Abstract:
A through casing formation evaluation tool string  1000, 2000, 3000  including a conveyance string  100 , a sonic array tool  200 , a pulsed neutron tool  400  and one or more downhole memory modules  160, 540, 550 . A method of through casing formation evaluation and casing and cementing integrity evaluation includes lowering a tool string into a cased wellbore; concurrently collecting data with the sonic array tool and pulsed neutron tool and transmitting at least a portion of the collected data via a conveyance string to a CPU located at the surface of the earth; storing a portion of the collected data in a memory module disposed in the tool string; removing the tool string from the wellbore; processing the collected data in the CPU to obtain selected rock property data about the one or more of the geologic formations and/or cement integrity.

Description:
CLAIM OF PRIORITY 
     This application claims priority under 35 USC §365(c) to International Patent Application Serial No. PCT/US2010/049146, entitled “Combined Sonic/Pulsed Neutron Cased Hole Logging Tool”, filed on Sep. 16, 2010, which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     This disclosure relates to formation and casing evaluation tools and methods of formation evaluation, and more particularly a combination sonic and pulsed neutron tool for formation evaluation through casing, and casing and cementing integrity evaluation and methods for use for same. 
     BACKGROUND 
     In many reservoirs throughout the world it is necessary to hydraulically fracture the reservoir to produce commercial quantities of oil and gas. In order to design such hydraulic fracture stimulation treatments it is desirable to understand the in-situ stress profiles. To calculate the in-situ stress profile it is desirable to have mechanical rock properties and pore pressure data in and around the target producing zones of the reservoir. Previously, it was necessary to obtain much of the needed data used in the stimulation designs with logs run in an open hole environment, while the well was being drilled, or in open hole logging runs after the desired interval had been penetrated and before casing had been placed in the wellbore. Obtaining the data in an open hole environment while the drilling rig is on location results in the well operator incurring the cost of the drilling rig time while the logging operation is conducted. Additionally, it is sometimes necessary to remove the drill string and bit and then rerun the drill string and bit to the bottom of the hole and remove it again (aka “make a wiper trip in and out of the hole”) to circulate and condition the drilling fluids (aka “drilling mud”) to prepare the open hole for formation evaluation tools. This conditioning of the open hole results in additional costs for the drilling fluids and additional rig time costs. Use of an open hole formation evaluation tool (aka “open hole logging”) has some risks. In highly deviated and/or horizontal wells it is sometimes difficult to get the open hole formation evaluation tools (aka “logging tools”) to the portion of the wellbore in the desired geologic intervals, necessitating additional rig time and expense. It is also possible that the logging tools may become stuck in the wellbore which may necessitate expensive retrieval operations (aka “fishing operations”) to retrieve the stuck logging tools. If the logging tools are not able to be retrieved, it may be necessary to drill a replacement portion for the wellbore or even abandon the wellbore and drill a new well. 
     A need exists for obtaining formation evaluation data (aka “log data”) to be used in wellbore design and hydraulic fracture stimulation design in an alternative manner to open hole logging. A further need exists for a cased hole combination logging tool for use in analyzing casing(s) and cement integrity in a well bore. 
     SUMMARY 
     The present disclosure provides an alternative through casing formation evaluation tool to open hole formation evaluation tools by combining pulsed neutron and sonic technology in a mono-cable format for use in a single cased hole logging run. This is an efficient and cost saving approach to obtaining the desired formation evaluation data (aka “log data”) for well design and hydraulic stimulation design and for a cased hole combination logging tool for use in analyzing casing(s) and cement integrity in a wellbore. Since the wellbore is cased, the drilling rig may be removed before a logging run using the tool of the present disclosure, and therefore considerable money is saved by avoiding the rig time incurred during open hole logging. The combined tool and method of the present disclosure also saves money by making only a single cased hole logging trip versus several trips necessary to obtain the data using individual tools each in a single logging run. Risk of losing logging tools in the well is minimized by using cased hole logging versus open hole logging. It is generally easier to get the logging tools to the desired geologic zones in a cased hole as opposed to an open hole, especially in highly deviated or horizontal wellbores. Risk of losing tools in a cased hole is minimized by using a single logging run with the combination tool in the cased hole instead of multiple runs with single tools. 
