煤储层贾敏效应形成与排采控制机理研究

Based on the research background that the damage problem of coal reservoir in the in-situ coalbed methane (CBM) devolepment and Jamin effect of coal reservoir is the important reason for the damage in coal reservoir, focusing the scientific problem of geological and engineering condition in which Jamin effect of coal reservoir forms and the control mechanism of discharge and mining , based on the data of CBM development in south of Qinshui basin , using independently designed device on unsteadystate dual-phase displacement and steadystate dual-phase flow as main experiment platform , combining mathematical modeling and numerical simulation on CBM gas-water dual-phase flow , research on the engineering performance characteristic and production influence of Jamin effect of coal reservoir, the relationship of geologic feature of coal reservoir development and CBM development process and Jamin effect, the law of gas-water dual-phase flow in CBM development, the discharge and mining control of Jamin effect of coal reservoir and the process optimize of Jamin effect remission is made , expecting that the system of evaluation methodology on Jamin effect of coal reservoir is formed, revealing the mechanism of formation of immiscible liquid-liquid and gas-liquid dual-phase flow Jamin effect of coal reservior and control of discharge nd mining in CBM well , forming optimized system of construction process in CBM development and production operation and providing scientific basis for promoting the CBM well productivity and the recovery ratio of resource.

基于原位煤层气开发工程中煤储层伤害问题突出，煤储层贾敏效应是储层伤害重要原因的研究背景，聚焦煤储层贾敏效应形成地质、工程条件与排采控制机理这一科学问题，以沁水盆地南部煤层气田煤层气开发工程数据为基础，利用自主设计的非稳态两相驱替、稳态两相渗流装置为主要实验平台，结合煤储层气-水两相渗流数学建模与计算机数值模拟，开展煤储层贾敏效应的工程表现特征与生产影响、煤储层开发地质特征及煤层气开发工艺与贾敏效应的关系、煤层气开发过程气-水两相渗流规律、煤储层贾敏效应排采控制及缓解贾敏效应工艺优化等内容的研究，以期建立煤储层贾敏效应评价方法体系，揭示煤储层液-液、气-液不相混溶两相渗流贾敏效应形成及煤层气井排采控制机理，形成优化的原位煤层气开发施工工艺及排采作业制度，为提高煤层气井产能及资源采收率提供科学依据。

项目基于煤层气开发中储层伤害问题突出，贾敏效应是主要伤害原因的研究背景，聚焦煤储层贾敏效应形成的地质、工程条件与排采控制机理这一科学问题，以黔西土城区块煤层气开发工程数据为基础，利用自主设计的非稳态气水两相渗流装置为主要实验平台，结合气水相渗影响下的储层数值模拟，开展了两相驱替下煤储层启动压力梯度、相渗及应力敏感性，煤储层气水两相渗流规律，贾敏效应的排采表现与影响机理，贾敏效应的排采控制及缓解贾敏效应的排采制度优化等内容的研究。结果表明：由于气阻、液阻共存，且气、水粘度存在较大差异，贾敏指数（I=ΔPw/ΔPo）不适用于煤储层贾敏效应动态评价。含水饱和度、渗透率等对启动压力梯度、相渗曲线及应力敏感性的影响显著，可用来表征煤储层贾敏效应的强弱。水驱条件下，饱水煤样启动压力梯度最低；随着自由水饱和度降低，克氏渗透率0.044mD的煤样启动压力梯度由0.67MPa/cm增大至0.89MPa/cm；气驱条件下，含水饱和度对启动压力梯度的影响则表现出相反的趋势。煤储层渗透率越低，启动压力梯度越大；干燥煤样克氏渗透率由0.079mD降至0.044mD，水驱启动压力梯度由0.37MPa/cm增大至0.89MPa/cm。水驱条件下，饱水煤样具较高的初始水相渗透率，且表现出较强的应力敏感性；气驱条件下，饱水煤样的初始气相渗透率远低于干燥煤样，同样表现出较强的应力敏感性。煤层气井排采过程中，随着游离气增多、气泡变大，水相渗流的启动压力梯度增大，水相渗透率亦快速下降，贾敏效应逐渐增强；受此影响，压裂液难以排出导致压降漏斗扩展困难，是气井难以高产、稳产的重要原因。煤层气井见套压后持续憋压，气水产量大幅波动，非连续性排采均可产生严重的贾敏效应，导致“气锁”或“水锁”伤害。合层开发煤层气井上部产层暴露后，套压回升导致气体“反侵”入暴露产层，近井地带形成液相低渗区，将导致上部暴露产层产水、产气量快速下降。煤层气井排采应坚持“连续、缓慢、稳定”的原则，见套压前严格控制液面降幅以提高压裂液返排率，憋压阶段限定最高套压，保持气水产量的相对稳定。为了延长合层开发煤层气井的稳产时间，可在套压＞0.5MPa时主动暴露上部产层，并杜绝套压后期大幅回升。本研究揭示了煤储层贾敏效应的形成机理，提出了贾敏效应排采控制措施及优化的合层排采方案，为相似地质条件下煤层气开发工艺优化提供了理论依据。