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Introduction:
There is a long standing dispute concerning the presence of measurable and possibly economic amounts of precious metals in certain naturally occurring brine waters. This report specifically considers the possible presence of precious metals in brine waters and other waste co-products that are generated during oil and gas production.
The detection methods described below are easily applied, chemically straightforward, inexpensive to use, and require essentially no hazardous chemicals. It is this author's opinion that the precious metal association as described is indicative of certain geochemical processes that are involved in the formation of oil and gas. Only a few samples from widespread locations of oil and gas production have been evaluated in this study. They all, however, have yielded qualitatively similar results suggesting the possibility of a much broader and more basic concept. The recovery procedures discussed here are currently part of a much broader Patent Pending status.
Sample Evaluation:
The water samples used for testing consisted of produced brine from oil and gas fields located in Oklahoma, New Mexico, and eastern China. They were taken from various stages of production, oil-water separation, and down-hole brine disposal. No attempt was made to preserve these samples other than their storage in newly purchased, clean, plastic 5-gallon water containers with lids. The bottom sediment samples evaluated in this study were exclusively from Chinese oil fields located southwest of Beijing. These samples consisted of particulates from gravity separated tank bottoms that were routinely dredged from large sludge pits, stacked in piles, and allowed to drain. Grab samples from these piles were in the order of 5 to 10 pounds and were stored in sealed plastic bags.
Initially, aliquots of each of the brine water samples were vacuum filtered using 0.5 micron membrane papers and the filtrate was analyzed for dissolved precious element content using mainly gravimetric procedures. No precious elements were detected in any of the filtrates that were analyzed. However, when the filter residue from these samples was observed using a 45X laboratory stereoscopic microscope, variable amounts of very small (in the order of 400 to 600 mesh) particles of metallic gold and silver were identified in all of the residue samples. Many of these precious metal particles were partially to totally coated with a thin layer of an asphaltene-like substance. Subsequent fire assaying and gravimetric analysis of these residues confirmed the microscopic gold and silver identification.
Brine Samples:
Following is a simple procedure for the recovery and identification of suspended particulate matter contained in unfiltered oil field brine water. It should be noted that even if the brine sample appears to be clean and without any apparent suspended particulate matter, very fine-grained suspended material may be present and recoverable using this procedure.
1. Using a clean 5-gallon container (plastic bucket) add a measured amount of the brine sample; 16 liters is suggested. If available, use a small laboratory agitator for mixing the brine water; if not stir manually.
2. Add 3 to 5 drops of Triton X-100 (a non-toxic, nonionic surfactant manufactured by Rohm & Haas). Maintain agitation for 30 minutes.
3. Continue agitation and add 75 grams of commercial filter-grade diatomaceous earth. Continue agitation for 30 minutes.
4. Cease agitation and let slurry settle for approximately 1 hour. Carefully decant and discard the supernate. For a visual identification of contained gold and silver and a possible indication of the presence of platinum-group elements it is suggested that the remaining residue from the decant be washed into a shallow gold pan. This residue may then be carefully pan concentrated and observed microscopically.
5. The residue (or pan concentrate) from the decant is placed in a beaker and while agitating the pH is lowered to approximately 4-5 with HCl. After a few minutes the pH is then raised to approximately 9 with VenMet (a reducing agent consisting of a dispersion of sodium borohydride in sodium hydroxide: use with care; manufactured by Rohm & Haas).
6. After the VenMet reaction has ceased (approximately 15 to 30 minutes), the reduced slurry is vacuum filtered and the washed filter residue dried at approximately 300 degrees C.
7. The dried residue may be assayed using conventional methods such as fire assay or ICP/AES.
The metallic gold values recovered from the various oil field brines tested in this study ranged from 0.7 mg/liter to 5.5 mg/liter. The metallic silver values likewise recovered ranged from 0.2 mg/liter to 8.2 mg/liter. These gold and silver values were determined by conventional fire assay methods. It is important to note that none of these brine samples gave negative test results for gold and silver. There were no observed consistent ratios of recovered gold to silver, however, it should be noted that the subject brine samples came from all aspects of brine production and disposal. No attempt was made at determining a material balance of suspended particulate matter from any producing well or field. The values recovered are only indicative of the general order of magnitude of abundance. It is strongly suspected that platinum-group elements were also present in the residue samples derived from at least some of the tested brines.
Bottom Sediment Samples:
The only bottom sediment samples evaluated in this study were from a complex of oil fields located southwest of Beijing, China. These samples were randomly taken from piles of bottom sediment that were formed from the dredging of settled particulates in large oil sludge pits. These pits were being filled with tank bottoms from large oil-water gravity separation units. The samples contained approximately 90 percent medium to coarse-grained silicates that were produced from the friable oil reservoir rocks. This oversized matrix material is easily removed from the much finer-grained precious metal particles by a combination of screening and pan concentration. This procedure exposes the approximately 400 to 600 mesh metallic gold and silver; some of which has no visible coating and some of which is coated with an asphaltene-like substance. Since larger amounts of material are conveniently available from these dredged samples, as compared to that recovered from brine water residues, the presence of numerous fine-grained, black to gray, metallic spheroids and pelletal material is more readily apparent. In the author's experience, these unique mineral forms and occurrence suggest the possible presence of platinum group metals.
In order to obtain a more representative estimate of the quantitative abundance of precious metals in bottom sediment material it is suggested that the same procedure used to evaluate the brine samples be also used to evaluate bottom sediment samples. Among other advantages, when using this procedure much of the oily substance can be removed from the sample. Depending on the composition of the sample, additional Triton X-100 and diatomaceous earth may have to be used.
As there was a sufficient amount of concentrate residue available from these bottom sediment samples for spectrographic determination, the panned concentrate from one of the bottom sediment samples was submitted for commercial ICP/AES analysis. The results were: Au = 0.229 Troy ounces per ton, Ag = 2.874 Troy ounces per ton, Pt = not detected, Pd = 0.024 Troy ounces per ton.
Conclusion:
It is the general purpose of this communication to both report the possibly ubiquitous presence of very fine-grained, metallic gold, silver, and at least some platinum-group elements, in produced oilfield waste products and to hopefully encourage others to confirm these observations. The potential theoretical and practical applications of the observations made in this study are enormous. Why hasn't this unusual precious metal occurrence been previously described? Apparently, the answer is, "We just didn't look!"
A. C. Johnson, Jr., PhD. http://www.acjohnson.us This website considers new and innovative concepts and procedures that pertain to mineral and oil and gas exploration and development.
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