Title:
Drilling fluid recovery
Kind Code:
A1


Abstract:
A method for recovering drilling fluid from a mixture containing drilling fluid and other components, the mixture resulting from a wellbore operation including the pumping of drilling fluid, the method including producing a mixture of flocculant with a spent drilling fluid mixture containing drilling fluid and contaminants, heating the mixture, and separating drilling fluid from the mixture. This Abstract is provided to comply with the rules requiring an abstract which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure and is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims, 37 CFR 1.72(b).



Inventors:
Gaddis, Emerson Clifford (Pasadena, TX, US)
Pierce, Dale Alton (The Woodlands, TX, US)
Morgan, Kenneth Arnold (Magnolia, TX, US)
Application Number:
11/981600
Publication Date:
04/30/2009
Filing Date:
10/31/2007
Primary Class:
International Classes:
E21B21/06
View Patent Images:



Primary Examiner:
HRUSKOCI, PETER A
Attorney, Agent or Firm:
National Oilwell Varco (Houston, TX, US)
Claims:
What is claimed is:

1. A method for recovering drilling fluid from a mixture containing drilling fluid and other components, the mixture resulting from a wellbore operation including the pumping of drilling fluid, the method comprising producing a mixture of flocculant with a spent drilling fluid, the spent drilling fluid containing drilling fluid and contaminants, heating the mixture, and separating drilling fluid from the mixture.

2. The method of claim 1 wherein the heating is effected by injecting steam into the mixture.

3. The method of claim 1 wherein the mixture is in a flow conduit and the steam is injected into the mixture within the flow conduit.

4. The method of claim 2 wherein the mixture is in a pressure vessel and the steam is injected into the mixture within the pressure vessel.

5. The method of claim 2 wherein the mixture is heated to a temperature between 160° F. and 705° F.

6. The method of claim 1 wherein the mixture is produced in a mixing apparatus, the mixing apparatus comprising a high speed mixer, the method further comprising producing the mixture in the high speed mixer.

7. The method of claim 1 in which no emulsifier is added to the mixture.

8. The method of claim 1 wherein the flocculant is in a combination of flocculant and water, the flocculant present at between 0.00125% and 0.5% of the total volume of the combination.

9. The method of claim 8 wherein the flocculant is present as 0.0025% of the total volume of the combination.

10. The method of claim 8 wherein the water is present by volume between 5% to 20%.

11. The method of claim 1 wherein the spent drilling fluid is pumped from an active rig mud system, the method further comprising feeding separated drilling fluid back to the active rig mud system.

12. The method of claim 1 wherein the separating is effected with centrifuge apparatus.

13. The method of claim 12 wherein the centrifuge apparatus produces a stream of recovered drilling fluid in which the ratio by volume of drilling fluid to water is at least 90 to 10.

14. The method of claim 1 further comprising emulsion testing separated drilling fluid to determine if it is acceptable for re-use.

15. The method of claim 1 wherein the contaminants include solids, the method further comprising processing separated drilling fluid to remove solids with a largest dimension between 3 microns and 30 microns.

16. The method of claim 1 further comprising feeding the heated mixture to a tank in which solids in the mixture settle out and are removed before the separating step.

17. The method of claim 1 in which drilling fluid is continuously separated from the mixture.

18. A method for recovering drilling fluid from a mixture containing drilling fluid and other components, the mixture resulting from a wellbore operation including the pumping of drilling fluid, the method comprising producing a mixture of flocculant with a spent drilling fluid, the spent drilling fluid containing drilling fluid and contaminants, heating the mixture, separating drilling fluid from the mixture, wherein the heating is effected by injecting steam into the mixture, wherein the mixture is heated to a temperature between 160° F. and 705° F., wherein the mixture is produced in a mixing apparatus, the mixing apparatus comprising a high speed mixer, the method further comprising producing the mixture in the high speed mixer, wherein no emulsifier is added to the mixture, wherein the flocculant is in a combination of flocculant and water, the flocculant present at between 0.00125% and 0.5% of the total volume of the combination, wherein the water is present by volume between 5% to 20%, wherein the separating is effected with centrifuge apparatus, wherein the centrifuge apparatus produces a stream of recovered drilling fluid in which the ratio by volume of drilling fluid to water is at least 90 to 10, and wherein drilling fluid is continuously separated from the mixture.

