Abstract: The invention is a method for reducing lost circulation of aqueous or oil based drilling fluids wherein one or more water absorbent polymers are dispersed in a hydrocarbon fluid which is injected into the lost circulation zone. The hydrocarbon carrier fluid initially prevents water from contacting the water absorbent polymer until such water contact is desired. Once the hydrocarbon slug containing the polymer is properly placed at the lost circulation zone, water is mixed with the hydrocarbon slug so that the polymer will expand with the absorbed water and substantially increase in size to close off the lost circulation zone.

Abstract: The invention is a method for reducing lost circulation of aqueous or oil based drilling fluids wherein one or more hydrocarbon absorbent polymers are dispersed in an aqueous carrier fluid which is injected into the lost circulation zone. The aqueous carrier fluid initially prevents hydrocarbon from contacting the hydrocarbon absorbent polymer until such contact is desired. Once the aqueous polymer slug is properly placed at the lost circulation zone, a hydrocarbon is mixed with the aqueous slug so that the polymer will expand with the absorbed hydrocarbon and substantially increase in size to close off the lost circulation zone.

Abstract: Circulating and non-circulating well-drilling fluids are provided comprising parenchymal cell cellulose. In accordance with a preferred embodiment, improved viscosity and fluid loss control in circulating well-drilling fluids are obtained from the inclusion of parenchymal cell cellulose in such fluids. In accordance with another preferred embodiment, certain polymers, especially anionic polymers, and polymers derived from hemicellulosic materials are admixed with parenchymal cell cellulsoe in well fluids to provide synergistic fluid loss control and other beneficial properties. Methods for the employment of circulating and non-circulating well fluids employing parenchymal cell cellulose are also disclosed.

Abstract: Nondamaging treating fluids containing sparingly soluble hydrated borate bridging agents having a particle size distribution within the range about 1 micron to about 2000 microns are disclosed. The treating fluids comprise an aqueous salt solution having a density from about 1.0 g/cm.sup.3 to about 1.20 g/cm.sup.3, the hydrated borate bridging agent in an amount sufficient to bridge and seal off a subterranean formation contacted by the treating fluid, and a viscosifier and suspension additive in an amount to provide sufficient viscosity to maintain the bridging agent in suspension. A fluid loss control additive may be added to enhance the fluid loss control and formation sealing capacity of the treating fluid.Well treatments may be practiced by pumping or discharging the fluid or a slug or pill of the fluid into an oil, gas, water, injection or storage well where operations are to be conducted in which it is desired to temporarily plug the permeable zone while such operations are carried out.

Abstract: The disclosed invention is a novel drilling fluid additive for use in reducing lost circulation in wellbores and a method for employing the invention additive for reducing such lost circulation. The invention additive is lime encapsulated by a reaction-preventive protective casing to prevent the lime from reacting with clays in the borehole until it is desired to breach the casing. The reaction-preventive protective casing may be a film which will dissolve after a desired time of residence in the borehole or a film or waxy substance which will dissolve or melt at a desired temperature in the borehole, releasing the lime to react with clays in the formation or in the borehole to form a cement-like mass.

Abstract: Well servicing agents and processes for use with fluids circulated into wells penetrating subterranean formations in the earth's crust. Circulation losses of well servicing fluids including drilling muds, workover and completion fluids, and the like, are alleviated by incorporating a particulate material into the servicing liquid. The particulate material is formed of a thermoplastic polymer in a flexible, elongated laminar form in which its length is substantially greater than its width and its width substantially greater than its thickness. A second particulate material in a rigid granular form may be employed an admixture with the laminar particulate material. A particular lost circulation agent is a blend of a particulate thermoplastic polymer in a flexible, elongated form and a particulate thermoset polymer in a rigid granular form with the ratio of the laminar material to the granular material being at least 1:6.

Abstract: A slurry excavating method for excavating the ground or drilling a hole using excavating slurry containing a powder of water absorbing resin. This method makes it easy to prevent the slurry from flowing into gaps in the ground or cracks in fractured shale layer or fissile layer while excavating the ground.

