页岩气聚集条件及含气量计算——以四川盆地及其周缘下古生界为例

Shale Gas Accumulation Conditions and Gas Content Calculation: A Case Study of Sichuan Basin and Its Periphery in the Lower Paleozoic

为了研究页岩气聚集条件及含气量的影响因素、计算方法,根据页岩气聚集机理、聚集特征将页岩气聚集的因素分为内部因素和外部因素。内部因素主要包括页岩有机地球化学参数、矿物组成以及物性参数等,外部因素主要包括深度、温度、压力等。通过对四川盆地及其周缘下寒武统和上奥陶统—下志留统41块黑色页岩的有机地球化学参数、矿物组成、物性参数、深度、温度、压力等因素对页岩含气量影响作用的分析,可知反映内部因素的有机碳含量、总烃含量、石英含量、粘土矿物含量、孔隙度(裂缝)、密度、黄铁矿含量和碳酸盐含量等8个参数对页岩气聚集具有重要影响。通过对"二参数"、"六参数"、"八参数"与含气量的多元线性回归得出计算页岩含气量的计算公式,据此公式计算的含气量与实测值吻合良好,且参数越多对页岩含气量的预测越准确。本文建议在条件允许的情况下,尽可能多地利用各种参数对页岩含气量进行预测,以达到更好的预测效果。在勘探早期,建议采用简单易得到的两个最主要参数——有机碳含量和孔隙度进行页岩含气量的计算。

Based on theory and condition of shale gas accumulation, shale gas accumulation factors in this study are classified into internal and external ones so as to better study accumulation conditions and calculation methods of gas content. The internal factors include geochemical parameters, mineral compositions and petrophysical parameters of shale, while the external factors include reservoir depth, temperature and pressure, etc. Geochemical analysis of 41 black shale samples from Lower Cambrian and Upper Ordovician and Lower Silurian strata in Sichuan basin and its surrounding area shows that mineral compositions, physical features, depth, temperature and pressure affect the shale gas contents and also reflect eight internal parameters （organic carbon, total hydrocarbon content, quartz content, clay minerals, porosity, density, pyrite and carbonate contents） which have important influence over shale gas accumulation. A formula of calculation for shale gas contents was obtained using the multivariate linear regression analysis between two parameters, six parameters, or eight parameters and gas content, and results based on this formula is in good agreement to in site measurement. The more parameters, the more precision. The study recommends that if conditions permitting, it is better to use more parameters to predict the shale gas content in order to achieve better results. It is also suggested that at the early stage of exploration, two leading parameters （organic carbon content and porosity） should be given priority to calculate the shale gas content.