Main Control Factors Of Shale Gas Content And Its Quantitative Models

The geological reserves of shale gas are abundant in our country, roughly comparable to the US. So strengthen the shale gas exploration and development is not only an urgent requirement for meeting the needs of oil and gas in our country, but also the planning for national energy development strategy. However, the research of shale gas has just started in our country, the related theories about it need to breakthrough and improved. Gas content, as one of the main parameters of shale gas geology theory, has a very important role in promoting the research about the shale gas accumulation mechanism and also has important guiding significance in evaluation accuracy of shale gas resource and confirming preferred zone.This paper takes Tarim Mesozoic mud shale as the research object. According to the experimental results, we analyze geological characteristics of the study area and construct the relationships between adsorbed gas and the facts of organic carbon content, quartz, clay minerals, Ro, porosity, specific surface area of rock, respectively. The organic carbon content and specific surface area are preferably selected as the main factors influencing gas content in Tarim Basin Mesozoic shale. And the organic carbon content is the most primary controlling factor, so a single factor control model between adsorbed gas content and organic carbon content is established. The correlation coefficient of model is 0.742. Based on the single factor model, the multi-factor prediction model for shale gas content is built by using multivariate fitting method. Moreover, the reliability of two models is verified and the adsorbed gas content is mostly between 0.581 m3/t and 2.720 m3/t by the models.Since free gas occurs in the hole, it is mainly affected by the total pore volume, specific surface area, pressure and temperature. Thus the model of free gas content and these four factors is established. The free gas content of Tarim Basin in Mesozoic calculated by the model is mostly between 0.079~1.226 m3/t. The total gas content including free gas content and adsorbed gas content is about 0.660 m3/t to 3.946 m3/t, which is abundant.Furthermore, the ideal model of the relationship between the proportion of absorbed gas and free gas content occurring in the pore and the pore radius is also established in this paper. The model shows that, under the ideal conditions, the adsorbed gas content is far less than the free gas content in Tarim Basin. Therefore, comparing the adsorbed gas content in actual stratum(between 20.5%- 79.5%), we predict the adsorbed gas mainly hosted in kerogen, and this view is simple demonstrated.