JPH0377835B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a heavy brine solution containing zinc bromide and at least one soluble salt selected from the group consisting of calcium chloride and calcium bromide.
brine solutions, particularly those containing hydroxyethylcellulose with low fluid loss. In recent years, the scope of practical use of clear brines for use in the oil and gas industry has expanded significantly with the use of soluble zinc salts, particularly zinc bromide. As a result, clear brines now have the advantage of allowing liquids to reach densities as high as 19.2 pounds per gallon (2.3 g/cm ³ ) at ambient temperature and pressure. High density clear brines are widely used. Plugging of hole tunnel
as completion fluids to minimize perforation tunnels, prevent formation infiltration, and minimize mechanical problems; as workover fluids for similar reasons;
packer fluids that facilitate the movement or recovery of the packer
as; hole enlargement (underreaming), gravel packing and sand control (sand control).
as kill fluids or ballast fluids used in wire-line work; and as drilling fluids. Density 1.7g/ ^cm3 (14.2 lbs/gallon (ppg))
The following clear brines are commonly formulated to include sodium chloride, sodium bromide, potassium chloride, calcium chloride, calcium bromide, or mixtures of these salts. Density is 1.8g/ ^cm3
(approximately 15.1 ppg) can be prepared with calcium chloride and calcium bromide, but clear brines in this density range generally contain soluble zinc salts if the brine must have a low crystallization temperature. It is prepared as follows. Zinc bromide is preferred because brines containing it are less corrosive than brines containing zinc chloride. A clear brine having a density greater than 1.8 g/cm ³ (approximately 15.1 ppg) is prepared containing zinc bromide. Generally, hydroxyethylcellulose (HEC)
and xanthan gum polymers,
Compatible with fluids that do not contain zinc salts. However, at high densities, the hydration of these thickeners is significantly slow. HEC is generally considered unsatisfactory for use in zinc salt containing fluids. We have now discovered that HEC functions as a liquid loss control additive in certain heavy brines where HEC does not function effectively as a thickener. These heavy brines contain: 1) about 16 to about 20 weight percent zinc bromide; or 2) greater than 20 weight percent zinc bromide and at least (2X-33) weight percent, where X is zinc bromide. %] concentration of calcium chloride, containing any of the following. It is therefore an object of the present invention to provide a heavy brine solution containing zinc bromide and at least one soluble salt selected from the group consisting of calcium chloride and calcium bromide, and an amount of hydroxyethylcellulose that reduces liquid loss. The goal is to provide the following. Another object of the invention is to have a density of about 1.70 to about 1.92.
g/cm ³ (about 14.2 to about 16.0 ppg), zinc bromide and at least one soluble salt selected from the group consisting of calcium chloride and calcium bromide, and an amount of hydroxy to reduce liquid loss. To provide a heavy brine solution containing ethylcellulose. Yet another object of the invention is that the density is from about 1.70 to about
A heavy brine solution containing zinc bromide and at least one soluble salt selected from the group consisting of calcium chloride and calcium bromide in a range of 1.92 g/cm ³ (about 14.2 to about 16.0 ppg). It is an object of the present invention to provide a method for reducing losses. The heavy brine used in the present invention contains zinc bromide,
and at least one soluble salt selected from the group consisting of calcium chloride and calcium bromide. In one embodiment of the invention, the concentration of zinc bromide is about 16 to
It should be in the range of approximately 20% by weight. Preferably, the zinc bromide concentration is 18% or less and the calcium chloride concentration is 5(X-17)% or less (where X is % zinc bromide). In another embodiment of the invention, the brine must contain greater than 20% by weight zinc bromide and at least (2X-33)% by weight concentration of calcium chloride, where X is % zinc bromide. A preferred brine is about 1.70 to about 1.92 g/cm ³ (about
14.2 to about 16.0 ppg). Generally, heavy brines are prepared by mixing together various standard commercially available brines, such as: density about 1.32 to about 1.39 g/cm ³ (about 11.0
a calcium chloride brine with a density of 1.70 g/cm ³ (14.2 ppg); and a calcium bromide brine with a density of 2.30 g/cm ³ (19.2 ppg).
