Abstract:
A method and system to passively monitor cement integrity and reservoir/formation parameters near the wellbore at all depths and orientations outside a wellbore. Different types (pressure, temperature, resistivity, rock property, formation property etc.) of sensors are “pumped” into place by placing them into a suspension in the cement slurry at the time a well casing is being cemented, by placing them in gravel pack used in frackpacking, or by a deflected drilling tool. The sensors are either battery operated, or of a type where external excitation, (EMF, acoustic, RF etc.) may be applied to power and operate the sensor, which will send a signal conveying the desired information. The sensor is then be energized and interrogated using a separate piece of wellbore deployed equipment whenever it is desired to monitor cement or formation conditions. This wellbore deployed equipment could be, for example, a wireline tool.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Technical Field  
           [0002]    The present invention relates to a method and apparatus for placing sensors downhole in a well to monitor relevant formation characteristics. Specifically, the sensors can be flowed into the formation in the cement, or other suitable material, used to case the well. Alternatively, the sensors can be physically bored into the formation with a device described herein.  
           [0003]    2. Description of the Related Art  
           [0004]    Understanding an oil-bearing formation requires accurate knowledge of many conditions, such as critical rock and formation parameters at various points in the zones or formations that the oil bearing formation encompasses. Fluid pressure in the formation, its temperature, the rock stress, formation orientation and flow rates are a few examples of measurements taken within the formation which are useful in reservoir analysis. Having these formation/rock measurements available external to the immediate wellbore in wells within a producing field would facilitate the determination of such formation parameters such as vertical and horizontal permeability, flow regimes outside the wellbores within the formations, relative permeability, water breakthrough condensate banking, and gas breakthrough. Determinations could also be made concerning formation depletion, injection program effectiveness, and the results of fracturing operations, including rock stresses and changes in formation orientation, during well operations.  
           [0005]    In addition to understanding oil bearing formations, the condition of the material used to set casing in a well is of critical interest in monitoring the integrity of a well completion. While cement is commonly used to set casing, other materials such as resins and polymers could be used. So while the term cement is used in this description, it is meant to encompass other suitable materials that might be used now or in the future to set casing. Pressure, temperature and stress, are a few examples of measurements taken within the cement that might be useful in determining the condition of the cement in a well. Various types of transducers placed near the cement/wellbore interface could be used to monitor the condition of the rock or formations outside the wellbore. Having these formation/rock measurements available external to the immediate wellbore in wells within a producing field would facilitate the determination of such formation parameters such as vertical and horizontal permeability, flow regimes outside the wellbores within the formations, relative permeability, potential fines migration, water breakthrough, and gas breakthrough. Determinations could also be made concerning formation depletion, fines migration, injection program effectiveness, and the results of fracturing operations, including rock stresses and changes in formation orientation, during well operations.  
           [0006]    Historically, reservoir analysis has been limited to the use of formation measurements taken within the wellbores. Measurements taken within the wellbore are heavily influenced by wellbore effects, and cannot be used to determine some reservoir parameters. Well conditions such as the integrity of the cement job over time, pressure behind the casing, or fluid movement behind the casing cannot be monitored using the wellbore measurements.  
           [0007]    Therefore, it is desirable to have a method and system that may be used to passively monitor reservoir/formation parameters at all depths and orientations outside a wellbore as well as having a method and system to passively monitor cement integrity. It is further desirable to have a method and system to take these measurements without compromising the casing, cement or any other treatment outside or inside the casing.  
         SUMMARY  
         [0008]    The present invention provides a method and system that may be used to passively monitor cement integrity and reservoir/formation parameters near the wellbore at all depths and orientations outside a wellbore. These measurements may be taken without compromising the casing, cement or any other treatment outside or inside the casing. In addition, sensors may be deployed in many more locations because of the non-intrusive nature of reading the sensors once they are in place.  
           [0009]    In one embodiment, different types (pressure, temperature, resistivity, rock property, formation property etc.) of sensors are “pumped” into place by placing them into a suspension in the cement slurry at the time a well casing is being cemented. The sensors are either battery operated, or of a type where external excitation, (EMF, acoustic, RF etc.) may be applied to power and operate the sensor, which will send a signal conveying the desired information. The sensor may then be energized and interrogated using a separate piece of wellbore deployed equipment whenever it is desired to monitor cement or formation conditions. This wellbore deployed equipment could be, for example, a wireline tool. Having sensors placed in this way allows many different types of measurements to be taken from the downhole environment. Looking at readings taken at different locations will allow directional properties such as permeability to be examined. Sensors placed close to the wellbore can be used to monitor the well integrity by disclosing information about cement condition, casing wear/condition etc. Sensors placed closer to the cement/wellbore interface provide reservoir or rock property measurements, which may be used in reservoir analysis.  
