Abstract: A process for circulating an aqueous foam in a wellbore includes the steps of forming a foam from an aqueous composition having a determined pH value, injecting the foam into a well so that it circulates from the surface to the well bottom and then back from the well bottom to the surface, and then changing the pH value of the foam when it returns to the surface. The aqueous composition from which the foam is made includes at least one ionic surfactant whose charge does not practically depend on the pH value and a polyampholytic polymer whose global charge depends on the pH value. This composition gives the foam the property that when the pH of the foam is varied at the surface of the well, the charge of the polyampholytic polymer is modified and the foam becomes destabilized and breaks more readily.

Abstract: The present invention is directed to a method of cleaning a well riser. In particular, the method comprises the steps of suspending in a drill pipe from the surface a circulating tool in the well riser, and causing the circulating tool to axially collapse so as to open one or more radial outlets in the tool and allow cleaning fluid to be expelled out of the tool and impact on the inside of the well riser.

Abstract: There is a provided a liner setting tool for running liner or casing into a well bore which comprises an elongate body for attachment to the casing or liner, but which allows for movement of the liner setting tool relative to the liner or casing. The elongate body has radial outlets which may be closed or open in alternative states, whereby these radial outlets may be used for circulating fluid in order to clean the well bore.

Abstract: An apparatus and method for drawing small milling debris into a combination milling and debris retrieval tool, during the performance of the milling operation. A milling tool has a fluid intake port near its lower end, where debris-laden fluid is drawn into the milling tool and subsequently into a separator section. The separator section has a debris deflection tube and a screen for separating the debris from the fluid. Fluid is drawn into the tool by either a set of eductor nozzles or a downhole motor and pump.

Abstract: A process for cleaning-up drilling and completion fluid filtercakes using an aqueous wash containing water and cationic salts of polyaminocarboxylic acids at neutral or acidic pH.

Abstract: A method of oil/gas well stimulation. Firstly, positioning a venturi-style pumping apparatus (12) in a wellbore (14) within a selected production zone (16) of an oil/gas producing formation (18). The pumping apparatus (12) is connected to a first conduit (21) and a second conduit (25). Secondly, activating the pumping apparatus (12) to induce a flushing of fluids and contaminants from the oil/gas producing formation (18) into the wellbore (14). Thirdly, pumping power fluid that powers the pumping apparatus (12) via the first conduit (21) and directing a portion of the power fluid through at least one fluidizing nozzle (15) to sufficiently fluidize contaminants to enable the contaminants to be removed from the wellbore (14) along with pumped fluids by the pumping apparatus (12) via the second conduit (25).

Abstract: A method and apparatus are disclosed in which alkane-utilizing bacteria are used to reduce fouling of injection and recovery wells. Fouling materials such as combinations of bacteria and metal oxides that would otherwise clog the wells are prevented from depositing on the wells. In a preferred embodiment, a butane substrate and an oxygen-containing gas are injected near a well inlet or outlet to stimulate the growth of butane-utilizing bacteria which are effective at reducing or eliminating fouling of the well.

Abstract: A method and composition for removing deposits of heavy hydrocarbonaceous materials and finely divided inorganic particulate matter from wellbore and flowline surfaces using a composition containing an alkyl polyglycoside, an ethoxylated alcohol, a caustic and an alkyl alcohol.

Abstract: A composition and method for acidizing a formation in the presence of ferric ion, free sulfur and/or sulfides is disclosed. The composition employs a ferric ion reducing agent and a sulfide reactant separately or in combination. The ferric ion reducing agent is a thioalkyl acid. The sulfide reactant compounds include &agr;-diketones and saturated and &agr;-unsaturated cyclic ketones. In another aspect, the reducing activity of the thioalkyl acid is accelerated by the presence of a catalytic quantity of a compound or mixture of compounds which yield in acid solution cuprous ion, cupric ion or combinations thereof with iodide ion.

Abstract: A process for restoring the injectivity or productivity of a well penetrating a subterranean formation by injecting a micelle treating fluid into the subterranean formation via the well with the micelle treating fluid containing a 2% potassium chloride water solution and a mutual solvent containing alcohol, aromatic hydrocarbon and an alkyl or alkylaryl polyoxyalkylene phosphate ester surfactant, thereafter displacing the micelle treating fluid into the formation by injecting a gas into the well and contacting accumulated asphaltene precipitate and a low-gravity, high-viscosity, asphaltene-based crude in the subterranean formation with the micelle treating fluid to disperse the accumulation of asphaltene and to reduce the viscosity of the low-gravity, high-viscosity, asphaltene-based crude.

