Patent Publication Number: US-2011067860-A1

Title: System and method for obtaining formation fluid samples for analysis

Description:
BACKGROUND 
     The invention generally relates to a system and method for obtaining fluid samples from a surrounding formation. The samples are collected for analysis in determining characteristics of the formation and fluids contained in the formation. 
     A variety of sampling tools, such as modular dynamics formation tester tools (MDT tools) can be run into a wellbore to obtain and evaluate formation fluid samples. MDT tools have been used with single probes or two separate inflatable packers. The probe or separate packers are designed to insulate the formation fluid sample from well fluid in the wellbore while a pump in the MDT tool draws in the formation fluid sample. 
     However, the single probe type of tool is only capable of placing a limited surface in contact with the formation, and this limited contact can create difficulty in collecting formation fluid in a variety environments, including low formation permeability environments. The dual packer configuration can overcome some of these problems, but depressurization between the separate packers during sampling generates significant mechanical stress on the packers. Accordingly, the packers must be designed to withstand this mechanical stress which places substantial limitations on the range of applications for which the system can be designed. For example, the expansion capabilities of the packers may be limited and/or the packers can be subjected to severe damage when cycled multiple times. An additional problem associated with the dual packer configuration is the heightened stress placed on the formation. 
     SUMMARY 
     The present invention comprises a system and method for taking formation fluid samples from within a wellbore. A sole or single expandable packer is utilized to insulate the formation fluid sample from well fluid while the formation fluid sample is obtained. The design of the single packer enables the collection of formation fluid samples through a relatively large area without incurring detrimental mechanical stresses. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
         FIG. 1  is a front elevation view of a modular dynamics formation tester tool and a single expandable packer structure deployed in a wellbore, according to one embodiment of the present invention; 
         FIG. 2  is a view similar to that of  FIG. 1  but showing the single expandable packer structure in an expanded state, according to an embodiment of the present invention; 
         FIG. 3  is a front elevation view of a modular dynamics formation tester tool and a single expandable packer structure deployed in a wellbore, according to an alternate embodiment of the present invention; and 
         FIG. 4  is a flowchart illustrating one example of a sampling methodology, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those of ordinary skill in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. 
     The present invention relates to a system and methodology for obtaining and analyzing fluid samples from a formation. A system having an MDT tool and a single packer is deployed in a wellbore along a desired formation. The single packer is expanded against the wellbore wall adjacent the desired formation to seal off a sample collection region. A pump within the MDT tool is activated to create a suction in the sample collection region which draws in a formation fluid sample. The formation fluid sample can then be analyzed or directed to an appropriate collection location for analysis. 
     The use of the single packer design ensures the mechanical stress generated on the packer structure is substantially lower than the stress that would otherwise be generated on two or more separate packers. The single packer design further enables the construction of a formation fluid sample collection region along the packer that is at least as large as the surface area available when separate packers are utilized. Accordingly, in some applications, it becomes possible to reduce or weaken the structural capability of the single packer without sacrificing functionality or durability. The single packer design also facilitates substantially higher expansion ratios and an increase in the number of expansion/contraction cycles of the packer before failure. 
     Referring generally to  FIG. 1 , an embodiment of a formation fluid sampling system  20  is illustrated as deployed in a wellbore  22  formed in a formation  24  from which a formation fluid sample is to be obtained. The formation fluid sampling system comprises a single inflatable packer  26  combined with a modular dynamics formation tester (MDT) tool  28 . The MDT tool  28  and single inflatable packer  26  are deployed in wellbore  22  via a deployment system  30  that can comprise, for example, a cable, wireline, coiled tubing or other suitable deployment system. 
     The MDT tool  28  can be constructed in a variety of configurations depending on the specific sampling application. For example, the MDT tool may comprise sample sections, multi-sample sections, pump system sections, electric sections, hydraulic sections, OFA modules and other sections or modules in a variety of arrangements. MDT tools, in several configurations, are commercially available from Schlumberger Corporation. To facilitate explanation of the formation fluid sampling system  20 , however, the MDT tool  28  is illustrated as having an electric section  32 , a pumping system section  34 , and a sample section  36  for storing a formation fluid sample obtained through packer  26 . In some applications, sample section  36  may comprise a plurality of sample chambers individually activated by a surface control  38 . For example, when pumping system  34  is operated to draw formation fluid samples from a desired location, electromechanically actuated throttle/seal valves (not shown) can be controlled by surface control  38  to direct each individual formation fluid sample into an appropriate corresponding sample chamber. 
