Challenging Horizontal Open Hole Completion in Carbonates: A Case History on Mechanical Isolation and Selective Stimulation in Campos Basin, Brazil

Abstract

This paper describe in details the design and successful operation of an acid diversion completion system, which was used for first time in an exploratory project offshore Brazil. The most significant discoveries in a recent exploratory campaign in Campos Basin were in carbonate reservoirs. The first vertical well test showed a high heterogeneous and natural fractured carbonate reservoir. Considering the reservoir characteristics, analytical and numerical modeling was performed to assess the productivity of horizontal wells compared to vertical wells. As part of the Operator strategy of developing this oil field using maximum reservoir contact, a well test evaluation project in the open hole section, mitigating the risk of reducing the production, fractures cementation, etc. was performed. The whole project was developed to address the challenges of carbonate horizontal wells i.e. low permeability sections contributing marginally to the total production. A multistage horizontal open hole completion was designed and installed to perform a separately and selective stimulation in more than 3,000 ft of horizontal section. Previously, the most advanced technologies for open hole completions with mechanical isolation were reviewed to have the ability to perform multiples stimulations (fracture or matrix) in one continuous and more efficient operation. Based on final reservoir data obtained during the horizontal open hole navigation and a calibrated Geomechanical model, the acid diversion completion system was selected to perform an acid stimulation instead of a high pressure acid fracture job. The application was successfully run in this anisotropic carbonate reservoir and eight compartments were stimulated using an acid plant and high pressure pumps mounted on a Supply Boat dynamically positioned. More than 1000 barrels of stimulation fluid; a mixture of hydrochloride acid, and a visco-elastic agent to improve diversion were pumped stage by stage to the reservoir with a real time monitoring at the operator Support Center in Rio de Janeiro. After all the stimulation jobs and to prevent the high fluid losses, the well was shut in downhole using the reservoir formation isolation valve. A DST string was run. CT and Nitrogen were used to kick off the well and after 6 hours the well started to flow naturally, with first oil at surface within the first 8 hours of flow.