CLEANING OF DRILL CUTTINGS AND APPARATUS THERFOR

Abstract: The present invention comprises a process and apparatus for removing nonpolar organic contaminants including oil from particulate solids, wherein said solids are brought in contact with an extracting agent.

Description: CLEANING OF DRILL CUTTINGS AND APPARATUS THERFOR The present invention comprises a process and an apparatus for removing nonpolar organic contaminants including oil from particulate solid wherein said solids is brought in contact with an extracting agent. The use of natural gas as an extracting agent is also described in the present invention. Components from the drilling and well-operations represents 94% of total discharge of chemicals from the offshore oil industry in the Norwegian sector (Mil- jøsok report, 1996, OLF) . Oil-based drilling fluids have traditionally been favoured over aqueous based systems because they are more cost-efficient. The resent development in directional drilling techniques has further dictated the need for more efficient environmental friendly drilling fluids. Following the complete ban against the discharge of oil-based drill cuttings in the early 9CVs, a new generation of synthetic drilling fluids emerged. These fluids were based on alkyl-ester or- ethers and poly-alfa-olefines. They were classified as «non toxic» and were permitted to be discarded overboard. These synthetic drilling-fluids offers the same drilling performance as oil-based drilling-fluids, but at a significantly higher cost. Recent research indicates however that these synthetic fluids represent an envi- ronmental hazard, and their use is expected to be restricted in the near future (Miljøsok report, 1996, OLF). It appears that the industry has no other alternative than using oil-based drilling fluids in the future. The drill cuttings will either have to be disposed on-shore or re-injected into the reservoir. Both alternatives are extremely expensive. It appears however that re-injection is generally favoured by both the legislators and the industry. According to the Norwegian Pollution Control Authority there are not yet any specific guidelines for the disposal of produced sand, and it is generally assumed that the current guidelines and legislation for disposal of «drill cuttings* might also apply for produced sand. The maximum residual oil content for overboard disposal of drill cuttings is 1.0%. Sand or drill cut- tings with higher oil contents is considered «toxic waste» and has to be either re- injected into the reservoir or brought on shore for processing. The Norwegian patent application number 19953419 (PCT/NO00060), Inge Brun Henriksen et al, describes a method for NGL extraction-techniques for de-oiling of produced water. The process does not include removal of organic contaminants from solids. The use of supercritical extraction techniques to remove and recover oil from cut- tings was first proposed in 1981 by C.P.Eppig et al in US-patent no. 4.434.028. US 4.434.028 relates to a method and apparatus for removing oil and other organic constituents from inorganic-rich mineral solids, particulate drill cuttings. The solids to be treated are transferred into pressure vessel means wherein they are contacted with an extracting agent which is normally a gas such as e.g. dichloro- difluoromethane, propan, carbondioxide, ethane and ethylene. The gas is under condition of pressure and temperature to provide the extracting in a fluidic solvent state for the constituents to be removed. The extracting containing the constituents is withdrawn from the pressure vessel and depressurized and forms a two-phase system. The two-phase system can be separated by distillation into a vapour phase containing the extracting and a liquid phase containing oil and organic constituents. The method described in US 4.434.028 is a very expensive extraction process comprising the use of pure gas components as an extracting agent followed by compression- and to-steps distillation procedures to fully recover the extracting agent which is pure gas components. In order for the process to be eco- nomic feasible, full recovery of the extracting agent (99.7%) is required. The process described in US 4.434.028 is based on using liquid gas (i.e.CO 2 , Propane or Freon) to extract the oil and to fully recycle the gas (99.7%). The proposed process has apparently never been scaled up to an industrial plant . As the oilfields matures and the water-cut increases, more sand from the reservoir formation tends to follow the production stream in some oilfields. The sand settles in the separators and are periodically washed out and disposed by re-injection or brought ashore for disposal or processing. One object is therefore to provide an inventive and cost-effective process for cleaning of oily-drill cuttings and sand to allow overboard discard of the cuttings. The present invention concerning a method of extracting oil from drill cuttings and sand offshore. The method is based upon using natural gas liquid (NGL) as a solvent to extract the oil from the sous. The process has been successfully tested in 2 lab-scale and the results shows less than 1.0% by weight of the maximum residual oil content for overboard disposal of drill cuttings. Further, the present invention reduces