The Gulf Coast region’s Upper Jurassic Haynesville play in northern Louisiana and East Texas continues to be a real happening.
The play is defined by an organic shale interval approximately 200 feet thick stretching across approximately 6,000 square miles, according to AAPG member John Rhodes, manager at MXD Energy Partners LP, which is a prospect-generating company with working interest ownership in several areas of the play.
Anyone would be hard-pressed to pinpoint an onshore hydrocarbon play in Louisiana that has triggered the level of excitement attributed to the Haynesville. The play virtually up-ended the oil and gas business in this hydrocarbon-rich state where the coastal region activity has long held the spotlight while the many old fields in the north chugged along slowly as if on life support.
Once the Upper Jurassic Haynesville shale discovery well was announced by Chesapeake Energy in 2008, the land rush was on.
Leases quickly skyrocketed to the $25,000/acre range before the companies managed to take a collective deep breath and worked to promote a semblance of calm midst the near-chaos that enveloped this largely rural region.
Given the big bucks and production potential, calm is relative.
Petrohawk Energy plunged into the action early on and acquired substantial holdings.
“We have a program here that’s got decades worth of development,” said AAPG member Dick Stoneburner, COO at Petrohawk. “We think it’s prudent to learn as much as we can about this field – if you compromise data gathering and operational expertise, then you get behind.”
Initial production in the 20 MMcf/d range was announced for some wells relatively early in the play. However, first-year decline rates as much as 80 percent were a part of the rumor mill early on.
Data Treasure Trove
Given the number of uncertainties from the get-go, there’s good news for all in that the near lightening-fast development of the play has yielded a treasure trove of pertinent info to analyze.
Indeed, the rapid development of this play has resulted in a virtual explosion of new data that significantly contribute to understanding Jurassic stratigraphy and tectonics in the region, Rhodes said.
He commented that the productivity of the play is much less consistent than the structure and stratigraphy originally indicated, and noted that the fundamental determinants of Haynesville productivity are:
- Pre-Jurassic, tectonic influence on Haynesville stratigraphy.
- Variation of the Haynesville stress state caused by late Cretaceous volcanic and halokinetic tectonics and differential subsidence of the Gulf Coast passive margin.
“Additionally, the pressure and consequently the natural fracturing and energy within the Haynesville are impacted by stratigraphic variation of the juxtaposed Smackover, Cotton Valley lime and Cotton Valley Bossier intervals,” Rhodes said. “These intervals can act as conduits, baffles or seals to gas generated in the Haynesville.
“Where the Haynesville is isolated and can’t leak into anything else and there’s no faulting to let it leak, that’s where you have the highest and best productivity,” he noted.
Unlike many shale plays where completions target silty or carbonate zones within the shale that enhance porosity, permeability and brittleness, Rhodes commented that the Haynesville play is generally a homogeneous shale.
Productivity variation is difficult to discriminate based on log character, thickness or depth alone, but there have been observations that productivity may be enhanced as the interval becomes thinner.
Suggested causes for this are:
- Productivity decreases as shale thickens because of proximity to a deltaic source and a greater percentage of more ductile clays that impede effective fracturing.
- Thin areas are further removed from a deltaic source, leading to clearer water and more carbonate material in the shale, which makes the shale more brittle thereby enhancing fracturing.
The Haynesville shale is thickest in the salt basins, controlled by accommodation space and the proximity to the depocenters of clastic input, Rhodes noted.
Regarding the importance of pre-Jurassic structure, he said it’s important to differentiate between the well-known Sabine Uplift in this region and the Sabine Island.
“These two are frequently confused,” he said. “The Sabine Island is an old pre-Jurassic feature, whereas the Sabine Uplift is a younger Cretaceous feature – they have a separate genesis yet they’re frequently misrepresented as being synonymous.
“The most important feature relative to impact on the Haynesville is the island and not the uplift,” Rhodes emphasized. “Part of Sabine Island was emergent during the Upper Jurassic including Haynesville deposition, but most of the wells are located on the north flank and have Cotton Valley limestone or Smackover overlying Paleozoic sediments.”
Stress caused by the Sabine Uplift during the Upper Cretaceous tended to decrease total stress on the north flank of the Sabine and increase total stress on the south flank, Rhodes said. The current hingeline of the Haynesville structure is a likely focus of stress and correlates with the highest rate wells in the Haynesville shale.
“Pore pressure is increased by gas generation, which facilitates fracturing,” he added. “Pore pressure reduction by migration out of the Haynesville shale tends to impede natural fracturing.”
Emerging Sweet Spots
Owing to the relative newness of this play, it may be a tad early to tabulate an array of conclusions for the Haynesville play. However, Rhodes said sweet spots are emerging based on initial production rates, flowing pressure and decline rates.
He noted that production and log characteristics allow the play to be grouped into a few specific areas:
♦ Texas and Louisiana updip area includes southern Harrison and northern Panola counties in Texas along with southern Caddo, Bossier and northern De Soto parishes in Louisiana. The best wells are in southern Bossier Parish at the inflection into the North Louisiana salt basin and near a major regional fault.
♦ Louisiana downdip trend includes Louisiana’s southern De Soto, Red River and northern Sabine parishes. This area has some of the best wells with nearly all being above average. Pore pressure is generally high, and most of the area is at the hingeline into the salt basin.
♦ Panola platform in southern Panola, northern Shelby, northern Nacogdoches and Rusk counties in Texas has relatively poor production as the Haynesville Shale can be thin or even absent. Also the gas can migrate out of the system via the Cotton Valley limestone.
♦ Texas downdip area includes southern Nacogdoches, southern Shelby, northern San Augustine and northern Sabine counties; it’s contiguous with the Louisiana downdip area in Sabine Parish. Pore pressure is high here, and the wells are among the best in the play.
♦ North Louisiana and East Texas salt basin areas share the same characteristics, and correlation is difficult as the Bossier and Haynesville shales look similar with the latter missing its characteristic high resistivity. The shale is thicker than average and pore pressure is high, suggesting the potential may be greater than indicated by the few wells that already penetrate the interval.
It’s all still new and exciting, but certain aspects of the play were always evident.
“There were some old wells from Smackover exploration in the region,” Rhodes noted. “The pressure based on just mud weights from those early wells pretty much mimics what we’re seeing in productivity now.
“You could see the trends in the old drilling.”