WO1998006792A1

WO1998006792A1 - Composition and method for viscosifying brines

Info

Publication number: WO1998006792A1
Application number: PCT/US1997/014335
Authority: WO
Inventors: George T. Colegrove; Walter Gregory Rakitsky; Thomas Raymond Sifferman
Original assignee: Monsanto Company
Priority date: 1996-08-16
Filing date: 1997-08-15
Publication date: 1998-02-19
Also published as: AU3981897A

Abstract

A rheologically improved ready-to-use activated composition and method useful with such composition for viscosifying aqueous brines is provided which can be used for applications such as drilling, workover and completion in brines by the addition of reticulated bacterial cellulose as a viscosifying agent to such brines followed by activation whereby the brine is viscosified. A method of increasing the viscosity and/or suspension ability of a brine having dissolved therein any salt which comprises mixing said brine with reticulated bacterial cellulose and activating same. A proces is also provided for producing an enhanced composition whereby reticulated bacterial cellulose is admixed with a brine and thereafter the admixture is activated by thorough mixing and dispersion of reticulated bacterial cellulose in the brine.

Description

TITLE

COMPOSITION AND METHOD FOR VISCOSIFYING BRINES

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to novel aqueous brine compositions and methods for the use of such compositions containing reticulated bacterial cellulose. These compositions are useful for several applications, including oil field completion, drilling or workover fluids .

Due to an increased desire to control oil well production costs, more attention is being drawn to enhanced techniques which can provide greater efficiency in oil well drilling, completion and workover operations. It is recognized that better use of fluids having improved properties in the oil field can dramatically enhance and extend formation life, a valuable asset. Proper selection and use of fluids in these applications can significantly effect the formation and productivity and mechanical performance of the well.

Description of the Related Art

Various agents have been employed in oil well drilling, workover and completion fluids over the years. Several illustrative patents and literature articles hereinafter following illustrate the practice of drilling, workover and completion applications m oil wells .

Hydroxy ethyl cellulose (HEC) is added to drilling fluids to viscosity the drilling fluid. UK Patent

Application GB 2,075,041 A published November 11, 1981, discloses the use of HEC for thickening brine.

"Clear Water Brines Minimize Formation Damage" by Gary Poole in Oil and Gas Journal, July 13, 1981, pages 151 to 161 and incorporated herein in its entirety by reference discloses that clear water brines are an effective way to minimize formation damage, provide well bore stability and control downhole pressures and that the use of bromide salts provide wellbore stability, assure maximum formation protection and provide adequate hydrostatic pressure control.

U.S. Patent 4,350,601 which issued to Mosier et al . , on September 21, 1982, discloses viscosifiers for addition to high zmc salt brines used as oil well workover and completion fluids which are prepared from polysacchaπde gums or gelatin by treatment with formaldehyde and/or an aliphatic dialdehyde containing from 2 to 6 carbons.

U.S. Patent 4,359,392 which issued to Ralph H. Rygg on November 16, 1982, discloses processes for the stabilization of modified cellulose in brine solutions useful for well completion and workover. Copper species are disclosed to be added to such fluids in an amount effective substantially to decrease the rate of decomposition of such cellulose at temperatures above about 225°F.

U.S. Patent 4,415,463 to Mosier et al . , which issued November 15, 1983, discloses viscosifier for addition to high zmc salt brines, used as oil well workover and completion fluids which are prepared from natural polysaccharide gums by treatment with a basic nitrogen reagent, such as a quaternary ammonium compound, hexamethylene tetramme, or dimthylol urea.

"Fluid-Loss Control Through The Use of a Liquid Thickened Completion and Workover Brine" by T.E. Hudson et al., JOURNAL OF PETROLEUM TECHNOLOGY, October 1983, pages 1776-1782, incorporated herein by reference in its entirety, discloses that a new thickening agent was developed for controlling fluid loss of clear brines which can be very expensive and also discloses that from a safety standpoint, the loss of clear brines to a formation may create a reduction in hydrostatic pressure which could increase the potential of a well kick or blowout .

SPE/IADC, 13441, "Clear Brine Drilling Fluids: A Study of Penetration Rates, Formation Damage, and Wellbore Stability in Full-Scale Drilling Tests" by P.A. Doty, Dow Chemical Company, 1985, incorporated herein m its entirety by reference compares the performance of CaCl₂/CaBr? clear brine fluid with that of lignosulfonate water based and oil invert emulsion based fluids in a series of laboratory drilling tests.

U.S. Patent 4,554,081 issued to Borchard et al . , on November 19, 1985, discloses high density well drilling, completion and workover brines said to have low fluid loss to subterranean formations which are in contact therewith which comprise water, one or more inorganic salts and an additive for reducing fluid loss. The additive is disclosed to comprise water soluble binary or ternary copolyτners formed from vinyl monomers.

U.S. Patent 4,900,457 issued to Clarke-Sturman and Sturia on February 13, 1990, discloses aqueous polysaccharide compositions comprising 0.03 to 5% w/v of a water soluble polysaccharide, 5 to 20 weιght% of at least one salt of at least one mono or divalent cation, wherein at least 0.05% w/v (w/v=weιght per unit volume) , based on the composition of the at least one salt is formate, the balance of the at least one part, if any, being at least one halide, a process for preparing the compositions, and their use m well- drillmg operations.

U.S. Patent 5,009,797 which issued to Glenn S. Penny et al . , on April 23, 1991, discloses a concept related to hydraulic fracturing of geological formations at selected levels of wells drilled for recovery of hydrocarbons. The concept relates to the addition of relatively small quantities of a bacterial cellulose to hydraulic fracturing fluids containing a gellant to improve their rheological properties. Proppant suspension is said to be markedly improved and friction loss through well casings is said to be significantly reduced, resulting in lower pumping energy requirements .

