Ancestral Basin Architecture:

A Possible Key to the Jurassic Haynesville Trend

Bruce J. Martin¹ and Thomas E. Ewing²

¹25630 Zion Lutheran Cemetery Rd., Tomball, Texas 77375

²Yegua Energy Associates LLC, 19240 Redland Rd., Ste. 200, San Antonio, Texas 78259

EXTENDED ABSTRACT

Ancestral Gulf Coast Basin architecture is responsible for defining much of the Jurassic Haynesville shale mudstone trend. Less extended basement blocks created during Early and Middle Jurassic rifting and overlain by a variable thickness of Callovian salt ultimately formed the foundation of large Haynesville (Gilmer) carbonate platforms that provide boundaries to the Haynesville organic shale trend. Localized salt movement influenced Haynesville deposition where areas of thicker salt deposition coincide with basement features. Subsequent salt movement on the flanks of these features allowed for local fairways of salt deflation, which received a thicker Haynesville organic shale sequence and experienced less subsequent disruption. For the most part, salt movement in the Sabine Uplift area was completed during the Late Jurassic. Post-Jurassic faulting was therefore minimized, preventing leakage of oil or gas from the Haynesville organic shale reservoirs.

The ancestral Sabine platform complex acted as the nucleation site for the unique characteristics of the Haynesville shale mudstone reservoirs. Upwelling along eastern flanks of the ancestral Sabine platform where west-flowing paleocurrents impinged on the platform, provided thicker, more favorable reservoir facies of Haynesville organic shale reservoirs. An understanding of salt movement via analysis of gravity-magnetic data closely tied to seismic and well control provides an inexpensive, yet effective means of mapping large areas. High-resolution gravity and magnetic mapping may provide even further insights for exploitation, especially considering the cost of regional 3D seismic.

Presently, the full extent of the Haynesville trend along the Sabine platform is not fully defined, due to lack of deep control. This is particularly true along the Texas side, where thick Haynesville/Bossier flanking wedges are unexploited and are beyond present economic limits. Should these wedges provide favorable facies when tested, exploration may shift to a deeper southern extension of the trend.

In certain areas, younger Jurassic faulting is coincident with reactivated basement trends providing geothermal pathways. These pathways may have allowed hydrothermal fluid migration into the overlying Haynesville shale mudstone reservoirs and certain Haynesville carbonate reservoirs. Mineral assemblages due to thermochemical sulfate reduction have been found near these faulted areas which may indicate the migration of hydrothermal fluid. In at least one case, dissolution by such fluid migration has resulted in a substantial void in the Haynesville carbonate section. How pervasive such voids and mineralization may be is unknown due to limited control. However, a high geothermal signature is prevalent in the southern and eastern parts of the Haynesville play area.

Future exploration of the Haynesville trend will depend upon duplicating key factors found in the Sabine area. Workflows utilizing reconnaissance tools as highlighted in this paper will allow companies to update their basin architecture models. Applying unconventional exploration workflows and understanding of hydrothermal flows to the Jurassic salt basins will unlock many potential areas, allowing for revitalization of a mature region.

REFERENCES CITED

Ewing, T. E., 2001, Review of Late Jurassic depositional systems and potential hydrocarbon plays, northern Gulf of Mexico Basin: Gulf Coast Association of Geological Societies Transactions, v. 51, p. 85-96.

Ewing, T. E., 2009, The ups and downs of the Sabine Uplift and the northern Gulf of Mexico Basin: Jurassic basement blocks, Cretaceous thermal uplifts, and Cenozoic flexure: Gulf Coast Association of Geological Societies Transactions, v. 59, p. 253-269.

Martin, B. J., and T. E. Ewing, 2009, Ancestral basin architecture: A possible key to the Jurassic Haynesville trend: Gulf Coast Association of Geological Societies Transactions, v. 59, p. 511-515.

	Figure 1. Possible origin of the Haynesville organic shale (based on Ewing, 2001, 2009 [this volume]). West to northwest-directed paleocurrents inferred for the Late Jurassic impinged on the Sabine shoal complex, built on the older basement high blocks, leading to upwelling of fertile deep waters and deposition of organic matter.
	Figure 2. Full log suite for the Haynesville shale interval, from the Getty #1 Mangham well, Panola County, Texas. The Haynesville shale is here 430 ft (131 m) thick and is overlain directly by the Bossier shale.
	Figure 3. Magnetic depth to basement in the Sabine area, also showing significant fault zones and salt features. Fractured Haynesville limestone and dolomite is productive in the Stockman trend of Shelby County; Haynesville shale is prevalent over most of the area shown. Depth to basement map courtesy of Earthfield Technology.
	Figure 4. Geothermal gradient contours, magnetic linears, and two wells with evidence of hydrothermal alteration in the Shelby County area. Gradient contours shown are degrees Fahrenheit per 100 ft (e.g., 2.8°F / 100 ft = 51°C / km) from bottom-hole temperature data.