Abstract
<jats:p>Relevance. The vereian deposits of Perm Region are characterized by heterogeneous geological structure, and the wells producing from them exhibit a rapid decline in fluid production rates during the initial production period. This complicates both short-term and long-term hydrocarbon production planning. The relevance of this work is driven by the need for a quantitative forecast of the productivity index change in producing wells operating in the vereian deposits. This work enables a quantitative assessment of the "reservoir–well" system degradation through changes in the productivity index and can be used to enhance well production forecast accuracy and optimize their operating conditions. Aim. To develop a methodology for determining and forecasting changes in the oil well productivity index over time based on actual field data, and to identify key factors affecting the rate of productivity index decline in producing wells. Object. Oil-producing wells exploiting the vereian carbonate deposits in the Southern group of fields in Perm Region. Methods. An analysis of historical well test data was performed for wells meeting specific research criteria. The well productivity index was normalized relative to its initial value and approximated by a linear function. Multiple linear regression was chosen as the forecasting algorithm due to its high interpretability, making it well-suited for scientific research. The authors built a multiple linear regression model for coefficient a (the slope of the linear function approximating the normalized productivity index) based on a set of geological and physical reservoir parameters and technological well performance indicators. The statistical significance of the factors was assessed using the t-test (P-value), the unique contribution of each factor was evaluated via Partial R², and a preliminary analysis for multicollinearity among the initial features was conducted. Results. A linear decline in the productivity index of producing wells was established; the average drop in the productivity index for the studied wells during the first five years of operation is ~35%. The authors developed the empirical multiple linear regression model, linking the rate of productivity index decline with initial reservoir pressure near the well, oil degassing level, drawdown value, and other field factors. The developed model demonstrates high quality metrics (R²=0.75). The practical application of the obtained results lies in the ability to forecast production decline for new producing wells exploiting vereian deposits and to optimize their operating conditions. The developed methodology is suitable for application when a similar set of initial data is available. For citation: Stepanenko I.B., Lekomtsev A.V. Methodology for assessing the productivity index change in oil wells (case study of the vereian deposits in Perm Region). Bulletin of the Tomsk Polytechnic University. Geo Assets Engineering, 2026, vol. 337, no. 3, pp. 202–220. https://doi.org/10.18799/24131830/2026/3/5500</jats:p>