Active well rate management is a simple way to increase recovery in brown fields while minimizing costs and preserving existing field/well fluid handling constraints. In this work, we present the application of an efficient flow-based surveillance technique to drive rate management decisions for the 8th Tortonian reservoir in the Vienna Basin, Austria. The 8th Tortonian is a typical example of a decade-long peripheral water flood on a long, steady decline for which it is difficult to justify expensive drilling/workover programs. Active rate management to improve sweep patterns presents a cheap solution to increase recovery. In case of the 8th Tortonian, Euro 10,000 (US$13,000) were spent to modify well rates resulting in ∼5700 m³ (∼35000 STB) incremental oil recovered over a 30-month period. The current oil rate remains above the oil rate before the start of the project.
Our approach takes advantage of streamline-derived well allocation factors (WAF's) that quantify injector-producer connections. It is simple and efficient to estimate WAF's using total historical well fluid rates, well locations, and a geological model. The geological model can vary in complexity from being a single homogenous layer to a sophisticated, 3D geo-model. With the WAF's known, the efficiency of each injector/producer pair can be estimated by using the historical observed phase rates times the well allocation factors. Well pair efficiencies are the starting point for the rate management approach described in this work.
A simple, single homogenous layer system was used in conjunction with historical rates and well locations to estimate the WAF's for the 8th Tortonian reservoir. Connections were compared to available tracer data, and an area of interest was subsequently selected based on streamlines and tracer data both indicating recovery by injected water. A key constraint was to maintain the total gross rate of the area selected at current capacity. New target rates we determined and implemented resulting in a 30% increase of oil rate over a 30 month period. Considering the simplicity and efficiency of the approach, this is a notable result. The production response of the selected wells showed an increased recovery in conjunction with a decreasing watercut suggesting contact with previously unswept oil. All operations and modifications were done at minimum cost. There were no perforation changes or acidizing jobs involved and rate changes were obtained simply by changing pump sizes or increasing the number of strokes by changing the V-belt pulley.