Solids control means success in the Barnett Shale natural gas fields beneath Fort Worth, Texas
Story and photos by Rich Cook, editor
Nicknamed "Cowtown," Fort Worth, Texas, is known as the center of the Texas cattle industry. Today, visitors can enjoy Old West-style cattle drives, visit the opry for live country music and watch rodeos at the Fort Worth Stockyards, the only remaining cattle stockyard in the United States. The Old West comes alive every year during the Fort Worth Stock Show and Rodeo that runs from mid-January to mid-February. Held annually since 1896, it is the oldest continually running livestock show and rodeo.
Today, the city covers nearly 300 mi2 (780 km2) in Tarrant and Denton counties and serves as the county seat of Tarrant County. With a population of just below 700,000, Fort Worth is the seventeenth largest city in the United States and is the fifth largest city in Texas.
Fort Worth began life in 1849 as a U.S. Army camp built to protect the surrounding cattle ranches from the Mexican army and marauding Native American tribes. The fort was first named Camp Worth in honor of Major General William Jenkins Worth. General Worth served in the Texas army under General Zachary Taylor during the Mexican War in which Texas gained independence from Mexico at the Battle of San Jacinto on April 21, 1836. After Texas became the 28th state in 1845, Worth was appointed to head the Department of Texas. He died of cholera in early 1849 just a month after proposing a line of forts along the western Texas frontier.
General William S. Harney took command of the Department of Texas and ordered a camp built at the confluence of the West Fork and Clear Fork of the Trinity River. This was the first Camp Worth. The original camp was moved to the top of the bluff overlooking the Trinity River later that year and is the site of the current Fort Worth courthouse. The camp was officially renamed Fort Worth by the U.S. War Department on Nov. 14, 1849. No trace of the original camp remains today.
The small outpost soon became a stop along the legendary Chisholm Trail, a dirt path used to drive cattle from ranches in South Texas to railheads in Kansas. Cowboys stopped in the small settlement for supplies as they moved their herds of longhorn cattle north. The last stop in civilization before the long haul across the wild expanses of North Texas, Oklahoma and Kansas, Fort Worth offered cowboys gambling and carousing in local saloons. This area of town became known as Hell's Half Acre, the biggest collection of bars, dance halls and bawdy houses south of Dodge City, Kansas.
With the arrival of the Texas and Pacific Railway in 1876, the town boomed and grew quickly as the center of the Texas cattle industry. Settlers from the U.S. South, still suffering the effects of the U.S. Civil War (1861-1865), moved west and settled in the growing community.
For the next 100 years, Fort Worth was known as a rough and bawdy town where cowboys came to gamble away their few dollars. Many outlaw gangs hid out in the city's Acre where shootings, knifings, muggings and brawls were a nightly event. The town newspaper claimed "it was a slow night which did not pan out a cutting or shooting scrape among its male denizens or a morphine experiment by some of its frisky females." By the early 20th century, many preachers and lawmen made attempts to clean up the town, with limited success.
The second boom came to Fort Worth in the early 1980s when new drilling methods and technologies opened up the Barnett Shale to exploration.
The Barnett Shale is a natural gas source bed made up of shale that consists of very fine grain particles of quartz and clay minerals. The rock formation is extremely hard and almost completely nonporous and impermeable. It is known as a tight gas reservoir, meaning that the gas is not easily extracted from the very hard rock formations. It lies between 6,500 ft (1,981 m) and 10,000 ft (3,048 m) below the surface.
Over the course of 100 million years during the Paleozoic era, Texas was a shallow ocean three times. Deposits of phytoplankton and zooplankton were laid down during each successive flooding and after another 300 million years, became natural gas now found in the Barnett Shale. The mud in which the phyto- and zooplankton were deposited hardened to become the shale itself. As more layers of sediment settled on top of the mud and plankton, the increasing pressure turned the mud into shale and the plankton into natural gas and oil.