Abstract: A non-aqueous system for cleaning a section of a subterranean well bore and installing a water based fluid system into the well bore. The well bore may be an open hole or contain a casing string therein. A series of spacer fluids are introduced into the well bore to displace the drilling fluid in order to clean and water wet the section of well bore. In the preferred embodiment, three spacers are pumped into the well bore including a first spacer containing a solvent, a second spacer containing a solvent and a third spacer containing a surfactant. A water based fluid system may thereafter be introduced into the well bore. The water based fluid system will be a completion fluid in the preferred embodiment.

Abstract: Improved metal corrosion inhibitors, acid compositions containing the inhibitors and methods of using the acid compositions are provided by the present invention. The metal corrosion inhibitors are basically comprised of one or more acetylenic alcohols and hexamethylenetetramine.

Abstract: A wash nozzle for wellbore washing operations has been invented, the wash nozzle, in one aspect having a central mandrel with a top, a bottom, and a fluid flow bore therethrough from top to bottom, at least one mandrel port through the central mandrel for fluid flow from within the central mandrel's fluid flow bore to an exterior of the central mandrel, a hollow sleeve rotatably mounted around the central mandrel, and at least one sleeve port through the sleeve for fluid flow from within the sleeve from the exterior of the central mandrel to an exterior of the sleeve, the at least one sleeve port defined by a wall on the sleeve. In one aspect the wash nozzle includes apparatus for selective rotation of the sleeve about the mandrel. In one aspect flow through the wash nozzle is stopped to effect sleeve rotation and, in one particular aspect, flow through the nozzle is then re-established. Methods have been invented using such wash nozzles for wellbore washing operations and/or cuttings removal.

Abstract: The use of high flash point, low vapor pressure compositions for injection into, and coating of, gas and oil wells and surrounding underground hydrocarbon bearing formations and processing equipment for the purpose of removing scale, paraffins, tars, and other viscous constituents. Treatment results in increased flow of gas and/or oil and decreased adhesion of soils and scale in all aspects of oil and gas recovery, including hydrocarbon bearing formations, casings, lines, and pumping equipment. The composition contains about 40 to 99 wt. % of a fatty acid alkyl ester blend and about 1 to 25 wt. % of at least one lower alkyl glycol ether.

Abstract: A system capable of removing scale deposits from an interior metallic surface of a conduit includes a mixture including a plurality of substantially spherically shaped solid particles and fluid, a mixture delivery tubing insertable into the conduit, and a nozzle attached to the mixture delivery tubing. The nozzle includes a plurality of nozzle jets and is capable of ejecting the mixture to loosen scale deposits from the interior metallic surface of the conduit.

Abstract: The invention relates to a process for facilitating the disposal of flowable and pumpable working fluids based on emulsifiers containing W/O invert emulsions--more particularly corresponding auxiliaries of the type used in geological exploration, such as oil-based w/o invert drilling muds--and for the simplified cleaning of solid surfaces soiled therewith, if desired using flowable spraying aids, the process being characterized in that, by selecting and adapting the emulsifiers/emulsifier systems to the oil phase of the invert emulsion, temperature-controlled phase inversion is achieved at temperatures below the in-use temperatures of the w/o invert emulsions, but above the freezing point of the aqueous phase and in that disposal and cleaning are carried out at temperatures in and/or below the phase inversion temperature range.

Abstract: The present invention provides a method for cleaning debris from a bore and includes injecting hydrophilic fibers selected from the group consisting of polyolefins, polyesters and nylons, suspended or dispersed in a water based or oil based liquid into the bore and forcing the suspension through the length of the bore, to its open end. In particular, the suspension is directed through sections of the bore holding quantities of debris formed from the drilling operation. The suspension loosens the debris and sweeps substantial quantities of debris from the bore, and acts to suspend the debris in the liquid in static suspension at times when the liquid is not being forced through the bore.

