Process for removing mercury from tools and equipment

Abstract

A process for removing a heavy metal, such as mercury (Hg), from thturboe surface of a component used in the oil and gas industry, such as a sampling bottle or piece of equipment, is provided. The process includes applying an organic solvent, which includes iodine, to the surface of the component and then applying an aqueous solution to the surface. The organic solvent can also include toluene, xylene, a mixture thereof, or suitable organic solvents. The aqueous solution can consist of anions that form a soluble complex with the heavy metal, such as thiosulfate (S2O3)2-, iodide (I-), or a thiosulfate salt. According to another embodiment, the aqueous solution includes I2 and I-, and the process further includes applying an acid having a pKa ranging from -14 to 2 to the surface followed by deionized water.

Description

PROCESS FOR REMOVING MERCURY FROM TOOLS AND EQUIPMENT TECHNICAL FIELD

[0001] This disclosure relates to a process for removing heavy metals, such as mercury, from tools and equipment used in the oil and gas industry. BACKGROUND

[0002] This section is intended to introduce the reader to various aspects of art related to various aspects of the present disclosure, which are described and / or claimed below. This discussion is believed to help provide the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light and not as admissions of prior art.

[0003] In the oil and gas industry, heavy metals, such as mercury (Hg), can be naturally present in trace amounts in reservoirs and produced fluids. It is important to accurately determine Hg levels in upstream reservoirs, reservoir fluids, crude oils, and downstream refinery units, fuels, and products. The accurate determination of Hg is often essential for process equipment design considerations, mercury removal requirements when processing hydrocarbons, and product quality assessment. For example, reliable sampling of the fluids to determine Hg levels during exploration and in appraisal wells in the oil and gas industry provides an essential reference to estimate Hg levels that will be present in produced fluids. The reliable sampling and determination of Hg levels also enable the in-time incorporation of appropriate Hg management approaches and related economic assessments.

[0004] However, many processes used to analyze Hg in downhole fluid samples historically have been found unreliable. Causes of the unreliability include the presence of residual Hg on the surfaces of the bottles used for the sampling, significant adsorption of theHg on the inner surfaces of the bottles used for the sampling, and insufficient recovery of the residual Hg in the sampling bottles. These bottles can be formed of various materials, such as polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), metals, and glass. Methods used to decrease adsorption of the Hg in the bottles include applying a coating, such as Dursan® or Sulfinert®, to the inner surfaces of the bottles and post-rinsing the bottles. However, it remains a challenge to recover and reliably analyze residual Hg from sampling bottles fully.

[0005] Another problem associated with mercury presence within value chain of the oil and gas industry is that trace levels mercury present in produced fluids can deposit and accumulate on production facility equipment, such as production tubing, flowlines, separators, and storage tanks. The equipment is typically made of metal, such as stainless steel, nickel, copper, titanium, molybdenum, or alloy. Characterizing and removing mercury from impacted equipment can be a challenging task for operations.

[0006] Thus, there remains a need to improve methods used to remove mercury from tools and equipment used for different purposes and stages in the oil and gas industry, ranging from appraisal to production and final decommissioning. SUMMARY

[0007] A summary of certain embodiments disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass various aspects that may not be set forth below.

[0008] One aspect of the disclosure provides a process for removing a heavy metal, such as mercury (Hg) from a surface of a component used in the oil and gas industry. Theprocess includes applying an organic solvent to the surface and applying an aqueous solution to the surface after applying the organic solvent. The organic solvent includes iodine (I2), and the aqueous solution includes anions that form a soluble complex with the heavy metal.

[0009] Another aspect of the disclosure provides a process for removing a heavy metal from a surface of a component used in the oil and gas industry, wherein the process includes applying an organic solvent containing iodine (I2), to the surface; applying an aqueous solution including I2and I- to the surface after applying the organic solvent; and applying an acid to the surface after applying the aqueous solution. The acid has a pKa ranging from -14 to 2.

[0010] Another aspect of the disclosure provides a process for removing mercury from a surface of a component used in the oil and gas industry, wherein the process includes applying an organic solvent containing iodine (I2) to the surface; and applying an aqueous solution to the surface after applying the organic solvent. The aqueous solution includes anions that form a soluble complex with mercury, or the aqueous solution includes I2 and I-. The process further includes measuring the amount of mercury in a fluid in contact with the surface after applying the organic solvent and the aqueous solution to the surface. DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0011] The disclosure generally relates to a multi-step process for removing a heavy metal, such as mercury (Hg), from containers, tools, instruments, equipment, or other components used in the oil and gas industry. Although the remaining sections of the disclosure will refer to Hg removal, it is noted that the disclosure could additionally or alternatively relate to removing another metal from a surface. The Hg can be present in different forms, including elemental Hg or in an Hg-containing compound. When the process includes removing Hg from a container, such as residual mercury present on the interiorsurfaces of a sampling bottle, the sampling bottle can be reused, and the amount of Hg present in a future fluid sample can be accurately measured. The removal of Hg allows for a more accurate estimate of Hg level present in a production fluid or reservoir. The removal of Hg also cleans and prevents damage to the surface of the container, tool, instrument, or piece of equipment. The process disclosed herein can also reduce the amount of Hg that has been adsorbed into the surface of the container, tool, instrument, or piece of equipment. More specifically, the process generally includes applying an organic solvent and an aqueous or water-based solution to a surface, such as a surface of the container, tool, or equipment that has been exposed to mercury.

