Classification evaluation method for Chang 7 oil group of Yanchang formation in Ordos Basin

Abstract The Chang 7 oil group in the Ordos Basin has the characteristics of a tight lithology, a low formation pressure coefficient and strong reservoir heterogeneity. To better determine reasonable developmental technical countermeasures, oiliness, seepage capacity, and compressibility evaluations are combined. Using a combination of field practice and laboratory experiments, six types of sweetness classification evaluation parameters are screened: oil saturation, longitudinal oil layer structure coefficient, average pore throat radius, gas-oil ratio, brittleness index, and minimum horizontal principal stress. By combining the relationships among variables with the initial production from directional wells, the gray correlation method is used to quantify the weights of the contributions of evaluation parameters to production. On this basis, using the difference method for the curve slope, a sweetness evaluation and classification method for the Chang 7 oil group is constructed, and it solves the difficult problem of quality difference classification for the Chang 7 oil group and provides a reference basis for the optimal design of well patterns and fracturing reconstruction parameters.