支撑剂对干热岩人工裂隙导流能力影响机制研究

Proppant stimulation is an effective approach to improve flow property of fractured rock mass and it has been widely used in oil and gas exploitation. However, there has very limited application of this technique due to the lack of knowledge of proppant stimulation on fractured hot-dry-rock under geothermal exploitation. In this proposal, granite samples are collected from a geothermal reservoir in Gonghe basin of Qinghai province. Flowing testes will be carried out to investigate the influences of proppant size combination on permeability of fractures. Then, proppant with most effectively stimulation effects will be pumped to fractured rock mass and the aperture will be monitored. Furthermore, the distribution of the proppant in the rock mass will be recorded. In order to examine the proppant collapse under high temperature and stress, compression tests will be implemented. The aperture change will be monitored and the proppant collapse will be recorded using acoustic technique. The process of the proppant collapse will then be discussed. Finally, the proppant transfer and the collapse will be numerically studied using LBM-DEM method and the mechanism for proppant stimulation on fractured granite will be revealed. This study will provide some key supports to geothermal exploitation.

支撑剂刺激是一种提高裂隙岩体渗透率的有效措施，已被广泛应用于石油和天然气开采。由于对干热岩储藏条件下支撑剂导流机制认识不足，其应用受到极大限制。本项目以青海共和盆地热储层花岗岩为研究对象，进行支撑剂组合方式的裂隙渗流试验，揭示裂隙导流能力变化规律。进行裂隙泵入试验，监测裂隙开度变化并统计支撑剂分布特征，获得影响裂隙导流能力的关键因素。进行高温高压下支撑剂破碎试验，监测裂隙变形及支撑剂破碎过程，揭示裂隙导流能力变化及支撑剂破碎的力学机理。最后，应用离散格子玻尔兹曼和离散元耦合方法，再现支撑剂运移及变形破碎的动态过程，揭示支撑剂影响裂隙导流的机制。成果可为支撑剂在干热岩地热能开采提供关键理论支持。

干热岩型及中深部无水地热资源储量丰富，但由于深部地应力较大，裂隙很容易闭合，导致开采非常困难。增加裂隙的渗透率是成功开采该类型地热资源的关键所在。针对这个问题，本项目在前人的研究基础上探讨了利用支撑剂来支撑和润滑裂隙的剪切刺激效果，进一步揭示了支撑剂对裂隙导流能力的提升机制。通过野外采样，制作含单裂隙的花岗岩样品，进行了不同支撑剂组合的裂隙渗流试验，结果表明支撑剂粒径越大对裂隙渗流提升效果越显著，在支撑剂达到1.0mm 时，渗透系数比无支撑剂提升100余倍；进行了含支撑剂裂隙直剪试验，探讨了支撑剂在剪切过程的力学作用机制，研究表明支撑剂可以起到润滑作用，从而极大降低了剪切的峰值强度，甚至直接达到残余强度；监测裂隙开度变化并分析了渗透性变化，发现剪切错位是影响裂隙导流能力的关键因素；进行剪切过程中支撑剂破碎试验，利用声发射（AE）监测裂隙了裂隙变形及支撑剂破碎过程，揭示了大颗粒支撑剂破碎比例高，更好地起润滑剂作用有利于剪切起裂，小颗粒支撑剂破损较少，更好的起到支撑裂隙开度的作用。研究成果在中深部无水型及深部干热型地热资源开发有广泛的应用前景。