Williston Basin’s prolific Bakken a catalyst for rig designs that deliver extra horsepower, mobility, automation
By Katie Mazerov, contributing editor
Less than a decade ago, Williston, North Dakota, was a mere dot on a map in a state associated with long, cold winters and the movie “Fargo.” Today, the town sits at the epicenter of the biggest oil boom to hit the Lower 48 in recent history. Thanks to significant oil production in the Williston Basin’s unconventional Bakken formation, North Dakota has earned a new claim to fame as the No. 2 oil-producing state, surpassing Alaska and trailing only Texas.
While estimates of recoverable reserves vary and have changed over the years as technology has advanced, the North Dakota Department of Mineral Resources now puts recoverable reserves in the Bakken at 10 billion bbls of crude oil and 2 billion bbls of oil equivalent (BOE) associated gas, said the agency’s director, Lynn Helms. More than half of the 7,100 wells that have been drilled in the Williston Basin are in the Bakken.
“The potential of this play is enormous and will be the focus for the next 10 to 15 years,” Mr Helms said. In June, oil production in the Bakken reached just over 660,000 bbls/day and is expected to grow significantly for the next two to three years, then sustain at high levels for eight to 12 years, he indicated.
In 2011, 2,017 new wells were brought online in the Bakken, a number that will be eclipsed this year with the addition of 2,800 wells. “Brand-new wells are seeing initial production rates of 900 bbls/day,” he noted.
Often characterized as a “layer cake” with sometimes complicated geology and long, extended-reach laterals with measured well depths as long as 22,000 ft, the Bakken has served as a proving ground of sorts for rig designs and technology that take into account everything from the geology and well profiles to weather, manpower challenges and lack of infrastructure.
“Downhole motor technology, along with reaming-while-drilling and electromagnetic measuring-while-drilling (MWD) technologies have been critical for us in exploiting the Bakken,” said Mark R. Williams, senior vice president of exploration and development for Whiting Petroleum, one of the three most active operators in the Bakken and one of two companies that made the first commercial discoveries in the play back in 2005. Over the past six months, Whiting produced 90,000 bbls of oil from the Bakken and associated Three Forks play.
“The standardization of the 1,600-hp and larger mud pumps is allowing us to drill wells in as short a time as 12 days and increase our rates of penetration (ROP) dramatically,” Mr Williams said. “Reaming-while-drilling technology eliminates the need for us to spend two to three days cleaning out the hole when we finish drilling, and electromagnetic MWD tools allow us to measure various properties of the well while we’re drilling, which results in a savings of another one to two days.”
The company also has adopted a drilling wells on paper (DWOP) practice that breaks down the drilling operation into a series of processes, with rig crews focused on achieving the maximum technical limit for each stage. The program has resulted in a reduction of up to seven days in drilling time, Mr Williams noted.
Life beyond the Bakken
But the play is just one of seven petroleum systems, or “pools,” that have been identified in the Williston Basin, suggesting “huge potential in upcoming years, much more than just the Bakken,” said Dr Steve Sonnenberg, professor of petroleum geology at the Colorado School of Mines and chair of the Bakken Research Consortium, a group of 35 companies researching the various aspects of the play.
Encompassing much of North Dakota, parts of South Dakota and Montana and extending into Saskatchewan and Manitoba, Canada, the Williston Basin was deposited in the late Devonian and early Mississippian periods. The basin also includes the shallower Tyler play, where the first horizontal test using Bakken drilling technology is planned for Q4 this year; the deeper Mission Canyon and Red River plays; Duperow; Winnipegosis and Winnipeg Group. Operators also have conducted exploratory drilling in the Exshaw formation in northwestern Montana and Alberta, a region formed at the same time as the Williston Basin with very Bakken-like organic shale.
While most experts agree there will be life beyond the Bakken, for now the focus is the Bakken, which includes the Lower and Upper Bakken shale intervals that were drilled and perforated decades ago. With high total organic carbon (TOC) content, both serve as good source rock for the Middle Bakken, a silty dolomite rock formation sandwiched between the two like an Oreo cookie, and the main area currently being developed, Dr Sonnenberg said.
“From a reservoir engineering standpoint, the reservoir is very tight with low porosity and low permeability, requiring horizontal drilling and multi-stage fracturing to make it produce,” he explained. The Bakken formation also includes the underlying Three Forks interval, where a number of companies are producing, and the Lodgepole formation on top. A newly identified thin zone, the Pronghorn (formerly known as the Sanish), lies below the Lower Bakken and is being explored by some operators.
