Abstract
The light hydrocarbon content ( S 1 ) of shale oil is lost in aboveground experimental measurements, which do not accurately reflect actual underground light hydrocarbon content and cannot meet the demands of resource quantity calculation. Based on field and laboratory experimental data from the second member of the Kongdian Formation in the Cangdong Sag, Bohai Bay Basin, the retained oil and movable oil contents in shale were calculated using a mathematical formula, and the total resources were quantified. The correction coefficient of S 1 from pyrolysis and the adsorption of oil by the total organic carbon (TOC) were determined to be 1.25 and 100 mg/g, respectively. The calculated parameter movable oil content ( S movable ) and the corresponding calculation formula of S 1 are proposed. The lower limit of S 1 is 100 mg HC/g rock, the TOC content is 4 wt % and 6 wt %, and the corrected movable oil content of 3 mg/g and 6 mg/g, respectively, will be of great significance in shale oil geology and engineering. The optimal geological and engineering settings are divided into three categories and eight subcategories on the basis of these findings. Methods for evaluating total, movable, and recoverable oil resources from shale are discussed, which elucidate a new method for quantitative evaluation and ranking of shale oil resources. This approach is suitable for application in other shale oil exploration and development areas globally.
Highlights
Compared with North American shale oil, China’s lacustrine oil shales are quite different in terms of reservoir and fluid properties and reservoir transformation characteristics [1, 2]
The total organic carbon (TOC) content varies greatly from 0.7% to 28%; the vitrinite reflectance is generally lower than 1.0%; the light oil content is relatively small; the porosity and permeability are relatively poor, and the pore throat diameter is less than 300 nm; the fluid viscosity is up to 350.0 MPa·s; the density is between 0.67 and 0.94 g/cm3 [4,5,6]
Pyrolysis S1 combined with the oil saturation index OSI (S1/TOC) is the key parameter for shale oil bearing and mobility evaluation [11, 12]
Summary
Compared with North American shale oil, China’s lacustrine oil shales are quite different in terms of reservoir and fluid properties and reservoir transformation characteristics [1, 2]. There are three principal evaluation methods for shale oil resource evaluation: analogy, volumetric, and genetic methods [8]. The analogy method is used to estimate oil and gas resources by comparing it with oil and gas fields with similar geological characteristics. S1 is the key parameter for shale oil bearing evaluation, which is consistent with the concept of oil saturation in sandstone reservoirs. Pyrolysis S1 combined with the oil saturation index OSI (S1/TOC) is the key parameter for shale oil bearing and mobility evaluation [11, 12]. Methods for accurately correcting S1 parameters to reflect the quantity of free oil in the underground shale
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