Since more than half of the world’s crude oil is stored in naturally fractured reservoirs, and easy-to-produce oils are diminishing over time, more and more research has been focused on understanding fractured reservoirs' complex production behavior. Natural fractures can be determined via FMI logs and classified according to their aperture into groups. This work features the effect of major, medium, minor, and hairline fractures on oil production in primary production, waterflooding, and gas injection in a carbonate reservoir. Numerous simulation cases were run under different conditions to study the effects of different fracture sets on production. Firstly, synthetic 2D models were created as a fundament for the 3D cube model. Primary production, waterflooding, and gas injection were studied in these models, and the results are discussed in this work. Furthermore, a sector from a real giant fractured carbonated field was taken, and with the lessons learned from the synthetic models, it was studied for primary production. Verification of the results was found by getting results that follow the historical production data of the real field sector. Moreover, sensitivity runs were conducted with the 3D cube model for waterflooding and gas injection, and dimensionless numbers for these runs were calculated. The capillary number, defined as the capillary force over the viscous, and the gravity number, defined as the gravitational force over the viscous, gives insight into which forces flow through the fractured reservoir is governed.
Based on the obtained results from the synthetic and real field sector models, fractures play a key role in production. Ignoring any of the present fracture types, especially the major ones, might underestimate the reservoir’s capabilities for natural depletion. In the case of waterflooding, fractures also promote higher recovery and better displacement, whereas, for the gas injection, faster breakthrough times were observed. The pperformance during gas injection was found to be more dependent on matrix permeability changes compared to waterflooding. This statement is also confirmed with dimensionless numbers, where for the gas injection, higher recoveries were found under matrix-dominated flow. Waterflooding, on the other hand, shows more sensitivity towards fracture properties.