Located in western Oklahoma, the Cana Woodford is a relatively new unconventional shale gas play. The first horizontal well was drilled there in 2007. Full field development is presently underway using two key technologies (horizontal drilling and multistage hydraulic fracturing), which have been successful in the economic development of other shale gas plays. With true vertical depths (TVDs) ranging from 10,500 to 15,400 ft, and lateral lengths ranging from 2,500 to 5,200 ft, unique challenges have been encountered with respect to the design and implementation of the hydraulic fracturing program. This paper focuses on completion issues encountered and the steps taken to identify the problems and develop solutions.
Early completion efforts in the Cana field were characterized by extreme difficulties in placing designed fracture treatments and inconsistencies in both job implementation and well performance. It was recognized early on that if the play was going to be successful, improvements to the completion process (and specifically the hydraulic fracture treatments) were necessary to allow for consistent job placement and adequate performance evaluation. A systematic approach to identifying these problems led to design changes to the Cana Woodford stimulation program. These changes have significantly improved consistency when placing designed volumes during the hydraulic fracture stimulation process. This consistency has allowed for a more detailed evaluation of well performance and has provided insight into which parameters (e.g., fluid volumes, proppant volumes, perforation configuration) have the most impact on well performance. Continued analysis will result in further optimization of treatment parameters, improving the overall economics of the play.
Case histories are presented, which demonstrate the effect of design changes on job execution. These wells typically have 5 ½" casing from surface to TD and the lateral section is cemented. Well operators have drilled the laterals such that transverse hydraulic fractures are expected.
During the initial exploration phase and early part of field development, breakdown and fracture initiation were extremely difficult and inconsistent. Proppant placement for the first 28 wells completed ranged from 16 to 98% of designed volumes, and averaged 70%. Since implementation of specific design changes, proppant placement in the last 81 wells has ranged from 68 to 105%, with an average placement of 90%. Additionally, the total proppant placed has increased from an average of 150,000 lbm/stage to more than 300,000 lbm/stage. Initial results indicate that these improvements in placement and consistency have improved overall well performance, and further modifications continue to be made.
This paper documents the impact of identifying and solving various problems associated with fracture initiation and job implementation in the Cana Woodford shale gas play. This approach has led to improved placement techniques, which could be adapted and applied to similar resource plays.