Patent Publication Number: US-8983819-B2

Title: System, method and computer program product to simulate rupture disk and syntactic foam trapped annular pressure mitigation in downhole environments

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to downhole simulators and, more specifically, to a system to determine the annular pressure buildup along a wellbore in response to the presence of a rupture disk and/or syntactic foam. 
     BACKGROUND 
     The existence of trapped annular pressure and wellhead movement caused by production temperatures is known in the industry. Traditionally, mitigation techniques have been limited to the analysis of the presence of gas cap, leak off, volume bleed, and annular venting conditions. Although rupture disks and syntactic foam are known in the industry, there exists no means to analyze the effects that such mitigation techniques have on the annular pressure buildup or final system pressure equilibrium of the wellbore. 
     Accordingly, in view of the foregoing shortcomings, there is a need in the art for a systematic analysis that predicts and/or determines the effect that the use of rupture disks and syntactic foam would have on trapped annular pressure and wellhead movement. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a block diagram of a downhole mitigation system according to an exemplary embodiment of the present invention; 
         FIG. 2  is a flow chart illustrating data flow associated with an exemplary methodology of the present invention; 
         FIG. 3  is a screen shot of an interface having various wellbore configuration windows according to an exemplary embodiment of the present invention; 
         FIG. 4  is a screen shot illustrating a Wellbore configuration according to an exemplary embodiment of the present invention; and 
         FIG. 5  is a screen shot illustrating an annular fluid expansion summary utilizing an exemplary embodiment of the present invention. 
     
    
    
     DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Illustrative embodiments and related methodologies of the present invention are described below as they might be employed in a system for analyzing the effects of mitigation techniques on trapped annular pressure and wellhead movement in downhole environments. In the interest of clarity, not all features of an actual implementation or methodology are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. Further aspects and advantages of the various embodiments and related methodologies of the invention will become apparent from consideration of the following description and drawings. 
       FIG. 1  shows a block diagram of downhole mitigation system  100  according to an exemplary embodiment of the present invention. In one embodiment, downhole mitigation system  100  includes at least one processor  102 , a non-transitory, computer-readable storage  104 , transceiver/network communication module  105 , optional I/O devices  106 , and an optional display  108 , all interconnected via a system bus  109 . Software instructions executable by the processor  102  for implementing software instructions stored within mitigation simulator  110  in accordance with the exemplary embodiments described herein, may be stored in storage  104  or some other computer-readable medium. 
     Although not explicitly shown in  FIG. 1 , it will be recognized that downhole mitigation system  100  may be connected to one or more public and/or private networks via appropriate network connections. It will also be recognized that the software instructions comprising mitigation simulator  110  may also be loaded into storage  104  from a CD-ROM or other appropriate storage media via wired or wireless means. 
       FIG. 1  further illustrates a block diagram of mitigation simulator  110  according to an exemplary embodiment of the present invention. As will be described below, mitigation simulator  110  comprises drilling prediction module  112 , production prediction module  114 , casing stress module  116 , tubing stress module  118 , multi-string module  120 , and an annular pressure buildup (“APB”) module  122 . Based upon the input variables as described below, the algorithms of the various modules combine to formulate the downhole mitigation analysis of the present invention. 
     Drilling prediction module  112  simulates, or models, drilling events and the associated well characteristics such as the drilling temperature and pressure conditions present downhole during logging, trip pipe, casing, and cementing operations. Production prediction module  114  models production events and the associated well characteristics such as the production temperature and pressure conditions present downhole during circulation, production, injection, gas lift and shut in operations. Casing stress module  116  models the stresses caused by changes from the initial to final loads on the casing, as well as the temperature and pressure conditions affecting the casing. 
     Tubing stress module  118  simulates the stresses caused by changes from the initial to final loads on the tubing, as well as the temperature and pressure conditions affecting the tubing. The modeled data received from the foregoing modules is then fed into multi-string module  120  which analyzes and then models the annular fluid expansion and wellhead movement present in a system defined by the original input variables. Thereafter, the data modeled in multi-string module  120  is then fed into APB module  122 , which models the annular fluid expansion and wellhead movement in light of defined mitigation techniques that provide additional volume for the fluid to expand without increasing pressure. Persons ordinarily skilled in the art having the benefit of this disclosure realize there are a variety modeling algorithms that could be employed to achieve the results of the foregoing modules. 
       FIG. 2  illustrates the data flow of downhole simulation system  100  according to an exemplary methodology of the present invention. At step  200 , the mechanical configuration of the well is defined using manual or automated means. For example, a user may input the well variables via I/O device  106  and display  108 . However, the variables may also be received via network communication module  105  or called from memory by processor  102 . In this exemplary embodiment, the input variables define the well configuration such as, for example, number of strings, casing and hole dimensions, fluids behind each string, cement types, and undisturbed static downhole temperatures. As will be described later, this configuration data also defines characteristics of rupture disks and/or syntactic foam used for mitigation. Based upon these input variables, at step  202 , using drilling prediction module  112 , processor  102  models the temperature and pressure conditions present during drilling, logging, trip pipe, casing, and cementing operations. At step  204 , processor  102  then outputs the initial drilling temperature and pressure of the wellbore. 
     Further referring to  FIG. 2 , at step  206 , processor  102  outputs the “final” drilling temperature and pressure. Here, “final” can also refer to the current drilling temperature and pressure of the wellbore if the present invention is being utilized to analyze the wellbore in real time. If this is the case, the “final” temperature and pressure will be the current temperature and pressure of the wellbore during that particular stage of downhole operation sought to be simulated. Moreover, the present invention could be utilized to model a certain stage of the drilling or other operation. If so, the selected operational stage would dictate the “final” temperature and pressure. 