The Barnett Shale covers approximately 17 counties mostly to the west and south of Fort Worth. It is estimated to cover over 5,000 mi2 (13,000 km2). It is believed to be the largest onshore natural gas reservoir in the United States. The United States Geological Survey estimates that the shale contains 27 trillion ft3 (765 billion m3) of gas and it is still actively being discovered.
The Barnett Shale is named for John W. Barnett, who settled in San Saba County in the late 1800s. He named a stream that ran through his ranch the Barnett Stream. Years later, in the early 20th century, geologists on a mapping exercise discovered an outcropping of the thick, black, organic-rich shale near the stream and named it the Barnett Shale.
In the 1950s, wildcatters discovered that the Barnett Shale was a natural gas field, but it was not until the 1980s that the technology evolved to the point where the natural gas deposits were accessible. It was only in the last five to 10 years that it has been economically feasible to extract the natural gas.
The Barnett Shale consists of three major sections. The core area lies within Fort Worth's city limits including Tarrant and Denton counties. The secondary area is outside Fort Worth to the southwest and north, including Parker, Johnson, Montague and Cooke counties. The outermost region includes Clay, Jack, Palo Pinto, Hood, Somervell, Erath, Hamilton, Bosque and Hill counties.
Because the core areas of the Barnett Shale are within the city limits of Fort Worth, operators face special problems that operators either offshore or drilling far from cities never face.
In particular, operators within Barnett Shale contend with local governments and neighborhood associations that are wary of natural gas wells being drilled in their neighborhoods and close to their schools. A few citizen groups have formed in Fort Worth to combat the drilling in neighborhoods and around the city. One, Fort Worth Citizens Against Neighborhood Drilling Ordinance (FWCanDo!), believes that gas drilling and related activities are a threat to people, property and wildlife. According to the FWCanDo! website, they are concerned with issues like soil, water and air contamination. They argue that rigs in close proximity to business and schools present undo hazards.
Canadian operator EnCana Oil & Gas Inc., along with many of the operators in the Barnett Shale, have self-imposed environmental policies to limit, if not eliminate, environmental hazards. EnCana works with local governments, neighborhood associations and groups like FWCanDo! through a program called EnCana Cares to find common ground so that they can continue to drill wells in close proximity to heavily populated areas while staying safe and environmentally friendly.
These groups are also concerned with the noise and light that inevitably comes from the 24-hour-a-day drilling operations. Many areas now require sound barriers around rigs, especially those drilling near neighborhoods. The heavy curtains block much of the sound from the rig, enabling a normal life to continue in the neighborhoods.
Damage done to the infrastructure of the area is a common issue raised by governments and area groups. Heavy machinery moving through roads designed primarily for residential traffic can cause significant damage to the roads and underground water or sewage systems. Many local governments are imposing tariffs as compensation for damage caused to local roads by heavy trucks and machinery.
Because of the often tight quarters in which the rigs are operating, traditional methods of waste disposal and mud storage cannot be used. Reserve pits are still used in outlying areas of the Barnett Shale where space and terrain allow, but many areas within Fort Worth itself do not allow them. There is simply no space.
Environmental concerns also dictate the use of closed loop systems that do not dump waste into a pit but contain the drilled cuttings. Fort Worth has mandated that all wells drilled within city limits must be drilled using a closed loop system.
For operators like EnCana, using a closed loop system whenever possible makes more sense both environmentally and financially.
The costs associated with upgrading a rig to the closed loop system are comparable to the cost of digging a reserve pit. In areas with significant rock that must be removed to build the pit, costs can exceed $100,000. And that cost is just for digging the pit; it does not include costs to close the pit once the rig is removed.
"It just makes more sense to go with the closed loop system," said David Roule, group lead for North Texas drilling and completions at EnCana, "The costs are comparable and it is much more environmentally friendly."
In addition to the challenges that come from drilling in and around the seventeenth largest city in the United States, operators like EnCana face the normal costs of drilling wells. Because of the geological structure of the Barnett Shale, drilling wells and extracting the natural gas once had been prohibitively expensive and technologically challenging.
