Shale porosity measurement by the saturated oil method: Removing the contribution from oils dissolved in kerogen

Shale porosity measurements have crucial scientific and economical applications in unconventionalpetroleum systems. As a standard technique, liquid saturation methods, including water saturation (WS)and oil saturation (OS), have been widely used to measure the porosity of many rock types. For clay-richshale reservoirs with high organic matter content, it is well known that the WS method may cause clayswelling and induce structural changes in the pore system. The OS method affects the accuracy ofporosity measurements because of some of the oil being dissolved by kerogen within the shale;however,this has not received sufficient research attention. In this study, we compare the previously reported andnewly tested OS porosities with helium (He) expansion porosity. Results show that OS porosity generallyexceeds the He porosity. Furthermore, the higher the total organic carbon (TOC) content and lower thematurity of shale, the greater the difference between the OS and helium porosities. When using the OSmethod, the effect of kerogen-dissolved oil causes an overestimation of the shale porosity by ~30%. To thebest of our knowledge, this is the first time to note the kerogen-dissolve oil effects on OS porosity. Herein,we propose a new, simple, and effective correction method for estimating OS porosity that involvessubtracting the kerogen-dissolved oil content from raw OS porosity. In addition, the quantification modelof kerogen-dissolved oil capacity is established, taking into account the abundance and maturity oforganic matter. Taking the He porosity as the benchmark, the absolute error of the corrected OS porositydoes not exceed 1% and the average relative error is only ~10%. The obtained results can help improve theaccuracy of shale porosity evaluation methods.

The key parameter of shale oil resource evaluation: Oil content

The United States has become the world's largest oil producer of shale oil. China has abundant shale oil resources, but its resource potential has not yet been exploited. The core of the evaluation is the selection of parameters and their reliability. By combining the parameters of the shale oil resource evaluation, we investigated the key parameters in the evaluation model and reviewed the research results. The adsorption and retention of heavy hydrocarbons, loss of light hydrocarbons, and original oil saturation are key in the evaluation of shale oil resources. The adsorption and retention of heavy hydrocarbons can be determined by the pyrolysis, FID curve, and hydrocarbon generation kinetics of shale before and after extraction. The loss of light hydrocarbons mainly occurs in coring(change in temperature and pressure),sample treatment, which can be evaluated using the GC spectrum, rock pyrolysis, crude oil volume coefficient, mass balance, component hydrocarbon generation kinetics, and other methods. The original oil saturation evaluation includes indirect, direct, logging, and simulation methods. The most reliable parameters can be obtained by using the sealed or pressure-maintained coring immediately after thawing(without crushing), and the recovery of light hydrocarbon loss is critical for the resource evaluation of medium to high mature shale. Therefore, the experimental determination of shale oil content and the study of the influencing factors of the parameters should be strengthened.