Efficient calculation of transient fields in multilayered media
A scheme for computing fields radiated by transient sources residing above a grounded multilayered medium is proposed. First, the causality trick is invoked to obtain a new representation of the field excited by transient sources. Second, starting from this representation, a novel approach to rapidly computing this field assuming that the mutilayered stack is electrically thin, is developed. Third, the approach is applied to the accelerated calculation of multilayered transient fields.
Leaky-wave analysis of transient fields due to sources in planarly layered media
The transient field due to canonical sources in planarly layered media is obtained using a leaky-wave analysis. By proper choice of integration paths in both the complex frequency and complex wavenumber planes, transient fields are obtained exactly as a temporal inversion integral over a discrete sum of residues. The residues include both proper and improper surface-wave modes, analytically continued into the complex frequency plane. The method is applicable for all times of interest, although for certain source-receiver locations an "early-time" period is identified which encompasses the specular reflection from the nearest interface, and during which time the residue series requires special treatment. The presented analysis leads to a computationally simple and efficient method for obtaining transient fields due to sources in layered media. Results are shown for the transient potential due to line and point sources over a grounded dielectric slab, although the technique is applicable to multiple planar layers.
Mississippian Barnett Shale: Lithofacies and depositional setting of a deep-water shale-gas succession in the Fort Worth Basin, Texas
The Mississippian Barnett Formation of the Fort Worth Basin is a classic shale-gas system in which the rock is the source, reservoir, and seal. Barnett strata were deposited in a deeper water foreland basin that had poor circulation with the open ocean. For most of the basin's history, bottom waters were euxinic, preserving organic matter and, thus, creating a rich source rock, along with abundant framboidal pyrite. The Barnett interval comprises a variety of facies but is dominated by fine-grained (clay- to silt-size) particles. Three general lithofacies are recognized on the basis of mineralogy, fabric, biota, and texture: (1) laminated siliceous mudstone; (2) laminated argillaceous lime mudstone (marl); and (3) skeletal, argillaceous lime packstone. Each facies contains abundant pyrite and phosphate (apatite), which are especially common at hardgrounds. Carbonate concretions, a product of early diagenesis, are also common. The entire Barnett biota is composed of debris transported to the basin from the shelf or upper oxygenated slope by hemipelagic mud plumes, dilute turbidites, and debris flows. Biogenic sediment was also sourced from the shallower, better oxygenated water column. Barnett deposition is estimated to have occurred over a 25-m.y. period, and despite the variations in sublithofacies, sedimentation style remained remarkably similar throughout this span of time.