Variations in reservoir seismic properties can be correlated to changes in saturated-fluid properties. Thus, the determination of variation in petrophysical properties of carbonate-bearing rocks is of interest to the oil exploration industry because unconventional oils, such as bitumen (HHC), are emerging as an alternative hydrocarbon reserve. We have investigated the temperature effects on laboratory seismic wave velocities of HHC-bearing carbonate rocks belonging to the Bolognano Formation (Majella Mountain, central Italy), which can be defined as a natural laboratory to study carbonate reservoir properties. We conduct an initial characterization in terms of porosity and density for the carbonate-bearing samples and then density and viscosity measurements for the residual HHC, extracted by HCl dissolution of the hosting rock. Acoustic wave velocities are recorded from ambient temperature to 90°C. Our acoustic velocity data point out an inverse relationship with temperature, and compressional (P) and shear (S) wave velocities show a distinct trend with increasing temperature depending on the amount of HHC content. Indeed, samples with the highest HHC content show a larger gradient of velocity changes in the temperature range of approximately 50°C–60°C, suggesting that the bitumen can be in a fluid state. Conversely, below approximately 50°C, the velocity gradient is lower because, at this temperature, bitumen can change its phase in a solid state. We also propose a theoretical model to predict the P-wave velocity change at different initial porosities for HHC-saturated samples suggesting that the velocity change mainly is related to the absolute volume of HHC.

中文翻译：

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从实验室到模型，随着温度升高，含沥青碳酸盐的岩石物理性质变化

储层地震特性的变化可以与饱和流体特性的变化相关。因此，确定含碳酸盐岩石岩石物性的变化是石油勘探行业关注的问题，因为非常规石油（例如沥青（HHC））正在作为一种替代性的碳氢化合物储量出现。我们已经研究了温度对属于Bolognano组（意大利中部马耶拉山）的HHC含碳酸盐岩石实验室地震波速度的影响，该岩石可以被定义为研究碳酸盐岩储层性质的天然实验室。我们对含碳酸盐样品的孔隙率和密度进行了初步表征，然后对残留的HHC进行了密度和粘度测量，这些残留的HHC是通过HCl溶解在宿主岩中提取的。记录从环境温度到90°C的声波速度。我们的声速数据指出了与温度成反比的关系，根据HHC含量的不同，压缩（P）和剪切（S）的波速随温度升高显示出明显的趋势。确实，具有最高HHC含量的样品在大约50°C–60°C的温度范围内显示出较大的速度变化梯度，这表明沥青可以处于流体状态。相反，在低于约50°C时，速度梯度会降低，因为在此温度下，沥青会以固态改变其相。我们还提出了一个理论模型来预测HHC饱和样品在不同初始孔隙率下的P波速度变化，这表明速度变化主要与HHC的绝对体积有关。