     The initial and final drilling temperature and pressure values are then fed into casing stress module  116 , where processor  102  simulates the stresses on the casing strings caused by changes from the initial to final loads, as well as the temperature and pressure conditions affecting those casing strings, at step  208 . At step  210 , processor  102  then outputs the initial casing mechanical landing loading conditions to multi-string module  120  (step  216 ), Referring back to step  200 , the inputted well configuration data may also be fed directly to multi-string module  120  (step  216 ). In addition, back at step  204 , the initial drilling temperature and pressure data can be fed directly into multi-string module  120  (step  216 ). 
     Still referring to the exemplary methodology of  FIG. 2 , back at step  202 , processor  102  has modeled the drilling temperature and pressure conditions present during drilling, logging, trip pipe, casing, and cementing operations. Thereafter, at step  212 , these variables are fed into production prediction module  114 , where processor  102  simulates production temperature and pressure conditions during operations such as circulation, production, and injection operations. At step  214 , processor determines the final production temperature and pressure based upon the analysis at step  212 , and this data is then fed into multi-string module  120  at step  216 . 
     Referring back to step  212 , after the production temperature and pressure conditions have been modeled, the data is fed into tubing stress module  118  at step  226 . Here, processor  102  simulates the tubing stresses caused by changes from the initial to final loads, as well as the temperature and pressure conditions affecting the stress state of the tubing. Thereafter, at step  220 , processor  102  outputs the initial tubing mechanical landing loading conditions, and this data is fed into multi-string module  120  (step  216 ). At step  216 , now that all necessary data has been fed into multi-string module  120 , the final (or most current) well system analysis and simulation is performed by processor  102  in order to determine the annular fluid expansion (i.e., trapped annular pressures) and wellhead movement. 
     Thereafter, at step  222 , processor  102  performs an APB analysis of the wellbore (using APB module  122 ) as defined by the data received from multi-string module  120 . Here, taking into account defined rupture disk and syntactic foam data, APB module  122  will analyze and simulate the annular fluid expansion (i.e., trapped annular pressure) and wellbore movement over the life of the defined wellbore. In doing so, processor  102  will calculate a final APB for the wellbore that will be defined by the minimum of the initial calculated pressure buildup (“Pb”), annular vented pressure (“Pv”), syntactic foam volume (“Pfv”), and the maximum of differential Pleak (Pl−Ph) and Pdisk (Pd−Ph), as described below. Thereafter, at step  224 , processor  102  outputs the final APB. Accordingly, the methodology illustrated in  FIG. 2  may be used to simulate well designs according to desired mitigation techniques, even in real-time through linkage of final thermal operating conditions to the desired downhole event. 
       FIG. 3  illustrates a user interface  300  utilized to defined wellbore characteristics and mitigation data according to an exemplary embodiment of the present invention. At step  200 , user interface  300  is displayed on display  108 . In window  302 , a list of user-specified string characteristics are displayed. Windows  304  and  306  are used to define initial conditions and annulus options, respectively. In window  308 , the mitigation options can be defined to include any number of rupture disks per string and their respective depths, burst ratings, and collapse ratings. In window  310 , the well configuration can be defined to include a specified collapse volume of syntactic foam, crush volume percentage, Pcrush pressure, and Pcrush temperature. Syntactic foams belongs to a class of material known as cellular solids, and they are characterized by internal porous structure. The pore spaces usually are reinforced with glass or carbon fiber glass beads. The behavior of syntactic foam is determined principally by its crush pressure, Pcrush. Pcrush, or crush pressure, is the hydrostatic pressure that causes the foam modules to crush catastrophically until all the pore spaces either have collapse or are filled with the invading fluid. When this happens, crushes cease. 
     A vented or unvented annulus  311  may also be defined. Lastly, window  312  allows definition of the final conditions such as, for example, a production operation and a corresponding time period. After the well configuration data has been defined via interface  300 , downhole simulation system  100  simulates the effects that the defined rupture disks and syntactic foam would have on the APB over the specified life of the well. 
     As described above, the present invention allows definition of annular fluid expansion mitigation techniques that provide additional volume for fluid to expand without increasing pressure. In exemplary embodiments of the present invention, rupture disks and syntactic foam are utilized as the mitigation mechanisms. By placing a sufficient volume of crushable syntactic foam in the annulus during subsequent well operations (e.g., production), additional volume is provided to allow the fluid to expand without increasing pressure. As the pressure increases downhole, the syntactic foam would crush, thereby providing additional volume. Rupture disks provide outer and inner wall casing protection, as they can be designed to fail upon a specified internal or external pressure, or at a given temperature. 
     A summary description of the mathematical logic utilized by mitigation simulator  110  will now be briefly described, as persons ordinarily skilled in the art having the benefit of this disclosure would readily understand. In the fluid expansion modeling of the present invention, the two primary factors affecting heat up pressures are the thermal expansion of confined annular fluids and the radial or axial movement of the enclosing casings. These effects are coupled through pressure and must be solved simultaneously. The thermal fluid expansion for a given annulus may be determined as follows: 
     Assuming that vertical dimensions are fixed, conservation of mass requires:
 