U.S. Patents 5,179,076 and 5,244,877 which issued to Julianne Elward-Berry on January 12, 1993, and

September 13, 1993, respectively, disclose that a water-based fluid for use in the drilling of wells. This fluid is reported to be rheological ly stable over a wide temperature range, from room temperature to at least about 475°F., thus reducing drilling time m high temperature applications; typically necessitates minimal disposal rates in operation; is resistant to temperature induced carbonate gelation; creates a thick filter cake; and combines the low toxicity of a water- based fluid with the performance stability of an oil- based fluid. As further disclosed m these patents, this drilling fluid comprises a water-based colloidal suspension of certain readily available drilling fluid components, including clay, parenchymal cell cellulose ("PCC") and an inorganic salt.

U.S. Patent 5,350,528 which issued to John A. Westhal et al . , on September 27, 1994, discloses that the addition of relatively small quantities of a bacterial cellulose to hydraulic fracturing fluids comprising conventional gellants confers several advantageous properties, improves their rheological properties for hydraulic fracturing of geological formations.

Proppant suspension is markedly improved and friction loss through well casings is significantly reduced, resulting in lower pumping energy requirements. In particular, high viscosities are achieved.

U.S. Patent 5,362,713 which issued to Westland et al . , on November 8, 1994, discloses that the addition of relatively small quantities of reticulated bacterial cellulose to well bore drilling muds improves their rheological properties. A preferred reticulated cellulose disclosed in this Westland et al . , patent is one produced under agitated culture conditions using strains of a bacterium from the genus Acetobacter. This patent discloses that reticulated bacterial cellulose is used in combination with conventional gellants to provide improved drilling muds.

BRIEF SUMMARY OF THE INVENTION

The inventors have discovered that reticulated bacterial cellulose may be employed as a viscosifying agent with a brine (s) whereby after activation of an admixture of the reticulated bacterial cellulose and brine, the resulting rheological properties (viscosity and/or suspension ability) of the brine (s) are enhanced. Addition of the reticulated bacterial cellulose to the brine provides a resulting admixture which may then be thoroughly mixed by processing it through a blendor or device to activate it The resulting brine is viscosified and ready to use.

Many of the following definitions are based on the earlier referenced patents and Drilling Terminology by R.M.Y. Praillet of Ingersoll-Rand Company, published by Compressed Air Magazine, Washington, D.C. in 1980, which is incorporated herein in its entirety by reference .

As employed herein, the term "improved rheological properties" includes an improvement or increase in the viscosity or the suspension ability (generally indicated by the yield stress) of the activated brine after treatment with reticulated bacterial cellulose and activation.

As employed herein, the term "viscosity" means the internal resistance offered by a fluid to flow which is a phenomenon attributable to the attractions between molecules within a liquid and is a measure of the combined effects of adhesion and to the liquid environment. Although viscosity slows the fall rate of particles, even to the point that particles fall very slowly such that they do not seem to fall m a reasonable time, they are still moving very slowly. In order to get complete suspension (no fall velocity) , a yield stress is needed to maintain the particles in suspension .

As employed herein, the term yield stress is the critical shear stress that must be exceeded before movement can begin. The yield stress is the resistance to initial flow, or represents the stress required to start fluid movement. Therefore, yield stress is indicative of the suspension ability of a fluid.

Oil field applications generally involve operations where there is contact with a subterranean formation, but they may also include surface equipment such as gathering lines, pipelines, separators, etc. The brines proposed in this invention might be used for any or all of these oil field applications, but the emphasis in this patent application is for the fluids in contact with a subterranean formation. Completion, workover, and drilling fluids fit this definition as described below. However, gelled plugs/pigs made with bacterial reticulated cellulose (with a co-agent) could also be used in lower salinity, especially fresh water in pipelines and other equipment for several purposes, such as removing debris.

As employed herein, the term "completion" means to perform one or more of a variety of oil field operations, including, but not limited to, cementing, using spacers, perforating, gravel packing, installing casing, underreaming, milling and a variety of stimulation techniques such as acidizing, fracturing and the like.

As employed herein, the term "drilling" means to bore a hole, such as in the earth. Generally this is for evaluating or producing a reservoir (formation) for oil, gas, or water. A drilling fluid is used for several functions, including removing the cuttings from the hole. A "drill- " fluid is often used while drilling the production zone.

As employed herein, the term "workover" means to perform one or more of a variety of remedial operations on a producing oil well with the intention of restoring or increasing production. Examples of workover operations include but are not limited to deepening, plugging back, pulling and resetting the liner, squeeze cementing, shooting and acidizing. A workover fluid includes any type of fluid used n the workover operation .

The preferred reticulated bacterial cellulose of this invention comprises a bacterial polysaccharide made from a fermentation process although other cellulose may be employed if desired. A particularly desired reticulated bacterial cellulose is available from Monsanto Company, 800 North Lindbergh Boulevard, St. Louis, Missouri 63167; U.S.A., as Cellulon^® Reticulated Bacterial Cellulose. Currently, the NutraSweet Kelco Company, A Unit of Monsanto Company, is manufacturing this product.

Several U.S. patents disclose the preparation of the preferred bacterial cellulose which has been discovered to be used this invention including for example, U.S. Patent 5,079,162 issued to Arie Ben-Bassat et al . , on January 7, 1992, and U.S. Patent 5,144,021 which issued to Arie et al . , on September 1, 1992, which disclose a method and media for producing bacterial cellulose under agitated culture conditions resulting in sustained production over an average of 70 hours of at least 0.1 gram/liter per hour are achieved. A unique reticulated cellulose product is produced using the methods and conditions claims and may be in the form of a sheet characterized by substantial resistance to densification and great tensile strength when produced by sheet forming means. Strains of Acetobacter that are stable under agitated culture conditions and that exhibit substantially reduce gluconic and keto-gluconic acids production are described.

A particularly preferred reticulated bacterial cellulose for use with the present invention is one produced under agitated culture conditions using strains of a bacterium from the genus Acetobacter. Reticulated bacterial cellulose is typically a white or off white colored solid which may be dispersed in ordinary tap water, seawater or added directly or indirectly to a brine solution.

