Abstract:
Systems and methods for extracting hydrocarbon gas utilize a vacuum chamber with a mud chamber portion that is expandable and contractible. Gas is extracted at vacuum pressures.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates generally to systems and methods used to flow drilling muds and to extract gas from such muds. 
         [0003]    2. Description of the Related Art 
         [0004]    A standard drilling process includes circulating drilling mud through a well to establish well control, cutting removal and bit cooling. When drilling through a medium containing gas, condensate or oil, the hydrocarbons are released from the penetrated interval. The released gas is then transported to the surface in the drilling mud. Additional gas may be released into the mud from the oil or condensate due to changing conditions from subsurface to surface. The amount of released gas, not bound or trapped in or on the cuttings, depends on the porosity, permeability and hydrocarbon saturation of the formation. 
         [0005]    Mud logging is a commonly applied service in the hydrocarbon production industry and relates to extraction and measurement of hydrocarbons which are present in the drilling mud. Measurements are conducted at the surface during drilling operations with a mass spectrometer, a gas chromatograph, or a combination of both. Of particular relevance to the industry are the hydrocarbons which are released from the penetrated lithological units and recorded at the surface once they become evaporated into gaseous phase under atmospheric conditions. Ideally, the measured hydrocarbons are only from the milled formation and can, therefore, provide highly valuable information when correlated with the corresponding depth and corrected for artifacts like recycled connection and/or tripping gas. 
         [0006]    Depending upon the mud and hydrocarbon combination, the amount of each hydrocarbon in solution or present in gas phase may vary. Conventional hydrocarbon extraction (C1 to C8) is accomplished by feeding mud through a vessel with a mechanical agitator and sucking the evaporated hydrocarbons from the headspace of the device (gas trap) towards the measuring unit. Based upon the measured hydrocarbon compositions and the fluid type used for the drilling operation (water-based mud, oil-based mud and synthetic oil-based mud) features like gas/oil contacts and oil/water contacts can be determined. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention provides systems and methods for extracting hydrocarbon gas from drilling mud. The described systems and methods utilize a degassing device with a degassing chamber. The degassing chamber has at least one mud chamber portion into which mud is flowed and which is expandable and contractible. 
         [0008]    A first embodiment for a mud pump and extraction system is described which includes a degassing chamber with a mud chamber portion. A degassing member in the form of a piston is axially moveable within the degassing chamber to expand or contract the mud chamber portion of the degassing chamber. Mud within the mud chamber portion will have gas extracted from it when the mud chamber portion is expanded. In a described embodiment, the degassing chamber is operably associated with a supply of hydrocarbon-bearing drilling mud as well as a mud collection sump to which degassed mud is flowed. Also in a described embodiment, the degassing device is operably associated with a gas collection trap to which extracted gas is flowed following extraction. The gas collection trap is associated with a gas analysis device which preferably includes a gas chromatograph and/or a mass spectrometer. A preferred method of transmitting extracted gas from the vacuum chamber to the gas collection trap is to flow the extracted gas into a gas sample line which uses a suction flow of air to transport the extracted gas. 
         [0009]    An alternate embodiment is also described wherein the mud pump and extraction system includes a degassing device in the form of a rotary extractor. A degassing member in the form of a rotor is movable in rotary fashion within a degassing chamber. As the rotor rotates, a mud chamber portion of the degassing chamber is expanded to extract gas from drilling mud. 
         [0010]    In exemplary operation of mud pump and gas extraction systems in accordance with the present invention, hydrocarbon-bearing mud flows into a degassing chamber in a degassing device. The mud chamber portion of the degassing chamber is then expanded to extract gas from the mud. The mud chamber portion is then contracted as extracted gas is removed from the mud chamber portion via a gas suction valve. Degassed mud is flowed to the mud collection sump. Extracted gas is directed from the degassing chamber to the gas collection trap and is subsequently analyzed by a gas analysis device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    For a thorough understanding of the present invention, reference is made to the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings, wherein like reference numerals designate like or similar elements throughout the several figures of the drawings and wherein: 
           [0012]      FIG. 1  is a schematic plan view of a wellbore with an associated mud pump and gas extraction device and other components in accordance with the present invention. 
           [0013]      FIG. 2  is a side, cross-sectional view of an exemplary mud pump and gas extraction device in accordance with the present invention. 
           [0014]      FIG. 3  is a side, cross-sectional view of the mud pump and gas extraction device of  FIG. 2 , during a mud suction stroke. 
