摘要
页岩气藏CO_(2)蓄能压裂过程中,前置注入的超临界CO_(2)溶于地层水或滑溜水会形成弱酸性的CO_(2)水溶液。为了明晰前置注入的超临界CO_(2)的化学溶蚀效应对于后续页岩气储层压裂裂缝扩展及岩石物性的潜在影响,采用一套小尺寸真三轴压裂模拟系统,对含方解石充填天然裂缝的页岩开展了地层温度压力条件下压裂模拟实验;结合声发射监测和CT扫描,研究了CO_(2)水溶液作用下的岩石破裂机制;进而通过水岩作用实验定量评价了岩石性质的改变情况。研究结果表明:(1)在较高水平应力差下(8 MPa),滑溜水不易使高强度胶结的天然裂缝开启,趋于形成简单缝,声发射事件点主要分布于起裂点附近;(2)CO_(2)水溶液在地层温度压力条件下,对页岩基质和天然裂缝中的钙质充填矿物存在溶蚀作用(0.5 h即可发生),并且随着温度和时间的增加,溶蚀程度显著增强,使得页岩层理、天然裂缝抗拉强度降低,同时孔隙度和渗透率增大,最终促进页岩层理和天然裂缝的开启、形成复杂的水力裂缝且明显以剪切破裂为主。结论认为,CO_(2)前置注入引发的化学效应有助于提高页岩气水力压裂裂缝的复杂程度和改善储层的岩石物性;超临界CO_(2)前置蓄能压裂技术具有较广阔的应用前景。
During the CO_(2)energy storage fracturing of shale gas reservoirs,pre-injected supercritical CO_(2)is dissolved into formation water or slick water to form CO_(2)solution of weak acidity.In order to clarify the potential influences of the chemical corrosion effect from the pre-injected supercritical CO_(2)on the subsequent hydraulic fracture propagation and petrophysical properties of shale gas reservoirs,this paper carries out fracturing simulation experiments on the shale specimens with calcite filled natural fractures under reservoir temperature and pressure by using a set of small-scale true tri-axial fracturing simulation system.Then,the rock breaking mechanisms under the action of CO_(2)solution are investigated by means of acoustic emission monitoring and CT scanning.Finally,water-rock interaction experiments are performed to quantitatively evaluate the change of petrophysical properties.And the following research results are obtained.First,when the horizontal stress difference is large(8 MPa),slick water cannot easily activate the natural fractures of strong cementation,the rock tends to form simple hydraulic fractures,and the acoustic emission events are distributed mainly near hydraulic fracture initiation points.Second,the shale matrix and the calcareous filling minerals in natural fractures can be corroded by CO_(2)solution under reservoir temperature and pressure(immediately after 0.5 h),and with the increase of temperature and time,its corrosion degree increases greatly,so as to decrease the tension strength of shale bedding and natural fractures while increasing porosity and permeability,and eventually promote the activation of shale bedding and natural fractures and the formation of complex hydraulic fractures dominated by shear failure.In conclusion,the chemical effect induced by CO_(2)pre-injection is conducive to increasing the complexity of hydraulic fractures in shale gas reservoirs and improve the petrophysical properties of reservoirs.What’s more,the supercritical CO_(2)pre-injection and energy storage fracturing technology is promising in the application prospect.
作者
邹雨时
李彦超
李四海
ZOU Yushi;LI Yanchao;LI Sihai(State Key Laboratory of Petroleum Resources and Prospecting,China University of Petroleum,Beijing 102249,China;Shale Gas E&D Project Department,CNPC Chuanqing Drilling Engineering Co.,Ltd.,Chengdu,Sichuan 610052,China)
出处
《天然气工业》
EI
CAS
CSCD
北大核心
2021年第10期83-94,共12页
Natural Gas Industry
基金
国家自然科学基金项目“CO2作用下致密储层的力学特性与压裂缝网形成机制实验研究”(编号:51704305),“页岩油储层水力压裂压后关井作用机理研究”(编号:51974332)。