Bacterial cellulose produced by microorganisms capable of producing cellulose such as those of the genus Acetobacter, Pseudomonas, Agrobacterium, and the like may be employed according to methods of the present invention. Preferred bacterial cellulose is produced by a strain of Acetobacter bacterium cultured under agitated cell culture conditions. As used herein the term "reticulated bacterial cellulose" as used in the specification and claims herein, refers to cellulose produced by microorganisms using fermentation techniques that is characterized by a highly reticulated, branching interconnected network of fibers and that is insoluble in water.

As employed herein "brine" typically includes such compositions as those containing salt and water and would illustratively include water saturated with or containing common salt (sodium chloride) or any strong saline solution containing such other salts as calcium chloride, z c chloride and the like. Brine also includes heavy brmes which have higher densities and often higher concentrations of salt. Illustrative of brmes useful herein includes such brmes sold under the trademark BARABRINE™ completion/workover fluids sold by Baroid, P.O. Box 1675, Houston, Texas 77251 or formates from OSCA, Inc., P.O. Box 80627, Lafayette, LA 70598 and/or Cabot Performance Materials, Beaver Run Road, Revere, PA. 18953.

Brmes are used instead of fresh water to primarily control formation pressures and also to minimize hydration, swelling, dispersion of formation clays. Brmes are used also to minimize small cuttings. Previous patents using reticulated bacterial cellulose have had a co-agent (another ingredient) . The co-agent seems to be added to allow the reticulated bacterial cellulose to be activated and to be effective in the system. The three previously referenced Weyerhaeuser Company patents are for muds and frac fluids. In muds, the patent suggests drill solids, bentomte, or soda ash as the co-agent. The two fracturing patents have a gellant, such as guar, modified guars, xanthan gum, or cellulose, recommended as the co-agent.

In fact, it was initially assumed that a co-agent, such as carboxymethylcellulose (CMC) , might be needed in the harsh environment (high ionic strength) of these brine systems. Although co-agents can be used to change the rheological properties of the br es, they do not seem to be needed.

OBJECTS OF THE INVENTION

It is an object of this invention to provide a novel activated reticulated bacterial cellulose - aqueous composition which has improved rheological properties of viscosity and/or yield stress which result in improved suspension and transport properties for solids .

It is yet another object of this invention to provide a novel activated aqueous - reticulated bacterial cellulose composition and method for using that composition which can provide higher thermal stability.

It is another object of this invention to provide novel activated reticulated bacterial cellulose-brine compositions that have reduced fluid loss. Those skilled in the art realize that other additives, such as other cellulose, described in this application and also in previous publications, can be used to control

Oil field applications include drilling, workover, and completion applications.

Novel activated reticulated bacterial cellulose brine systems can also have industrial applications.

The above and other objects are achieved in this invention which is more fully described hereinafter.

DETAILED DESCRIPTION OF THE INVENTION

This invention comprises an improved rheological activated composition comprising reticulated bacterial cellulose and brine.

The inventors have discovered that reticulated cellulose is particularly useful m high density brines because reticulated cellulose provides outstanding rheological properties (such as viscosity and suspension ability) to the brmes. These enhanced properties allow the more expensive high density brine to suspend solids, to control fluid loss, etc. This is a functionality improvement of this invention and can be seen when the reticulated cellulose is used in an amount of about 0.1 to about 20 pounds (on a 100% active basis) per barrel of said brine. The reticulated bacterial cellulose may also be used in an amount from about 0.5 to about 3 (on a 100% active basis) pounds of reticulated bacterial cellulose per barrel of brine. Cellulon^® Reticulated Bacterial Cellulose may be purchased as a nominal 20% by weight active (i.e., it is supplied as wet cake with about 80% by weight water) so that 5 pounds Cellulon^® Reticulated Bacterial Cellulose contain about one pound of reticulated bacterial cellulose, the latter on a 100% active basis. Preferably the amount of reticulated bacterial cellulose in an activated composition of this invention is in the range from about 1 to about 9 pounds per barrel of brine although greater or lesser amounts of reticulated bacterial cellulose may be employed if desired.

Our invention has several embodiments including a first embodiment which is an improved rheologically activated composition consisting essentially of water, reticulated bacterial cellulose and salt or salts. In practicing this embodiment, a salt or salts containing monovalent cation (s) is preferred.

A second embodiment is an improved rheologically activated composition comprising water, reticulated bacterial cellulose and salt or salts containing divalent cation (s) .

A third embodiment is an improved rheologically activated composition comprising water, reticulated bacterial cellulose and salt or salts of formic acid.

In our formulations reticulated bacterial cellulose is typically present in the range from about 0.1 to about 20 pounds of reticulated bacterial cellulose per barrel of said composition and more preferably reticulated bacterial cellulose is present in the range from about 0.5 to about 9 pounds of reticulated bacterial cellulose per barrel of said composition.

In a first embodiment, the salt is typically potassium or sodium chloride or potassium or sodium bromide or a mixture of these salts.

In a second embodiment salts may be employed which can be selected from calcium chloride, calcium bromide, and z c bromide. In a third embodiment, the salt (s) employed can be a salt of formic acid which is selected from the group consisting of sodium, potassium and cesium salts of formic acid.

In these various embodiments, the salt is typically present in various concentrations up to and including the saturation point of said salt or salts. A preferred salt is a mixture of monovalent and divalent salts.

In another embodiment one can use as a salt a mixture of monovalent and formic acid salts or alternatively a mixture of a salt containing divalent cation (s) and formic acid salts.

In yet other embodiments, the salt may be a mixture of a salt(s) containing divalent cation(s) and formic acid salts and if desired, one may use as a salt, a salt which is a mixture of monovalent cation(s), divalent cation (s) and formic acid salts.

The inventors have discovered a method for controlling the rheological properties of an activated brine which comprises adding an effective amount of reticulated bacterial cellulose to a brine and thereafter applying sufficient activation energy to produce said activated composition.

