Abstract: A flow diverter and a vacuum blower for vibrating screen separator assembly. The flow diverter decelerates and increases the exposed surface of materials. The exhaust blower removes vapors from the materials.

Abstract: A method to significantly reduce mounding on the seafloor near oil drilling operations comprising the steps of: mixing drilling fluids with organic contaminates in a high shear mixer; adding a solidification agent which expands when hydrated and electrolytically attracts said organic contaminates to its surface; adding a cellulosic additive in an amount between 1 and 50 wt % based on the amount of said organic contaminate in the drilling fluid forming a mixture; adding a cell transport agent in an amount between 0.5 wt % and 10 wt % based on the amount of said organic contaminate in the drilling fluid, wherein said cell transport agent is capable of transporting large organic molecules through cell walls and neutralizing said mixture to a pH of between 7 and 8 to said mixture; and mixing at a high shear rate until said mixture forms a fine powder, dispersing said fine powder into the sea.

Abstract: A method for recirculating fluid in a well system includes drilling a first well bore from a surface to a subterranean zone, and drilling an articulated well bore that is horizontally offset from the first well bore at the surface and that intersects the first well bore at a junction proximate the subterranean zone. The method also includes drilling a drainage bore from the junction into the subterranean zone, and receiving gas, water, and particles produced from the subterranean zone at the junction via the drainage bore. The gas, water, and particles are received from the junction at the surface, and the water is separated from the gas and the particles. The method also includes determining an amount of water to circulate, and recirculating a portion of the separated water according to this determination.

Abstract: A system which receives as inputs various measurements of solids and liquids in a clarification system and, from these measurements, determines the various constituents and their fractional makeup within the system. The measurements may be made manually or mechanically, but are preferably made manually. From a quantitative analysis of easily accessible sample points, data is acquired and plugged into a spread sheet program, which numerically and graphically displays the breakdown of the constituents which make up the solids and liquids discharged from a treatment stage or of the entire system.

Abstract: An agitation system for a mud tank to prevent core material initially suspended in the drilling mud, from settling. The method agitates sludge and eliminates the need to hand shovel sludge from the tank after dumping. The method comprises the step of pumping mud taken from within the tank through a permanently mounted rubber nozzle directed at mud on a bottom portion of the tank. In a preferred aspect of this invention the tank is a cylindrical and longitudinally mounted on a truck for waste mud hauling, and has a rear end cap hinged to a top portion of the tank, so that when a front portion of the tank is marginally elevated and the end cap is hinged opened, mud dumps from a rear end portion of the tank.

Abstract: A method for selecting an emulsifier for isolating free hydrocarbons in a given drilling system and a method of using the emulsifiers to treat drill cuttings to isolate free hydrocarbons, including bitumen.

Abstract: A composition for oil and gas drilling fluids containing organic contaminants comprising: a solidification agent; cell transport agent; a cellulosic additive; and wherein said composition comprises enough solidification agent to enable the solidification agent to electrolytically attract the organic contaminates to the surface of the solidification agent when hydrated.

Abstract: Method for the removal and recovery of the oily component from cuttings coming from the drilling of oil wells by treatment of the cuttings with a solvent, which can be compressed to the liquid state, at a pressure value ranging from 45 to 80 bar and a temperature corresponding to the saturation value.

Abstract: Method for the removal and recovery of the oily component from cuttings coming from the drilling of oil wells by treatment of the cuttings with a solvent, which can be compressed to the liquid state, at a pressure value ranging from 45 to 80 bar and a temperature corresponding to the saturation value.

Abstract: A composition and method for treating oil and gas drilling fluids containing organic contaminants comprising: a solidification agent and a cellulosic additive; and wherein the composition comprises enough solidification agent to enable the solidification agent to electrolytically attract the organic contaminates to the surface of the solidification agent when hydrated.

Abstract: A method and an apparatus for storage and transport of drilling waste is provided. A number of storage containers (12) are anchored to the sea bed by means of anchors (15) and cables (13). The location of the containers (12) is marked with buoys (17). The containers (12) are of adjustable buoyancy, and are arranged to remain below the surface of the sea. Drilling waste is macerated on board a drilling vessel (18), and pumped via conduits (20) into the containers (12). Once the containers (12) are full, a tug (22) collects the containers (12) and transports them to an onshore waste recycling facility, while empty tanks are returned to the drilling vessel (18) to be reused. The containers (12) may be arranged to agitate stored waste, either by means of an internal agitator, or by virtue of fins or paddles mounted on the containers (12), to rotate the containers in response to sea currents.