           [0010]    In another embodiment, the sensors are placed into the formation at or outside the wellbore and may be interrogated whenever it is desired to monitor well or formation conditions. One method of placing the sensors into the formation is to use technology similar to side bore coring tools which remove samples in a direction that is perpendicular to the wellbore. Another method involves placing the sensors into the gravel slurry used for gravel packing and frackpacking operations thus allowing the sensors to migrate into the formation with the fracpack.  
           [0011]    There are many advantages of the proposed system. First, non-intrusive downhole measurements may be taken from numerous locations in the downhole environment. Next, the integrity of the cement job can be closely monitored for initial quality, and degradation with time. Further, many transducers may be placed into the well with relatively low deployment cost. Also, very accurate measurements can be taken because of transducer placement outside the wellbore. Also, very long service life of transducers is achieved because power is supplied by a wellbore device capable of supplying transducer excitation power. Finally, fluid movement and pressure behind the casing may be measured by comparing the many available downhole measurements.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:  
         [0013]    [0013]FIG. 1 shows a flow chart for placing sensors within the cemented casing of a wellbore.  
         [0014]    [0014]FIG. 2 depicts a wellbore with sensors located within the cemented casing.  
         [0015]    [0015]FIG. 3 shows a flow chart for placing sensors into the formation.  
         [0016]    [0016]FIG. 4 depicts a wellbore and formation with sensors located in the formation.  
         [0017]    [0017]FIG. 5 shows a flow chart for placing a sensor into a formation by drilling laterally away from a wellbore.  
         [0018]    FIGS.  6 A- 6 C depict a tool for drilling away from a wellbore and placing a sensor into a formation.  
     
    
     DETAILED DESCRIPTION  
       [0019]    A presently preferred embodiment of the present invention for placing sensors into a wellbore casing will now be described with reference to FIGS. 1 and 2. FIG. 1 shows a flowchart of a preferred embodiment of a method for placing sensors into a wellbore casing. FIG. 2 illustrates a cross-sectional view of a wellbore and casing with sensors placed therein.  
         [0020]    A wellbore  240  is drilled into the earth using conventional methods and tools well known to those skilled in the art (step  110 ). Sensors  210  are placed into a cement slurry (step  120 ). A casing is placed into wellbore  240  and the cement slurry containing sensors  210  is pumped into wellbore  240  to provide a cemented casing  240  (step  130 ). A wellbore device (not shown in FIG. 2) is then placed into wellbore  240  (step  140 ). Sensors  210  are then interrogated with the well bore device (step  150 ). The wellbore device could be for example a wireline tool or a drill pipe conveyed system. Sensors  210  will typically be transducers which are either battery operated, or of a type where external excitation (EMF, acoustic, RF, etc.) may be applied to power and operate the transducer, which will send a signal conveying the desired information. Sensors  210  may be interrogated whenever desired to monitor cement or formation conditions. Sensors  210  may be of many different types such that many different types of conditions may be monitored. Such monitored conditions include pressure, temperature, resistivity, rock properties, and formation properties. Other monitored conditions include, but are not limited to, paramagnetic properties, magnetic fields, magnetic flux leak, pulse eddy current, and polar spin. Looking at different readings taken at different locations will allow directional properties such as permeability to be examined. Sensors  210  placed close to the wellbore can be used to monitor the well integrity by disclosing information about cement condition, casing wear/condition etc. Sensors  210  placed closer to the cement/wellbore interface provide reservoir or rock property measurements which may be used in reservoir analysis.  
         [0021]    There are many advantages to placing sensors within the cemented well casing. Non-intrusive downhole measurements may be taken from numerous locations in the downhole environment. The integrity, such as micro-annulus, of the cement job can be closely monitored for initial quality and degradation with time. Many sensors may be placed into the well with relatively low deployment cost. Very accurate measurements can be taken because of sensor placement outside of the wellbore. Very long service life of the sensors because the power is supplied by a wellbore device capable of supplying transducer excitation power. Fluid movement and pressure behind the casing may be measured by comparing the many available downhole measurements.  
         [0022]    Turning now to FIGS. 3 and 4, a method of placing sensors into a formation will be described. FIG. 3 depicts a flow chart for a presently preferred method of placing sensors into a formation. FIG. 4 shows a cross-sectional view of a well bore and formation with sensors located within the formation.  
