Detailed Comparison of Processed Sand vs. Unprocessed Sand vs. High-Strength Proppant for Fracturing Applications

Abstract

A detailed study comparing various properties and attributes of local Saudi Arabian sand (processed and unprocessed) and high-strength proppant (HSP) for hydraulic fracturing applications is discussed. Further, quartz grain crystallinity, texture, quality, and mechanical durability (strength) are described and an insight into the prospects of sand application viability during hydraulic fracturing is provided. An in-depth comparison of processed sand, unprocessed sand, and readily available HSP widely used in the industry was performed. It is well known that the Middle East region, particularly Saudi Arabia, has an abundance of sandstone formations ranging from the Cambrian to Quaternary age; outcrops of these formations extend from northern to southern parts of Saudi. These formations have varying grain sizes and other physical attributes that must be studied to grade their possible performance as hydraulic fracturing proppants. Unprocessed sand samples were collected from various central and southern Saudi sandstone formations. Petrographic analysis, including thin section and scanning electronic microscopy (SEM), was conducted on sand samples to quantify the percentage of polycrystalline quartz grains and define their surface features. Crush-resistance testing was performed on the samples to compare the mechanical durability of the sands and HSP. The results of this study confirmed that polycrystalline quartz grains are more abundant in coarse-grained sandstones than those fine-grained. Mechanical durability decreased with an increased percentage of polycrystalline quartz grains, strained grains (with undulose extinction), and surface features. The metamorphic nature of the quartz grain source rock and intense chemical weathering along the quartz grain surface reduce its strength. HSP demonstrates greater mechanical durability compared to processed and unprocessed sand, keeping in mind, the processed sand was from a specific sandstone formation. The suitability of Saudi sandstones for the petroleum industry's use is dependent on the mechanical durability of quartz grains, which, in turn, depends on the source and chemical weathering of those grains. Comparatively, HSP is more durable and mechanically strong; however, processed sand has an edge over unprocessed sand.