Abstract: A composition and method for treating oil and gas drilling fluids containing organic contaminants comprising: a solidification agent, and a cell transport agent; wherein the composition comprises enough solidification agent to enable the solidification agent to electrolytically attract the organic contaminates to the surface of the solidification agent when hydrated.

Abstract: A method is disclosed for drilling a wellbore employing a drilling fluid providing the advantages of easy pumpability of a low viscosity fluid with the drill cuttings suspension capability of a highly viscous fluid. The viscosity of the fluid is also easily and quickly adjustable so that the fluid rheology may be adapted during drilling as the subterranean conditions change. These advantages are obtained by including in said fluid a reversibly crosslinkable polymer and an encapsulated crosslink activator. The crosslink activator causes crosslinking after the fluid is in the wellbore. The crosslinking is reversed at the well surface to reduce the viscosity of the fluid to enable the drill cuttings to be easily removed. Crosslink activator is added back to the fluid and the fluid is returned to the borehole. The amount of crosslink activator and/or crosslinkable polymer may be adjusted in the fluid to change the fluid rheology to conform the fluid to changes in the well conditions as monitored real time.

Abstract: The current invention provides methods of using and drilling and servicing fluid compositions for depositing and removing filter cake from the walls of a well bore. The compositions make use of particulate solid bridging agent comprised of a salt of an organic acid. The bridging particles are dissolvable by a clean-up solution comprised of a mild solvent that is less corrosive than the conventional strong mineral acids used for this purpose.

Abstract: A system for heating drilling, completion, and/or stimulation fluids including acidizing liquids but not limited to; entering or exiting a wellbore, the system including a principal heat exchange vessel; a first inlet for introducing heat transfer media into fluid flow lines within the vessel; an outlet for flowing the heat transfer media from the vessel; a second inlet for introducing fluids returning from or returning to the well bore for receiving heat from the heating fluid within the fluid flow lines in the vessel; an outlet for flowing the heated downhole fluids from the vessel to be returned down the borehole; a heater for heating the heating fluid to a desired temperature before returning the heating fluid to the heat exchange vessel. Optimally, the drilling or completion fluid would be heated to 50° to 60° F. above ambient temperature.

Abstract: A method and apparatus is provided for removing fluids, particularly entrained and/or adherent fluids, from drill cuttings generated during the well drilling process. A generally cylindrical wire-wrapped screen having a bore therethrough rotates about its longitudinal axis. Suction pressure is applied through the inner bore of the cylindrical wire-wrapped screen. As fluid-laden drill cuttings are deposited on the outer surface of the cylindrical wire-wrapped screen, fluids are drawn off of the cuttings and evacuated from the inner bore of the cylindrical wire-wrapped screen. Solid components of the cuttings remain on the outer surface of the cylindrical wire-wrapped screen and eventually roll off the screen. A scraper member is provided to agitate cuttings deposited on the outer surface of the cylindrical wire-wrapped screen.

Abstract: Methods and materials for chemically enhanced drilling of oil/gas wells are disclosed. The use of drilling fluids containing chemicals that dissolve formation constituents results in the creation of boreholes. Fluids containing acids such as hydrochloric acid, formic acid, acetic acid, or combinations thereof have been found to be especially useful in chemical drilling of formations containing basic minerals such as calcium carbonate. The use of acid has the further advantage of simultaneously stimulating the borehole.

Abstract: A vertical, centrifugal separator used for drying drill cuttings prior to transport or further processing. The separator is adapted to receive scavenged heat from any source and is further adapted to include internal conveyers, thereby lowering the overall operating profile and providing increased cuttings retention time within a heated environment.

Abstract: A fluid filtration system of well workover fluids, the system comprising: a first settling tank which stores fluid; a second settling tank which stores fluid; a low pressure pump in fluid communication with the first and second settling tanks; a low pressure filter in fluid communication with the first and second settling tanks; a high pressure pump in fluid communication with the second settling tank; and a high pressure filter in fluid communication with the second settling tank, wherein the high pressure filter comprises: an inlet; an outlet; a plurality of input feed lines in fluid communication with the inlet; a plurality of output feed lines in fluid communication with the outlet; a plurality of filter canisters, wherein at least one filter canister is in fluid communication with each input feed line and each output feed line.

