Boring or penetrating the earth – Processes – Boring with specific fluid
Reexamination Certificate
2001-06-14
2003-06-24
Suchfield, George (Department: 3672)
Boring or penetrating the earth
Processes
Boring with specific fluid
C166S294000, C166S295000, C166S300000, C507S104000, C507S120000, C507S140000, C507S204000, C507S225000, C507S269000, C523S130000
Reexamination Certificate
active
06581701
ABSTRACT:
BACKGROUND-FIELD OF INVENTION
This invention concerns the use of specially crosslinked polyacrylamide, water absorbing polymers for reducing lost circulation when aqueous drilling fluids are used and a method for reducing such lost circulation. These polymers are able to reach various levels of areas of fissures and thief zones before absorbing enough water and to expand to plug those fissures and thief zones.
BACKGROUND
Drilling fluids or drilling muds as they are sometimes called, are slurries of solids used in the drilling of wells in the earth for the purpose of recovering hydrocarbons and other fluid materials. Drilling fluids have a number of functions, the most important of which are lubricating the drilling tool and drill pipe which carries the tool, removing formation cuttings from the well, counterbalancing formation pressures to prevent the inflow of gas, oil or water from permeable rocks which may be encountered at various levels as drilling continues, and holding the cuttings in suspension in the event of a shutdown in the drilling and the pumping of the drilling fluid.
For a drilling fluid to perform these functions and allow drilling to continue, the drilling fluid must stay in the borehole. Frequently, undesirable formation conditions are encountered in which substantial amounts or, in some cases, practically all of the drilling fluid may be lost into the formation. Drilling fluid can leave the borehole through large or small fissures or fractures in the formation or through pores in the rock matrix surrounding the borehole.
Most wells are drilled with the intent of forming a filter cake of varying thickness on the sides of the borehole. The primary purpose of the filter cake is to reduce the large losses of drilling fluid to the surrounding formation. Unfortunately, formation conditions frequently are encountered which may result in unacceptable losses of drilling fluid to the surrounding formation despite the type of drilling fluid employed and filter cake established.
A variety of different substances are often pumped down well bores in attempts to reduce the large losses of drilling fluid to fractures and the like in the surrounding formation. Different forms of cellulose are preferred materials by some persons. Other substances which are pumped into well bores to control lost circulation are: almond hulls, black walnut hulls, bagasse, dried tumbleweed, kenaf, paper, coarse and fine rice. These and a number of other prior art materials are described in U.S. Pat. No. 4,498,995.
Another process that is employed to close off large lost circulation areas is referred to in the art as gunk-squeeze. In that process, a quantity of a powdered bentonite is mixed into diesel oil and pumped down the well bore. Water injection follows and the water and bentonite will harden to form a gunky, semi-solid mass which can reduce lost circulation. This process must be carefully controlled; first the bentonite must be kept dry until it reaches the desired location in the well and then problems frequently occur in trying to mix the bentonite and water in the well. This method is disclosed in U.S. Pat. No. 3,082,823.
Many of the methods devised or proposed to limit lost circulation involve the use of water expandable materials. The black walnut hulls and other nut hulls have been found to undergo some swelling when used in this operation. (see Glowka et al, Journal of Petroleum Technology, March 1990, pages 328 & ff.) Cremeans in U.S. Pat. No. 4,217,965 teaches the use of compressed, swellable, pelletized cottonseed hulls in combination with cottonseed meal, bentonite, residual lint and a surface active agent. The advantage of this compressed material is that it does not expand quickly when added to the drilling fluid but only after it is well down the well bore.
Another swellable material sometimes used is a water expandable clay such as bentonite which may be mixed with another ingredient to form a viscous paste or cement. U.S. Pat. No. 2,890,169 discloses a lost circulation fluid made by forming a slurry of bentonite and cement in oil. The slurry is mixed with a surfactant and water to form a composition comprising a water-in-oil emulsion having the bentonite and cement dispersed in the continuous oil phase. As this composition is pumped down the well bore, the oil expands and flocculates the bentonite which, under the right conditions, forms a cake on the wellbore surface in the lost circulation area. Hopefully, the settling of the cake of the walls will cause the emulsion to break thus causing the previously emulsified water to react with the cement to form a solid coating on the cake. But such a complex process can easily go wrong.
U.S. Pat. No. 3,448,800 discloses another method wherein a water soluble polymer is slurried in a non-aqueous medium and injected into a well. Another slurry of a mineral material such a barite, cement or plaster of paris is subsequently injected into the well to mix with the first slurry to form a cement-like plug in the wellbore.
U.S. Pat. No. 4,261,422 describes the use of an expandable clay such as bentonite or montmorillonite which is dispersed in a liquid hydrocarbon into the well. After injection the clay will expand on contact with water in the formation. Thus it is hoped that the expanding clay will close off water producing intervals, but not harm oil producing intervals.
A similar method is disclosed in U.S. Pat. No. 3,078,920 which uses a solution of a polymerized methacrylate dissolved in a non-aqueous solvent such as acetic acid, acetic anhydride, propionic acid and liquid aliphatic ketones such as acetone or methyl-ethyl ketone. The methacrylate will expand on contact with formation water in the water producing formations in the well.
It has also been proposed to mix bentonite with water in the presence of a water soluble polymer which will flocculate and congeal the clay to form a much stronger and stiffer cement-like plug than will form when bentonite is mixed with water alone. U.S. Pat. No. 3,909,421 discloses such a fluid made by blending a dry powdered polyacrylamide with bentonite followed by mixing the powder blend with water. U.S. Pat. No. 4,128,528 claims a powdered bentonite/polyacrylamide thickening composition prepared by mixing a water-in-oil emulsion with bentonite to form a powdered composition which rapidly becomes a viscous, stiff material when mixed with water. U.S. Pat. Nos. 4,503,170; 4,457,594; 4,445,576; 4,442,241; and 4,391,925 teach the use of a water expandable clay dispersed in the oily phase of a water-in-oil emulsion containing a surfactant to stabilize the emulsion and a polymer dispersed in the aqueous phase. When the emulsion is sheared, it breaks and a bentonite paste is formed which hardens into a cement-like plug. The patent discloses the use of such polymers as polyacrylamide, polyethylene oxide and copolymers of acrylamide and acrylic or methylacrylic acid.
U.S. Pat. No. 4,124,748 discloses a cross-linked copolymer of a vinyl ester and an ethylenically unsaturated carboxylic acid or derivative thereof that can absorb about 200 to 800% of its weight in water and expand substantially in volume when doing so. U.S. Pat. No. 3,997,484 is typical of a group of related patents by Fanta, Doane and co-workers at the USDA Northern Regional Laboratory which describe various water swellable polymers made by grafting acrylonitrile onto starch and then hydrolyzing the resultant copolymers. These polymers are capable of absorbing large amounts of water very rapidly with the concomitant swelling have been used in a specific form as lost circulation materials as described below. The rights to use these patents have been granted to several companies and some are commercially available. Advances on this technology have been regularly made to the present time. For example, U.S. Pat. No. 5,065,822 teaches the use of a polyvalent metal such as iron which is formed as the ingredients are passing down the borehole to contact a previously placed starch hybrid polymer, thus crosslinking the polymer to make the polymer fo
Broadleaf Industries Inc.
Suchfield George
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