19. A system for recovering drilling fluid from a spent drilling fluid mixture, the spent drilling fluid mixture including drilling fluid and contaminants, the system comprising a tank apparatus for mixing water and flocculant to produce a water-flocculant mixture, a mixing apparatus for receiving and mixing the water-flocculant mixture with spent drilling fluid to produce a drilling fluid mixture, heating apparatus for receiving and heating the drilling fluid mixture to produce a heated drilling fluid mixture, and separation apparatus for receiving the heated drilling fluid mixture and for separating drilling fluid from the drilling fluid mixture.

20. A method for wellbore operations comprising pumping drilling fluid with an active rig mud system into and from a wellbore, pumping spent drilling fluid from the wellbore with the active rig mud system to a mixer, pumping a water-flocculant mixture to the mixer, mixing with the mixer the spent drilling fluid and the water-flocculant mixture producing a primary mixture, heating the primary mixture, feeding heated primary mixture to separation apparatus, with the separation apparatus producing re-usable drilling fluid separated from the primary mixture, and feeding the separated re-usable drilling fluid back to the active rig and system for re-use.

Description:

BACKGROUND OF THE INVENTION

1. Field of the Invention

This present invention is directed to drilling wellbores in the earth, to systems for recovering drilling fluid (“mud”) used in such operations, and methods of the use of such systems.

2. Description of Related Art

The prior art discloses a wide variety of drilling fluid pumping, treatment, and recovery systems, apparatuses, and methods, including, but not limited to, the disclosures in U.S. Pat. Nos. 6,944,547; 6,918,453; 6,802,378; 6,533,946; 6,193,070; 6,050,348; 5,853,583; 5,465,799; 5,310,285; 5,129,468; 4,995,465; 4,913,585; 4,854,397; 4,548,525; 4,192,392; 3,658,138 (all said patents incorporated fully herein for all purposes).

By rotating a drill bit carried at an end of a drillstring wellbores are formed in the earth. In certain systems, to drill a wellbore, the drill bit is rotated by a downhole mud motor carried by the drilling assembly and/or by rotating the drill pipe (e.g. with a rotary system, power swivel, or with a top drive system). A drilling fluid, also referred to as “mud,” is pumped under pressure from a pit or container at the surface by a pumping system at the surface.

Drilling fluid or mud can serve a variety of purposes. It can provide downhole hydrostatic pressure that is greater than the formation pressure to control the pressure of fluid in the earth formation being drilled and to avoid blow outs. The mud drives a downhole drilling motor (when used) and it also provides lubrication to various elements of the drill string. Commonly used drilling fluids are either water-based or oil-based fluids. They can also contain a variety of additives which provide desired viscosity, lubricating characteristics, heat, anti-corrosion and other performance characteristics.

During drilling, the mud that is pumped downhole by the mud pump system is discharged at the bottom of the drill bit and returns to the surface via the annular space between the tubulars of the drillstring and the wellbore inside (also referred to as the “annulus”). In certain aspects, the drilling mud is, initially, a suspension or solution of a suitable agent with a specific density, viscosity and chemical composition suitable for a particular geological stratum. These agents can include bentonite, oil, lignosulphonates and biopolymers, i.e. polysaccharides. During drilling, the fluid becomes laden with material from the ground, drilled cuttings, and debris and a mud results, its viscosity, density and composition varying as the mud circulates. Consequently, the viscosity, density and concentration in respect of minerals increases constantly and finally these properties can render the mud no longer suitable for operation. It is then necessary to discharge at least some of the mud and replace it by new fluid. In most cases, this renewal requires prior separation of solids dispersed in the mud. If the solids are inadequately separated, the liquid generally has a very high density, so that a large quantity of fresh fluid has to be added to dilute it suitably.