     In the illustrated embodiment, MDT tool  28  is able to selectively expand single packer  26  when desired for the collection and analysis of a formation fluid sample. For example, MDT tool  28  and single packer  26  can be designed so the MDT tool is able to selectively inflate the packer which causes it to expand against the surrounding wellbore wall. Once expanded, a formation fluid sample can be drawn in through the packer structure. 
     The illustrated single packer  26  comprises fixed mechanical ends  40  and  42  which define the longitudinal extremities of the packer. An inner sealing bladder  44  is positioned between fixed ends  40  and  42  and may be selectively inflated by pumping system  34  via a supply conduit  46 , such as a hydraulic tube. Radially outward of inner sealing bladder  44 , an expandable mechanical structure  48  is positioned to provide support for the overall packer structure. The expandable mechanical structure  48  also can be used to provide space for routing one or more conduits  50 , e.g. hydraulic hoses, through which fluid samples are obtained and directed to a collection location, such as sample section  36 . The expandable mechanical structure  48  may comprise a variety of mechanical elements, including longitudinal slats, crisscrossing slats, mesh material or other materials or structures that accommodate repeated cycles of expansion and contraction. 
     The single expandable packer  26  further comprises at least two seal members  52  and  54  that are longitudinally separated to create a formation fluid sample intake region  56  through which formation fluid samples are drawn into packer  26  from the surrounding formation  24 . The seal members  52  and  54  are designed to form a seal against a surrounding wall  58  that defines wellbore  22 . The seal members are formed from appropriate sealing materials and may comprise elastomeric covers, e.g. rubber covers. In the embodiment illustrated, seal members  52  and  54  are positioned along the exterior of expandable mechanical structure  48  and may be located adjacent fixed ends  40  and  42 , respectively. In fact, the longitudinally outlying ends of seal members  52  and  54  may be connected to fixed ends  40  and  42 , respectively. 
     With further reference to  FIG. 1 , an expandable screen  60  may be positioned along an exterior of expandable mechanical structure  48  in the fluid sample intake region  56 . Expandable screen  60  blocks the influx of sand or other fines that would otherwise enter single packer  26  with the formation fluid sample. The fluid sample intake region  56  is generally enclosed other than expandable screen  60  and the one or more conduits  50 . Thus, when single packer  26  is expanded and pumping system  34  is operated to create a decreased pressure or suction along conduit  50 , formation fluid is drawn in through expandable screen  60  and along conduit  50  to the desired collection location. In the embodiment illustrated, the seal members  52  and  54  are located at opposed longitudinal ends of expandable screen  60 . 
     Referring generally to  FIG. 2 , the single expandable packer  26  is illustrated in its expanded configuration. A fluid, such as well fluid, has been directed by pumping system  34  into the interior of inner sealing bladder  44  via supply conduit  46 . The delivery of fluid via supply conduit  46  causes inner sealing bladder  44  to expand radially which forces mechanical structure  48 , screen  60  and seal members  52 ,  54  to also expand radially outward. The radial expansion drives seal members  52 ,  54  against wellbore wall  58  to seal off fluid sample intake region  56 . The seal members  52 ,  54  create sealing contact regions  62  that enable the creation of a low-pressure area within conduit  50  and expandable mechanical structure  48  proximate fluid sample intake region  56 . It should be noted the pumping system  34  can be designed to pump fluid in a manner similar to that used in conventional dual packer configurations. 
     By creating a low-pressure area, i.e. suction, a formation fluid sample is drawn into sample intake region  56  from the surrounding formation  24 . The seal at contact regions  62  enables passage of the formation fluid sample through expandable screen  60  and into the one or more conduits  50  for transport to sample section  36  without being contaminated by wellbore fluid. The suction can be created by operation of pumping system  34 . For example, the pump used to inflate inner sealing bladder  44  can be reversed to draw the formation fluid sample into the packer structure. Alternatively, separate pumps can be used to expand the packer and to draw in the fluid sample, respectively. A valve system  64  also can be incorporated into the design and controlled via surface control  38  and/or electric section  32  to selectively control flow through supply conduit  46  and sample conduit  50 . In one embodiment, the single pump can be used to inflate the inner sealing bladder  44  and to subsequently draw in the fluid sample while valve system  64  holds fluid within inner sealing bladder  44  to prevent premature contraction and release of packer  26 . 
