Patent Application
20080164068
1. Field
Embodiments disclosed herein relate generally to a system and method for cleaning drill cuttings. Specifically, embodiments disclosed herein relate to a system and method for cleaning oil-contaminated drill cuttings with a washing fluid containing degassed water.
2. Background Art
When drilling wells in earth formation, drill cuttings are generated. That is, as a drill bit pulverizes or scrapes the earth formation at the bottom of the borehole, small pieces of formation are dislodged by the cutting action of the teeth on the drill bit and left behind. Drilling fluid circulating through the surface and the bottom hole carries the solid particles of rock and formation to the surface. The fluid exiting the borehole from the annulus is a slurry of drill cuttings in drilling fluid. The drill cuttings are removed before the drilling fluid may be recycled.
Typically, drill cuttings which are transferred to the surface are contaminated by oil or oil-based drilling fluid and, therefore, need to be cleaned for an environmentally safe disposal. Without cleaning such oil-contaminated drill cuttings, the drill cuttings are required to be moved from the offshore rig to an onshore disposal facility, which may increase the overall cost of oil production.
A variety of systems and techniques have been developed to clean oily contaminants from drill cuttings. In one example, the oil is burned off the drill cuttings by a thermal procedure. In another example, the oil is cleaned using solvents or detergents. However, these conventional methods may cause other environmental problems as a result of the chemicals used or oil burned. Furthermore, the conventional methods may be expensive because they require using and disposing of chemicals and/or transporting drill cuttings to an onshore location.
Accordingly, there exists a need for an improved system and method for safely cleaning oil-contaminated drill cuttings prior to disposal.
In one aspect, embodiments disclosed herein relate to a system for cleaning drill cuttings, the system including a degassing module configured to substantially degas water; a washing module in fluid communication with the degassing module configured to wash drill cuttings with a washing fluid containing the degassed water; a gassing module in fluid communication with the washing module configured to gas the washing fluid; and an oil removal module in fluid communication with the gassing module configured to separate oily contaminants from the gassed washing fluid.
In another aspect embodiments disclosed herein relate to a method for cleaning drill cuttings, the method including substantially degassing water; washing drill cuttings with a washing fluid containing the degassed water; gassing the washing fluid; and separating oily contaminants from the gassed washing fluid.
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.
In one aspect, embodiments disclosed herein relate to a system and method for cleaning drill cuttings. In another aspect, embodiments disclosed herein relate to a system and method for cleaning oil-contaminated drill cuttings with a washing fluid containing degassed water.
Water which has been exposed to air typically contains the equivalent of several teaspoonfuls of dissolved gas per liter. By removing such gases entrained in water, the water can become miscible with oil. That is, if gases that are dissolved in water are removed, the water will spontaneously mix with oil. In this regard, Pashley et al has shown that oil and water mix spontaneously to form a cloudy emulsion when almost all the gases have been removed from a water-oil mixture by repeatedly pumping off the gases (see Pashley, R. M. et al, J. Phys. Chem. B 109, pp 1231-1238 (2005), see also http://www.nature.com/news/2005/050124/full/050124-3.html).
In one or more embodiments disclosed herein, drill cuttings having oily contaminants on them are cleaned with washing fluid containing degassed water, which is oil-soluble. The washing fluid may also contain additives, such as corrosion inhibitors, iron control agents, and other washing liquids, in addition to degassed water After washing, the washing fluid goes through a gassing module to entrain gasses, thereby recovering the oil-insolubility of normal water. Oily contaminants which become separable from the washing fluid are removed by further processing.
Process Overview
The washing module 140 is designed to remove oily contaminants on drill cuttings 112. In one or more embodiments, drill cuttings 112 may be subject to a preliminary separation stage to separate drill cuttings from process fluids before being fed to the washing module 140. In such a separation stage, drill cuttings and other solid particulates are removed from process fluids using a shale shaker, vibratory separator, etc. In the washing module 140, various actions to remove oily contaminants from the drill cuttings 112 may be performed. Washing may be performed in a batch process, a continuous process, or a combination thereof. For example, in one embodiment, the drill cuttings 112 may be submerged in the washing fluid 111 or pass through a stream of the washing fluid 111. In some embodiments, washing may be assisted by a shaker, a vibrator, a rotator, a screw, a heater, or other similar devices known in the art. For example, in one embodiment, an accompanying shaker and heater may shake and warm a tank containing degassed water and drill cuttings in order to facilitate washing. In the washing module 140, a separator such as a centrifuge (not shown) may be installed to separate solids containing drill cuttings from the remaining fluid.
