Abstract:
A process for the manufacture of a water based drilling fluid additive comprising the steps of: (a) mixing hydrophobic carbon black and either a surfactant or a dispersant and (b) shearing the mixture of step (a) under a sufficiently high mechanical shear for a sufficient time to convert the hydrophobic carbon black into hydrophilic carbon black. This invention is also directed to a water based drilling fluid additive prepared according to the above process and the use of the additive in a water based drilling fluid.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a drilling fluid additive to provide enhanced fluid loss properties, enhanced wall cake thickness, enhanced bore hole stability, enhanced temperature stability, enhanced defoaming qualities, and enhanced film forming qualities to the drilling fluid. 
     BACKGROUND OF THE INVENTION 
     In drilling wells for the purpose of producing oil or gas from subterranean deposits, a fluid known as drilling mud is used to perform several functions necessary to successfully complete each well. This drilling fluid or mud performs many functions such as lubricating the drill string, cleaning the bore hole, and exerting sufficient pressure to the sides of the bore hole to prevent the entrance of liquids or gases into the bore hole from the formation being penetrated. 
     The drilling fluid must have a low fluid loss to prevent excessive loss of fluid into the formation by depositing an impervious filter cake on the sides of the bore hole. The thickness of the filter cake is usually directly proportional to the volume of fluid loss. Therefore, the lower the fluid loss the thinner the filter cake. Maintaining the diameter of the bore hole being drilled is critical to a successful operation. If the fluid loss is high, then the wall cake will be thick and therefore, the desired diameter of the well bore will be reduced. 
     Fluid loss additives most commonly used to control the fluid loss and also the wall cake thickness are bentonite clays, polymers, lignites, and surfactants. 
     Carbon black is basically pure carbon which exists in extremely small particle diameters of approximately 13 to 75 millimicrons. Carbon black particles have a high surface area. The surface area of a carbon black particle is approximately 25 to 500 square meters per gram and has an oil absorptive capacity of 45 to 300 cc per 100 grams. 
     Carbon black is organophilic and has an extremely high affinity for oils, phenols, alcohols, fatty acids, and other long carbon chain products normally used in drilling fluids. 
     Carbon black is insoluble and maintains its individual particle identity through mixing and handling procedures commonly used in the drilling mud industry. Carbon black will remain completely stable and finite at temperatures up to 3000° F. The hardness of carbon black, in addition to its high affinity for lubricating substances, makes it an excellent carrier to extremely tight fittings, such as a metal to metal contact. Coated with lubricant, the ultra-fine particle size penetrates openings and scratches not normally penetrable with other solids in the drilling fluid system. 
     However, carbon black that has not been chemically treated is basically hydrophobic and will not readily mix with water or water based drilling fluids. Thus, it is difficult to use carbon black as an effective drilling fluid additive. 
     SUMMARY OF THE INVENTION 
     Accordingly, one object of the present invention is to provide a new and improved method of applying carbon black based products to the drilling fluid to thereby drastically reduce the screening of the carbon black out of the drilling fluid as the drilling fluid passes through the rig shaker. 
     In fact, the instant invention will allow 99.9% of this carbon black based material to pass through a 200 mesh shaker screen. This reduced screening allows the carbon black based material to remain in the drilling fluid system indefinitely and creates a more economical and environmentally safe method of achieving the benefits of the carbon black. 
     Another object of the present invention is to provide a carbon black dispersion which provides an improved particle size distribution of the carbon black particles. 
     Another object of this invention is to provide a method of adding the carbon black product to the drilling fluid in such a manner that the person adding the product will not be subjected to the fine dust while adding the product in a dry form through the mud hopper on the drilling rig. 
     Another object is to improve the lubricating properties of the drilling fluid. 
     Another object is to improve the rheology properties of the drilling fluid. 
     A still further object is to improve the defoaming properties of the drilling fluid. 
     The present invention accordingly provides a process for the manufacture of a water based drilling fluid additive. The process comprises the steps of: 
     (a) mixing hydrophobic carbon black and either a surfactant or a dispersant, and 
     (b) shearing the mixture of step (a) under a sufficiently high mechanical shear for a sufficient time to convert the hydrophobic carbon black into hydrophilic carbon black. 
     In one embodiment, the mixture further contains hydrophobic asphaltite that is converted by shearing into hydrophilic asphaltite. 
     The present invention also provides a water based drilling fluid additive prepared according to the above process. 