     The data obtained with the combined tool of the present disclosure provides formation measurements through casing(s) and cement. The tools may obtain data on casing(s) string and cement integrity; fluids saturations and rock properties of the reservoir; including DTC (compressional slowness); DTS (shear slowness); minimum horizontal stress profile; porosity; simple mineralogy; matrix sigma; pseudo density; and full wave information. The robustness of the gathered data is useful for optimal well design and for improved hydraulic fracture and acidization stimulation design and placement used in completing and stimulating the well and for determining the integrity of one or more casing strings and cement in the wellbore. 
     In some embodiments, the combined tool string may be less than 3 inches in outside diameter, thereby allowing for ease of conveyance of the tool string in small internal diameter cased wellbores, tubing, drill pipe and within highly deviated and horizontal wellbores (aka “high dog leg” severity). 
     The combined pulsed neutron and sonic cased hole formation evaluation may be accomplished in several ways: real time gathered data transmitted via an electrical or fiber optic cable, or wired continuous rod; memory mode by storing a portion of the gathered data in memory module(s) in the tool string and conveyed on above cables or slickline or wired continuous rod; and in a hybrid telemetry method where a portion of the gathered data is transmitted via an electrical or fiber optic cable or continuous wired rod and a portion of the gathered data is stored in the memory modules(s) in the tool string and retrieved when the tool string is removed from the wellbore. 
     The collected data is processed in a CPU at the surface to obtain more robust rock property data about the one or more geologic formations. The rock properties are selected from the group consisting of Poisson&#39;s Ratio, Young&#39;s Modulus, compression slowness, shear slowness, minimum horizontal stress profile and inelastic measurements leading to simple mineralogy and matrix sigma (Spwla — 2009_T), Sigma (or capture cross-section) and ratio measurement for porosity (SPE30597) and pseudo density (SPE94716). The robustness of the processed rock property data is useful for optimal well design and for improved hydraulic fracture and acidization stimulation design and placement used in completing and stimulating the well and for determining the integrity of one or more casing strings and cement in the wellbore. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic of a first implementation of a combination sonic and pulsed neutron tool for formation evaluation through casing; 
         FIG. 2  is a schematic of a second implementation of a combination sonic and pulsed neutron tool for formation evaluation through casing; 
         FIG. 3  is a schematic of a third implementation of a combination sonic and pulsed neutron tool for formation evaluation through casing; and 
         FIG. 4  is a functional schematic of possible combinations of the elements of a combination sonic and pulsed neutron tool and system. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     Referring now to  FIG. 1 , wherein there is illustrated a schematic of a first embodiment of the combination logging tool string  1000  for use inside of a cased wellbore. The logging tool string  1000  is conveyed into the wellbore on a conveyance string  100  which may include one or more of the following: an electric and/or fiber optic cable  101 ; a slickline cable  102 ; a wired conveyance rod  103 ; coiled tubing string  104 ; and a wired coiled tubing string (including electrical cable and/or fiber optics)  105 . The tool string  1000  includes: a gamma ray/casing collar telemetry module  110  connected to a first crossover tool  112 . A second crossover tool  114  may be used to connect the first crossover tool to a first end  210  of a sonic array tool  200 . The sonic array tool may include centralizers  230 . A third crossover tool  116  may be used to connect a lower end  220  of the sonic array tool to a flexible sub  300  (aka “serpentine or knuckle joint”) that allows decoupling of a centralized tool. A pulsed neutron tool  400  may be connected at a first end  410  to a second end of the flexible sub  300 . In some embodiments, in the tool string  1000 , the sonic array tool  200  is disposed above the flexible sub  300  and the pulsed neutron tool  400  is disposed below the flexible sub. Alternatively, the pulsed neutron tool  400  may be disposed above the flexible sub  300  and the sonic array tool  200  may be disposed below the flexible sub  300 . If the pulsed neutron tool  400  is below the sonic tool  200 , a crossover tool  116  may be used to receive either a termination bull plug  119  at the lower end of the tool string or, alternatively, an additional crossover  120  may be attached to crossover  116  to connect to additional tools (not shown) that may be used in the string  1000 . If the sonic tool  200  is positioned below the neutron tool  400 , then a crossover tool  118  may be used to receive either a termination bull plug  119  at the lower end of the tool string  1000  or, alternatively, an additional crossover  120  may be attached to crossover  118  to connect to additional tools (not shown) that may be used in the string  1000 . 
