With extensive rig upgrades that have taken place in the Bakken over the past few years, the addition of top drives has been one of the primary reasons operators are able to drill such extended-reach laterals, explains Luke Clausen, DTC Energy Group chief operating officer.
“Top drives make the drilling process much faster and more efficient,” Clausen stated. “They cut out a majority of the problems associated with making connections and are a solution to many of challenges associated with extended-reach directional wells.”
Some of the key benefits of using top drives include the enabling of longer drilling intervals, better steering of the bottom hole assembly, the ability to handle higher amounts of torque, and a significant reduction in the frequency of stuck pipe.
“With a top drive, you’re able to drill with three joints per stand, 90 feet at a time,” Clausen said. “With a Kelly rig, you’re only able to drill 30 feet, one joint at a time.”
He continued, “A top drive also gives you a greatly enhanced ability to steer the bottom hole assembly, making drill pipe connections just a few feet from the bottom versus 45 feet with a Kelly rig.”
This ability to drill 90 feet at a time while making significantly quicker and fewer drill pipe connections allows for a much faster, more efficient process.
A way to quantify the efficiency of using a top drive over a Kelly rig is to compare the total distance the drill bit travels throughout the entire drilling process – including lifting up and down while making connections.
“On a 27,000-foot well, for example, a drill bit will have to travel an extra 3,000 feet to make connections,” he continued. “With a Kelly rig, that number is 54,000 feet.”
A top drive will have to make 300 connections on a 27,000-foot well, or one connection every 90 feet. During each connection, the drill bit will lift up and back down 5 feet, for a total travel distance of 10 feet per connection. Traveling 10 feet for each of the 300 connections equates to a total of 3,000 feet of connection travel for the drill bit.
On the same well, a Kelly rig would require 900 connections, or one connection every 30 feet. During each connection, the drill bit would lift up 45 feet and lower back down 15 feet, for a total travel distance of 60 feet per connection. Traveling 60 feet during each of the 900 connections results in a total of 54,000 feet of connection travel for the drill bit.
“When you do the math, the difference is surprising,” Clausen summarized. “It really shows how much more efficient top drives are.”
Top drives are also able to handle higher amounts of torque.
“Greater depths require much greater torque to get the bit to start turning,” Clausen explained. “Top drives let torque in and out much more easily. And they allow you to hold the direction and angle you need for a longer period of time than with a Kelly rig, keeping you better on target.”
Top drive efficiencies also help reduce the frequency of stuck pipe, saving time and reducing costs.
“Top drives enable shorter drilling times and 51,000 feet less travel distance for the bit,” Clausen stated. “There are two-thirds fewer connections, and they offer the ability to quickly engage the pump or rotate the string at any time during tripping operations.”
This is a tremendous increase over a very short period of time, with maximum total well depths being 21,000 feet with 10,000-foot laterals just three years ago. Today, total well depths are reaching up to 27,000 feet or more with 16,000-foot laterals.