Increasingly complex oil and gas wells in a climate of declining resources have made tools like rotating control devices a necessity in drilling operations today. “RCDs are essential drilling tools for horizontal, underbalanced and managed pressure drilling operations,” said John Baer, Mid-Continent operations manager, Helmerich & Payne International Drilling Company (H&P). “Their primary purpose is to control the flow from the wellbore to reduce the risk of blowouts when oil, gas, geothermal and coal gas methane wells are being drilled. More than half of all US land drilling programs use an RCD for some reason to drill at least one section of a well.” But the use of RCDs carries risk and uncertainty because they are often supplied by third-party vendors whose knowledge of ratings and maintenance is generally not the same as drilling contractors, Mr Baer said in an address at the 2009 IADC Well Control Conference of the Americas & Exhibition in Denver on 26 August.
“More than half of all US land drilling programs use an RCD for some reason,” he said. “Horizontal and directional drilling accounts for nearly 70% of the wells being drilled today. And as horizontal wells increase, so does the need for RCDs.” In addition, 10% of RCDs being used today are for underbalanced drilling.
And while the API established specifications for manufacturers of RCDs in API16RCD in 2005 to improve the margin of safety, hazards remain, particularly with the single-control RCDs, Mr Baer said.
“In US land operations, single-control RCDs are the most common and can pose problems, particularly for stripping rubbers, which strip annulus returns from the drillstring and transfer drillstring rotational torque,” he explained. “Tripping pipe wears the stripping rubbers, making the failure of a single-control head a potentially hazardous situation, and stripper rubber materials don’t always match the well conditions,” Mr Baer said.
Such concerns put greater responsibility on drilling contractors to ensure the equipment they are renting meets the required specifications for RCDs. An alternative solution is the use of a dual-element design, which offers a number of advantages to further enhance the margin of safety. Among them, Mr Baer noted, is an expanded annular sealing. “The top rubber gets a ‘free ride’ because it doesn’t see much until the bottom rubber begins to fail, providing greater assurance it can maintain its stretch fitness,” he explained. The dual-control design also ensures less leakage than the single-element design, he added.
In terms of cost, the daily rental cost for the dual-element design is up to three times that of the single-element design, but the dual RCD reduces nonproductive time in a particular zone because the stripper rubbers don’t need to be changed or checked. “Dual elements buy some time before both lose stretch tightness,” Mr Baer said.
“With all the uncertainty surrounding the hazards of single-element RCDs, the dual-element design increases the margin of safety for high-pressure wells, especially when drilling and tripping with greater than 500 psi,” he said.