裂隙表征对羊八井地热田基岩热能开采影响的数值模拟研究

The Yangbajing geothermal field is the first high-temperature hydrothermal convective geothermal field in China, and the research and development of Yangbajing geothermal field is of great importance for electric power supply of Lhasa. The exploration data of well ZK4001 at north of the field prove that there is a high-temperature fractured granite reservoir at depth of 950～1350m, and this reservoir is mainly within mylonitized granite, granitic mylonite and fractured granite; this fractured granite reservoir has an average temperature of 248℃, with a highest temperature of 251℃ and a pressure of 8.01～11.57MPa. However, presently there is a lack of understanding of the fracture characteristics of this fractured reservoir, and there is no systematic study on the fracture characterization method of this reservoir. Based on these, this project mainly aims at researching the influences on heat production potential of the fracture characterization with numerical method. It includes three parts: (1) the available scopes and conditions of equivalent porous method (EPM), double porosity method (DPM) and multiple interacting continua ( MINC); (2) the congruent relationships between EPM and DPM or MINC; (3) the influences on heat production potential of the fracture characterization method of the 950～1350m reservoir at Yangbajing geothermal fields. The research results of this project will provide important reference for future exploitation of deep high-temperature fractured granite reservoir, and establish good fundament for development program design and thermal performance optimization at Yangbajing geothermal field.

羊八井地热田是我国第一个水热对流型的高温地热田，研究与开发羊八井热田对保证西藏电力供应有重要意义。北区ZK4001井的勘探资料显示热田在950～1350m深处存在一个高温裂隙热储层，岩性为碎裂花岗岩、糜棱岩化花岗岩、碎斑状花岗岩，热储层平均温度248℃，最高251℃，压力介于8.01～11.57MPa。目前对该基岩储层的裂隙特征尚不清楚，对其裂隙表征方法尚未开展系统研究。 在此基础上，本申请拟采用数值模拟方法研究裂隙表征方法对储层产热性能的影响，具体包括：（1）等效多孔介质法、双孔隙度法和多重作用连续体法在表征裂隙时各自的适用范围和条件；（2）等效多孔介质法与双孔隙度法、多重作用连续体法之间的对应关系；（3）不同裂隙表征方法对羊八井热田950～1350m深度基岩储层热能开采的影响。项目的研究结果将为未来开发羊八井热田深部高温热储提供重要的参考，为开采方案设计和采热性能优化奠定良好的基础。

深部地质探测显示羊八井地热田北区井ZK4001内950～1350m深处存在一个裂隙基岩热储层，平均温度为248℃，压力介于8.01~11.57MPa。在此基础上，本申请拟采用数值模拟方法研究裂隙表征方法对储层产热性能的影响，具体包括：（1）等效多孔介质法、双孔隙度法和多重作用连续体法在表征裂隙时各自的适用范围和条件；（2）等效多孔介质法与双孔隙度法、多重作用连续体法之间的对应关系；（3）不同裂隙表征方法对羊八井热田950～1350m深度基岩储层热能开采的影响。通过研究发现当裂隙间距处于3～25m时，采用EPM方法能获得和MINC方法一致的结果；当裂隙间距处于25～300m时，随着裂隙间距的增大，EPM方法的结果和MINC方法的结果偏差逐渐增大，因此当裂隙间距处于25～300m时，不宜采用EPM方法模拟裂隙型地热储层。