Earth boring – well treating – and oil field chemistry – Earth boring – Contains organic component
Reexamination Certificate
1998-03-11
2001-09-18
Warden, Jill (Department: 1743)
Earth boring, well treating, and oil field chemistry
Earth boring
Contains organic component
C507S261000
Reexamination Certificate
active
06291405
ABSTRACT:
This invention relates to a water miscible glycol base drilling fluid for application in drilling highly active shale formations. The high performance drilling fluid of this invention provides shale stabilization and swelling inhibition of active and swellable shale. In addition to shale stabilization and swelling inhibition of shale, the drilling fluid of this invention provides anti-bit balling and anti-sticking properties to the drilled cuttings during the drilling operation.
The glycol base drilling fluid of this invention has a continuous phase which is predominantly glycol and a particulate phase which consists of solids carried or suspended in the continuous phase. It may also contain immiscible liquids which are emulsified into the continuous phase during use. In the case of water-misible-glycol base drilling fluids, water incorporated into the drilling fluid becomes part of the continuous phase and is not emulsified into it.
During oil and gas drilling operations, long sections of argillaceous formations having clay minerals as major constituents, such as shales, mudstones, siltstones, and claystones, often have to be penetrated before reaching the hydrocarbon bearing zones. Various drilling problems, such as bit balling, swelling or sloughing of wellbore, stuck pipe, and dispersion of drilled cuttings, are frequently encountered while drilling such formations. This is especially true when using water-based drilling fluids and can result in tremendous losses of operation time and increases in operation costs. Because of their tendency to become unstable on contact with water, such argillaceous formations are also commonly referred to as water-sensitive shales.
The unstable tendency of water-sensitive shales can be related to water adsorption and hydration of clays. When a water-based mud comes in contact with shales, water adsorption occurs immediately. This causes clays to hydrate and swell resulting in stress and/or volume increases. Stress increases can induce brittle or tensile failure of the formations, leading to sloughing cave in, and stuck pipe. Volume increases, on the other hand, reduce the mechanical strength of shales and cause swelling of wellbore, disintegration of cuttings in drilling fluid, and balling up of drilling tools. The best way to minimize these drilling problems is to prevent water adsorption and clay hydration from occurring, and oil-based drilling fluids are believed to be the most effective for this purpose.
The inhibitive action of oil-based drilling fluids arises from the emulsification of brine in oil, which acts as a semi-permeable barrier that materially separates the water molecules from being in direct contact with the water-sensitive shales. Nevertheless, water molecules may flow through this semi-permeable barrier when the water activity of the oil-based drilling fluid differs from that of the shale formation. To prevent water molecules from being osmotically drawn into shale formations, the water activity of the oil-based drilling fluid is usually adjusted to a level equal to or less than that of the shales. Due to their detrimental impacts on environments, oil-based drilling fluids are subject to more stringent restrictions in their usage, and oftentimes water-based drilling fluids must be used instead. Thus, there is a need to improve the inhibitive properties of water-based drilling fluids so that water adsorption and hydration of clays can be controlled and/or minimized.
Treating, water-based drilling fluids with inorganic chemicals and polymer additives is a common technique used to reduce hydration of shales. For example, the use of potassium chloride to stabilize shale formations was disclosed in U.S. Pat. No. 1,460,788; and it is still widely used by the industry for this purpose. Chemicals containing other inorganic cations, such as sodium, calcium, ammonium, cesium, etc., also have been claimed to provide or improve shale stabilization when used alone or with polymer additives in water-based drilling fluids. Examples of such chemicals and methods of use are disclosed, for example., in U.S. Pat. Nos. 4,142,595 and 3,843,524. Discussions on the shale stabilizing mechanisms of inorganic cations and polymer additives can be found in the literature.
In addition to inorganic cations and polymer additives, water-soluble organic polar compounds also can be used to provide shale stabilization and swelling inhibition. For example, the use of polyhydroxy alcohols, such as glycerol, glycol, sorbitol and erytlhritol, for combating heaving shales is disclosed in U.S. Pat. No. 2,191,312; the use of mixtures consisting of polyvalent metal-guanidine complexes, cationic starches, and polyglycols for shale stabilization is disclosed in U.S. Pat. No. 4,719,02; and the use of water-soluble glycol compounds and their derivatives for shale swelling inhibition is disclosed in U.S. Pat. Nos. 4,963,273, 4,941,981, and 4,830,765.
High concentrations of glycols and similar compounds not only increase the drilling fluid cost, but also can cause severe problems with hydration of polymer additives, control of mud properties, and suspension of weighting agents, especially at high mud weights and high solids contents. This again can be related to the lack of water, which helps many mud additives to solubilize and function properly. Therefore, in order to reduce cost and particularly to minimize these undesirable side effects, the concentration of glycols and similar compounds has been minimized in prior art applications of glycols in drilling fluids. See for example UK Patent Publication GB 2251876 A, and European Patent Application 92300151.5, Publication no. 0 495 579 A3. The use of greater than 40% water in prior art glycol base drilling fluids have, however, limited their ability to inhibit the clay swelling and the problems of drilling associated with swelling of the clay. The instant invention is not so limited.
Accordingly, the glycol-based drilling fluid of this invention is contrary to the use of greater than 40% of water in the drilling fluid art. U.S. patents in the drilling fluid art that include at least reference to the inclusion of glycols in drilling fluids include: U.S. Pat. No. 2,191,312 (Cannon); U.S. Pat. No. 4,780,220 (Peterson); U.S. Pat. Nos. 4,830,765 (Perricone et al); 4,941,981 (Perricone et al); U.S. Pat. No. 4,963,273 (Perricone et al); U.S. Pat. No. 4,498,994 (Heilweil); U.S. Pat. No. 5,076,373 (Hale et al); and U.S. Pat. No. 5,083,622 (Hale et al); and U.S. Pat. No. 5,248,664 (Hale et al.). Also, UK patent application no. 9420934.3 (Wilson), PCT international application no. PCT/NO 88/00063 (Ardo) and PCT/WO 96/19545 (Van Slyke). Thus, it would be an advancement in the art to provide an improved glycol-based drilling fluid that can prevent water adsorption and shale hydration more effectively using high concentration of glycols, while eliminating the problems that can be expected at high concentrations of glycols.
Glycol-based drilling fluids have been developed in which the base fluid consists of water-soluble glycol(s) or a mixture of same with up to 30% fresh or saline water. These glycol-based drilling fluids exhibit better lubricity than water-based muds and lower environmental impact than oil-based muds.
It is preferred that the glycols in muds of this invention have a viscosity of less than 50 cP at 120 degrees F. in order to avoid excessively viscous muds. Also it is preferred that polymer additives for fluid loss control, for instance, be soluble in the glycol used in the mud. Salts, surfactants, polymers, or other additives can be added to the muds to achieve, where desired, special performance characteristics, e.g., to facilitate formation evaluation or to control heaving shales.
To combat the problems of sticking and bit balling of downhole tools associated with surface swelling an anti-sticking agent is added to the drilling fluid of this invention.
The density of glycol-based drilling fluids may be increased by adding conventional weighting agents such as barite, iron oxide, dolomite, calcium carbonate or so
Lee Li-Jien
Patel Arvind D.
Stamatakis Emanuel
Cagle Stephen H.
Cross LaToya
Howrey Simon Arnold & White , LLP
M-I LLC
Warden Jill
LandOfFree
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