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Simple well plans are becoming a thing of the past.
Maintaining a low equivalent circulating density (ECD) in downhole environments is a necessary step in avoiding nonproductive time (NPT).
“Wellbore integrity, including lost circulation, can account for a significant amount of nonproductive time,” said Chip Miller, vice president of Halliburton’s Baroid business line, speaking at a press conference on April 30 during the Offshore Technology Conference in Houston.
“Operators are drilling more complex wells in difficult reservoirs. ECD, or equivalent circulating density, refers to the increase in bottomhole pressure associated with circulating fluids. Fluids interact with the pipe as it circulates through the well bore. The ensuing friction can drastically increase pressure at the bottom of the hole.
“Why is this important?” Miller asked. “Forty-four percent of our customers’ nonproductive time comes with events related to wellbore integrity,” he said.
Wellbore integrity basically refers to problems arising from pressure-related situations. Reducing lost circulation, wellbore integrity issues and stuck pipe all have their basis in what the pressure is at the bottom of the hole.
Maintaining a constant circulating density requires drillers to work within a window between two separate limits of downhole pressure. The first one is the pore pressure window, which is the pressure of the fluids inside the rock at any given section in the well bore. Drilling must occur above this pressure to avoid fluids incursion into the annulus from the reservoir rock or any of the intervals above the bit. The upper section of this window is the fracture gradient. If the fracture gradient is exceeded the rock can be fractured. Small cracks and opened pore space can reverse the flow, forcing drilling fluids into the reservoir rock.
“Both of these are areas we don’t necessarily want to be in during the well construction phase,” Miller said. To maintain well integrity, pressures must be managed between the pore pressure and fracture gradient window.
Today’s drilling environments include deepwater, high-angle designs, drilling through depleted zones, extended-reach drilling designs, and slimhole applications. Each of these applications narrows the window between pore pressure and fracture gradient.
Halliburton has developed several advanced components that offer low ECD options to combat challenges associated with well integrity.
New technologies included in the solution are the Low ECD Fluid Enhancement Package, VersaFlex Low ECD System, Commander 1000 Top-Drive Cementing Head, and the high-pressure shearing unit. The company’s cement head allows operators to manage the pressure cycles received while cementing casing in place. Starting and stopping can cause difficult drops and rises in downhole pressure. The head is designed to maintain a consistent flow rate thereby offering a consistent pressure profile downhole. The head is also fully remote control. The dynamic control allows personnel to keep a safe distance while operating all of the necessary functions during cementing operations.
The company’s Protech CRB centralizer can reduce the coefficient of friction by 50% in some operations. This reduction means less hammering when running casing. Less hammering translates into less friction, which makes it easier to maintain a constant ECD.
The system is not tied to placing all of the centralizers in the same location. With increased flow-by throughout the annulus, ECD is further enhanced. “In some cases, we can see as much as a 95% increase in flow area, reducing frictional pressure drops, further managing the ECD that is applied to the formation,” said Hank Rogers, global technical advisor for cementing casing equipment, Halliburton.
A driller’s primary objective to maintaining hydrostatic pressure of the fluid column below the fracture gradient while maintaining well control is drilling in challenging, complex downhole environments. According to Halliburton, their low ECD solutions aid in reducing overall fluid viscosity to reduce frictional forces; allow drilling fluids, spacer, and cement to flow freely into the casing and up the annulus to avoid lost circulation; and increase bypass circulation rates while not exceeding the fracture gradient of the formation to pressure buildup.
The goal is keep a pressure column consistent throughout all phases of well construction. “As operators drill more complex well bores in difficult reservoirs, this low ECD solution uses an integrated-technology approach to address our customers’ ECD issues, increase efficiency, and maximize recovery,” Miller said.