A study of numerical simulations for enhanced geothermal reservoir parameters and thermal extraction based on microseismic data
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摘要:
发展清洁、稳定、可再生的干热岩型地热资源对于缓解能源危机、减轻环境污染、改善人类健康具有重要意义。增强型地热系统(Enhanced Geothermal System，EGS) 是一项改造干热岩天然储层，高效开发地热能资源的先进技术。以澳大利亚库珀盆地地热储层为研究对象，基于水力压裂实测微震数据，建立了三维分区均质渗透率模型和非均质渗透率模型，分别进行储层温度场、流场及采热性能变化的研究，并对比其差异。结果表明：在同样的注采流量下，由于非均质模型中微震事件集中于井口附近，进而形成明显的优势流动通道，流体从注入井更快流向生产井，温度下降速度相对更快，分区均质模型中优势流动通道没有非均质模型明显，温度下降速度较慢；地热模型运行期间分区均质模型的采热量变化相对稳定，降幅为3.74%，非均质模型采热量降幅较大，为12.72%。分区均质模型的模拟结果相比于非均质模型，温度下降幅度小、采热量高；但实际储层中的渗透率分布不均，分区均质模型的模拟采热量相比实际采热量偏高，因此在实际应用中，非均质模型的模拟结果对实际工程更具参考意义。
Abstract:The development of clean, stable, and renewable hot dry rock geothermal energy is significant for alleviating the energy crisis, reducing environmental pollution, and improving human health. Enhanced geothermal system (EGS) is an advanced technology for developing geothermal energy efficiently by stimulating hot dry rock reservoir. This technology involves a complex hydro-thermal coupling process. A numerical approach is usually applied for analyzing heat extraction. In this paper, taking the geothermal reservoir of the Cooper basin in Australia as the research object, two models–a 3D zonal homogeneous permeability model and a heterogenious permeability model – are established based on the measured microseismic data of hydraulic fracturing. The latter one is inversed from microseismic data. The temperature field, seepage field and thermal performance of the reservoir are numerically studied, and their differences are compared and analyzed. The results show that with the same injection-production flow rate, fluid flows more quickly from the injection well to the production well while the temperature drops relatively more rapidly in the inhomogeneous model due to the dominant channel revealed by dense microseismic events near the wellbore. In the homogeneous model, the dominant flow channel is not as pronounced as in the previous model, and the temperature decreases more slowly. During the operation of the geothermal reservoir model, the change in heat recovery of the zonal homogeneous model is relatively stable, with a decline of 3.74%, and that of the inhomogeneous model is rather obvious, with a decline of 12.72%. Compared with the inhomogeneous model, a smaller temperature drop and a higher heat recovery exist in the homogeneous model. However, the permeability in the actual reservoir is uneven, and the simulated heat recovery of the zonal homogenization model is higher than the actual recovery. Therefore, the simulation results of the inhomogeneous model have more reference significance for practical engineering.
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Key words:
- EGS /
- microseismic data /
- permeability /
- hydro-thermal coupling /
- numerical simulation
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表 1 分区均质模型中岩石物理性质参数
Table 1. Parameters of rock in the zonal homogenization model
区域 密度
/（kg·m−3）比热
/（J·kg−1·K−1）孔隙度/% 导热系数
/（W·m−1·K−1）压缩系数
/（10−10 Pa−1）上层花岗岩 2 700 960 0.01 3.395 5.00 改造区 2 700 960 1.40 3.395 5.00 下层花岗岩 2 700 960 0.01 3.395 5.00 
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表 2 循环工作流体的物理性质参数
Table 2. Parameters of the circulating fluid
密度
/（kg·m−3）比热
/（J·kg−1·K−1）导热系数
/（W·m−1·K−1）黏度
/（Pa·s）压缩系数
/（10−10 Pa−1）水 1 000 4 200 0.6 0.001 5.0
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表 3 分区均质模型不同渗透率下生产井中的模拟流量与实际流量
Table 3. Simulated flow and actual flow of production wells in the homogeneous model with different permeabilities
试验 渗透率/m2 时间/d 模拟流量/（m3·s−1） 实测流量/（m3·s−1） x y z 1 6.00×10−13 1.20×10−12 4.00×10−14 42 0.074 9 0.015 5 2 2.00×10−13 4.00×10−13 4.00×10−14 42 0.023 8 3 1.50×10−13 3.00×10−13 4.00×10−14 42 0.017 6 4 1.40×10−13 2.80×10−13 4.00×10−14 42 0.016 4 5 1.30×10−13 2.60×10−13 4.00×10−14 42 0.015 2 6 1.20×10−13 2.40×10−13 4.00×10−14 42 0.014 0 7 1.00×10−13 2.00×10−13 4.00×10−14 42 0.011 6
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表 4 非均质模型不同渗透率相关参数下生产井中模拟流量与实际流量
Table 4. Simulated flow and actual flow of production wells in the heterogeneous model with different permeability related parameters
试验 渗透率计算相关系数 时间/d 模拟流量/（m3·s−1） 实测流量/（m3·s−1） B1 B2 B3 1 3.00×10-5 1.50×10-5 2.5 42 0.030 2 0.015 5 2 4.00×10-5 1.50×10-5 2.5 42 0.029 3 3 4.00×10-5 2.00×10-5 2.5 42 0.021 2 4 5.00×10-5 2.00×10-5 2.5 42 0.015 8 5 5.00×10-5 2.50×10-5 2.5 42 0.008 6
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