Evaluation of Sand and Ceramic Proppant Performance Under Thin Layer/Monolayer Conditions of Unconventional Hydraulic Fractures
Authors: Fuss Tihana , Shi Jingyu , Bottiglieri Stephen , Herskovits Raphael 
Published: April 2016

Production data analysis of neighboring wells in Williams County, ND shows some 100% ceramic proppant completions do not show adequate production improvement needed to justify the additional cost of ceramic proppant. These results are contradictory to laboratory API proppant pack conductivity (API RP 19-D) or proppant pack mechanical strength (API RP 19-C) measurements which predict superior performance of all types of ceramics compared to sand. This study evaluates the ability of current API procedures to predict proppant behavior in horizontal wells and suggests a modified API testing procedure which considers the performance of thin layer/monolayer proppant packs improving the correlation between the laboratory and well production data.

The study also compares the mechanical strength of 20/40 and 30/50 white sand, clay based economy lightweight ceramics and bauxite based intermediate strength ceramics using standard and modified API RP 19-C crush resistance tests. During testing, load cell volumes range from the standardized 4lb/ft2 to the modified 0.5 and 0.25lb/ft2. 0.5 and 0.25lb/ft2 volumes simulate proppant behavior in hydraulic fractures with frac widths approaching 0.12″ and 0.07″, respectively. Mechanical failure of proppants is quantified by comparing proppant size distribution pre- and post-stress application using a Horiba CAMSIZER. Failure of proppants is also measured using in-situ high pressure CT scanning protocol that enables visualization of the proppant failure as a function of applied load, proppant type and proppant pack thickness.

The study establishes large differences in mechanical performance of tested materials under thick (4lb/ft2) and thin (0.5 and 0.25 lb/ft2) proppant bed height conditions. In the case of white sand, even at pressures as low as 4,000psi, the amount of material failure is 3 times higher at 0.5lb/ft2 and 5 times higher at 0.25lb/ft2 compared to the API standard (4lb/ft2). Both types of tested ceramic proppants also show a higher % of mechanical failure in lower bed height conditions. While the mechanical performance of the tested ceramic proppants is better than that of sand, the performance of clay based economy lightweight ceramics at 8,000psi is drastically reduced and begins to approach that of sand. This is most prominent for 30/50 mesh distribution samples.

In situ high-pressure CT scanning identifies two different failure mechanisms in the tested proppants.The study then compares laboratory data to publicly available well production data in Williams County, ND. Production increases seen in 100% ceramic completions shows a strong correlation to laboratory measured performance of proppant at 0.5 and 0.25lb/ft2.

This paper quantifies the effect of reduced fracture thickness to the performance of different proppant types. In addition, this paper introduces a novel in-situ high pressure CT scanning protocol and provides unique insight into proppant failure mechanisms found in thin, unconventional fractures.