Abstract:
An apparatus and related methods for removing hazardous trace elements from hydrocarbon reservoir effluent is implemented by placing an adsorbing volume of material designed to adsorb the hazardous trace elements into the vicinity of a producing formation face at a downhole location; and letting the reservoir effluent flow through the volume of adsorbing material

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to apparatus and methods for removing mercury from formation effluents such as liquid and gaseous hydrocarbons and water. 
       BACKGROUND 
       [0002]    The production of hydrocarbon fluids from subterranean reservoirs through wells drilled into the formation often results in the inadvertent production of contaminants or trace elements washed out of the formation by the production flow. Mercury, in particular, is known as a contaminant of hydrocarbon production in many geographical areas. 
         [0003]    The typical concentrations of mercury in the gas phase production streams ranges from 50 to 180 micro gram/standard cubic meter of gas. In liquid phase production the level of concentrations of mercury varies typically from 10 to 1000 parts per billion (ppb). In the known reservoirs mercury occurs predominantly in elemental form. It can also be found in ionic form or as an organic compound. 
         [0004]    When present in sufficient concentration, the contaminated production becomes unsuitable as feed flow for downstream refineries and the contaminant has to be removed before entering the refining process. The various known mercury removal processes can be categorized in accordance with the underlying principle used in the process as: 
         [0005]    1) Chemical
       a. Extraction method   b. Absorption/Complexation   c. Ion exchange   d. Precipitation   e. Reduction       
 
         [0011]    2) Physical
       a. Filtration   b. Flocculation/Agglomeration   c. Adsorption   d. Molecular Sieve   e. Membrane Separation       
 
         [0017]    3) Mechanical
       a. Cyclone—Centrifugation       
 
         [0019]    4) Biological
       a. Plant—Phytoremediation   b. Bacteria   c. Enzyme—bioremediation       
 