           [0015]      FIG. 4  is a side, cross-sectional view of the mud pump and gas extraction device of  FIGS. 2-3 , now during a mud gas extraction stroke. 
           [0016]      FIG. 5  is a side, cross-sectional view of the mud pump and gas extraction device of  FIGS. 2-4 , now shown during gas extraction from the pump chamber. 
           [0017]      FIG. 6  is a side, cross-sectional view of the mud pump and gas extraction device of  FIGS. 2-5 , now shown during a mud discharge stroke. 
           [0018]      FIG. 7  is a side, cross-sectional view of an alternative embodiment for a mud pump and gas extraction device in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]      FIGS. 1-5  is a schematic plan view which illustrates an exemplary mud pump and gas extraction system  8  which includes a degassing device  10  in accordance with the present invention. As  FIG. 1  depicts, the degassing device  10  is typically located proximate a supply  12  of drilling mud which has been returned up the annulus of associated wellbore  14 . It is noted, however, that the invention is not limited to use with drilling mud that is returned from a wellbore annulus. Rather, any drilling mud, including mud that is to be pumped into a wellbore might also be used. The drilling mud within the supply  12  contains hydrocarbon gas which is to be extracted. A reciprocating device  16  is located proximate the mud pump and extraction device  10  and is used to actuate a piston within the degassing device  10 , as will be described. A gas sample line  18  is also located proximate the degassing device  10 . At the downstream end  20  of the gas sample line  18  is a gas collection trap  22 . A vacuum pump  24  is operably associated with the gas sample line  18  at its downstream end  20  so as to draw air through the gas sample line  18  from the upstream end  26  toward the downstream end  20  and the gas collection trap  22 . A gas analysis device  28  is operably associated with the gas collection trap  22  in order to analyze properties of gas collected within the gas collection trap  22 . In preferred embodiments, the gas analysis device  28  includes a gas chromatograph and/or a mass spectrometer. 
         [0020]    Now also referring to  FIGS. 2-5 , it can be seen that a first mud conduit  30  transmits mud from the drilling mud supply  12  to the degassing device  10 . A second mud conduit  32  extends from the degassing device  10  to a mud collection sump  34 . As best shown in  FIGS. 2-5 , the exemplary degassing device  10  includes an outer housing  36  which defines a degassing chamber  38  within. A piston  40  and shaft  42  are retained within the degassing chamber  38  and are reciprocally moveable within. The piston  40  serves as a degassing member which will extract, gas from the drilling mud via axial movement within the degassing chamber  38 . The shaft  42  and piston  40  are moved axially within the degassing chamber  38  by the reciprocating motor  16  which operates to generate suction and discharge strokes. 
         [0021]    The outer housing  36  is provided with a mud inlet valve  44  and a mud outlet valve  46 . Preferably, both the mud inlet valve  44  and mud outlet valve  46  are one-way valves. The mud inlet valve  44  only permits mud to flow into the degassing chamber  38  when open. The mud outlet valve  46  only permits mud to flow out of the degassing chamber  38 . 
         [0022]    A gas sample conduit  48  is located outside of the outer housing  36  and allows fluid transmission between the degassing chamber  38  and the gas sample line  18 . The gas sample conduit  48  is preferably under vacuum or at least at a pressure lower than that of the degassing chamber  38  so that gas will flow out of the degassing chamber  38 . A gas suction valve  50  is located between the degassing chamber  38  and the gas sample conduit  48 . The gas suction valve  50  is preferably a one-way valve such that, when the gas suction valve  50  is open, fluid will flow from the degassing chamber  38  to the gas sample conduit  48 . 
         [0023]    The mud inlet valve  44 , mud outlet valve  46  and gas suction valve  50  are operably interconnected with a controller  51  which governs the opening and closing of these valves as described herein in coordination with the strokes of the reciprocating motor  16 . The controller  51  may comprise a programmable digital computer with suitable programming for carrying out the general valve control steps described herein. 
         [0024]      FIG. 2  shows an initial position for the degassing device  10  wherein the piston  40  is located at the proximal wall  52  of the degassing chamber  38  such that essentially no fluid is located between the piston  40  and the proximal wall  52  of the degassing chamber  38 . Mud inflow and mud outflow valves  44  and  46  are closed. In  FIG. 3 , the piston  40  is moved away from the proximal wall  52 . The mud inflow valve  44  opens and mud  54  flows into the mud chamber portion  56  of the degassing chamber  38 . Next, the mud pump inflow valve  44  is closed, as depicted in  FIG. 4 , as the piston  40  is further moved away from the proximal wall  52 , thereby increasing the size of the mud chamber portion  56  within which the mud is contained. As this occurs, gas is extracted from the mud  54 . 
