Application of Lithofacies Models to Characterize Unconventional Shale Gas Reservoirs and Identify Optimal Completion Intervals

Abstract

Unconventional shale gas reservoirs are economically viable hydrocarbon prospects, and their development has rapidly increased in North America. These reservoirs must be routinely drilled horizontally and hydraulically fracture stimulated to maximize production rates. Identification of the different chemostratigraphic units or lithofacies that make up these reservoirs is crucial for devising completion strategies because some lithofacies are more favorable to gas recovery due to their organic content and geomechanical characteristics.Lithofacies are indicative of eustatic changes during deposition and are typical geo-markers related to the preservation and amount of accumulated Total Organic Carbon (TOC) for a given basin. Gas content is related to TOC and varies according to lithofacies. Based on the mineralogical and TOC content, some lithofacies are favorable for gas production (e.g., siliceous lithofacies) and the geomechanical properties of these lithofacies often possess low fracture gradients that are conducive to forming extensive fracture fairways for recovery of gas. Other lithofacies can be fracture barriers and zones of fracture propagation attenuation (e.g., carbonate lithofacies).A shale gas facies expert system was developed with the goal of chemostratigraphically characterizing different shale plays and utilizing an integrated petrophysical reservoir evaluation approach to identify optimal completion intervals. This system can aid operators design selective completion strategies, which can potentially reduce fracturing expenses and optimize well productivity. The expert system incorporates a combination of density, neutron, acoustic, nuclear magnetic resonance and geochemical logging measurements. This system first characterizes the lithofacies based on their geochemical makeup and then flags the most favorable and unfavorable zones using a simple "stop-light" approach based on the petrophysical and geomechanical properties.

Multiproxy geochemical characterization of Kommugudem Formation, Krishna Godavari Basin, India: Implication on hydrocarbon potential and shale brittleness

“…Kommugudem Formation on basis of mineralogy indicates similar composition as brittle zones of the Barnett Shale Formation (Figure 11a,b). The Barnett Shale consists of 20.0 to 80.0% quartz with a wide range of mineralogical variation resulting in seven different lithofacies, while Kommugudem Formation has quartz ranging from 40.97 to 91.19% (Loucks & Ruppel, 2007; Mitra, Warrington, & Sommer, 2010). A further similarity is explored based on the form of minerals, which is governed by post‐depositional alterations.…”

Verification and Application of Sequence Stratigraphy to Reservoir Characterization of Horn River Basin, Canada

“…The transgressive systems tract represents high TOC and pyrite contents with high porosity. The abundance of pyrite influences brittleness, and therefore affects the completion quality and reservoir reserve estimates [34].…”

Lithofacies Types, Assemblage Characteristics, and Sedimentary Evolution Model of Lacustrine Shale in Dongyuemiao Formation of Fuxing Area

“…In terms of petrological research, comprehensive investigations have been carried out using core descriptions, thin section analysis, scanning electron microscopy, and X-ray diffraction analysis. At the same time, the heterogeneity of different types of shale lithofacies is reflected in its sedimentary structure (lamina and paleontology), organic matter content, and diagenesis (Surdam and Stanley, 1979;Bohacs et al, 2000;Loucks et al, 2007;Mitra et al, 2010;Xu et al, 2020a). Studies on the lacustrine shale of the Shahejie Formation in the Bohai Bay Basin have revealed that its lithofacies is divided into felsic shale, mixed shale, dolomite and carbonate shale, and massive, layered, and laminar shale (Ma et al, 2017;Bai et al, 2020;Li M. et al, 2020;Wu et al, 2020).…”