The inventors have also discovered a process for completing, working over or drilling an oil or gas well whereby an effective amount of a composition of this invention is added to said well during said completion, workover or drilling operations.

The inventors have also discovered a brine fluid for use as a completion fluid wherein said reticulated bacterial cellulose is present in an amount in the range from about 0.1 to about 20 pounds (on a 100% active basis) of reticulated bacterial cellulose per barrel of fluid and preferably, reticulated bacterial cellulose is present in an amount in the range from about 0.5 to about 3 pounds per pound of reticulated bacterial cellulose per barrel of fluid.

The inventors have also discovered a brine fluid for use as a workover fluid containing reticulated bacterial cellulose wherein said reticulated bacterial cellulose is present in an amount in the range from about 0.1 to about 20 pounds (on a 100% active basis) of reticulated bacterial cellulose per barrel of fluid and more preferably the reticulated bacterial cellulose is present in an amount in the range from about 0.5 to about 20 pounds of reticulated bacterial cellulose per barrel of fluid.

Applicants have further discovered a brine fluid for use as a drilling fluid containing reticulated bacterial cellulose wherein said reticulated bacterial cellulose is present in an amount in the ranged from about 0.1 to about 20 pounds (on a 100% active basis) of reticulated bacterial cellulose per barrel of fluid and more preferably the reticulated bacterial cellulose is present in an amount in the range from about 0.5 to about 3 pounds of reticulated bacterial cellulose per barrel of fluid.

Both brmes and saturated brines may be employed in the practice of this invention. However, preferably a heavy (higher density) brine is employed in the practice of this invention. Illustrative but non limiting types of heavy br es which may be employed in a composition and process of this invention include those comprising calcium chloride, calcium bromide and zmc bromide and mixtures thereof and the like although other similar brmes may be employed herein if desired. In the practice of this invention, a heavy brme typically contains salt from a nominal amount up to and including saturation. Brine densities can range from above that of about water (8.33 pounds/gallon) to more than about 20 pounds/gallon.

A method of controlling viscosity of a brme is also provided which comprises the addition of a reticulated bacterial cellulose to a brine, preferably a heavy brine wherein the composition comprising the reticulated bacterial cellulose and brine is activated by thorough mixing and dispersion of the reticulated bacterial cellulose in the brme.

In the practice of this invention, reticulated bacterial cellulose can be a fermentation broth (liquid) , wet cake, or a powder, but is preferably used as a solid, such as wet cake or dry powder.

Further, in practicing this invention, reticulated bacterial cellulose can be added to a volume of brme or water directly with salt added later to form a treatment composition. After activation, as for example by imparting mechanical shear energy to the mixture of reticulated bacterial cellulose and brme to impart thorough mixing and dispersion of the reticulated bacterial cellulose m the brme, that treatment composition can thereafter be pumped to the drill bit or through the annulus of the well or injected into the oil well bore. In practicing this invention an effective amount of reticulated bacterial cellulose is added to the brme to achieve viscosity and/or yield stress.

The reticulated bacterial cellulose may be added to the brme and pumped through the drill bit to activate the reticulated bacterial cellulose if desired. Without being bound by theory, it is believed that activation energy is required to thoroughly disperse reticulated bacterial cellulose through the brine from reading this specification, those of skill in the art will recognize that sufficient activation energy has been applied to the admixture of reticulated bacterial cellulose and brine when the admixture appears homogeneous, e.g. visually uniform and reaches maximum viscosity without further ga in viscosity.

If desired a Waring, VerTishear or Silverson blender/blendor or alternate mechanical device may be used to impart sufficient activation energy to a composition of this invention in the lab while centrifugal pumps, modified pumps or shear devices can be used in larger systems, such as in the field.

Reticulated bacterial cellulose may be added to a brme to create an admixture and that admixture may then be run through a Waring blendor or equivalent mechanical shear device for a sufficient time, preferably in the range from about 0.5 to about 30 minutes whereby sufficient shear is imparted to the admixture to cause activation of the reticulated bacterial cellulose.

Typically the Waring^® blendor disclosed herein is of the type which is used in the laboratory although in large scale operations, a larger scale blendor or similar mechanical equivalent will likely be useful.

Alternatively this activation energy may be supplied by a centrifugal pump if desired or by alternate means. Those of skill in the art will recognize from the teachings of this disclosure that the amount of shear necessary to activate a mixture of reticulated bacterial cellulose and brme in carrying out the process of this invention will vary according to the composition of the admixture but general will be at least that shear energy sufficient to fully or substantially activate the reticulated bacterial cellulose in the brme.

Other additives known to be used in brmes include corrosion inhibitors, breakers, fluid loss control additives, oxygen scavengers, b ocides as well as mixtures thereof and the like. These additives have specific other purposes and are not generally used to improve the rheological properties of the brmes (which is the purpose of this invention) . However, they may be employed herein.

The specific manner of carrying out the invention will be easily seen by one of skill in the art using the guidance provided herein.

Various illustrations of the compositions of this invention and a process for practicing the invention are provided in nonluni ing EXAMPLES hereinafter following .

EXAMPLES

The viscosity of reticulated bacterial cellulose in several brmes was measured and compared to the viscosity of HEC or XANVIS^® Biopolymers in the same type solutions at the same concentration levels to illustrate advantages of this invention.

CELLOSIZE^® Polymer HEC- 10 (Hydroxyethyl Cellulose) is a general -purpose viscosifier for low-solids drilling, completion, and workover fluids supplied by Union Carbide. Specifically designed for use in an oil field, CELLOSIZE HEC-10 is a free-flowing granular material that has been surface-treated to facilitate the preparation of clear homogeneous fluids.