Subsequently, a washing fluid 141 including oily contaminants passing through the washing module 140 is fed to a gassing module 170 to entrain gasses into the washing fluid 141, thereby converting the oil-soluble degassed water in the washing fluid 141 to oil-insoluble water. In order to make degassed water oil-insoluble, gases may be injected into the gassing module 170. Examples of gases that may be injected include, but are not limited to, oxygen, nitrogen, carbon dioxide, argon, helium, hydrogen, neon, krypton, nitrogen oxide, and hydrocarbon gases such as methane, ethane, propane, and butane. In one embodiment, aeration (i.e., the process of dissolving air in a liquid) is carried out in the gassing module 170. Gases may be injected by any method known in the art. Gas bubbles may be generated, for example, by an aeration device using a porous hose. Gas bubbles are injected for a predetermined time such that the water in the washing fluid 141 entrains sufficient gasses to recover the lipophobicity. In one embodiment, bubbles may be injected into the washing fluid 141 for a minute, two minutes, or several minutes. In another embodiment, bubbles may be injected into the washing fluid 141 for an hour, two hours, or several hours. One of ordinary skill in the art will appreciate that the amount of time selected for injection of bubbles in the washing fluid may be selected based on a variety of factors, for example, the amount of washing fluid 141 in the gassing module 170 or the amount of oily contaminants in the washing fluid 141, and does not limit the scope of embodiments described herein.
In some embodiments, a gassed washing fluid 171 from the gassing module 170 is fed into an oil removal module 180 to remove oil in the washing fluid 171. In one embodiment, the oil removal module 180 may include a coalescing tank for the removal of oil from the washing fluid 171 and a flocculation tank for fluid flocculation. Recovered oil from the coalescing tank may be sent to an intermediate bulk container (IBC) for storage or piped directly to the client. After the washing fluid 171 flows through the oil removal module 180, an oil-removed washing fluid 181 from the oil removal module 180 may be transferred to a solids removal module 190 for separating solids remaining in the washing fluid 181. Solids 192 removed in the solids removal module 190 and solids-removed washing fluids 191, 191′ may be transferred for further process, disposal, or reuse, as will be described in more detail.
Degassing Module
Shown in
In one embodiment, the degassing module 210 may be purged prior to operating the degassing module 210. For example, the degassing module 210 may be purged for a few minutes, such as approximately ten minutes, prior to operation. In one embodiment, ventilation air is flowed through the degassing module 210. Ventilation air may be supplied to the degassing module 210 from a ventilation supply module (not shown). Additionally, the tank 220 may comprise a pH analyzer (not shown) that monitors the pH of the water in the tank 220. The tank 220 may further comprise a mechanical degasser 226. In this embodiment, the water 201 passes through the mechanical degasser 226, wherein centrifugal force is exerted on the water 201. The centrifugal force of the mechanical degasser 226 multiplies the force acting on the entrained gas bubbles, for example, nitrogen and oxygen, to increase buoyancy of the gas bubbles, thereby releasing an amount of entrained gas bubbles from the water. The increase in buoyancy of the gas bubbles accelerates the bubble-rise velocity. As the bubbles rise toward the surface, they escape the water. One of ordinary skill in the art will appreciate that any device known in the art that will exert a centrifugal force on fluid, thereby reducing the amount of entrained or dissolved gases in the water, may be used.
One commercially available degasser that may be useful in this application is a MI SWACO® CD-1400, available from M-I, LLC (Houston, Tex.). The mechanical degasser 226 may be coupled to the tank 220. Water passes through the mechanical degasser 226, wherein a centrifugal force is exerted on the water to facilitate removal of entrained gases from the water. The mechanical degasser 226 may be controlled by a programmable logic controller (PLC) 223a that activates the mechanical degasser 226 once the level of water in the tank 220 reaches a predetermined level for safe operation of the mechanical degasser 226. At least one blower 224, 225 may be coupled to the mechanical degasser 226 to extract gas removed from the water. In one embodiment, entrained gases may be removed and sent to a gas treatment module (not shown), a storage (not shown) or released into the air.
