基于地质统计学方法确定干热岩体天然裂隙分布格局

The hot dry rock (HDR), which is a clean and renewable energy source, widely exists in China and the world. Due to the low porosity and low permeability in HDR, hydraulic fracturing is commonly conducted to create connected fracture network for heat extraction, and the effect is dependent on the natural fracture pattern. However, as HDR is deeply buried, the fracture pattern is difficult to measure. To overcome this difficulty, the combination of geostatistical inference, tracer test, solute transport modeling and parameter inversion is proposed to infer the fracture pattern. The multiple point geostatistics simulation is applied to infer the fractures in HDR, based on the fractures measured at the outcrop with lithology and geological background similar to the target HDR. The primary estimation of fractures is converted to the permeability tensor, and is then incorporated into a solute transport model to predict the breakthrough curves (BTC) under the boundary conditions of the tracer test. The modeled BTC is compared to the observed one, and according to the errors, the iterative cokriging inverse method is employed to update the permeability. The combined methods would allow a reasonable construction of fracture pattern.

干热岩型地热资源作为一种清洁可再生能源具有巨大的开发利用价值。为了开采干热岩中的地热资源，人们通常采用人工水力压裂的方法刺激干热岩体形成连通的裂隙网络以增强其渗透性。人工压裂效果与岩体中天然裂隙的空间分布格局密切相关。然而，干热岩深埋于地下，其中的裂隙不易直接测量；此外，干热岩场地钻孔数量较少，通过测井等方法获得的裂隙相关信息有限。本项目拟采用地质统计、示踪试验、溶质运移模拟和参数反演相结合的手段开展干热岩体裂隙分布研究：根据地表露头区岩体的裂隙分布，利用多点地质统计方法推演干热岩体裂隙分布格局；基于单井注/抽示踪试验和溶质运移模拟验证所推演的裂隙分布；根据试验和模拟所得的示踪剂浓度的差异，采用迭代协克里格反演算法调整裂隙分布。此次研究对干热岩体天然裂隙分布进行正反演确定，所得结果将为干热岩型地热资源的开发提供有力的依据。

干热岩储层结构(包括天然裂隙结构及与周围储层水力联系)分析是开展储层裂隙建造和热能获取的重要基础。此次研究以青海共和-贵德盆地干热岩开发靶区为研究区，通过野外调查和样品采集测试，获得干热岩体露头区天然裂隙以及能间接反映储层属性的浅表水化学、岩矿成分数据；建立了新的流体渗流-温度-同位素耦合迁移模拟程序，以更好地连接浅表观测数据和地下多场耦合过程及储层属性，发现了地热系统中流体密度差异能够引起同位素分馏；在此基础上，基于协克里格原理建立了多参数联合反演算法，用于贵德盆地构建热储结构。所开发的多场耦合模拟与反演程序对于认识地热系统结构具有重要意义，所建立的贵德盆地地热成因模式对于该地区地热资源开发具有重要参考价值。