That was until horizontal drilling and hydraulic fracturing, or fracing, was introduced in the Barnett Shale in the early 1980s.
Only since 2000, when natural gas prices rose, have these techniques really allowed the Barnett Shale to be fully explored.
Horizontal drilling offers significant advantages over traditional vertical drilling, especially in a reservoir like the Barnett Shale. Instead of a small concentrated drainage area, the horizontal well spreads the useful area out along the entire length of the lateral section. This effectively increases the wellbore from a few feet to between 3,000 ft (914 m) and 4,000 ft (1,219 m). Each well is drilled vertically to just above the Barnett Shale and then the curve to horizontal is started. By the time the gradual curve, typically with doglegs of between 8 degrees per 100 ft (30 m) to 12 degrees per 100 ft (30 m), reaches the horizontal, the wellbore is in the Barnett Shale.
While drilling a horizontal well is more expensive than drilling a vertical well, this allows more wells to be placed on a single pad. Up to 20 wells can be placed on a single pad, although EnCana typically places a maximum of five wells on a pad. EnCana has recognized the financial benefit of multi-well pads in recent years and sees it as the future of their operations within the Barnett Shale. Costs like damages and pad construction costs can be split across all of the wells.
"Multi-well pads are a big area that allows us to reduce costs," said Roule. "We calculated that with two wells on a single pad, we can recognize a significant savings and greater savings with each additional well."
The second technological advance that has opened up the Barnett Shale is hydraulic fracturing, or fracing. Fracing is a method by which water is pumped, at high pressure, into the well. The water finds its way into the natural fissures in the shale. The high pressure behind the water fractures the fissures, causing them to open up. Once open, the natural gas inside the shale can more easily seep out into the wellhead and be extracted.
Because the shale is under significant pressure, the fissures sometimes reclose after the fracing water is removed. To counter this, operators will sometimes mix sand in with the fracing water. When the water is removed, the sand stays in the fissures and prevents them from closing up again.
The availability of water, both for fracing and completion of wells, is a potential future problem for operators in the Barnett Shale. It takes as much as 75,000 bbls of water per stage to complete a well and wells may have as many as seven stages.
Historically, operators paid land owners a fee to use pond water. Now the Texas Commission on Environmental Quality (TCEQ) regulates the water from ponds. If an operator uses water for fracing or completion then returns it to the pond, it becomes the property of the TCEQ and is therefore subject to additional costs. Some companies drill water wells next to the natural gas wells to provide the required water.
Dewatering, the process of recovering excess water from the waste material removed from the mud in a closed loop system, has great potential to resolve this problem in the Barnett Shale. M-I SWACO gained permission to run dewatering systems on one EnCana rig as an experiment to show how they can save time, money and effort.
Dewatering allows operators to recover excess water from the closed loop system and store it in frac tanks for later use instead of paying for disposal at a land farm. M-I SWACO dewatering solutions use polymers to draw fine solids together to form larger clumps. The clumps are separated from the water in decanting centrifuges and are then removed for disposal. The water can then be treated and reused for fracing, well completion or reuse in the drilling fluid system. Added to a solids control system, dewatering only adds about $300 to the daily rig costs and saves operators from trucking in large amounts of water.
Today, EnCana and other operators face tighter budgets and the need to reduce the cost of drilling each well. For EnCana, the best way to achieve this is to drill faster. In fact, they set the record in early 2008 for drilling the fastest lateral section of a well in the Barnett Shale, achieving 3,500 ft (1,067 m) of drilling in 17 1⁄2 hours.
"We achieved an instantaneous ROP of 390 ft/hr (119 m/hr) with no signs of the hole trying to pack off," said Roule. "We've yet to find the limit with respect to ROP and hole cleaning."
M-I SWACO provided the mud and solids control systems for that record.
And even when not setting records, EnCana is pushing the perceived limits of ROP. High ROPs mean fewer days on the job and greater savings per well. In 2005, they averaged 26.6 days per well from spud to TD. In 2006, the average dropped to 22.1 days per well. In 2007, it dropped to 15.4 days. Through 2008, they have averaged about the same number of days per well as 2007. By removing the new EnCana wells in the Wise, Cooke and Denton counties where drilling is tougher due to the geology, their average spud to TD time in 2008 was 14.8 days.