In one embodiment, the degassing module 210 comprises fluid samplers 237 that extract samplings of the water. In this embodiment, the degassing module 210 further comprises an entrained gas measurement 236. The entrained gas measurement 236 may be any known device for measuring the amount of gases entrained in liquid. For example, the entrained gas measurement 236 may measure gases entrained in water by sampling a predetermined volume of water and gauging the weight of the water. Alternatively, the entrained gas measurement 236 may sample a predetermined weight of water and gauge the volume of the water. Those having ordinary skill in the art will appreciate that measuring may also occur on a continuous basis. For example, entrained gas may be measured by gauging exit streams from the degassing module 210 using a tracer dilution technique.
Once the entrained gas concentration of the water has reached a predetermined concentration, the water may be transferred or flowed to another module, for example, a washing module (described in further detail below with reference to
Washing Module
In one embodiment, the washed drill cuttings may be removed by a centrifuge (not shown) which may be coupled to the washing container 346. In another embodiment, cleaned drill cuttings may remain in the washing container 346 while the washing fluid 311 containing degassed water and oily contaminants removed from drill cuttings are removed from the washing container 346. For example, the fluids may drain through perforated holes (not shown) which may be formed in the bottom of the washing container 346 and recovered afterwards. Alternatively, the fluids may be pumped out of the washing container 346 and fed to a subsequent stage. Recovered drill cuttings may be sampled and disposed of or subject to further cleaning prior to disposal. In this embodiment, the washing fluid 311 containing degassed water is transferred to a gassing module after washing.
Shown in
Drill cuttings may be washed by any method known in the art, and is not limited herein. One of ordinary skill in the art will appreciate that there are numerous washing devices known in the art that may be used to clean drill cuttings with degassed water. The aforementioned washing modules may be used either separately or in combination. For example, drill cuttings may be washed by the flusher 343 as shown in
Gassing Module
Gassing or aeration needs to be performed for substantially considerable amount of time, such that, the water in the washing fluid 471 can entrain sufficient gasses to recover the lipophobicity. In one embodiment, gassing of the washing fluid 471 may be performed for a minute, two minutes, or several minutes. In another embodiment, gassing of the washing fluid 471 may be performed for an hour, two hours, or several hours. One of ordinary skill in the art will appreciate that the amount of time selected for gassing the washing fluid 471 may be selected based on a variety of factors, for example, the amount of washing fluid 471 in the gassing tank 470 or the amount of oily contaminants in the washing fluid 471, and does not limit the scope of embodiments described herein. As air is injected by the aeration device 476 into the washing fluid 471, the degassed water in the washing fluid 471 becomes oil-insoluble and oily contaminants flocculate. The flocculated oily contaminants 478 may migrate to the upper surface of the washing fluid. In one embodiment, the flocculated oily contaminants 478 may be removed at an outlet 477 and drained. One of ordinary skill will appreciate that any method known in the art for removing flocculated oil in water, for example, filters or oil traps, may be used without departing from the scope of the embodiments disclosed herein. After a predetermined time of gassing, the gassed fluid may be transferred to an oil removal module for further oil removal operations.
Oil Removal Module
As shown, the washing fluid 171 containing gassed water enters a first compartment 444 of a coalescing tank 442 having three compartments. A level sensor 456 coupled to the coalescing tank 442 measures the level of gassed water contained in the coalescing tank 442. In one embodiment, the level sensor 456 may be a wire rope sensor disposed inside the first compartment 444 of the coalescing tank 442. Emulsion breakers 469 may be added to the washing fluid 171 by a pump 466 coupled to the coalescing tank 442 to facilitate oil removal from the washing fluid. The washing fluid may then flow over a coalescing filter 460 and a coalescing oil trap 461 that remove oil entrained in the washing fluid 171 and into a second compartment 463 of the coalescing tank 442. The washing fluid 171 in the second compartment 463 may then flow through a weir arrangement 465 into a third compartment 467 of the coalescing tank 442. Oil recovered from washing fluid in the coalescing tank 442 may be transferred to an IBC for storage or piped for reuse.
In one embodiment, washing fluid from the coalescing tank 442 is pumped through a hopper 447 by a pump 445, for example, a centrifugal pump 445, and into the flocculation tank 451. As the washing fluid is pumped through the hopper 447, flocculating chemicals, for example, bentonite, may be added and mixed with the washing fluid. In one embodiment, the flocculating chemicals may be added manually. One of ordinary skill in the art will appreciate, however, that other methods of adding flocculating chemicals to the hopper 447 may be used without departing from the scope of embodiments disclosed herein. The washing fluid may then flow into the flocculation tank 451, wherein suspended particles in the washing fluid aggregate, forming a floc or a mass of fine suspended particles. A mixer 448 or agitator may be disposed in the flocculating tank 451. In one embodiment, the treated washing fluid from the oil removal module 180 may be transferred to another module, for example, a solids removal module 190, by a transfer pump 453 for further processing.
