Composite Plug Milling Efficiency Improvement Through Rheology Control - Lessons Learned From The Horizontal Completions In The Duvernay Shale
- Darren Huynh (Shell Canada Energy) | Oleg Medvedev (Shell Canada Energy) | Saad Hamid (Sanjel Corp) | Yossi Kartika Anas (Sanjel Canada)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 27-29 October, Amsterdam, The Netherlands
- Publication Date
- Document Type
- Conference Paper
- 2014. Society of Petroleum Engineers
- fluid rheology, plug mill out, plug and perf, milling bha, coiled tubing
- 2 in the last 30 days
- 237 since 2007
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The Duvernay Formation in North Western Alberta holds an estimated 443 trillion cubic feet of gas and 61.7 billion barrels of oil. Horizontal wells are drilled and completed with multiple fractures to maximize the reservoir contact. The most common technique used for hydraulic fracturing in these wells is the plug n’ perf method. Once the fracturing operation is completed, the plugs must be milled out using coiled tubing to restore wellbore access, as well as to put the well into production. While much emphasis is placed on improving fracture design and proppant placement in order to yield maximum production, optimizing the milling process typically focuses on mill bits, motors, and plug designs. Mill bit design and motor life have considerably improved as a result of intensive research and development in this field. New plug designs promise quick disintegration during milling. However, little attention has been directed toward understanding solids transportation and movement in the well bore. Rules of thumb are still commonly used to pump gel sweeps or determine the number of wiper trips needed when milling plugs or cleaning a well bore. As a result, current milling practices leave a significant amount of debris in the well bore, and pipe sometimes sticks due to cuttings or plug debris not transported to surface as a result of inadequate rheology. These risks not only jeopardize the safety of operations but incur extra completion costs.
In an effort to improve plug milling efficiency, a new technique was introduced during a well completion project in the Duvernay shale. The objective of this technique was to optimize the entire milling process while focusing on fluid rheology. This paper describes case histories comparing the results before and after the implementation of this innovative concept. It also outlines the benefits realized in terms of savings and the impact on project economics. The lessons learned and best practices developed during this process are shared to improve the understanding of milling process.
Unconventional hydrocarbon reservoir development is on the rise to help fulfill the global hydrocarbon demand. There are an estimated 3.3 trillion barrels of recoverable oil shale globally stretching over 33 countries. One of these promising unconventional reservoirs is the Dunvernay Formation located in Alberta, Canada. Situated above the carbonate Swan Hills platform, the Dunvernay Formation is made up of mostly organic-rich calcareous mudstones and marlstones formed during the Middle to Late Devionian period (Figure 1). It has extremely low permeability on the order of 2- 4 microDarcies and holds a large amount of hydrocarbon in the form of gas, condensate, and oil. The hydrocarbon is trapped in thin beds with rich silt/shale, bases making it a challenging yet exciting target for many oil companies.
Similar to many unconventional reservoirs, the Dunvernay Formation requires multistage hydraulic fracturing (also known as fracking or fraccing) to stimulate the formation before hydrocarbon can be produced. Fraccing is a resource and energy intensive process which requires sand and fluid (in most cases water) with chemical additives to be pumped into the formation at a high pressure and rate. One of the most common fraccing techniques is plug n’ perf, where composite plugs and perforating guns are pumped down a horizontal well to isolate the different frac stages within the wellbore. The perforating guns loaded with explosive are used to puncture the casing and create openings to the formation for fluid and sand to be pumped in. This step is repeated up the wellbore in the desired formation.
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