Ternary Rock Typing : a novel solution to multi-scale multi-discipline rock typing for carbonate rocks
Tawfik, Basem Nazih Mohamed
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The static and dynamic characteristics of carbonate reservoirs are very challenging to sedimentologists, geologists, petrophysicists, and reservoir engineers. The multi-scale and multi-discipline nature of carbonate characterization complicates any global rock typing workflow that aims to satisfy all disciplines and datasets. The heterogeneity of pore space and pore network systems obscures the understanding of the interaction between rock, pore and fluid, and hence there is no simple relationship between pore type distribution and depositional environment for carbonate reservoirs. The challenge is to accurately assign the complex pore system properties to their sedimentological rock container for vertical and lateral predictability. In this thesis, a novel Ternary Rock Typing (TRT) application and workflow combines depositional facies, wireline logs, routine core analysis, capillary pressure data and relative permeability curves from three parameters representing rock, pore and fluid interaction. The three parameters proposed are porosity, permeability and irreducible water saturation represented in the shape of a 3D ellipsoid. The complex interaction of rock, pore and fluid affect the location, shape, orientation and relative position of the three-parameter ellipsoid. The quality control of derived rock types by saturation height functions becomes an integral part of defining a Ternary Rock Type (TRT). A Ternary Rock Typing (TRT) methodology using TRT software was developed as part of this thesis was tested against a synthetic data set. It was then tested on 1D and 3D domains using 6 cored wells from an actual carbonate field. The data included sedimentological core description, wireline logs, routine core analysis, and SCAL data. The utilization of TRT is subdivided into several applications: rock typing scheme, concept, workflow, plot and software. All of the previous applications can be adapted to work with TRT or accompanied by any of the other rock typing methods. The TRT proved to perform well in 1D and 3D static modelling environments where it proved to predict the oil in place for the limestone and dolostone of the highest storage and flow capacity rock types compared to the reference based model. The TRT technique can be used as a raw unguided solely data driven approach (rTRT) or as a guided "sedimentologically" data driven approach (gTRT). The guided TRT (gTRT) uses seed points from the centre of ellipsoids representing "sedimentological facies" for the ternary rock typing algorithm to predict the likelihood for rock typing clusters and thus paves a link between sedimentological facies, wireline logs, RCA and SCAL data. The TRT was also tested against two simulation models, the first of which is an active water drive and the second is an injector/producer scheme with no water drive. The TRT model also proved to accurately model barriers, baffles and flow units. Thus, it gave the best fluid movements compared to other rock typing schemes. This affects the production and completion strategy. It also affects water breakthrough, fingering, channelling, and by passed oil. The impact of changing rock typing scheme on static and dynamic models is seldom quantified, as it creates too great a number of realizations often not feasible to dynamically simulate. A subset is usually chosen for the simulation testing. The TRT workflow disregards rock typing schemes that are not satisfying the static and dynamic interrelationships, and hence minimizes the effort of simulating unnecessary models.