Abstract
In the field development stage, it is typical to use water injector wells to maintain reservoir pressure and maximize oil recovery factor. In many cases, these water injectors are drilled in the edge areas of the reservoir, often having reduced properties which leads to challenges in water injection. This study describes best recommended methodology for improving the injectivity in such wells through hydraulic fracturing, particularly in an open hole type of completions in carbonate rocks.
The study represents an integrated approach covering all aspects of well completion and stimulation with use of advanced simulation software. Medium permeability reservoir was considered as a target of the research with extended reach well candidates. Sensitivity analyses were done for the various types of completion and near wellbore zone status – damaged, non-damaged, stimulated with longitudinal fracture and stimulated with multiple transverse fractures. The injectivity index was calculated for each scenario based on a model which was calibrated with injection history match.
Both proppant and acid fracturing scenarios were modeled and described in detail within the study showcasing the advantages of multiple acid fracturing stages with transverse orientation. Considering open hole completion, a technique with dynamic diverters based on degradable multi-size particulates was shown to be an optimum in terms of operational efficiency and cost-effective solution to enhance injectivity. To ensure representative comparison, a fixed volume of acid was simulated in each scenario, irrelevant to the number of generated fractures. Thus, scenarios of lower number but larger size fractures were compared to a scenario of higher number but lower size of the fractures under essentially the fixed cost of well completion. Analysis have shown that increasing the number of fractures brings higher injectivity rates and more reliable connectivity of the open hole wellbore with the fractures aimed at bypassing the near wellbore damage. Overall, existing skin factor (positive 8) was calibrated based on history match leading to more than double reduction of injectivity index when compared to a non-damaged reservoir. When the open hole wellbore is stimulated with massive acid fracturing, the injectivity index is increased by a factor of 10 to 15 from base case or by a factor of 5 to 7 from zero skin scenario.
The study represents one of the few documented projects of large size fracturing in water injector wells completed with open holes. Innovative method introduced to maximize number of fractures via injecting degradable diverting pills for the enhanced operational efficiency. Comprehensive modeling approach including fracturing and injectivity sensitivity studies are described to serve as a useful tool to engineering society in the middle eastern countries.