It is a calcium bromide/zinc bromide solution containing about 20% calcium bromide and about 57% zinc bromide. Solid calcium chloride and solid calcium bromide are also used in conjunction with these brines to prepare the heavy brines used in this invention. However, in the practice of this invention, it is preferred that only the solution be utilized for brine formulation. Standard brine mixing/preparation tables are available from various manufacturers and distributors of these commercially available brines. Used as a liquid loss inhibitor in the present invention
HEC polymers are solid particulate materials that are water-soluble or water-dispersible gums that increase the viscosity of the system when dissolved or dispersed in an aqueous medium. HEC polymers are produced by treating cellulose with sodium hydroxide and then reacting it with ethylene oxide. It is generally a high-yield, water-soluble, nonionic material. Each anhydroglucose unit in the cellulose molecule has three reactive hydroxyl groups. The average number of molecules of ethylene oxide that will be bound to each anhydroglucose unit in cellulose is referred to as the molar degree of substitution of the bound substituents. The average number of hydroxyl groups on each anhydroglucose unit that is reacted with ethylene oxide is referred to as the degree of substitution. It is generally preferred to use HEC polymers with a molar degree of substitution greater than 1. Usually dried and powdered hydrophilic polymers e.g.
Adding HEC to water hydrates the polymer particles, but prevents immediate hydration inside the particles or prevents them from dispersing into the aqueous medium. Therefore,
To obtain a homogeneous system, strong shear, long mixing times,
and/or high temperatures must be applied. We believe that HEC and other hydrophilic polymers are
It has been found that heavy brine can be activated to become viscous at room temperature. Activated HEC compositions and HEC activation methods are disclosed in the following US patent applications:
No. 119805 entitled Dispersible Hydrophilic Polymer Compositions (filed February 8, 1980); No. 146286 entitled Aqueous Brine Thickening Compositions and Thickening Processes (filed February 8, 1980);
(Filed on May 5th). Other hydrophilic polymer activation methods include
No. 196,367 (filed October 14, 1980) entitled Dispersible Hydrophilic Polymer Compositions. The activated HEC composition comprises: 1) HEC and a solvating agent consisting of a water-miscible polar organic liquid, the HEC and the solvating agent comprising 1: HEC and a water-miscible polar organic liquid;
When uniformly mixed at a weight ratio of 2 to 2, it provides a mixture in which substantially no liquid solvating agent is liberated even after being left in a closed container at room temperature for one week;
and a diluent consisting of an organic liquid that is not a solvating agent. 2) HEC; an aqueous liquid; and a water-soluble polar organic liquid; when HEC and the liquid are uniformly mixed at a weight ratio of 1:2, no release occurs even after standing in a closed container at room temperature for one week. It consists of one that gives a mixture in which no liquid is present. PH of the aqueous liquid
is preferably greater than 7.0. Generally speaking, virtually any organic compound that passes the solvation test described above has been found to act as a solvating agent to a usable extent. Preferred solvating agents include, but are not limited to, aliphatic glycols having 2 to 5 carbon atoms, such as ethylene glycol, 1,2-propanediol, 1,4-butanediol, 1,3-pentanediol, and the like. ; Glycerol, 1,2,3-butanetriol,
2~ such as 1,2,3-pentanetriol etc.