Abstract: A process for plugging a porous formation in a well bore which comprises pumping a shear-thickening composition into drill pipe in the well under conditions of low shear to the point desired to be plugged at which point the composition is forced through the orifices of a drill bit at the end of the drill pipe and subjected to high shear of at least about 1,000 sec..sup.-1 which forms a paste in the well bore which plugs the porous formation. The shear-thickening composition comprises a water-in-oil emulsion having granular bentonite dispersed in the continuous oily phase, wherein the oily phase has a polyamine derivative surfactant dissolved therein, and the aqueous phase comprises an aqueous solution of a polyacrylamide and a polycarboxylic acid. This process may be used for plugging wells having depths in excess of 8,000 feet.

Abstract: Disclosed is a method of and compositions for reducing the fluid loss from a drilling fluid which allows a low colloid, enhanced penetration rate drilling fluid to be used in a drilling operation. The invention provides a concentrated suspension or pill of a fluid loss control additive and a seepage loss control additive in a liquid which is compatible with the drilling fluid. This pill is circulated throughout a borehole containing the drilling fluid and thereafter isolated from the drilling fluid upon reaching the surface. The fluid loss control additive and the seepage loss control additive deposit on the sides of the borehole, thus reducing the loss of fluid to the formations drilled, and the excess not deposited is subsequently isolated from the drilling fluid so as not to be dispersed throughout the drilling fluid and substantially increasing the colloid content of the drilling fluid.

Abstract: A fibrous mass or fluff comprising a fibrous absorbent and a water-swellable hydrophilic polymer absorbent is injected into a borehole during well drilling process. The fibrous mass or fluff forms an essentially fluid-tight plug when wetted with water and acts to reduce drilling fluid loss via penetration of porous subterranean structure or formation openings.

Abstract: A method for pneumatically transferring particluate solid materials into an earth formation penetrated by a well bore is shown. A gas is flowed into the well bore to establish the desired injection rate and pressure. A particulate solid material is then added to the established gas flow passing into the well bore by flowing a gas containing an entrained particulate solid material into the established gas flow to thereby transfer the solid particulate material pneumatically into the well bore.

Abstract: The present invention relates to a process for the plugging of a porous formation which may be encountered during the drilling of a well. The process entails plugging of the porous formation by means of a polymeric solution containing pseudo-emulsion spheres. These particles penetrate the pore structure within a formation. Eventually, sufficient numbers of the spheres will accumulate within the pores, blocking further flow through the formation by both the pseudo-emulsion particles and any aqueous solutions. The pseudo-emulsion system is formed by a process which includes the steps of forming a solvent system of an organic liquid or oil and a polar cosolvent, the polar cosolvent being less than about 15 weight percent of the solvent system being less than about 100 cps; dissolving a neutralized sulfonated polymer in the solvent system to form a solution, a concentration of the neutralized sulfonated polymer in the solution being about 0.01 to about 0.

Abstract: A drilling mud, or other drilling fluid containing particulate expanded aggregates is effective to seal the fractures and openings and prevent lost circulation of the mud or fluid in a well. The expanded aggregates used are inorganic clays, shales and slates which are heat treated at temperatures up to about 3000.degree. F. to produce an expanded lattice structure having a series of interconnecting passages. The expanded aggregates are added to any conventional drilling mud, or other drilling fluids, either water-based or oil-based, in an amount sufficient to stop the fractures and openings in the formation. The proportion of the aggregates in the drilling mud, or other drilling fluid, will be varied as needed and will usually range from 1-33 parts by weight per 100 parts by weight of drilling mud. Water-based and oil-based drilling muds containing expanded aggregates are novel compositions.

Abstract: Deep drilling is facilitated by the following steps practiced separately or in any combination:(1) Periodically and sequentially fracturing zones adjacent the bottom of the bore hole with a thixotropic fastsetting fluid that is accepted into the fracture to overstress the zone, such fracturing and injection being periodic as a function of the progression of the drill.(2) Casing the bore hole with ductile, pre-annealed casing sections, each of which is run down through the previously set casing and swaged in situ to a diameter large enough to allow the next section to run down through it.(3) Drilling the bore hole using a drill string of a low density alloy and a high density drilling mud so that the drill string is partially floated.

Abstract: A process for plugging a porous area of well bore which comprises pumping a shear thickening composition into the well under conditions of low shear to the portion of the well bore desired to be plugged at which point subjected to high shear to form a paste which plugs or seals the porous area. The shear thickening composition comprises a water-in-oil emulsion having granular bentonite dispersed in the oily phase, said oily phase having both an oil soluble amine and a polyamine derivative surfactant dissolved therein. The aqueous phase will preferably comprises a polyacrylamide solution. This process may be used for plugging wells having depths in excess of 8,000 feet.

