This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 124797, ’Monobore Completion System Provides Low-Cost Completion Option,’ by Don Ingvardsen, SPE, and Jim Kritzler, SPE, Baker Hughes, originally prepared for the 2009 SPE Annual Technical Conference and Exhibition, New Orleans, 4-7 October. The paper has not been peer reviewed.
Many wells completed today could be classified as short-life or harvest wells. Some of these would not be economically feasible using high-end completion components and methods. Monobore wells can be a solution to this problem. The full-length paper discusses several methods in which monobore well design can save considerable time while lowering the overall completion cost.
When a well has a single produc-tion-tubing size from the pay zone to the surface of the completion, it is categorized as a “monobore” comple-tion. Although there are certain limita-tions to this type of completion, there are many advantages that make it a very attractive alternative to conven-tional completions. Drilling cost and reduced equipment list are the great-est motivators to pursue a monobore well because they directly affect the cost to complete. Most of these wells would not have been feasible if the only option was to complete them in a more traditional manner. However, if there were a system that reduced rig time and decreased the equipment list (e.g., packers and sliding sleeves), while still safely completing the well, these wells would move from the category of unfeasible or marginal to profitable or, in some cases, highly profitable. One of the early methods was simply cementing the completion in the well-bore. Later options include staging the cement process to include equipment that would increase the life of the well and ensure its safe operation.
Significant time and effort have been expended to develop a more reliable system for completing these wells and increasing their productivity, making them even more attractive. Specially designed cement-through components, including safety valves and gas lift (GL) equipment, can be credited with mov-ing these monobore completions to the next level. The inclusion of a reli-able safety valve speaks for itself with regard to producing these wells safely, but introducing the GL alternative at the beginning has increased the over-all production significantly. Wells that were estimated to produce 500 to 600 B/D were improved to 1,200 to1,400 B/D. The majority of these completions have been completed in the Gulf of Thailand, but there are other fields in the world that are candidates for this system, and equipment has been mobi-lized to some of those areas.