alkylene triol with 6 carbon atoms;
Amides having 1 to 4 carbon atoms such as formamide, acetamide, dimethylformamide, etc.; and mixtures of these various compounds are included. A diluent generally can be any organic compound or material that is not a solvating agent. Generally, the diluent is a liquid that does not appreciably swell the HEC polymer, i.e., after the one week solvation period described in the above test to determine the solvating agent, the diluent
There are no free liquids and no semi-solid or viscous mixtures are formed. Non-limiting examples of diluents include liquid aliphatic and aromatic hydrocarbons having from 5 to 10 carbon atoms; kerosene, diesel oil, isopropanol, alkylene glycol ethers, vegetable oils, and the like. Water-soluble or water-miscible organic liquids are particularly preferred, with alkanols having at least 3 carbon atoms, ethylene glycol monoalkyl ethers, dialkylene glycol monoalkyl ethers, and the like being most preferred. The diluent maintains the polymer composition in a liquid, injectable state at about 20°C. However, it will be appreciated that the amount of diluent can be lowered if desired, and that the final amount of diluent used will depend on the type of shear available to disperse the thickener. Generally, desirable thickeners that are injectable liquids contain from about 10 to about 25% by weight
It has been found that compositions can be made from HEC polymers, from about 2 to about 70% by weight diluent, and from about 5 to about 88% solvating agent. HEC has been added to heavy brines to increase the viscosity of the brine so as to reduce the rate of loss of the heavy brine to the formation by contact. Normally, in the absence of bridging particles, hydroxyethylcellulose
HEC provides poor liquid loss control in well-hydrated brine. See, eg, US Patent Application No. 161,444 (entitled Thickened Heavy Brine, filed June 20, 1980). As disclosed in U.S. Patent Application No. 161,444, filed June 20, 1980, we have discovered that HEC effectively gels or thickens brine when zinc bromide concentrations are less than about 20% by weight. I discovered that it is not sticky. In fact, while brines containing no zinc bromide or brine solutions containing high concentrations of zinc bromide can be thickened with HEC, the two thickened solutions can be mixed to create a solution with a zinc concentration of less than about 20% by weight. We have found that when HEC is made, the viscosity of the mixed brine is essentially the same as if no HEC was present. As shown herein, in certain heavy brines where HEC is a less effective thickener,
It is a feature of the present invention that HEC functions as an excellent liquid loss control additive. The HEC-containing brine of the present invention is cloudy compared to the clear brine obtained when the HEC is completely or nearly completely hydrated. That is, it is opaque. HEC is not completely dissolved in these brines, resulting in
At least a portion of the HEC can be utilized to act as a bridging agent to reduce liquid loss in these brines. In the practice of this invention, it is preferred that the HEC is activated to hydrate in these heavy brines at room temperature. The concentration of HEC is only needed to be sufficient to reduce brine liquid loss. Preferably HEC
The concentration is about 0.71 to about 14.3 mg/cm ³ (about 0.25 to about 5.0 pounds per 42 gallon barrel (ppb)), more preferably about 0.71 to about 8.6 mg/cm ³ (about 0.25 to about 3.0 ppb). It is another aspect of the present invention to provide a method for reducing liquid loss of heavy brines containing zinc bromide and at least one soluble salt selected from the group consisting of calcium chloride and calcium bromide, The method consists of formulating a brine to contain from about 16 to about 20 weight percent zinc bromide and mixing the brine with a liquid loss reducing amount of HEC as described above. Yet another aspect of the invention is to provide a method for reducing liquid loss of heavy brines containing zinc bromide, calcium chloride and calcium bromide, the method comprising: Formulate a brine to contain at least (2X-33) weight percent concentration of calcium chloride, where X is % of zinc bromide, and mix the brine with an amount of HEC to reduce liquid loss as described above. consists of doing. In order to more fully illustrate the invention, the following non-limiting examples are provided. EXAMPLE A heavy brine having the compositions listed in Table 1 was