the investment and operation costs to a fraction of that which was proposed in US 4.434.028 since NGL is available from the production flw-lines at most oil and gas production facilities. Further, the present process is considerably distinct from other extraction processes in that it is carried out with no «solvent- recovery». One further object with the present invention is a significant saving in chemical costs and utility requirement compared to re-injection or on-shore disposal of drill cuttings. The present invention comprises a process for removing nonpolar organic contaminants including oil from particulate solids, wherein said solids are brought in contact with an extracting agent in which: a) the particulate solids are conveyed into a pressure vessel to which an extracting agent is added in the form of natural gas liquids (NGL), whereby the organic contaminants from the particulate solids are dissolved in the extraction agent to form a single phase solution; b) whereafter said solution containing the extraction agent and nonpolar organic contaminants without any separation is added to a production flow; c) and the clean particulate solids are discarded. It is an object of the present invention that the extracting agent is a condensate collected from a production flow in the form of natural gas liquid. The cleaned particulate solids contains less than 1 % by weight of organic nonpolar contaminants, more preferably less than 0.5% by weight . The particulate solids comprise drill cuttings and sand in the present invention. An apparatus for removing nonpolar organic contaminants from drill cuttings is also described in this invention where said contaminated drill cuttings are contacted with an extractant to form a solution of said extractant and said contaminants, comprising: - means for discarding clean drill cuttings after said contacting; - means for conveying said solution to a production flow. A scope of the invention is also the use of natural gas liquid as an extracting agent for removing organic nonpolar contaminants including oil from particulate solids. The present process comprises the use of condensate (NGL) as a solvent to clean the drill cuttings and sand. Use of natural gas liquid according obtained from the production flow-line of oil and gas producing facilities is also object of the present invention.The NGL is conveyed from one of the production condensate flows at e.g. an oil drilling platform and used as a solvent and subsequently added back to the production mainstream. A preliminary evaluation of the gas-condensate streams at several Nort Sea oilfields (Statfjord, Sleipner, Valhall, Ekofisk, Forties, Andrew) indicates that condensates (NGL) with the right thermodynamic properties to act as a solvent are available in sufficient quantities at these production fa- cilities. It is most likely that most oil and gas production facilities in the North Sea have access to such condensates. The use of a NGL flow for extracting and subsequently adding the extract into the main production flow is a novel and cost-effective process. The process is carried out without «solvent-recovery» and with minimum utility requirement. Figure 1 shows the experimental set-up for the extraction of drill cuttings with NGL. NGL is conveyed from e.g. a NGL container (1) through a valve (2) and a pump (3), and further trough the pipe 4. The NGL is conveyed through a valve 5 and further pumped to an extracting cell (6) in which the drill cuttings are cleaned. The flow (7) containing NGL and the organic contaminants may optionally be conveyed to a production flow-line. The Figure 2 shows a phase diagram of the available NGL, and figure 3 showes the residual oil versus void volumes of NGL. Exampel 1 Three different types of oil based drill cuttings (Interdrill NT) were used for the experimental validation, as presented in Table 1. The oil and water content was de- termined by applying the standard distillation procedure, using a retort. Table 1 : Drill cuttings overview. Well 34/10-D4H 34/10-G- 30/3-A9A (Gullfaks) 2T2H (Veslefrikk) (Gullfaks) oil content (wet sam7.2 8.1 18.6 ple) oil content (dry sam7.8 9.0 20.7 ple) water content 7.8 9.5 10.1 The two Gullfaks samples look very similar though the one from well 34/10-D4H has bigger particles than the one from 34/10-G-2T2H. The 34/10-D4H sample from a Shetland formation is described as interbedded sands and siltstone. The drill cuttings from Veslefrikk contain mainly sand particles. Experimental Set-up Figure 1 shows the experimental set-up for the extraction of drill cuttings with NGL. The NGL was pumped through the extraction cell and afterwards passed through a sapphire glass window which enabled visual control of the flow. The oil was collected in a glass bottle after choke valve and weighted. The volume of the whole cell is 737 ml and the volume for the extraction of the drill cuttings 537 ml. All experiments were conducted at 30 bar, 60°C with a NGL with composition corresponding to an average molecular weight of 57.9. Total composition is presented in Table 2 and the corresponding phase-diagram in Figure 2. The pressure and temperature conditions for extraction is determined by the phase diagram of the available NGL. The following conditions must be met: 5 • The