Field Development Issues and Newly Developed Sector Pattern with Horizontal Multistage Fractures Wells Completed in Mid-Permeability Oil Reservoir Under Waterflood
Authors: Butula K. K. , Vereschagin S. , Malyshev V. , Stashevsky V. 
Published: October 2016

This paper addresses the failure of field development pattern design where horizontal wells with multistage fractures (HWMSF) are being drilled and are completed in low- to- mid-permeability oil-bearing conventional reservoirs [k&lt;100 mD] where the field is under waterflooding.

A novel and optimum pattern for HWMSF has been developed to promote economic success and avoid the issues with current HWMSF production wells that exhibit either early water breakthrough or higher-than-planned decline in fluid rates.

The analysis and thorough numerical reservoir modeling exercise of the currently used well patterns used in waterflooding reveal that the completion design, azimuthal orientation, and operating condition of the HWMSF production well and injector wells are suboptimal. The result of such field development is either an early-time relatively high production rate followed by a steep production decline and water breakthrough or low initial production and even lower late-time production. In either case, the HWMSF are not economically viable, and operators search for alternative methods to revitalize production from HWMSF. Such an alternative are the proposed changes in initial completion and operational practices.

With the introduction of the new HWMSF completions as production wells, the injection-production well pattern design in conventional reservoirs that was applicable for vertical, subvertical, slanted, and S-shaped hydraulically fractured wells must be adjusted to ensure waterflooding remains effective in the changed completion environment.

The novel pattern devised consists of placement of a row of HWMSF production wells and, between the production wells, a row of injection HWMSF. This is different from all known patterns in that both injector and producer HWMSF are drilled in the direction of minimum horizontal stress and hydraulically fractured. The wells are completed in such way that the hydraulic fractures on both wells are spaced out in a controlled manner, and the ports as well as the injection and production are controlled. This way, the pattern allows for high early production rate and high late-time production rate and reduces the risk of early water breakthrough while preventing uncontrolled fractures in injector wells. The completion design—including the hydraulic fractures and the wellbore hardware, the position, azimuthal orientation, and spacing of the injector and producer wells—is critical to the optimization of hydrocarbon production and the recovery of reserves and is explained in the paper.

The paper describes the novel method of developing conventional oil-bearing formation by drilling HWMSF as injector and producer wells. The wells are drilled in line with minimum horizontal stress and are completed in such way that fractures are fully controlled during fracture placement and later during the wells' operations. This results in maximizing the early production oil rate, minimizing production decline, and minimizing risk of water breakthrough, therefore maximizing the economic results and the recovery factor.