煤层排烃系数的定量计算方法——以临清坳陷东部康古4井为例

QUANTITATIVE CALCULATION OF HYDROCARBON EXPULSIVE COEFFICIENT OF COAL FORMATION—TAKE WELL KANGGU-4 IN THE EAST OF LINQING DEPRESSION AS AN EXAMPLE

煤层作为一种重要的煤成气源岩和特殊的储集岩,在热演化程度一定的前提下,其生气量和甲烷生成量是一定的,其吸附气量与排出量互为增减,并处于动态平衡。根据这一认识,首次提出定量计算煤层排烃系数的思路与方法。利用热压模拟试验确定煤的不同显微组分的生气量;针对不同地区、不同层位煤层显微组分组成不同的特点,提出采用公式法计算煤层的甲烷生成量;同时重点对Kim建立的煤层甲烷含量与煤的变质程度和埋深的关系曲线进行了计算机拟合,得到不同演化阶段埋深与吸附气量的关系曲线和方程,用以预测煤层的含气量。以临清坳陷东部康古4井区石炭—二叠系煤层为例进行了煤层排烃系数的计算,计算出的甲烷生气量与模拟甲烷生气量可比性较好,但仍存在小于5%的误差;计算出的煤层排烃系数随煤层成熟度的增高而增大,由低演化阶段的77%逐渐增至高演化阶段的90%以上。

Coal formation is not only an important source rock but also a kind of important reservoir of coal-formed gas. In a definite thermoevolutional degree, the generated gas quantity and methane quantity are also definite. The adsorption quantity and the expulsion quantity are convertible and in a dynamic equilibrium state. The method of calculating compulsive coefficient can be obtained according to this understanding. In this article, a method to calculate the gas-generated quantity was put forward based on the thermal-pressure simulating tests, by which the gas-generated quantities of different microlithotypes in different coal formations in different areas can be determined. At the same time, a way to determine the coal formation absorption quantity is introduced briefly. The curve showing the relations of coal formation methane content and it＇s metamorphic grade and burial depth developed by Kim was fitted using computer. A series of curves showing the relationship between burial depth and absorption quantity during different evolutional periods are gotten. These can be used to predict gas-generated quantities. All the methods have been used to calculate the gas-generated quantity of Permo-Carboniferous coal formation and absorption coefficient in well Kanggu-4 area in the east of Linqing Depression. The calculated methane quantity matches the simulated methane quantity with the error less than 5 %. The calculated hydrocarbon expulsive coefficients are increased with increased maturities, from 77% in the low evolutional period to 99% in the high evolutional period.