XANVIS^® Biopolymers is a registered trademark of Monsanto Company for a premium biopolymer xanthan gum manufactured for the Kelco Oil Field Group of the NutraSweet Kelco Company, a Unit of Monsanto Company. Xanthan gum which is an extracellularly produced gum is made by the heteropolysachharide-producing bacterium Xanthomonas compestris by whole culture fermentation of a medium comprising a fermentable carbohydrate, a nitrogen source and other appropriate nutrients. An example of commercially available xanthan gum is XANVIS^® Biopolymer from the NutraSweet Kelco Company, a unit of Monsanto Company. Processes for producing xanthan gum are described in a number of patents, including United States Patent Nos . 4,316,012, 4,352,882 and 4,375,512 and U.S. 5,362,312.

XANVIS^® Biopolymer is a premium quality xanthan product which is recommended for use where formation protection, solids suspension and improved hole cleaning are primary concerns.

As shown in Table 1 below provided for illustration purposes, there are several brmes m which reticulated bacterial cellulose would likely be effective as a viscosifymg/suspension agent in the practice of this invention although any soluble salt or mixtures of salts such as NaCl , KC1 , or mixtures thereof, would suffice as well as salts of formates including sodium, potassium, cesium formate and mixtures thereof . The technical reference for Table 1 is Completion and Workover Fluids, by NL-Baroid CWOF™, Figure 3.1, 1983 and S.K. Howard, SPE 30498, "Formulate Brmes for Drilling and Completion: State of the Art", presented at the SPE Annual Technical Conference and Exhibition, Dallas, TX October 22-25, 1995, which is incorporated herein ts entirety by reference.

g/cc = grams per cubic centimeter lb/gal = pounds per gallon

The compositions (salts) of some of the brines is given in Table 2. Some of the brines are commercially available and were tested on "as received" basis.

Compositions of Typical Brines

g - grams ml = milliliter lbs = pounds gal = gallon Table 2

Both the Fann and Brookfield viscometers are rotational devices (see Table 3

Equipment Manufacturers

Table 3

The Fann 35 Visco eter is a commonly used oil field device shown on page 11 m "Recommended Practice on the Rheology and Hydraulics of Oil-Well Drilling Fluids": API Recommended Practice 13D, Third Edition, June 1, 1995, which is incorporated herein by reference.

Fann 35 Series Viscometers are versatile instruments for research or production use. These can be used wherever a regulated- frequency power source is available. Twelve total test speeds permit measurement over an extended shear-rate range. Test speeds of 600, 300, 200, 180, 100, 90, 60, 30, 6.3, 1.8, and 0.9 rpm are available via a synchronous motor driving through an SR 12 gear box and then through the precision gearing, as defined for Model 35. The additional 10:3 speed reduction is selectable through a two-position gear-shift lever. Standard Rl rotor sleeve, Bl bob and FI torsion spring and stainless steel sample cup are often used. For some of this testing a F0.2 spring was used to give 5 times the dial deflections.

The DV-III Brookfield Rheometer is designed for use with Brookfield spmdles and coaxial cylinders, or with cone-and-plate sensing systems. It is available in all standard Brookfield torque calibrations, and is fully compatible with all Brookfield accessories. There are about 2500 speeds from 0.1 rpm through 250 rpm in steps as small as 0.1 rpm

Cylindrical Spmdles: These sp dles (LV #1 to #4) provide a scientifically defined spindle geometry for calculating shear stress and shear rate values as well as viscosity. In all other respects their operating parameters are similar to those of disc spindles. Cylindrical spmdles are particularly valuable when measuring non-Newtonian fluids, and are applicable to any Brookfield Viscometer model with the use of the appropriate range table. Standard Brookfield Viscometer Spindles are constructed of 302 stainless steel. Optional choices include 316 stainless steel or Kynar coating for increased durability and corrosion resistance. DV-III Specifications: Electrical: Auto-sensing voltage and frequency; Signal Output: 01-VDC% scale (Brookfield); 0-4 VDC temperature (-100°C to 300 °C) ; RS 232 serial (computer or printer) . RHEOCALC software computer requirements: Computer Type: IBM PC-AT or true compatible with 640K RAM (80386 or higher) ; Color/Graphics: CGA, EGA, VGA (VGA recommended); Ports: RS 232 serial port for rheometer; RS 232 serial port if temperature control is required; (Brookfield Thermosel , Baths & Coolers); Parallel port for printer.

The Hamilton Beach Drink Mixer is specially designed to meet the strength, durability and space requirements of users. It has been adapted to oil field usage. Its three powerful, separate motors all operate individually. Typical electrical specifications are: Motors: (3) Universal, AC-DC; Voltage: 120; Wattage: each, 125: combined 375; Amperage: each 1: combined 3 ; Weight: 30 lbs.; Horsepower: each 1/7; Cycles: Up to 75; No. speeds: 3 (each motor); R.P.M., no lead: 13,000 low speed, 16,000 medium speed, 18,000 high speed; Switches: individual heavy-duty rocker speed control switches: separate automatic on-off switches; Length, cord set: (Heavy-duty, 3-wire, grounded plug). Other Specifications: Motor mountings: Rubber cradled to minimize noise vibration; Bearings: Permanently lubricated ball bearings mounted in rubber for noise suppression; Housing: Polycarbonate: die-cast zinc with charcoal brown color; Front panel: Stainless steel; Height: 20"; Width: 16³/β"; Depth: 8^"; Shipping weight : 33 lbs. TEST PROCEDURES; GENERAL PROCEDURE

The procedures used m making up the solutions illustrated hereinafter are described below The mixing instructions are followed by the measurement techniques for viscosity and yield stresses.

MIXING PROCEDURES;

The Cellulon^® Reticulated Bacterial Cellulose, the HEC and the XANVIS^® Biopolymers were mixed in the brmes with shear devices appropriate for each polymer.