Whiting has drilled 140 wells in the play, initially drilling short laterals of 5,000 ft. The company quickly embarked on drilling longer single laterals with staged completions, which has proved to be a game-changer in the Bakken, Mr Williams said. “Over time, we began realizing that we got better results with more stages,” he said. “We are now typically running 40 stages per well.”
On average, Bakken wells feature a vertical section of 10,000 ft with laterals from 9,500 to 10,000 ft for a “perfect L shape,” Mr Williams continued. Operators can hold a 2-sq-mile lease space by drilling a single well and establishing production, then return several months later, put a pad at one end of the unit and drill several wells, often alternating between the Middle Bakken and the underlying Three Forks zone.
“In most cases, when we’re fracturing the Bakken, we’re also fracturing the Three Forks,” he said. “In many parts of the formation, a combination of the two zones is what we hope to achieve.”
Rigs that can move long distances from county to county are optimum for drilling the initial held-by-production (HBP) wells, Mr Williams explained. “These rigs need to be able to break down into as few truckloads as possible because trucking in the region is hard to get and expensive. For the subsequent pad drilling, we need rigs that can skid easily from well to well.”
Whiting is also doing some production in the Red River and Mission Canyon pools, located near the southern end of the basin and in some areas, extending over the Montana-North Dakota state line. “For the most part, this is conventional drilling, and we’re using older, vertical-style rigs to find the reserves. However, the rigs need to be mobile and, ideally, truck-mounted,” Mr Williams said. Operators also are testing horizontal drilling applications for drilling the 11,000-ft vertical wells in these plays.
Permian, East Texas provide initial fields for new-design rig
By Katie Mazerov, contributing editor
Globe Energy Services has designed a five-axle land rig providing quick rig-up/rig-down operations, a mast with 116 ft of clearance and an adjustable drilling floor. Two of the new Mustang 600 Class rigs have been deployed to the Permian Basin for unconventional oil shale wells, and a third is working in the Kilgore gas field in East Texas. A fourth rig will be added this fall, also to the Kilgore field. Opportunities to deploy additional rigs to the Bakken and Eagle Ford are possible as well, according to Johnny Slaughter, vice president of well services. “The taller mast is a key element of this new rig, because the operator can rig up and clear the wellhead control equipment from the ground instead of a ramp,” Mr Slaughter said.
Keeping the rig on the ground rather than on a platform enhances safety by providing more stability, he said. Transportation costs associated with moving a ramp to the well site also can be reduced. Further, Mr Slaughter noted that 96-ft to 112-ft masts on more conventional rigs may have problems clearing taller wellhead control equipment.
Automated features include a hydraulic floor and operator control platform that can be operated from two positions – 1 ft to 15 ft, and 15 ft to 30 ft. The floor allows the slips to be centered if the rig-up is slightly off to one side, eliminating the hazard of the slips catching on the floor while pulling pipe out of the hole, Mr Slaughter said.
Faster trip times
The rig has a 1 1/8-in. tubing line that provides line strength up to 276,000 lbs and allows blocks to be strung on six lines to reach maximum derrick and line rating, resulting in faster trip times. “If we need to go to 290,000 lbs, which is full derrick strength, we can put the blocks on eight strings,” Mr Slaughter said.
Another key design element is a safe mode air adjustor for reducing pressure on the air slips when entering or exiting the wellbore. “Historically, this has been a challenge because when there is too much pressure on the slips, rig operators have accidentally hit the slip control valve and dropped a joint or a stand of pipe in the hole,” he explained. “By reducing the air pressure, the slips won’t kick out, thus eliminating the hazard of dropping pipe in the hole.”
Mounted on a five-axle carrier, the rig maintains optimum highway weight and height tolerances, he said. “The rig is small enough to compete with other smaller rig designs for tight locations and shallow wells.”
For drilling contractors, the Bakken has served as a catalyst for designing rigs that deliver the horsepower, mobility and automation that are driving production. With 57 active rigs out of a total Bakken rig count of 230, Nabors Drilling USA (NDUSA) is the largest contractor in the play. The company’s PACE-B (programmable AC electric) Series rig, a box-on-box, 1,500-hp model with a walking system, was built specifically for the Bakken and has consistently drilled 21,000-ft wells in less than half the time of most rigs in the basin, said Joey Husband, senior vice president and general manager of NDUSA.
Nabors currently has 25 PACE-B Series rigs in the region and will add four more later this year. “This rig is well suited for the Bakken, which is unique because the local infrastructure is under a lot of pressure,” Mr Husband said. “Drilling generates a lot of other activity, such as trucking and transportation, water delivery, fuel consumption, and delivery of parts and supplies.”