[0012] According to one embodiment, the process is applied to a container or tool used for downhole sampling of a fluid, typically a fluid contained in a reservoir. The container is typically formed of polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), metal, or glass. The container can be a bottle or another type of container. Prior to applying the organic solvent and the aqueous solution, the process includes flashing any gas or liquid out of the container.

[0013] After the gas or liquid is removed from the container, the process includes applying the organic solvent to the surface of the container to wash residual mercury from the surface of the container. Typically, the container is rinsed with the organic solvent. The organic solvent contains iodine (I2) and can also include a suitable organic solvent including those having a carbon number ranging from C7 to C20, such as between C7 and C18, for example between C7 and C16. Specific, non-limiting examples of organic solvents include toluene, xylene, or a mixture thereof. The boiling point of the organic solvent typically ranges from 93 ℃ to 316 ℃, for example from 110 ℃ to 304 ℃), or for example from 137 ℃ to 301 ℃.

[0014] The iodine concentration in the organic solvent typically ranges from 200 mg / L to 10,000 mg / L. However, iodine concentration in the organic solvent could be less than 200 mg / L or higher than 10,000 mg / L. An amount of the organic solvent can be applied to the container a single time or multiple times to adequately wash the surfaces of the container. The organic solvent is then flashed out of the container.

[0015] Once the organic solvent is removed from the container, the aqueous solution is applied to the surfaces of the container to further remove Hg and help to ensure Hg recovery from the bottle. Typically, the container is rinsed with the aqueous solution. Different compositions can be used for the aqueous solution. According to one embodiment, the aqueous solution contains anions that can form soluble complexes with mercury, specifically Hg2+. These anions include, but are not limited to thiosulfate (S2O3)2-, iodide (I-), and other complexing agents. Other example complexing agents include thiosulfate salts, such as sodium thiosulfate. A typical dosage of complexing agent is about 0.05 to 0.15 weight percent (wt. %), for example 0.10 wt. %, based on the total weight of the aqueous solution. However, the dosage can be increased or decreased, depending on the estimated amount of Hg present.

[0016] According to another embodiment, the aqueous solution applied to the surface of the container contains I2 and I- (I2 / I-), and then an acid digestion is applied to the surface of the container. In other words, the container is typically rinsed with an acid. According to example embodiments, the acid used for the acid digestion step is sulfuric acid (H2SO4). Other suitable acids include hydrochloric acid (HCl), phosphoric acid (H3PO4) and nitric acid (HNO3). The pKa of the acid typically ranges from -14 to 2, for example -10. According to one example, the process includes applying 100ml of aqueous solution containing 0.4 M KI / 0.2M I2 to the container, and then rinsing the container with 100 ml of H2SO4 having a pH ranging from 2.0 to 2.2. Finally, the process includes applying deionized (DI) water to thesurface. Typically, this includes rinsing the container with the DI water. This step is especially important when the process includes the acid digestion step.

[0017] According to another embodiment, the process is applied to equipment used in the oil and gas industry, for example a tank, pipe, instrument, production tube, flowline, separator, or storage tank. The equipment is typically used to store or transport production fluid, or fluids and gases used to manufacture the production fluid. The equipment is typically formed of metal, such as stainless steel, nickel, copper, titanium, molybdenum, or alloys thereof. Prior to applying the organic solvent and the aqueous solution, the process preferably includes removing any gas or liquid from the surface of the equipment.

[0018] As in the first embodiment, the process includes applying the organic solvent containing iodine to the surface of the equipment to wash residual mercury from the surface. According to example embodiments, the organic solvent further includes toluene or xylene. The iodine concentration in the organic solvent typically ranges from 200 mg / L to 10,000 mg / L. However, iodine concentration in the organic solvent could be less than 200 mg / L or higher than 10,000 mg / L. The organic solvent can be circulated to enhance the efficiency of the Hg removal. An amount of the organic solvent can be applied to the surface a single time or fresh organic solvent can be applied to the surface multiple times, as needed, in order to wash the surface adequately. Next, the organic solvent is removed from the surface.

[0019] As in the first embodiment, the process includes applying the aqueous solution to the surface of the container to remove Hg from the surface further. Different compositions can be used for the aqueous solution. According to one embodiment, the aqueous solution contains anions that can form soluble complexes with mercury, specifically Hg2+. These anions include but are not limited to, thiosulfate (S2O3)2-, iodide (I-), and other complexing agents.