Abstract: A method and apparatus for treating for disposal oil-contaminated clay substrates such as drill cuttings from drilling with an oil-based mud. If necessary, the substrate is pretreated with an aqueous emulsion breaker such as alkylbenzenesulfonic acid. The substrate is mixed under high shear conditions with a mineral acid such as sulfuric acid. This can be done in an agitated reactor with sequential addition of the organic and inorganic acids. The substrate is then mixed with alkaline earth such as lime in a second agitated reactor. The reactions between the acid(s), alkaline earth and substrate are exothermic and provide heat to vaporize the oil, reaction products and water. Recoverable constituents in the vapor can be condensed in a vapor collection system. The treated substrate is essentially free of oil and has a controlled water content.

Abstract: An improved method and apparatus for processing deleterious material on a floating vessel during transportation from a well to a disposal site. The vessel contains equipment for the slurrification and agitation of the deleterious material. Such equipment includes storage tanks, slurrification units, and agitation units, as well as transfer equipment such as flow lines and vacuum or pump means. The deleterious material is transferred from the drill site to the storage tanks on the vessel. The vessel then transports the material to a disposal site, such as an injection well. During transportation, the deleterious material is processed. Such processing can include slurrification and/or agitation of the deleterious material to maintain the slurry, adding fluid if necessary. Once at the disposal site, the deleterious material slurry is then transferred from the vessel to the disposal site.

Abstract: A method of drilling sub-sea oil and gas production wells in which a liquid hydrocarbon substance, such as a natural gas liquid, is injected into the drilling mud supplied to the well in order to reduce the mud density. The method of the present invention enables reduction and control of the hydraulic pressure of the drilling mud while drilling production wells in deep water, thereby to require fewer casing runs which eventually yields better oil productivity.

Abstract: A method of minimizing the quantity of solids deposited in a reserve pit of the type used in drilling oil and gas wells. The method is applicable to well sites where drilling is facilitated by the use of drilling fluid and cuttings are generated by a drill bit, lifted to the surface and deposited at a well bore. The method consists of separating cuttings from associated drilling fluid and conveying larger cuttings to a solids storage location, thus bypassing the reserve pit for a good deal of the solid waste generated at a drilling site. Residual drilling fluid is directed to a reservoir such as a suction tank where it can be reused in further drilling operations. Over time the residual drilling fluid in the suction tank will increase in viscosity to the point where the residue is no longer suitable as drilling fluid. Thereupon, a portion of the residue may be discarded from the suction tank to the reserve pit and water or drilling chemicals added to the suction tank to revitalize the drilling fluid.

Abstract: A subsea wellhead assembly has the capabilities of communicating from the outer surface of an outer wellhead housing to a casing annulus. Seals between the outer and inner wellhead housings define an annular chamber when the inner wellhead housing lands. The outer wellhead housing has a communication port formed through one of its sidewalls. The inner wellhead housing has a passageway extending from the annular chamber to the bore of the inner wellhead housing. The casing annulus located radially inward of the inner wellhead housing is in communication with the outer surface of the outer wellhead housing through the passageway, the annular chamber between the seals, and the communication port.

Abstract: Hydrocarbon contaminants in drill cuttings generated in an oil drilling operation are removed by mixing the drill cuttings with an agglomerant to produce a pre-treatment mixture; heating to vaporize the hydrocarbon contaminants under a condition in which vapor entrainable particles of the drill cuttings are agglomerated by the agglomerant, and caking of drill cuttings is inhibited; drill cuttings having a reduced content of the contaminant are removed, and vaporized hydrocarbons having a reduced content of vapor entrainable particles are recovered. In this way, the particulate content of vapors escaping from the drill cuttings is reduced.

Abstract: A system and method for developing and recycling drilling fluids at the site of a subterranean well is described, thus eliminating the need for transporting the fluids to the site.

Abstract: A method and apparatus is provided for removing fluids, particularly entrained and/or adherent fluids, from drill cuttings generated during the well drilling process. A generally cylindrical wire-wrapped screen having a bore therethrough rotates about its longitudinal axis. Suction pressure is applied through the inner bore of the cylindrical wire-wrapped screen. As fluid-laden drill cuttings are deposited on the outer surface of the cylindrical wire-wrapped screen, fluids are drawn off of the cuttings and evacuated from the inner bore of the cylindrical wire-wrapped screen. Solid components of the cuttings remain on the outer surface of the cylindrical wire-wrapped screen and eventually roll off the screen. A scraping member is provided to agitate cuttings deposited on the outer surface of the cylindrical wire-wrapped screen.

