Evaluation of Steam Injection in a Fractured Heavy-Oil Carbonate Reservoir in Iran

Abstract

Abstract Steam injection in naturally fractured heavy oil reservoirs provides an extremely challenging problem as well as a potentially effective and efficient improved oil recovery method. Coupling of the two distinct and contrasting matrix and fracture systems results in a highly non-linear problem, and it gets even more complicated as a result of steep changes in fluid properties due to the thermal effects of steam injection. Modeling and designing an optimum steam injection operation in such systems requires an accurate characterization and representation of a naturally fractured heavy oil reservoir and steam injection operation parameters and dynamics1. In this communication, the results of a feasibility study of steam injection in a highly fractured carbonate reservoir are discussed. The field is a giant structure located in south west of Iran at the coast of Persian Gulf. It is a symmetrical anticline with 56 mile length and 10 mile width in the surface with about 3.6 billion barrels of initial oil in place. The initial pressure is 927 psi at 1700 ft depth. The gravity of the oil is 7.24 °API with viscosity of about 2700 cp. The Geological model was constructed based on the available 2D and 3D seismic investigation and conventional core data from different samples. Extensive fracture characterization has been conducted using core data as well as the petrophysical interpretation using imaging logs. Dynamic reservoir simulation model with thermal option has been developed and used for optimization of different parameters for steam injection and their effect on reservoir performance and recovery factor. Reservoir simulation of the field showed that steam injection could improve oil recovery from zero up to nearly 12 %. Furthermore, the results illustrated that the important parameters for designing the steam injection are different strategies for perforating, well spacing, well type, pattern type and size. Additionally, the effect of other parameters such as injected steam quality, oil-water capillary pressure in matrix blocks, steam injection and oil production rate have been studied.