The Haynesville shale (also known as the Haynesville/Bossier) is situated in the North Louisiana Salt Basin in northern Louisiana and eastern Texas, with depths ranging from 10,500 to 13,500 ft (3,200 to 4,115 m). The Haynesville is an Upper Jurassic-age shale bounded by sandstone (Cotton Valley group) above and limestone (Smackover formation) below.

Although the Haynesville has been known for years, its active life as a prolific gas play began only in 2008. The Cotton Valley and Smackover are both well known in the industry.With the advent of horizontal drilling and hydraulic fracturing techniques, the play found its day in the sun.

Well data for the Louisiana portion of the Haynesville shale as of Dec. 2, 2010, is shown. (Source: Louisiana Department of Natural Resources)

In 2008 both Petrohawk Energy Corp. and Chesapeake Energy Corp. moved into the region, although several companies now are moving to liquid-rich plays such as the Marcellus and Eagle Ford. Low gas prices have lightened the motivation for extensive Haynesville operations, yet the play maintains a high potential for development should the market begin to favor gas. The play has an estimated reserve of 717 Tcf of gas in place, with 251 Tcf considered to be technically recoverable. Advances in technology surely will unlock a major portion of Haynesville potential within the next five to 10 years.

Haynesville characteristics
The Haynesville differs dramatically from other nearby plays such as the Barnett, Woodford, and Fayetteville as it is Jurassic in age; these other plays are older (Mississippian and Pennsylvanian). In addition to comprising younger sediments, the Haynesville is deeper and hotter than any other US shale play.

“It’s not so much deeper geologically; it’s deeper pressure-wise,” said Rob Fulks, director, Unconventional Projects at Weatherford International Ltd. “The Haynesville has a very steep pressure gradient.”

Operators working in the Haynesville are dealing with HP/HT drilling and completion conditions.

While these conditions provide a specific set of challenges for drilling and completion operations, they also provide the Haynesville’s attractive qualities. “Because the Haynesville has so much more overburden pressure, it has the ability to retain much more free gas, which is being held down with compression forces,” Fulks said.

From a resource development perspective, Haynesville wells are known for much higher initial pressure (IP) as compared to other shale plays. High IPs typically translate into estimated ultimate recovery(EUR).While high IPs usually diminish over a period of time, the decline rates experienced in Haynesville wells tend to be more dramatic. The question most producers want to answer is, “What is the decline curve?” For the Haynesville, decline rates commonly average 80% to 85% in year one. A well that comes in at 20 MMcf/d can be down to 4 MMcf/d within the first year. However, rapid decline is not necessarily a bad thing. “If you had a well that was producing 3 to 4 MMcf/d, that’s still a good well,” Fulks said. “It’s just such a dramatic difference from where it came on.”

While the rapid decline rates are not exactly a deterrent to Haynesville development, companies such as Petrohawk are looking at methods to mitigate decline and possibly increase the overall life of those wells. In a 1Q 2010 conference call May 5, 2010, Floyd Wilson, CEO of Petrohawk, said, “Our restricted rate program in the Haynesville is yielding some very exciting results.”

The company’s restricted rate program was developed from a 2009 pilot program. By using smaller choke sizes on its Haynesville wells, Petrohawk has lowered its IPs in the hope of extending well life into a period featuring more favorable gas prices. The company is looking to increase Haynesville EUR, but the restricted rate program is a fairly new development. “The decline rate is about half – it is 40% to 50% in the general sense – at the worst,” Wilson said.

The Haynesville tends to be a dry-gas only play, so it does hold a disadvantage in an era of low gas prices. But a positive aspect for the Haynesville is that it remains one of the most prolific gas plays in the US – based on initial rate and EUR, the Haynesville is ranked first when it comes to gas. Despite the rapid rate of decline in Haynesville wells, the EURs are the highest among other US gas plays.

Drilling characteristics
Average well costs are published at US $7.5 million, although some evidence suggests that this sometimes can be higher. Average drilling time varies, but typically ranges from 35 to 50 days.

The primary challenge for Haynesville drilling is the use of HP/HT MWD tools. While technology is advancing in this sector, very few tools can survive temperatures above 325°F (163°C). Haynesville temperatures consistently range from 325°F to 350°F (163°C to 177°C) and sometimes higher. Combining high pressures and temperatures with the abrasion associated with drilling through the Travis Peak section (a hard formation that can prove troublesome for dillers) creates a challenging environment.

Many LWD/MWD tools on the market are designed to work in these temperatures. While there is no guarantee that these tools will have a long life, they will work, which is the main issue. Additional advances are taking place in the application of rotary steerable systems for Haynesville operations. A typical Haynesville well drills to 9,500 ft (2,896 m) and builds angle to a horizontal lateral that extends to an average length ranging from 3,500 to 5,000 ft (1,067 to 1,524 m). Putting stress on the bottomhole assembly through the curve section often requires drillers to stop before continuing. Extra trips can cost valuable rig time.

Rotary steerable tools such as Weatherford’s Revolution are helping to save time by allowing drillers to build curve and proceed through the entire lateral without pulling out to change the bit.

“If the bit match is done correctly, entire runs of 4,000 ft (1,219 m) plus can be made with a single bit in some pretty tough drilling,” Fulks said. This highly engineered solution is helping operators save time and money.

Hydraulic fracturing is an area where the Haynesville has benefitted most. The average frac job in the play ranges from 10 to 15 stages, depending on stage length. Average completion cost in the Haynesville is approximately $3 million per well.

A number of companies are working on developing more effective fracing techniques that develop more complex fractures. Fracture networks can be affected by several factors, including perf placements, lateral lengths, and specific fracing techniques. While most operators prefer the factory approach to fracing all wells in a similar manner, research shows that tailoring jobs on a stage-by-stage, or at least well-to-well, basis can improve overall production. For example, with two horizontal laterals, being able to conduct either zipper fracs or simul-fracs can help to create improved fracture complexity.While this approach could increase finding and development costs in the near term, technology could improve and provide more return on investment in the long term.

Plug-and-perf completions are common for dry-gas scenarios; open-hole systems are not common in the Haynesville. One thing is certain — the completion end of the business is an area that will be targeted for innovation in the future. Determining the effectiveness of each stage will require much more analysis. A common theory is that some stages in an average completion contribute more than others.

“Being able to do more analysis on stage-by-stage productivity and the innovations that derive from that will be an area of technology development for some time,” Fulks said.