Mixing Cellulon^® Reticulated Bacterial Cellulose in brines ;

Initially, the brmes (such as Table 1) were made by adding the proper amount of salt(s) to distilled water (as shown in Table 2) and dissolving the salt (s) completely. Some brmes were commercially available. Once the br e was prepared, it was poured into a two speed Waring blender, the Cellulon^® Reticulated Bacterial Cellulose was added, and it was mixed for 30 seconds at the high speed setting. The two heaviest mixtures (CaBr_? at 14.2 lbs/gal, ZnBr₂ at 20.2 lbs/gal) were mixed for a full minute to insure proper dispersion. The 1 ppb level of Cellulon^® Reticulated Bacterial Cellulose was achieved by adding 5.26g of the 19.2% solid Cellulon^® Reticulated Bacterial Cellulose wetcake to 350 ml of premade brine. At the end of the mixing, the mixture was degassed for 3-5 minutes under vacuum. Mixing the Cellulon^® Reticulated Bacterial Cellulose directly in fresh water and then adding the salts did not give as good (high) a viscosity, as when using the wet-cake product.

Mixing HEC in Brines;

The brines were prepared in a commonly used manner that was similar to the one for Cellulon^® Reticulated Bacterial Cellulose The HEC solution was made by slowly adding lg of HEC-10 into 350 ml of br e that was stirring at approximately 800 rpm on a bench top mixer. The solution was then allowed to stir for an additional 15 minutes. The solutions were examined 24 hours after mixing for any gel formation. Solutions that showed signs of gel formation were mixed an additional 30-60 minutes to help dissolve the gel prior to any testing.

All parts in this application are by weight throughout unless otherwise specifically stated.

Mixing Xanvis^® Biopolymers In Brines;

The XANVIS^® Biopolymers solutions were made my slowly adding 1 gram of XANVIS^® Biopolymers powder to 350 ml of brine that was stirring at approximately 4500 rpm (rpm = revolutions per minute) on the Hamilton Beach mixer. After all the powder was added in, the speed was increased to 11,000 rpm and the solution was mixed for an additional 55 minutes. Both the XANVIS^® Biopolymers and HEC mixtures were degassed for about 3- 5 minutes.

Suspension Ability;

The suspension capabilities of the Cellulon^® Reticulated Bacterial Cellulose and HEC samples were compared by observing suspension or settling of spheres, by calculating the resultant yield stress, and by measuring the yield stresses on both the Brookfield and Fann viscometers.

The yield stress is the critical shear stress that must be exceeded before movement can begin. The yield stress is the resistance to initial flow, or represents the stress required to start fluid movement. Therefore, it is indicative of the suspension ability of a fluid.

The suspension ability can easily be observed by placmg particles, such as spheres, in the brme and watching if the particle falls or stays suspended the brme. The suspension ability depends on the yield stress, which is predicted to be proportional to the product of the diameter of the sphere and the density difference between the sphere and the brme. Ruby, with a specific gravity of 4.02, was used for most tests since its red color allowed smaller particles to be seen easily m the brines. The largest size, clear glass spheres, with a specific gravity of 2.61, could be seen easily.

Red ruby spheres ranging in size from 1.0 millimeter to 6 millimeters as well as a 6 millimeters glass spheres were placed into the mixtures and it was noted then whether the sphere was suspended or not . To insure that the initial downward velocity of the spheres was not causing them to sink, a metal spatula was used to bring the spheres gently into the mixture. The metal spatula was then carefully removed. On the smaller spheres, the weight of the sphere alone was not enough to break the water tension and slight downward pressure (^"just enough to break the water tension) was applied via a metal spatula.

Yield Stress Calculations (Via Suspension Tests) ;

The following formula was used to calculate the theoretical yield stress range of the samples based on how they performed on the suspension tests:

Yield Stress = (diameter of sphere/6) x (density of sphere- density of fluid) The lower limit for the range was calculated based on the diameter and density of the largest ruby that could be suspended and the upper limit for the range was calculated based on the diameter and density of the smallest ruby that could not be suspended. Yield Stress (Brookfield) :

The yield stress measurement were done using the standard protocol hereinafter with the following exceptions. The test determines a "relaxation" yield stress. First, the Cellulon^® Reticulated Bacterial Cellulose was in brme as opposed to the freshwater Cellulon^® Reticulated Bacterial Cellulose that was used m the standard protocol. In addition, the standard protocol had a conversion factor (0.16) for obtaining yield stress (dynes/square centimeter) from torque readings following conversio for the LV-1 spmdle only. Therefore, for samples that required other spmdles, the n factors were calculated:

LV-2 = 0.47 LV-3 = 1.58 LV-4 = 10.43 These factors were generated by getting the torque reading for 2 or 3 solutions using two different spmdles and calculating a conversion factor based on the difference between these two readings.

Standard Protocol

Gel Strength Tests (Fann) ;

Gel strength is also a type of shear stress reading that is obtained with a Fann viscometer. It is the ability or the measure of the ability of a colloid to form gels. Gel strength is a pressure unit usually reported in lb/100 sq t. It is a measure of the same mterparticle forces of a fluid as determined by the yield point, except that gel strength is measured under static conditions, and the yield point under dynamic conditions. The common gel -strength measurements are initial and the 10-mιnute gels. The measured 10 -minute gel strength of a fluid is the maximum reading (deflection) taken from a direct-reading viscometer after the fluid has been quiescent for 10 minutes. The reading is reported in lb/100 sq ft. See API RP 13B for details of test procedure.

The gel strength of the samples were measured on the Fann 35 (f = 0.2, Rl-Bl) viscometer. This involved shearing the samples at 600 rpm for 30 seconds, letting them sit undisturbed for either 10 seconds or 10 minutes, and then measuring the highest dial reading that is obtained when the viscometer is turned on to 3 rpm.

RESULTS ;

Viscosity and suspension capability are often the most important physical properties, besides density, that are of interest in viscosified brines.