     In another embodiment, single expandable packer  26  is provided with at least one heating element  66 , as illustrated in  FIG. 3 . Heating elements  66  can be positioned within expandable mechanical structure  48 , as illustrated, or they can be positioned in other regions along the flow path followed by the formation fluid sample as it enters and flows through the packer structure. Power can be supplied to heating elements  66  via conductors  68  to heat the incoming fluid sample for analysis. The ability to heat the fluid sample enables analysis of a greater variety of fluid samples from a greater number of environments, including the analysis of high viscosity/cold fluids and the taking of other measurements that are not readily performed without the addition of heat. 
     The single expandable packer design also is conducive to constructing an overall packer wall thickness that is thinner than conventional systems. Thus, even if the packer does not fully recover its initial diameter after many cycles, the packer can be retrieved through the wellbore even when restrictions exist in the wellbore. Furthermore, the single expandable packer design allows the creation of a large communication area between the packer structure and the well fluid. This allows the packer structure to maintain balance with the hydrostatic pressure, thus reducing any negative impact of hydrostatic pressure on packer performance. The single expandable packer design also enables an increased expansion ratio relative to conventional systems. For example, the diameter of the single expandable packer  26  can increase by a ratio of more than 2 to 1 when expanded from its contracted state, as illustrated in  FIG. 1 , to its expanded state, as illustrated in  FIG. 2 . By way of one specific example, the single expandable packer can be manufactured with an outside diameter of approximately 5 inches and inflated to seal against the inside diameter of a well, i.e. wellbore wall  58 , having a diameter of approximately 11 inches. Of course, the actual diameter of single packer  26  and the expansion ratio selected depends on the specific application parameters, including size of the wellbore and type of equipment with which the packer is utilized. 
     One embodiment of a methodology for operating the formation fluid sampling system  20  can be described with reference to the flowchart illustrated in  FIG. 4 . In this embodiment, MDT tool  28  is initially combined with single expandable packer  26 , as illustrated by block  70 . Subsequently, the single packer  26  is moved downhole into wellbore  22  by deployment system  30  until the single packer is positioned at a desired formation location, as illustrated by block  72 . Once properly positioned, pumping system  34  directs a fluid, such as well fluid, through supply conduit  46  to the interior of inner sealing bladder  44 . The filling of inner sealing bladder  44  expands single expandable packer  26  until seal members  52  and  54  seal against the surrounding wellbore wall  58  to seal off fluid sample collection region  56 , as illustrated by block  74 . The sealed sample collection region  56  enables pumping system  34  to create a low-pressure region in conduit  50  and fluid sample intake region  56 , the low-pressure region effectively drawing fluid into single packer  26  from the surrounding formation, as illustrated by block  76 . The formation fluid sample is then directed to a desired sample collection location, such as sample section  36 , via the one or more conduits  50 , as illustrated by block  78 . 
     Following collection of the formation fluid sample, single packer  26  can be collapsed by removing fluid from the interior of inner sealing bladder  44 , as illustrated by block  80 . The removal of well fluid from bladder  44  can be achieved by pumping system  34  and the appropriate reversal of the pumping system or adjustment of the valve system  64  to route fluid out of the inner sealing bladder. The removal of fluid from bladder  44  allows the bladder, along with mechanical structure  48 , screen  60  and seal members  52 ,  54 , to collapse inwardly away from surrounding wellbore wall  58 . Once collapsed or contracted, the single packer can be moved to another desired formation location to obtained one or more additional samples, as illustrated by block  82 . 
     As described above, the single expandable packer system provides a unique and desirable system and methodology for collecting formation fluid samples. It should be noted, however, that a variety of components other than those illustrated can be used with the MDT tool or incorporated into the single expandable packer. For example, expansion mechanisms other than inflatable inner sealing bladder  44  can be used to selectively expand the packer structure. Additionally, a variety of materials and configurations can be used to construct expandable mechanical structure  48 , expandable screen  60  and seal members  52  and  54 . 
     Accordingly, although only a few embodiments of the present invention have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this invention. Such modifications are intended to be included within the scope of this invention as defined in the claims.