Abstract

In 2009 Rick Lewis with SCHLUM-BERGER suggested cut-offs for Pe (< 4.0 barnes/electron) and Bulk Density (RHOb < 2.53g/cc) that can be used to define potential organic-rich “Shale” reservoirs. Walls and others (2012 & 2014) used RHOb and Pe data obtained from core data [Dual Energy CT Scanner] to determine shale “sweet spots” in the Eagle Ford Shale using the following cut-offs Pe <3.0 and RHOb < 2.50g/cc.

A recent paper by Wang and Carr (2013) presented an opportunity to test these cut-offs with core derived shale lithofacies. Wang and Carr (2013) subdivided the Marcellus into the following seven lithofacies.

OSS – Organic Siliceous Shale [best reservoir potential]

OMS – Organic Mixed Shale

OMD – Organic Mudstone [ductile]

GSS – Grey Siliceous Shale

GMS – Grey Mixed Shale

GMD – Grey Mudstone [ductile]

CARB – Carbonate

Along with the mineralogical analysis Wang and Carr (2013) included Pe and RHOb data for each of the seven lithofacies. A plot of their log data on a Pe versus RHOb cross plot revealed that only the best lithofacies [OSS] plotted with Pe < 4 [3.5] and RHOb < 2.53 [2.39].

Case studies will be presented from the following reservoirs: 1.) Permian Wolfcamp Midland Basin, 2.) Permian Wolfcamp Delaware Basin, and 3.) Permian Avalon Shale Delaware Basin, In these case studies the Pe versus RHOb log facies will be compared to the geomechanical properties, NMR data, and mineralogical data depending on the logging suites of the individual case studies. It will be important to note in the case studies how the Pe versus RHOb log facies compares with the geomechanical properties.

In wells with no ITTc and ITTs data the Pe versus RHOb cross plot can be used to delineate the vertical distribution of potential reservoir quality “shale”. These delineated zones have the potential to fracture under stress [low Poisson’s Ratio], and for the fractures to remain open [high Young’s Modulus].