Wells – Processes – Chemical inter-reaction of two or more introduced materials
Reexamination Certificate
2001-06-11
2002-12-03
Suchfield, George (Department: 3672)
Wells
Processes
Chemical inter-reaction of two or more introduced materials
C166S305100, C166S308400, C507S215000, C507S216000, C507S217000, C507S255000, C507S267000, C507S276000, C507S277000, C507S903000, C507S904000, C507S922000
Reexamination Certificate
active
06488091
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods and compositions for treating subterranean well formations, and more specifically, to improved subterranean formation treating fluid concentrates, treating fluids and methods of using the treating fluids.
2. Description of the Prior Art
Producing subterranean formations penetrated by well bores are often treated to increase the permeabilities or conductivities thereof. One such production stimulation treatment involves fracturing the formation utilizing a viscous treating fluid. That is, the subterranean formation or producing zone therein is hydraulically fractured whereby one or more cracks or “fractures” are produced therein. Fracturing may be carried out in wells that are completed in subterranean formations for virtually any purpose. The usual candidates for fracturing or other stimulation procedures are production wells completed in oil and/or gas containing formations. However, injection wells used in secondary or tertiary recovery operations for the injection of fluids may also be fractured in order to facilitate the injection of the fluids.
Hydraulic fracturing is accomplished by injecting a viscous fracturing fluid into a subterranean formation or zone at a rate and pressure sufficient to cause the formation or zone to break down with the attendant production of one or more fractures. As the fracture is created a portion of the fluid contained in the viscous fracturing fluid leaks off into the permeable formation and a filter cake comprised of deposited gelling agent is built up upon the walls of the fracture which then helps to prevent or reduce further fluid loss from the fracturing fluid to the formation. The continued pumping of the viscous fracturing fluid extends the fractures and a proppant such as sand or other particulate material may be suspended in the fracturing fluid and introduced into the created fractures. The proppant material functions to prevent the formed fractures from closing upon reduction of the hydraulic pressure which was applied to create the fracture in the formation or zone whereby conductive channels remain through which produced fluids can readily flow to the well bore upon completion of the fracturing treatment.
The fracturing fluid must have a sufficiently high viscosity to retain the proppant material in suspension as the fracturing fluid flows into the created fractures. A viscosifier has heretofore often been utilized to gel a base fluid whereby a fracturing fluid having the high viscosity needed to realize the maximum benefits from the fracturing process is provided. After the high viscosity fracturing fluid has been pumped into the formation and fracturing of the formation has occurred, the fracturing fluid generally has been caused to revert into a low viscosity fluid for removal from the formation by breaking the gel. The breaking of viscosified fracturing fluids has commonly been accomplished by adding a breaker to the fracturing fluid prior to pumping it into the subterranean formation.
The fracturing fluids utilized heretofore have predominantly been water based liquids containing a gelling agent comprised of a polysaccharide such as guar gum. Guar and derivatized guar polymers such as hydroxypropylguar are economical water soluble polymers which can be used to create high viscosity in an aqueous fluid and are readily crosslinked which further increases the viscosity of the fluid. While the use of gelled and crosslinked polysaccharide fracturing fluids has been highly successful, the fracturing fluids have not been thermally stable at temperatures above about 200° F. That is, the highly viscous gelled and crosslinked fluids lose viscosity with time at high temperatures. To offset the loss of viscosity, the concentration of the gelling agent has been increased which involves increased cost and causes increased friction pressure in the tubing through which the fluid is injected into a subterranean formation which makes pumping of the fracturing fluids more difficult. Thermal stabilizers such as sodium thiosulfate have been included in the fracturing fluids to scavenge oxygen and thereby increase the stabilities of the fracturing fluids at high temperatures. However, the use of thermal stabilizers also increases the cost of the fracturing fluids.
Another problem which has been experienced in the use of gelled and crosslinked polysaccharide fracturing fluids involves the breaking of such fracturing fluids after fractures have been formed. Breakers such as oxidizers, enzymes and acid release agents that attack the acetal linkages in the polysaccharide polymer backbone have been used successfully.
In order to make the heretofore used gelled and crosslinked polysaccharide fracturing fluids carry sufficient proppant, the concentration of the crosslinking agent utilized has often had to be increased which in turn increases the cost and viscosity of the fracturing fluid. The water based fracturing fluids including gelled and crosslinked polysaccharide gelling agents have had significantly reduced fluid loss as compared to other fracturing fluids which reduces or eliminates the need for costly fluid loss additives. However, because the gelled and crosslinked polysaccharides have had high molecular weights, the filter cake produced from the viscous fracturing fluid on the walls of well bores penetrating producing formations and in fractures formed therein is often very difficult to remove.
Another problem experienced in the use of a water based fracturing fluid including a gelled and crosslinked polysaccharide gelling agent is that it must be mixed in holding tanks for a considerable length of time for hydration of the gelling agent to occur. During the fracturing process carried out in a well, the hydrated fracturing fluid generally is pumped out of the holding tanks, mixed with proppant and other additives on the fly and pumped down the well bore to the formation being fractured. If during the job, the down hole pressure profile and other parameters that are obtained in real time indicate that a change in the fracturing fluid properties is required, that is, a change in the fracturing fluid viscosity to prevent a screen out of the fracture or the like, it is generally impossible to do so since it takes a very long time for a change to be made and for the changed fracturing fluid to reach the formation being fractured. Another problem related to pumping the fracturing fluid from holding tanks and combining the proppant material, crosslinker and other additives used on the fly is that the procedure requires the use of expensive metering and other similar equipment.
Finally, in many environmentally sensitive areas, the water based fracturing fluids containing polysaccharide gelling agents must be recovered from the well and disposed of by environmentally appropriate means which increases the overall cost of the fracturing treatment.
Thus, there are needs for improved subterranean formation treating fluids and methods whereby the fluids are not thermally unstable, do not produce insoluble residues, have high proppant carrying capacities, produce easily removed filter cake, do not have to be hydrated in holding tanks for long periods of time, can have their properties changed during use and can be recovered and reused if desired.
SUMMARY OF THE INVENTION
The present invention provides subterranean formation treating fluid concentrates, improved treating fluids which can be utilized for fracturing as well as various other subterranean formation treatments and methods of using the treating fluids which meet the needs described above and overcome the deficiencies of the prior art.
A subterranean formation treating fluid concentrate of this invention is basically comprised of water and a depolymerized substantially fully hydrated polymer. The treating fluid concentrate can also include a variety of additives required to be in treating fluids produced utilizing the concentrate such as pH adjusting compounds for adjusting the pH of the treating fluid
Barrick David M.
Bowles Bobby K.
Cole R. Clay
Heath Stanley J.
Parker Mark A.
Dougherty Clark
Halliburton Energy Service,s Inc.
Kent Robert A.
Suchfield George
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