U.S. Pat. No. 4,353,803 discloses an admixture of waste (oil-well) drill cuttings, drilling fluid and by-products of rotary drilling that are separated into good-quality water and high-density solids by chemical and mechanical means in original earthen-mud storage and/or reserve pits. The treatment produces two useful benefits: (1) good-quality water (useful for agriculture or for drilling a new well) is recovered, and (2) resulting concentrated solids are of such a high density that the land area occupied by and containing such dewatered solids can be immediately leveled and restored to the same use it had before the well was drilled. The effect is a reduction in energy of at least 75 to 85 percent over some methods of hauling whole mud off by trucks to a commercial waste-disposal site. In one aspect this patent discloses a flocculant useful for waste drilling-fluid reserve pit treating wherein the reserve pit contains an aqueous spent oil-well drilling mud including an anionic colloid selected from the group consisting of drilling-fluid grade lignosulfonate and alkaline-soluble lignite, the flocculant consisting essentially of from 24 to 49 parts by weight of aluminum sulfate per part by weight of polyacrylamide homopolymer having from 130 to 500 pendant amide groups per pendant carboxylic-acid or carboxylic-acid-salt group and having a molecular weight in the range of from 10,000 to 5 million.

U.S. Pat. No. 4,482,459 discloses a continuous process for the reclamation of a slurry of waste drilling mud fluids and water normally resulting from drilling operations. The process comprises the steps of conducting the drilling mud slurry to a slurry surge tank for liquid solid separation by chemical and physical methods. The mud slurry is subjected to a primary solids separation unit after pH adjustment is used to initiate coagulation and an organic flocculant is added to aid flocculation of the solids. The water is then subjected to a secondary solids removal, and the solids recovered are reintroduced in the primary solids separation unit. Thereafter the water obtained from the secondary solids removal is then subjected to a chemical oxygen demand reduction unit having a carbon adsorption unit or reverse osmosis membrane units therein to remove organic matter or dissolved solids to produce water meeting environmental discharge requirements. The solids removed from the primary solids separation unit are converted to a cake meeting leachate requirements for other beneficial use. In one aspect the patent discloses a method of rendering a waste drilling fluid slurry from oil wells containing cuttings, formation fluid solids and liquids and the like, safe for environmental discharge both in a liquid and solid cake state comprising the steps of: (a) conducting the uphole drilling fluids to a continuous flow process having a slurry surge tank for chemical conditioning by addition of an inorganic acidic coagulant permitting settling and thickening; (b) subjecting the thickened mud slurry under flow from step (a) thereafter to a primary solids separation unit where an organic flocculant of the group of polyacrylamides is added to aid flocculation of the solids and from which solids of less than 50% moisture content and water are produced; (c) subjecting the water from (b) to a secondary solids removal unit, chemically conditioning and reintroducing the solids recovered back to the primary solids separation unit; (d) subjecting the water obtained from the secondary solids removal step (a) to a chemical oxygen demand reduction unit having a carbon adsorption unit for removal of organic substances or a reverse osmosis unit for removal of organic substances and dissolved solids including chlorine compounds to meet environmental discharge requirements; (e) removing the treated primary solids from step (b) consisting of an environmentally compatible cake meeting environmental leachate requirements for disposal as landfill on or off the drill site.

U.S. Pat. No. 4,913,585 discloses methods in which waste drilling mud is stabilized for earthern burial. The waste drilling mud may be treated by flocculating, aggregating, agglomerating and dewatering the waste drilling mud and separating out free water. The free water may be reused or disposed of in a disposal well. The thickened, dewatered drilling mud solids may be further treated with a water absorbing binder to produce a residue which has sufficient bearing strength to support an earthen overburden and may be disposed of by burial. Suitable flocculating, agglomerating and dewatering polyelectrolytes may be used, including polyacrylamides, quarternary amine polymers and mixtures thereof. The water absorbing binders may include inorganic and organic materials, such as natural and synthetic water absorbing gums, polymers and inorganic colloidal absorbers. In one aspect the patent discloses a method of treating a waste drilling mud residue having drilling mud solids suspended in an aqueous base comprising adding flocculating polymer to the waste drilling mud, the flocculating polymer consisting essentially of a mud solids flocculating polymer selected from the group consisting of acrylamide polyelectrolytes, quarternary amine polymers and mixtures thereof, the mud solids flocculating polymer being effective to agglomerate the drilling mud solids, flocculate the agglomerate drilling mud solids and separate free water from the flocculated drilling mud solids to produce a concentrated residue of wet drilling mud solids having a reduced volume and mass.

