Earth boring – well treating – and oil field chemistry – Earth boring – Contains inorganic component other than water or clay
Reexamination Certificate
1998-02-12
2001-06-19
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Earth boring
Contains inorganic component other than water or clay
C106S633000, C405S052000, C405S263000, C405S267000, C507S110000, C507S111000, C507S118000, C507S119000, C507S120000, C507S121000, C507S122000
Reexamination Certificate
active
06248697
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to fluids for use in boring and excavating operations. More specifically, this invention relates to earth-stabilization and earth-support fluids, their composition, and techniques for preparing, using, and maintaining them. The compositions and methods are useful in creating boreholes, tunnels and other excavations in unstable soils and earth formations, especially those composed partially or wholly of sand, gravel or other granular or permeable material. The fluids of the invention, when used according to the methods of the invention. have unique dual functionality as excavating fluids and as earth-grouting or soil-hardening compositions.
BACKGROUND
In earth boring and excavating for wells, deep foundations. tunnels and other geotechnical applications. fluids or muds have been used to hold open and maintain the stability of boreholes and excavations. These fluids or muds have used hydrostatic pressure and controlled interaction with the earth to accomplish their functions. The excavations have been kept full of the fluids or muds during the excavating or boring process, with or without circulation of the fluids.
Separately in processes for improving the cohesion and load-bearing properties of granular or unconsolidated soils and other unstable granular earth formations or materials. reactive compositions have been injected into and mixed with the soils to cause solidification or hardening of the soils. These reactive compositions have comprised silicates cementitious grouts and other materials. The application of these soil-improvement materials and techniques has been done as a prelude to excavating, drilling, tunneling, or pile-driving, in order to render the soils resistant enough to support deep excavations for things such as foundation systems such as bored piles, or to bear the weight of structures erected on pad-type foundations or spread footings. These processes whereby weak soils are prepared to receive excavations for things such as foundation systems or other geoconstruction elements are generally referred to as ground improvement.
In a typical sequence of events for the construction of structures on poor soil, ground improvement techniques are used, followed by excavating or drilling to create deep foundation elements such as diaphragm wall panels, barrettes, or bored piles. Frequently the excavations or borings are made with the help of a fluid or mud as described above. In this two-step process the weak soil is first strengthened by ground improvement techniques such as reactive silicate injection or mixing, then excavations are created in or through the strengthened soil with the help of an excavating fluid or drilling mud. Finally, reinforced concrete is formed in the excavations in order to create a competent deep construction system.
In the prior art, silicates and silicate-reactive compounds have been injected into or mixed with granular, rubberized or vugular earth formations, fills or other materials in advance of or during pauses in drilling or excavating, to strengthen or solidify the earth formations. Polymer-based fluids have been used for excavating and drilling, to support the walls of the excavations or wells. And silicates have been added to drilling muds in attempts to prevent heaving of shales. What is unknown in the prior art is the formulation and effective application of a single fluid which is both and at the same time a drilling mud or earth support fluid and a reactive, soil-permeating, silicate-based chemical-grouting ground-improvement or ground-solidification agent which is effective in the presence of unstable earth environments (e.g. sand).
The instant invention offers an improvement over the prior arts for both the stabilization of boreholes, earth excavations and the like; and ground improvement. An adaptation of the invention is useful during the preparation of guide-walls for diaphragm walls and the solidification of near-surface zones of loose soil.
DESCRIPTION OF THE INVENTION
The instant invention is a composition and method of application for a dual-purpose excavating and soil-strengthening fluid composed of: water; water-dispersible polymers; alkalies; optionally soil or earth solids; various forms of sodium silicate; and, optionally, sodium aluminate, calcium chloride, carbon dioxide and chlorine gas, citric, sulfamic or other acids and salts thereof salts, or other crosslinking or catalytic agent which assists in making the sodium silicate—slurry solution somewhat insoluble to totally insoluble. The fluid's multi-purpose nature is expressed in its functions as (1) an earth-support fluid as known in the prior art, and (2) a soil-strengthening fluid which functions in a manner similar to silicate “chemical grouts” known in the prior art (3) a weighting agent to increase the specific gravity of a slurry system. The novelty lies in the accomplishment of the earth support function (as performed by drilling muds, etc.) concurrently and in combination with the chemical grouting or ground improvement function (as previously performed by reactive silicate injection and/or soil mixing prior to excavating or boring).
The fluids of the invention are preferably based on aqueous dispersions of water-dispersible polymers, and may contain inorganic buffers, polycationic additives, soil or mineral solids and other materials as disclosed in the prior art and in U.S. Pat. No. 5,407,909 and U.S. Pat. No. 5,663,123 the contents of which are hereby incorporated herein by reference. In expressing the current invention, these prior-art fluids are modified by dosing with sodium silicate and, optionally, sodium aluminate. The silicate, by being present in the excavating fluid, permeates the weak or unstable layers of granular earth material or fills which are penetrated by the excavating or boring machinery. The silicate reacts with the naturally occurring soil components under excavation, along with any introduced crosslinking or catalytic agents. The degree of strengthening, increased cohesion, or hardening is developed by enhancing or preventing alteration of weak bonds among the granular earth material, or by forming a glasslike siliceous matrix within the soils present. This effect is achievable in granular formations and soils such as gravel and sand; in filled areas and irregular materials such as rubberized concrete and mixed fills in and around old foundation systems; in sand-bearing soils such as clayey sand, sandy clay, silty sand and sandy silt; and in other permeable, elastic, granular or partially-granular earth formations such as glacial tills. oolite, shell beds, vugular or fractured rocks, rock washes and decomposed rock materials.
Because the fluids of the invention are low-solids fluids based on polymers, the whole fluid, when formulated with lower concentrations of or without fluid loss control provisions or additives, is able to permeate sandy earth formations more freely than can bentonite-based fluids, which deposit a low-permeability cake on the face of the formation. The bentonite filter cake allows principally water to pass into the formation, leaving most of the colloidal or water thickening constituents of the fluid in the filter cake. The soil-permeation characteristics of polymer-based fluids facilitate the fluids' ground improvement functionality when silicates are present in the fluids, because the silicates (and optional aluminates) are carried by the permeating whole fluid into the pore system of the formation surrounding the excavation. The fluids of the invention can also incorporate bentonite at up to about 3% wt./vol. Such polymer-extended, bentonite-containing fluids can exhibit soil-permeation characteristics sufficiently similar to pure polymer fluids that they can be useful in expressing the excavating fluid or composition of the invention, as well as the methods of the invention.
Fluids containing bentonite at concentrations greater than about 3% can also be used to express a method, if not a composition, of the invention. When bentonite-based fluids
Goodhue, Jr. K. Gifford
Holmes Max M.
Norman Clinton Scott
Wilkerson, III John M.
Cagle Stephen H.
Howrey Simon Arnold & White
KB Technologies Ltd.
Tucker Philip
White Carter J.
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