Long Term Conductivity vs. Point Specific Conductivity Available to Purchase

Long term conductivity of proppants, currently defined by API RP 19D, has been used since the early 1970's as the standard for evaluating the conductivity and permeability of proppants for use in hydraulic fracturing. Proppants are typically tested across their useful range in 2,000-psi (137.89-bar) increments (i.e. 2-4-6-8K-psi…) and held 50 hours at each stress level, ramp rates between each stress and the test temperatures are also defined by API RP 19D. Frac sand is tested at 150°F (65.5°C) and ceramic proppants at 250°F (121.11°C). Proppant suppliers use this, among other testing parameters, to develop data to market their products to the industry. As with any standard, the test has its limitations. The test is expensive, time consuming and in many cases does not match the application.

Point specific 50 hour (PS50) conductivity tests follow the procedures outlined in API RP 19D but use a point specific stress and point specific temperature, modeling a specific application. Although not yet sanctioned by the API, the test can generate meaningful data in less time, for a specific purpose and save money. Point specific testing has maximized Research & Development budgets and increased the time to market for new products. Operators have benefited by tailoring proppants for their specific well conditions.

In this work we plan to compare point specific test data to API RP 19D data over a range of stress and time as the industry pushes the envelope on the applicable stress for proppants. Aven, Tang and Weaver brought out that "it is normal to observe a continuous decline in conductivity, although less than 5% on a daily basis, if the measurement is carried longer than two days. It is rare that the system actually achieves equilibrium conductivity during that time, but the rate of change of conductivity does slow down¹."

Could the point specific test be extended to achieve equilibrium and still be comparable to existing data from the standardized test? Multiple tests were conducted to compare these two methods of conductivity tests at normal duration, a point specific 50 hour (PS50) conductivity test and the API RP 19D conductivity test which the test spends 50 hours at each 2,000 psi (137.89-bar) increment. Results presented in this paper will help answer these questions and aid engineers make more informed decisions faster and with a lower economic cost.