Regional assessment of the Eagle Ford Group of South Texas, USA: Insights from lithology, pore volume, water saturation, organic richness, and productivity correlations

Abstract

A comprehensive regional investigation of the Eagle Ford Shale linking productivity to porosity-thickness (PHIH), lithology ([Formula: see text]), pore volume (PHIT), organic matter (TOC), and water-saturation ([Formula: see text]) variations has not been presented to date. Therefore, isopach maps across the Eagle Ford Shale play west of the San Marcos Arch were constructed using thickness and log-calculated attributes such as TOC, [Formula: see text], [Formula: see text], and porosity to identify sweet spots and spatial distribution of these geologic characteristics that influence productivity in shale plays. The Upper Cretaceous Eagle Ford Shale in South Texas is an organic-rich, calcareous mudrock deposited during a second-order transgression of global sea level on a carbonate-dominated shelf updip from the older Sligo and Edwards (Stuart City) reef margins. Lithology and organic-matter deposition were controlled by fluvial input from the Woodbine delta in the northeast, upwelling along the Cretaceous shelf edge, and volcanic and clastic input from distant Laramide events to the north and west. Local oxygen minimum events along the South Texas margin contributed to the preservation of this organic-rich source rock related to the Cenomanian/Turonian global organic anoxic event (OAE2). Paleogeographic and deep-seated tectonic elements controlled the variations of lithology, amount and distribution of organic matter, and facies that have a profound impact on production quality. Petrophysical modeling was conducted to calculate total organic carbon, water saturation, lithology, and porosity of the Eagle Ford Group. Thickness maps, as well as PHIH maps, show multiple sweet spots across the study area. Components of the database were used as variables in kriging, and multivariate statistical analyses evaluated the impact of these variables on productivity. For example, TOC and clay volume ([Formula: see text]) show an inverse relationship that is related to production. Mapping petrophysical parameters across a play serves as a tool to predict geologic drivers of productivity across the Eagle Ford taking the geologic heterogeneity into account.

Position-specific 13C distributions within propane from experiments and natural gas samples

“…IIs kerogen (Hammes et al, 2016;Sun et al, 2016). It has experienced a range in thermal maturities from early oil window through wet and dry gas maturity, across a range of areas in the deposit.…”

Workflow for Probabilistic Resource Estimation: Jafurah Basin Case Study (Saudi Arabia)

“…Figure 7a presents a published (qualitatively scaled) water saturation distribution for the three tiers of the Jafurah Basin [17,18]. Based on the Eagle Ford analogy, the maximum and minimum water saturation were assumed to be 0.1 and 0.7, respectively, as presented by Hammes et al [50]. Assuming that all three TWQ tiers are prolific target zones, a digitization technique was utilized using the midpoint of each water saturation histogram column to obtain a normalized frequency distribution (Figure 7b).…”

Recovery Mechanisms for Cyclic (Huff-n-Puff) Gas Injection in Unconventional Reservoirs: A Quantitative Evaluation Using Numerical Simulation

“…The hydraulic fractures are modeled as discrete fractures that interact with the matrix and wells through the non-neighbor connections using a dual permeability formulation. The matrix properties were assumed to be homogeneous throughout the model and set to 8% porosity and 100 nanodarcys (nd) [26]. The initial water saturation was set at 37.5% which is the range of water saturations observed for the Eagle Ford [26].…”

“…The matrix properties were assumed to be homogeneous throughout the model and set to 8% porosity and 100 nanodarcys (nd) [26]. The initial water saturation was set at 37.5% which is the range of water saturations observed for the Eagle Ford [26]. Since, in many places, little water is produced from the Eagle Ford, we assumed that the initial water was also the irreducible water saturation.…”