         [0025]    The subsequent step is illustrated in  FIG. 5 , wherein the gas suction valve  50  is then opened as the piston  40  is moved toward the proximal wall  52  to help evacuate the extracted gas from the mud chamber portion  56 . Thereafter, the mud outflow valve  46  is opened ( FIG. 6 ) allowing now degassed mud to flow from the mud chamber portion  56  to the mud collection sump  34 . 
         [0026]    Hydrocarbon gas which has been extracted from the drilling mud  54  passes through the gas suction valve  50  and gas sample conduit  48  and into the gas sample line  18 . Extracted gas is then transported to the gas collection trap  22  via gas sample line  18  under the impetus of suction generated by vacuum pump  24 . The extracted gas can then be analyzed by gas analysis device  28 . 
         [0027]      FIG. 7  illustrates an alternative degassing device which can be used in place of degassing device  10  described previously. Except where otherwise noted, the system within which the alternative degassing device operates is the same as the mud pump and extraction system  8  described earlier. The alternative degassing device is a rotary extractor  60  which includes an outer housing  62  which encloses an elliptical degassing chamber  64 . Mud inlets  66  and mud outlets  68  allow communication of mud into and out of the degassing chamber  64 . In the depicted embodiment, there are two mud inlets  66  and two mud outlets  68 , each of which providing communication with separate portions of the degassing chamber  64 . Gas sample conduits  48  extend from the degassing chamber  64  to gas sample lines  18 . Although two separate gas sample lines  18  are shown, it will be understood that there might be only a single gas sample line  18  into which both gas sample conduits  48  will feed. A gas suction valve  50  is incorporated into each gas sample conduit  48 . 
         [0028]    A triangular rotor  70  having curved lobes  72  is retained within the degassing chamber  64 . The rotor  70  has a central opening  74  lined with gear teeth  76 . A rotary shaft  78  is disposed within the central opening  74 . The rotary shaft  78  has a gear  80  mounted upon it with teeth  82  which intermesh with gear teeth  76  of the central opening  74 . The rotor  70  is rotated in an eccentric, rotational manner within the degassing chamber  64  of the housing  62  in a manner similar to the movement of the rotor of a rotary (Wankel) engine. The rotary shaft  78  is rotated by an external prime mover, shown schematically at  84 , in the direction indicated by arrow  86 . Due to gear engagement, the rotor  70  will then be rotated eccentrically within the degassing chamber  64  in the direction indicated by arrows  88 . Rotation of the rotor  70  causes mud to flow into the chamber  64  via mud inlets  66 . It is further pointed out that each of the mud inlets  66  in the described embodiment draws mud from mud supply  12 , and each of the mud outlets  68  flows mud leaving the degassing chamber  64  to mud collection sump  34 . 
         [0029]    As the rotor  70  is rotated, gas is extracted from the drilling mud. The inventor has determined that expansion of fluid within a rotary cycle is effective to remove gas from the drilling mud. Mud is drawn into an intake portion  90  of the degassing chamber  64  via mud inlets  66  during the initial stage of the rotary cycle. Then the inlet valves  44  are closed. Mud is then moved from the intake portion  90  to a mud chamber portion  92  of the degassing chamber  64  as the rotor  70  is rotated and moved within the degassing chamber  64 . The mud chamber portions  92  are here expanded in volume during this stage of the cycle. As the mud is expanded, gas is freed from the mud and can be removed via the gas suction valves  50  and gas sample conduits  48 . Degassed mud is then compressed by the rotor  70  and exits the degassing chamber  64  via the mud outlets  68  as valves  46  are opened. It is noted that in one full rotation of the rotor  70  there are two reciprocating cycles: one in a mud chamber portion  92  in each half of the degassing chamber  64  (see  FIG. 7 ). Therefore, in a preferred embodiment, there are two mud inlets  66  and two mud outlets  68  as well as two gas sample conduits  48 . It should be understood that, while the degassing member of degassing device  10  is the piston  40 , the degassing member of the degassing device  60  is the rotor  70 . 
         [0030]    Those of skill in the art will recognize that numerous modifications and changes may be made to the exemplary designs and embodiments described herein and that the invention is limited only by the claims that follow and any equivalents thereof.