Modified API/ISO Crush Tests With a Liquid-Saturated Proppant Under Pressure Incorporating Temperature, Time, and Cyclic Loading: What Does It Tell Us?

Abstract

Abstract The American Petroleum Institute (API) crush tests for proppants found in recommended practices (e.g. RP 56, 58, & 60) are typically used to compare the crush resistance of recognized API proppant sizes at a predetermined stress under dry and ambient conditions (API, 1995). This procedure has remained the same through several API committees since the early 1980swithout change. More recently, the International Organization for Standardization, ISO 13503–2, reviewed the procedure and made only slight changes, most notably in the time for which the stress is to be applied (ISO, 2006). The "new" procedure from ISO gives no indication of how the stress changes the overall mesh distribution. It also sheds no light on how key factors such as moisture, temperature, time, or cyclic loading change performance characteristics. This work addresses these issues. The down-hole environment where the proppants are placed is wet, hot, and pressurized. Incorporating these variables into a modified API test procedure for crush resistance better represents actual down-hole conditions to which a proppant is subjected. This information is critical in establishing required propped fracture conductivity, and thus, proppant selection. In this study a standard API crush cell was modified for pressurized fluid flow at temperature and used to quantify the effects of the parameters described as compared to standard API crush tests. Tests were performed on the following proppants: light weight ceramic (LWC), intermediate density ceramic (IDC), and high strength bauxite(HSB). Modified testing exposes critical proppant failures under conditions that more closely simulate those experienced downhole; these failures are not be revealed by current standard API/ISO test procedures. The modified procedure results in an improved method for better understanding downhole proppant pack performance. Introduction Proppant behavior and propped fracture conductivity have been studied in the laboratory since the earliest days of fracturing in the late 1940s (Gidley, 1989). Since that time a variety of mechanisms have been examined that are extrinsic (e.g. non-Darcy flow, cyclic loading, gel damage, etc.) and intrinsic (Krumbein shape factors, mineral content, acid solubility, etc.) to proppant performance in the fracture. However, extrinsic influences are not included in API or ISO industry standards for evaluating proppant crush resistance as this test is only a quality control procedure. Differences in performance and durability from one proppant to another can be the result of manufacturing factors including raw material mineralogy. Including extrinsic factors in testing can help to differentiate proppant performance under conditions that more closely reflect those downhole (Colt, 1995). Extrinsic factors, such as temperature, time, and cyclic loading and their effect on fracture flow capacity have been examined extensively in previous literature. Yet, this paper makes the effort to incorporate these factors synergistically into standardized crush testing for proppants. Liquid saturation of man-made proppants under pressure with exposure to these extrinsic factors enables one to differentiate proppants in a more relevant environment. This in turn will influence proppant selection and classification (Freeman, 2006 & 2008).