Seismic Inversion Research And Application Of Shale Gas Reservoir Brittleness

This paper mainly studies the brittleness of shale gas reservoir, based on summarizing the brittleness research methods of domestic and foreign typical shale gas reservoir layers, taking Longmaxi shale gas formation Jiaoshiba area Sichuan basin as the target, has carried out the brittleness research and application through prestack seismic data inversion.One of the key to explore and develop shale gas is the forced fracture characteristics, brittleness is the important index to evaluate it. Now, core data mineral composition analyzing is the most popular adopted method to evaluate shale gas reservoir brittleness, but the brittleness distribution in plane is limited. This paper has analyzed the core minerals and interpretated well log in vertical, through the method of seismic data inversion in horizon, focusing on the Longmaxi shale gas formation Jiaoshiba area, has built an compatible processing for brittleness evaluation and evaluated the brittleness distribution pattern, pointed the high brittle formation and area. In this work, the achieved results are as follows:(1)The meaning of shale gas reservoir brittleness is different from other material brittleness concept. The brittleness of shale gas reservoir is to evaluate the capability that primary pore and induced fracture form multi-dimensional fracture of connectivity in local or global under the external force. The brittleness of shale gas reservoir is not only to describe the ease of fracturing, but also to characterize the density of fracture and the connection between the induced fracture and the primary fracture and porosity.(2)The main influence factors of shale gas reservoir brittleness are mineral compositions, the development degree of porosity and fracture, confining pressure, anisotropy. The confining pressure and the anisotropic characteristics of shale gas reservoir should be considered when designing horizontal well and fracturing.(3)The effect is different that different brittleness evaluation model based on mineral components apply in different regions. The sedimentary background of shale gas reservoir, mineral characteristics and other factors should be considered fully when choosing the brittleness evaluation model based on mineral components Quartz and feldspar are selected as brittle minerals, carbonate, iron ore and clay are considered as non-brittle minerals in Longmaxi shale gas formation Jiaoshiba area. The following brittleness evaluation model based on brittle minerals is suitable for the Longmaxi shale gas formation of Jiaoshiba area.(4)The shale gas reservoir brittleness from seismic inversion should be carried out through prestack inversing. Prestack simultaneous inversion method has certain applicability in shale gas reservoir brittleness. The brittleness prestack inversion method should be selected based on the the seismic data quality and the number of wells. The brittleness index should be calculated before carrying out brittleness inversion according to the coring data and well logging data, which is to be compared with the inversed brittleness index. The effect are different that different brittleness evaluation models based on elastic parameters. The following brittleness evaluation model based on elastic parameters is suitable for the Longmaxi shale gas formation of Jiaoshiba area.BI=E/PR, E stands for Young’s modulus, PR stands for Poisson ratio(5)In the longitudinal direction, brittleness of the first segment and the second segment are better than the third segment, brittleness of the second segment is the best and inhomogenous, the lower section of the first segment is better. In the plane, the brittleness of JY2 area and JY3 area are fine, and JY1 well area is relatively weak.