Two primary criteria describe proppants utilized in fracturing: type (e.g. - sand) and mesh size (e.g. - 30/50), where mesh size refers to the number of wires per inch in the standard U. S. sieve screens. For a proppant to meet API RP-19C (API, 2006) specifications, 90% of the material sample (by weight) must fall between the screens of the largest and smallest specified mesh size. These size specifications provide the user of proppants a method of choosing a proppant, and comparing products from different suppliers, but still allows a wide variance in particle size within each sieve distribution. Laboratory conductivity tests demonstrate that limiting sieve distribution to standard sizing per API specifications is not a requirement to obtain adequate conductivity performance, or a sufficient descriptor of proppant performance.

The industry has for the most part, limited its choices of proppants to API sizing criteria. It should be noted however, that within each standard mesh range (40/70, 30/50, 20/40, etc.) there is allowed a doubling of size from the smallest to largest particle diameter. There can be a significant difference in size distribution and performance between two proppants, both of which meet the API specification for a given mesh distribution. The difference in distribution can be recognized by determining the median particle diameter of the proppant sample. API RP-19C defines the median diameter as the fiftieth mass percentile (d50) in the distribution.

Thousands of conductivity tests have demonstrated a very strong correlation between median particle diameter and conductivity for each specific type of proppant. The correlation provides a methodology of predicting the conductivity of differing mesh distributions within a specific standard mesh size designation, or for mixed distributions of various particle sizes. This correlation can be successfully applied to regional, non-standard, sand samples.

The ramification of the correlation of median particle diameter to conductivity suggests that standard mesh distributions are somewhat arbitrary and that using non-standard size distributions is not necessarily a negative. Recognizing that sieving capacity is often a bottleneck to output, choosing to provide non-standard sizing may lead to greater production for a processing facility. Given potential proppant supply constraints in the industry, such a shift in proppant supply may lead to significantly improved sand availability and cost benefits to operators.

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