The Tight Sandstone Reservoir in Pyramid Structure, Upper Paleozoic of Erdos Basin

spire of stone building in Pyramid, the ancient Egyptian burial tomb of the king and queen are the most typical. Because of its grand scale, its sides are composed of plurality of triangular or triangular surfaces which are connected to the top, the area is very small, even a spire shaped, resembling Chinese characters in "gold" word, so the image is translated as "Pyramid". For a long time, archaeologists, scientists and sociologists studied Pyramid features of structure, function and use from different point of view, which forming the extended meanings of modern Pyramid. The structure of Pyramid is a universal selforganizing form of nature and human society. It has the characteristics of stability, many kinds of multi-level organization form and the direction of the evolution of hierarchy. In sociology, the structure of human society is the image of "Pyramid". Knowledge structure is also shaped in Pyramid. Fang Jinqing et al (2013) proposed the concept of ecological Pyramid, human needs Pyramid, life network complexity Pyramid and a variety of types of network Pyramid and other concepts. Pyramid structure is also widely used in finance, writing, population sociology, health and other aspects of life. On the permeability spectrum, the gas reservoir is a continuous spectrum, the tight sandstone reservoir is in the low value of the permeability spectrum. Tight sandstone reservoir is a relative concept, which can not be determined with a permeability value. Since the tight sandstone reservoir is a self organized structure formed under the cocontrol of sedimentation and diagenesis, it can be described by Pyramid structure. Statistics show that in the tight sandstone reservoir development basin or region, the conventional reservoir is located in the top of Pyramid. (Air permeability is more than 1mD), there are still 15% ~ 10% conventional reserves left, which formed 揹essert area?. Generally, although the factors such as technology and price are key factors that affect the exploration and exploitation of tight sandstone, the optimum selection of "dessert" should be the most effective method for reducing the cost of exploration and development of tight sandstone. The exploration and development of natural gas in the upper Paleozoic of Ordos Basin reveals the structural features of the tight sandstone with Pyramid structur. Take the 8th segment of Shihezi Formation as an example, statistical analysis of 40000 groups of data of permeability shows that samples of permeability less than 0.5md is 78.42%, samples of permeability among 0.5mD and 1mD is 10.38%, samples of permeability exceeding 1md is 11.2%, which means ?Dessert area? of tight sandstone reservoir in the 8th segment of Shihezi Formation accounts for 11.2%. The permeability distribution of tight sandstone reservoir in an area of SuLige gas field is also with Pyramid structure (Fig.1). It’s permeability is mainly less than 0.5mD, and is about 68.59%. Samples of permeability between 0.5mD and 1mD is 17.28%, samples of permeability exceeding 1mD is 14.14%. The pore characteristics of tight sandstone reservoir also have Pyramid structure(Fig.2). We analyzed a total of 256 samples of high pressure mercury injection experiment data of the 8th segment of Shihezi Formation and the 1th segment of Shanxi Formation in Sulige gas field. According to Radius frequency distribution of the pore throat, we can calculate the proportion of micron scale pore throat (The pore throat diameter, r≥1 m), sub micron scale pore throat (The pore throat diameter, 0.1μm≤r<1μm) and nano scale pore throat (The pore throat diameter, r< 0.1μm). Class I reservoirs (K≥1mD) are mainly of Sub WEI Xishan, LUO Shunshe, SUN Liuyi, REN Junfeng, ZHAO Huitao, and LIU Xiaopeng, 2015. The Tight Sandstone Reservoir in Pyramid Structure, Paleozoic of Erdos Basin. Acta Geologica Sinica (English Edition), 89(supp.): 104-105.