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Rapid Characterization of Strata in the Delaware Basin by FTIR Modeling


Infrared (IR) Spectroscopy is an analytical method that measures the dipole movements of species as they vibrate or rotate. The infrared portion of the electromagnetic spectrum ranges from 0.78 to 1000 micrometers (12800 to 10 cm-1). IR is split into three regions: near, mid, and far. The mid and far regions are very useful in identifying organic and inorganic material. The mid-IR region ranges from 4000 to 200 cm-1. This region includes a combination of clays, organics, carbonates, and other mineral species. The far-IR region ranges from 200 to 10 cm-1. This region can be used to supplement the middle IR region for identifying and characterizing specific minerals within a group. Infrared analysis of geological materials initiated in the 1950s; however, few attempts have been made to amalgamate all mineral components into a universal model. The development of such a model requires the tedious task of deconvoluting each spectrum and comparing minute changes in both mid and far range. Recent instrumentation and computer modeling additions to the FTIR platform make complex deconvolutions of high-resolution spectra possible, at a fraction of the traditional time and effort. FTIR has the capability of producing a spectrum that represents a distinct compositional fingerprint that is molded by elemental, mineral, and organic species within each rock layer. The resultant model provides a rapid evaluation of the elemental composition, mineralogy, and source rock that can be used for reservoir appraisal. A FTIR-based mineral model was created by characterizing cuttings samples from five Delaware Basin wells, spanning the Wolfcamp D through Avalon stratigraphic interval. The model was created using five major groups: TOC, tectosilicates, total clays, total carbonates, phyllosilicates. These five groups were split into additional components: quartz, K-spar, plagioclase, pyrite, calcite, dolomite, albite, mica, rutile, chlorite, and apatite. The model is underpinned by 35 XRF, 35 TOC, 35 XRD, and 35 pyrolysis analyses. The correlation coefficient for each major group was greater than 0.99, except for TOC, which was at 0.92. The compiled components ranged from 0.90 to 0.99.