Turbidity in Frac Sand from Proximity Mines in the Permian Basin: Is it Detrimental to the Fracture System?
Authors: Anschutz D. , McGill M. , Fleming S. , Landis C. , Cage T. 
Published: January 2025

Regional and proximity sand mines dominate the landscape in the Permian Basin of West Texas and Southeast New Mexico. Vast Cenozoic Monahans Formation sands offer critical, long-term sustainable proppant supply, specifically in-basin sand, for Permian Basin unconventional exploration and development. The industry is investing in a wide range of processing methods to develop the dune fields of West Texas. The regional variation of the dune fields and stratigraphy introduce complexities that require adaptation of ore processing to improve the quality of the final product. The focus of this study is to show how the concentration and type of contaminates in the sand, indicated by turbidity measurements, could alter the performance as a proppant system. Turbidity is produced by multiple mineral contaminants (silts and clays) in the otherwise quartzose sand that are not efficiently removed during processing. This paper classifies this suspended material into three groups: silicates (quartz, feldspar, etc.), clay (phyllosilicates), and caliche (calcium carbonate). This study focuses on the correlation between the composition and content of these admixtures and the hydraulic conductivity of the stimulated reservoir.

This study presents the results of an integrated effort to characterize compositional aspects of the Monahans sands with respect to their conductivity performance. Controlled laboratory experiments, including turbidity measurements, conductivity, and X-ray diffraction (XRD), are conducted on sand samples from multiple locations in the Permian Basin. The objective is to understand the effect of contaminants on the performance of the sand without the formation core interface. Field samples evaluated varied in turbidity levels of less than 250 Nephelometric Turbidity Unit (NTU) to greater than 2500 NTU. Northern white sand (NWS), with similar sizing, was used to compare additional physical features between sands, i.e., roundness, sphericity, etc. Ultimately, all findings were integrated with mineralogical analysis to assess the impact of turbidity and specific minerals, such as quartz, feldspar, and various clay minerals, on conductivity.

The results of this work indicate that 1) in-basin sands yield highly variable and generally higher turbidity than mid-continent sands, 2) both the level and mineral composition of the turbidity itself can significantly impact the permeability and conductivity of a stimulated resource, Finally, the differences in the physical features between regional sands and NWS may require additional investigation of API Standard testing methodology.

While the value of the in-basin Monahans Sands to the future of Permian Basin unconventional resource development is undisputed, oilfield operators and industrial sand producers can unlock additional value by adapting mineral processing and treatments to the specific geology of these deposits. Versatile, in-process, and down-hole solutions are available to enhance the performance of fracturing fluids while addressing the inherent variability of these sand deposits.