Abstract: A lost circulation controller for use in drilling fluids formed from cocoa bean shell material having a particle size distribution from 2 to 100 mesh (U.S. Std.) with at least about 25 percent by weight of said particulate material being from 2 to 10 mesh (U.S. Std.).

Abstract: The fluid loss and viscosity loss characteristics of a water expandable bentonite clay are substantially improved by extruding the clay through die openings while, at the same time, passing a wiper or scraping blade across the entrance of the die openings. In this manner, very inexpensive and low grade clays can be substantially improved and thus modified making such clays acceptable in fluid loss and viscosity for use in a drilling fluid or mud.

Abstract: A method of sealing fractures and openings in an earth formation traversed by a well bore comprises adding particulate expanded aggregates to a drilling mud, or other drilling fluid, circulating through the well bore, which aggregates seal the fractures and openings and prevent lost circulation of the drilling mud, or other drilling fluid. The expanded aggregates used are inorganic clays, shales and slates which are heat treated at temperatures up to about 3000.degree. F. to produce an expanded lattice structure having a series of interconnecting passages. The expanded aggregates are added to any conventional drilling mud, or other drilling fluids, either water-based or oil-based, in an amount sufficient to stop the fractures and openings in the formation. The proportion of the aggregates in the drilling mud, or other drilling fluid, will be varied as needed and will usually range from 1-33 parts by weight per 100 parts by weight of drilling mud.

Abstract: A spacer comprising the water-in-oil emulsion portion of a shear-thickening well control fluid is used to separate drilling mud from the shear-thickening fluid in the drill pipe in the well bore to avoid premature thickening of the shear thickening fluid in the drill pipe. The shear-thickening well control fluid comprises a water-in-oil emulsion in which is dispersed granular particles of hydratable, water expandable clay.

Abstract: A device for applying plugging mix to well walls comprises installed in series and interconnected a piston having passages for the flow of a fluid and spring-biased locking members for fixing the position of the device with respect to a drilling string, and a head carrying vanes for applying plugging mix to well walls and a bit for drilling-off the mix installed at the distal end of the head. The head has passages for the flow of the fluid. The vanes are made in the form of two plates installed on opposite sides of the head at an angle with respect to its axis of rotation, the vanes being radially movable with respect to the axis of rotation. The piston, the head and the bit are of a diameter which is slightly smaller than the nominal inside diameter of the drilling string.

Abstract: A method and an apparatus for excavating pile holes of various shapes, including a pile hole with a widened bottom and a pile hole with a widened top and widened bottom, by means of an excavating bit and widening bits.

Abstract: Disclosed is a compacted paper lost circulation material for use in arresting or preventing a lost circulation condition in well bore drilling operations and a method of forming same. The lost circulation material generally comprises comminuted paper, water and a non-foaming, water soluble surfactant which has been compressed to form a pellet. When added to a circulating drilling fluid, the pellet disperses to form particulate wetted paper which plugs fractured or vugular porosity in an earth stratum which othewise creates a lost circulation condition in the drilling fluid.

Abstract: A lost circulation material is described wherein a mixture of flexible flakes, fibers and granular particles, preferably shredded paper, mineral wool and calcium carbonate, respectively, which, when maintained in a carrying liquid being circulated through a well during drilling operations, acts to stop the loss of drilling fluid into permeable or fractured formations. The seal on the formation can be degraded by contact with an acidizing acid, such as hydrochloric acid, allowing a potential hydrocarbon producing formation to be reopened for production after a seal has been effected using the material of the invention.

Abstract: The instant invention is directed to shear thickening fluids which comprise a water-swellable material (clay), present in a sufficient concentration so as to be capable of forming a stiff paste upon interaction with the water used, and water wherein the clay and water are kept separated by an intervening hydrocarbon-surfactant composition. The intervening oil phase prevents the interaction between the water and the clay phases and results in a stable, nonreacting, pumpable composite until such time as the oil envelope is ruptured by application of a sufficiently high shear force. Upon such rupture, the materials interact rapidly forming a semi-rigid stiff paste. Various well-control problems, such as oil and gas with blowouts, can be controlled by use of the above-described composite. The composite is pumped down the well pipe.

