Patent Publication Number: US-6664522-B2

Title: Method and apparatus for sealing multiple casings for oil and gas wells

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application in a continuation-in-part of application Ser. No. 10/084,986 filed Feb. 27, 2002 which is a continuation-in-part of application Ser. No. 09/539,184 filed Mar. 30, 2000, now issued on May 7, 2002 under U.S. Pat. No. 6,384,389. 
    
    
     INTRODUCTION 
     This invention relates to a method and apparatus for sealing oil and gas wells and, more particularly, to a method and apparatus for sealing any or a plurality of multiple casings that may be used in oil and gas wells. 
     BACKGROUND OF THE INVENTION 
     The leakage of shallow gas through the casing cement used in well completion is often a problem in oil and gas wells. Such leakage is generally caused by inherent high pressures in oil and gas wells and can create environmental problems and compromise well safety. This leakage most often occurs because of cracks or other imperfections that occur in the cement that is injected into the well during well completion procedures between the surface and production casings. 
     Techniques for preventing shallow gas leakage are disclosed in Rusch, David W. et al, “Use of Pressure Activated Sealants to Cure Sources of Casing Pressure”, SPE (Society of Petroleum Engineers) Paper 55996. These techniques use the application of an epoxy sealing technique. One disadvantage in using the technique taught by Rusch et al is that high pressure differentials across the source of leakage are required. 
     There is disclosed and illustrated a method and apparatus for subterranean thermal conditioning of petroleum in oil wells in Canadian patent application 2,208,197 (Isted) which application was laid open in Canada on or about Dec. 18, 1998. This document teaches the use of an electrical induction technique to provide heat to oil, particularly high viscosity heavy oil and oil containing high proportions of wax. Electrical induction is thought to be a much preferred method to supply heat to oil within a well because of the combustibility of the hydrocarbon products. Further, the benefits of this technique over the previous steam application technique include the fact that the steam used may cause damage to the permeability of the reservoir. This change may adversely affect oil production. 
     The use of electrical induction by Isted which is disclosed in the above-identified &#39;197 application, however, is not contemplated to be also useful for sealing an annular space between surface and production casing. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, there is provided a method for melting a material in any of a plurality of casing annuluses of an oil or gas well, said method comprising positioning said material to be melted at a predetermined location within said any of said annuluses and applying heat to said material, melting said material by said application of said heat and terminating said application of said heat following said melting of said material thereby to allow said material to solidify within said any of said annuluses to form a seal within said any of said annuluses. 
     According to a further aspect of the invention, there is provided an apparatus for melting material in any of a plurality of casings annuluses of an oil or gas well, said material to be placed into said any of said annuluses and to assume a predetermined location within said any of said annuluses, heating apparatus to apply heat to said material at said predetermined location within said any of said annuluses and to melt said material within said any of said annuluses and a switch to initiate and terminate said application of said heat from said heating apparatus to said material. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     Specific embodiments of the invention will now be described, by way of example only, with the use of drawings in which: 
     FIG. 1 is diagrammatic cross-sectional view of an oil or gas well particularly illustrating the location of the eutectic metal and the induction apparatus according to one aspect of the invention; 
     FIG. 2 is an enlarged diagrammatic cross-sectional view of an oil or gas well particularly illustrating the cement used in setting the production and surface casings relative to the metal used for sealing the annulus; 
     FIG. 3 is a diagrammatic side cross-sectional view of a magnetic induction assembly positioned in a vertical well and being in accordance with the present invention; 
     FIG. 4 is a diagrammatic side cross-sectional view of one of the magnetic induction apparatuses from the magnetic induction assembly illustrated in FIG. 3; 
     FIG. 5 is a diagrammatic plan cross-sectional view, taken along section lines V—V of the magnetic induction apparatus illustrated in FIG. 4; 