     By way of example, a Halliburton mono-cable telemetry module model 1553 may be used in combination with Halliburton&#39;s slim bore hole sonic array tool (SBSAT) and Halliburton&#39;s pulsed neutron tool model RMT-i or TMD-3d (1553). The flexible sub  300  may be Halliburton&#39;s 6-6 flex connector. It will be understood that other telemetry modules and sonic array tools and neutron tools and flexible subs manufactured and provided by Halliburton and/or other third parties may be used in implementations of the present disclosure. 
     By way of further explanation, the present disclosure as discussed above may use a continuous wired rod ( 103 ) that includes the features of encapsulating fiber optic and/or copper wire within a smooth, round semi rigid outer layer(s). The rigidity of the continuous wired rod may allow pushing/pulling tool strings, possibly eliminating mechanical tractors. 
     Referring now to  FIG. 2 , wherein there is illustrated a schematic of an alternative implementation of the combination logging tool string  2000  for use inside of a cased wellbore. The logging tool string  2000  is conveyed into the wellbore on a conveyance string  100  which may include one or more of the following: an electric and/or fiber optic cable  101 ; a slickline cable  102 ; a wired conveyance rod  103  (see discussion hereinafter); coiled tubing string  104 ; and a wired coiled tubing string (including electrical cable and/or fiber optics)  105 . The tool string  2000  includes: a memory module  150  which is connected to a crossover tool  114 . The memory module is connected to a first end  210  of a sonic array tool  200 . A crossover tool  116  may be used to connect the lower end  220  of the sonic array tool to a flexible sub  300 . A pulsed neutron tool  400  is connected at a first end  410  to a second end of the flexible sub  300 . In some embodiments in the tool string  1000 , the sonic array tool  200  is disposed above the flexible sub  300  and the pulsed neutron tool  400  is disposed below the flexible sub  300 . Alternatively, the pulsed neutron tool  400  may be disposed above the flexible sub  300  and the sonic array tool  200  may be disposed below the flexible sub  300 . If the pulsed neutron tool  400  is below the sonic tool  200 , a crossover tool  116  may be used to receive either a termination bull plug  119  at the lower end of the tool string or, alternatively, an additional crossover  120  may be attached to crossover  116  to connect to additional tools (not shown) that may be used in the string  2000 . If the sonic tool  200  is positioned below the neutron tool  400 , then a crossover tool  118  may be used to receive either a termination bull plug  119  at the lower end of the tool string or, alternatively, an additional crossover  120  may be attached to crossover  118  to connect to additional tools (not shown) that may be used in the string  2000 . 
     Referring now to  FIG. 3 , wherein is illustrated a schematic of an alternative implementation of a combination logging tool string  3000 . The alternative tool string  3000  is similar to the first embodiment of the combination logging tool string  1000  for use inside of a cased wellbore. The tool string  3000  is conveyed into the wellbore on a conveyance string  100  which may include one or more of the following: an electric and/or fiber optic cable  101 ; a slickline cable  102 ; a wired conveyance rod  103  or coiled tubing string  104 ; a wired coiled tubing string (including electrical cable and/or fiber optics)  105 . The tool string  3000  may include: a gamma ray/casing collar telemetry module  110  which is connected to a first crossover tool  112 . A second crossover tool  114  may be used to connect the first crossover tool to a first end  210  of a sonic array tool  200 . A third crossover tool  116  may be used to connect the lower end  220  of the sonic array tool to a flexible sub  300 . A pulsed neutron tool  400  is connected at a first end  410  to a second end of the flexible sub  300 . In some embodiments in the tool string  1000 , the sonic array tool  200  is disposed above the flexible sub  300  and the pulsed neutron tool  400  is disposed below the flexible sub  300 . Alternatively, the pulsed neutron tool  400  may be disposed above the flexible sub  300  and the sonic array tool  200  may be disposed below the flexible sub  300 . The alternative tool string  3000  further includes a memory module  150  connected to the sonic array tool  200  and may include a second memory module  150  connected to the pulsed neutron tool  400 . If the pulsed neutron tool  400  is below the sonic tool  200 , a crossover tool  116  may be used to receive either a termination bull plug  119  at the lower end of the tool string or, alternatively, an additional crossover  120  may be attached to crossover  116  to connect to additional tools (not shown) that may be used in the string  2000 . If the sonic tool  200  is positioned below the neutron tool  400 , then a crossover tool  118  may be used to receive either a termination bull plug  119  at the lower end of the tool string  3000  or, alternatively, an additional crossover  120  may be attached to crossover  118  to connect to additional tools (not shown) that may be used in the string  3000 . 