Abstract: An apparatus and method for circulating fluid in a borehole is described. The apparatus comprises a tubular assembly (1; 40; 60) which has an axial through passage (21, 18; 47; 19) between a fluid inlet (21) and first fluid outlet (19). The fluid inlet (21) and the first fluid outlet (19) are connected (13, 20) in a work string which is supported from the surface above the borehole. There is a second outlet (16; 42, 48) which extends generally transversely of the assembly (1; 40; 60). An obturating member (9) is moveable between a first position in which the second fluid outlet (16; 42, 48) is closed and a second position which permits fluid flow through the second outlet (16; 42, 48). An engagement mechanism (12, 6, 7; 68, 69) is moveable between an engaged configuration in which the obturating member (9) is maintained in one of the first and second positions, and a disengaged configuration in which the obturating member (9) is in the other of the first and second positions.

Abstract: The invention concerns a method for underground mining comprising the following steps: circulating in a well a foaming composition containing surfactants with cloud point higher than the temperature of the underground formation, heating the composition returning from the bottom to a temperature higher than the cloud point. The invention also concerns a system and a foaming composition based on water for implementing the method. The invention is useful for drilling and oil well completion operations requiring the use of a low-density fluid.

Abstract: Well stimulation and purging compositions for enhancing oil and gas production. The compositions include two base solutions which are typically used in combination with each other in well cleanup, well stimulation and formation purging applications. The first base solution is an anionic surfactant characterized by an aqueous solution of ether sulfate, isopropanol anhydrous, ammonium bisulfide, and either potassium chloride or a clay stabilizer formulation. In treatment of oil and gas wells, the solution is capable of reducing surface tension of well fluids and dissipating and dispersing various solids and minerals by dehydrating the well bore and well formation. The composition flocculates and foams the solids, minerals, water and condensate to the well surface.

Abstract: A method and apparatus for cleaning the producing areas of water wells including screens and the surrounding formations. Chemicals that may be used for cleaning the well are applied through a surge tube and forced from the tube by gas such as carbon dioxide. At the same time, gas is injected into the well through an injection line which terminates below the surge tube. The opposing forces from the chemical application and gas injection drive the chemicals through the screen, gravel pack, and into the formation to dislodge and dissolve materials that tend to plug the well. When the chemical application and gas injection are stopped, the pressure in the well is reduced to draw the dislodged materials into the well. They are removed by a submersible pump or gas lift.

Abstract: A method for removing filtercake from a subterranean borehole comprising drilling the borehole with a drilling fluid that includes additives to form a filtercake having an oxidation-degradable component, preferably a polysaccharide. The filtercake is contacted with a clear brine containing bromine or bromate generating agents to degrade the polymers within the filtercake. The brine contains bromide salts and an oxidant capable of delayed oxidation of the bromide to bromine at downhole conditions.

Abstract: A treatment for wells and/or subterranean formations in which a pre-treatment fluid is introduced prior to a polymer-containing treatment fluid, such as a hydraulic fracturing fluid. The pre-treatment fluid may contain an enzyme and/or oxidative breaker effective to degrade the polymer in the polymer-containing treatment fluid. The enzyme or oxidative breaker of the enzyme pre-treatment fluid enhance degradation of polymer filter cake from the reservoir-side of the filter cake during flow-back of the treatment fluid.

Abstract: A hydrocarbon producing well is treated by first igniting a gas generating charge in the well to clean out perforations communicating between the casing and the formation without creating high permeability channels adjacent the perforations or fracturing the formation in a macroscopic sense. Then, a treatment liquid is injected into the wells by a gas generating propellant charge placed in the production string and then ignited. The propellant charge is designed to produce a minimum horsepower sufficient to push the liquid more-or-less equally through all of the open perforations. The propellant charge is designed to produce a maximum horsepower which is less than what is necessary to fracture the formation. Basically, the combustion rate of the propellant charge is reduced by one of a multiplicity of techniques to produce a long, relatively slow combustion rate.

Abstract: An apparatus and method of rehabilitating the stagnant bottom of water wells using existing well equipment including a pump and a pressure tank, augmented by valves and a conduit that extends from the surface to near the bottom of the stagnant region at the well bottom. Water pumped from the well is returned under pressure to the well bottom where it displaces the fouled contents of the stagnant region at the well bottom. This elevates the contents of the well bottom to a position above the pump intake, where the contents can then be pumped to waste.