U.S. Pat. No. 5,422,012 discloses a method of removing suspended solids from drilling fluid includes preparing a dilute solution of flocculant and water, delivering a batch of the drilling fluid into the solution and agitating the mixture. The solids flocculate and then separate readily leaving a generally clear water layer on top of a solids layer. The solids are removed from the mixture by delivering them to a solids-liquid separator such as a shale shaker where the solids are discarded and the water is reclaimed and reused. Preferably, drilling mud is treated to remove solids while a well is being drilled and the reclaimed water is used in subsequent drilling operations. In one aspect the patent discloses a method of removing drilled solids from drilling fluid, comprising providing a tank partially filled with a flocculant-water solution substantially free of suspended drilled solids; then adding drilling fluid, including drilled solids and water, to the tank and flocculating the drilled solids; then delivering a mixture of the flocculated drilled solids and the water to a separator and separating the mixture into a first stream comprising mainly flocculated drilled solids and a second stream comprising mainly water; and collecting the first stream.

U.S. Pat. No. 6,193,070 discloses a solids separation system used to separate solids, such as cuttings from drilling fluids used in well drilling operations. The system includes a settling tank having transverse baffles defining a fluid receiving chamber, a fluid output chamber and one or more intermediate chambers. Fluid introduced into the fluid receiving chamber can flow in a sinuous path through apertures in the baffles to the fluid output chamber. Solids settle to the bottom of the settling tank. A material conveyor, preferably an auger, extends along a bottom surface of the settling tank to an outlet port in the fluid receiving chamber. A centrifuge is connected to the output port to receive fluid in which solids have been concentrated. Fluid output from the centrifuge is reintroduced into the settling tank. The apparatus and method of the invention permit a single centrifuge to be used to handle a higher volume of fluid than is possible with conventional methods and apparatus. This provides significant cost savings. In one aspect the patent discloses apparatus for removing solids from fluids, the apparatus comprising: (a) a settling tank comprising: (i) a fluid receiving chamber at a first end of the tank; (ii) a fluid output chamber at a second end of the tank; (iii) a plurality of transverse apertured baffles extending across the tank between the fluid receiving chamber and the fluid output chamber, the baffles defining one or more intermediate chambers between the fluid receiving chamber and the fluid output chamber; (iv) a material conveyor extending along a lower side of the tank to an outlet port at the first end of the tank, the material conveyor comprising a motor driving the material conveyor to carry materials in a direction toward the outlet port; and, (v) a fluid outlet at the second end of the tank; and, (b) a centrifuge comprising: (i) an inlet in fluid communication with the outlet port of the settling tank; and, (ii) a fluid outlet in fluid communication with the fluid receiving chamber of the settling tank.

U.S. Pat. No. 6,533,946 discloses an apparatus for cleaning and recycling slurry such as well-drilling slurry or mud, which has an inlet for receiving a supply of drilling slurry contaminated with particulates; first screening means for coarse filtering the slurry; a slurry tank, with mixing means within said tank for mixing slurry filtered by the first screening means; an outlet conduit for discharging slurry from the tank; a cyclonic separator for separating the slurry received from the tank into a first stream containing relatively coarse particulates, and a second stream containing relatively fine particulates; a second, fine, screening means for receiving the first stream and removing particulates therefrom, and discharging the resulting screened fluid into the tank; a discharge conduit for receiving the second stream from the cyclonic separator, and directing the stream back into the tank, and into a discharge outlet for re-use for forming a usable-slurry; pump means for cycling the slurry through the system on a continuous basis; and control means for controlling the operation of the system.

BRIEF SUMMARY OF THE INVENTION

The present invention discloses, in at least certain aspects, a system for recovering valuable drilling fluid, (e.g., but not limited to, clean oil, diesel fuel, synthetic oil, olefins) the system including apparatus for preparing a flocculant mixture; apparatus for mixing the flocculant mixture with spent (used) drilling fluid containing contaminants (e.g. drilled cuttings, debris); and apparatus for heating the resulting mixture of spent drilling fluid and flocculant mixture. In certain aspects the resulting mixture, following heating, is further processed to produce usable drilling fluid.

In certain aspects, the flocculant mixture contains a relatively small amount of flocculant by volume compared to the total volume of spent drilling fluid being treated plus flocculant mixture. In certain particular aspects, the amount of flocculant ranges, by volume as a percent of the total volume, between 0.00125% and 0.5% and, in one aspect, is 0.0025%.