Abstract: An improved method and apparatus for processing deleterious material on a floating vessel during transportation from a well to a disposal site. The vessel contains equipment for the slurrification and agitation of the deleterious material. Such equipment includes storage tanks, slurrification units, and agitation units, as well as transfer equipment such as flow lines and vacuum or pump means. The deleterious material is transferred from the drill site to the storage tanks on the vessel. The vessel then transports the material to a disposal site, such as an injection well. During transportation, the deleterious material is processed. Such processing can include slurrification and/or agitation of the deleterious material to maintain the slurry, adding fluid if necessary. Once at the disposal site, the deleterious material slurry is then transferred from the vessel to the disposal site.

Abstract: A system and method for removing particles from a well bore penetrating a possible hydrocarbon producing formation, according to which drilling fluid is mixed with a weighted material, and the mixture is introduced into a well bore so that the mixture scours any particles accumulated in the well bore. A well-completion fluid is introduced into the well bore that dissolves the weighted material.

Abstract: A method and apparatus for treating for disposal oil-contaminated clay substrates such as drill cuttings from drilling with an oil-based mud. If necessary, the substrate is pretreated with an aqueous emulsion breaker such as alkylbenzenesulfonic acid. The substrate is mixed under high shear conditions with a mineral acid such as sulfuric acid. This can be done in an agitated reactor with sequential addition of the organic and inorganic acids. The substrate is then mixed with alkaline earth such as lime in a second agitated reactor. The reactions between the acid(s), alkaline earth and substrate are exothermic and provide heat to vaporize the oil, reaction products and water. Recoverable constituents in the vapor can be condensed in a vapor collection system. The treated substrate is essentially free of oil and has a controlled water content.

Abstract: Disclosed is a method of producing a pressurized stream of substantially inert gas. The method comprises collecting the exhaust gases from an internal combustion engine, directing the exhaust gases into the intake of a compressor for compressing to a desired pressure, and recirculating a portion of the compressed exhaust gases back to the intake of the compressor such that the pressure of the exhaust gases within said compressor intake is maintained above atmospheric pressure. Also disclosed is an apparatus for producing a pressurized stream of substantially inert gas utilizing the described method.

Abstract: A method for controlling drilling mud density at a location either at the seabed (or just above the seabed) or alternatively below the seabed of wells in deep water and ultra deep water applications are disclosed. The mud recirculation system may be used in conventional drill bit drilling operations or with drilling with casing operations. The present invention combines a base fluid of lesser density than the mud required at the wellhead to produce a diluted mud in the riser. By combining the appropriate quantities of drilling mud with base fluid, a riser mud density at or near the density of seawater may be achieved. The present invention also includes a wellhead injection device for attachment to the wellhead and for injecting the base fluid into the rising drilling mud at a location below the seabed. The riser charging lines are used to carry the low-density base fluid to the injection device for injection into the drilling mud below the seabed.

Abstract: Low concentrations, 1-10% of potassium salt, especially potassium formate, are used in a drilling fluid in oil production. Preferably they are used with guar derivatives, most preferably carboxymethyl hydroxypropyl guar. The concentration of potassium formate is maintained at the desired level by adjusting the potassium formate to maintain a desired Zeta potential in the circulating drilling fluid. The potassium formate/guar derivative composition may be used in the substantial absence of hydrophilic clay additive.

Abstract: A system and method for controlling drilling mud density at a location either at the seabed (or just above the seabed) or alternatively below the seabed of wells in deep water and ultra deep water applications are disclosed. The present invention combines a base fluid of lesser density than the mud required at the wellhead to produce a diluted mud in the riser. By combining the appropriate quantities of drilling mud with base fluid, a riser mud density at or near the density of seawater may be achieved. The present invention also includes a wellhead injection device for injecting the base fluid into the rising drilling mud. The riser charging lines are used to carry the low density base fluid to the injection device for injection into the return mud. At the surface, the diluted return mud is passed through a treatment system to cleanse the mud of drill cuttings and to separate the heavier drilling mud from the lighter base fluid.

