1. Field of the Invention
This invention relates to a improves lost circulation drilling fluid.
2. Description of the Prior Art
In the drilling of wells in the earth, various types of drilling mud, or other drilling fluid, are used to remove cuttings from the well and for a variety of other purposes. One problem which occurs from time to time is the loss of circulating drilling mud, or other drilling fluid, into cracks and fissures or overly porous formations deep in the earth. A variety of additives have been developed in an attempt to solve the problem of "lost circulation" and "thief formations". Examples of various "lost circulation" additives and other methods of treating lost circulation zones and "thief formations" are disclosed in the following prior art patents:
Sidwell U.S. Pat. No. 2,561,075 discloses the use of expanded volcanic rock particles as "lost circulation" additives in drilling mud, or other drilling fluid. These materials, however, are very fragile and form a poor seal in porous formations.
Armentrout U.S. Pat. No. 2,648,522 discloses the use of coarse aggregate (gravel) and expanded perlite in drilling mud, or other drilling fluid, to bridge the space between the particles of aggregate in sealing a porous formation.
Armentrout U.S. Pat. No. 3,219,111 is concerned with the problem of lost circulation and uses an expanded marine shale, having a closed, hermetically sealed, porous structure, as a mud, or other drilling fluid, additive.
Coyle U.S. Pat. No. 3,208,523 utilizes Attapulgite clay as a lost circulation additive for drilling mud, or other drilling fluid.
Sauber et al. U.S. Pat. No. 3,253,664 uses a mixture of asbestos and diatomite as a lost circulation additive in a drilling mud, or other drilling fluid.
Cox U.S. Pat. No. 3,568,782 discloses the use of popcorn as a lost circulation additive for drilling mud, or other drilling fluid.
Messenger U.S. Pat. No. 3,724,564 and Kelly U.S. Pat. No. 3,724,565 disclose the introduction of an aqueous mixture of a dispersing agent, an inert particulate material and a water dispersible oleophilic colloid into a well to stop lost circulation.
Taylor U.S. Pat. No. 3,788,405 uses organic materials such as straw, wood fiber, nut shells, etc. as lost circulation additives for drilling mud, or other drilling fluid.
Messenger U.S. Pat. No. 3,788,406 uses an oil wettable granular material, e.g. Gilsonite or ground coal, as a lost circulation additive.
Hessert U.S. Pat. No. 3,818,998 utilizes cellulose ethers, polysaccharides and polyacrylamides cross linked to a gel structure as lost circulation additives.
Messenger U.S. Pat. No. 3,987,855 uses an oil wettable dispersing agent and barite as lost circulation additives.
Bailey U.S. Pat. No. 4,014,394 uses a magnesium oxide/bentonite slurry at a pH less than 9.7 in a drilling mud, or other drilling fluid. The additive swells under conditions of use to plug the formation.