Two wells were designated "risk-reward" where service company profits were tied to well productivity in order to jump-start technology implementation. A number of improvements were made to increase fracture conductivity including switching from sand to RCS, using higher proppant concentrations, and reducing gel loadings. Significant increases in effective fracture length corresponded with the introduction of higher quality proppant. In a large dataset spanning 5 years, average well production was improved by nearly 100% with more effective treatments.
Recommendations for stimulation optimization in mature fields often meet with opposition from operators who are wary of changes in the design of well completions. Often, inertia exists among personnel because they are comfortable doing things the way they have been doing them and because they want to avoid the potential risk of a new idea. A common set of concerns regarding low-permeability gas reservoirs is how much the changes will cost and whether or not they will result in adding new reserves. To answer these questions, the reservoir must first be studied and analyzed so that a reasonable prediction can be made regarding the maximum potential of the well. An effective approach is to form an integrated team made up of specialists from both the operating and service companies to gather and process comprehensive information. This information should include data from reservoir engineering, drilling, petrophysics, geology, stimulation design, and production and completion operations.
This team approach was applied to the low-permeability Lewis and Almond sands in the Wamsutter field in southwest Wyoming. A team began studying the reservoir in 1998 to better understand the problems that prevented the wells from producing at their maximum potential. The team was challenged with the following tasks:
- Determine whether or not the wells were already performing as well as they could.
- Establish a benchmark by which to measure the success of any changes.
- Identify the major causes of underperformance.
- Apply new technologies and techniques to overcome the causes of underperformance.
- High-grade pay based on log evaluation, individual zone testing, and production logging.
- Design stimulation treatments that maximize the net present value from the well.
- Document the effect of specific changes in completion practices.
At the outset, a benchmark of the 90-day average production rate was established based on existing results. As a result of this ongoing effort, the original benchmark has been exceeded by over 100% over the past five years. The average production for these wells has also increased more than 50%.
Author(s): Mike Mullen, Rich Dickerman, Jack Stabenau, Halliburton; Martin Dobson, Charles Ohlson, Marathon Oil Company
Paper Number: SPE 90792