Historically, carbon dioxide (CO2)-foamed fracturing fluids were used to stimulate wells in the Waltman field in Wyoming—due to the low formation permeability and rock properties—and have been proven effective, but still not perfect. Limitations on the amount of proppant placed near water zones and formation damage from polymer residuals were the main drawbacks. A never ending quest for efficiency and higher production rates called for different options. One of those options was the recently developed CO2 viscoelastic surfactant (VES) fluid system. It has recently been employed to eliminate the disadvantages of the traditional polymer-based fluid. This VES-CO2 fluid system combines the benefits of viscoelastic surfactant-based fluid—such as low formation damage, superior proppant transport, and low friction pressures—with carbon dioxide advantages of enhanced cleanup and better hydrostatic pressure. This fluid was recently selected for the fracturing treatments on three wells. Initial production from these wells was observed in the range of 5 to 7 MMcf/D, significantly greater than neighboring wells' gas rates of 2 MMcf/D stimulated with polymer-based fluid. Introduction The Waltman-Cave Gulch field complex is located on the northeast flank of the Wind River Basin, 50 miles west-northeast of Casper, Wyoming (Kuuskraa et al. 1996), Figure 1. Production from this complex was established in 1959 from Lance formation. The full extent of the Lance sands in the Cave Gulch (shallow) structural accumulation was rediscovered in 1994. The production boundaries of Waltman-Cave Gulch are not yet established. Current development priorities are defining the deep Frontier, Muddy, and Cloverly reservoirs and extending the Cave Gulch (shallow) accumulation to the southeast and northwest. The Waltman-Cave Gulch complex is located on the Waltman Anticline, a north-south trending asymmetric fold of Laramide age. The fold is bound on the west by a high angle reverse fault. The complex produces from three geologically distinct accumulations, the Waltman (stratigraphic), Cave Gulch (shallow), and Cave Gulch (deep), Figure 2. All the wells discussed in this paper are located in Waltman (stratigraphic) accumulation, and completed in Lance formation.
Recent development of horizontal well completions and stimulation methods enhanced the development of conventional and unconventional resources. Multistage fracturing allowed oil and gas operators to stimulate long laterals in continuous and efficient operations that increase the reservoir contact, thus increasing the recovery of oil and gas. Oil and gas operators work to improve the efficiency of multistage fracturing treatments by developing and integrating enabler hardware, processes and chemical technologies to enhance the fracturing operations and reduce cost. This paper reviews and discusses the different types of horizontal wells with multistage fracturing completions and stimulation techniques including plug-and-perf, abrasive jetting, just-in-time perforation, sliding sleeve systems, coiled-tubing conveyed fracturing systems and annular isolation methods. The efficiency of the multistage fracturing treatments depends on multiple factors comprising the operational time and cost associated with different type of completions such as plugs and sleeves, different intervention operations such as wireline or coiled-tubing and different stage distribution and pumping designs. Combination of multiple multistage fracturing methods resulted in hybrid cost-effective treatments. In addition, multistage fracturing fluids diversions contribute significantly to the stimulation efficiency. Different types of diversion methods are discussed for each stimulation system. This paper provides a comprehensive summary of the operational practices, fracturing methods, and different multistage fracturing completions in horizontal wells while emphasizing on the recent advancements available in the market. The ability to develop an efficient and effective multistage fracturing operation is based on understanding the reservoir requirements, and identifying logistical and resource challenges at the geological location where the operation is taking place. The developed solutions would be an integration of currently available process, with proper completions, materials and development of innovative enabler technologies to accomplish optimum procedures. In recent years, several enabler technologies were developed to address the challenges within the existing multistage fracturing operations. The electronic monobore sliding sleeve was developed to address the limitation caused by small ball seat (baffle) in ball actuated sliding sleeve completions. Plug-and-perf operation was enhanced by applying the Just-In Time Perforation (JITP) method by developing a new perforation gun assembly that cuts operation time. Development of autonomous completion elements with the ability to navigate and self-destruct after accomplishing the job helped to reduce the number of trips into the well that greatly affected the operation efficiency. Completion elements and diverters built from dissolvable materials eliminated the drill-out and cleanout operations, which reflect positively on the efficiency of the fracturing process. Reviewing current advancements of multistage fracturing completions and treatments can pave the way for further operation optimization and cost reduction.
This paper describes the design, implementation details, and the added value of deploying a 15 kpsi Multi-Stage Fracking (MSF) system with an open hole (OH) metal expandable packer. The system would be an additional enabler for successful OH MSF system deployment, especially for wells with concerns over wellbore stability (pack off and/or washouts), getting stuck while running with the completion string to the deployment depth and in Extended Reach Drilling (ERD) wells. The system used four (4) stages deployed in a 5-7/8″ open hole with a length of 3,000 ft. The completion equipment was successfully deployed. Rigless activities commenced by fully expanding the packers (with 12,400 psi), before the multistage fracturing was conducted successfully. The slim Outer Diameter (OD), the ability of drill pipe rotation, the 15 kpsi fracturing capabilities in hole size up to 6.5 inches and the lack of internal moving parts like sleeves or mandrels; enabled the system to deliver the fracking capabilities required with challenging OH conditions. The system provided reservoir compartmentalization with 15 kpsi capabilities between different stages, 15 kpsi fracturing capabilities in hole size up to 6.5 inches and slim outer diameter to enable the deployment of the completion string into challenging open hole conditions. Furthermore, the system has the ability of drill pipe rotation to enable the deployment of the completion equipment to overcome any obstruction while running in hole and no internal moving parts, which lessen the mechanical failure risks. The 15 kpsi MSF with metal expandable frac packer system has the following novel features in wells with wellbore stability (washouts) concerns, where the 15kpsi fracturing capabilities in hole size up to 6.5 inches, as well as long seal length. As for wells with wellbore stability (pack-off) concerns, the system provides relatively slim OD, for smoother running and, that, can be helpful in wells with differentially stuck concerns. Also, it provides better reliability and robustness, as there are no internal moving parts.
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