Integrating Completion and Drilling Knowledge Reduces Trouble Time and Costs on the Pinedale Anticline

Abstract

The Pinedale anticline of southwest Wyoming has proved technically challenging to drill and cement. This tight gas reservoir has more than 5,000 ft of vertical-pay interval in stacked-lenticular sands. With pore pressures ranging from normal to more than 16.5 lbm/gal, unplanned circulation losses were negatively impacting drilling and cementing operations. In early 2002, desired top of cement (TOC) was being achieved on only 31% of the production casings. As a result, one of three things would occur:• Stimulation treatments would not go to the intended zones, resulting in no production for completion dollars spent. As a result, petrophysical evaluations of entire intervals were being questioned.• Costly remediation treatments had to be conducted during completion operations to isolate zones before they could be completed.• Production reserves were at risk or deferred because of inadequate annular isolation.Completion engineers use fracturing applications to enhance well performance, while drilling with drilling-induced fracturing is difficult to manage. In both disciplines, knowing fracture and pore pressures is critical. A process was developed to determine and calibrate pore pressures and minimum horizontal stresses for the design of hydraulic-fracturing treatments and production prediction. Fracture-extension-pressure variation with depth was measured on each well completion. Mechanical rock properties were measured in the laboratory to validate calculations from openhole logs that were used in the fracturing simulator. The data were validated further by post-matching the simulator with fracturingtreatment data. The question was asked: "Why not use these fracture data to prevent drilling-induced fracturing?"Because of losses and wellbore-stability issues, completion data from offset wells were incorporated into casing and mud programs. Underbalanced drilling techniques were also introduced, which in turn, created obvious problems for the cement design. Best practices were incorporated, including foam cement, on a selective basis. As a result, cement tops are now reaching the desired heights 100% of the time. Even in cases in which there has been no circulation when the cement job is started, desired cement tops have been achieved. As a result, costly remediation efforts have been eliminated, saving an estimated U.S. $1.3 million/year. All the desired pay intervals are being isolated so that the decision to complete reservoir intervals is based on reservoir quality, rather than mechanical issues with the wellbore. Production can now be attributed to given pay intervals with confidence, aiding in proper evaluation of entire sections of the reservoir.