The unconventional has just become conventional. At least, that's the impression given by Samantha Shepard of BP. Shepard delivered a presentation on the company's experience with casing drilling at the recently concluded SPE/IADC Drilling Conference in Amsterdam, the Netherlands. Drilling conference veterans will recall that just 2 years ago Tesco's president, Bob Tessari, introduced the concept of casing drilling to a somewhat skeptical audience. The BP paper answered many industry questions.
Shepard reviewed BP's objectives. In addition to a strong commitment to health, safety and the environment, the company wanted to prove wells could be successfully drilled without tripping. To do so it was willing to undertake a multiwell drilling program in southwestern Wyoming's Wamsutter field. Shepard highlighted five new pieces of equipment unique to casing drilling:
• a top drive with split blocks, which allows easy access to the string for logging tools and bit changeout;
• a casing clamp that permits torque transfer while providing hanging support;
• a drilling lock that locks in the bottom of casing to transmit torque to the bottomhole assembly (BHA);
• a wireline-retrievable BHA; and
• automatic drilling controls that give the driller complete control of the drilling operation from a single console.
Results were dramatic. Using an average 10-day-per-well benchmark from conventional drilling in Wamsutter, BP and Tesco made excellent headway ramping up the learning curve. From the rig's debut at 60 days, the drillers quickly applied their newly learned experience so that wells 5 and 6 averaged 11.5 days each. When cementing time is factored-in, the combined drilling and cementing operations beat the same combination on conventionally drilled and cemented wells.
There were some rough spots along the way. The team had to contend with abnormal torque, casing connection failure, bit balling, casing wear, effective circulation density and hole-cleaning issues. But because of their commitment to a multiwell approach, BP was able to carefully analyze these challenges and develop solution sets as it proceeded. By not allowing unrealistic expectations to kill the project at the first setback, BP was able to persevere.
For its part, Tesco has undertaken a double challenge. In addition to working with its customer to resolve drilling issues involving equipment or techniques, the company has focused on logistics to reduce mobilization, transportation and demobilization times. The casing drilling rig breaks down into compact trailer loads that can be easily transported to the next location where they are staged and erected in a logical, efficient sequence. Recognizing that many applications for the rig will be low-margin projects, Tesco has managed to build maximum logistical efficiency into the design, returning benefits to itself and its customers.
Shepard enumerated some applications for which casing drilling has distinct advantages:
• batch drilling and setting surface casing in a field development program;
• setting protective pipe to defeat shallowwater flow;
• running casing in difficult holes; and
• drilling in depleted reservoirs.
Many good ideas never fulfill their promise because the companies involved lack the resolve to stay the course. Not so BP. Given these encouraging results, the company intends to continue its casing drilling program in Wamsutter.

Comments