Abstract:
A gas-separator for separating trapped gases from drilling fluids retrieved from a well-bore being drilled is disclosed. The gas-separator includes a cylindrical separator which is capable of rotating on its longitudinal axis when fluid and gases flow out through fluid ejection ports, which access the center bore of the cylindrical separator. The fluid ejection ports have a narrower cross-section towards the center bore and a wider cross-section at the opposite end, and are preferably aligned substantially tangentially with periphery of center bore, such that outflow of drilling fluid (and gases) from the center bore through the ejection ports induces a rotational torque on the cylindrical separator. Spinning of cylindrical separator enhances the gas-separation effect.

Description:
FIELD OF THE INVENTION 
     This invention relates to gas-separators used for recycling of drilling fluid, and especially, to gas-separators used for separating trapped gases from recycled drilling fluid. 
     BACKGROUND 
     Crude oil and natural gas deposits generally are deep within the earth. To extract oil and gas, a well-bore is drilled into the earth and then crude oil is pumped up using submersible pumps, often in a series. 
     A well-bore is drilled from an oil-rig on the surface of earth using a rotating drilling bit. The drilling bit is driven using a continuous flow of compressed drilling fluid (also known as “drilling mud”) supplied through a conduit, known as a drill string. 
     When driven, the drilling bits cut through the earth and move deeper in, leaving a tubular well-bore. The inflowing compressed drilling fluid which drives the drill bits gets released at the bottom of the bore, and due to continuous pressurized drilling fluid inflow, released drilling fluid is pushed back to surface of the earth through free space available between the well-bore and the drill string. 
     On its way back to the surface of the earth, the released drilling fluid carries away with it:
         loose dirt and rock from the bore (most of which is generated during cutting action of the drill bits);   gases (both trapped gases which were released while drilling the bore and gases which seeped into the bore from gaseous zones/formations surrounding the bore); and   water and other fluids (including both trapped water and fluids which were released while drilling the bore and others which seeped into the bore from regions/formations surrounding the bore).       

     After reaching the surface of the earth, the used drilling fluid is collected, filtered and processed for reuse. 
     Apart from driving the drill bits, the drilling fluid also:
         serves as a lubricant for the drilling bit;   removes the debris produced by the drill bits while cutting the bore and aids in further deepening it;   helps cool the drill bits under friction from cutting of the earth bed; and   provides hydrostatic pressure in the bore which reduces inflow, seeping in and unwanted escape of oil, gases and fluids from regions surrounding the bore.       

     For a drilling fluid to be able to perform its desired functions, the correct composition and viscosity of drilling fluid must be maintained throughout the cycle. As drilling fluid is recycled, foreign material (such as rock debris and trapped gases) must be filtered out, and it must otherwise be processed to maintain the correct composition and viscosity. If trapped gases are not removed, the drilling fluid cannot provide the desired hydrostatic pressure. Additionally, as trapped gases may be flammable (such as methane or natural gas), there can be a risk of fire or explosion if they are not removed. Some trapped gases, including especially nitrogen and sulfur gas, can react with and corrode the drilling equipment, including the pumps. Trapped gases in the drilling fluid can also cause cavitation or even ‘gas-lock’ in the pumping equipment. 
     Over the years, various gas separators have been proposed for removal of trapped gases in the drilling fluid. Currently known gas-separators suffer from drawbacks including inefficiency in gas separation or otherwise; from lack of commercial viability; difficulty in installation in the limited available space of the bore; and inability to protect the pumping equipment. Hence, there&#39;s an acute need for a gas-separation equipment that overcomes the deficiencies of the prior art separators. 
     SUMMARY 
     The invention is a gas separator for separating trapped gases, including corrosive gases such as sulfur and nitrogen, from drilling fluid (or “mud”), including such fluid recycled from a well-bore which is being drilled. 
     The gas separator includes a cylindrical separator which is capable of rotating on its longitudinal axis. The cylindrical separator includes a hollow bore and multiple gas ejection ports communicating with the hollow bore. The ports include channels having a narrower cross-section towards the hollow bore and a wider cross-section towards exit of the fluid ejection port, to permit gas expansion on exit. Further, each of said hollow channels is aligned transverse to the axis of the cylindrical separator and substantially tangentially with the periphery of the hollow space such that an outflow of fluid (including gases) contained in said hollow bore through fluid ejection port induces a rotational torque onto the cylindrical separator. 