Abstract: A method for removing filtercake from a subterranean borehole comprising drilling the borehole with a drilling fluid that includes additives to form a filtercake having an oxidation-degradable component, preferably a polymer. The filtercake is contacted with a precursor that forms an oxidizing agent at downhole temperatures to degrade the polymers within the filtercake. Alternatively one or more catalysts for activating the precursor of an oxidizing agent is embedded within the filtercake. The catalyst activates the precursor as the precursor is flushed over the filtercake and remains in contact with the filtercake to form an oxidizing agent to degrade the oxidation-degradable agent and decompose the filtercake. The remaining particles of decomposed filtercake are then flushed away.

Abstract: Method for reducing the viscosity of clogging hydrocarbons in an oil well. The method utilizes a tube type heat exchanger enabling heated gases to pass through feed water coils to heat the water to a predetermined temperature and at a pressure which prevents any flashing or phase change of the feed water within the heat exchanger. From the heat exchanger the heated feed water passes through a conduit which empties into the oil well. The well is open to atmosphere so that the feed water undergoes a phase change or flashing when it is introduced into the oil well. The resulting combined steam and hot water reduce the viscosity of the hydrocarbons sufficiently to facilitate their flow out of the oil well.

Abstract: A method for cleaning a wellbore plugged with deposits of heavy hydrocarbons and finely-divided inorganic solids by circulating a surfactant composition containing an alkyl polyglycoside, an ethoxylated alcohol, a caustic and an alkyl alcohol through the wellbore with a coiled tubing.

Abstract: An improved method for cleanout of subterranean wells, such as hydrocarbon wells, is disclosed, the method being characterized by utilization of specified translocating fibers and/or platelets to aid in reduction of undesired fluids in the wellbore.

Abstract: A method of operating a drill string tool for use in a wellbore formed in an earth formation is provided. T he method comprises rotating an upper drill string part while a rotation transfer assembly transfers the rotation of a first element to a second element so as to rotate a lower drill string part in order to drill a section of a wellbore, inducing a controller to disengage the rotation transfer assembly so as to allow the first element to rotate relative to the second element by virtue of bearings, and rotating the upper drill string part about its longitudinal axis while the lower drill string part remains substantially stationary.

Abstract: A method and assembly for treating a portion (e.g. horizontal) of a wellbore for removing solids and for producing fluids therefrom. The assembly is comprised of dual flowpaths (e.g. tubing strings) extend from the surface into the portion of the wellbore to be treated and produced. A liner is connected on the lower end of the first flowpath while the second flowpath terminates within the upper end of the wellbore portion. A treating fluid is flowed down the first flowpath and through the liner into the wellbore to wash and entrain solids therein. The treating fluid and solids are then circulated back to the surface through the second flowpath. After treatment, the second flowpath is closed and fluids are produced through the liner and to the surface through the first flowpath.

Abstract: An acidic fluid that is useful in stimulation and workover operations, and in particular, in matrix acidizing treatments, comprises an acid, such as hydrochloric acid; water; an aliphatic aldehyde having 1-10 carbon atoms; and an aromatic aldehyde having 7-20 carbon atoms. The aliphatic aldehyde preferably has 1-6 carbon atoms. Glyoxylic acid and glyoxal are especially preferred aliphatic aldehydes. The aromatic aldehyde preferably has 7-10 carbon atoms. Cinnamaldehyde is especially preferred.

Abstract: A cleaning device for a well bore which is adapted to be connected to a drill string for insertion into the well bore and through which cleaning fluid is pumped, comprises an elongated outer sleeve having an axially extending through bore therein and at least one port in the side wall of the outer sleeve, each of which ports is axially spaced along the outer sleeve. An elongated inner sleeve having, an axially extending through bore therein is coaxial with and axially slidable within the outer sleeve. An annular seating collar is located within the through bore in the inner sleeve and at least one port is provided in the side of the inner sleeve. The ports are axially spaced along the inner sleeve. Pressure sensitive stops means serve to retain the inner sleeve in place within the outer sleeve at each of a plurality of predetermined axially spaced positions in turn.

