Palaeomagnetism of the Mississippian Barnett Shale, Fort Worth Basin, Texas

Abstract

A palaeomagnetic study of four oriented cores was conducted to better understand the timing of diagenetic events in the Mississippian Barnett Shale, a primary source rock and the unconventional gas reservoir in the Fort Worth Basin, Texas. Thermal demagnetization removes a present-field modern viscous remanent magnetization (VRM) as well as a chemical remanent magnetization (CRM) that has shallow inclinations and streaked south–SE-directed declinations. The VRM was used to orient the CRM data for one well and it produced a similar streak of directions. The streaking of directions could represent a mixing trend between two or more CRMs. Specimens from bedding-parallel and NE subvertical mineralized fractures contain a CRM that is interpreted to be of Pennsylvanian age and to have formed in response to burial diagenetic processes. NE- and NW-oriented vertical fractures are common to rocks that contain late Permian to Triassic CRMs. Sr and sulphur isotope results from vein minerals around NE fractures suggest the CRM could be related to fluids sourced from the Ouachita front. The SE directions in the streak could be explained if the northern part of the basin experienced a component of anticlockwise rotation of up to 20° in the Pennsylvanian.

An integrated paleomagnetic, rock magnetic, and geochemical study of the Marcellus shale in the Valley and Ridge province in Pennsylvania and West Virginia

“…Although a significant number of events have occurred during the diagenesis of the Marcellus Subgroup, there has been little alteration of the mechanical stratigraphy. This is different than other studies of shales like the Barnett which has had significant alteration as noted by the presence of sulfates and silicates in the matrix and veins [ Dennie et al ., ]. It is important to note that these conclusions may apply more directly to the carbonate‐rich beds in the Marcellus Subgroup as the specimens from this study were mostly wackestones, while mudstones and analysis of clay‐rich specimens were limited.…”

“…Research focusing on shales has long been neglected due to the assumption that all shales essentially look the same. The discovery of shale gas units such as the Barnett Shale in Texas and Marcellus Subgroup in the Appalachian Basin has resulted in new research on shales which indicates that shales can be heterogeneous because of depositional [e.g., Lash and Engelder , ] and diagenetic processes [e.g., Gale et al ., ; Dennie et al ., ]. Diagenesis of shales can alter the mechanical stratigraphy of shales which is important to recognize before exploiting them for their resources.…”

Mineralogy-based brittleness prediction from surface seismic data: Application to the Barnett Shale

“…Dennie (2010) and Dennie et al (2012) find evidence of postdepositional Figure 12. Extracted λρ-μρ from each microseismic event location corresponding to (a) well C and (b) well D (well locations are shown in Figure 10c).…”

A Diagenetic Study of the Wolfcamp Shale, Midland Basin, West Texas

“…At the University of Oklahoma, the paragenesis of several North American shales from different depositional basins and tectonic settings were compared. Paragenetic sequences were constructed for the Marcellus Shale (Devonian), Woodford Shale (Devonian/Mississippian), Barnett Shale (Mississippian), and Haynesville Shale (Jurassic) (Dennie et al, 2012;Benton, 2013;Roberts, 2014;Steullet, 2014;Manning, 2015) in order to compare authigenic mineralogy and also timing of diagenetic events (Figure 16). Authigenic minerals, such as, calcite, dolomite, quartz, barite, celestine, anhydrite, sphalerite, and albite are found in all five shale units.…”

“…Hiemstra and Goldstein, 2005). Within the Barnett Shale monazite and stillwellite are identified above the Barnett/Viola unconformity, which are minerals linked to potential hydrothermal fluid origins (Dennie et al, 2012). Within the Marcellus Shale, sylvite was identified within the two cores (Steullet, 2014).…”