Integrated Carbonate Field Management Using Forward Stratigraphic Modelling Approach. Case Study of a Field in Central Luconia
Authors: Uli D. A. , Mithani A. H. , Ali Kartina , Abu Mansur Roslan B , Masoudi Rahim , Tewari Raj Deo , Jirim Shamsudin , Harith Z. Z. , Mohammad M. H. , Kanesan T. , Kolupaev A. , Lee Y. 
Published: October 2017

The paper discusses an innovative methodology of designing a carbonate reservoir model on a field in Central Luconia for planning further optimal field development and reservoir management & surveillance (RMS) using a Forward Stratigraphic Modelling (FSM) approach. Understanding of carbonate reservoir architecture is important for successful, stable hydrocarbon production and reservoir management plan. This understanding on early stages can help to prevent unpredictably low productivity & recovery, early water breakthrough and design field-customized RMS formulation.

Complex depositional and diagenetic facies distributions in carbonate reservoir are the main challenges for development and production of hydrocarbon from carbonate fields worldwide. They are often naturally unique geologically, and exhibit complex porosity systems and permeability characteristics, which drastically influence whole cycle of reservoir management and surveillance. Geostatistical approach is often unable to capture the geological heterogeneity which leads to oversimplification of the carbonate reservoir model. Many uncertainties would be present in forecasted hydrocarbon and water production, volume in place and reserves estimation, optimal well design and locations, which effects the whole Field Development Strategy. This further becomes a challenging task in high mobility fluids like gas of Central Luconia with 90% of gas production in Central Luconia beingfrom Carbonate Reservoirs. With the complexity of the carbonate characteristics and its uncertainties, it is crucial for PETRONAS to reinvent its approach towards managing carbonate field and embrace the new ideas beyond those normal practices.

By years of research and development of numerical computer simulations, FSM has proved to be a complementary alternative process-based approach to create a better carbonate reservoir model which is geologically realistic and obeys stratigraphic principles.

The method used in the FSM approach is to first set the modelling input parameters which mostly represents the main depositional processes such as conditions of wave energy & direction, paleobathymetry, carbonate production rate, eustatic changes, amount of subsidence etc. These input parameters are obtained from an integrated approach of analysis on all hard data available including understanding of modern analogues to create a conceptual model at time of deposition. Once these input parameters have been identified, the simulation is computed to provide a first-pass model which is validated with hard data. If present mismatch, the input parameters will be tweaked and another simulation is computed. The steps are repeated until an acceptable match between the model results and the hard data is obtained.

There will be numerous uncertainties available as many different input parameters may still provide different model results which matches the existing hard data available. Thus, a sensitivity and uncertainty analysis is computed to understand the most influential input parameters for creation of the reservoir model and also provide multiple model realizations which best represents the available hard data.FSM uncertainties are combined with G&G and dynamic uncertainties to have a robust model which can guide a formulation of optimal development and RMS planning.The innovative workflow applied at field scale allowed the modelling of highly heterogeneous, complex carbonate field which honours core, well logs, and seismic data.The application of this workflow honouring core, well logs, and seismic data as an alternative to conventional stochastic methodologies help to prevent field problems related to heterogeneity mis-modelling (simplification) in future such as unpredicted fast water breakthrough, reserves under/overestimation, field underperformance and help in the formulation and development of reservoir management strategies plan.