In certain aspects, heating of the spent-fluid/flocculant mixture is achieved by heating the mixture to between 160° F. to 400° F. In one particular aspect, such heating is achieved by injecting live atmospheric steam into the mixture, either into a conduit through which the mixture is passing or in a pressurized vessel.

In certain aspects, the mixture, following heating, is processed further to separate fluid from solids. In one aspect, such separation is done by centrifuge apparatus. In one aspect, the centrifuge apparatus produces solids which are discharged and a liquid mixture which is either a mixture with acceptable characteristics to be re-introduced into a rig mud system or a mixture which is fed to settling apparatus which produces recovered fluid (e.g. oil) which can be re-used and water. Optionally, the heated mixture is fed to a holding tank prior to centrifugation, in which, in one aspect separative settling occurs. Optionally, the solids discharged from the centrifuge apparatus are treated thermally and fluids are recovered thereby.

In one particular aspect the fluid (e.g. recovered oil) produced by separation following heating is tested with an emulsion stability testing apparatus to determine if the fluid is acceptable for re-emulsifying (if necessary) for re-use as drilling fluid.

Accordingly, the present invention includes features and advantages which are believed to enable it to advance drilling fluid recovery technology. Characteristics and advantages of the present invention described above and additional features and benefits will be readily apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments and referring to the accompanying drawings.

What follows are some of, but not all, the objects of this invention. In addition to the specific objects stated below for at least certain preferred embodiments of the invention, other objects and purposes will be readily apparent to one of skill in this art who has the benefit of this invention's teachings and disclosures. It is, therefore, an object of at least certain preferred embodiments of the present invention to provide new, useful, unique, efficient, nonobvious drilling fluid recovery systems and methods of their use;

Such systems and methods in which a mixture of flocculant material and spent mud is heated to facilitate separation of acceptable fluid;

Such systems and methods in which a relatively low amount of flocculant, by volume, is used.

Certain embodiments of this invention are not limited to any particular individual feature disclosed here, but include combinations of them distinguished from the prior art in their structures, functions, and/or results achieved. Features of the invention have been broadly described so that the detailed descriptions that follow may be better understood, and in order that the contributions of this invention to the arts may be better appreciated. There are, of course, additional aspects of the invention described below and which may be included in the subject matter of the claims to this invention. Those skilled in the art who have the benefit of this invention, its teachings, and suggestions will appreciate that the conceptions of this disclosure may be used as a creative basis for designing other structures, methods and systems for carrying out and practicing the present invention. The claims of this invention are to be read to include any legally equivalent devices or methods which do not depart from the spirit and scope of the present invention.

The present invention recognizes and addresses the problems and needs in this area and provides a solution to those problems and a satisfactory meeting of those needs in its various possible embodiments and equivalents thereof. To one of skill in this art who has the benefits of this invention's realizations, teachings, disclosures, and suggestions, other purposes and advantages will be appreciated from the following description of certain preferred embodiments, given for the purpose of disclosure, when taken in conjunction with the accompanying drawings. The detail in these descriptions is not intended to thwart this patent's object to claim this invention no matter how others may later attempt to disguise it by variations in form, changes, or additions of further improvements.

The Abstract that is part hereof is to enable the U.S. Patent and Trademark Office and the public generally, and scientists, engineers, researchers, and practitioners in the art who are not familiar with patent terms or legal terms of phraseology to determine quickly from a cursory inspection or review the nature and general area of the disclosure of this invention. The Abstract is neither intended to define the invention, which is done by the claims, nor is it intended to be limiting of the scope of the invention in any way.

It will be understood that the various embodiments of the present invention may include one, some, or all of the disclosed, described, and/or enumerated improvements and/or technical advantages and/or elements in claims to this invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

A more particular description of embodiments of the invention briefly summarized above may be had by references to the embodiments which are shown in the drawings which form a part of this specification. These drawings illustrate certain preferred embodiments and are not to be used to improperly limit the scope of the invention which may have other equally effective or legally equivalent embodiments.

FIG. 1 is a schematic view of a system according to the present invention.

FIG. 2 is a schematic view of a system according to the present invention.

