Application of inorganic whole-rock geochemistry to shale resource plays: an example from the Eagle Ford Shale Formation, Texas

Abstract

Shale resource plays continue to be the most actively explored and developed hydrocarbon plays in North America. However, despite the intense activity surrounding the shale plays, understanding the controls on reservoir quality and successfully exploiting shale formations remains challenging. Using examples primarily from the Eagle Ford Formation, this paper demonstrates how inorganic whole-rock geochemical data can be used to help with the development of shale plays. Elemental data are used to provide regional stratigraphic correlations and provide sufficiently high resolution characterization to enable horizontal well-bores to be related back to pilot holes. The same elemental data used for chemostratigraphy can also be used to model mineralogy and total organic carbon, determine paleoredox facies and provide information on the formation brittleness, all valuable information in the exploitation of shale resource plays. The methodologies demonstrated here in the Eagle Ford Shale Formation have been used extensively in other North American shale plays and are readily applicable to any of the newly emerging shale gas resource play around the World.

Chemostratigraphic Characterization of Siliciclastic Rocks in Parts of the Eastern Dahomey Basin, Southwestern Nigeria

“…3 and 4) and element ratios, termed key indices, are used to construct a chemostratigraphic zonation scheme, which is typically hierarchical. Based on geochemical data obtained from the study area, synthetic chemical logs were created (after Ratcliffe et al, 2012) using PETREL software to enable the characterization of the study area into geochemical packages and geochemical units necessary for chemical delineation ( Figure. 3 and 4). As can be observed from figures 3 and 4 above, the surface and subsurface geology of the study area have been chemostratigraphically subdivided into two Geochemical Packages and three Geochemical Units based on the plot of elements and element ratios such as U(Uranium), Zr(Zirconium), P(Phosphorus), Th/U(Thorium/Uranium), Cr(Chromium), Mo(Molybdenum), EFV(Enrichment factor of Vanadium) where (EFV) = changes in oxygenation of bottom waters, (U) = changes in total organic carbon contents (TOC), (Th/U) = amount of clastic input versus organic content, (P 2 O 5 ) = changes in biogenic apatite, which relate to surface productivity, (Zr) = terrigenous supply, (Cr) = mafic input.…”

“…The subsurface geology of siliciclastic rocks in Ijagun ( Figure.3) is subdivided into two geochemical packages. Package 1 and 2 which sandwich the Maximum Flooding Surface (MFS) suggested by the high value of Uranium (U) on the chemical log corresponds to high organic content (Ratcliffe et al, 2012). Across this MFS there is a decrease in the level of oxygenation of the bottom water with increasing depth, suggested by the vanadium enrichment factor (EFV) log ( Figure. 4).…”

“…The geochemical packages are further subdivided into three units: (Unit 1) represents a record of low /no information which is probably a gap in sedimentation or unconformity as suggested by zero/nil Zircon (Zr) log kick (Ratcliffe et al, 2012). At this interval, there is no record of biogenic productivity (as indicated by the absence of P 2 O 5 log Kick) and no record of terrigenous supply.…”

Geoquímica inorgánica como indicador de procedencia y ambiente sedimentario en sucesiones de lutitas negras: los depósitos transgresivos titonianos (Formación Vaca Muerta) de la Cuenca Neuquina, Argentina

“…En particular, la relación entre K 2 O versus Al 2 O 3 puede considerarse una medida de la contribución de argilominerales a la cuenca (Ratcliffe et al, 2012) y por ende de los aportes de productos de meteorización. No obstante, debe tenerse en cuenta que tanto el potasio como el magnesio pueden haber sido captados del agua de mar (März et al, 2009), por lo que resultan indicadores menos seguros de aportes detríticos.…”

“…Entre los elementos traza, se considera que el Th indica los aportes clásticos a la cuenca (cf. Takesue, 2010;Ratcliffe et al, 2012). En el caso del intervalo estudiado, su mayor proporción en los tipos litológicos fangolíticos respecto a las rocas que han incorporado componentes de origen intracuencal o no terrígenos, en especial los carbonatos (Tabla 1), puede considerarse una medida de la relación entre los aportes terrígenos y la productividad.…”