     When drilling fluid (having trapped gases) is pumped into the gas separator under pressure, it&#39;s delivered to the hollow bore. Continuous inflow forces the drilling fluid (and gases) to exit the bore through the hollow channels and the wider part of the ejection ports. Due to the alignment and configuration of hollow channels and ejection ports, while the gas in the fluid is exiting the ports, it expands and provides the rotational torque (or spinning force) to the cylindrical separator, which in turn generates momentum (sometimes called “centrifugal force”) on the drilling fluid in the hollow bore, and forces more gas trapped in the drilling fluid towards the fluid ejection ports—thereby enhancing the gas separation effect. 
     After the drilling fluid and gases exit the hollow bore through the ejection ports, the separated gases and the drilling fluid follow different paths. While the gases may travel towards one or more gas exit ports on an outer barrel surrounding the first chamber and into the casing space, the gas cleansed drilling fluid travels through the separator and towards drilling fluid pumps which pump the cleansed fluid towards the drill bits. 
     The gas-separator may be placed in the well-bore, attached in the drilling tool string, during drilling. Several can be used in a series, perhaps even some at the surface and some in the well-bore. It is preferably placed upstream of pumping equipment to remove damaging gases from the drilling fluid prior to pump intake. 
     Embodiments of the present invention will be discussed in greater details with reference to the accompanying figures in the detailed description which follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exploded view of parts of a gas separator in accordance with a first embodiment of the present invention. 
         FIG. 2  illustrates a cross-sectional view of the gas separator in accordance with the first embodiment of the present invention. 
         FIG. 3  illustrates a cross-sectional view of the portion of the gas separator of  FIGS. 1 and 2  featuring the fluid ejection ports. 
         FIG. 4  illustrates positioning of the gas-separator in accordance with the first embodiment of the present invention and the overall process of drilling fluid recycling and gas separation during drilling. 
         FIG. 5  is a cross-sectional view of a portion the of gas separator illustrating the gas separation therein. 
         FIG. 6  is a cross-sectional view of a portion the of gas separator illustrating the fluid flow therein. It should be understood that the drawings and the associated descriptions below are intended and provided to illustrate one or more embodiments of the present invention, and not to limit the scope of the invention. Also, it should be noted that the since the drawings are intended to describe the invention with better clarity, they may not be necessarily drawn to scale. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to a first embodiment of a gas separator of the invention. As illustrated in  FIG. 1 , gas-separator  100  includes a hollow cylindrical barrel  102 , first fixture  104 , first bearing  106 , a cylindrical separator  108 , second bearing  110  and a second fixture  112 . The distal ends of fixtures  104  and  112  ( 126  and  158 , respectively) screw into mating portions of a drilling tool string, as shown schematically in  FIG. 4 , but not otherwise. 
     The hollow cylindrical barrel  102  further includes multiple gas exit ports  114  (though more or fewer may be used). In a well-bore, gas exit ports  114  permit gases to pass into the space between the barrel  102  and the casing of the well-bore. Portions of inner surface of the barrel  102  proximal to each of the two ends  116  and  118  are threaded so as to allow, respectively, portions  122  of fixture  104  and  160  of fixture  112  to be screwed into the barrel  102 . Threaded portion  120  mates with portion  160  (note that the threaded portion corresponding to end  116  which mates with portion  122  remains hidden in  FIG. 1 , but is shown in  FIG. 2 ). 
     Fixture  104  includes dual-sided (inner and outer side) threading on connector  122 , a mid-portion  124 , a tapered threaded extension  126  to connect to the drilling fluid line and a bore  128  running through all portions of fixture  104  (bore  128  is illustrated in  FIG. 2 ). 
     In gas-separator  100 , portion  134  of first bearing  106  is screwed into the interior of portion  122  of fixture  104 , and the outer threaded side of connector  122  is screwed into end  116  of barrel  102 . First bearing  106  includes, in addition to threaded portion  134 , a first cylindrical receiver  130  and an apertured rim  132 . The apertured rim  132  further includes several hollow delivery channels  138 . Once first bearing  106  is affixed to first fixture  104 , bore  128  becomes accessible to hollow delivery channels  138  through hollow region  136  included within threaded portion  134 . 