     FIG. 6 is a diagrammatic side, cross-sectional view of the primary electrical connection from the magnetic induction assembly illustrated in FIGS. 3 and 4; 
     FIG. 7 is a diagrammatic end cross-sectional view, taken along section lines VI—VI of the primary electrical connection illustrated in FIG. 6; 
     FIG. 8 is a diagrammatic partial side cross-sectional view of the male portion of the conductive coupling from the magnetic induction assembly illustrated in FIG. 3; 
     FIG. 9 is an end elevation view of the male portion of the conductive coupling illustrated in FIG. 8 taken along IX—IX of FIG. 8; 
     FIG. 10 is a side elevation sectional view of a portion of the male portion of the conductive coupling illustrated in FIG. 8; 
     FIG. 11 is a side sectional view of a female portion of the conductive coupling of the magnetic induction assembly illustrated in FIG. 3; 
     FIG. 12 is a side sectional view of the male portion illustrated in FIG. 8, coupled with the female portion illustrated in FIG. 11; 
     FIG. 13 is a side sectional view of the adapter sub of the magnetic induction assembly illustrated in FIG. 3; 
     FIG. 14 is an end sectional view taken along lines XIV—XIV of FIG. 13; 
     FIG. 15 is a schematic of a power control unit used with the magnetic induction assembly according to the invention; 
     FIG. 16, appearing with FIG. 14, is an end sectional view of a first alternative internal configuration for the magnetic induction apparatus according to the invention; 
     FIG. 17 is an end sectional elevation view of a second alternative internal configuration for the magnetic induction apparatus according to the invention; 
     FIG. 18 is an end sectional view of a third alternative internal configuration for the magnetic induction apparatus according to the invention; 
     FIG. 19 is a diagrammatic side elevation sectional view of the instrument and sensor components used with the magnetic induction assembly according to the invention; 
     FIG. 20 is an end elevation sectional view of a production tubing heater illustrated in FIG. 3; and 
     FIG. 21 is a diagrammatic side cross-sectional view similar to FIG. 2 but illustrating a plurality of annuluses within an oil or gas well according to a further aspect of the invention. 
    
    
     DESCRIPTION OF SPECIFIC EMBODIMENT 
     Referring now to the drawings, the surface and production casings of an oil or gas well generally illustrated at  100  are illustrated at  101 ,  102 , respectively. The outside or surface casing  101  extends from the surface  105  (FIG. 2) of the formation downwardly and the production casing  102  extends downwardly within the surface casing  101 . An annulus  110  is formed between the production and surface casings  101 ,  102 , respectively. It will be appreciated that FIG. 2 is intended to diagrammatically illustrate an offshore well while FIG. 3 is intended to diagrammatically illustrate an onshore oil or gas well. 
     An injection port  103  extends downwardly from the surface into the annulus  110  between the surface and production casings  101 ,  102 . The injection port  103  is used not only to inject certain fluids into the annulus  110  but is also used to carry small shot pellets  104  in the form of BB&#39;s which are poured into place via the injection port  103 . The small shot pellets  104  are preferably made from an eutectic metal; that is, they have a relatively low melting point and can be liquified by the application of certain heat as will be explained. The injection port  103  further and conveniently may carry a suitable marker or tracer material such as radioactive boron or the like which is added to the shot  104  so that the location of the eutectic metal in the annulus  110  can be detected with standard well logging tools to ensure proper quantities of the metal being appropriate situated. 
     An electrical induction apparatus generally illustrated at  111  is located within the production casing  102 . It may conveniently comprise three inductive elements  112 ,  113 ,  114  which are mounted on a wire line  120  which is used to raise or lower the induction apparatus  111  so as to appropriately locate it within the production casing  102  adjacent the shot pellets  104  following their placement. 
     The induction apparatus  111  will be described in greater detail. 
     More than one magnetic induction apparatus  111  (FIG. 3) may be used and they may be joined together as part of a magnetic induction assembly, generally indicated at  126 . A magnetic field is induced in and adjacent to well casing  102  by means of the magnetic induction apparatus  111  thereby producing heat. 
     The magnetic induction assembly  126  includes an adapter sub  128 , a electrical feed through assembly  130 , and a plurality of magnetic induction apparatus  111  joined by conductive couplings  132 . 
