潜江凹陷潜江组盐间页岩油储层地震岩石物理特征分析

Seismic rock physical characterization of a shale oil reservoir in the Qianjiang Formation of Qianjiang Sag,China

潜江凹陷潜江组页岩油因其独有的陆相盐湖沉积特征导致储层“甜点”预测困难,亟需开展基础性的岩石物理实验研究,以明确页岩油储层不同岩性、物性和地震弹性参数间的变化规律。为此,对研究区F井的47块岩心进行了岩石物理声学测试,并结合常规物性测试,系统地分析了盐间页岩油储层地震弹性性质的变化规律,研究了识别岩性的参数,确定了对有利储层敏感的弹性参数。结果表明,盐岩和大部分盐间页岩样品表现为各向同性,而具有矿物成层和层理裂缝发育的岩石则各向异性显著。纵、横波速度、杨氏模量、体积模量和纵波阻抗可用于识别岩性,而纵、横波速度比和泊松比等参数不适用于区分岩性。此外,发现石英含量与纵波速度和纵波阻抗具有相关性,也可用于岩性识别。最后确定了有利储层的敏感弹性参数,盐间页岩层:密度ρ大于2.2g/cm3、杨氏模量大于44.38GPa、纵波阻抗大于11.06g/cm3·km/s;利用纵波阻抗与纵、横波速度比的交会、杨氏模量与泊松比的交会方法区分有利储层时,会出现严重的叠置现象,而拉梅系数λ和密度ρ乘积(λρ)以及剪切模量μ和密度ρ乘积(μρ)可以相对较好地区分有利储层,其参数范围分别满足38.02GPa·g/cm3<λρ<67.38GPa·g/cm3和39.51GPa·g/cm3<μρ<53.84GPa·g/cm3。此结果与测井解释结果吻合度较好,说明了测井解释的可靠性。研究结果还可为岩石物理理论建模以及测井解释和地震“甜点”预测工作提供数据支撑。

The shale oil in the Qianjiang Formation of Qianjiang Sag originated in a unique sedimentary environment featuring a continental saline lake.Its peculiar history makes the identification of reservoir sweet spots difficult and warrants a dedicated petrophysical investigation to clarify the spatial patterns of lithologies,physical properties,and seismic elastic parameters.In this study,in addition to the determination of physical properties,rock acoustic tests were conducted on 47 block cores from well F in the target area to systematically evaluate the spatial patterns of the seismic elastic properties of the intersalt shale oil reservoirs,identify favorable lithologies,and evaluate the sensitive elastic parameters of the reservoirs.According to the experimental results,the salt rocks and most of the intersalt shale samples behave isotropically,while the rocks with mineral stratification and bedding fractures exhibit significant anisotropy.Moreover,it was observed that information on shear wave velocity,Young's modulus,shear modulus,and P-wave impedance can be used to classify the lithology,whereas the ratio between P-wave and S-wave velocities and the Poisson's ratio are not suitable for this purpose.In fact,the P-wave velocity and impedance are correlated with the quartz content;hence,they can be used for lithology identification.Finally,the sensitive elastic parameters of favorable reservoirs were determined.Such reservoirs can be regarded as intersalt shale oil reservoirs,for which the density is greater than 2.2g/cm3,Young's modulus is greater than 44.38GPa,and the P-wave impedance is greater than 11.06g/cm3·km/s.In the process of identifying favorable reservoirs,there is an overlapping when making a convergence analysis with P-wave impedance and the ratio of P-wave and S-wave velocity,Young's modulus and Poisson's ratio.By combining Lame coefficient and densityλρas well as shear modulus and densityμρdata,favorable reservoirs can be effectively identified if the following conditions are met:38.02GPa·g/cm3<λρ<67.38GPa·g/cm3 and 39.51GPa·g/cm3<μρ<53.84GPa·g/cm3.The results obtained by the proposed approach were consistent with the interpretation of well log data,confirming that the proposed approach can be used to support sweet spots prediction,logging interpretation,and theoretical modeling of rock physics.