FIG. 3 is a schematic view of a system according to the present invention.

FIG. 4 is a schematic view of a system according to the present invention.

Presently preferred embodiments of the invention are shown in the above-identified figures and described in detail below. Various aspects and features of embodiments of the invention are described below and some are set out in the dependent claims. Any combination of aspects and/or features described below or shown in the dependent claims can be used except where such aspects and/or features are mutually exclusive. It should be understood that the appended drawings and description herein are of preferred embodiments and are not intended to limit the invention or the appended claims. On the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the appended claims. In showing and describing the preferred embodiments, like or identical reference numerals are used to identify common or similar elements. The figures are not necessarily to scale and certain features and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness.

As used herein and throughout all the various portions (and headings) of this patent, the terms “invention”, “present invention” and variations thereof mean one or more embodiment, and are not intended to mean the claimed invention of any particular appended claim(s) or all of the appended claims. Accordingly, the subject or topic of each such reference is not automatically or necessarily part of, or required by, any particular claim(s) merely because of such reference. So long as they are not mutually exclusive or contradictory any aspect or feature or combination of aspects or features of any embodiment disclosed herein may be used in any other embodiment disclosed herein.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a system 10 according to the present invention with a make-up apparatus 12 for producing a mixture of flocculant and water. In certain aspects, the amount of flocculant, by volume, in the resulting mixture is between 0.00125% and 0.5%, and, in one particular aspect, is 0.0025%. The apparatus 12 includes a tank 14 into which are fed (pumped and metered) water (line 16) and flocculant (in aqueous solution) in line 18. Optionally, an agitation apparatus 15 agitates the material in the tank 14. A metering pump 19 pumps the resulting water/flocculant mixture to mixing apparatus 20. In certain aspects, the resulting mixture is by volume, between 5 to 20% water.

As spent drilling fluid mixture containing drilling fluid (oil-based or water-based) and contaminants from a mud source 24 used in wellbore operation (e.g. drilling, reaming) which has drilling fluid and contaminants (drilled cuttings and/or debris) therein is pumped by a pump 22 from a mud source 24 to the mixing apparatus 20. In certain aspects, the material is mixed for between 2 and 15 minutes. The resulting mixture of spent drilling fluid and water/flocculant mixture is pumped to heater apparatus 20. The heater apparatus 20 heats the mixture, e.g. to a temperature between 160° F. to 200° F. (or up to 400° F. up to 705° F.) to decrease viscosity and/or break down emulsion.

Following the heating step, the heated resulting mixture is sent from the heater apparatus 30 for further processing.

The mixing apparatus 20 (as may be true for any embodiment of the present invention) is, in one aspect, a high speed (500 rpm to 19,000 rpm) high shear mixer; and, in one particular aspect, is a 10,000 rpm mixer. As an example, and not by way of limitation, a commercially available TURRAX (trademark) mixer is used.

In certain particular aspects the metering pump 19 (as may be true for any embodiment of the present invention) pumps the water/flocculant mixture to the mixing apparatus at between 10 and 50 gallons per minute and, in one particular aspect, at 30 gallons per minute.

In one aspect, the mud source 24 is a mud feed tank. In other aspects the mud source 24 is a direct feed from an active rig mud system (as may be true for any embodiment of the present invention).

As may be true with any system and method according to the present invention, including those of FIGS. 2-4, acceptable recovered fluid from further processing apparatus 30 may be fed back in a continuous process (see dotted line, FIG. 1) to the mud source 24 (which may be an active rig mud system).

In the embodiments of FIGS. 2-4 numerals as in FIG. 1 indicate like parts or apparatuses.

FIG. 2 shows a system 100, like the system of FIG. 1, with a centrifuge apparatus 102 which receives the mixture following heating. The centrifuge apparatus 102 produces separated solids (line 104) which are discharged to storage and/or disposal apparatus 106, and a stream of fluid 110 which contains drilling fluid (e.g. recovered oil) and water. The stream 110 can be further processed, fed to storage, used as fuel, or re-introduced to an active rig mud system. In certain aspects, the centrifuge apparatus 102 produces a stream of recovered oil in which the ratio by volume of oil to water is at least 90 to 10, in one aspect a ratio of 95 to 5.

