The paper introduces and validates productivity logging, an advanced production-logging interpretation methodology based on pressure transposition, deconvolution, and transient analysis, designed for vertical reservoir diagnostics in multilayer formations. The approach overcomes the limitations of conventional multi-rate production logging tests (PLT) based solely on inflow performance relationship (IPR) analysis and delivers extended diagnostic capabilities. It enables estimation of formation pressure, productivity index, transmissibility, and skin factor for each interval in commingled wells, providing deeper reservoir insight and supporting quantitative evaluation of production-enhancement opportunities in multilayer systems.
Advanced multi-rate PLT-PTA analysis performs pressure transposition by simulating borehole flow and matching it to pressure records acquired at different times and depths during the PLT survey. The transposed data simulate the pressure response across each inflow or injection interval and, when coupled with flow rate responses fr om the PLT, are used to deconvolve a single-rate transient pressure response, as if the well were undergoing a conventional well test on each inflow or injection interval independently. Each reconstructed transient response is interpreted using conventional pressure transient analysis (PTA), providing estimates of formation pressure, productivity index, transmissibility, and skin factor.
The technology was extensively tested through numerical simulations of commingled production and injection in multilayer formations with realistic data contamination. The simulations were conducted in triple-rate mode with total durations ranging from one to three days, covering formations with permeability from 0.1 mD to 1,000 mD and saturated with water, oil, or gas. Conventional IPR-based interpretation under these conditions demonstrated substantially nonlinear behavior and poor accuracy in predicting formation pressure and productivity. In contrast, the productivity logging methodology showed a reliable ability to retrieve reservoir properties even in complex cases, such as behind-casing or borehole crossflow during production or injection.
Field applications of productivity logging encountered limitations similar to those of conventional PLT, primarily related to the limited accuracy of flow-rate estimation from mechanical spinner tools and, in some cases, operational constraints preventing the well from being tested at sufficiently different rates. However, in all cases wh ere the well could be tested at a minimum of three distinct flow rates with measurable spinner response, productivity logging reliably retrieved the target reservoir properties, including formation pressure, productivity index, transmissibility, and skin factor. The results were indirectly verified through subsequent shut-in pressure buildup analysis and stabilized IPR interpretation derived from long-term triple-rate PLT data.
Conventional multi-rate PLTs require prolonged stabilization at each flow rate to ensure a constant productivity index and linear pressure–rate behavior on the IPR plot. Without proper stabilization, the accuracy of formation pressure and productivity estimates becomes unreliable. productivity logging provides a time-efficient (typically one to three days) and technically robust alternative for formation characterization, enabling reliable layer-specific evaluation and supporting selective stimulation and waterflood optimization planning in multilayer reservoir systems.
