Hydraulic fracturing, when applied in concert with horizontal drilling, has led to a rejuvenation and revolution in the oil and gas industry that has been felt globally. When once development and reserve addition opportunities in the US were deemed to be very limited now technically recoverable reserves for both oil and gas in the US are viewed as abundant, and long-lived (EIA 2016). Yet hydraulic fracturing itself relies on the placement of proppants and the performance of those proppants to succeed. The earliest hydraulic fracture stimulations utilized poorly sorted river sand as proppant. Since this first experiment with proppants, the industry has evolved with a broad range of proppant choices although natural sand of some type remains by far the proppant of choice for a variety of reasons. Technology has advanced in many ways since the first fracture stimulation. For the past thirty years, the Stim-Lab Proppant Consortium has engaged in a continuous program of building knowledge and understanding in the behavior of all types of proppants used in hydraulic fracturing. Arguably no other body of knowledge about proppants exists that compares in extent and detail with that accumulated by the Consortium. There are many basic understandings about the behavior of proppant packs under downhole reservoir conditions that have been developed through thousands of tests that have been performed through the work of the Consortium. These include the effects of proppant type, grain failure, fines migration, embedment, non-Darcy and multi-phase flow, cycling, loading, packing arrangement, fracture fluid damage and others. All of these effects can be at work simultaneously to negatively affect flow in the propped fracture and the recognition of these effects assists to explain observed well performance. This paper will present basic understandings of proppant performance that are sometimes misunderstood or wrongly applied and will assist the practicing engineer in well diagnostics and stimulation design. It will also present and describe predictive performance models developed for proppants that in turn leads to the most comprehensive simulation of proppant performance under realistic downhole conditions available in the industry.
Summary The earliest hydraulic-fracture stimulations used poorly sorted river sand as the proppant. Since this first experiment with proppants, the industry has evolved to offer a broad range of proppant choices although, by far, natural sand of some type remains the proppant of choice for a variety of reasons. For the past 30 years, an industry Consortium has engaged in a continuous program of building knowledge and understanding in the behavior of all types of proppants used in hydraulic fracturing. There are many basic understandings about the behavior of proppant packs under downhole reservoir conditions that have been developed through thousands of tests that have been performed through this work. These include the effects of proppant type, grain failure, fines migration, embedment, non-Darcy and multiphase flow, cycling, loading, packing arrangement, fracture-fluid damage, and others. All these effects can be at work simultaneously to negatively affect flow in the propped fracture, and the recognition of these effects assists in explaining observed well performance. This paper will present current knowledge of proppant performance that is sometimes misunderstood or wrongly applied and will assist the practicing engineer in well diagnostics and stimulation design.
The testing of proppants to determine conductivity and permeability at closure stress is an important aspect of the design and evaluation of hydraulic fractures. The data obtained from these tests are important for proppant suppliers and manufacturers in evaluating their sources of supply or in adjusting or modifying manufacturing processes. For the operator it is a basis for comparing performance, quality and value. An understanding of how this data is obtained and its limitations is important in its use and application. The knowledge gained in the industries' understanding of the behavior of proppants has led to modifications and improvements to the conductivity testing apparatus and in test procedures.Critical components of the equipment and test procedures, including loading of the cell, flow rates and cell design, will affect the test results to a greater or lesser degree. Thus it is important to clearly take into account the various components of the cell and how they may influence conductivity measurements. Further, the standard conductivity apparatus can be used to evaluate various proppant damage mechanisms such as gel damage, embedment, spalling, and stress cycling. At the same time an understanding of the limitations of the data must be appreciated to avoid misuse and misapplication. And while improvements have been made to the acquisition of this data, there remain some barriers to test repeatability that are inherent to the materials being evaluated.
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