Abstract: A fluid filtration system of well workover fluids, the system comprising: a first settling tank which stores fluid; a second settling tank which stores fluid; a low pressure pump in fluid communication with the first and second settling tanks; a low pressure filter in fluid communication with the first and second settling tanks; a high pressure pump in fluid communication with the second settling tank; and a high pressure filter in fluid communication with the second settling tank, wherein the high pressure filter comprises: an inlet; an outlet; a plurality of input feed lines in fluid communication with the inlet; a plurality of output feed lines in fluid communication with the outlet; a plurality of filter canisters, wherein at least one filter canister is in fluid communication with each input feed line and each output feed line.

Abstract: A system and method for controlling formation pressures during drilling of a subterranean formation utilizing a selectively fluid backpressure system in which fluid is pumped down the drilling fluid return system in response to detected borehole pressures. A pressure monitoring system is further provided to monitor detected borehole pressures, model expected borehole pressures for further drilling and control the fluid backpressure system.

Abstract: The present invention relates to a method and to a fluid for drilling or workover in a well running through a porous permeable formation, wherein a water-based well fluid circulates in said well. In the method, at most 3% by weight of a composition obtained from fat, or an oil, and an alcohol, is added to the fluid in addition to the conventional constituents for such a fluid, the chain lengths of the acid and alcohol parts being chosen such that the ester thus obtained has sufficient dispersion in water, compatibility with said constituents, does not form an emulsion with the reservoir oil and adsorbs sufficiently on the porous formation.

Abstract: Frac sand from a well completion operation is transported to a recycling facility by truck. The frac sand is passed into a washing facility where is it separated from frac sand carrier residue, clays, drilling mud and metal particles. The wash water used in the washing facility is settled and re-used. Mud from the settled wash water is removed and re-used in drilling operations. The frac sand is removed from the washing facility by an inclined dehydration screw, and discharged into a counterflow hot air drying facility. Dust from the drying facility is collected and removed. Hot frac sand from the drying facility is passed through a chiller, and collected. The collected material is sized, and stored for re-use.

Abstract: A water-base fluid for use in drilling wells and other drilling operation includes a shale which swells in the presence of water. The fluid preferably includes: an aqueous based continuous phase, and a shale hydration inhibition agent having the formula: H2N—R—{OR′}x—Y in which R and R′ are alkylene groups having 1 to 6 carbon atoms and x is a value from about 1 to about 25. The Y group should be an amine or alkoxy group, preferably a primary amine or a methoxy group. The shale hydration inhibition agent should be present in sufficient concentration to reduce the swelling of the shale. The fluid may be used for formulating drilling fluids such as invert emulsion drilling muds or clear brine drilling fluids. The fluid may also be used in the slurrification and disposal of drill cuttings that contain water swellable clays or shales.

Abstract: Hydrocarbon contaminants in drill cuttings generated in an oil drilling operation are removed by mixing the drill cuttings with an agglomerant to produce a pre-treatment mixture; heating to vaporize the hydrocarbon contaminants under a condition in which vapor entrainable particles of the drill cuttings are agglomerated by the agglomerant, and caking of drill cuttings is inhibited; drill cuttings having a reduced content of the contaminant are removed, and vaporized hydrocarbons having a reduced content of vapor entrainable particles are recovered. In this way, the particulate content of vapors escaping from the drill cuttings is reduced.

Abstract: The invention provides a method for treating drill cuttings, preferably marine cuttings, preferably in situ, so that the cuttings can be discharged into the environment, preferably back into marine waters without causing oxygen depletion of marine sediment. In a preferred embodiment, the treatment emulsifies and then encapsulates free hydrocarbons in the marine cuttings.

Abstract: A method and apparatus is provided for removing fluids, particularly entrained and/or adherent fluids, from drill cuttings generated during the well drilling process. A generally cylindrical wire-wrapped screen having a bore therethrough rotates about its longitudinal axis. Suction pressure is applied through the inner bore of the cylindrical wire-wrapped screen. As fluid-laden drill cuttings are deposited on the outer surface of the cylindrical wire-wrapped screen, fluids are drawn off of the cuttings and evacuated from the inner bore of the cylindrical wire-wrapped screen. Solid components of the cuttings remain on the outer surface of the cylindrical wire-wrapped screen and eventually roll off the screen. A scraping member is provided to agitate cuttings deposited on the outer surface of the cylindrical wire-wrapped screen.

