油页岩原位注蒸汽开采中孔隙裂隙演化与渗透特性研究

Shale oil and gas exploitation in oil shale by heat injection can improve the insufficient output of conventional oil and gas in China. To study the oil shale in-suit exploitation by steam injection, an oil shale mine in Jimsar, Xinjiang is taken as target area, and the following research are planned to be conducted:1）By using the micro CT scanning and acoustic detection methods, the occurrence and development of oil shale pore and fissure from initiation and propagation to evolution of connectivity will be researched in the process of oil shale pyrolysis superheated steam, so that to establish the digital model of pore structures in oil shale under the different confining pressures and temperatures. 2）By high temperature three axial penetration experiment, the evolution characteristics and mechanical properties of oil shale permeability will be studied under the thermal-mechanical coupling condition, and obtain the critical condition of rupture of oil shale rock pyrolysis. The quantitative relationship between permeability and rock mechanics parameters with temperature evolution will be established in different bedding orientation.3）Based on percolation theory, the flow characteristics and the influence on the connectivity of seepage channel of oil shale pyrolysis oil products will be studied.4）On the basis of experimental results and the related theory, the mathematic flow model of shale oil driven by steam in oil shale will be established, and numerical simulation will be conducted to study the flow and immigration law of shale oil by the steam, and to evaluate the drive efficiency of steam. It is expected to provide a scientific basis for in situ thermal recovery oil shale gas exploration.

对油页岩进行加热开采页岩油和页岩气能够缓解我国常规油气产量不足的问题。本项目以新疆吉木萨尔县某油页岩矿为研究对象，以原位注蒸汽开采油页岩为研究背景，拟开展以下研究：1）采用显微CT扫描和声波探测的方法，研究注入过热水蒸汽热解过程中，油页岩孔隙发生、发展及裂隙从起裂、扩展到连通的演化特征；2）通过高温三轴渗透实验台研究热-力耦合作用下，油页岩渗透性和力学特性的演化特征，获得油页岩热解破裂的临界条件，揭示在不同层理方向上，渗透率和岩石力学参数随温度演化的定量关系；3）基于逾渗理论，研究油页岩热解油质产物的流动特征及其对渗流通道连通性的影响规律；4）依据实验研究结果和相关理论建立油页岩内部水蒸汽驱动油质产物流动的数学模型，进行数值计算，研究在水蒸汽驱动作用下，油页岩中油质产物的流动运移规律，并对水蒸汽驱动效率进行分析评价。从而为原位注蒸汽开采油页岩油气工程提供科学依据。

在原位注热开采油页岩的过程中，蒸汽注入后，油页岩的孔隙结构、力学特性和渗透性发生变化，从而影响油气产率。本项目以原位注蒸汽开采油页岩为背景，开展了以下研究：1）利用过热水蒸汽热解系统对油页岩试件进行热解，采用CT扫描、高压压汞和扫描电镜法对热解后试件的孔隙结构进行表征，得到：经过高温蒸汽作用后，油页岩内部孔隙裂隙发生了明显的变化，350℃之前孔隙率相对较低，300℃时裂隙开始萌生，350℃有较为明显的裂隙形成，并在油页岩内部沿着层理面方向形成了渗流通道；随着有机质的大量热解，油页岩内部的孔隙裂隙及孔隙团规模在不断增大，600℃时的孔隙率达23.08%。2）通过对比分析传导、对流加热模式下油页岩的孔隙裂隙结构得到：蒸汽具有扩孔和“对流剥蚀”效应、可降低页岩油的粘度、在高温下可与页岩油发生加氢裂解反应，所以蒸汽对流加热后，油页岩的孔隙率高于传导加热。3）过热水蒸汽作用下，渗透率随着温度的变化规律为：350℃之前油页岩处于低渗透率阶段，并且由于油页岩有机质软化生成沥青质的影响，350℃渗透率下降出现低值；350～600℃为热解的主要阶段，随着热解的不断深化，渗透率迅速增大。4）利用高温单轴压缩试验系统对油页岩试件进行实时控温条件下的加载实验，得到：抗压强度随温度升高经历了降低-稳定-降低-再上升的变化过程，100℃和400℃强度出现下降；弹性模量在25～100℃降低，100℃～300℃处于稳定，300℃～600℃升高。5）开展了油页岩压裂热解开采的数值模拟研究，得到油页岩原位注蒸汽开采中渗流场、温度场、应力场的变化及原位注蒸汽开采的优势。研究结果为实现大规模油页岩原位注蒸汽开发提供了有利技术支撑。