高变质煤区的煤层气可采性

PRODUCIBILITY OF COALBED METHANE IN HIGH RANK COALS

高变质煤中煤层气的勘探开发是一个极具探索性的新领域。重新认识和正确评价高变质煤煤层气的可采性是突破这一领域的关键。对美国密执安盆地安特里姆页岩气的地质背景、成因、赋存和产出机理、气产能地质控制因素及其成功开发经验进行的全面分析表明，以吸附状态存在于无内生裂隙储集层中的天然气，能够仅凭借密度较高、延伸较长、走向多变且开后性较好的外生裂隙而大量产出。我国东部具备形成外生裂缝系统的构造动力条件，能够充分改善高变质煤煤层气的可采性，东部地区高变质煤分布区煤层气的可采性应明显好于安特里姆页岩气的可采性，因而具有良好的勘探开发前景。

The exploration and development of coalbed methane in high rank coals ranging in maximum vitrinite renectance from 1. 9% to 6.0% is a new and sophisticated exploration field. The crux of breaking through this field is to re-understand and correctly evaluate the coalbed methane producibility of the coals. This paper presents a viewpoint which is obtained after overall looking into the geologic settings, origin, storing and producing mechanisms, controls of gas productivity, and successful experience of the Antrim shale gas of the Michigan basin, that is, adsorbed natural gas retained in the reservoirs without endogenic fractures can be commercially produced only relying on the exogenic fractures which are characteford by higher intensity, longer extension, more variable orientation and wider aperture. Based on this new viewPoint, a prelifornary analysis of the tectonic stress field evolutionary process for post-coal-accumulating stage in eastern China is made. The result indicates that eastern China has the tectonic dynamic settings which are suitable for creating the exogenic fracture system of improving the coalbed methane producibility of the high rank coals and the coalbed methane producibility of the high rank coals in eastern China may be significantly better than that of the Antrim shale gas in the Michigan basin and, as a result, the exploration prospects of the coalbed methane of the high rank coals in eastern China are encouraging.