Cost per well has stayed roughly the same through this four-year period while individual costs rose. This demonstrates how reducing the number of days on a well can balance or reduce costs of drilling as expenses rise.
For example, in 2006 EnCana spent about $300,000 more per well than in 2005, but this was due to an increase in the number of horizontal wells, which are by nature more expensive than traditional vertical wells.
Cost per well dropped half a million dollars in 2007 but increased slightly in 2008 due to the increased costs of fuel and steel used in casing. In 2008 EnCana also began drilling more wells in Denton and Wise counties where wells are typically deeper, ROPs are slower due to harder layers of rock and wells have more hole problems.
"While we're spending that $50,000 per day in the curve and the lateral, we can save $2,000 per hour for every hour we can shave off on these wells," said Roule.
"The only way we can do that is to stay on top of people to keep ROPs up and hole issues to a minimum."
At first, many field people resisted the high ROPs, insisting that it was not possible to control the solids well enough to maintain the required rates of penetration. Traditionally, EnCana and other operators had limited penetration rates in the laterals to 150 ft/hr (46 m/hr) due to concerns about hole cleaning.
"We told the guys out in the field, 'if you drill yourself stuck due to high penetration rates, we will personally come out, shake your hand and congratulate you on finding the limits of ROP,'" Roule said. "We never saw one sign of the hole trying to pack off."
The key is keeping the hole clean. Since mud is recycled through the well in the closed loop system, removing the cuttings from the mud is vital to maintaining the high ROP. And it is not just the large cuttings that have to be removed. Small particles, down to the ultra fines, must also be removed or the mud properties will deteriorate to the point that the drill string can easily become stuck, significantly adding to the cost of drilling the well.
M-I SWACO solids control equipment directly affects the time to drill a hole by keeping the solids down, reducing hole cleaning problems and allowing for faster penetration. In November, EnCana began using M-I SWACO solids control equipment on their rigs. They are renting centrifuges and tanks from M-I SWACO, who also provides the personnel to manage and maintain the solids control equipment.
"What we do is add solids control equipment," said Lincoln Tolleson, senior account representative. "We keep the drilling fluid clean by mechanically separating the solids from the liquids to reduce the volume of dilution required to maintain the desired fluid properties. For example, if you have a 100 bbl mud system and you add 25 bbl of dirt, you've got to add more fluid to maintain the original properties. Suddenly you have more volume than your 100 bbl mud system can accommodate and that extra volume has to go somewhere. It costs the operator money to build the additional volume and to get the extra volume to the land farm for disposal. This is where we save the operators money. Now, with our help, they can comply with internal, governmental or environmental regulations and do it economically."
In M-I SWACO mud schools, instructors use a can of whole kernel corn as an illustration. With the kernels whole, it is easy to pour the contents of the can into a bowl. It is easy to stir the corn with its water because the particles are large and do not absorb the water. When the particles are reduced in size, as when the corn is put into a blender, it becomes much harder to pour.
"Poor solids control leads to unwanted dilution, and for closed loop jobs that can mean many truckloads of drilling fluid being hauled in and out of the lease roads that can wind through neighborhoods and schools," said Gary Fout, senior project engineering advisor. "If proper control of low gravity solids is not achieved, the drilling fluid can become very thick and PV (plastic viscosities) can go off the chart. Drilling with high LGS (low gravity solids) can lead to stuck pipe, slow rates of penetration, premature bit failure, worn drill string, damaged pump parts and other issues."
With M-I SWACO solids control systems now in place on EnCana rigs, the company is confident in its ability to continue to keep their holes clean even when drilling at high ROPs. And as budgets tighten, forcing closer controls on everything from solids control to water supplies, M-I SWACO is well positioned to provide the environmental solutions to operators in the Barnett Shale for years to come.
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