Structural Feature And Its Control On Reservoir Properties Of The Longmaxi Formation In Nanchuan Area

The structural features of Nanchuan region was analyzed and summarized. The regional tectonic evolution and its implications on the tectonic evolution of the research area were respectively summarized and explored. The development characteristics of pore and fracture of the Longmaxi formation shale were analyzed from the perspective of the macro and micro levels. The permeability characteristics and dynamic variation of the Longmaxi formation shale were analyzed through the triaxial seepage test and pulse permeability test. The structural controlling on the development of pore and fracture and its effects on permeability were discussed.Geological structure in the study area can be divided into two types of structure. It was mainly consisted of NNE-NE, nearly SE and NWW structures. Among of them, the NNE-NE structures are the most main structures. Folds more development, while faults less in research area. High angle-nearly vertical shear joints and tensional joints develop widely. NE-SW(30°~50°),NNW-SSE(330°~350°)and NWW-SEE(275°~290°) are predominant directions. The research area mainly experienced Caledonian movement,Indosinian movement, Yanshan movement and Himalayan movement. Yanshanian is the main deformation phase. The early Yanshanian movement plays a key role in the forming process of tectonic framework of the research are.The pore types and pore structure parameters of the Longmaxi formation shale were analyzed by using scanning electron microscopy, mercury injection experiment and Nitrogen adsorption experiment. It mainly develops intergranular pore, intragranular pore and organic pore. Mainly are micropore and small pore. Porosity rangs from 0.88%-4.45%,sorting is better, skewness is fine, open pore is more and pore connectivity is good. Pore diameter less than 10 nm provides the main pore volume and surface area.The development types, occurrence, scale and filled characteristics of macrofracture and microfracture of the Longmaxi formation shale were analyzed based on joints observations in the field, core description and microscopic observation. It shows that tectonic fractures and layer foliation seam are most developed in research area, NE-SW,NNW-SSE, NWW-SEE fractures are most developed. High angle-vertical fractures are most developed while horizontal fractures are not developed. Completely filling fracture and half filling fracture account for about half and fillings are basically full of calcite.The permeability characteristics of Longmaxi formation shale were analyzed by using triaxial seepage device and pulse permeability measuring instrument. It founds that permeability are negatively related with gas pressure and stress difference. In parallelbedding shale samples, the average permeability respectively are 0.241 m D and 0.112 m D in hinge zone and flank. Porosity and permeability were positively correlated.The structural controlling on the physical properties of shale reservoirs was analyzed from the aspects of structural deformation, tectonic stress field, structure position. It founds that strong structural deformation is easy to form fractures, tectonic stress field controls development direction and open of fractures, fracture system is more developed in hinge zone affected by the different influence of folds in different parts of the structure. And pore and fracture of shale reservoir more development, more conducive to improve the permeability of reservoir.