Abstract: An aqueous displacement fluid composition is used as a spacer fluid composition to change one type of drilling mud for another type of drilling mud or in cementing operations downhole, to clean downhole hardware in wellbores. The method comprises introducing into a wellbore an aqueous displacement fluid composition, such as a spacer fluid, to displace downhole wellbore fluids, having an improved rate of emulsification and a high capacity for emulsifying hydrocarbons, and aqueous fluid compositions. The aqueous displacement fluid composition introduced into wellbores contain mixtures of:a) water;b) a polyoxyalkylene monool surfactant represented by the formula: ##STR1## wherein R.sub.1 is a hydrocarbyl group, R.sub.2 is a C.sub.1 -C.sub.3 alkyl group, and the weight average of w+x is at least about 5; andc) a polyoxyalkylene monool surfactant represented by the formula: ##STR2## wherein R.sub.1 is a hydrocarbyl group, R.sub.2 is a C.sub.1 -C.sub.

Abstract: An apparatus for cleaning subterranean wellbores is described. The apparatus comprises a sleeve member which is fixed to a part of the drillstring and a rotatable jet head with nozzles through which an abrasive fluid is discharged. The nozzles are mounted such that the fluid jet is directed to an area of the wellbore immediately adjacent to a leading edge of the sleeve. The nozzle head is restricted in its protrusion out of the sleeve.

Abstract: A method and apparatus for treating a long interval within a wellbore wherein a treatment fluid is delivered to selected levels within the interval by blocking flow to certain zones while allowing flow to others. A treatment tube extends substantially through the interval and is comprised of a perforated conduit which is open at its upper end and which has a plurality of openings spaced along its length. Each of the openings have a valve seat within the conduit at its entrance which is adapted to receive a valve to seal and block flow through that opening. In operation, a treatment fluid is flowed through the treatment tube and out the openings into different levels within wellbore. At desired intervals, the valve are introduced into the treatment fluid and are carried into the treatment tube to seat at a respective opening to thereby block flow through that opening while allowing continued flow through others.

Abstract: A downhole wash tool for carrying out cleaning operations in a borehole. The tool has a housing on which a plurality of flow-blocking, diverters (e.g. steel) are mounted. The diverters move between a retracted position and an extended position wherein the diverters effectively block flow around the tool. A retainer normally maintains the diverters in their retracted position when in a first position and releases the diverters when in a second position. A spring normally biases the retainer towards its first position. The retainer is hydraulically-actuated through the housing to move it towards its second position. When the cleaning operation is completed, pressure in the workstring is relaxed whereupon the spring moves the retainer back to its first position to retract the diverters.

Abstract: A process for the thermo-hydraulic control of gas hydrates in subsea production and injection wells as well as pipelines which transport liquid or gaseous hydrocarbons is described, the process making use of a Nitrogen Generating System foamed or in solution. The control may signify the prevention of the formation of the gas hydrates or the dissolution of the gas hydrate plug already formed. Under conditions of use designed for the prevention of the formation of gas hydrates the SGN fluid prevents the thermal conditions leading to the gas hydrate plugs. Under conditions of use designed to dissolve the already formed gas hydrate plugs, the SGN fluid alters the thermo-hydraulic conditions which favor the gas hydrate plugs, so that they are dissolved and return to the water+gas phase.

Abstract: Novel abrasive particles for cleaning subterranean wellbores are described. The particles are rounded, preferably spherical, and has a hardness of 80 to 200 Vickers. The particles are preferably made of non-metallic material such as Calcite pellets. The new abrasives cause significantly less damage to the well tubulars than sand.

Abstract: A self-excited jet stimulation tool for cleaning and stimulating wells includes an elongated tubular first member adapted on an upper end for connection to a running string. The first member includes an upper portion with a central bore open to a top of the tool, and a lower portion having a cylindrical shaped cavity open to a bottom surface of the first member. The cylindrical cavity is internally threaded in a lower portion. The central bore of the first member is open to the cylindrical cavity for communication of fluids supplied by the running string. The tool further includes an elongated tubular second member having a top with a central flat circular portion and a central bore with a diameter larger than the diameter of the central bore of the first member but less than the diameter of the cylindrical cavity of the first member.

Abstract: The present invention provides a method for cleaning debris from a well-bore and includes the steps of injecting hydrophilic fibers selected from the group consisting of polyolefins, polyesters and nylons, suspended or dispersed in a water based or oil based liquid into a well-bore and forcing the suspension upwards, through the length of the well-bore, to its open end. In particular, the suspension is directed through sections of the well-bore holding quantities of debris formed from the drilling operation. The suspension loosens the debris and sweeps substantial quantities of debris from the well-bore.