The PACE-B rig, designed for safe, efficient multi-well pads, enables more wells drilled from a single location, reducing diesel consumption, gravel requirements and overall impact on the environment. “The rig can drill an area of 11 sq miles from a single Bakken location,” Mr Husband said. “Since introducing this technology to the Williston Basin in 2010, we’ve drilled 3.4 million ft with PACE-B rigs and achieved improved reliability.”
The pump horsepower and hydraulic torque specifications of the rig’s top drive system are designed with enough capacity to reach 21,000-plus ft well depths with long horizontal sections. The box-on-box design is climate-controlled with an enclosed system to allow for drilling in the winter. Dual fuel power systems take advantage of the natural gas available on site, reducing diesel fuel requirements.
“The beauty of this rig is that the walking system allows it to line up perfectly over each well, which allows for more efficient drilling,” Mr Husband said. “This precludes problems sometimes seen with conventional rail systems where conductor pipes are pre-set prior to the rig arriving on location and slightly off center from each other.”
For multi-well pads, the walking system allows a full setback of pipe to be left in the derrick, with stands made up, so the rig can walk to the next well and immediately start drilling. “This saves time and allows for simultaneous operations on the rig, he added. “For our customers who are drilling pads with up to seven or eight wells, we can quickly and efficiently walk down the well row as we drill.”
The rig also includes several automated features to keep workers out of the pipe-handling path. “Power catwalks allow a single operator on the rig floor, via remote control, to guide the pipe from the racks onto the catwalk up into the rig where the top drive retrieves the pipe and hoists it into position,” Mr Husband explained. The rigs have remote-controlled torque wrenches, allowing the driller to make or break connections while standing away from the machinery.
“Control of the rig is done with a human/machine interface where a driller in a cyber chair uses a joystick, PLC (programmable logic controller) and touchpad commands to operate the top drive, drawworks and iron roughneck in a climate-controlled environment with cameras and data monitors,” he continued. “This automation doesn’t necessarily target people reduction but allows our crews to engage in value-added tasks outside the critical path.”
Trend to automation
HSE and economics are drivers of rig innovations for National Oilwell Varco (NOV). The company has various models operating in the Bakken, including the IDEAL spec rigs, other fit-for-purpose designs and custom rigs for operators with specific requirements. All can be outfitted with cold-climate features such as environmentally enclosed mast systems.
“Like most unconventional plays, the Bakken features tight oil or gas formations, and every operator has a different way of drilling the hole – some are vertical, some horizontal and some are S curves,” said Jay Thiessen, onshore global business development manager. “In many cases, operators are going into areas where transportation is difficult or road conditions don’t allow wide loads. Sometimes the formations require higher-than-than usual horsepower, more hydraulics for pumping or have high-pressure zones that require a higher-pressure blowout preventer (BOP) stack. In cases of pad drilling, the spacing is often very tight.”
But while drilling plans vary, a common theme in the Bakken is that operators are drilling long, extended laterals, which is why pad drilling is so prevalent, said Niels Meissner, product technical manager for NOV. “For any unconventional tight oil or gas formation, in order to maximize the productivity of the well, an operator must maximize contact of the borehole with the productive part of the formation,” he said.
The company is designing rigs and equipment packages that are increasingly automated. “We’re looking at more drilling solutions that minimize personnel and that translate to more automation,” Mr Thiessen said. Features are currently still more semi-automatic in nature, keeping a person in charge versus relying on robotics. “For example, we’re developing a program for one customer where the driller pushes a button to initiate both the tripping and drilling cycles. More autonomous control systems, like our NOVOS system, will be coming onto the scene in the next few years, in the Bakken and elsewhere.”
Some of the more common newer rigs supplied for flexible application across all shale plays are designed with more hydraulic horsepower and have systems that enable higher torque performance, Mr Thiessen noted. These hydraulic slingshot-type structures include variations of design, such as drawworks that can be mounted on either the rig floor or ground, SteelToe rig moving systems that enable the rig to walk in the X/Y direction, an option for a mast that can raise or lower on both the V-door side or the drawworks side for space optimization, and the ability to keep the top drive in the mast for transit.
From a drilling performance perspective, the company has two top drive software enhancements that can be installed on any rig equipped with an NOV top drive, Mr Meissner explained. SoftSpeed is a top drive control software upgrade that reduces or eliminates stick-slip, which often occurs when drilling extended-reach or long lateral wells. Another top drive enhancement, Twister, enables the top drive to put minor oscillations in the drill string to reduce friction when slide drilling.
