlayer lamellation seam is formed by sedimentation, and mainly controlled by the difference of lithology between laminas, the greater the lithologic differences between lamina, the greater the lamellation seam between the layers are more development in the process of diagenesis. Clay minerals transformation seam is mainly affected by diagenesis and clay minerals content. Organic matter evolution seam is controlled by TOC content and maturity.The reservoir spaces of shale oil is similar to shale gas, it can also be divided into intergranular pores, intercrystal pore, secondary dissolution pore, organic pore and fracture. But shale oil has its unique characteristics, such as oil molecular weight and high viscosity, so the requirement for reservoir is also higher. Compared with shale gas, the maturity of TOC is low, so organic pores development is limited, and the occurrence status of shale oil in organic pores is difficult to exploit in current mining technology, so for shale oil, organic pore is not a king of effective reservoir space types. In the study area, siliceous components is very low, and in the form of collection is more rare, so the development of intergranular pore is limited. Because of high content of carbonate minerals, carbonate mineral intercrystal pore and secondary dissolution pores is relatively developed, especially in carbonate laminae, and the pores are almost filled by oil. In shale oil reservoir, fracture is not only play the role of flow channel, but also an important storage space of shale oil, many periods of structural movement resulted in structural cracks are very developed, and often filled by oil. Organic evolution seam is formed by abnormal pressure and the width of the crack often change from wide to narrow. This kind of fracture is the migration pathway of shale oil from hydrocarbon source rock to carbonate laminae pore, and it’s significant for shale oil’s enrichment. Clay minerals transform seam often parallel to the direction of bedding, and often filled by oil, which is a effective reservoir space. Interlayer lamellation seam is one of the most important types of reservoir space of shale oil, which extends very long and with good continuity, is an important seepage channel for shale oil.The occurrence ways of shale gas mainly includes adsorbed state, free state and dissolved state, different occurrence modes have different forms, and are affected by geological conditions and geological environment. Adsorbed shale gas can exist in almost any mineral surface in shale, so there are many impact factors for it, including TOC content and its types, organic matter maturity, clay mineral content, humidity, temperature and pressure. Free gas is mainly controlled by maturity, temperature, pressure and mineral species. Dissolved shale gas is related to maturity and humidity. The occurrence state of shale oil can also be divided into free, adsorbed and dissolved state. But due to the particularity of shale oil molecules, the adsorbed state shale oil is hard to mining under current technical conditions, so what we talk now is free state of shale oil which exists in pores and fractures or in the condition of high evolution exists in the form of condensate oil.