Case Studies Underbalanced Drilling
Field Revitalization using Underbalanced Drilling
Drilling Scenario
In a Smackover carbonate reservoir of the U.S. Gulf Cost, it was recognized that the use of conventional drilling and completion fluids was causing significant damage to the reservoir through the stacked sandstone and dolomite reservoir intervals. Production rates were significantly reduced, and even completion of development wells was an apparent problem. Reservoir pressures had also declined from 9,000 psi at initial production, to approximately 3,200 psi.
Underbalanced technology was identified as a possible solution that could be used to drill infill development wells and contribute to the economic revitalization of the field. Minimizing drilling fluid losses was desirable to expedite well clean up, and reduce the need for handling fluid returns during production.
Technical Challenges
The vertical development well was to be drilled to a depth of 18,300 feet, into a thermal environment where temperatures were expected to reach 340°F. The presence of hydrogen sulfide gas, combined with the proximity to a nearby residential neighborhood, required careful planning and analysis of the entire underbalanced drilling operation. Because of the potential risk involved, the service company had to design the drilling operation emphasizing proper safety measures. Once the design step was completed, permission from the state was needed in order to drill the well underbalanced.
Project Results
From what had been considered a marginal producing property, production rates increased from 6 to 16 million cubic feet of gas per day, with associated condensate production of 800 barrels per day. Natural gas from a nearby gas processing plant was used to create a diesel mist drilling fluid that significantly lowered the drilling costs of this operation. The successful and safe application of underbalanced drilling technology has allowed the operator to reclassify this gas property as a significant asset rather than a tired old gas field.
Assessment
1. Underbalanced drilling techniques have been successfully applied in overpressured formations.
A. TRUE
B. FALSE
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