Integrated Geology, Sedimentology, and Petrophysics Application Technologyfor Multi-Modal Carbonate Reservoirs
Authors: Sung R.R. , Clerke E.A. , Buiting J.J. , Ait Ettajer T. 
Published: May 2016

The complexity and heterogeneity of carbonate reservoirs makes them extremely difficult to characterize and develop. The very large reserve base in Middle East carbonate fields requires thorough field development strategies to optimize ultimate recovery and meet rate forecasts. The very highest quality 3D geological model and rigorous reservoir simulation is required. The geological model must combine all geological, geophysical, core, and rock property information together with interpretation data to deliver the best 3D representation of these complex carbonate reservoirs. These models rely on pertinent lithofacies derived from core descriptions using sequence stratigraphic processes, and static and dynamic fluid and pore architecture properties obtained from laboratory analyses of core and log data. Current understandings of our major limestone reservoirs have established that these reservoirs commonly contain nested multimodal pore systems. Extensive data sets have been obtained to determine and classify these pore systems by Clerke in a facies framework. These data differentiate various macro and micro pore throat families (the porositons of Clerke), their statistics, pore throat to pore body relationships and flow properties of the pore systems. Understanding the distribution of the hydrocarbon volumes in the various pore-type combinations (Rosetta Stone Petrophysical Rock Types) and then establishing proper recovery analyses and techniques could improve the field development strategies, explain reservoir high recoveries, and lead to optimal recovery.

The new application and workflow presented in this paper describes the model construction process from the sequence stratigraphic framework and facies to the billion cells geomodel and simulation. The process utilizes deterministic facies models derived from a sequence stratigraphic framework, facies-controlled geostatistical population of static rock properties and Rosetta Stone Petrophysical Rock Types (RSPRT) followed by controlled stochastic pore system parameter assignments. The workflow depends heavily on the use of abundant core description data available in a digital format. Macro and micro porosity volumes are assigned to each geological model cell. Then through incorporating multi-modal Thomeer petrophysical algorithms, critical reservoir attributes (permeability, relative permeability and time dependent spontaneous imbibition recovery) are calculated at each geocell. This technology unites and calibrates the diverse geoscience disciplines of geology, sedimentology, and petrophysics. We are applying this technology to Saudi Aramco carbonate fields. Significant bottom line impact is expected from this "Full Pore System" paradigm shift.

Introduction

Reservoir characterization and simulation for production requires a complete integration of all of the subsurface geoscience data and analysis. These subsurface disciplines: Geology, Sedimentology, Geophysics, Petrophysics, Reservoir Modeling and Reservoir Engineering acquire respective domain data samples, have data coded specific to each discipline and not necessarily tied to the reservoir integration. Even in today's production interpretation environment, obstacles continue to exist limiting the fully integrated use of information and observations by geologists, sedimentologists, petrophysicists, geological modelers and reservoir engineers.

In Saudi Aramco, the advent of very large computing systems and simulation systems allows the reservoir simulation to occur at nearly native vertical sampling rates with dense geocellular grids and no longer restrict the use of all of the geoscience data. This advance requires that our seminal geoscience data become even more tightly integrated.