     Each magnetic induction apparatus  111  has a tubular housing  134  (FIGS.  4  and  5 ). Housing  134  may be magnetic or non-magnetic depending upon whether it is desirable to build up heat in the housing itself. Housing  134  has external centralizer members  136  (FIG. 6) and a magnetically permeable core  138  is disposed in housing  134 . Electrical conductors  140  are wound in close proximity to core insulated dividers  142  which are used for electrically isolating the electrical conductors  140 . Housing  134  has may be filled with an insulating liquid, which may be transformed to a substantially incompressible gel  137  so as to form a permanent electrical insulation and provide a filling that will increase the resistance of housing  134  to the high external pressures inherent in the well  100 . The cross sectional area of magnetic core  138 , the number of turns of conductors  140 , and the current originating from the power control unit (PCU) may be selected to release the desired amount of heat when stimulated with a fluctuating magnetic field at a frequency such that no substantial net mechanical movement is created by the electromagnetic waves. Power conducting wires  141  and signal conducting wires  143  are used to facilitate connection with the PCU. For reduced heat release, a lower frequency, fewer turns of conductor, lower current, or less cross sectional area or a combination will lower the heat release per unit of length. Sections of inductor constructed in this fashion allow the same current to pass from one magnetic inductor apparatus  111  to another. 
     FIGS. 16,  17  and  18  illustrate alternative internal configurations for electrical conductors  140  and core  138  but are not intended to limit the various configurations possible. Where close fitting of inductor poles to the casing or liner is practical, additional magnetic poles may be added to the configuration with single or multiple phase wiring through each to suit the requirements. A number of inductors (i.e., core  138  with electrical conductors  140 ) may be contained in housing  134  with an overall length to suit the requirements and or shipping restraints. A multiplicity of housings  134  may connect several magnetic induction apparatuses  111  together to form a magnetic induction assembly  126 . These induction apparatuses  111  may be connected with flanged and bolted joints or with threaded ends similar in configuration and form to those used in the petroleum industry for completion of oil and gas wells. At each connection for magnetic induction apparatus  111 , there is positioned a conductive coupling  132 . Conductive coupling  132  may consist of various mechanical connectors and flexible lead wires. 
     The adapter sub  128  (FIG. 13) allows a cable, conveniently electrical submersible pump(ESP) cable  166 , to be fed into top  168  of magnetic induction assembly  126  although other types of cables are available. Adapter sub  128  comprises a length of tubing  170  which has an enlarged section  174  near the midpoint such that the ESP cable  166  may pass through tubing  170  and transition to outer face  172  of tubing  70  by passing through a passageway  76  in enlarged section  174 . Adapter sub  128  has a threaded coupling  178  to which the wellbore tubulars (not shown) may be attached thereby suspending magnetic induction assembly  126  at the desired location and allowing retrieval of the magnetic induction assembly  126  by withdrawing the wellbore tubulars. 
     ESP cable  166  is coupled to an uppermost end  168  of magnetic induction assembly  126  by means of electrical feed through assembly  130  (FIG.  6 ). These assemblies are specifically designed for connecting cable to cable, cable through a wellhead, and cable to equipment and the like. The connection may also be made through a fabricated pack-off comprised of a multiplicity of insulated conductors with gasket packing compressed in a gland around the conductors so as to seal formation fluids from entering the inductor container. Electrical feed through assembly  130  has the advantage that normal oil field thread make-up procedures may be employed thus facilitating installation and retrieval. Use of a standard power feed allows standard oil field cable splicing practice to be followed when connecting to the ESP cable from magnetic induction assembly  126  to surface. 