     The present invention further provides a water based drilling fluid comprising water and a water based drilling fluid additive as prepared above. 
     The present invention still further provides a process for enhancing the properties of a drilling fluid during the drilling of the well, by combining and circulating with a water based drilling mud, an additive as described above. The additive is mixed with the drilling mud in an amount to sufficiently reduce fluid loss and wall cake thickness. 
     The present invention still further provides a process of drilling a well with a rotary bit which comprises forming a bore hole with the bit while circulating a drilling mud through the bore hole. The drilling mud comprises an additive as described above and the additive is mixed with the drilling mud in an amount to sufficiently reduce fluid loss and wall cake thickness. 
     The process of the present invention offers a superior method of pre-dispersing and therefore wetting the surface area of the carbon black with a surfactant, emulsifier, or dispersant prior to adding the product to the drilling fluid. This process provides for a more even particle size distribution of the colloidal size particles as well as particles in the 1 to 200 micron size. 
     The present invention overcomes the &#34;fish-eye&#34; condition that occurs when fine carbon black particles are added to the drilling fluid. The fish-eye condition of the product is the balling up of many ultra-fine particles which might be partially water wet on the outside but still dry in the center of the ball. The fish-eye carbon black particle is then screened out of the drilling fluid by the rig shakers. 
     The present invention improves the economics and efficiency of defoamers. It is believed that the normally hydrophobic carbon black particle absorbs a film of the liquid defoamer around the entire surface area of each carbon black particle. The normally hydrophobic carbon black particle is also organophilic and preferentially wets with a hydrocarbon, usually an oil, alcohol, or like material. As this mixture or dispersion of carbon black and liquid hydrocarbon based defoamer is added to the water based drilling fluid, the carbon black particles separate and are rapidly propelled through the foam bubbles. 
     It is thought that these carbon black particles having a surface coating of the above mentioned defoamer is propelled over the surface of the water due to the hydrophobic nature of the defoamer coated carbon black particle. This phenomenon is thought to be due to the extremely small size of the coated carbon black particles and their lack of affinity for water. As these coated carbon black particles attempt to avoid the water in the drilling fluid, they are rapidly propelled to and fro. 
     This movement of the coated carbon black particles has the effect of bumping into bubbles and allowing the microcell of defoamer to break the surface tension of the bubble causing the bubble to break. Observing the addition of coated carbon black particles to the surface of water through a microscope allows one to observe this phenomenon. It is also advantageous to keep the defoamer on the surface or in the upper third portion of the drilling fluid while the drilling fluid is being agitated or mixed in the mud pits. 
     In the present invention, carbon black helps improve the bacterial degradation of hydrocarbons by forming microcells which allow greater surface area exposure for the bacteria to dissipate and thus destroy the hydrocarbon. It has been determined that a hydrocarbon sheen of any significant size on the surface of water is environmentally unacceptable due to the adverse effects on marine life. Almost all drilling fluids inadvertently contain a small percentage of a sheen forming hydrocarbon. This hydrocarbon could enter the drilling fluid as the drilling assembly penetrates a hydrocarbon laden sand or by simply adding it to the drilling fluid to obtain a specific benefit. 
     This phenomenon occurs due to the extremely small particle size of the carbon black and also due to the high absorptive properties of the carbon black. 
     These and other objects, features and advantages of the present invention will be made more apparent from the following description of the preferred embodiments. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the presently preferred embodiments of the invention. 
     In accordance with the present invention of manufacturing a water based drilling fluid additive, hydrophobic carbon black is mixed with a surfactant or dispersant. This mixture is then sheared under a sufficiently high mechanical shear for a sufficient time to convert the hydrophobic carbon black into hydrophilic carbon black. 
     In one embodiment, hydrophobic asphaltite is mixed with the hydrophobic carbon black and the surfactant or dispersant. Then, this mixture is sheared under a sufficiently high mechanical shear for a sufficient time to convert both the hydrophobic carbon black and hydrophobic asphaltite into hydrophilic carbon black and hydrophilic asphaltite. 
     As a result, the surface area of the carbon black is wetted and hydrophilic. This allows the carbon black product to remain dispersed and separated into individual particles which stack or plate out on the side of the well bore to reduce fluid loss. These finely dispersed, surface coated particles act as excellent plugging agents for improved fluid loss control. Similar advantageous properties are imparted to the asphaltite when it is present. 
