SISMAGE-CIG: OPTIMIZED MANAGEMENT OF THE UNCERTAINTY ASSESSMENT CHAIN
At Total, we are renowned for our cutting-edge expertise in assessing the uncertainties inherent in reservoir modeling. Our proprietary tools make it possible to fully integrate them and measure their combined impact on a field's production profiles. Now operating on Sismage-CIG (Geoscience and Reservoir Integrated Platform), these tools optimize our reservoir assessment and development strategies.
Approximate knowledge of reservoirs
As oil development projects require substantial investments, the steps of assessing uncertainty and defining risks are an important part of the decision-making process. For a reservoir, “uncertainty” is defined as the variation domain containing all possible representations of the reservoir; “risk” refers to the subset of the variation domain that would cause the development project to fail.
The geosciences and reservoir study chain is responsible for providing management with an objective, quantitative report on these uncertainties and their impact (on production profiles, reserves and any other factors that affect project profitability) so as to correctly assess the project risk.
Uncertainties are an integral part of a reservoir study. Reservoir data, whether 1D (drilling excavations, core samples or well logs), 2D or 3D seismic, involve a certain degree of uncertainty, which increases as one moves further away from the study area surrounding the wells (several hundred meters due to spatial correlation).
At any rate, the envelope, internal architecture and petrophysical attributes of the reservoir are uncertain in a significant portion of the area of interest. As a result, there are uncertainties with regard to existing volumes, well productivity over time (flow rates and fluid ratios) and the consequences of injection methods.
Process for quantifying uncertainties, from the generation of geological multi-realizations to the hydrocarbon maps. Sismage-CIG.
ALEA, JACTA/LIGHT-UP and EST: a geosciences chain of proprietary tools
Our proprietary tools were designed to explore the entire area of possibility and incorporate all uncertainties—structural (reservoir geometry), geological (filled volume of the reservoir) and dynamic (flow behavior of the reservoir)—at every stage of the study chain into a consistent, meaningful model. Under development continuously since the early 2000s, this chain of geosciences tools (ALEA, JACTA/LIGHT-UP, EST) has now been implemented on the Sismage-CIG (Geoscience and Reservoir Integrated Platform) platform.
- ALEA, renamed EASY ALEA when it was incorporated into Sismage-CIG, is used to evaluate the geophysical uncertainties resulting from the reservoir geometry (envelope and extent) for each major stage of the seismic interpretation process (data quality, interpreting horizon and fault picking, seismic-to-well ties, time/depth conversions, etc.). After being identified and quantified, all these uncertainties are compiled during multi-realization work and transmitted to the next “link” in the study chain.
- JACTA/LIGHT-UP is used to evaluate uncertainties resulting from the filled volume of the geological model (facies, petrophysical properties). This tool offers two approaches for managing geological uncertainties, both of which are based on evaluating uncertainties using the same configuration (identification and quantification). The LIGHT-UP approach explores the impact of each source of uncertainty on the existing hydrocarbon volume and combines these impacts to accurately estimate the distribution of this volume; the Jacta or multi-realization approach follows the same process as ALEA (multi-realization processing), in order to eventually deliver the probabilistic distribution of existing hydrocarbons.
Next part of the process: quantifying uncertainties for the deposits and the production profile for a field.
- EST, the last link in the chain, manages the flow simulator in order to orchestrate the calculation of dynamic uncertainties resulting from fluid mechanics and how these are produced, by examining all possible representations of the reservoir given the static uncertainties impacting it. At this stage, complex mathematical methods (experimental design) are used to limit the number of simulations. These operations are carried out by performing “smart” sampling of the areas of possibility with a limited number of calculation points. This last step is used to anticipate probabilistic production profiles and an overall distribution of the reserves in the field.
Integrated geosciences chain: optimal synergy with the 2G&R study workflow
Incorporating our uncertainty assessment tools into Sismage-CIG considerably fluidifies the workflow for this part of the studies. Formerly spread across a host of different software and various languages, the tools in the uncertainty chain are now fully integrated into and synergized with the 2G&R interpretation and modeling workflow. The benefits of this development include:
- easier migration of results from one tool to another, helping to ensure that seemingly minor hypotheses are not overlooked so that all uncertainties are better accounted for across all parameters,
- the ability to easily “replay” the whole workflow when a new hypothesis or new information is discovered (reinterpreting seismic acquisition, drilling a new well, lab results for recent core samples, etc.),
- the long-standing ALEA-JACTA-EST chain is enhanced thanks to the ongoing implementation of innovations from our R&D: tools for analyzing results (calculating connected volumes, creating probabilistic maps of the hydrocarbon column and selecting models) or new modeling techniques (multipoint statistical method for geostatic simulations, new object methods, etc.).