雄安新区高阳地热田热储高于庄组碳酸盐岩不同围压下破碎规律研究

Fragmentation law of carbonate rocks under different confining pressure in Gaoyuzhuang Formation,Gaoyang geothermal field,Xiong'an New Area

【研究目的】雄安新区高阳地热田D34钻孔为中国地质调查局中国地质科学院于2020年钻获的华北盆地最高温地热井,井口温度达123.4℃,出水量为94.5 m3/h,为使温度如此高的地热井的地热开发利用程度最大化,开展压裂增产是其重要举措。因此,为获取相关参数,以制定最优的压裂增产方案,本次研究拟厘清储层岩石在不同围压下的破碎规律。【研究方法】本文在前人研究的基础上,以D34井钻获的深部高于庄组热储碳酸盐岩为研究对象,开展了常规三轴抗压及抗拉实验。【研究结果】实验结果表明:(1)高于庄组碳酸盐岩拉伸强度特征与压缩强度特征相近,且表现出明显的压缩破坏特征。随着围岩压力的增加,抗压强度具有典型的二次增高特征。(2)抗压强度及裂隙展布形态随深度变化呈现出差异性,其中均匀发育的多裂缝和单一主缝为主要形式扩展。在20 MPa、40 MPa围压下,屈服强度分别与弹性模量、泊松比协同变化。(3)储层不同深度拉伸裂隙的扩展方式有所差异,较浅部拉伸裂隙主要以小幅度多级扩展为主,而较深部岩石则表现出均匀扩展态势。【结论】结合抗压和抗拉实验结果,认为热储高于庄组压裂增产效果较好,且储层浅部形成复杂压裂网络的可能性高于深部储层,但总体脆性指数分布差异较小,故认为无需对储层不同深度采取不同的压裂施工方案。

The paper is the result of geothermal geological survey engineering.[Objective]D34 well of Gaoyang geothermal field in Xiong'an New Area is the highest temperature geothermal well in North China Basin drilled by Chinese Academy of Geological Sciences and China Geological Survey in 2020.The wellhead temperature is 123.4℃,and the water output is 94.5 m3/h.Obviously,such high temperature corresponds with a relatively low flow.In order to provide important theoretical support for fracturing stimulation,this study intends to clarify the fragmentation law of reservoir carbonate rock under different confining pressures.[Methods]Based on previous studies,this paper takes the deep Gaoyuzhuang Formation reservoir carbonate rocks drilled from D34 well as the research object,and carries out conventional triaxial compression and tensile experiments.[Results]The experimental results show that:(1)The tensile strength characteristics of the reservoir carbonate rock in the Gaoyuzhuang Formation are similar with that of compressive strength,and shows obvious compression failure features.With the increase of the surrounding rock pressure,the compressive strength shows a typical secondary increase.(2)The compressive strength and the distribution of the fractures show differences with the depth.Among them,the uniformly developed multiple fractures and single main fractures are the main forms of expansion.Under the confining pressure of 20 MPa and 40 MPa,the yield strength changes synergistically with the Young's Modulus and Poisson's Ratio,respectively.(3)The expansion methods of tensile fractures are different with different depth.The shallower tensile fractures mainly expand with small amplitude and multistage expansion,while the deeper rocks show a uniform expansion trend.[Conclusions]Combined with the result of conventional triaxial compression and tensile experiments,it is concluded that the possibility of forming a complex fracturing network in the shallow part of the reservoir is higher than that in the deep part,but the overall brittleness index is less different,so there is no need to adopt different construction plans for different depths of the reservoir.