Viscosity values for HEC (hydroxyethylcellulose) , one of the current viscosifiers for brmes, and Cellulon^® Reticulated Bacterial Cellulose m various brmes at room temperature at 1 ppb (pounds of active polymer per barrel of brine) from a Fann™ 35 viscometer are listed in Tables 4 and 5, respectively The Cellulon^® Reticulated Bacterial Cellulose has much higher viscosities, especially at the low shear rates HEC Fann 35 Data

CO

09 CO

H m o

X m m

r σ»

N/A-Not Applicable

Table 4

Cellulon* Reticulated Bacterial Cellulose Fann 35 Data

CO IV⁾

Table 5

(low rp s) , than the HEC. These lower shear rates are more important since they correlate with low flow rate or static conditions that are more indicative of the actual viscosities that influence fluid loss. Some of the viscosities for the HEC systems may be higher than usual because of gelation that has resulted in these brines. This will be seen further in the next set of tables .

Tables 6 and 7 show suspension results for brines with HEC and Cellulon^® Reticulated Bacterial Cellulose, respectively, at 1 ppb. None of the brines with HEC suspend even the smallest (1.5 millimeter) ruby sphere (Table 6) , while all the Cellulon^® Reticulated Bacterial Cellulose brmes support the 1.5 mm ruby sphere at 1 pounds per barrel (ppb) (Table 7) . The calcium chloride and the sodium chloride/calcium chloride brmes support the 3 mm ruby spheres as well as the 6 mm glass spheres. A higher concentration of Cellulon^® Reticulated Bacterial Cellulose can be used to suspend the larger diameter spheres for all br es.

The inventors have listed gel strengths for the various br es with 1 ppb of HEC and Cellulon^® Reticulated Bacterial Cellulose in Table 7. Again, the HEC does not have any measurable gel strength, while Cellulon^® Reticulated Bacterial Cellulose has significant values.

Tables 6 and 7 report the yield stresses and gel strengths for HEC and Cellulon^® Reticulated Bacterial Cellulose, respectively, at 1 ppb. Most of the HEC brines had no yield stress, while those for Cellulon^® Reticulated Bacterial Cellulose were often 60 to almost 300 dynes/sq. cm based on calculations for the sphere suspension tests and the 6 to 10 dynes/sq. cm range when measured on a Brookfield viscometer. The gel strengths are very small (about 1 to 2 dynes/sq cm) CO

-E->

Table 6

Suspension Ability Of Cellulon* Reticulated Bacterial Cellulose

co n

Table 7

when measured on the Fann viscometer, but generally follow the same trends as the earlier yield stresses. The Brookfield yield values are an order of magnitude less than those calculated from the glass sphere settling tests but about an order of magnitude greater than the Fann gel strengths. This in not unreasonable since they are all based on different assumptions and procedures, but they follow similar trends.

The results for highest density brme -- zmc bromide -- are shown in Table 8. The zmc bromide brme with Cellulon^® Reticulated Bacterial Cellulose has increased viscosity, but no yield stress. The Cellulon^® Reticulated Bacterial Cellulose seems to be in solution this brine, while it is dispersed m the other brmes. Although there is no yield stress, the increased viscosity provides a reduced settling velocity. Therefore, the particles fall slower in this brme with Cellulon^® Reticulated Bacterial Cellulose than in the initial brine alone.

The Cellulon^® Reticulated Bacterial Cellulose did not always result in a stable system that has a significant increase in the viscosity and/or the yield stress of the initial brme. Without being bound by theory, there are two related properties that probably effect these results. One is the crystallization temperature that is the temperature at which salt crystals start to form in a given solution due to a decrease m temperature. A discussion of brine crystallization temperature is found m Testing of Heavy Brines, API Recommended Practice 13J, Second Edition, March 1996, which is incorporated herein m its entirety by reference. The other is saturation that occurs when no more salt can be dissolved into solution at that temperature. Perhaps the crystallization temperature in these cases is near the temperature at which testing was done and/or that the br e is saturated such that

there is not enough available free water for the reticulated bacterial cellulose to be dispersed in. However, by using different ratios of selected salts and/or lower densities for given salts, the reticulated bacterial cellulose has been effective at improving the viscosity and/or the yield stress (suspension ability) of these brines.

Cellulon^® Reticulated Bacterial Cellulose In Zinc Bromide

10

15

Table 8

Table 9 shows viscosity results for a high density (14.2 ppg) calcium chloride/calcium bromide brme with reticulated bacterial cellulose that only had a slight increase viscosity (more than the brine alone) and no suspension capabilities. Its crystallization temperature is less than about 6 °F but is still probably near room temperature. Changing the salt ratios and having more water gave the 13.0 ppg (ppg = parts per gallon) calcium chloride/ calcium bromide brine a stable, high viscosity and suspension capabilities at a crystallization point of 12 ^CF (much lower than the crystallization point for the 14.2 ppg brine) .

The calcium bromide with reticulated bacterial cellulose at 14.2 ppg had good viscosity and suspension capabilities. However, adding water to lower the density to 13.8 ppg also improved the effectiveness of the reticulated bacterial cellulose. Although the 13.8 ppg br e had less viscosity than the 14.2 ppg brine alone, the 13.8 ppg brine with reticulated bacterial cellulose had more viscosity (absolute and differential increase) than the 14.2 ppg brme with reticulated bacterial cellulose.

Formate br es are often viscosified with Xanthan gum. Therefore, formate brmes thickened with Cellulon^® Reticulated Bacterial Cellulose were compared with formate brmes viscosified with XANVIS^® Biopolymers in Table 10. Almost all of the Cellulon^® Reticulated

Bacterial Cellulose viscosity readings are larger than those of XANVIS^® Biopolymers. However, all of the yield stresses and gel strengths for the Cellulon^® Reticulated Bacterial Cellulose in Table 11 are greater than those for XANVIS^® Biopolymers. Also, the Cellulon^®

Reticulated Bacterial Cellulose suspends the spheres.