     In the present invention, the carbon black particles and asphaltite, if present, are in a state of dispersion having an average particle size much finer than their original size due to the shearing action in the environment of the surfactant or dispersant. In the present invention, the carbon black particles are in a state of dispersion having an average particle size much finer than the other drilling fluid additives. The carbon black particles, and asphaltite, if present, become dispersed into much finer particles which expose more surface area. This surface area is then exposed to the surfactant or dispersant which converts the hydrophobic carbon black particles, and hydrophobic asphaltite, if present, into hydrophilic carbon black particles and, hydrophilic asphaltite particles, respectively. The asphaltite and carbon black product thereby readily mixes and disperses with any water based drilling fluid. 
     Any inherently hydrophobic asphaltic material can be used in the present invention. A high grade mined pulverized gilsonite is preferred. 
     Preferred carbon black which can be used in the present invention is carbon black produced by furnace processes that range in size from 8 m 2  /gr to 150 m 2  /gr as determined by the nitrogen adsorption method or carbon black ranging in size from 35 cc/100 gram to 200 cc/100 gram as measured by DBP (Dibutylphthalate) absorption. 
     A more preferred carbon black which can be used in the present invention is carbon black in the particle size range of 70-120 m 2  /gram as determined by the nitrogen adsorption method or 75-125 cc/100 grams as determined by the DBP (Dibutylphthalate) absorption method. 
     Surfactants of the present invention can be selected from, for example, ethoxylated phenols, alcohols, glycols, or fatty acid type materials. A preferred surfactant is an ethoxylated glycol type surfactant. Dispersants of the present invention can be selected from, for example, potassium hydroxide, sodium hydroxide, or lignitic type materials. The surfactants and dispersants are either liquid or solid but are preferably liquid. 
     The mixture of the carbon black and the surfactant or dispersant are subjected to an extremely high mechanical shear to impart hydrophilic properties to the carbon black. The mixture should preferably be subjected to a shear of at least 1700 rpms for at least 60 minutes. When present in the mixture, the hydrophobic asphaltite is likewise sheared. 
     A typical method of shearing the liquid mixture is by using a high speed mechanical disperser such as a ROTOSTAT® 200XP-200, manufactured and sold by Admix, Inc. of Londonderry, N.H., U.S.A. 
     Optionally, the mixture comprising carbon black obtained after the shearing process may be adjusted to a pH of about 8 before the mixture is added to the drilling mud. The pH adjustment is a means to further disperse the solids of the invention in the liquid phase. 
     The carbon black is preferably used in an amount of about from 5% to 90% by weight of the additive mixture. About 50% by weight of the carbon black in the additive mixture is especially preferred. 
     If a surfactant is employed, the surfactant is preferably used in an amount of about from 5% to 90% by weight of the additive mixture. About 35% by weight of the surfactant in the additive mixture is especially preferred. 
     If a dispersant is employed, the dispersant is preferably used in an amount of about from 1% to 50% by weight of the additive mixture. About 10% by weight of the dispersant in the additive mixture is especially preferred. 
     In one embodiment, the additive material further comprises asphaltite in an amount of about from 5% to 80% by weight of the mixture. About 40-70% by weight of the asphaltite in the additive mixture is especially preferred. 
     The combination embodiment of utilizing asphaltite and carbon black together can lead to improved results over either carbon black or asphaltite alone. For example, in a mixture of approximately 60-70% by dry weight of asphaltite and about 30-40% by dry weight of carbon black, the mixture contains about 24.8% of particles smaller than 6 microns whereas asphaltite alone contain about 5.8% of particle smaller than 6 microns. The combination embodiment contains about 14.2% of particles smaller than 2 microns which would be considered colloidal in size. Not wishing to be bound by theory, it is believed that these colloidal particles function to bridge or plug the micro fractions of the well bore. 
     The additive mixture is mixed with the drilling mud in an amount to sufficiently reduce fluid loss and wall cake thickness. The additive mixture is preferably used in from about 1/2% to about 30% by volume of the drilling mud. The additive mixture is more preferably used in from about 2% to about 5% by volume of the drilling mud. 
     The additive can also include other components that are inherently hydrophobic prior to the shearing step. 
     The additive can be utilized in drilling fluids while drilling oil wells, gas, wells, mineral wells, water wells, or any other earth boring operation. 
     The specific examples below will enable the invention to be better understood. However, they are given merely by way of guidance and do not imply any limitations. 
    