Abstract: A sulfonated gilsonite used in a drilling mud for drilling a well wherein the sulfonated gilsonite is prepared by reacting at a temperature between 210.degree.-280.degree. F. with a mixture of water, gilsonite having a softening point of at least 300.degree. F., lignite, sulfonating compound and water soluble based compound for a period of time to sulfonate the gilsonite.

Abstract: An arrangement for full hole drilling, wherein a drilling bit having a passage for drilling fluid is attached to a drill pipe string. A hole wall former is provided above the bit for closing the space between the hole walls and the drill pipe string. A container containing a plugging material is provided in the interior of the drill pipe string immediately above the bit, which is adapted to let drilling fluid between the walls of said container and said drill pipe string. The bit has an axial bore of a diameter which is greater than the inside diameter of the container and which is adapted to receive the lower end of said container.

Abstract: A composition of matter and a method of making is provided for preparing slurries to seal permeable earth formations encountered in the drilling of wells. The composition of matter comprises finely divided paper, diatomaceous earth, and in a further embodiment, lime. Slurries of the composition of matter can be prepared using fresh water or salt water to form a water-based lost circulation fluid, or using oil to form an oil-based lost circulation fluid. A slug of the slurry is spotted at the locus of the permeable formation and defluidized to form a formation seal on which a mud sheath is then deposited.

Abstract: A drill string in a well bore has a mandrel extending longitudinally thereof adjacent the lower end of the drill string with a drill bit connected to the mandrel. Longitudinally extending helical groove means are provided in the mandrel and roller means are supported on the drill string and engaged with the helical groove means. Spring means is supported by the drill string and abuts the mandrel to tend to urge the mandrel longitudinally out of the drill string whereby the bit is urged into substantially continuous contact with the well bore bottom as the drill string is rotated during drilling operations. Valve means are provided for selectively circulating fluids from the drill string to the well bore above the drill bit, and when desired jar means may be incorporated in the drill string to impart an up or down jar thereto should the drill string become stuck or tend to become stuck during drilling operations.

Abstract: A composition of matter and a method of making is provided for preparing slurries to seal permeable earth formations encountered in the drilling of wells. The composition of matter comprises finely divided paper, diatomaceous earth, and in a further embodiment, lime. Slurries of the composition of matter can be prepared using fresh water or salt water to form a water-based lost circulation fluid, or using oil to form an oil-based lost circulation fluid. A slug of the slurry is spotted at the locus of the permeable formation and defluidized to form a formation seal on which a mud sheath is then deposited.

Abstract: In the recovery of hydrocarbon materials from subterranean formations, the simultaneous production or loss of other fluids such as water is inhibited by the selective introduction into the subterranean porous structure of discrete spheroidal microgels of a water-swollen or water-swellable, crosslinked polymer such as crosslinked polyacrylamide.

Abstract: By separating the woody ring portion of corncobs from the pith and chaff portions a lost circulation additive for drilling muds is produced which does not appreciably increase the yield point of the drilling mud. Improved particle size distributions for lost circulation additives is also given and claimed which permits low concentrations of the additive to produce seals withstanding 1000 psig.

Abstract: Magnetic material, such as discarded magnetic tape, is ground into small pieces and mixed with well drilling fluids. When the drilling fluids are lost in porous ground, cracks or fissures in the walls of the well, the magnetic tape will accumulate and serve to block the unwanted loss of the fluid. In the event that the fissures are of a size such that the tape will not block the flow, the magnetic properties of the tape may be utilized in combination with a standard well logging instrument to provide an indication of the exact location of the area of fluid loss. At that time, further remedial measures may be taken to block the undesired flow of fluid. For example, a cement slurry may be pumped into the well in the location of the crevices and thus form a permanent seal against loss of fluid.

Abstract: A method is disclosed for preventing loss of aqueous drilling fluid to porous formations penetrated by a well bore during drilling operations for oil and gas. The method utilizes readily available pelleted cottonseed hulls as the lost circulation material which is added to the drilling fluid and pumped down the well bore. The pelleted cottonseed hulls are composed of cottonseed hulls, cottonseed meal, bentonite, a residual amount of cottonseed lint and a surface active agent. The cottonseed hulls, cottonseed meal, bentonite, residual lint and surface active agent are heated in the presence of steam and compressed to form pellets. Because the pellets are in a compressed form, they do not expand when added to the drilling fluid until they are well down the well bore. The pelleted cottonseed hulls may also contain cottonseed oil. The pelleted cottonseed hulls are well known and widely used in the dairy cattle industry as a pelleted feed material.