     Threads  148  of second bearing  110  are screwed into threads  156  of cylindrical separator  108 . Cylindrical separator  108  includes first chamber  140 , support stub  142  and pivot stub  144 . The support stub  142  and pivot stub  144  fittingly mate with corresponding portions in bearing  106 . Lower side of stub  142  and the lower side of portion of fluid channel cylinder  162  rests on Bearing  106  and bearing  110  respectively, such that separator  108  can rotate freely on its axis. Bearing  110  includes cylindrical receiver  146  which accommodates fluid channel cylinder  162  and fluid injecting cylinder  164  of fixture  112 . 
     In the cylindrical separator  108 , first chamber  140  includes a hollow bore  150  (hollow bore  150  is illustrated in  FIG. 2 ) and includes several fluid ejection ports  152  near the end at which support stub  142  is positioned. Other locations or additional locations of ports  152  are within the scope of the invention. 
     Each of the fluid ejection ports  152  extend through outer wall of the first chamber  140 , and access hollow bore  150 , through a hollow channel  154  (two hollow channels  154  are illustrated in  FIG. 2 ). Hollow channels  154  are narrower towards the hollow bore  150  and have a widened section towards outer periphery of the first chamber  140 . Further, hollow channels  154  are oriented substantially tangentially with periphery of longitudinal hollow bore  150 , though other orientations which provide rotational force to separator  108  when fluid and gases flow out through ports  152  are also within the scope of the invention. An enhanced view of the preferred orientation of ports  152  (along with their corresponding hollow channels  154 ) is shown in  FIG. 3 . 
     The second fixture  112  comprises a cylinder  158 , a threaded cylinder  160 , a fluid channel cylinder  162 , a fluid injecting cylinder  164  and a longitudinal bore  168  running through each of the cylinder  158 , cylinder  160 , cylinder  162  and cylinder  164  (longitudinal bore  168  is more clearly illustrated in  FIG. 2 ). As illustrated in  FIG. 2 , the longitudinal bore  168  varies in shape and dimensions throughout its length. Starting from cylinder  158 , the longitudinal bore  168  becomes narrower towards the fluid injecting cylinder  164 . Further, the inner surface of cylinder  158  (which surrounds a portion of the longitudinal bore  168 ) is threaded to connect with threads on the drill string, and the outer surface of cylinder  160  is threaded to mate with threads  156  of separator  108 . 
     Fluid injecting cylinder  164  also includes one or more ports  166  to allow fluid venting and avoid excessive pressure build up inside fixture  112 . 
     Once portion  160  of fixture  112  is screwed into the threaded portion  120  of barrel  102 , the end  118  is sealed against the lower edge of cylinder  158 . 
     In the assembled gas-separator  100 , longitudinal bore  168  of fixture  112  extends through the second bearing  110  into the hollow bore  150  of the separator  108 . Further since longitudinal bore  168  extends into the hollow bore  150 , fluids vented by ports  166  are delivered into the hollow bore  150  (See  FIGS. 2 and 5 ). Gas-separator  100  also has an additional chamber  170  formed between the cylindrical barrel  102  and the cylindrical separator  108  (illustrated in  FIG. 2 ). 
     Implementation of gas-separator  100  in a well-bore for separating gases from drilling fluid will now be explained with reference to  FIGS. 2, 3, 4, 5 and 6 . The drilling fluid to be recycled (retrieved form a well-bore being drilled) includes trapped gases.  FIG. 4  illustrates positioning of the gas-separator  100  and an overall process of gas-separation within a well-bore  400  (having a casing  402 ). In  FIGS. 4, 5 and 6 , while the drilling fluid and its direction of flow is depicted by arrows  404 , the trapped gases in a drilling fluid are depicted as bubbles  406 . 