     Magnetic induction assembly  126  works in conjunction with a power conditioning unit (PCU)  180  located at the surface or other desired location (FIG.  3 ). PCU  180  utilizes single and multiphase electrical energy either as supplied from electrical systems or portable generators to provide modified output waves for magnetic induction assembly  126 . The output wave selected is dependent upon the intended application but square wave forms have been found to be most beneficial in producing heat. Maximum inductive heating is realized from waves having rapid current changes (at a given frequency) such that the generation of square or sharp crested waves are desirable for heating purposes. The PCU  180  has a computer processor  181  (FIG.  15 ). It is preferred that PCU  180  includes a solid state wave generating device such as silicon controlled rectifier(SCR) or insulated gate bipolar transistor(IGBT)  121  controlled from an interactive computer based control system in order to match system and load requirements. One form of PCU  180  may be configured with a multi tap transformer, SCR or IGBT and current limit sensing on-off controls. The preferred system consists of an incoming breaker, overloads, contactors, followed by a multitap power transformer, an IGBT or SCR bridge network and micro-processor based control system to charge capacitors to a suitable voltage given the variable load demands. The output wave should then be generated by a micro-controller. The micro-controller can be programmed or provided with application specific integrated circuits, in conjunction with interactive control of IGBT and SCR, control the output electrical wave so as to enhance the heating action. Operating controls for each phase include antishoot through controls such that false triggering and over current conditions are avoided and output wave parameters are generated to create the in situ heating as required. Incorporated within the operating and control system is a data storage function to record both operating mode and response so that optimization of the operating mode may be made either under automatic or manual control. PCU  180  includes a supply breaker  182 , overloads  184 , multiple contactors  186  (or alternatively a multiplicity of thyristors or insulated gate bipolar transistors), a multitap power transformer  188 , a three phase IGBT or comparable semiconductor bridge  190 , a multiplicity of power capacitors  192 , IGST  121  output semiconductor anti shoot through current sensors  194 , together with current and voltage sensors  196 . PCU  180  delivers single and multiphase variable frequency electrical output waves for the purpose of heating, individual unidirectional output wave, to one or more of magnetic induction apparatuses  111 , such that the high current in rush of a DC supply can be avoided. PCU  180  is equipped to receive the downhole instrument signals interpret the signals and control operation in accordance with program and set points. PCU  180  is connected to the well head with ESP cable  166 , which may also carry the information signals (FIG.  3 ). An instrument device  198  is located within each magnetic induction apparatus  111  (FIG. 19) for the purpose of receiving AC electrical energy from the inductor supply, so as to charge a battery  200 , and which, on signal from PCU  180 , commences to sense, in a sequential manner, the electrical values of a multiplicity of transducers  202  located at selected positions along magnetic induction apparatus  111  such that temperatures and pressures and such other signals as may be connected at those locations may be sensed and as part of the same sequence. One or more pressure transducers may be sensed to indicate pressure at selected locations and the instrument outputs a sequential series of signals which travel on the power supply wire(s) to the PCU wherein the signal is received and interpreted. Such information may then be used to provide operational control and adjust the output and wave shape to affect the desired output in accordance with control programs contained within the PCU computer and micro controllers. 
     Operation 
     In operation and with initial reference to FIGS. 1 and 2, the eutectic metal, conveniently solder and being in the form of BB&#39;s or shot  104 , is inserted into the annulus  110  by way of injection port line  103  which has allows installation of the shot  104  to a desired position within the annulus  110 . The solder shot  104  is inserted into the annulus  110  to such an extent that the annulus is filled with the shot  104  for a predetermined distance above the well cement  115  as best illustrated in FIG.  2 . Radioactive tracer elements can conveniently be added to the shot  104  thereby allowing standard well logging equipment to determine whether the correct location of the shot  104  has been reached and whether it is of consistent thickness or depth around the annulus  110 . 
     Thereafter, the electrical induction heating apparatus  111  is lowered into position within the production casing and its operation is initiated (FIG. 1) as heretofore described. The heat generated by the induction apparatus  111  is transmitted through the production casing  102  to the shot  104  and melts the eutectic metal  104 . This timing period can be calculated so that the required melting time period is reached and the temperature of the production casing to obtain such melting can be determined. 
     Following the melting of the shot  104  and, therefore, the sealing of the annulus  110  above the cement  115  between the surface and production casings  101 ,  102 , the operation of the electrical induction apparatus  111  is terminated and the apparatus  111  is removed from the production casing  102 . Any leakage through anomalies  116  in the cement  115  is intended to be terminated by the now solid eutectic metal  104 . Of course, additional metal may be added if desired or required. The use of the induction apparatus  111  to generate heat reduces the inherent risk due to the presence of combustible hydrocarbons. 