NGL has to be in liquid state at the pressure and temperature of extraction. • The NGL has to be in gaseous state at atmospheric pressure at the extraction temperature. It is apparent from the phase diagram of the available NGL (Figure 2) that at 60°C, the minimum extraction pressure is aproximatly 20 bar. The extraction cell was always first completely filled with the drill cuttings (about 630-660 g) and then completely flooded with NGL (about 600 ml) at a pressure of 30 bar, agitation was applied by turning the extraction cell up side down twice. Table 3 shows the results. The "void volume = 694 ml" is defined as the volume of NGL which can be added to the extraction cell containing the drill cuttings plus the volume of the tube connecting the cell to the choke valve. Table 2: Molar compositions of NGL Methane 0.0336 Butane 0.1848 Ethane 0.1272 Ipentane 0.1102 Propane 0.1984 Pentane 0.1620 Ibutane 0.0754 Hexane 0.1074 Table 3: Extraction of 623.7 g drill cuttings (34/10-D4H) with NGL at 30bar, 60°C V(liquid gas) void m(oil) removed [wt %] [ml] volumes collected oil Wet [g] [wt %] basis 694 1 0 0 7.20 932 1.3 4.9 10.9 6.46 1156 1.7 16.4 36.5 4.69 1268 1.8 21.3 47.4 3.92 1550 2.2 27.4 60.9 2.94 2060 3.0 33.3 74.1 1.97 2550 3.7 39.5 87.9 0.93 2920 4.2 41.4 92.1 0.61 3278 4.7 42.4 94.3 0.44 3914 5.6 43.2 96.1 0.30 4280 6.2 43.3 96.3 0.28 Figure 3 shows the residual oil content (related to the wet sample) on the drill cuttings versus the void volume of NGL injected. It is apparent from Figure 3 that the initial oil concentration of 7.2 wt % remains in the cell until it is flooded with the first void volume of NGL. Upon additional injection of NGL, a reduction of the oil content is evident. It is apparent that each time one void-volume is injected, the concentration is reduced by approximately 50%. The experimental data were consequently compared with the relationship expected from a pure dilution process. The following general equation were used for the dilution-model: C=Co * 0.5 (n"1) wherein: C 0 = Initial oil concentration C= Residual oil concentration n= number of void volumes injected The experimental data correspond very well with the graph for the dilution model as illustrated in Figure 3. It is apparent that the NGL-extraction of the oil from cuttings obeys the rules for dilution. Which indicates that the oil is already completely dissolved in the NGL at the first void volume. It is therefor reasonable to assume that the extraction process is fast and exhibits no significant mass-transfer restrictions. All drill cuttings which were tested, exhibited the same behaviour as presented in Figure 3 and the results are summarised in Table 4. Table 4:Oil concentration (weight %) before and after extraction with NGL Drill cuttings 34/10-D4H 34/10-G-2T2H 30/3-A9A (Gullfaks) (Gullfaks) (Veslefrikk) Initial concentration 7,2 9.0 18,6 Residual concentra0.28 0.37 0.22 tion (wet basis) Residual concentra0.26 0.34 0.20 tion (dry basis)

Claims: C L A I M S 1. A process for removing nonpolar organic contaminants including oil from par- ticulate solids, wherein said solids are brought in contact with an extracting agent in which: a) the particulate solids are conveyed into a pressure vessel to which an extracting agent is added in the form of natural gas liquids (NGL), whereby the organic contaminants from the particulate solids are dissolved in the extraction agent to form a single phase solution; b) said solution containing the extraction agent and nonpolar organic contaminants is conveyed to a production flow-line; c) and the clean particulate solids are discarded. 2. Process in accordance with claim 1 , wherein the extraction agent is a condensate collected from a production flow-line in the form of natural gas liquid. 3. Process in accordance with claim 2, wherein said nonpolar contaminants may not be quantitatively conveyed to a production flow-line. 4. Process in accordance with the claims 1-3, wherein the cleaned particulate solids contains less than 1 % by weight of organic nonpolar contaminants. 5. Process in accordance with the claims 1-4, wherein the cleaned particulate sol- ids contains less than 0.5% by weight of organic nonpolar contaminants. 6. Process in accordance with the claims 1 -5, wherein said particulate solids comprise drill cuttings. 7. Process in accordance with the claims 1 - 6, wherein said particulate solids comprise sand. 8. Apparatus for removing nonpolar organic contaminants from drill cuttings by contacting said contaminated drill cuttings with an extractant to form a solution of said extractant and said contaminants, comprising: - means for discarding clean drill cuttings after said contacting; - means for conveying said solution to a production flow line. 9. The use of natural gas liquid as an extracting agent for removing organic nonpolar contaminants including oil from particulate solids. 10. Use of natural gas liquid according to claim 9, where natural gas liquid is obtain from the production flow-line of oil and gas producing facilities. 10

Inventors: HENRIKSEN INGE BRUN, HENRIKSEN, INGE, BRUN
Applicants: CAGNIARD DE LA TOUR AS CTOUR, HENRIKSEN INGE BRUN, CAGNIARD DE LA TOUR AS (CTOUR), HENRIKSEN, INGE, BRUN
Application year: 1999
Main classification: E21B21
IPC codes: E21B21, E21B41