A New Hydraulic Fracturing Process

Abstract

In this new fracturing method, high-viscosity fracturing fluids are used to obtain greater fracture length and width. The technique is characterized by higher propagation pressures and lower fluid loss at the fracture face. A film of water surrounding the fracturing fluid reduces friction losses in the tubing, and this lowers surface treatment pressures and pumping power requirements. Introduction A new method has been developed in which high-viscosity fracturing fluids are used for stimulating production from formations having a wide range of production from formations having a wide range of permeabilities. The fluids that have been used to date permeabilities. The fluids that have been used to date have ranged generally from about 500 cp to about 100,000 cp at ambient temperatures. The new method is used commercially under the names "Superfrac", "Super Frac", and "Super Sand Frac". The preferred fluids for use in the new method are loose water-in-oil dispersions or emulsions prepared by blending brine and a surface-active agent into a crude oil or petroleum fraction that has these high viscosities. When properly prepared, these emulsions will not readily change composition in the presence of free water. The emulsions are isolated from the inner wall of the tubing string or casing by a film of free water during injection and are generally pumped with about the same pressure drop as 1-cp oil or water. Studies indicate that the free water is lost to the formation after the fluids enter the fracture and that the high viscosity fracturing fluid remains behind for propagation of the fracture and placement of the propping agent. propping agent. This technique can be used to fracture any formation, but it has particular advantageswhen a large fracture conductivity ratio cannot be realized with small proppants,when thick or high-permeability formations are to be fractured,when a well must be fractured through small-diameter tubing or casing, andwhen proppant must be carried great distances from the wellbore. This paper gives the relationships of fluid viscosity to fracture geometry and proppant placement, establishes the advantages of using high-viscosity fluids for stimulating high- and low-permeability formations, and tells how the high-viscosity fluid system is maintained and pumps and Field tests have shown that excellent, sustained productivity increases have been obtained with this new hydraulic fracturing process. Fracture Geometry The use of very viscous oils as fracturing fluids has several benefits, including good fluid-loss control, increased fracture width, and improved sand transport. Fluid Loss Control Since Howard and Fast showed that the rate of fluid leakoff from a fracture depends upon the resistance of the invaded zone, the resistance of the filter cake, and the resistance of the compressible formation fluids, much of the work on fracturing has been directed toward the use of water-based fluids that can be injected at high rates and toward the development of better fluid loss control additives. Results to date indicate that gelled fluids and other water-based systems generally have low viscosities under the temperature and shear conditions existing in most fractures, and also that fluid loss control additives are normally much less effective under dynamic filtration conditions than they were once thought to be. Increased fluid loss can explain many of the difficulties encountered in conventional fracturing operations. JPT P. 89

Laboratory True Triaxial Hydraulic Fracturing of Granite Under Six Fluid Injection Schemes and Grain-Scale Fracture Observations

“…Fourth, next on the above discussion, correlation between rock chips (natural proppants) and pulse pressurization needs further investigation. Researchers have noted that rock chips or spalls (and rock chunks under certain conditions) associated with the fracturing processes could influence the local stress field near hydraulic fractures and fracture propagation (Kiel 1977;Zang et al 2019). Additional increase in permeability can result from rock chips moving with the fluid to the fracture tip, causing local stress redistributions favoring the arrest and branching of fractures (Kiel 1977).…”

“…Researchers have noted that rock chips or spalls (and rock chunks under certain conditions) associated with the fracturing processes could influence the local stress field near hydraulic fractures and fracture propagation (Kiel 1977;Zang et al 2019). Additional increase in permeability can result from rock chips moving with the fluid to the fracture tip, causing local stress redistributions favoring the arrest and branching of fractures (Kiel 1977). This socalled Kiel process proposed as a method for creating dentritic (branching) fracture system was developed to enhance oil production in sedimentary rocks, and its fracturing mechanism does not fit hard and low-permeability granitic rocks.…”

“…This socalled Kiel process proposed as a method for creating dentritic (branching) fracture system was developed to enhance oil production in sedimentary rocks, and its fracturing mechanism does not fit hard and low-permeability granitic rocks. In contrast to the deduction by Kiel (1977) that rock chips and chunks are produced due to the spalling of fracture walls during the shut-in phase, Zang et al (2019) assume that rock chips are removed from the fracture walls through high-frequency vibrations loaded by a secondary pump (pulse pressurization) during fatigue hydraulic fracturing. Neither study has reported the specific mineral type of rock chips, or has provided further evidence to confirm the formation process of rock chips and their movement with fluid.…”

Laboratory hydraulic fracturing experiments on crystalline rock for geothermal purposes

“…Results reveal that quartz grains are easily split compared with Or and Mc, and rock chips of quartz grains were frequently observed inside hydraulic fractures, particularly when quartz grains were adjacent to orthoclase or microcline grains. The natural proppants (e.g., quartz chips) play a key role in forming dendritic fractures (Kiel, 1977) and particularly in the fatigue hydraulic fracturing process quartz fragments that are removed from fracture walls by pulse pressurization and transported toward the fracture tip can change the local stress field. Local stress changes as compared with conventional hydraulic fracturing can cause a broader fracture damage zone to form, which allows permeability to be increased by a factor of 5-10 compared with conventional HF in both sandstone (Patel et al, 2017) and granitic rock (Zimmermann et al, 2019).…”

Stresses and Displacements Around Hydraulically Fractured Wells

“…The success of a hydraulic fracturing treat ment is strongly dependent on the fluid conductivity of the fracture. Model studies have shown that fracture proppants form a bank which quickly reaches equilibrium height and then £rows away from the wellbore when conventional low viscosity carrier fluids are used.l,Z How= ever, as is pointed out by ¥~e1, 3 when very viscous fracturing fluids are used, very little settling of the proppant occurs while fluid is being pumped; only a small bank is deposited in the fracture with most of the proppant remaining suspended in the fluid. With viscous fluids currently in use any overflushing of the fracturing treatment can remove most of the proppant from the mouth of the fracture by pushing it further down the fracture.…”