Abstract: Apparatus and method of filling voids in a ground stratum in the vicinity of a well bore are enclosed. The apparatus is a self-contained device and, for example, it can be placed in the well bore in the vicinity of the voids to be plugged by dropping the apparatus down a drill string. Once in place it will automatically respond to the well pressure to provide the required plugging. To accomplish this the apparatus includes precursors of polymers such as precursors of polyurethanes, epoxy type polymers, polyesters or other polymers which are released from the apparatus and flow into the voids.

Abstract: Process for drilling a hole in the earth's crust in which the bottom of the drill hole is frozen in front of or near the drill bit by a cold driling liquid in which liquid particles that have been frozen to solid parts or have been solidified have been taken up whether or not by addition. In this way the bottom of the drill hole is always so hard -- also upon drilling in soft or plastic formations, such as clays, -- that use can be made of diamond drill bits or other drill bits normally used for hard formations, in order that the number of times a drill bit is to be replaced can be strongly reduced. The purpose of adding ice is to make it possible for a sufficient amount of frigories per unit of time to be introduced into the drill hole, so that at greater depths the temperatures at the drill bit are decreased to such a degree that here, too, use can be made of drill bits for hard formations here described.

Abstract: This invention concerns the production of very deep boreholes. A rotary drilling tool is suspended at one end of a very long line of supporting elements such as a cable. During at least the entire duration of the drilling operation, the borehole is filled at least partly with at least one substance which remains in a liquid state and has a density greater than the mean density of the drilled ground strata. Thus any infiltrations in the borehole and the drilling debris move naturally upwards to the free surface of the liquid substance filling the borehole.

Abstract: Improvements in the treatment of wells that penetrate subterranean formations are accomplished through the use of a polymer solution which includes a neutralized ionomeric polymer dissolved in an organic solvent and a polar cosolvent. The polymer has a backbone that is substantially soluble in the organic solvent and pendant ionomeric groups that are substantially insoluble in the organic solvent. The polar cosolvent solubilizes the pendant ionomeric groups such that the polymer solution upon introduction into the well has a viscosity less than about 20,000 centipoises and upon mixing with water the polar cosolvent is taken up by the water causing the polymer to aggregate and increase in viscosity sufficient to form a plug. The polymer solution may be used in well drilling operations, well completion operations, and secondary recovery operations.

Abstract: This specification discloses a method of controlling the loss of drilling fluid into a lost circulation zone of a subterranean earth formation penetrated by a well. A nonaqueous slurry of a hydratable material and an oleophilic clay is introduced into the well and mixed in the vicinity of the lost circulation zone with an aqueous liquid to form a soft plug.

Abstract: Lost circulation in a well occurring during drilling is reduced by aeration of clay-free, non-thixotropic, brine wellbore fluids comprising hydroxyalkyl cellulose and preferably magnesia as a stabilizer. The gas is easily and completely removed from the foam returned to surface with only a conventional degassing and gas busting equipment normally found in a solids removal system. The advantages of the clay-free, non-thixotropic, drilling fluids as known are preserved and the system allows rapid change from aerated to non-aerated fluid as required.

Abstract: A process and composition are described for use in drilling shale and especially in drilling the troublesome types of shale which heretofore have been impossible to drill effectively. The aqueous drilling fluid of this invention so effectively stabilizes the shale that additions to maintain the special drilling fluid can be discontinued or drastically reduced, once the shale formation has been penetrated and drilling below the shale could even be done with conventional drilling fluids.The drilling fluid contains between about 0.2 to 1.5 pounds per barrel of flaxseed gum together with potassium and/or ammonium salts. The potassium and/or ammonium salts are used in quantities to provide a concentration of the cation of the salt of at least 10,000 ppm. As the drilling fluid is a non-clay type, a non-clay viscosifier is used. Preferably, the cation concentration is tailored to drilling fluid salinity such that the cation concentration in parts per million is approximately equal to at least 10,000.times.(1+0.025.

Abstract: A bottom-positioned well drilling platform is provided with an enclosure in the lower part thereof which forms a chamber into which returning drilling mud and cuttings can be discharged. A pump and separate return line raise the mud alone from the chamber to the top of the platform while the cuttings remain in the chamber.

