Fracture conductivity, proppant

The fracture must be wide enough to permit entry of proppant to a distance sufficient to stimulate production. Tons of proppant are normally required to fill this void. Therefore the fracturing fluid must suspend the proppant long enough for it to be transported and placed, by flow, throughout the fracture. To preserve the maximum accessible flow area, the proppant should be uniformly suspended inside the entire propped fracture area while the fracture closes. Kaspereit(15), as well as Smith(16), has made the point that fracture conductivity can be a limiting factor. If the... 

McDaniel, B.W. "Realistic Fracture Conductivities of Proppants as a Function of Reservoir Temperature," SPE/DOE paper 16453, 1987 SPE/DOE Low Permeability Reservoirs Symposium, Denver, May 18-19. 

Foam fracturing fluid could improve sand ratio to ensure that fracturing fluid to carry proppant into the far-reaching cracks, thereby effectively increased the fracture conductivity. 

With hydraulic fracturing, fracture conductivity is maintained by propping open a fracture created with a solid material, such as sand, bauxite, ceramic, and certain lighter-weight materials. When used in hydraulic fracturing, these materials are referred to as proppants. 

As mentioned in chapter 2, fracture acidizing is an alternative to hydraulic (propped) fracturing in carbonates. With fracture acidizing, fracture conductivity is achieved by using acid to etch the walls of the created fracture. With hydraulic fracturing, fracture conductivity is achieved by filling the fracture with solid proppant to hold it open. 

To carry proppant material into the fracture to create a conductive path for produced fluids... 

Width assumes a great importance when one realizes that to maintain conductivity through the induced fracture it is nearly mandatory that the crack be filled with a solid spacing agent (called proppant) which will prevent the crack from closing completely after the hydraulic pressure on the well is released. 

Pye, D.S. Smith, W.A. "Fluid Loss Additive Seriously Reduces Fracture Proppant Conductivity and Formation Permeability," 1973 SPE Annual Meeting, Las Vegas, Sept. 30-0ct. 3. 

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. 

The width of the created fracture is maintained by using proppants that are mixed into the fracturing fluid during the stimulation process. The proppants prevent the fracture channel from closing after the treatment has been completed, and thus create a conductive path to assist the movement of hydrocarbons from the reservoir to the wellbore. 

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... 

Proppants hold the fracture walls apart to create conductive paths for the natural gas to reach the wellbore. Silica sands are the most commonly used proppants. Resin coating the sand grains improves their strength. 

When first employed in this application in the 1960s, well-fracturing operations were conducted typically at relatively modest temperatures (up to 150°F/65°C) [28]. However, as reservoir conditions became harsher (deeper wells), it was discovered that the traditional application of borates was limited because at higher temperatures it was observed that borates had reduced ability to gel the polymer and maintain the necessary viscosity for proppant suspension. This effect can be explained... 

Most carbonate acid treatments are conducted to remove or bypass formation damage, either real or perceived. If damage is not present, fracturing with acid or with proppant should be considered. If damage is present and believed to be very severe or very deep, fracture acidizing and propped fracturing are the preferred options. 

Another advantage of acid fracturing is that an acid frac can create conductivity to—but not within—an undesirable sandstone or shale interval. Furthermore, if effective etched conductivity can be imparted, flow turbulence in the fracture is expected to be less in an open acid fracture than in a fracture that contains proppant. 

Propped fracturing has an advantage for many carbonates. The leak-off coefficient, fracture shape, and proppant conductivity can be estimated or measured with a greater degree of confidence than for an acid fracture. This is because the fluid is nonreactive. A pretreatment data measurement frac, or mini-frac analysis, is an established technique used to generate appropriate design parameters for propped fracturing. 

In deep formations with high closure pressure, proppant may create a more conductive fracture than can be retained after closure of an add-etched fracture. This is also true in shallow, soft carbonates. A propped fracturing treatment may create a longer effective fracture length because fluid properties, especially leak-off, are not compromised by reactivity. 

If desired, a small proppant stage may be added at the end of an acid fracturing treatment to ensure final conductivity feeding the wellbore. This is not a common practice, but it may make sense. 

The shale s ability to fracture is of special interest (King, 2010). Mechanical behaviour of shale is important in hydraulic fracture stimulation where brittleness is an indication of the ability to not only initiate and place a hydraulic fracture, but also maintain its long-term hydraulic conductivity (Harris et al., 2011). Brittle shale may be more easily fractured, opening flow paths. Ductile shales may require more proppants (King, 2010). Two types of criterion are used ... 

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