         [0023]    A wellbore  440  is drilled using conventional techniques and devices well known to one skilled in the art (step  310 ). Formation samples are removed from the formations  420 ,  425 , and  430  using for example, a side bore coring tool, in a direction perpendicular to wellbore  440  (step  320 ). The maximum distance bored out with standard coring tools is typically around 4 feet from the wellbore  440 . One example of a side bore coring tool may be found in U.S. Pat. No. 5,209,309 issued to Wilson which is hereby incorporated by reference. Sensors  410  are then placed into the formations  420 ,  425 , and  430  (step  330 ). A sensor interrogating device is then placed into the wellbore (step  340 ). Sensors  410  are then interrogated whenever it is desired to gather some information that sensors  410  can gather (step  350 ).  
         [0024]    In one variation of this method, rather than removing formation samples with a side bore coring tool, the formations  420 ,  425 , and  430  are fractured and packed with gravel (“fracpacking”). Sensors  410  are placed in the gravel slurry prior to packing the fracture. Thus, sensors  410  are placed outside the wellbore and into the formation. Alternatively, perforations  460  can be made in the wellbore  440  casing and the sensors  410  allowed to migrate outside the wellbore  440  with the gravel slurry. The gravel slurry and fracpacking will be described in more detail below.  
         [0025]    As with sensors  210 , sensors  410  will typically be transducers which are either battery operated, or of a type where external excitation (EMF, acoustic, RF, etc.) may be applied to power and operate the transducer, which will send a signal conveying the desired information. Alternatively, the sensors  410  may be powered using fuel cell or power cell. The fuel cell or power cell may be part of the sensors  410  or built as an addition. Formation movement, noise or fluid flow (i.e. effluent flow) could be used to charge or recharge the cell power source. Sensors  410  may be interrogated whenever desired to monitor cement or formation conditions. Sensors  410  may be of many different types such that many different types of conditions may be monitored. Such monitored conditions include pressure, temperature, resistivity, rock properties, and formation properties. Other monitored conditions include, but are not limited to, paramagnetic properties, magnetic fields, magnetic flux leak, pulse eddy current, and polar spin. Sensors  410  placed close to the wellbore  440  can be used to monitor the well integrity by disclosing information about cement condition, casing wear/condition etc. Sensors  410  placed further into a formation or other surrounding substrate will provide very accurate reservoir or rock property measurements.  
         [0026]    It should be noted that sensors  210  and  410  may be calibrated before placement and may be recalibrated after placement in the formation or well casing. For example, a radio or acoustic signal may be sent to each or sensors  210  or  410 , after placement, initiating a calibration response in each of sensors  210  or  410 .  
         [0027]    There are many advantages to placing sensors outside the wellbore. Non-intrusive downhole measurements may be taken from numerous locations in the downhole environment. Very accurate measurements can be taken because of optimal transducer placement outside the wellbore Very long service life of transducers because power is supplied by a wellbore device capable of supplying transducer excitation. Direction formation properties may be measured by comparing the many available downhole measurements.  
         [0028]    The particulate material utilized in accordance with the present invention to carry sensors  410  into formations  420 ,  425 , and  430  is preferably graded sand which is sized based on a knowledge of the size of the formation fines and sand in an unconsolidated subterranean zone to prevent the formation fines and sand from passing through the gravel pack. The graded sand generally has a particle size in the range of from about 10 to about 70 mesh, U.S. Sieve Series. Preferred sand particle size distribution ranges are one or more of 10-20 mesh, 20-40 mesh, 40-60 mesh or 50-70 mesh, depending on the particle size and distribution of the formation fines and sand to be screened out by the graded sand.  
         [0029]    The particulate material carrier liquid utilized, which can also be used to fracture the unconsolidated subterranean zone if desired, can be any of the various viscous carrier liquids or fracturing fluids utilized heretofore including gelled water, oil base liquids, foams or emulsions. The foams utilized have generally been comprised of water based liquids containing one or more foaming agents famed with a gas such as nitrogen. The emulsions have been formed with two or more immiscible liquids. A particularly useful emulsion is comprised of a water-based liquid and a liquified normally gaseous fluid such as carbon dioxide. Upon pressure release, the liquified gaseous fluid vaporizes and rapidly flows out of the formation.  
         [0030]    The most common carrier liquid/fracturing fluid utilized heretofore which is also preferred for use in accordance with this invention is comprised of an aqueous liquid such as fresh water or salt water combined with a gelling agent for increasing the viscosity of the liquid. The increased viscosity reduces fluid loss and allows the carrier liquid to transport significant concentrations of particulate material into the subterranean zone to be completed.  
