Patent Number: 056132425
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates a schematic flow diagram showing the process disclosed in this invention. Solid waste, which contains mainly barium sulfate and trace amounts of radioactive material such as radium and are accumulated as scales during oil and gas production operations, is sent to a central solid waste processing chamber 10. Other naturally occurring radioactive material such as uranium or thorium may also deposited on the barium sulfate scale. Such solid waste can be delivered to the processing chamber 10 in a continuous manner. However, since the amount of solid waste to be processed is generally not very large, a batch mode is generally adequate. The processing chamber 10 contains an inlet 11 and an outlet 12 for receiving and exiting treatment water, respectively. The treatment water is produced from a first subterranean formation 20. The first subterranean formation 20 can be an aquifer or a partially or completely depleted hydrocarbon-bearing and water-bearing formation containing movable water. It is preferred that the first subterranean formation has a relatively high formation temperature, preferably at or above 300 degrees Fahrenheit. Such a high temperature is preferred because the solubility of barium sulfate increases significantly with temperature. It is also preferred that the produced water contains large amounts of other dissolved cations such as sodium, potassium, calcium, magnesium, ferric, ferrous, etc. It is well-known that the presence these cations decreases the activity of barium ions and thereby increases the solubility of barium sulfate. Therefore, it is preferred that the produced water contains at least 3% of total dissolved solids. Water is produced from the first subterranean formation 20 and delivered through a subsurface tubing system 21 and a surface tubing stem 22 into the inlet of the solid processing chamber 11. The solid processing chamber 10 may be provided with a mixing means 13, such as an impeller, a rotating rake, or any turbulence generating means. The solid processing chamber 10 should have enough space to provide enough residence time to achieve saturated or nearly saturated barium solution, in order to reduce the amount of water required. Water containing dissolved ions exits the solid processing chamber 10 through an exit means 12. Since pressure improves the dissolution of barium ions, it is preferred that a valve 15 or other pressure-maintaining means be placed at or after the exit means 12 to maintain means be placed at or after the exit means 12 to maintain a desired pressure inside the solid processing center 10. After the solid processing chamber 10, the treated water is injected into a second subterranean formation 30 via an injection surface piping system 32 and an injection subsurface tubing system 31. To maintain the treatment water at the desired temperature, it is preferred that all the surface pipes be insulated to prevent or minimize heat loss. Optionally, a heating means can be provided in the solid processing chamber 10. However, since the amount of water to pass through the processing chamber 10 is very large, it may not be practical to apply such external heat. A filter means 14 can be provided at or after the exit means 12 to avoid causing wellbore damage due to undissolved solids. The second subterranean formation 30 can be an aquifer or a hydrocarbon-bearing formation. It is preferred that the second subterranean formation 30 is a partially or completely depleted oil or gas reservoir. It is further preferred that the second subterranean formation 30 is a partially or completely depleted gas reservoir because of its favorable compressibility. In the preferred embodiment, the first subterranean formation 20 has a substantially greater formation pressure than the second subterranean formation 30. Such a naturally available hydraulic head allows the treatment water to circulate the solid waste treatment system of this invention without any externally applied pumping means. Since pumps are often the major source of fluid leaks, the process disclosed in this invention provides an essentially leak-proof and maintenance-free system for the disposal of radioactive solid waste in a safe, economic and environmentally acceptable manner. If the second subterranean formation underlies one or more permeable subterranean formations, the space between the injection subsurface tubing system 31 and the wellbore 33 should be carefully cemented to prevent any slippage of the injection water into any of the formations. Such a cementing is also desirable about the production subsurface tubing system 21. Most of the radioactive material contained in the injected water will be absorbed by the reservoir rocks in the second subterranean formation, therefore, they are stored in a very safe and environmentally acceptable manner. FIG. 2 depicts a schematic of the primary flow paths to carry out the present invention. The asterisks in FIG. 2 depict the points in the process of radiation monitoring. A production well 40 penetrates a production reservoir 42 and production fluid is forced under pressure or is drawn to a hydrocarbon separation unit 44. The hydrocarbon separation unit separates water and hydrocarbons from the production well 40. It typically consists of a heater/treater, chemical injection equipment for scale and emulsion control, a separator, a gas dehydrator, and associated piping. In known production systems, the separator 44 throughputs the produced water to a disposal well. A pre-processing/grinding unit 46 prepares naturally occurring radioactive material (NORM) for a subsequent dissolution or microemulsion processing. The unit 46 consists of a hydrocarbon separation unit where any liquids associated with the NORM are removed and recovered, if the concentration of the NORM is sufficiently high to make this process economically feasible. Separation of hydrocarbon liquids from the NORM in the unit 46 may further require de-emulsifying chemicals. When the hydrocarbons have been removed from the NORM, the unit also provides a means of wet grinding for reduction of the particle size of the solid waste. Slurry from the grinding unit 46 is passed to an acidification unit 48. This unit 48 comprises a process tank or vessel. NORM solids that are acid soluble, as well as non-NORM acid soluble materials, are removed in the acidification unit 48. Although barium sulfate is not very soluble in acid, other scale materials that are included with the barium sulfate are indeed soluble in acid. Such material include calcium and iron carbonate. Liquids and gases from this unit are injected into the produced brine for disposal into a disposal well 60 through an outlet line 50. The liquids and gases from the acidification unit 48 pass through a filtration unit 52, before injection into the disposal well, to minimize plugging of the disposal injection well 60. To assist in the injection of fluids into the disposal well, the system may include injection pumps 54, although with proper AP, the pumps are not required. Effluent from the acidification unit 48 passes to an enhanced emulsification/dissolution (EED) unit 56 which also comprises a process vessel or tank. Solid materials are passed from the acidification unit for dissolution of micro-emulsion (slurry) formation and disposal. If the process is micro-emulsion disposal, the solids from the EED unit 56 are disposed of downhole through a discharge line 58. If dissolution is used in the process, the solids from the EED unit 56 are returned to the acidification unit 48 via a return line 59 and water is disposed downhole into the well 60. As shown in FIG. 2, each of the pre-processing grinding unit 46, the acidification unit 48, and the EED unit 56 is encased in a jacket 61. In the present invention, solutions and gases and/or the microemulsion are disposed of in the disposal well 60. No gases or solutions, other than the recyclable reagents, are left on the surface. When reagents are expended, they are disposed of, along with other waste, down hole. No "live" acid is injected into the disposal well since the acid is neutralized before disposal. With proper management of the surface pressure of the system, the pressures push the fluids through the disposal well and no pumps are required for this purpose. However, certain geologic structures may require the use of pumps. As shown in FIG. 2, radioactivity is monitored at a number of points in the system to insure worker safety, as well as the environmental integrity of the system. Although it is assumed that some solid material will remain at the end of the disposal scheme, these will consist of produced sands and fines that are non-NORM and not readily soluble. These material are continuously monitored for radiation. No solids are released into the environment that violate regulations concerning NORM. This invention discloses a process for the safe and economic disposal of solid waste that contains radioactive material. Although the best mode contemplated for carrying out the present invention has been herein shown and described, it will be apparent that modification and variation may be made without departing from what is regard to be the subject matter of the invention. For example, although this invention contemplates to be most applicable in oil and gas production operations, it can be equally applicable to dispose radioactive solid wastes generated from other sources.