Multi-Scale Sedimentary Forward Reservoir Modelling: A Disruptive Solution for Simulating Heterogeneity in Carbonates. Application to the Kharaib-2 Reservoir Unit

Abstract

In mature hydrocarbon provinces, the intense operational activity on each field to monitor production through drilling and work-over operations, as well as the continuous updating of the reservoir models that drive these operations, leads each asset to concentrate its efforts on work at the scale of the field for which it is responsible. This focus is consistent with both data acquisition, which is targeted on the zones of interest, and with the restrictive use of this data prior to the modelling phase. By giving priority to statistics (Vertical Proportion Curves, occurrence tables between facies and rock-types, distributions of petrophysical variables, etc.), data analysis before modelling favors an understanding of reservoir heterogeneity at the scale of the field, to the detriment of a more regional understanding. Reservoir modeling techniques, which to date are essentially geostatistical, also maintain this focus on data rather than knowledge. By failing to challenge the relevance and the consistency of the geological concept used to apply interpolation techniques, the geostatistics-based modelling process deprives the user of the opportunity to validate or invalidate a number of assumptions that are nonetheless crucial in terms of model outcomes (Borgomano et al, 2020). On the other hand, effectively integrating at the regional scale the stream of data coming from the different fields would require a common framework and unifying concepts. In vast regions such as the Middle East, the size and density of wells in each field relative to the distance between fields makes it tricky to create this truly integrative framework. Synthetic or a selection of representative logs are thus used to build regional models. The distances between fields larger than the range of any variogram make also geological processes the only possible unifying concepts. Thus, geological models should be built by simulating the geological processes at the regional level and including several fields, in such a way as to be consistent in terms of geology, with little dependence on available data, and with a variable resolution adapted to needs and constraints. In the absence of such models, forecasting in prospective areas is always uncertain, even during intensive exploration. One of the major challenges of geological modelling is currently to test and validate at the regional scale the concepts used at the reservoir scale, to capitalize in regional models the detailed knowledge gathered in the fields, and to bring into reservoir models the regional understanding after validation. The disruptive approach presented in this paper addresses this issue, with a first application on the Kharaib-2, a carbonate reservoir unit from the Middle East.