         [0031]    A variety of gelling agents have been utilized including hydratable polymers which contain one or more functional groups such as hydroxyl, cis-hydoxyl, carboxyl, sulfate, sulfonate, amino or amide. Particularly useful polymers are polysaccharides and derivatives thereof which contain one or more of the monosaccharides units galactose, mannose, glucoside, glucose, xylose, arabinose, fructose, glucuronic acid or pyranosyl sulfate. Various natural hydratable polymers contain the foregoing functional groups and units including guar gum and derivatives thereof, cellulose and derivatives thereof, and the like. Hydratable synthetic polymers and co-polymers which contain the above mentioned functional groups can also be utilized including polyacrylate, polymeythlacrylate, polycrylamide, and the like.  
         [0032]    Particularly preferred hydratable polymers, which yield high viscosities upon hydration at relatively low concentrations, are guar gum and guar derivatives such as hydroxypropylguar and carboxymethylguar and cellulose derivatives such as hydroxyethylcellulose, carboxymethylcellulose and the like.  
         [0033]    The viscosities of aqueous polymer solutions of the types described above can be increased by combining cross-linking agents with the polymer solutions. Examples of cross-linking agents which can be utilized are multivalent metal salts or compounds which are capable of releasing such metal ions in an aqueous solution.  
         [0034]    The above described gelled or gelled and cross-linked carrier liquids/fracturing fluids can also include gel breakers such as those of the enzyme type, the oxidizing type or the acid buffer type which are well known to those skilled in the art. The gel breakers cause the viscous carrier liquids/fracturing fluids to revert to thin fluids that can be produced back to the surface after they have been utilized.  
         [0035]    The creation of one or more fractures in the unconsolidated subterranean zone to be completed in order to stimulate the production of hydrocarbons therefrom is well known to those skilled in the art. The hydraulic fracturing process generally involves pumping a viscous liquid containing suspended particulate material into the formation or zone at a rate and pressure whereby fractures are created therein. The continued pumping of the fracturing fluid extends the fractures in the zone and carries the particulate material into the fractures. Upon the reduction of the flow of the fracturing fluid and the reduction of pressure exerted on the zone, the particulate material is deposited in the fractures and the fractures are prevented from closing by the presence of the particulate material therein.  
         [0036]    As mentioned, the subterranean zone to be completed can be fractured prior to or during the injection of the particulate material into the zone, i.e., the pumping of the carrier liquid containing the particulate material through the slotted liner into the zone. Upon the creation of one or more fractures, the particulate material can be pumped into the fractures as well as into the perforations and into the annuli between the sand screen and shroud and between the shroud and the well bore.  
         [0037]    In another presently preferred embodiment, sensors are placed into a formation by drilling laterally away from a borehole. FIG. 5 shows a flow chart of this method. FIGS.  6 A- 6 C depict an instrument suitable for performing this method. As used herein, drilling laterally away from a borehole means in a direction greater than zero degrees away from the general longitudinal (as opposed to radial) direction of the borehole at that particular location and, thus, can include drilling up or down away from the borehole when the longitudinal direction of the borehole is horizontal with respect to the earth&#39;s surface. Furthermore, there is no requirement that drilling laterally away from a borehole mean normal or perpendicular to the surface of the wellbore.  
         [0038]    A borehole  602  is drilled using conventional methods well known to one skilled in the art (step  510 ). A sensor placement device  600  is then placed into the borehole  602  (step  515 ). Sensor placement device  600  consists of tubing  650 , a fluid diverter  634 , a control line  692 , outer tubing  636 , pistons  630  and  631 , a sensor  622 , a nozzle  632 , a deflector  610 , and a wire  624 . Tubing  650  is lowered into the borehole  602  from the earth&#39;s surface  693 . Tubing  650  may be coiled tubing of a type well known to one skilled in the art.  
         [0039]    Attached to tubing  650  are fluid diverters  634 . An opening  652  allows fluid to flow from tubing  650  through fluid diverters  634  and into control line  692  which is attached to fluid diverters  634  by Swagelok fittings. At the end of control tube  692  are two pistons  630  and  631 . Pistons  630  and  631  provide an offset area for pressure to work against so the outer tube  636  (also called a cylinder) will stroke downward upon application of pressure. This is the placement means for sensor  622 . Pistons  630  and  631  are rigidly attached to fluid or flow diverters  634 . In one embodiment, pistons  630  and  631  may be a smaller size of control line than outer tubing  636 . Although described herein with reference to two pistons, multiple pistons may be used as well and may be deployed in a variety of directions, such as, for example, up, down, or at an angle, without departing from the scope and spirit of the present invention.  