     A eutectic metal mixture, such as tin-lead solder  104 , is used because the melting and freezing points of the mixture is lower than that of either pure metal in the mixture and, therefore, melting and subsequent solidification of the mixture may be obtained as desired with the operation of the induction apparatus  111  being initiated and terminated appropriately. This mixture also bonds well with the metal of the production and surface casings  102 ,  101 . The addition of bismuth to the mixture can improve the bonding action. Other additions may have the same effect. Other metals or mixtures may well be used for different applications depending upon the specific use desired. 
     In a further embodiment of the invention, it is contemplated that a material other than a metal and other than a eutectic metal may well be suitable for performing the sealing process. 
     For example, elemental sulfur and thermosetting plastic resins are contemplated to also be useful in the same process. In the case of both sulfur and resins, pellets could conveniently be injected into the annulus and appropriately positioned at the area of interest as has been described. Thereafter, the solid material is liquified by heating. The heating is then terminated to allow the liquified material to solidify and thereby form the requisite seal in the annulus between the surface and production casing. In the case of sulfur pellets, the melting of the injected pellets would occur at approximately 248 deg. F. Thereafter, the melted sulfur would solidify by terminating the application of heat and allowing the subsequently solidified sulfur to form the seal. Examples of typical thermosetting plastic resins which could conveniently be used would be phenol-formaldehyde, urea-formaldehyde, melamine-formaldehyde resins and the like. 
     Likewise, while the heating process described in detail is one of electrical induction, it is also contemplated that the heating process could be accomplished with the use of electrical resistance which could assist or replace the electrical induction technique. Indeed, any heating technique could usefully be used that will allow the solid material positioned in the annulus to melt and flow into a tight sealing condition and, when the heating is terminated, allow the material to cool thereby forming the requisite seal. The use of pressure within the annulus might also be used to affect and to initiate the polymerization process when thermosetting resins are being used. For example, high pressure nitrogen or compressed air could be injected into the annulus to increase the pressure in order to enhance the polymerization process. 
     Reference is made to FIG. 21 wherein an oil or gas well is generally shown at  200  with the production casing  201  extending the deepest below the mud line  202  and the surface casing  203  being the uppermost casing and having the smallest longitudinal distance. In this instance, there are a plurality of casings between the production and surface casings  201 ,  203 , respectively, namely intermediate casings  204 ,  205 ,  206 . Such a configuration is particular used in offshore oil and gas wells with each of the intermediate casings  204 ,  205 ,  206  having progressively smaller longitudinal distances. Well cement  210  fills the area outside each successive casing and extends upwardly to the next outer casing thereby to form a seal between adjacent casings. For example, cement  210  extends from the bottom of casing  204  and upwardly into the annulus between casings  204 ,  210  thereby to seal the annulus above the cement  210 . 
     The technique according to the invention is likewise envisioned to be applicable in this event. For example, if there is found to be a fault in the casing cement as at  211  in FIG. 21, the material to be melted, conveniently a eutectic metal such as solder  212  in the correct quantity is placed between the casings  204 ,  250  in its old and unmelted form. When the correct position for the solder is reached, the application of heat from the heating tool  213  is initiated by the application of power through the switching arrangement as previously described. The heating tool  213  will increase the temperature of the solder to that required to liquify the material thereby forming a pool on the top of the cement  210  and extending about the annulus  211 . Upon the liquification process being completed, the application of the excitement or heating from the heating tool  213  will be terminated thereby allowing the liquid solid to again solidify thereby creating an impregnable barrier or seal between the casings  204 ,  205  and correcting the problems result from the fault  211  in the well cement. 
     While it is contemplated the induction heating technique will be used with a eutectic metal as previously described, other materials may well likewise be found useful also as previously described. Similarly, other heating techniques might also be useful such as the application of electrical resistance or any excitation of the otherwise solid material which can be used to create the liquid state and, upon excitation termination, will allow the material to solidify thereby forming the seal. 
     Many additional modifications will readily occur to those skilled in the art to which the invention relates and the specific embodiments described should be taken as illustrative of the invention only and not as limiting its scope as defined in accordance with the accompanying claims.