Field A is being developed by a drilling campaign.
The data acquired in this field during the exploration and appraisal phases have been limited to conventional triple combo tools, formation pressures and samples with various data quality. This limitation was essentially due to the need to perform the data acquisition using Though Logging Condition (TLC), e.g. pipe conveyed logging operations.
The Field A drilling operations require high mud weight in order to ensure well bore stability. This implies having wells drilled with high overbalance (more than 2000PSI). Conventional wireline operations have proven risky, with a high chance of getting stuck tools. Therefore, the pipe conveyed operation is the safer but costlier solution to get wireline data, thus limiting the number of runs to optimize the rig time.
In view of the lack of advanced tools such as NMR, image log and 3D resistivity tools, the field was firstly evaluated using a conventional petrophysical approach. Nonetheless, there were still some questions with regards to the discrepancy between low hydrocarbon saturations calculated from the conventional petrophysical evaluation techniques and the drill stem test (DST) performance results in some zones.
By relooking at all the available data it was possible to realize that the geological environment was prone to thin bed presence with sand thicknesses ranging from 0.5 to 1 meter. These sand / shale intercalations in the zones of interest decrease the resistivity readings and thus increase the water saturation when using conventional petrophysical evaluation techniques.
Re-evaluating the field with a different mind-set using the thin bed analysis approach has helped to reconcile DST outcomes with the formation evaluation results and has increased the estimated volume initially in place, thus making the field economics more robust. It has also helped to consider new zones to be perforated in the development wells, and therefore has increased the production well performance.
Based on the Field A experience and learnings, re-interpretation of wells in nearby fields located in the same geological environment are now being considered following the same re-evaluation approach to look for potential volume / reserve upside(s) through behind casing opportunities and new development wells targeting additional zones of interest.