The following materials were prepared by mixing together the indicated amounts of each. 2.30 g/cm ³ (19.2 ppg) calcium bromide/zinc bromide solution containing 20% calcium bromide and 57% zinc bromide; 1.70 g/cm ³ (14.2 ppg) containing 53% calcium bromide Calcium bromide solution; 1.39 containing 37.6% calcium chloride
g/cm ³ (11.6 ppg) of calcium chloride solution; and
Calcium chloride pellets containing 95% calcium chloride. After cooling to room temperature, 8.6 mg/cm ³ (3 ppb)
Activation of NATROSOL250HHR Hydroxyethyl Cellulose, or 8.6mg/cm ³ (3ppb)
NATROSOL250HHR (i.e. 20% HEC, 25% glycerin, 54.6% isopropanol, and 0.4%
(43g/ ^cm2 (15ppb) containing AB-O-SIL M5
composition) was added. Then, the heavy brine was roll-kneaded for 16 hours at room temperature and API RP
The rheology and liquid loss of 13B were determined. Next, roll knead the heavy brine at 65.6℃ (150〓) for 16 hours,
Cooled to room temperature and retrieved data for API RP 13B again. The data obtained are shown in Table 2. These data show that HEC-containing heavy brines can be formulated to exhibit very low API fluid loss, provided that the % zinc bromide in the brine
is in the range of about 16 to about 20% by weight, or the % zinc bromide is greater than 20% and the % calcium chloride is (2X-33)%, where X is the % zinc bromide in the brine. ] is larger. Preferably, the % zinc bromide ranges from about 18% to about 20% and the % calcium chloride is less than about 5(X-17)%. In this preferred range, the HEC is dissolved to such an extent that the viscosity of the heavy brine is observed to increase.
This data also shows that it is preferable not to include any solid calcium chloride in the heavy brine.

【table】

【table】

【table】

The present invention may be embodied in other specific embodiments without departing from its spirit or essential characteristics. The embodiments presented herein are therefore to be considered in all respects as illustrative and not as restrictive. The scope of the invention is indicated by the claims rather than by the foregoing description, and all modifications that come within the meaning and range of equivalents of the claims are therefore included within the invention.

Claims (1)

[Scope of Claims] 1. A heavy brine solution containing zinc bromide, at least one soluble salt selected from the group consisting of calcium chloride and calcium bromide, and an amount of hydroxyethyl cellulose that reduces liquid loss. , a solution in which the brine contains 16-20% by weight of zinc bromide. 2. The brine according to claim 1, having a density of 1.70 to 1.92 g/cm ³ (14.2 to 16.0 ppg). 3. The brine according to claim 2, wherein the concentration of hydroxyethylcellulose is 0.71 to 0.71.
14.3 mg/cm ³ (0.25-5.0 lb/42 gallon barrel). 4. The brine according to claim 2, wherein the concentration of hydroxyethyl cellulose is 0.71 to 0.71.
8.6mg/ ^cm3 (0.25-3.0 lb/42 gallon barrel)
something that is. 5. The brine according to claim 1, 2, 3 or 4, wherein the hydroxyethylcellulose is activated in the brine so as to be hydrated at room temperature. 6. A heavy brine containing zinc bromide, calcium chloride, and calcium bromide, and an amount of hydroxyethyl cellulose that reduces liquid loss,
a brine in which the brine contains greater than 20% by weight of zinc bromide and a concentration of at least (2X-33)% calcium chloride, where X is the weight% of zinc bromide in the brine; . 7. The brine according to claim 6, having a density of 1.70 to 1.92 g/cm ³ (14.2 to 16.0 ppg). 8. The brine according to claim 7, wherein the concentration of hydroxyethyl cellulose is 0.71 to 0.71.
14.3 mg/cm ³ (0.25-5.0 lb/42 gallon barrel). 9. The brine according to claim 7, wherein the concentration of hydroxyethyl cellulose is 0.71 to 0.71.
8.6mg/ ^cm3 (0.25-3.0 lb/42 gallon barrel)
something that is. 10. The brine according to claim 6, 7, 8 or 9, wherein the hydroxyethyl cellulose is activated in the brine so as to be hydrated at room temperature.