    
     EXAMPLE 1 
     Improved high pressure and temperature fluid loss and improved low pressure fluid loss 
     The fluids in Table 1 below were circulated through a 100 mesh screen 25 times, and then tests were run on the fluids in accordance with Table 1. 
     
                                           TABLE 1__________________________________________________________________________DECREASE IN HIGH AND LOW PRESSURE WATER LOSSCARBON BLACK ONLY ADDITIVE VS CARBONBLACK &amp; ASPHALTITE COMBINATION ADDITIVE                               2% BY VOLUME CARBON                                               PERCENTBASE       2% BY VOLUME CARBON                     PERCENT   BLACK &amp; ASPHALTITE                                               IMPROVEMENTMUD        BLACK ONLY ADDITIVE                     IMPROVEMENT                               COMBINATION ADDITIVE*                                               OVER BASE__________________________________________________________________________                                               MUD100 psi 25.6 cc        15 cc        41%       10.5 cc         59%fluid loss@ 80°500 psi 69.5 cc      31.8 cc        54%         22 cc         68%fluid loss@ 300°__________________________________________________________________________ *Known as BLACKNITE.sup.™ about 30-40% dry weight carbon black and 70%-60% dry weight asphaltite 
    
     Approximately 99.9% of the present invention additive remained in the drilling fluid after 25 circulations. These calculations were made by collecting the solid product trapped on the 100 mesh screen. No appreciable solid product was detected. 
     EXAMPLE 2 
     Decrease in the filer cake thickness 
     
                                           TABLE 2__________________________________________________________________________DECREASE IN FILTER CAKE THICKNESSCARBON BLACK ONLY ADDITIVE VSCARBON BLACK &amp; ASPHALTITE COMBINATION ADDITIVE                               2% BY VOLUME CARBON                                               PERCENTBASE       2% BY VOLUME CARBON                     PERCENT   BLACK &amp; ASPHALTITE                                               IMPROVEMENTMUD        BLACK ONLY ADDITIVE                     IMPROVEMENT                               COMBINATION ADDITIVE*                                               OVER BASE__________________________________________________________________________                                               MUD100 psi 9.2fluid loss@ 80°Cake   4/32      3/32           25%       2/32            50%Thickness500 psi 31fluid loss@ 300%Cake  11/32      8/32           27%       5/32            55%Thickness__________________________________________________________________________ *Known as BLACKNITE.sup. 
    
     This invention reduces the thickness of the filter cakes. The uniform individual particle size distribution provided better compaction medium which restricted the flow of liquids from the drilling fluid. 
     EXAMPLE 3 
     Improved lubricity of the drilling fluid-carbon black 
     
                       TABLE 3______________________________________PLATE    BASE       ADDITION OFPRESSURE MUD        2% INVENTION PERCENT(lbs)    (amperes)  (amperes)    REDUCTION______________________________________100      14          5           64%200      26          9           65%300      35         15           57%400      44         21           52%500      60         31           48%600      SEIZURE    44           DID NOT                            SEIZE______________________________________ 
    
     The lubricity refers to the lubricity characteristics of the drilling fluid in contact with the drill stem and bore hole walls. The drilling fluid lubricity was measured by the ability of the drilling fluid to reduce the coefficient of friction between two surfaces with the drilling fluid between the surfaces. The present invention reduced lubricity because it formed a film between the surfaces while minimizing wall cake build up. 
     EXAMPLE 4 
     Improved temperature stability of the flow properties of the drilling fluid-carbon black 
     The following results in Table 4 were achieved with the use of 13.5 ppg field water based drilling fluid. 
     
                                           TABLE 4__________________________________________________________________________@ 100° F.:     HOT ROLLED 16 HRS @ 275° F.BASE SAMPLE  1% INVENTION BASE SAMPLE                              1% INVENTION__________________________________________________________________________PV  32       26       PV  38       23YP   7        5       YP  10        3GELS    2/4      1/2      GELS                     2/6      0/1__________________________________________________________________________ PV = plastic viscosity YP = yield point GELS = gel strength 
    
     The reduction in yield from 7 to 5@100° F. and from 10 to 3@275° F. show that there were considerable improvements in rheology and gel strength controls. Thus, the invention also shows an added benefit of thinning drilling fluids. 
     Accordingly, this invention provides individual carbon black particles which plug off microfractures in the drilled formation to shut-off intrusion of the fluid into the formation. This invention therefore decreases the amount of capillary attractive forces present in the microfractures of the well bore. Not wishing to be bound by theory, it is believed that the extremely small particle size of the carbon black allows it to penetrate and bridge the fracture in the shale plane at the initial source. Other particles in the drilling fluids are too large to accomplish this. 
     It would be apparent to those skilled in the art that various modifications and variations can be made in the present invention without deviating from the scope or spirit of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided that these come within the scope of the following claims or their equivalents.