页岩气储层孔隙孔径分布表征及渗透率评价方法研究

Shale gas reservoir has the characteristics of extremely low matrix permeability, microcrack development and dynamic changes with gas production which causing great difficulties to logging evaluation. Focused on the challenges of shale gas reservoir’s permeability evaluation, taking the Sichuan basin and the peripheral shale gas reservoir as an example, by combining the matched core analysis test with gas seepage numerical simulation and well logging evaluation, then carried out corresponding research on key controlling factors of permeability, seepage mechanism and evaluation method. Firstly, based on both liquid nitrogen adsorption & constant speed high pressure mercury experiments and the NMR measurement with alternately saturated different fluids, special aperture distribution experiment like micro-crack conductive test under low resistance background, we will establish evaluation model and method of shale static permeability on the basis of pore size distribution. Secondly, on the basis of matched core experiments, by simulating the desorption ,diffusion and seepage process of methane in reservoir in different aperture size, pore pressure, wettability and gas saturated condition, quantitative evaluation method of dynamic permeability will be proposed. Finally, based on both new and conventional logging data, combined with static and dynamic evaluation model and method of permeability, we will establish a reasonable set of permeability logging evaluation model and method. The results of this project will be conductive to the final settlement of the shale gas reservoir permeability evaluation, which will play an important role for promoting China's shale gas projects with low cost, high effectiveness and sustainable development.

页岩气储层渗透率具有基质渗透率极低、微裂缝渗透性发育及随气体采出动态变化的特点，给测井评价造成很大困难。针对渗透率评价难题，以四川盆地及周缘页岩气储层为例，通过配套岩心分析测试实验、气体渗出过程数值模拟及测井评价相结合的方法，对渗透率主控因素、渗流机理及评价方法开展研究。首先，基于液氮吸附-恒速高压汞联测、交替饱和不同流体核磁共振测量、低阻背景下微裂缝导电测试等孔径分布专项实验，建立基于孔径分布的页岩静态渗透率评价模型和方法；其次，在配套岩心实验基础上，模拟不同孔径、孔隙压力、润湿性、含气饱和度条件下甲烷在储层中的解吸、扩散和渗流过程，提出页岩动态渗透率的定量评价方法；最后，基于新方法及常规测井资料，结合静动态渗透率评价模型和方法，建立一套合理的渗透率测井评价模型及方法。项目成果将有助于页岩气储层渗透率评价难题的最终解决，对推动我国页岩气低成本、高效益开发及其可持续发展发挥重要作用。

近年来，页岩和致密砂岩等非常规油气勘探开发取得重大进展，与常规储层不同的是，非常规页岩气储层、致密砂岩储层等具有低孔低渗、孔隙结构复杂，非均质性强，裂缝和微裂缝发育等特征，给储层渗透率的评价带来挑战。为了提高复杂储层渗透率的评价精度，发展复杂储层尤其是页岩气储层渗透率测井评价方法和技术，本研究重点针对页岩气储层的孔隙结构和渗透率定量评价，开展了配套的孔隙结构实验、渗透率评价模型和测井评价方法及应用研究。. 首先，开展了页岩孔隙结构配套实验及分析，明确了页岩孔隙结构特征及定量评价方法。通过FIB-SEM、高压压汞、液氮吸附和二氧化碳吸附的专项配套实验及水平渗透率和垂直渗透率的测试，获取了多种测试方法下页岩气储层的孔径分布特征及规律，利用液氮吸附-高压压汞联合测试孔径分布对饱和油和饱和水的核磁共振T2谱进行刻度，建立了二者之间的定量转换关系（Rd=52 T2）。 . 其次，优选地建立了复杂储层渗透率的评价模型。通过对页岩气储层和致密砂岩储层的高压压汞资料及毛管压力曲线的分析，分别提取了SWANSON, CP, R30, R10等孔隙结构参数，并以上述孔隙结构参数为基础，建立起对应的渗透率评价模型。研究表明，基于孔隙结构的渗透率评价模型精度上有明显的改进，能适用于复杂储层中渗透率的定量评价。. 最后，分别建立了基于新方法测井和常规测井的孔隙结构参数构建及渗透率评价方法。评价模型在国内焦石坝一期、二期、川西、威远等多个页岩气区块及鄂南致密砂岩储层中均取得了良好的评价效果，可为复杂储层评价和产能预测提供可靠的技术支撑。.综上可知，本研究针对复杂储层孔隙结构进行了系统实验研究和分析，提出和优选地建立了基于孔隙结构的渗透率评价模型。并分别利用核磁、成像等新方法测井资料对储层孔隙结构进行表征，从中提取出反映储层渗透性的孔隙结构参数对渗透率进行高精度评价，研究成果为复杂油气储层渗透率难题的解决及成果应用提供了可供参考借鉴的思路、方法及技术。