Inference of near-borehole permeability and water saturation from time-lapse oil-water production logs

In a synthetic reservoir model supported by an infinite-acting aquifer, the coupled flow algorithm integrates production logs acquired in time-lapse mode to construct a near-borehole reservoir model that describes depth variations of skin factor over the elapsed time. Feasibility studies show that the estimated petrophysical properties can be adversely influenced by the large volume of investigation associated with PL measurements. Moreover, undetectable fluid production across low-permeability layers decreases the sensitivity of production logs to layer incremental flow rate, thus increasing estimation uncertainty. Despite these limitations, estimated fluid saturation and permeability across high-permeability layers are within 15% and 20% of the corresponding actual values, respectively. The developed interpretation algorithm additionally integrates well logs and production logs acquired in an oil-water field example to construct a PL-calibrated near-borehole reservoir model. Results enable (a) the differentiation of low-permeability layers from highly-damaged formations, (b) the identification of layers accountable for high water production, and (c) the quantification of the added value of remedial workover operations to isolate water-producing layers. In addition, the coupled model is used to study sensitivity of production logs to near-borehole petrophysical properties. We show that production logs are mainly sensitive to formations' absolute and relative permeabilities, water saturation, and pressure.