 Mf=∫ρfAdz=∫ ( pf+Δpf )( A+ΔA ) dz,   Equation (1):
 
     where Mf is the fixed annular fluid mass, pf is the fluid density, A is the annular cross-sectional area, and Δ denotes the change from the initial to the final state. Initial densities are evaluated at setting pressures and temperatures, and final densities are evaluated at the operating conditions including heat pressures. 
     The net fluid volume change can then be determined as follows:
 
Δ Vf=∫ΔAdz=∫AΔpf /( pf+Δpf ) dz   Equation (2):
 
     After the casings are set, they are subjected to various types of incremental loads that result from changes in applied loads or wellbore pressures and temperatures. These load changes result in interactive string movements that cause the enclosed annular spaces to vary in volume. For a given annulus, the net volume change is computed by numerically integrating volume changes caused by the elastic deformation of the confining casing/tubing strings as follows:
 
Δ Va =π∫[(Δ ro   2 +2 Δroro )−(Δ ri   2 +2 Δriri )] dz+ΔVz,   Equation (3):
 
     where ri is the inside radius of the annulus (i.e., the outside radius of the inner casing or tubing); ro is the outside radius of the annulus (i.e., the inside radius of the outer casing); Δri and Δro refer to the incremental radial displacements at r=ri, and ro, respectively; and ΔVz is the volume change resulting from the change in annulus axial dimensions. A volume residual is then defined as follows:
 
 Vr=ΔVf−ΔVa,   Equation (4):
 
     where the pressure build up pbu is found until the Vr=zero. 
     Once leakoff pressure, pl, annular vent pressure, pv, rupture disk pressure, pd, and syntactic foam volume, Pfv, are specified, then:
 
Pressure build up ( Pbu )=min[ pb,pv,pfv ,max(0,( pl−ph ),( pd−ph ))],
         where ph is the hydrostatic pressure at leakoff depth.       

     Utilizing APB module  122 , processor  102  repeats this analysis for each sealed annulus. As a result, downhole simulation system  100  then determines the final APB along the wellbore, which will be the minimum of the Pb, Pv, Pfv, and the maximum of differential Pleak and Pdisk. Once multi-string equilibrium is attained, global well convergence is reached. As such, the present invention may also include a progressive failure analysis of rupture disk failure(s) in a multiple rupture disk per string scenario until the pressure system equilibrates. 
       FIG. 4  illustrates a screen shot  400  showing a well schematic displayed utilizing an exemplary embodiment of the present invention. The well configuration includes four annulus; A, B, C, D and E. Annulus A is expected to be vented to surface, while Annuli C, D and F are exposed to uncemented open holes, leaked to formation. Rupture disk(s)  402  has been installed in 9⅝″ protective casing with a designed burst disk rating to induce a fluids bled path from Annulus B to Annulus C, and eventually to leak to the formation. Also, in the event of a rupture disk collapse scenario (due to a rupture disk burst rating malfunction and annulus C pressures in excess to hydrostatic not leaking into formation), a volume of syntactic foam (designated by  404 ) by design has been installed along the 7″ production casing length to provide additional fluid volume pressure relief. In this exemplary embodiment, schematic  400  is presented in display  108 , showing the mitigation options applied to the analysis. 
       FIG. 5  illustrates a screen shot of the fluid expansion summary produced using exemplary embodiments of the present invention. After step  222 , once the analysis of mitigation system  100  is complete, fluid expansion summary  500  may be displayed via display  108 . As shown, each defined string annulus, its location, and corresponding pressures and volumes are detailed. In addition, a wellhead movement displacement summary is also included. 
     Although rupture disks and syntactic foam are described herein as mitigation options, those ordinarily skilled in the art having the benefit of this disclosure realize there are other mitigation options that could be simulated within the present invention, and this disclosure is meant to encompass those additional options as well. For example, other traditional mitigation options, such as annular vented (Annulus A as described in  FIG. 4 ), leak-off ( FIG. 4 , Annulus C, D, and E), as well as Gas cap volume and amount of volume bled ( FIG. 3 ) can be applied in combination with the rupture disk and syntactic foam to manage final trapped annuli pressure utilizing embodiments of the present invention. 
     Accordingly, exemplary embodiments of the present invention may be utilized to conduct a total well system analysis during the design phase or in real-time. It can also be used to analyze the influence that rupture disks and syntactic foam has on the thermal expansion of annulus fluids, and/or the influence of loads imparted on the wellhead during the life of the well, as well as the load effects on the integrity of a well&#39;s tubulars. Accordingly, the load pressures and associated wellhead displacement values are used to determine the integrity of a defined set of well tubulars in the completed well or during drilling operations. 
     Although various embodiments and methodologies have been shown and described, the invention is not limited to such embodiments and methodologies and will be understood to include all modifications and variations as would be apparent to one skilled in the art. Therefore, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the appended claims.