Integrated Uncertainty Study for Resources Evaluation Under Operational Constraints

Abstract

Total E&P has developed for its fields an integrated workflow to assess the 2G&R uncertainties which provides a Resource evaluation distribution through the integrated Geoscience platform. If the uncertainty study also considers the operational limitations by integrating them in the modeling process, the reliability of the outputs is clearly improved. The objective of this study was to provide an evaluation of In-Place and Resource on a deep-offshore discovery located in the Gulf of Mexico while assessing not only the multiple Geoscience uncertainties but also capturing the operational constraints identified for this future development. The discovery, located under a salt canopy with a thickness up to 18’000 feet, had limitation from seismic imaging for the field interpretation. The well penetrations proved that the reservoir was highly compartmentalized and most of the faults were not seen on seismic. On top of this lateral disconnection, for each of the compartments the fluid contact depends on the structural horizons which are, on their turn, uncertain. The bulk of the information comes from few appraisal wells. Last but not least, the completions of the future development wells should integrate the drilling and well architecture limitations. All these uncertainties and constraints were managed in an integrated workflow using a Monte-Carlo Nested Multi-Realization approach. First, the structural uncertainties impact the grid which is distorted for every realization. Second, the filling of the grid with facies and petrophysical properties is done considering global and local geostatistical uncertainties. The contacts distributions are defined for almost hundred compartments. For some of them, the contacts are defined as a function of a crest, for others – a function of a spill while both (crest and spill depths) vary with the structure from one realization to another. The dynamic uncertainties on the permeability multipliers and on the relative permeability curves are considered as well. The risk of having more active faults than seen on seismic is mitigated by randomly sealing additional faults. The modeling chain also takes into account the completion limitations on future development wells. The completion tally design (minimum distance between screens and total distance of the completion intervals) are tailored to every realization in an automatic manner. The novelty of this work is that the different sources of uncertainties and the operational constraints are not modeled in separated workflows (e.g.: geophysics + geology + dynamic + completion design) but included in a single automatic process while parametrizing their complex dependencies. Thus, the eventual interactions and non-linear effects of a combination of all parameters can be anticipated, therefore providing a more accurate evaluation for decision making and development options.