Preparation of Reference Materials for Rock Evaluation of Mudstone

As an oil and gas geochemical detection and analysis technology, rock pyrolysis is widely used in oil and gas exploration. Moreover, this technology is fast, economical, and effective in evaluating the hydrocarbon-generating potential of source rocks and identifying the oiliness of reservoir rocks. Rock pyrolysis standard materials are used for the calibration and quality monitoring of rock pyrolysis instruments, as well as being the key material basis for quantitative calculation of rock pyrolysis analysis parameters for source and reservoir rocks. At present, rock pyrolysis standard materials are relatively scarce, and most of the on-site mud logging rock pyrolysis tests use value transfer samples for instrument calibration and quality control, which brings uncertainties to data quality. At the same time, the rock pyrolysis standard material in China lacks the important parameter S₄ for source rock evaluation, while the rock pyrolysis standard material in foreign countries has only one value and cannot be used for gradient calibration. Therefore, it cannot meet the application and development requirements of rock pyrolysis analysis technology in oil and gas exploration.

To develop five kinds of reference materials for rock pyrolysis, with a certain gradient value of each parameter, which can satisfy the needs of conventional oil and gas testing in petroleum exploration.

Candidate samples were collected from dark mudstone, oil shale and carbonaceous mudstone in the Triassic Yanchang Formation, Permian Shanxi Formation, Taiyuan Formation and Carboniferous Benxi Formation in the Ordos Basin. After impurity treatment, jaw crushing, ball mill fine grinding, powder sieving 200 mesh, mixer mixing, ⁶⁰Co irradiation disinfection and sterilization, and passing the preliminary homogeneity test, the samples were packed and numbered.

For each candidate, 5×30 bottles of samples were randomly selected for uniformity testing, and the measured values of F were all less than F_0.05(29, 60). There was no significant systematic difference within and between groups of samples, and the uniformity was good. Short-term stability and long-term stability were tested by the straight line fitting method, and the slope of the fitting line |b₁| < t_0.05·S(b₁), had good stability. Eight laboratories adopted the rock pyrolysis analysis method for collaborative determination. All of the determination analysis data conformed to the normal distribution, and the determination results and corresponding uncertainties were obtained. The fixed value parameters are S₂, T_max, S₄ and reference value S₁, wherein the value range of S₂ is 2.01-11.90mg/g, the value range of T_max is 437-442℃, the value range of S₄ is 9.5-29.9mg/g.

In accordance with the national standard material research standards and specifications, five reference materials for rock pyrolysis, GBW(E)070323, GBW(E)070324, GBW(E)070325, GBW(E)070326 and GBW(E)070327, were successfully developed. The value of each parameter presents a certain gradient, which basically covers the content range of conventional pyrolysis analysis.