中高煤阶煤储层煤层气产出的煤岩学控制机理研究——以沁南和韩城地区为例

There were significant differences on the petrological composition and constitutive relation of coal reservoirs. So far, the research about the storage-permeable spaces characteristics of coal reservoirs and its coupling relationship with CBM production which are dominated by coal petrology is far from reaching the technology requirements of CBM development. During the CBM exploitation, the single well proration, commingling production, perforated intervals optimization, production system establishment are still at exploring stage. Clarifying the storage-permeable spaces characteristics controlled by coal petrology, the constitutive relation variation in internal or interlayer, and the reservoir physical properties response in CBM exploring process have become scientific problems and are urgent to be explored. Focusing on the middle-high rank coal reservoirs in the Qinnan and Hancheng areas, the research is devised to develop in following aspects: 1. Reveal the appearing characteristics of coal reservoir physical properties and the developing and evolving mechanism of their heterogeneity based on the depiction of macroscopic-microcosmic layers, collate the three-phase medium interaction characteristics of gas-liquid-solidity; 3. Combine the reservoir conditions controlled by coal facies, the reservoir physical properties evolvement in the process of coalification and the reservoir physical properties response during CBM prodution, reveal the expression form and mechanism of internal or interlayer contradiction. The adapted descriptivist theory and method of coal petrology in layer-interlayer, macroscopic-microcosmic and initial-dynamic will be proposed, and it will provide the scientific basis for effectively avoid and defuse the heterogeneity contradictions during reservoir reformation and drainage and recovery.

煤储层煤岩组成及本构关系差异显著。目前煤岩学主控的煤储层储渗空间特征及其与产能耦合关系研究远不能满足煤层气开发需求，煤层气开发中单井配产、多层合采、层段优化、排采制度的建立等仍然处于探索阶段，阐明煤岩制约下的储层有效孔渗空间发育特征、层内（间）本构关系变化及煤层气开发过程储层物性响应成为亟待探索的科学问题。本项目将以沁南、韩城中、高煤阶煤储层为对象，重点研究：1、在煤储层宏观-微观煤岩分层刻画基础上，揭示煤储层物性显现特征及非均质性发育演化机理；2、从煤体本构关系，厘定气-水-固三相介质相互作用特点，建立煤岩组构与可动流体空间、有效孔渗空间配置关系；3、将煤相控制的储层条件、煤化过程储层物性演化与煤层气开发过程储层物性响应结合，揭示层内（间）矛盾表现方式与作用机制。通过研究提供适配的层内-层间、宏观-微观和初始-动态煤岩描述理论和方法，为有效规避和化解储层改造及排采过程储层非均质性矛盾提供

煤储层煤岩组成及本构关系差异显著。然而，目前煤岩主控的煤储层储渗空间特征及其与产能耦合关系研究远不能满足煤层气开发需求。以沁南、韩城中、高煤阶煤储层为研究对象，通过井下煤岩观察、室内实验测试、测井数据反演，动态数据分析等方法，精细描述了煤岩制约下的储层有效孔渗空间发育特征、层内（间）本构关系变化及煤层气开发过程中储层的物性响应，揭示了煤层气开发过程储层物性动态变化、层内及层间矛盾表现方式及其煤岩学控制机理，探索了有效规避和化解煤储层改造及煤层气排采过程中储层非均质性矛盾的技术途径。结果表明，韩城矿区主要以半暗煤和暗淡煤为主，其次为半亮煤和光亮煤。从光亮煤到暗淡煤，灰分产率、镜质组含量、微裂隙密度、煤岩密度、孔裂隙连通性及分形维数依次降低，而矿物质含量则依次增加，同时，在半暗煤裂隙中常见成层的方解石和黄铁矿充填现象。暗淡煤及半暗煤常与煤岩顶、底板或泥岩夹矸接触，尤以前者居多，而煤岩类型序列中部普遍为半亮煤，光亮煤含量较少。光亮煤因小于2nm微孔的比表面积最大，故具有最高的甲烷吸附能力，最低的气体解吸效率。光亮煤气体扩散系数最大，半亮煤和半暗煤次之，暗淡煤最小。从光亮煤到暗淡煤，原煤渗透率和孔隙度呈现逐渐降低的趋势。韩城地区多层合采较单层排采效果好，双层合采较三层合采效果好，层间矛盾发生的原因在于物质组成、压力系统、气藏成藏条件的差异。为规避层间矛盾，提高气井产能，建议增加含有3号煤层合采井的比例，井位部署及压裂时应避开断层，尤其注意监测裂缝是否沟通含水层。