By Heather Douglas
“The hottest places in hell are reserved for those who, in times of great moral crisis, maintain their neutrality.” Dante Alighieri (1265 – 1321), Dante’s Divine Comedy: The Inferno (published 1472).
It’s no secret the deeper the well, the hotter the temperature and the higher the downhole pressure. Unlike Dante’s The Inferno, the oil and gas industry has ignored moral neutrality, and instead, focused on worker safety, while plumbing the depths of the Earth’s abyss.
It’s also no surprise these wells — usually natural gas from deeply buried shales or shallow, steam heated heavy oil — encounter downhole temperatures of 150 to 180 degrees Celsius or more, and pressures of 20 to 80 million Pascal (mPa). Not only do these wells stretch conventional equipment specs, but each poses a special challenge to worker safety — during drilling and production testing operations.
Canadian producers have been drilling high-temperature, high pressure (HTHP) wells since the 1960’s while drilling in northern British Columbia and southern Northwest Territories. HTHP wells were also encountered in late 1970s, when drilling companies explored offshore Newfoundland and Labrador. Back then, the engineers worried how to control kicks – the invasion of reservoir fluid into the wellbore – and ultimately blow-outs. The engineers routinely calculated maximum volumes, formation fluid flow rates, peak temperatures, and pressure rates for a worst-case scenario, so they could order the appropriate number of blow-out preventers, upgraded chokes, extra safety valves, kill lines, and pressure sensors. The extra equipment was costly, but gave workers more tools to prevent offshore disasters.
Today’s onshore deep shale wells are different. Operators have the benefit of using mud coolers to lower the temperature of the drilling mud to provide safer drilling conditions for roughnecks and reduce costs to their bottom-lines. When mud is circulated in a wellbore, the mud coolant system balances the different heat transfers so the bottom-hole is cooler than the formation temperature while the top-hole is warmer. The amplitude of this deviation, and the temperature difference between the lower-most and the top, depends on the mud flow rate.
Canadian Mud Coolers
Mud Cooling International Inc. (MCII), launched in December 2010, is a family-owned business conveniently headquartered in Calgary, AB. It is the only Canadian firm supplying mud coolers to well sites on this side of the border – the competition is American-based – and every (MCII) unit can be quickly mobilized to a far-flung location.
According to Ed Fercho, MCII’s vice president, marketing, each mud cooler unit is a closed loop system. “Each unit has an excellent run-time capacity and consists of double-plated Alpha Laval AM20 low LMTD (log mean temperature differential) and is made of titanium alloy, to minimize corrosion. The heater exchanger plates are spaced to allow circulation of the fine drilled solids.”
Cooling happens when the ethylene glycol fluid flows through the coolant side of the heat exchanger. Andrew Fercho, MCII’s president and CEO, says, “The low LMTD design of the systems allows the active drilling fluid to hold steady within 10 – 15 degrees of the current ambient temperature. The coolant fluid is circulated through a fan coil fluid/ambient air heat exchanger by a centrifugal pump.”
Temperature is controlled by a thermostat in the cold drilling fluid stream return line, Fercho Jr. adds. It modulates a bypass valve in the fan coil heat exchanger loop. This keeps the active drilling fluid temperature in the suction tank at 45 to 55 degrees Celsius where returning drilling fluid, at the shaker, is greater than 65 degrees Celsius. “It’s simple. We put cooling mud down and pull hot mud out, recycle it, then put the cooling mud down again.” Reducing the bottom hole temperature, by using a cooled drilling fluid, results in less tool failures and eliminates heat stress failure of well bore formations.
Units Used Extensively
Today, MCII’s cooler units are used by operators drilling deep shale gas wells, in northeastern British Columbia (in areas such as the Horn River Basin), as well as Lloydminster area heavy oil and Fort McMurray SAGD (steam-assisted gravity drainage) oil sands operations. Each unit has an excellent run-time capacity. Operators have, also, successfully used these coolers in the Pointed Mountain, Fox Creek, Obed, Nordegg, Ricinus, Burmis, and Coleman areas.
MCII’s cooling system offers a number of benefits:
• Lowers the risk of flash points for oil-based drilling fluids;
• Provides another line-of-defense for crew safety by preventing hazardous burns;
• Lowers evaporation rates and reduces hydrocarbons released into the atmosphere;
• Ensures greater accuracy whenever downhole measurement devices (MWD) or logging tools are used because it reduces thermal stress;
• Lessens the usage of additives; and
• Increases the life of elastomers or packers to prevent leakage from the well.
The Fercho’s are proud of the stellar safety record their cooling units have achieved. “Every one of our units has an excellent safety record. None has suffered any incidents while operating,” Fercho Sr. reports. “Our people are fully certified and stay on-site 24-hours a day, until the drilling program is finished. We set up the equipment and remove it from site.”
MCII helps the producer’s bottom-lines. “Our units enable companies to reduce the number of days it takes them to drill a well,” adds Fercho Sr. “By adding a cooler, a major operator shortened its program by four to six weeks in NE B.C. where daily operating costs can exceed $100,000.”
Many producers are fans. MCII’s client list includes Shell Canada, Nexen-CNOOC, Chevron, Apache, Imperial Oil, and Quicksilver Resources Canada drilling in NE B.C. and MEG, Husky, and Shell for heavy oil and oil sands operations.
Plumbing the over-heated zones above hell is safer, thanks to MCII’s mud cooling system. Neither the producers nor the roughnecks have a reason to suffer either an existential crisis or maintain moral neutrality.
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