Solids Removal and Filtration Module
In one embodiment, a washing fluid from another module, for example, the oil removal and flocculation module 170, may be pumped through a containment 550 coupled with a belt filter 553. In one embodiment, the belt filter 553 comprises a conveyor 540 having a filter medium 559. In one embodiment, the filter medium 559 may comprise polyester. One of ordinary skill in the art will appreciate, however, that a filter of any of a number of materials may be used so long as it filters out solid material from the washing fluid. As the washing fluid flows through the filter medium 559, solid materials 557 are removed from the washing fluid and retained on the filter medium 559. As washing fluid continues to flow through the filter medium 559, the solid materials retained on the filter medium 559 increases and may blind or clog the filter medium 559. Accordingly, the level of washing fluid on the filter medium 559 increases due to a blockage of flow. A predetermined level of washing fluid on the filter medium 559 may trigger a forward motion (indicated by arrow C) of the conveyor 540 and filter medium 559. In one embodiment, a sensor 558 may detect the level of washing fluid on the filter medium 559. The filter medium 559 is conveyed out of the containment 550, removing the retained solid materials out of the solid materials removal and filtration module 190 for disposal 192. In one embodiment, a sensor 558 may detect the flow rate of the washing fluid through the filter medium 559.
The washing fluid that flows through the filter medium 559 of the belt filter 553 may then flow into a storage tank 554. Once the washing fluid reaches a predetermined height in the storage tank 554, the washing fluid may be transferred by a pump 562, for example, by a centrifugal pump, to at least one filter canister wherein solids particles and hydrocarbons may be removed from the washing fluid. Each of the at least one filter canister comprises a filter, for example, a bag filter or a cartridge filter. In one embodiment, the washing fluid is pumped to a first filter canister 556 of a series of three filter canisters, wherein the first filter 556 canister is coupled to a second filter canister 563 and the second filter 563 canister is coupled to a third filter canister 564. In this embodiment, a plurality of bag filters 565 may be disposed inside the first filter canister 556 to remove solid particles from the washing fluid.
In one embodiment, three bag filters may be disposed in the first filter canister 556 that remove solid particles larger than about 20 microns from the washing fluid. The washing fluid may then flow through the first filter canister 556 and into the second canister 563. A plurality of filter cartridges 566 may be disposed inside the second filter canister 563 for removal of solid particles from the washing fluid. In one embodiment, 28 filter cartridges may be disposed inside the second filter canister 563 that remove solid particles larger than about 10 microns from the washing fluid. The washing fluid may then flow from the second filter canister 563 to the third filter canister 564. A plurality of filter cartridges 566 may be disposed inside the third filter canister 564 for removal of hydrocarbons from the washing fluid.
In one embodiment, 28 filter cartridges may disposed in the third filter canister 564 that remove hydrocarbon larger than about 10 microns. One of ordinary skill in the art will appreciate that the number of filter canisters, the number of filters within a filter canister, and the size of the particles removed by each filter may vary without departing from the scope of embodiments disclosed herein. In one embodiment, differential pressure transducers 567 may be coupled to each filter canister to detect clogging of the filters. In this embodiment, the pressure transducer 567 may signal an operator if the filters become plugged so that the filters may be cleaned or replaced. After the washing fluid has flowed through the filter canisters, the washing fluid 191 may be transferred to another module for further process, disposal, or storage. Alternatively, the washing fluid 191′ may be transferred to a degassing module for reuse.
Embodiments disclosed herein may include one or more of the following advantages. Embodiments disclosed herein can provide an effective and environment-friendly system and method for cleaning oil-contaminated drill cuttings. Embodiments disclosed herein use a washing fluid containing degassed water for cleaning drill cuttings and, therefore, reduce the need to use toxic chemicals and solvents. In addition, because drill cuttings cleaned in accordance with embodiments disclosed herein may have less chemicals and oil on their surface, the drill cuttings may be disposed of offshore without causing environmental problems. Accordingly, advantages in cost and environmental-friendliness may be obtained.
While the present disclosure has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the disclosure as described herein. Accordingly, the scope of the present disclosure should be limited only by the attached claims.
This application, pursuant to 35 U.S.C. § 119(e), claims priority to U.S. Provisional Application Ser. No. 60/871,392, filed on Dec. 21, 2006. That application is incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60871392 | Dec 2006 | US |
