Understanding The Uncertainties…

Understanding The Uncertainties In Geomodeling Process, An Awareness for Risks Mitigation (Case Study of “S” Field, East Sulawesi)

Kwartono, Neni Herawati , Sugiyanto, Anies Baasir


The uncertainty is exist from subsurface to surface facililties, effecting a large element of decisions making. These uncertainties, without exception, exists across the workflow within all the process of “S” field development plan. This paper is focus on describing the uncertainty in the 3-D static geomodeling process. The information from uncertainty analysis provides an understanding of the reservoir behaviour for accurate assessment and reservoir performance prediction. Uncertainty analysis, along with sensitivity quantification,  could also be used to identify which area requires a detail consideration, or where more data collection is required.
The key uncertainty in “S” 3-D geomodeling  have been analized to map the risks that may encountered in the future. It includes seismic interpretation, time to depth conversion, porosity-permeability transform for a certain facies, facies prediction for un-cored intervals, facies/properties distribution based on geostatistics, water contact,and water saturation analysis from cappilary pressure/J-function analysis.
The uncertainty analysis was commenced by defining a base case model, represents the best  estimation. Subsequently,  uncertainty parameters were varied to quantify the effect of each variable toward OGIP and impact of sensitive variable on reservoir performance.  The Monte Carlo technique was applied by certain distribution method. In “S” case, a triangular distribution was selected. After a thousand realizations (runs), the representative P10,P50 and P90 of OGIP were plotted in a histogram.
In further process, uncertainty will also be analyzed in dynamic model (history matching and production forecasting) in accordance with fracture existence and the relative permability end point estimation. It is suspected that those two variables impact the cummulative gas production and water coning that imply on plataeu time (deliverability).


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