--> --> Abstract: Geologic Framework of the Southeastern Portion of the U. Jurassic Haynesville/Bossier Shale Gas Play, Northwest Louisiana, by Paul R. Smith, Alan Kornacki, Holly Moore, Noureddine Yahi, Nathan Suurmeyer, Ron Mart, and Andrea Reynolds; #90124 (2011)

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Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Geologic Framework of the Southeastern Portion of the U. Jurassic Haynesville/Bossier Shale Gas Play, Northwest Louisiana

Paul R. Smith1; Alan Kornacki1; Holly Moore1; Noureddine Yahi1; Nathan Suurmeyer1; Ron Mart1; Andrea Reynolds1

(1) Shell, Houston, TX.

The Upper Jurassic (Early Kimmeridgian) Haynesville and Bossier formations are composed of organic-rich, argillaceous to calcareous silty mudstones that were deposited on a broad, sediment-starved shelf with an average water depth of about 150-300 feet. The Hayneville averages 120 - 150’ thick and is approximately equal parts terriginous clay (from deltas), biogenic carbonates (forams and other fossil fragments), and silt grains (possibly of windblown origin). Prodelta clay from southward-advancing deltas causes the Haynesville section to thicken northward. The thick areas have poorer reservoir quality and lower percent total organic carbon (TOC) due to dilution of the organic matter. The lower proportion of silt and carbonate in the thicker zones causes the rock to be more ductile, possibly resulting in reduction of total stimulated rock volume from hydraulic fracturing. The negative impact of clay is believed to be an important control on gas productivity.

The Upper Jurassic Bossier (Late Kimmeridgian to Tithonian) is >2000’ thick over the southeastern play area. In the north, it interfingers with the southward-advancing Cotton Valley and Terryville deltaic silts and sands. Clay content in the Bossier is generally higher and organic content lower than in the Haynesville. Within the Bossier sequence, the Mid- Bossier (150-300’ thick) is associated with a regional maximum flooding surface and is the most gas productive Bossier section due to being the most organic-rich and having the best reservoir and geomechanical properties. The Upper and Lower Bossier tend to be organically lean (hence had less gas generated and retained) and have less favorable reservoir properties (due to more clay). Burial history studies show relatively uniform passive margin subsidence that began after early Jurassic rifting, and continued until about Oligo-Miocene time. The region then experienced about 5000’ of uplift, which brought the Haynesville-Bossier into economic drilling depths.

Present-day TOC content in the Haynesville and Mid-Bossier is 2-5%, and the original richness prior to kerogen maturation is calculated to be 3-10%. The predominant kerogen in both units is Type II (oil-prone) and the thermal maturity is VR>2.0-2.5% (dry-gas window). Geochemical studies indicate that the gas was generated in-place through kerogen maturation, with organic-rich zones (Haynesville and Mid-Bossier) having generated and retained the most gas.