A key in evaluating tight oil reservoirs is determining what oil is producible as free oil versus non-producible adsorbed oil and bitumen. The separation of free oil from adsorbed oil and bitumen using only conventional well logs is difficult at best. Rylander and others, 2013 noted importance of this problem when they reported that "comparing recovery efficiencies computed from the free hydrocarbon volume is a superior way of comparing the effectiveness of hydraulic fracture stimulation."

An early attempt to determine free oil content was outlined by Jarvie, 2012 called Oil Saturation Index [OSI] that used data from RxEval Pyrolysis. Then Kausik and others, 2015 and later Reeder and others, 2016 developed a method named Reservoir Producibility Index [RPI] to determine the free oil content using NMR data.

This paper is presented to demonstrate the application of the technique called Reservoir Producibility Index [RPI] applied to the analysis of tight oil reservoirs as a way to identify moveable free oil. Examples from the Mississippian Limestone in Oklahoma and the Permian Wolfcamp in West Texas illustrate the use of this technique. In the Wolfcamp an RPI cut-off is used to determine a volumetric measure of the free oil content.

Theory and Methods

Oil Saturation Index [OSI] based on S1 and TOC data from RxEval Pyrolysis (Jarvie, 2012) is used to determine the amount of free non-adsorbed oil in a tight oil reservoir.

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