XRF elemental and mineralogical analysis of core sample and well cuttings in granite wash area of Wheeler County, Texas

Abstract

X-Ray Fluorescence (XRF) technology is used in the oil and gas industry to supplement traditionally-acquired well data and to assess mineralogical variability in a non-destructive manner. The application and usefulness of this technology permits many smaller oil and gas companies to spend limited research funds on other areas besides expensive and labor-intensive NMR/SEM/XRD testing. This paper demonstrates XRF technology used for a mineralogical study of the Granite Wash area in Wheeler County, Texas. The Granite Wash is 160 miles long and 30 miles wide and is located in Western Oklahoma and the Texas panhandle and is Pennsylvanian (Morrowan) in age. The most productive stratigraphy in this region comes primarily from several detrital washes derived from the Wichita-Amarillo Uplift (Railroad Commission of Texas). The geologic characteristics of this region range from coarse conglomerates to sandstone, shale, and turbidite sequences and this is reflected in the complexity and heterogeneity of the reservoirs. The XRF datum are correlated to CoreLab analyses of spectral gamma ray and radioactive elements, confirming the interpretation of the composition of sandstones and organic markers in the subsurface. The heavy and radioactive elements are also helpful in assisting the geologic interpretation to indicate possible maximum flooding surfaces and source rocks containing hydrocarbons. This study also confirms the presence of chlorite and carbonate cements which can have significant effects on porosity and permeability and can lead to and more accurate reservoir characterization of future oil and gas wells. The data from the XRF instrument is also able to support the user in interpreting and recognizing drilling muds that have infiltrated formations and altered the chemical composition of the formation rocks. Plots of pyrite versus clay content define trends across the different wells and can help build the subsurface geologic understanding. Finally, the similarities in the readouts of the XRF data are compared with BakerHughes’ Rockview nuclear magnetic resonance test to confirm elemental composition and the use of this instrument in assessing the mineralogy and lithology of future oil and natural gas reservoirs.