High pressure rock fracturing

During well completion it is sometimes desirable or necessary to treat or stimulate the producing zone to improve permeability of the rock and to increase the flow of oil or gas into the casing. This may be accomplished by use of acid or by injection of fluid and sand under high pressure to fracture the rock. Such a trcatniciit usually improves the ability of the rock to allow fluid to flow through it into the well bore. At this point the drilling and completion phases have ended. 

Fracture acidizing is a technique to increase the productivity of oil wells. Here acid is injected at high pressures to fracture the rock and form a channel that extends out from the well bore. As the acid flows through the channel it etches the sides of the channel to make it larger and thus less resistant to the flow of oil. Eterive an equation for the concentration profile of acid and the channel width as a function of distance from the well bore. 

Acid fracturing is an oil well stimulation process in which acid (HCl or HF, depending on the rock structure) is injected into an oil well at sufficiently high pressure to fracture the porous media or to widen existing natural fractures. Various principles of surface chemistry are employed in this process in order to avoid excessive and costly fluid loss, and to decrease the rate of acid spent. 

High-pressure squeeze cementing operations are utilized where the hydraulic pressure is used to make new channels in the rock formations (by fracturing the rock) and force the cement slurry into these channels. 

Flow in undisturbed rock normally is radial toward a site of lower pressure (the wellbore). The fracture crack created by high pressure injection usually forms perpendicular to the least principle stress that exists in the rock. The induced fracture intersects and disrupts the radial flow pattern such that flow becomes linear and more direct to the well. This phenomenon has been intensively examined and discussed by authors working in the discipline of rock mechanics as applied to hydrocarbon reservoirs. Hydraulic fractures created in oil and gas wells grow mainly vertically, parallel to the wellbore as depicted in Figure 1 and extend on either side of the perforated wellbore as "wings11 (7-11). 

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. 

If very high pressure is required to inject the fluid, then the reservoir rock may fracture. Although this will improve the injectivity, it may result in containment issues (including fracturing the caprock). Fracturing the injection reservoir is prohibited by law in Alberta and probably in other jurisdictions as well. 

Hydraulic fracturing may combine water, acid or crude oil with sand at high pressures to produce new cracks and enlarge existing ones in the reservoir rock. As this fluid is removed, it leaves the sand behind to prop open these fractures. In the Permian Oil Basin of the United States, frac-... 

Caine, J.S., Evans, J.P., Forster, C.B. 1996. Fault zone architecture and permeability structur. Geology 24(11) ppl025-1028. Rutqvist, J. Noorishad, J., Tsang, C. Stephansson, O. (1998). Determination of fracture storativity in hard rocks using high-pressure injection testing. Water Res. Res. 34(10) pp 2551-2560. 

Abstract We analyse the effect of thermal contraction of rock on fracture permeability. The analysis is carried out by using a 2D FEM code which can treat the coupled problem of fluid flow in fractures, elastic and thermal deformation of rock and heat transfer. In the analysis, we assume high-temperature rock with a uniformly-distributed fracture network. The rock is subjected to in-situ confining stresses. Under the conditions, low-temperature fluid is injected into the fracture network. Our results show that even under confining environment, the considerable increase in fracture permeability appears due to thermal deformation of rock, which is caused by the difference in temperature of rock and injected fluid. However, for the increase of fracture permeability, the temperature difference is necessary to be larger than a critical value, STc, which is given as a function of in-situ stresses, pore pressure and elastic properties of rock. 

EARTH CRUST STRUCTURE AS A RESULT OF ROCK FRACTURING AT HIGH PRESSURE AND TEMPERATURE CONDITIONS... 

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