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).
Qualifying proppant performance prior to a frac job, or simply verifying proppant performance after a frac job, can add significant value to propped fracture stimulations. Through a blend of established practices and new technology, data can be generated that will give an engineer insight into how specific proppants are designed to perform. This is without running expensive and time consuming conductivity and permeability tests on every job. A primary objective is to establish representative, reliable and reproducible data via a sample collected from a large mass. American Petroleum Institute (API) Recommended Practices (RP) identifies three primary tenets:representative sampling from a flowing stream,standardized testing with calibrated equipment, andsample retention for follow-up evaluation. Application of these practices ensures that proppant test data is valid (e.g. representative, reliable, and reproducible). Yet, these practices alone typically quantify quality but do not qualify proppant performance.1, 2, 3 Correlation of valid well-site proppant data with published information (literature, web-sites, or fracturing simulators) enables one to identify disparities. Any differences in part may be the result of mining anomalies, manufacturing defects, transportation abuse, and/or contamination. These can directly impact the delivered performance of your chosen proppant. Since proppant flow capacity or conductivity is a key measure of that performance, some empirical results have been assimilated for well-site and public data. As a consumer, having information that describes the proppant at the well-site is important to deciding application and value. By compiling historical well-site proppant data one can set a minimum threshold of required properties or specification. This provides the opportunity to identify a greater range of proppants (e.g. substitutions) that meet reservoir, economic, and supply chain needs. Lastly, this paper introduces new patent-pending technology that enables well-site proppant sampling and evaluation before the fracturing treatment. Having pre-frac data gives one the opportunity to make any necessary changes in fracture design and implementation to get the most from available proppant. It also provides for a detailed inspection of the well-site delivered proppant supply. For instance, one can isolate and sample each pneumatic trailer, monitor associated pneumatic discharge pressures, provide representative split samples for fracturing fluid compatibility testing, etc. Case histories, onshore and offshore, support "qualifying proppant performance". Introduction As stated in previous literature4, proppant conductivity or performance is very important in the design of propped fracture stimulation treatments. It is equally important that the designed performance arrive at the well-site to protect your investment. How does one ensure that occurs? Current quality control practices, which are often static and cursory, do not provide the scientific basis to evaluate quality, let alone performance. This is because those methods, which do not follow API recommended practices, are not subscribed to by the supply chain as a way to obtain representative, reliable, and reproducible data. All too often, static or scooped samples are extracted for measurement. As a result, the entire proppant mass has not been sampled and has not been evaluated. This paper demonstrates how to apply quality control practices in order to evaluate, promote, and qualify proppant performance at the well-site. Doing so will provide the best opportunity to match designed and delivered propped fracture performance expectations.
Unconventional completions have experienced many different trends within the last decade. Many of the changes are based on learnings using conventional fracture mechanisms and studies. Previous studies evaluated the impact of various parameters on proppant transport by pumping a premixed proppant laden slurry into an open, homogenous slot to visually monitor proppant distribution. Basic flow characteristics can be captured with this type of traditional tests; however, it misses significant factors of unconventional fracture mechanisms including tortuosity, variable width, leak-off, and the ability for in-situ analysis of the materials after being pumped. This paper discusses the need and development of new equipment with innovative features, and several revolutionary laboratory techniques that were specifically applied to further understand proppant and fluid behavior in unconventional reservoirs. Unconventional fracture characteristics learnings from industry's advanced field studies were included while defining the features of new comprehensive test equipment to represent the unconventional fracture mechanisms. This ultimately led to the construction of a large, sectional, 10'x20’ slot flow wall. The twenty-five sections of the wall were modified to accommodate a wide variety of testing regimes and flow patterns. Additionally, the pumping equipment delivering the proppant laden slurry was upgraded to adhere to today's completion designs. Through the use of large fluid tanks, proppant hoppers, a mixing blender tub, pump and flow loop, shear history, and multiple types of proppant and fluid were integrated into the test procedures to better replicate current pump schedules. Flow meters, pressure transducers, a densitometer, and linear variable differential transformers were installed to monitor the movement of the material and structure throughout the test. After testing, the patent-pending equipment is designed for disassembly for detailed analysis on the proppant and fluid. Equipment can also be modified on a smaller scale to create a winged fracture, transverse fracture and a tilted fracture, all of which are necessary when analyzing fracture and proppant transport behavior in an unconventional reservoir. The new, comprehensive, large and tortuous slot flow equipment allowed the creation of a customized tortuous path for the proppant and fluid for twenty feet before exiting the structure into separate effluent tanks. The slot has an original width of 0.5 inches but can be tailored to establish varying slot widths and/or complete obstructions using panel inserts. With multiple inlet points, fracture growth can be documented with a total of one hundred side panel leak-off ports and eight additional leak-off ports along the top. To maximize learnings from each test, innovative test practices were applied such as, dying the frac sand of different mesh size groups to visualize the segregation of the proppant while pumping, and mounting 10-15 cameras throughout the structure to document slurry behavior through the acrylic panes. Data analyzed included, but was not limited to, a sieve analysis, proppant concentration, fluid viscosity, and proppant conductivity testing on the samples. The testing demonstrated a significant impact on proppant transport, dune generation, and dune structure after shut-in through a tortuous path with varying fracture width and leak-off ports as compared to standard slot flow test. This paper introduces novel, comprehensive, large, and tortuous slot flow testing equipment with features to represent the unconventional fracture behavior. Advanced equipment capabilities, test procedures and data collection methodology allow the industry to optimize the selection and deployment of various fracturing materials and treatment designs for unconventional well production enhancement.
The sands employed as fracturing proppant have been historically qualified for that purpose based upon their ability to meet quality standards described by the American Petroleum Institute (API, 1995) and more recently, by the International Organization for Standardization (ISO, 2006). Notable products meeting those standards include white sands from the Ottawa deposits in the north central United States, and the so-called brown sands from deposits in central or the "heart" of Texas. Until recent times, these "quality" sand deposits provided sufficient supplies for the ongoing needs. However, the unprecedented surge of hydraulic fracturing activities over the past few years has resulted in demand outpacing the supply for sands that meet these requirements.Consequently, many 'new' sand deposits are being evaluated for use in fracturing applications, but unfortunately, a great many of those when subjected to API / ISO standards fail to make the grade in one area or another. Interestingly, it is commonly similar criteria which are being failed including acid solubility, sphericity & roundness, crush strength, and particle distribution. Thus, one is given cause to question the relevance of some testing practices on 'real world' performance of sand in a fracturing treatment.
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