Controls on Vertical and Horizontal Flow in a Carbonate Reservoir that Impact Gasflooding and Waterflooding

Abstract

Abstract Identifying the location and quantification of flow units is critical to managing a reservoir's production and achieving maximum recovery. Gas injection is planned in a limestone reservoir offshore Abu Dhabi. To understand the benefits of future full field gas flooding, a pilot covering three reservoir units is underway. Ten wells were drilled and significant log/core data acquired. Interference tests within a reservoir unit in single wells and between-wells have revealed useful insights into the vertical and lateral continuity of barriers and conduits to flow. Recovery efficiency is driven by these contrasts in the reservoir sublayers. Significant variations in permeability occur over short vertical distances due to local facies and diagenetic changes, including dissolution events, distorting associations between porosity and permeability. Porosity cannot predict permeability to better than 1.5 decade on a logarithmic scale in this reservoir. Experimenting with NMR, Stoneley wave responses on one well, we were able to improve our predictive capabilities by combining the strengths of each tool. Predicted values fell mostly within half a log cycle of the whole core measurements. Vertical interference testing with a multi-probe Modular Dynamic Formation Tester (MDT*) used in a totally new way and using single well numerical models, proved useful in defining vertical barriers to flow. Cross-well interference testing proved that some of these barriers are discontinuous and act as baffles. Mobilities obtained from the MDTs, mimicked permeability contrasts measured in core. These contrasts confirmed the rapid response time seen in the cross-well interference tests. A full field simulation model with local grid refinement was able to match the cross-well interference test data. The integration of core description, whole core/plug physical properties, downhole electrical images, NMR, conventional logs, mobility, down-hole vertical as well as cross-well interference tests is presented and their impact discussed.