Abstract:
The inventors have invented a method to recover oil from sediments and residues from the oil field operations, comprising a series of water, solids and solvent contacting units to separate the silt and solids from the hydrocarbon phase into the water phase and a ceramic membrane filtration system for the recovery of the solvent.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to an enhanced method and system for the removal of silt from residues generated in oil field operations and the extraction of the hydrocarbon phase present in them. 
       BACKGROUND 
       [0002]    In oil field operations, large volumes of solid waste is generated from well perforation, flowback with solids (sand and silt), and other solids with hydrocarbons, which end up in waste disposal facilities. 
         [0003]    In order to recover some valuable hydrocarbons from these wastes, the typical operation in these sites is to deposit all the residues together in large lined open pits. Once the pit is full to a certain level, water is introduced to allow the hydrocarbon phase to be leached out, forming an additional phase on top of the aqueous phase. The hydrocarbon layer is scraped off and collected to be sold. Large solids remain in the solid phase along with some hydrocarbons, and the hydrocarbon phase has some amount of silt in the form of clays and other fine particles. The water used, if recovered, is sent to an emulsion breaker process to recover the emulsified oil present. 
         [0004]    For the purpose of this application, silt is defined as small solid particles which pass through a 200 mesh screen, and may include for example, clays, fine sands and other small size solid particles. 
       SUMMARY OF THE INVENTION 
       [0005]    In order to speed up the process and to remove the silt, several procedures have been proposed based on using water and a solvent to allow the entrapped silt to be separated from the hydrocarbon layer and these fine solids to be captured by the water layer, producing a cleaner hydrocarbon phase for sale. 
         [0006]    By reducing the salt and silt content of the oil, substantial savings can be obtained by the refineries, so a larger premium is paid for these recovered hydrocarbons. 
         [0007]    Simple washing of the oily waste with water separates the larger particles of solids from the mixture, and silt covered with hydrocarbons is distributed between the water and hydrocarbon phases, producing a low quality oil product. The silt removed in the water phase retains a considerable amount of hydrocarbons which are desired to be recovered, and the oil phase retains a considerable amount of silt which is desired to be removed. 
         [0008]    The use of an appropriate solvent to allow the hydrocarbon covering the silt to be detached from its surface is proposed in the present patent. A petroleum distillate will help the hydrocarbon phase to be detached from the silt surface. The selected hydrocarbon distillate should not contain too much high boiling point hydrocarbons, since they tend to form emulsions with water, which may hinder their solvency efficiency. The use of solvent will also reduce the viscosity of the hydrocarbon phase and allow it to flow more easily. The solvent will dissolve the low to medium molecular weight hydrocarbons present, and a separation process based on ceramic membrane filtration is presented to recover such solvent. 
         [0009]    Even though a hydrocarbon recovered stream including silt may be used in refining processes, the presence of such silt will decrease the life expectancy of the refining process and may hinder the efficiency of the system. Therefore, a pre-treatment process is usually in place in the refineries to maximize the efficiency and process life of their equipment. 
         [0010]    The main objective of the present invention is to provide a process for the effective recovery of the hydrocarbon phase present in sediments and residues generated by oil field operations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  shows a process diagram for one embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    According to the preferred embodiment of the present invention, a Raw Stream  1  of oil field operations waste containing hydrocarbons, water, silt and solids is fed to Mixer  41 , along with a solvent-rich Stream  22  coming from units downstream, to start the separation of the different phases present. 
         [0013]    The Mixed Stream  2  of solids, silt, hydrocarbons and solvent exits Mixer  41  and is fed into First Settling Unit  43 . As the solvent starts acting over the solution, a Top Solvent Stream  5  with dissolved hydrocarbons is taken from the top of the First Settling Tank  43  and recirculated to the bottom of the First Settling Tank  43  in order to help fluidize the bed within it and increase the separation. 