Cellulon^® Reticulated Bacterial Cellulose was added to 10.0 lb/gal sodium chloride/ potassium chloride and 12.6 Ib/gal sodium bromide br es at concentrations from 0.25 ppb up to 20 ppb. As shown in Table 12, the viscosities could not be measured at the higher concentrations. Although it was possible to add up to 20 ppb, the preferred range is about 0.5 ppb up to about 9 ppb. The yield stress is reported in Table 13 and shown in FIG. 1 for these same brines. While the yield stresses are fairly small for the lower concentrations of Cellulon^® Reticulated Bacterial Cellulose, they are significant for the intermediate and higher concentrations. As noted, however, the readings for the 20 ppb concentrations were offscale.

Fann 35 Viscosity Results for Various Crystallization Points

ppb=pounds per United States barre ( gal ons, oi ie d)

Table 9

(A

C OB CO

Ά c H rn co x m m

H

3 c r m r

Table 10

Suspension Ability (Yield Stress) Of Cellulon^' Reticulated Bacterial Cellulose In Formate Brines

(0 c

CD C/> H

H

C H m

CΛ x m m

H

3 c m ro σ>

Table 11

Table 12

Effect Of Concentration on Viscosity

-P-.

Table 12 (contd. from previous page)

Cellulon^® Reticulated Bacterial Cellulose Yield Stress and Constant Shear Viscosity at Different Concentrations

ppb=pouπds per Uni ted States barrel (42 gallons, oil field) ***= Indicates off scale readings

Table 13

Although the invention has been described above in terms of some specific embodiments which are set forth in considerable detail, it should be understood that this description is by way of illustration only and that the invention is not necessarily limited thereto, since alternative embodiments and operating techniques will become apparent to those skilled in the art in view of this disclosure. Accordingly, modification are contemplated which can be made without departing from the spirit of the aforedescribed invention.

Claims

WHAT IS CLAIMED IS:

1. An improved rheologically activated composition consisting essentially of water, reticulated bacterial cellulose and salt or salts.

2. The improved rheologically composition of claim 1, wherein said salt or salts contains monovalent cation (s) .

3. An improved rheologically activated composition comprising water, reticulated bacterial cellulose and salt or salts containing divalent cation (s) .

4. An improved rheologically activated composition comprising water, reticulated bacterial cellulose and salt or salts of formic acid.

5. The composition of claims 1, 2, 3 or 4 wherein said reticulated bacterial cellulose is present m the range from about 0.1 to about 20 pounds (on a 100% active basis) of reticulated bacterial cellulose per barrel of said composition.

6. The composition of claim 5 wherein said reticulated bacterial cellulose is present in the range from about 0.5 to about 3 (on a 100% active basis) pounds of reticulated bacterial cellulose per barrel of said composition.

7. The composition of claim 2 wherein said monovalent cation (s) is potassium or sodium chloride or potassium or sodium bromide or mixtures of these salts.

8. The compositions of claim 3 wherein said divalent cation (s) are selected from calcium and zinc, and said salts are selected from calcium chloride, calcium bromide and zinc bromide.

9. The composition of claim 4 wherein the salt(s) employed as said salt of formic acid is selected from the group consisting of sodium, potassium and cesium salts of formic acid.

10. The composition of claim 1, 2, 3 or 4 wherein said salt is present at various concentrations, up to and including the saturation point of said salt or sal ts .

11. The salt of claims 2 or 3 wherein said salt(s) is a mixture of salt(s) containing monovalent and divalent cation (s) .

12. The salt of claims 2 or 4 wherein said salt is a mixture of salt(s) containing monovalent cation (s) and formic acid salts.

13. The salt of claims 3 or 4 wherein said salt is a mixture of salts containing divalent cation (s) and formic acid salts.

14. The salt of claims 2, 3 or 4 wherein said salt is a mixture of salt(s) containing monovalent and divalent cation (s) and formic acid salts.

15. A method for controlling the rheological properties of an activated brine which comprises adding an effective amount of reticulated bacterial cellulose to a brine and thereafter applying sufficient activation energy to produce said activated composition.

16. A process for completing, working over or drilling an oil or gas well whereby an effective amount of the composition of claims 1, 2, 3 or 4 is added to said well during said completion, workover or drilling operations .

17. A brine fluid for use as a completion fluid wherein said reticulated bacterial cellulose is present in an amount in the range from about 0.1 to about 20 pounds (on a 100% active basis) of reticulated bacterial cellulose per barrel of fluid.

18. The fluid of claim 17, wherein said reticulated bacterial cellulose is present in an amount m the range from about 0.5 to about 3 pounds (on a 100% active basis) reticulated bacterial cellulose per barrel of fluid.

19. A brine fluid for use as a workover fluid containing reticulated bacterial cellulose wherein said reticulated bacterial cellulose is present m an amount in the range from about 0.1 to about 20 pounds (on a 100% active basis) of reticulated bacterial cellulose per barrel of fluid.

20. The fluid of claim 19 wherein said reticulated bacterial cellulose is present in an amount m the range from about 0.5 to about 3 pounds (on a 100% active basis) of reticulated bacterial cellulose per barrel of fluid.

21. A brine fluid for use as a drilling fluid containing reticulated bacterial cellulose wheri-n said reticulated bacterial cellulose is present in an amount in the ranged from about 0.1 to about 20 pounds (on a 100% active basis) of reticulated bacterial cellulose per barrel of fluid.

22. The fluid of claim 21 wherein said reticulated bacterial cellulose is present in an amount m the range from about 0.5 to about 3 pounds (on a 100% active basis) of reticulated bacterial cellulose per barrel of fluid.

23. The fluid of claim 17, wherein said reticulated bacterial cellulose is present m an amount in the range from about 0.5 to about 9 pounds (on a 100% active basis) per pound of reticulated bacterial cellulose per barrel of fluid.

24. The fluid of claim 19, wherein said reticulated bacterial cellulose is present in an amount m the range from about 0.5 to about 9 pounds (on a 100% active basis) per pound of reticulated bacterial cellulose per barrel of fluid.

25. The fluid of claim 21, wherein said reticulated bacterial cellulose is present in an amount in the range from about 0.5 to about 9 pounds (on a 100% active basis) per pound of reticulated bacterial cellulose per barrel of fluid.