Abstract: A method and composition for removing deposits of heavy hydrocarbonaceous materials and finely divided inorganic particulate matter from wellbore and flowline surfaces using a composition containing an alkyl polyglycoside, an ethoxylated alcohol, a caustic and an alkyl alcohol.

Abstract: Method and apparatus for removing drill cuttings from a deviated wellbore drilled with coiled tubing, and more particularly method and apparatus for removing "cuttings beds" from a significantly horizontal wellbore drilled with a downhole motor by creating flow of fluid in the wellbore at a critical flow rate, above a flow rate range designed for the drilling.

Abstract: Apparatus and methods for completing deviated and vertical sections of well borehole are disclosed. Drill string in moved into and out of the well borehole in one continuous piece without breaking it into smaller sections. A slotted casing section is attached to the lower end of the drill string and forced to a target production zone by inserting the drill string into the well borehole using a vertical chain drive. Once positioned typically in a production zone, the slotted casing string is disconnected from the drill string and the drill string is removed. Intermediate casing is then positioned in the borehole to extend from the top of the slotted casing string into surface casing, and the intermediate casino string-borehole annulus is cemented.

Abstract: Contaminants are removed from oil well components by high pressure jets of hot water. The water and removed contaminants are retained and moved by suction to a holding tank for environmentally acceptable disposal. Rod strings move through a housing assembly which is attached to the pumping tee of the well. Nozzles in the housing assembly apply the water. The water and contaminants are sucked from an outlet in the lower bell cap of the housing assembly. The nipple in the bell cap extends upward at least to the upper edge of the bell cap to prevent water and contaminants from entering the well. Suction is provided by a suction pump which draws air from the holding tank. To decontaminate a tube one end of the tube is sealed off and a tee fitting assembly is attached to the other end. A nozzle fitting on a hose (termed a snake) propels itself through the tube as it removes contaminants. The contaminants and water from the nozzles exit through the tee fitting into a hose to the holding tank.

Abstract: A well treatment tool is installed along the sucker rod string of a well, within the surrounding production tube string. The tool provides for the distribution of a treatment fluid (solvent, etc.) within the fluid being pumped or flowing from the well. The tool receives treatment fluid through the hollow sucker rod string, and distributes the fluid through a valve which is set at a predetermined pressure. When the treatment fluid pumped down the sucker rod string from the surface exceeds the predetermined opening pressure of the valve, the treatment fluid is distributed into the production tube string through one or more passages in the tool. The present tool may be used simultaneously with well production, with fluid (oil, etc.) rising up the production tube string, carrying the treatment fluid therewith. The treatment fluid is thus distributed throughout the local fluid processing system, including pipelines from the well, any initial treatment operations, and any storage tanks.

Abstract: A method for removing a gravel-pack screen from a wellbore. of a well which has been "gravel packed". When it is desired to remove the screen from the wellbore, a washstring is lowered down the wellbore and into the interior of said screen. A wash fluid is then flowed fluid down the washstring and out through said screen into said mass of gravel surrounding the screen to fluidize, loosen, and remove said gravel. Once the mass of gravel has been loosen, the screen can then lifted upward out of said wellbore by applying a normal upward force the workstring which suspends the screen within the well.

Abstract: The present invention provides methods of cleaning up a producing interval of a well bore drilled using a synthetic oil-water emulsion drill-in fluid. The methods basically comprise contacting filter cake and drill-in fluid on the walls of the well bore with three treatment fluids in three stages, the first and second treatment fluids being comprised of water, a filter cake dissolving acid, a mutual solvent and an emulsion penetrating agent. The third treatment fluid is comprised of water, a filter cake dissolving acid and a water wetting surfactant.

Abstract: Aqueous and non-aqueous systems for cleaning a section of a subterranean well borehole and casing prior to cementing. A series of spacer fluids are introduced into the borehole to displace drilling fluid and to provide clean and water wet casing and borehole surfaces of the cleaned section of well bore. The cleaned section of the well bore will provide surfaces for superior bonding of the cement to the surfaces.

Abstract: A method is provided for improving the effectiveness of cleaning up wells in a subterranean formation. The treatment is made more effective by first treating the well with a clean-up fluid that enzymatically degrades residual polymeric viscosifiers followed by removing solids contained in drill-in fluids.