煤层气评价重要参数及选区原则

Important parameters in the evaluation of coalbed gas and principles for screening exploration target.

控制煤层气成藏的因素不同于常规油气和固体煤，评价参数和选区标准、采气方式都有特殊性。根据国内外煤层气勘探开发的实际资料，提出１０项重要评价参数的分级方案，其中６项（煤层总厚度，含气量，地解比，孔隙半径，原始渗透率，灰分含量）分为４级，４项（含气饱和度，割理，有效地应力，资源丰度）分为３级。煤层气勘探的基本思路是找向斜、找斜坡，既要避开水动力强冲刷区和浅埋藏区，又要有承压水封堵条件和侧向水封堵条件，同时煤层既要有好的储集物性，物性又不能太好而导致煤层气散失。总结我国３０多个地区１５０多口煤层气勘探试验井的成败经验，借鉴国外煤层气勘探成功实例，针对我国煤层气分布地质特点，提出煤层气勘探选区评价的１１项原则。表２参３（王孝陵摘）

Factors controlling the formation of coalbed gas reservoirs differ from those reservoirs derived from petroleum and solid coal seam. Evaluation parameters and criteria for screening exploration targets and method of gas production have some peculiarities. According to the actual data in exploration and development of coalbed gas at home and a broad a program including items for evaluation and grading are suggested in which 6 items (total thickness of coal seams, amount of gas contained OOIP/desorption ratio, pore radii, initial permeability, ash co ntent) are divided into 4 grades, and 4 items (gas saturation, fissuring, effective geostress, reserve abundance) are divided into 3 grades. The main concepts in the exploration of coalbed gas are to find synclines, to locate slopes and to avoid the strongly hydrodynamic flooding region, but possess the sealing conditions provided by pressure hydrology and lateral water movement, and coal seams should have rather good reservoir properties, however the properties will not be too good to cause the dissipation of the gas. Experiences of over 150 gas wells in more than 30 regions are summarized. With the successful examples of those explored coalbed gas wells, and according to the geological distributions of coalbed gas in our country 11 principles were suggested for the selection of exploration region.