FIG. 3 shows a system 200 according to the present invention which has an emulsion stability testing apparatus 202. A further processing apparatus 204 produces separated solids (line 206) and a stream of fluid 208 (e.g. recovered oil). The emulsion stability testing apparatus tests the emulsion stability of the fluid in the stream 208. In one aspect after emulsion stability testing, a recovered oil/water mixture is further emulsified to maintain the solubility of all components when mixed together. The ES (emulsion stability) number in volts refers to the electrical conductivity of the mixture. Pure oil is a nonconductor and will have a high ES value. Water is a good conductor and will have a low ES value. An ES value of 0-150 volts means the mixture is a weak emulsion. A value of >1000 means the mixture is strongly emulsified. This information indicates a measure of compatibility of the material with water. If the emulsion level is unacceptable, the material can be recycled. If the level is acceptable, the material can be fed to an active rig mud system. In some cases a trial-and-error procedure is used to adjust this level until suitable stability is achieved, i.e., until the material does not separate into layers.

FIG. 4 shows a system 300 according to the present invention in which the heater apparatus is a steam injection system 310 which includes a steam generator 312 and steam injector apparatus 314 for injecting live steam into the spent-mud/flocculant mixture from the mixing apparatus 20. In one aspect, live steam is injected into a line or conduit conveying the mixture to heat the mixture e.g. to between 160° F. and 400° F. and, in one case, to between 160° F. and 200° F. In one particular aspect, the steam is injected at a pressure up to 3210 psia at a temperature up to 705° F. In one aspect, the spent fluid/flocculant mixture is heated with the live injected steam in a vessel in which the total pressure is maintained between atmospheric pressure and an upper pressure (in one aspect, an upper pressure of up to 3210 psia).

Optionally, the heated mixture is fed to a holding tank 322 and then to a centrifuge 330. The tank 322 can provide gravity settling of materials and settled solids can be removed in a line 323. With no tank 322 present, the heated mixture is fed directly to the centrifuge 330.

The centrifuge 330 (or centrifuges if a plurality of centrifuges are used) produces separated solids in a line 332 which are fed to storage and/or disposal 334 and a stream of fluid 336.

The stream of fluid 336 which is, e.g. recovered fluid, e.g. recovered oil, flows either to an active rig mud system 340 or to a settling apparatus 350. Valves 342, 352 selectively control flow to these apparatuses and systems.

The settling apparatus 350 includes a settling tank 354 from which separated water exits in a line 356 and recovered fluid, e.g. oil, flows out in a line 358. The recovered fluid may flow to the active rig mud system or to storage or disposal. Optionally, in one particular aspect, the spent-mud/flocculant mixture is fed into a pressure vessel 360 (shown in dotted lines, FIG. 4) and the live steam is injected into the pressure vessel. In one aspect, the pressure in the pressure vessel is maintained between atmospheric pressure and a pressure of 50 psi gauge.

Any system according to the present invention, including the embodiments of FIGS. 1-4, can be used to separate fine particulate solids, e.g. solids ranging in a largest dimension between 3 to 30 microns, from spent drilling fluid. Flocculant changes these fine particles to facilitate their agglomeration and, thus, their separation from the spent fluid.

In certain aspects, and in certain aspects of each of the embodiments of FIGS. 1-4, no demulsifier is added at any point in the methods. Demulsifiers can make it more difficult to reconstitute drilling fluid and can also necessitate the use of additional stabilizing chemicals. In certain aspects, any embodiment according to the present invention, including those of FIGS. 1-4, obtain a recovered oil fluid in which the ratio of recovered oil to water is 90 to 10 or greater. This minimizes the amount of fresh oil which must be added to produce a satisfactory re-usable reconstituted oil based fluid.

The flocculant used in embodiments of the present invention may be any suitable commercially available flocculant; for example those disclosed in U.S. Pat. Nos. 6,193,070; 5,422,012; and 4,913,585.

