Hydraulic fracturing proppant

Naturally occurring polysaccharides and their derivatives form the predominant group of water-soluble species generally used as thickeners to impart viscosity to treating fluids [1092]. Other synthetic polymers and biopolymers have found ancillary applications. Polymers increase the viscosity of the fi ac-turing fluid in comparatively small amounts. The increase in fluid viscosity of hydraulic fracturing fluids serves for improved proppant placement and fluid loss control. Table 17 summarizes polymers suitable for fracturing fluids. 

Relatively small quantities of a bacterial cellulose (0.60 to 1.8 g/liter) in hydraulic fracturing fluids enhance their rheologic properties [1425]. Proppant suspension is enhanced and friction loss through well casings is reduced. 

P. D. Ellis and B. W. Surles. Chemically inert resin coated proppant system for control of proppant flowback in hydraulically fractured wells. Patent US 5604184,1997. 

Roodhart, L. Kuiper, T.O. Davies, D.R. "Proppant Rock Impairment During Hydraulic Fracturing," SPE paper 15629, 1986 SPE Annual Technical Conference and Exhibition, New Orleans, October 5-8. 

McDaniel, B.U. and Hoch, O.F. "Realistic Proppant Conductivity Data Improve Hydraulic Fracturing Treatment Design," paper No. 87-38 73, 1987 Annual Technical Meeting of the Petroleum Society of CIM, Calgary, June 7 10. 

Hydraulic fracturing is a method of stimulating production of oil or gas from rock formations. A fluid is pumped under conditions of high pressure and high rate Into the formation to fracture it. The fluid also carries sand or a similar proppant material into the fractures. When the pumping is stopped and the hydraulic pressure is released at the wellhead, the fracture partially closes on the sand leaving a highly permeable channel for the oil or gas to flow back to the well. 

To optimize processes that are based upon the interaction between microstructure and flow (for example, proppant placement in hydraulic fracture of geologic formations [oil recovery], separations processes for biological materials, mixing and dispersion of additives in blenders, crystal growth and solidification processes). 

Hydraulic fracturing in conjunction with gravel packing (87-90) creates a short wide fracture that is packed with gravel (proppant) sized to prevent solids production. A high flow rate into the well can be maintained without solids production because fluid flows across the fracture face at rates below the critical solid production rate. 

We discuss the suspensions used in well stimulation and hydraulic fracturing processes. The following sections pertain to various types of suspensions used in well stimulation and fracturing processes, their rheological characterization and hydraulic properties, behavior of suspensions in horizontal wells, a state-of-the-art review of proppant settling velocity and proppant transport in the fracture, presently available measurement techniques for suspensions and their merits, and, finally, a summary and conclusions on the use of suspensions in well stimulation. Future industry needs for better understanding of the complex behavior of suspensions are also mentioned in this section. 

Suspensions or slurries used for well stimulation are prepared by adding a known quantity of proppant to the carrier fluid of choice to obtain a desired proppant concentration. The proppant concentration is usually referred to as the amount of solids added in a gallon of carrier fluid. A 20-40 U.S. mesh size is the most commonly used proppant for hydraulic fracturing. However, other particle sizes such as 8-12, 8-16, 10-20, 12-20, and 40-60 mesh are also used. 

Hydraulic properties, that is, friction-loss calculations of proppant-laden fluids or slurries, are very important not only in the design of any hydraulic fracturing treatment but also in real-time monitoring of fracturing treatments. Recent advances (27, 28) in real-time fracture analysis have necessitated an accurate knowledge of bottomhole treating pressure (BHTP). To estimate BHTP, an accurate prediction of friction pressures of fluids in the flow conduit is required. It is possible to obtain the BHTP from the surface pressure with the following equation ... 

One of the most important factors in the effectiveness of the hydraulic fracturing treatment is the ability to predict the settling velocity of proppant under fracture conditions. The transport of proppant and the final distribution of proppant in the fracture highly depends on the accurate estimation of settling velocity of proppant. The length of the propped fracture, the conductivity of the propped fracture, and height of the propped fracture are consequently affected by the settling velocity. 

McMechan and Shah (66) conducted large-scale testing of the settling behavior of proppants in fracturing fluids with a slot configuration to model realistically the conditions observed in a hydraulic fracture. The... 

Polymer requirements are dictated by the specific application. In drilling, the polymers must be shear stable and provide a means of suspending and removing formation cuttings. For use in hydraulic fracturing, the polymeric fluid must also suspend solid proppants, help control fluid loss, reduce friction and provide viscosity for the creation of fracture width. However, after the treatment the polymer containing fluid must be degradable, so that it can be readily returned from the formation and not interfere with oil and gas production. 

API Recommended Practice RP-60 (1995) Recommended Practices for Testing High-Strength Proppants Used in Hydraulic Fracturing Operations. American Institute of Petroleum Engineers, Washington, D.C. 

Propping agents/proppant—Silica sand or other particles pumped into a formation during a hydraulic fracturing operation to keep fractures open and maintain permeability. 

Many shale gas service companies use groundwater pumped directly from the formation or treated water for their fracturing jobs. In some well stimulations, proppants are not needed to prop fractures open, so simple water or slightly thickened water can be a cost-effective substitute for an expensive polymer of foam-based fracturing fluid with proppant (Ely, 1994). Hydraulic fracturing performance is not exceptional with plain water, but, in some cases, the production rates achieved are adequate. Plain water has a lower viscosity than gelled water, which reduces proppant transport capacity. 

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