Abstract: A method for drilling a well through a subterranean formation containing one or more zones of unconsolidated dolomite, wherein the drilling operation is interrupted periodically to consolidate the newly drilled incompetent dolomite by the injection of a sequence of reactant slugs comprised of (I) an aqueous solution containing an acid, a surface active agent and a precipitating agent for silicates, (II) an aqueous solution containing a water-soluble silicate, and (III) an aqueous solution containing a precipitating agent for silicates.

Abstract: This invention concerns the production of very deep boreholes. A rotary drilling tool is suspended at one end of a very long line of supporting elements such as a cable. During at least the entire duration of the drilling operation, the borehole is filled at least partly with at least one substance which remains in a liquid state and has a density greater than the mean density of the drilled ground strata. Thus any infiltrations in the borehole and the drilling debris move naturally upwards to the free surface of the liquid substance filling the borehole.

Abstract: Method and apparatus for processing drilling mud wherein mud containing lost circulating material is passed from the well to a separator device where it is separated from the drilling mud and is reintroduced into the drilling mud after the mud has been cleaned of undesirable solid particulate. In the separator, the lost circulating material is retained on a coarse screen while the mud and drilling solids pass to a finer mesh screen. The finer mesh screen removes the drilling solids and allows the mud to pass to the mud tank. The separator includes structure to recirculate the lost circulating material to the mud tank.

Abstract: Zones of lost circulation and other undesired fluid communication channels into a wellbore are sealed by isolating a volume in the well including such a zone and applying greater than formation pressure to a novel slurry spotted in the zone until it hardens into a solid, drillable seal. Redrilling the bore can be accomplished even in soft, geologically young formations, without damaging the seal. The slurry contains per barrel from 5-50 pounds diatomaceous mix (see below), from about 35 to about 350 pounds of oil well cement, and at a minimum about 5 to 6 pounds of a flake type lost-circulation agent. Preferably, the weight per barrel of lost circulation agents is in the range of about 15 to 30 pounds of a mixture containing flakes, fibers, and hard granules.Diatomaceous mix is powdered diatomaceous earth containing about 2% of ground lime and 8% of ground asbestos fibers.

Abstract: An improved offshore drilling method and apparatus are disclosed which are useful in preventing formation fracture caused by excessive hydrostatic pressure in a drilling riser. Gas is injected into the riser to provide the lift necessary to return the drilling fluid to the surface and to reduce the density of the drilling fluid. The rate of gas injection overlifts the drilling fluid to the extent that the pressure of the fluid is reduced to less than that of the seawater surrounding the riser. Seawater is permitted to flow into the lower end of the riser in response to the differential pressure between the drilling fluid and seawater so that the pressures of the drilling fluid and the seawater approximately equalize.

Abstract: An improved offshore drilling method and apparatus are disclosed which are particularly useful in preventing formation fracture caused by excessive hydrostatic pressure of the drilling fluid in a drilling riser. One or more flow lines are used to withdraw drilling fluid from the upper portion of the riser pipe. Gas injected into the flow lines substantially reduces the density of the drilling fluid and provides the lift necessary to return the drilling fluid to the surface. The rate of gas injection and drilling fluid withdrawal can be controlled to maintain the hydrostatic pressure of the drilling fluid remaining in the riser and wellbore below the fracture pressure of the formation.

Abstract: The disclosure provides an aqueous hydroxy-aluminum drilling fluid having a ratio of hydroxy groups to aluminum atoms in the range of from 1.0 to 2.7 and a concentration of at least 0.5 molar and including an effective amount of a polymer selected from the group consisting of polyvinylpyrrolidone and polyvinyl alcohol and a corrosion inhibitor.

Abstract: A system and method for emplacing a relatively large casing under and spanning an obstacle such as a river is disclosed. The casing is emplaced along the path of a previously bored and placed existing pilot string running beneath the obstacle. The pilot string extends typically in an inverted arcuate contour from a first position at or near ground level on one side of the obstacle to a second position at or near ground level on the other side of the obstacle. The system includes apparatus for concentrically reaming the pilot hole to an enlarged diameter and entraining the cuttings from the excavated annulus of the reaming operation in drilling mud. The casing is advanced along the reamed pilot hole in following relationship to the reaming apparatus. A seal is provided between the outer surface of the leading portion of the casing and the reamed pilot hole so that the drilling mud containing the entrained cuttings flows into the leading end of the advancing casing.

Abstract: A magnesium oxide-bentonite slurry having a controlled gelation time and capable of gelling to a firm set gel is used to restore lost circulation during well drilling operations.