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 V_b, grain volume V_g, and pore volume V_p). 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 (V_b, V_g, V_p), 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 (R_o < 1.2%), where the increase reached up to 0.56%. (2) Drying temperatures exceeding 105℃ led to the removal of interlayer water in clay minerals and a systematic reduction in pore volume (average decrease of 4.2%), while drying at 90–105℃ for 24–36 h was identified as the optimal parameter balancing efficient dehydration and structural preservation. (3) Among volume parameter measurements, the error in V_b measurement was the primary source of porosity data dispersion (its error was on average 3.8 times that of V_p error). (4) The optimized direct measurement method (measuring V_p and V_g) 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 V_p and V_g) effectively addresses error propagation in volume measurement, enabling high-precision porosity testing.