[0020] According to both embodiments, to apply the organic solvent and the aqueous solution, the process includes applying a pre-wash solvent to the surface of the container or equipment and then collecting a sample of the pre-wash solvent in order to determine the level of Hg present prior to applying the organic solvent and aqueous solution. After applying the organic solvent and aqueous solution, the process includes applying a post-wash solvent to the surface and collecting a sample of the post-wash solvent in order to determine the level of Hg present after applying the organic solvent and aqueous solution. If multiple cycles of the organic solvent and aqueous solution are applied to the surface, a sample of the post-wash solvent can be collected and analyzed to determine the Hg concentration after each cycle. The concentration of the Hg present in the pre-wash solvent sample can be compared to the concentration of the Hg in the post-wash solvent sample to determine the efficiency of the Hg removal process. The process could alternatively include rinsing the container or other surface with the post-wash solvent after applying the iodine-containing aqueous solution and before the acid digestion step. An example of the pre-wash and post-wash solvent is ethylene glycol monobutyl ether (EGMBE), also referred to as 2-butoxyethanol.

[0021] There are several advantages associated with the two-step Hg removal process described herein. One advantage is that the risk of corrosion related to using an iodine solution (in the organic solvent) as a rinse is minimized since the process includes applying the aqueous solution immediately after the iodine solution. Applying iodine in the organic solvent, instead of in the aqueous solution, significantly lowers the corrosion risk. The iodine used in the organic solvent can dissolve or mobilize different forms of Hg, including elemental and Hg-containing compounds, such as HgS.

[0022] The specific embodiments described above have been shown by way of example, and it should be understood that these embodiments may be susceptible to various modifications and alternative forms and can also be used in any appropriate combination. Itshould be further understood that the claims are not intended to be limited to the particular forms disclosed, but rather to cover all modifications, equivalents, and alternatives falling within the spirit and scope of this disclosure.

Claims

CLAIMS 1. A process for removing a heavy metal from a surface of a component used in the oil and gas industry, the process comprising the steps of: applying an organic solvent to the surface, the organic solvent containing iodine (I2); and applying an aqueous solution to the surface after applying the organic solvent, the aqueous solution including anions that form a soluble complex with the heavy metal.

2. The process according to claim 1, wherein the organic solvent includes has a carbon number ranging from 7 to 20.

3. The process according to claim 1, wherein the iodine concentration in the organic solvent ranges from 200 mg / L to 10,000 mg / L.

4. The process, according to claim 1, wherein the anions include at least one of thiosulfate (S2O3)2-, iodide (I-), and a thiosulfate salt.

5. The process, according to claim 1, wherein the heavy metal is mercury (Hg).

6. The process, according to claim 1, wherein the component is a container for sampling a fluid.

7. The process according to claim 6, wherein the container is formed of polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), metal, or glass.

8. The method of claim 1, wherein the organic solvent has a boiling point ranging from 93 ℃ to 316 ℃.

9. The method of claim 8, wherein the equipment includes at least one of a tank, pipe, instrument, production tube, flowline, separator, and storage tank.

10. The method of claim 8, wherein the equipment is formed of stainless steel, nickel, copper, titanium, molybdenum, or an alloy.

11. A process for removing a heavy metal from a surface of a component used in the oil and gas industry, the process comprising the steps of: applying an organic solvent to the surface, the organic solvent containing iodine (I2); and applying an aqueous solution to the surface after applying the organic solvent, the aqueous solution, including I2and I-; applying an acid solution to the surface after applying the aqueous solution, the acid having a pKa ranging from -14 to 2.

12. The process, according to claim 11, wherein the organic solvent has a carbon number ranging from 7 to 20.

13. The process according to claim 11 further including applying deionized water to the surface after applying the acid.

14. The process, according to claim 11, wherein the heavy metal is Hg.

15. The process, according to claim 11, wherein the component is a container for sampling a fluid.

16. The process, according to claim 15, wherein the container is formed of polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), metal, or glass.

17. A process for removing mercury from the surface of a component used in the oil and gas industry, the process comprising the steps of: applying an organic solvent to the surface, the organic solvent contains iodine (I2); applying an aqueous solution to the surface after applying the organic solvent, the aqueous solution including anions that form a soluble complex with mercury, or the aqueous solution including I2and I-; and measuring the amount of mercury in a fluid in contact with the surface after applying the organic solvent and the aqueous solution to the surface.

18. The process, according to claim 17, wherein the organic solvent includes has a carbon number ranging from 7 to 20 and a boiling point ranging from 93 ℃ to 316 ℃.

19. The process according to claim 17, wherein the iodine concentration in the organic solvent ranges from 200 mg / L to 10,000 mg / L.

20. The process, according to claim 17, wherein the component is a container, tank, pipe, instrument, production tube, flowline, separator, or storage tank.