     As illustrated in  FIG. 4 , in the well-bore  400 , the gas-separator  100  is placed upstream of the PDM motors and pumps (together depicted as  408 ) in a drilling tool string  410 . Removal of the trapped gases, especially nitrogen and sulfur, from the drilling fluid protects the motors and pumps  408  (especially the rubber components of these motors and pumps  408 ). The motors and pumps  408  receive gas-cleansed drilling fluid  404  from the gas-separator  100 , and pass on compressed/pressurized gas-cleansed drilling fluid to drilling bits  412  lying beneath (downstream). When driven by compressed gas-cleansed drilling fluid  404 , the drilling bits  412  continue to dig the well-bore  400  further. After driving the drilling bits  412 , the drilling fluid  404  is pushed upwards towards the surface of the well-bore  400 . On its way to the surface, the drilling fluid  404  carries away material (loose soil, rock chips) and fluids in the well-bore (such as gases  406  and water) along with itself. On reaching the surface, retrieved drilling fluid  404  (including foreign materials such as soil, rock chips, gases and liquids) is collected at recycling units  414  for removal of non-gaseous foreign material. Thereafter, the drilling fluid  404  (along with trapped gases  406 ) is pumped into the drilling tool string  410 . In the string  410 , the drilling fluid  404  (along with trapped gases  406 ) is delivered to the gas-separator  100  for removal of gases  406 . After separation, while the gases  406  exit the gas-separator  100  through gas exit ports  114  and are delivered into space between string  410  and casing  402 , gas-cleansed drilling fluid  404  is delivered to PDM motors and pumps  408 . Finally, motors and pumps  408  deliver compressed gas-cleansed drilling fluid  404  to drilling bits  412 , and the process repeats as described. A cover  416  is useful to maintain desired drilling fluid pressure within the well-bore  400 . It is noted that since the illustration provided in  FIG. 4  is intended to provide a simplified understanding of gas-separation, and other arrangements of components are within the scope of the invention. 
       FIGS. 5 and 6 , illustrate the process of gas separation within the gas-separator  100 . The process of gas-separation from drilling fluid  404  (having trapped gases  406 ) starts with pumping a continuous flow of the compressed/pressurized drilling fluid  404  (having trapped gases  406 ) into the gas-separator  100  through the longitudinal bore  168 . After being fed into the longitudinal bore  168 , the compressed drilling fluid  404  (along with trapped gases  406 ) travels through it and gets delivered into the hollow bore  150 . As bore  150  fills with the drilling fluid  404  (and gases  406 ), due to continuous pressurized inflow, the drilling fluid  404  (and gases  406 ) contained within bore  150  are forced into channels  154  and ultimately ejected from corresponding fluid ejection ports  152 . Due to the alignment and configuration of hollow channels  154  (and their corresponding fluid ejection ports  152 ) as described above, while the drilling fluid  404  (and gases  406 ) exit the fluid ejection ports  152 , they provide a rotational torque (or spinning force) to the cylindrical separator  108 . As a result of continuous ejection of drilling fluid  404  (and gases  406 ) through fluid ejection ports  152  (and corresponding continuous generation of rotational torque), the cylindrical separator  108  starts spinning about its longitudinal axis. Spinning of cylindrical separator  108  leads to application of centrifugal force on the drilling fluid contained within bore  150  which moves it towards the ports  152  and increases the gas separation from the drilling fluid  404 . 
     After exiting through ejection ports  152 , drilling fluid  404  (and gases  406 ) enter the second chamber  170 . In the second chamber  170 , buoyant gas bubbles  404  travel towards gas exit ports  114  on barrel  102 . While the gases which pass through gas exit ports  114  on the barrel  102  escape up to the surface, gas-cleansed drilling fluid  404  flows into the hollow delivery channels  138  and then to bore  128 . From bore  128 , the gas cleansed drilling fluid travels to motors and pumps  408 , and from there, to drilling bits  412 . So, from the second chamber  170 , separated gases and the cleansed drilling fluid follow different paths. 
     Embodiments of gas-separators provided by the present invention are readily deployed in the limited available space within a well-bore. As a result of efficient gas-separation, gas-separators of the invention effectively protect pumping equipment against corrosion, and also against problems such as cavitation (or ‘gas-locking’) of pumping equipment, and accumulation of inflammable gases (such as methane or natural gas). Additionally, due to efficient gas-separation, gas-separators of the invention also effectively contribute in maintenance of necessary hydrostatic pressure in the well-bore, because they help maintain the requisite composition and viscosity of the recycled drilling fluid. 
     It is to be understood that the foregoing description and embodiments are intended to merely illustrate and not limit the scope of the invention. Other embodiments, modifications, variations and equivalents of the invention are apparent to those skilled in the art and are also within the scope of the invention, which is only described and limited in the claims which follow, and not elsewhere.