         [0014]    Current embodiments of the invention use flow velocities from 2 to 10 ft/sec, based on the viscosity of the hydrocarbon phase and the amount of solids present; the flow is necessarily slower with more solids and less viscous fluid. 
         [0015]    After a period of time, a Solids Phase Flow  4  leaves from the bottom of the First Settling Tank  43 , after which it mixes with Stream  11  to create Stream  6  and enters Second Settling Tank  45 , along with Settling Water  12 , which removes the remaining attached hydrocarbons and solvents from the large particle size solids remaining in the process fluid. 
         [0016]    The addition of the Settling Water  12  allows the formation of a light solvent-hydrocarbon layer on the top of the processing fluid in the Second Settling Tank  45 ; the solvent-hydrocarbon layer is an intermediate aqueous phase with some silt included. 
         [0017]    The process fluid containing larger particle size solids phase at the bottom of the Second Settling Tank  45 , from where it is discharged practically clean of hydrocarbons as Disposal Stream  7 . 
         [0018]    The aqueous phase is removed from the middle section of Second Settling Tank  45  as Stream  9 , which is split into a Stream  10  which is sent to an emulsion breaking process outside the scope of this system and Stream  11 , which is mixed with Solids Phase Flow  4  coming from First Settling Tank  43  to produce Stream  6  and fed into the Second Settling Tank  45 . The Solvent Phase  8  leaves from the top of the exits from the top of Second Settling Tank  45 , mixes with Stream  21  coming from units downstream to produce Stream  22  and is sent back to the Mixer  41  to start the extraction of hydrocarbons. 
         [0019]    The solvent and hydrocarbon phase from the First Settling Tank  43  is extracted from the top into Stream  3  and transferred to a Third Settling Tank  47 , where phase separation occurs. The top layer is rich in solvent and hydrocarbons, essentially silt-free, and it is removed from the top of the unit into Stream  14  and sent to a Solvent-Hydrocarbon Recovery Tank  53  which will be used to feed the Solvent Recovery Unit  55 . 
         [0020]    The lower portion of the process fluid in the Third Settling Tank  47  includes water and silt, and is removed from the unit&#39;s bottom as Stream  13  and sent to a Fourth Settling Tank  49 , mixing with freshly recovered solvent from Stream  28  to produce Stream  15 , which is fed to the Fourth Settling Tank  49  to be able to further remove the hydrocarbons from silt, and allowed to settle into separate phases. During this process, a solvent-hydrocarbon rich layer is formed at the top of the Fourth Settling Tank  49 , and extracted into Stream  17 , where it is mixed with Stream  20  from units downstream to produce Stream  21 , which is recirculated to Mixer  41 . An intermediate water-silt layer forms in the middle to bottom section of the Fourth Settling Tank  49  and exits into Stream  16  to be transferred to Fifth Settling Tank  51 . 
         [0021]    Before entering Fifth Settling Tank  51 , the water-silt Stream  6  is mixed with more water coming from Stream  25  coming from Fifth Settling Tank  51  and Stream  33  coming from the Solvent-Hydrocarbon Recovery Tank  53 , to further clean the silt. 
         [0022]    Inside Fifth Settling Tank  51 , a top layer rich in solvent and hydrocarbons detached from the silt is extracted from its top into Stream  20  and sent back to the Mixer  41  to help with the separation. Stream  20  is mixed with Stream  17  from Fourth Settling Tank  49  to produce Stream  21  and sent back to Mixer  41 . An intermediate layer of water is formed which is extracted in Stream  23 , purging excess water into Stream  24  and sent to a water recovery system. The remainder water from Stream  23  continues on Stream  25  and mixes with Stream  6  coming from s Fourth Settling Tank  49 . And finally, a silt-rich layer, essentially free of hydrocarbons is discharged from the bottom into Stream  19  and sent to waste disposal. 
         [0023]    The solvent recovery system is essential to the economic feasibility of the process. In the preferred embodiment, a Ceramic Membrane Filtration System (CMFS)  55  is used for this purpose. The Solvent-Hydrocarbon Recovery Tank  53  feeds the Ceramic Membrane Filtration System  55 , which contains solvent and hydrocarbons essentially free of silt. 
         [0024]    Some water may be present in the Solvent-Hydrocarbon Recovery Tank  53  carried out by the process. If such is the case, water is allowed to settle to the bottom of the Solvent-Hydrocarbon Recovery Tank  53 , a hydrocarbon rich layer deposits on top of the aqueous layer, and a solvent-rich layer is formed at the very top of the Solvent-Hydrocarbon Recovery Tank  53 . From this top layer, a Stream  26  is fed to the Ceramic Membrane Filtration System  53  to concentrate the large-chain hydrocarbons by permeating the lighter components present in Stream  26 . 
