Integrated Uncertainty Assessment for Project Evaluation and Risk Analysis

SummaryThe main technical contribution of the study presented in this paper was, by an integrated assessment of uncertainties in geophysics, geology and reservoir engineering, to provide a rational basis with risk analysis for the management of uncertainties in the development of the field and therefore better decision making.The objective of the study was to integrate the uncertainties identified on the Lambda Lower & Upper reservoirs and to quantify their impact on Gross Rock Volume (GRV), Oil Originally in Place (OOIP), recoverable reserves and production profiles.The work was carried out in five main steps:Determination of the distribution of the GRV. Building of a representative cloud of geological full field models (1000 equiprobable models) integrating geophysical, sedimentary and petrophysical uncertainties. Determination of the distribution of OOIP. Sorting and selection of a representative subset of reservoir models to quantify dynamic uncertainties. Modelisation by means of experimental design of the impact of dynamic uncertainties on the representative subset of geological models. Integration of static and dynamic uncertainties to assess statistical distributions of recoverable reserves, production profiles and plateau duration using experimental design technique coupled with multi-variable regression and Monte-Carlo simulations.The following results were obtained:– probability distributions of GRV – probability distributions of OOIP for each reservoir (Lower & Upper) and for each zone of the Upper reservoir – probability distributions of recoverable reserves and production profiles – probability distribution of production plateau duration – probability estimation of different models, associated with quantiles 10, 50 and 90 of the OOIP and Np distributions – measure of the weight of the main uncertainties on the OOIP and reserves.