Abstract: An apparatus and method for removing and recovering up to 98 percent of the residual drilling mud and fluids from drill cuttings for reuse and storing the drill cuttings in a relatively dry state thereby reducing cuttings volume requirements for storage and transport thereby reducing constipation of the drilling process due to disposal congestion. The present invention further provides methods for collecting and transferring drill cuttings in either dry or wet states to various locations on or adjacent the rig for processing, containerization, transport and disposal, thereby reducing handling and contamination thus simplifying recycling while reducing cost.

Abstract: In a method and arrangement for reducing dust-related problems in rock drilling, air and liquid mist is supplied into a drilling hole to moisten the dust that comes off the drilling hole. The air and moistened dust exiting from the drilling hole are led to a dust separator, dust portions that collect into the dust separator being removed therefrom at suitable intervals. When dust is to be removed from the dust separator's filter, liquid is supplied to the portion below the filter in a mist-like form or as small droplets in connection with the dust removal to moisten the dust which then falls out of the lower end of the dust separator.

Abstract: A method for treating a drilling fluid is provided, which method includes the steps of providing a drilling fluid, providing a drilling fluid additive in the form of superparamagnetic nanoparticles, mixing the drilling fluid additive with the drilling fluid so as to provide a treated drilling fluid, and exposing the treated drilling fluid to a magnetic field so as to recover the superparamagnetic nanoparticles.

Abstract: A drilling fluid homogenizer and method of homogenizing drilling fluid which produce a non-clogging homogenized drilling fluid at a high throughput, in an open-loop process. The non-clogging homogenized drilling fluid is capable of being created at high rate so that the non-clogging homogenized drilling fluid is available on demand to eliminate halting of drilling operations. The drilling fluid homogenizer is coupled in series with the closed-loop designed drilling fluid system and is adapted to homogenize water-based drilling fluid and other drilling fluid types, such as, synthetic drilling fluid during drilling operations on demand.

Abstract: A drill cuttings slurry process system is disclosed for defluidizing earth drill cuttings, thereby extracting valuable drilling additives and returning them to the drilling system while producing a dense, drier material which may be discharged directly in the environment at or near the well being drilled or chemically treated for distillation and/or better dissolution into the environment, thereby reducing, cost in transportation and environmental treatment chemicals thus reducing environmental contamination. The system comprising a cuttings press having solids/fluids separation a dryer and/or a retort for flashing off any residual petroleum residue and moisture, a fines grinder and a chemical injection system. The retort including an analyzer system for weighing and determining rate of throughput and analyzing the cuttings for residual petroleum residue content prior to discharge to environment or further refinement prior to reinjection into the well or transport to environmental depository sites.

Abstract: Oil drill cuttings, containing an oil-based mud, may be treated by mixing the cuttings with an organic solvent. The oil drill cuttings are then separated from the organic solvent and extracted oil. The organic solvent is then separated from the oil, and mixed with the extracted oil drill cuttings to extract additional oil therefrom. The oil drill cuttings are again separated from the organic solvent and oil, the oil separated from the solvent, and recombined with the oil from the first extraction step. The oil base and other mud components are recycled, depending on the treatment procedure, for subsequent use in drilling.

Abstract: A mud tank cleaning system, is formed from a mud tank having confining walls. An opening is provided in the confining walls of the mud tank. A removable cover is mounted on the mud tank over the opening. A sweep is mounted in the mud tank and is operable to sweep mud in the mud tank towards the opening in the confining walls. A sweep drive mechanism is operably connected to the sweep for operating the sweep. A hydrovac vehicle is formed of a frame mounted on wheels, a mud tank mounted on the frame, a water tank mounted on the frame, a water pump mounted on the frame and hydraulically connected to the water tank to pump water from the water tank for use in hydrovac operations, a blower mounted on the frame and connected by lines to the mud tank for removing fluids from the mud tank; and a boom line mounted on the mud tank for conveying fluidized materials to the mud tank.

Abstract: A method of drilling sub-sea oil and gas production wells in which a liquid hydrocarbon substance, such as a natural gas liquid, is injected into the drilling mud supplied to the well in order to reduce the mud density. The method of the present invention enables reduction and control of the hydraulic pressure of the drilling mud while drilling production wells in deep water, thereby to require fewer casing runs which eventually yields better oil productivity.