The Geological Modeling Analysis Of Shale Gas:

Shale system refers to shale formations which contain natural gas that are in some cases interbedded in mezzanine or adjacent rocks. In order to explore such unconventional resources economically, it is necessary for us to do basic research on shale gas enrichment and distribution regularities to expand the shale gas exploration and development fields to optimize production. In recent years a variety of attempts have been made to study shale gas exploration. In this paper, the geo-statistical methods were used to study shale gas enrichment rules in Changning area. The shale gas enrichment law is the main focus of reservoir characterization in nowadays oilfield development. It is therefore of particular importance to understand the main shale gas parameters distributed underground. Geological modeling and analysis was undertaken to digitize the study on shale gas target layer from spatial perspective, using three-dimensional visualization analysis on shale gas sweet spots elements to determine the high-quality gas-rich shale.This paper mainly adopts theories and methodologies of sedimentary geology, geo-statistics, stochastic modeling method to do geological modeling in the research area, which can objectively reflect the underground shale gas reservoirs’sweet spots’ elements distributed in three-dimensional space. The petro-physical data of the actual work area is combined with geological data to establish the shale gas’sweet spots’ elements model to describe the shale gas reservoir and spatial distribution of its enrichment elements in order to provide the basis for shale gas development in Changning area.The main results of this study are as follows:1、The gas shale enrichment parameters in work area:(1) Hydrocarbon feature-TOC content in work area is mainly ranged from 1.12% to 3.56% and averaged 1.98%; Ro is ranged from 1.4% to 3.56%, and averaged 2.56%; The organic matter type is Ⅰ and Ⅱ1, which is also conducive for shale gas generation. (2) Reservoir features-Porosity in work area is mainly distributed from 0 to 9.1%, the mean is about 5.12%; Permeability value is small, but and has little influence on gas distribution; Various types of micro-cracks developed in the formation, is favorable for shale gas migration in the reservoir. (3) Production features-Clay mineral content in work area ranged from 18% to 40%, the corresponding brittle mineral content is mainly concentrated from 60% to 82%, the brittleness mineral content is high, which is good for hydraulic fracturing.2、Based on the seismic data, synthetic seismograms of two wells in the study area was completed:Ning201, Ning201-H1 well, the relationships stratigraphic correlation and lithology was established according to the rock layers calibration. The seismic reflection boundary layer top and bottom location tracking of the two members of Longmaxi formation was also completed. According to the isochronous charts at the top surface of the Longmaxi formation, the first and the second member of Longmaxi formation have the same structural inheritance.3、Based on the structural interpretation of Longmaxi formation, the seismic horizons data in Changning district is organized, the three dimensional lattice frame of the area is modeled, the structure modeling which is consistent with the actual structure in Changning district is established, and the accurate lattice model provides good stratigraphic framework for the follow-up establishment of gas shale ’sweet spot’ parameters model.4、The logging and geochemical data is combined with geological data of the study area, the research of shale gas ’sweet spot’ parameters with different types of logs is established by using linear regression to derive mathematical models for the ’sweet spot’ factors.5、he mathematical models of ’sweet spot’ parameters is combined with stochastic geo-statistical methods to build geologic model, then analyzed as follows:The ’sweet spot’ parameters in the first member are better than those in the second member. Clay mineral content is about 5% to 40% and average26%; Brittle mineral content is about 60% to 95% and averaged 75%which is good for hydraulic fracturing; The organic carbon content in the first member of Longmaxi formation is high, mainly between 1.2% and 3.5%, and averaged 2.14%, which is a sign of favorable hydrocarbon potential; Vitrinite reflectance R0 ranges from 1.0% to 3.36% and averages 2.54%, which is an indication that the shale is mature for gas generation; Porosity is 3.6%～8.36% and averages 6.54% which means good reservoir property. Permeability is about 0.008md～ 0.026md, which is relatively not a main parameter in the shale reservoir properties.6% Based on the previous analysis, the ’sweet spot’ parameters of shale gas have a high correlation with each other especially in gas content relating to TOC, vitrinite reflectance, followed by the shale porosity, brittle mineral content. Combining such correlation, the gas content which is considered the evaluation criteria of enrichment degree is integrated with the ’sweet spot’ parameters to build the corresponding mathematical and geological model. From the established shale gas ’sweet spot’ model, it can be found that the first member of Longmaxi formation has a high gas content in the gas-containing planar distribution map throughout the whole Changning area. The region containing shale gas is mainly located in the north and northeast of the work area and around the well site, and there is also a small amount of shale containing gas in the southwest region. In the three-dimensional geological model, we can conclude that the gas content in the first member is higher than that in second member of Longmaxi formation, and is therefore favorable target area for exploring. It provides a strong basis for future exploration and development of shale gas reservoirs.