Abstract

Uncertainty analysis is usually conducted during field development, in order to quantify the uncertainty within the field, its impact on the recovery and the development strategy used in developing the field. However, uncertainty analysis usually focuses on field level, with little or no analysis done on the direct impact of well placement within uncertain region and it's impact on the field recovery i.e. well level uncertainty analysis. In order to investigate this and as a part the field phase development strategy, a thorough uncertainty analysis was conducted both on the field and well level. The field level uncertainty was done in order to quantify the reservoir uncertainty, and its effect on the production plateau length. The well level uncertainty was done, in order to optimize well placement and its effect of future recovery.

In order quantify the uncertainty in the field, the main uncertain parameters and their respective ranges were first identified using the data available. Once defined their respective impact on stock tank oil initially in place (STOIIP) and cumulative production was calculated by sensitivity analysis. Monte Carlo simulation was then used to combine the different parameters, in order to obtain a pessimistic, base and optimistic case. Well level uncertainty analysis was conducted using FSCAT analysis, to ensure that based on the current well location, future well location and cumulative production to date, each well was capable of delivering the predicted rate forecasted. Wells within high uncertain regions or with lower potential in meet production plateau were highlighted for relocation in the field development strategy.

The main uncertainty parameters identified in the field based on existing data were, oil water contact (OWC), Pressure Volume Temperature (PVT) oil formation volume factor (Bo), saturation height (rock type), structure and reservoir connectivity (poro/perm). Sensitivity analysis showed that structure has the highest impact on the STOIIP, while reservoir connectivity showed the smallest impact. The well level uncertainty analysis used a combination of conventional and streamline simulator, in order to produce a more robust form of decline curve analysis (DCA) using FSCAT analysis. This analysis allowed the calculation of the remaining oil per well that can be produced.

This paper describes how the uncertainty analysis was conducted on a field and well level, by combining the conventional simulator (compositional) and streamline simulator. As a result of this uncertainty analysis, the P10, P50 and P90 cases were created. The base case (P50) showed it is possible to maintain plateau to 2043. The well level analysis showed that, each well could produce the forecasted production based on its current location in the base case (P50). Wells potential map could be used in optimizing well placement.

Novel/Additive Information: Combined conventional and streamline simulation, in order to conduct a more robust uncertainty analysis and improved well placement strategy in field development.

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