页岩气储层吸附解吸机理研究

The adsorption and desorption behavior in the nanoscale pores of shale gas reservoir is not only the basic theory in shale gas seepage and productivity prediction, but also the key scientific problem in shale gas reservoir development. Three main problems are studied for reser adsorption and desorption in unconventional shale gas reservoir. (1) The microscopic pore structure of the hypertight shale gas reservoir is presented using scanning electron microscopy (SEM) and nitrogen adsorption isotherms at 77K。(2) The adsorption and desorption dynamic equilibrium tests are carried out in shale gas reservoir, experimental equipments that are used for supercritical gas adsorption and desorption are established, the characteristic of adsorption and desorption in shale gas reservoir with different temperatures and pressures are clarified with different kinds of gas and their mixture gases, then the force between the molecules and potential energy are calculated, the adsorption gas state on supercritical condition is also determined, and adsorption and desorption mechanism of shale gas in supercritical condition are proclaimed. (3) In view of the supercritical adsorption characteristic, the supercritical adsorption isotherm equations are developed, and thinking of inhomogeneity distribution of energy on the surface of shale, the prediction models on adsorption and desorption of shale gas are developed. Based on the above research, the inauthenticity of the traditional model on shale gas adsorption and desorption are overcomed, and the findings provide theoretical support and the solving methods for the determination of gas content and reservoir evaluation of shale gas reservoir.

页岩气藏纳米级孔隙中气体吸附解吸行为是研究页岩气藏渗流和产能预测的基础，是页岩气藏开发理论中关键的科学问题。（1）针对页岩气藏超致密油气储层，开展页岩岩芯扫描电镜、低温氮气吸附实验，描述页岩非常规油气储层微观孔隙结构；（2）开展页岩气储层气体吸附解吸动态平衡实验，建立页岩超临界气体吸附解吸仿真实验装置，模拟不同纯组分气体以及不同比例混合气体在不同温度和压力下页岩储层的吸附解吸特征，分析吸附分子间的作用力和势能，确定超临界条件下气体吸附的状态，揭示页岩储层超临界气体吸附解吸机理和多组分气体的竞争吸附行为；（3）基于页岩超临界气体吸附特性，建立超临界气体吸附等温线方程，考虑页岩储层表面能量的不均一性，建立页岩气储层吸附解吸预测模型。通过上述研究，克服传统页岩气吸附解吸模型的非真实性，为页岩储层含气性能确定、储量评价提供理论支撑和解决方法。

我国页岩气资源量与美国相当，但是对页岩气开发研究尚为空白。页岩储层致密，广泛存在纳米级孔隙，常规的微米级油气储层表征方法难以描述这种纳米油气的储层形态。页岩储层埋藏较深，所处环境为高温高压，如何模拟地层条件下页岩气吸附解吸过程以及探讨吸附解吸机理是目前亟待解决的问题。本项目通过氩离子抛光技术和场发射扫描电镜定性观察页岩孔隙形态，采用低温液氮吸附和高压压汞相结合的方式定量表征页岩孔隙结构，改进传统煤层气吸附解吸实验装置，建立一套适合页岩气吸附解吸实验装置，考虑到页岩高压吸附，矫正过剩吸附量为绝对吸附量，通过分析影响页岩气吸附的关键因素和计算热力学参数，探讨页岩气吸附解吸机理，进而建立预测页岩气超临界吸附的简化局部密度（SLD）模型。研究结果表明，页岩储层孔隙可划分为5种类型：有机质纳米孔、黏土矿物粒间孔、岩石骨架矿物孔、古生物化石孔和微裂缝。其中，有机质纳米孔和黏土矿物粒间孔是页岩中发育最广泛的两种孔隙类型。页岩主体孔径为中孔。小于50nm的微孔和中孔提供了主要的比表面积和孔体积，是气体吸附和存储的主要场所。页岩气储层吸附评价应以绝对吸附量为基准。总有机碳含量和孔隙结构特征是控制富有机质页岩吸附能力的关键因素，粘土矿物对低有机碳含量的页岩的吸附起重要贡献作用。等量吸附热随着页岩吸附量的增加并不是恒定不变的。SLD模型在低压下（<3MPa）略微偏离实验数据，但能较好的拟合高压下吸附等温线和吸附最大值现象，并且拟合参数合理，达到了一般的临界温度以下的吸附模型所不能处理的效果。页岩气储层孔隙结构表征及地层条件下的吸附解吸机理研究，对页岩气储量预测、渗流规律研究以及产能预测具有重要意义。