Optimization of Porosity Testing Methods for Shale Oil Reservoirs and Application in the Jurassic System of the Sichuan Basin

Porosity is a core parameter in the evaluation of shale oil reservoirs. The accuracy of its measurement is constrained by two main issues: the lack of standardized pretreatment procedures (oil washing and drying) and an unclear error propagation mechanism resulting from the selection of different volume parameters (bulk volume Vb, grain volume Vg, and pore volume Vp). To systematically analyze the influencing factors on porosity test results and establish a high-precision testing method, 8 sets of 16 core samples from Jurassic shale oil reservoirs in the Sichuan Basin were selected. Comparative porosity experiments were conducted using differentiated pretreatment workflows (with/without oil washing, gradient temperature/duration drying) and measurements of different volume parameters (Vb, Vg, Vp), with reference materials introduced to optimize the measurement method. The results showed the following: (1) Oil washing significantly released pore space, with an average absolute increase in porosity of 0.32%, particularly more pronounced in low-maturity samples (Ro Vb measurement was the primary source of porosity data dispersion (its error was on average 3.8 times that of Vp error). (4) The optimized direct measurement method (measuring Vp and Vg) significantly enhanced the repeatability and accuracy of porosity results (with a 76.8% reduction in repeatability error). In conclusion, oil washing pretreatment is essential prior to porosity testing in shale oil reservoirs (especially for low-maturity samples); strict control of drying temperature (≤105℃) is critical for obtaining accurate pore volume; and the optimized method (direct measurement of Vp and Vg) effectively addresses error propagation in volume measurement, enabling high-precision porosity testing.