中国科学院重庆绿色智能技术研究院机构知识库

The acoustic response of bedding hard brittle shales is the foundation of well logging data interpretation during the shale gas development process.To better understand the ultrasonic penetration through bedding shale reservoirs, we first collected the shale outcrops from the Lower Silurian Longmaxi Shale in southeast Chongqing, and transversely isotropic large rock samples were preliminarily screened with the velocity test method to acquiring comprehensive knowledge on the propagation characteristics of the ultrasonic wave of bedding shale reservoirs.On this basis, cores were drilled from different bedding direction, meanwhile multi-frequency ultrasonic transmission, experiments were performed in the laboratory, thereby to get the law of acoustic wave propagation in different bedding directions. The following findings were obtained. a. Rock samples used in the experiments are mainly composed of black shale, gray and black shale, dark gray shale and silty mudstone, the porosity of which ranges from 1.5% to 2.5%, and the permeability of which is mostly less than 1 mD. b. With the increase of the bedding angle within the range of 0°-90°, the wave velocity decreases obviously while the attenuation coefficient increases. c. There is a good negative correlation between the wave velocity and porosity. Attenuation coefficient increases with the increase of porosity and its increasing degree becomes greater with the increase of the bedding angle. d. The wave velocity and the frequency both increase in a logarithm tendency, the dispersion phenomenon is obvious, and the attenuation coefficient increases with the increase of frequency. The above experimental results about the correlation between rock acoustic properties and bedding formation of shales provide a reliable experimental basis, based on which an accurate formation rock strength profile and wellbore stability analysis can be established in the process of shale gas development.

层理发育的硬脆性页岩的声波响应特征是页岩气开发过程中测井资料应用的基础,为获得对层理性页岩储层超声波传播特性的认识,选取渝东南地区下志留统龙马溪组野外露头岩块,通过波速初步筛选出横向各向同性的大岩样,在此基础上钻取不同层理方向的小岩柱,进行室内多频率超声波透射实验,以获取不同层理下的声波传播规律。实验结果表明:①实验用岩样以黑色、灰黑色及深灰色页岩、粉砂质泥岩为主,孔隙度变化范围为1.5%~2.5%,大部分岩样的渗透率小于1 mD;②在0°~90°范围内,随层理倾角的增加,波速减小趋势明显,衰减系数增加;③波速与孔隙度呈现较好的负相关性,随孔隙度增加,衰减系数增加且增加程度随层理倾角变大而加剧;④波速与频率呈对数增加的趋势,频散现象明显,衰减系数随频率增加而增大。所得到的页岩层理与声波属性相关性的实验结果,可为页岩气开发过程中建立准确的地层岩石强度剖面及井壁稳定分析提供实验依据。