Demonstrating the Value of Early Incorporation of Dynamic Data during Probabilistic Assessment for a Niger Delta Gas Condensate Reservoir

Abstract

The paper aims to highlight the importance of using adequate dynamic data to ground-truth reservoir simulation models early in the production life of a field. This study also highlights the benefits of adequate instrumentation and data capture, as well as the need to review assumptions made for green fields in their first few production years. This study reviews two vintages of probabilistic assessment for an offshore gas condensate reservoir. An earlier probabilistic assessment for the case study reservoir was built based primarily on core data from two analogous reservoirs, one of which was from the same field, prior to the availability of bottom hole pressure and drawdown data. Initial history match and forecasts showed a significantly poor production performance with significant impact on the condensate reserves volumes from the single well in the reservoir. Following the acquisition of pressure data from the downhole gauges and pressure transient analyses results, the model recalibrated in line with estimated distance to boundaries, drawdown and productivity indices. Incorporating the additional data from the downhole instrumentation during the history match showed the earth model severely underestimated the permeability of the reservoir. Matching the drawdown and well test data required a significant permeability multiplier for the low and mid case models for the reservoir. A comparison of results from both model vintages showed significant differences in the expected production plateau for the reservoir and consequently reserves estimates. These finding demonstrates value of the acquisition of multiple downhole dynamic data and the pitfalls with reservoir performance forecasts and reserves assessments when simulation models are not adequately constrained with dynamic well data early in the production life of the reservoir.