The present invention discloses, in at least certain aspects, methods for recovering drilling fluid from a mixture containing drilling fluid and other components, the mixture resulting from a wellbore operation including the pumping of drilling fluid, the methods including: producing a mixture of flocculant with a spent drilling fluid; the spent drilling fluid containing drilling fluid and contaminants; heating the mixture; and separating drilling fluid from the mixture. Such methods may include one or some, in any possible combination, of the following: wherein the heating is effected by injecting steam into the mixture; wherein the mixture is in a flow conduit and the steam is injected into the mixture within the flow conduit; wherein the mixture is in a pressure vessel and the steam is injected into the mixture within the pressure vessel; wherein the mixture is heated to a temperature between 160° F. and 705° F.; wherein the mixture is produced in a mixing apparatus, the mixing apparatus comprising a high speed mixer, the method further including producing the mixture in the high speed mixer; adding no emulsifier to the mixture; wherein the flocculant is in a combination of flocculant and water, the flocculant present at between 0.00125% and 0.5% of the total volume of the combination; wherein the flocculant is present as 0.0025% of the total volume of the combination; wherein the water is present by volume between 5% to 20%; wherein the spent drilling fluid is pumped from an active rig mud system, the method further including feeding separated drilling fluid back to the active rig mud system; wherein the separating is effected with centrifuge apparatus; wherein the centrifuge apparatus produces a stream of recovered drilling fluid in which the ratio by volume of drilling fluid to water is at least 90 to 10; emulsion testing separated drilling fluid to determine if it is acceptable for re-use; wherein the contaminants include solids, the method further including processing separated drilling fluid to remove solids with a largest dimension between 3 microns and 30 microns; feeding the heated mixture to a tank in which solids in the mixture settle out and are removed before the separating step; and/or continuously separating drilling fluid from the mixture.

The present invention discloses, in at least certain aspects, a method for recovering drilling fluid from a mixture containing drilling fluid and other components, the mixture resulting from a wellbore operation including the pumping of drilling fluid, the method including: producing a mixture of flocculant with a spent drilling fluid, the spent drilling fluid containing drilling fluid and contaminants; heating the mixture; separating drilling fluid from the mixture; wherein the heating is effected by injecting steam into the mixture; wherein the mixture is heated to a temperature between 160° F. and 705° F.; wherein the mixture is produced in a mixing apparatus, the mixing apparatus including a high speed mixer, the method further including producing the mixture in the high speed mixer; wherein no emulsifier is added to the mixture; wherein the flocculant is in a combination of flocculant and water, the flocculant present at between 0.00125% and 0.5% of the total volume of the combination; wherein the water is present by volume between 5% to 20%; wherein the separating is effected with centrifuge apparatus; wherein the centrifuge apparatus produces a stream of recovered drilling fluid in which the ratio by volume of drilling fluid to water is at least 90 to 10; and wherein drilling fluid is continuously separated from the mixture.

The present invention discloses, in at least certain aspects, a system for recovering drilling fluid from a spent drilling fluid mixture, the spent drilling fluid mixture including drilling fluid and contaminants, the system including: a tank apparatus for mixing water and flocculant to produce a water-flocculant mixture; a mixing apparatus for receiving and mixing the water-flocculant mixture with spent drilling fluid to produce a drilling fluid mixture; heating apparatus for receiving and heating the drilling fluid mixture to produce a heated drilling fluid mixture; and separation apparatus for receiving the heated drilling fluid mixture and for separating drilling fluid from the drilling fluid mixture.

The present invention discloses, in at least certain aspects, a method for wellbore operations including: pumping drilling fluid with an active rig mud system into and from a wellbore; pumping spent drilling fluid from the wellbore with the active rig mud system to a mixer; pumping a water-flocculant mixture to the mixer; mixing with the mixer the spent drilling fluid and the water-flocculant mixture producing a primary mixture; heating the primary mixture; feeding heated primary mixture to separation apparatus; with the separation apparatus producing re-usable drilling fluid separated from the primary mixture; and feeding the separated re-usable drilling fluid back to the active rig and system for re-use

In conclusion, therefore, it is seen that the present invention and the embodiments disclosed herein are well adapted to carry out the objectives and obtain the ends set forth. Certain changes can be made in the subject matter without departing from the spirit and the scope of this invention. It is realized that changes are possible within the scope of this invention and it is further intended that each element or step recited herein is to be understood as referring to the step literally and/or to all equivalent elements or steps. This specification is intended to cover the invention as broadly as legally possible in whatever form it may be utilized. All patents and applications identified herein are incorporated fully herein for all purposes.