         [0025]    A solvent-rich Stream  27  leaves the Ceramic Membrane Filtration System  55  and used for the extraction process. Stream  27  is divided into Stream  29  which recovers the excess solvent produced in the extraction process, and Stream  28  which is sent back to mix with Stream  13  from Fourth Settling Tank  49  to produce Stream  15  to be fed into Fifth Settler Tank  51 . 
         [0026]    The concentrate from the Ceramic Membrane Filtration System  55  is sent back to the Solvent-Hydrocarbon Recovery Tank  53  and allowed to settle. Water is extracted from the bottom of the Solvent-Hydrocarbon Recovery Tank  53  into Stream  31  to be mixed with a fresh Water Stream  32  to produce Stream  33  which is sent back to Fifth Settler Tank  51  after mixing with Streams  25  and  16 . The hydrocarbon rich layer is extracted from the middle section of the Ceramic Membrane Filtration System  55  into Stream  34  and transferred to transport tanks for sale. 
         [0027]    For all separators included in the described process, the equipment of pressure release valves allows for the removal of gases generated in the process, which in turn can be used to fluidize the solids-hydrocarbon-solvent mixture in the First Settling Tank  43  in Stream  35 . Gases such as carbon dioxide or nitrogen may be used to help the fluidization process, but due to the nature of the solvent, air or oxygen are to be avoided inside the units to prevent any explosive environment. 
       EXAMPLE 
       [0028]    Waste sludge from a waste disposal site in south Texas was fed to the process, along with a petroleum distillate solvent with a boiling point range between 140° F. and 300° F. The apparent composition by weight of the sludge is 35% solids, 30% hydrocarbons, and the water as the remainder. The solvent is fed to the unit in a proportion of 3 parts to 1 part of sludge. (Several feed ratios were experimented but only the results from the mentioned one are presented here.) The amount of solvent depends on the density and viscosity of the waste stream to be treated. In this case, since the hydrocarbon phase has a gravity around 30° API, a 3:1 ratio of solvent to sludge was used, resulting in 95% of the hydrocarbons present in the sludge recovered in a stream with less than 1% silt. The solvent was able to be reused in the process even though it increased its density by 10%, and it still retained its solvency. 
         [0029]    In this example, the recovered hydrocarbon phase ended up around 36° API. The ceramic membrane elements used in the process were alumina-based, with pore size of 100 nm, 19 channels and 6 mm channel diameter for a 0.358 m2 surface area per element. 
         [0030]    Without further elaboration, it is believed that one skilled in the art can, using the description herein, utilize the present invention to its fullest extent. The embodiments described herein are to be construed as illustrative and not as constraining the remainder of the disclosure in any way whatsoever. While the preferred embodiments have been shown and described, many variations and modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. Accordingly, the scope of protection is not limited by the description set out above, but is only limited by the claims, including all equivalents of the subject matter of the claims. The disclosures of all patents, patent applications and publications cited herein are hereby incorporated herein by reference, to the extent that they provide procedural or other details consistent with and supplementary to those set forth herein. 
         [0031]    A legend of the drawing and elements of the invention: 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Raw Stream 1 
                 Settling Water 12 
               
               
                   
                 Mixed Stream 2 
                 Water Stream 32 
               
               
                   
                 Solids Phase Flow 4 
                 Stream 33 
               
               
                   
                 Top Solvent Stream 5 
                 Stream 35 
               
               
                   
                 Disposal Stream 7 
                 Mixer 41 
               
               
                   
                 First Settling Tank 43 
                   
               
               
                   
                 Second Settling Tank 45 
                   
               
               
                   
                 Third Settling Tank 47 
                   
               
               
                   
                 Fourth Settling Tank 49 
                   
               
               
                   
                 Fifth Settler Tank 51 
                   
               
               
                   
                 Solvent-Hydrocarbon Recovery Tank 53 
                   
               
               
                   
                 Ceramic Membrane Filtration System 55