“The technology also aids the directional driller in maintaining tool face, or orientation of his directional drilling tools,” he said. “For example, the driller can input a certain desired rotational angle into the system, and Twister will automatically compute and rotate the top drive a specific degree to achieve the desired angle of rotation downhole.”
Safety is another major focus. The Stand Transfer Vehicle (STV), for example, performs the pipe-racking function for either double or triple stands of pipe with a scissor arm mounted where a worker normally would stand to do the job. “This is an efficient and cost-effective system that maintains tripping operations of the rig, mimicking the work of a derrickman in process, while safely removing him from the fingerboard,” said NOV product technical manager Joel Heinen. “This has great benefit in a place like the Bakken with harsh weather conditions.”
Bakken by the numbers
Estimates of recoverable reserves: 10 billion bbls of crude oil; 2 billion bbls of oil equivalent associated gas
Daily oil production for June 2012: Just over 660,000 bbls
New wells: 2,017 brought online in 2011; 2,800 anticipated for 2012
Initial production rates: 900 bbls/day
Source: North Dakota Department of Mineral Resources
Extending the laterals
In line with the trend toward multi-well pads, Marathon Oil is drilling on more two-well and four-well pad locations and plans to go as high as six to eight wells per pad, or more, using modern rig technology such as Helmerich & Payne’s (H&P) FlexRig 3s, said Jim Thompson, Marathon’s drilling and completions manager for the Bakken. “The multi-well pads limit the footprint and the impact on the infrastructure and communities,” he explained. “In some areas, especially the Badlands, the topography is such that the only way we can effectively develop certain acreage is to drill from a multi-well pad.”
Marathon Oil has been operating in the play since 2006 and, in May, reached a milestone when it spudded its 300th Bakken well. The company announced in August plans to reduce its rig count from eight to five rigs due to the impact of lower commodity prices on the US crude and natural gas liquids markets. With a five-rig program, the company said it expects to maintain its projected 2012 exit rate of 30,000 bbls of oil equivalent per day and to retain its core acreage in the play.
“We intentionally brought in the H&P Flex3 rigs because they are modular by design and can move more quickly, saving time in terms of rig-cycle times,” Mr Thompson said. “These rigs also have safety built into the modularity to help protect workers, so we are well aligned with them culturally. We also benefit from consistent rig crews.”
Marathon Oil is seeing average measured well depths of approximately 20,500 ft; however, in the Badlands around the Missouri River and Lake Sakakawea, operators are drilling longer, 2 ½-section wells and looking at three-section wells for depths from 22,000 to 26,000 ft. “The geography of the area necessitates the need for longer laterals,” Mr Thompson said. “There also are ranges where we need extended lengths to drill under the lake.”
H&P has 35 rigs operating in the Bakken, approximately 65% of which are FlexRig3s, which is designed to accommodate a single-direction skid system that allows the rig to drill either a single-well pad or a single row of wells on a pad, said David Millwee, H&P’s vice president for performance solutions. The company has yet to venture into the basin’s experimental formations. “When we first arrived in the Bakken in 2006, we were drilling 16,000- to 18,000-ft measured depth wells with laterals of 6,000 to 8,000 ft,” he said. “We’re now drilling 10,000- to 12,000-ft laterals and recently extended to 14,000-ft laterals.”
The Flex3 rig, which has a fully integrated AC drive system, has a skid feature that allows the rig to skid effectively from well to well in a matter of hours. “The rigs also can move from pad to pad or well site to well site in three to four days. They are more efficient than traditional rigs,” Mr Millwee said. “This is important because trucks and cranes are in short supply. Also, the thaw and ice break-up on the roads take longer in this area.”
H&P is also running its Flex4S rigs in the area. These rigs have similar design features as the Flex3 but are built specifically for pad drilling and incorporate an X/Y skidding system to be used for multi-well pad drilling in the Bakken.
Introduced in 1998, the FlexRig is now in its fifth generation. “The Flex3 has been a workhorse for H&P since 2002, improving drilling times and reducing costs for operators,” Mr Millwee said. “The characteristics of the rig are set up very well to drill the 22,000-ft and greater measured well depths we’re now seeing in the Bakken.”
PACE is a registered term of Nabors Industries. IDEAL, NOVOS, SteelToe, Twister and SoftSpeed are trademarked terms of National Oilwell Varco. FlexRig is a trademarked term of Helmerich & Payne.