         [0040]    Overlying control line  692  is outer tubing  636 . Outer tubing  636  is pushed onto pistons  630  and  631  and remains in a retracted position until pressure is applied. Upon application of pressure, nozzle  632  provides a jetting action for the fluid, which effectively cuts through the formation. As nozzle  632  erodes the formation material, the outer tubing  636  is allowed to move downwards. Sensor  622  is attached to the inside of outer tubing  636  by a threaded carrier sub that has an open ID to allow fluid to bypass to nozzle  632 . Outer tube  636  has a nozzle  632  at one end. Sensor  622  is attached to outer tubing  636 , either by integration into the housing wall or surface mounting, and is connected to wire  624  that connects sensor  622  to a surface electronics  690 . Surface electronics  690  may include a recorder to record the data received from sensor  622  for later processing possibly at a remote site and may also include processing equipment to process the data received from sensor  622  as it is received. Furthermore, surface electronics  690  may be attached to display devices such as a cathode ray tube (CRT) or similar computer monitor device and/or to a printer.  
         [0041]    After sensor placement device  600  has been placed down hole (step  515 ), the fluid pressure inside tubing  650  is increased (step  520 ). The pressure may be increase by, for example, a pump on the surface is connected to the coiled tubing  650 , which provides the high pressure source required to operate the drilling operation or by a subsurface powered pump. The increased fluid pressure causes fluid to flow through opening  652  into fluid diverter  634  which diverts fluid into control line  692  causing sensor pods  680  to extend (step  525 ). Water may be used as the working fluid unless this will adversely affect the formation sandface. In such event, a conventional mud may be used. The fluid may also be a treated liquid comparable with the reservoir to minimize formation damage and may possibly be enhanced with friction reducing polymers and abrasives to enhance jet drilling efficiency. The fluid flows from control line  692  into outer tubing  636 . The fluid exits outer tubing  636  through nozzle  632 . The fluid exiting through nozzle  632  cuts through the surrounding rock, thus drilling the sensor pod  680  into place as housing  636  continues to extend exerting pressure on sensor pod  680  (step  530 ). Deflector  610  causes sensor pod  680  to be deflected outward into the formation  604 .  
         [0042]    The surface  612  of deflector  610  can have an angular  611  displacement away from the surface of tubing  650  of just greater than zero degrees to almost 90 degrees depending on the direction an operator wishes to place sensor pod  680 . The greater the angular  611  displacement, the more sensor pod  680  will be deflected away from tubing  650  such that an angular  611  displacement of almost 90 degrees will result in the sensor pod being deflected in a direction almost perpendicular to the surface of tubing  650 . Deflector  610  may be constructed from any suitably hard material that will resist erosion. For example, alloy stainless steel is an appropriate and suitable material from which to construct deflector  610 . Typically, deflector  610  is welded to the base pipe and deflector  610  has a port drilled through it to allow fluid passage.  
         [0043]    Once sensor pod  680  has been drilled into the formation  604 , control line  692  may be retracted out leaving sensor pod  680  in the formation (step  535 ). By leaving control line  692  in place rather than removing it after sensor placement, wire  624  may be better protected. Sensor  622  remains connected to surface electronics  690  via wire  624 . Wire  624  can be an electric wire capable of carrying electronic signals or it can be a fiber optic cable.  
         [0044]    It should be noted that sensor  622  may be recalibrated after placement of sensor  622  downhole in the formation. Such calibration may be accomplished, for example, by means of transmissions via wire  624  or may be through radio and/or acoustic signals.  
         [0045]    To aid in understanding the present invention, refer to the following analogy. Consider a garden hose with a nozzle attached to the end. With the end of the nozzle pushed into the ground, increase the water pressure in the garden hose. The water exiting the nozzle provides an effective drilling tool that allows the hose to be pushed into the ground. This is the principle behind the present invention. The outer tubing will stroke downwards as the formation material is removed. The wire attached to the sensor must have enough length to accommodate the stoke length of the cylinder. The wire may feed through the deflector and continue up the outside of the coiled tubing. This may be useful if the coiled tubing is removed after sensor placement. Otherwise as discussed above, the wire will remain inside the coiled tubing where it is better protected.  
         [0046]    Although the present invention has been described primarily with reference to interrogating the sensors with a wireline tool, other methods of interrogating the sensor may be utilized as well without departing from the scope and spirit of the present invention. For example, the sensors could be interrogated by something built into the completion or by a reflected signal that could power up and interrogate the sensor or sensors.  
         [0047]    The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to best explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.