         [0023]    The above listed apparatus and methods are described in many documents including: 
         [0024]    (1) Oekon, J. R. &amp; Suyanto, P. T.: “Operating History of Arun Liquefied Natural Gas Plant,” SPE 12456, Journal of Petroleum Technology, May 1985, 863-867. 
         [0025]    (2) Pongsiri, N.: “Initiatives on Mercury,” SPE Prod. &amp; Facilities 14 (1), February 1999. 
         [0026]    (3) Manchester, S. Wang, X., Kulaots, I. &amp; Hurt, R. H.: “High Capacity Mercury Adsorption on Freshly Ozone-Treated Carbon,” NIH Public Access, PMC 2009, March 1. 
         [0027]    (4) Mishra, S. P. &amp; Vijaya,: “Inorganic Particulates in Removal of Heavy Metal Toxic Ions—Part X: Rapid and Efficient Removal of Hg (II) ions from Aqueous Solutions by Hydrous Ferric and Hydrous Tungsten Oxides,” Journal of Colloid Science 296 (2006) 383-388. 
         [0028]    (5) Hsi, H. C., Rood, M. J., Abadi, M. R., Chen, S. &amp; Chang, R.: “Mercury Adsorption Properties of Sulfur-Impregnated Adsorbents,” Journal of Environmental Engineering 128 (11) (Nov 2002) 1080-1089. 
         [0029]    (6) Easterly L. A., Vass, A. A., Tyndall, R. L.: “Method for removal and recovery of Mercury”. U.S. Pat. No. 5,597,729, 1997. 
         [0030]    (7) Li, Y. H., Lee, C. W., Gullett, B. K.,: Importance of Activated Carbon&#39;s Oxygen Surface Functional Groups on Elemental Mercury Adsorption.” Fuel, 2003; 82 (4) 451-457 as well as the U.S. Pat. No. 6,537,444 to T. C. Frankiewicz and J. Gerlach and No. 5,460,643 to W. Hasenpusch and H. Wetterich among many others 
         [0031]    Given that mercury can have a corrosive effect on tubing and other subterranean and surface production installation well before reaching any refinery, the known methods of scrubbing or removing it from the produced flow of hydrocarbon at the point of entry to the refining process can be regarded as a problem. In the light of these corrosive and other adverse effects on the operation of production installations in boreholes and the surface, it is seen as an object of the present invention to provide tools and methods to remove mercury as early as possible from the production stream. 
       SUMMARY OF INVENTION 
       [0032]    Hence according to a first aspect of the invention there is provided an apparatus and related methods for removing hazardous trace elements from hydrocarbon reservoir effluent by placing an adsorbing volume of material designed to adsorb the hazardous trace elements into the vicinity of a producing formation face at a downhole location; and letting said reservoir effluent flow through said volume of adsorbing material. 
         [0033]    In a preferred embodiment, the trace element is mercury. 
         [0034]    In a variant of the invention apparatus the adsorbing volume is a coating or layer applied to parts of downhole tubing or screens. Alternatively, the adsorbing volume is solid body or a volume of granular material confined by downhole tubing or screens. It can be placed between the face of the formation and sand screen or gravel packs or as part of a sand or gravel pack or behind (when looking in direction of the production flow) such a sand screen or gravel pack. 
         [0035]    In a preferred embodiment of the invention, the adsorbing volume can be regenerated to restore adsorbing properties. This is best achieved through a flushing treatment from the surface or by retrieving the adsorbing material. 
         [0036]    These and other aspects of the invention are described in greater detail below making reference to the following drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0037]      FIGS. 1-4  show examples in accordance with the invention in a schematic view and in various cross-sections; and 
           [0038]      FIG. 5  is a flowchart illustrating steps in accordance with an example of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    Whilst many among the above listed known methods for removing trace elements, e.g. based on chemical, physical, mechanical or biological processes, may be applied in a form suitable for placement with a subterranean hydrocarbon producing well, the following examples are use known mercury adsorbing materials in various forms. The aim of these examples is to place the removal or scrubbing process as close as possible to the location where the producing face of the reservoir formation meets the completion installation. 
         [0040]    The first example as shown in  FIG. 1 . illustrates schematically a section of tubing  10  for downhole installation at least partially coated with mercury adsorbing materials  11 . The adsorbing material used in the example can be selected from a variety of known materials such as 1) Sulfur impregnated activated carbon (sulfur impregnation can have adsorption capacity of 4,509 micro gram/gram of adsorbent). 
         [0041]    2) Silver impregnated molecular sieve 
         [0042]    3) Metals like copper oxides/sulfides 
         [0043]    4) Ozone-treated carbon surface (mercury adsorption capacity of carbon increases by a factor of 134) 
         [0044]    5) Hydrous Ferric oxide (HFO) and hydrous tungsten oxide (HTO) 
         [0045]    6) Nanoparticles and other materials as for example referred to in the above cited documents. 
         [0046]    In  FIG. 1  a part of a slotted liner  10  which itself is the bottom part of a well bore production installation is shown covered with a porous coating of sulfur impregnated activated carbon  11 . The particles are embedded in a thin layer of hardened epoxy to withstand the downhole installation process and the pressure and temperature at the downhole location. As the production flow passes through and along the coated section, mercury is adsorbed and immobilized within the matrix of the adsorbing material  11 . The material can be regenerated using a flushing treatment from the surface or by removing and/or re-coating the installation using for example one or a combination of the methods described below. 
         [0047]    Other parts of the known subterranean well installation, such as piping, casing, screen, slotted liners, can be similarly treated either prior to installation or after being installed as a variant of the known downhole remedial treatment in which in which for example the coating material is pumped downhole and hardens on exposed surfaces. For an installation prior to the downhole deployment, the coating may be further protected by a sacrificial layer of polymeric material or wax which is allowed to dissipate under downhole conditions following the installation. 
         [0048]    Another example of the present invention is shown in  FIG. 2 . The figure shows in a schematic manner a section of the subterranean completion  20 . The section shown is filled with an absorbing material  21  enclosed within a meshed container to prevent it from migrating downstream with the production flow. The section  20  is designed to be (periodically) removeable from the well in order to be able to either replace or regenerate the absorbing material  21 . 
         [0049]    In further examples, the adsorbing materials  31  in enclosed within one or more slotted or meshed-wire compartments  32  mounted onto well tubing  30  at the reservoir face.  FIG. 3A  shows such a compartment filled with an adsorbing fibrous material  31   a,  whereas in  FIG. 3B  the compartment is filled with a mixture of gravel or sand and particles of activated carbon or adsorbing ceramic particles  31   b.  The installation of such screens is identical to the placement of conventional pre-packed screens. 
         [0050]    However the adsorbing material can also be combined with a gravel or sand pack or, alternatively, replace such a pack.  FIG. 4  shows the adsorbing material  41  placed into the annulus between the completion tubing  40  with a supporting screen  42  and the casing  43 , filling perforations and fractures in the formation  44 . A similar approach can be used in an open hole environment where the casing  43  would not be present. 
         [0051]    In the event the adsorbing material described above approaches saturation or is found to be contaminated, it can be regenerated by a number of different methods, including 
         [0052]    1) Mercury solubilizing chemical injection into the sandface region, including soaking the sandface equipment for a pre-designed time and producing back the chemical, treating and disposing the mercury saturated medium in a controlled environment; or 
         [0053]    2) introducing thermal heating/cooling to release the mercury from the completion string and recovering, treating and disposing the mercury saturated medium in a controlled environment. 
         [0054]    These proposed methods have the advantage of regenerating the adsorbing material at the downhole location, thereby avoiding the need to remove the well tubing. 
         [0055]    A flow chart of steps in accordance with an example of the invention is shown in  FIG. 5 . The method includes the step  51  of initially placing a porous volume of adsorbing material supported by well tubing in vicinity of the producing rock face. Then the production flow is allowed to pass through or along the absorbing material (Step  52 ) and mercury is removed from it (Step  53 ). The material may be regenerated in an optional step  54  before continuing the process. However depending on the concentration of the trace element and capacity of the absorbing material, it can be calculated that in most cases the initial amount of adsorbing material remains effective for years. 
         [0056]    Moreover, while the preferred embodiments are described in connection with various illustrative apparatus and methods, one skilled in the art will recognize that the apparatus and methods may be embodied using a variety of specific procedures and equipment. Accordingly, the invention should not be viewed as limited except by the scope of the appended claims.