     Referring to  FIG. 4 , there is illustrated a functional schematic of possible combinations of the elements of a formations evaluation system  500 . The system may include a CPU  510  located at the surface. A mono conductor  512  may be used to transmit data up or down the mono-cable to or from the formations evaluation tools comprising the tool string when the tool string is lowered into a cased wellbore. The mono-cable is connected to a telemetry module  514 . A downhole tool bus  530  is included in the tool string. A gamma ray casing collar module  520  may be included in the string. A pulsed neutron module  522  and a sonic array module  524  may be included as is illustrated in section  570  of the system. In a hybrid embodiment  580 , memory bank modules  540  may receive and store data from one or more of the gamma ray/casing collar tool  520 , the pulsed neutron tool  522 , and the slim array sonic tool  524 ; alternatively, an additional memory bank module  550  may be included in the tool string system  500  to receive and store data from one or more of the gamma ray/casing collar tool  520 , the pulsed neutron tool  522 , and the slim array sonic tool  524 . The tool string may further include a battery pack and a memory CPU module  560 . 
     The tool string  1000 , as previously described, may be assembled by connecting a conveyance string  100  to a gamma ray/casing collar telemetry module  110 ; connecting a flexible sub  300  at first end to a sonic array tool  200 ; connecting a pulsed neutron tool  400  at a second end of the flexible sub. Alternatively, the pulsed neutron tool  400  may be disposed above the flexible sub  300  and the sonic array tool  200  may be disposed below the flexible sub  300 . In operation, the tool string is lowered into the cased wellbore via the electric mono-cable. The tool string is passed inside the well casing across one or more geologic formations which are outside the wellbore casing. Data is collected with the sonic array tool and the pulsed neutron tool and transmitted via the electric mono-cable to a CPU  510  located at the surface of the earth. The collected data is processed to obtain selected rock property data about the one or more geologic formations. The rock properties are selected from the group consisting of Poisson&#39;s Ratio, Young&#39;s Modulus, compression slowness, shear slowness, minimum horizontal stress profile, porosity, simple mineralogy, matrix sigma, and pseudo density. Additionally, the tool string  1000  may gather data for determining the integrity of one or more casing strings and cement in the wellbore. The pulsed neutron log may gather data on gas effect and fluid flow behind and between casing strings. The sonic tool may gather data on the cement bond between the casing and the cement and the cement and the formation. 
     The tool string  2000 , as previously described, may be assembled by connecting a slickline  102  or coiled tubing string  104  to a sonic array tool  200 . The flexible sub  300  is connected at one end to the sonic array tool  200  and at a pulsed neutron tool  400  at a second end of the flexible sub. Alternatively, the pulsed neutron tool  400  may be disposed above the flexible sub  300  and the sonic array tool  200  may be disposed below the flexible sub  300 . In operation, the tool string  2000  is lowered into the cased wellbore via the slickline or coiled tubing string. The tool string is passed inside the well casing across one or more geologic formations outside of the cased wellbore. Data is collected with the sonic array tool and the pulsed neutron tool and stored in the memory module(s)  150 . The tool string  2000  is removed from the wellbore and the collected data is retrieved from the memory module  150  and processed to obtain selected rock property data about the one or more geologic formations. The rock properties are selected from the group consisting of Poisson&#39;s Ratio, Young&#39;s Modulus, compressional slowness, shear slowness, minimum horizontal stress profile, porosity, simple mineralogy, matrix sigma, and pseudo density. Additionally, the tool string  2000  may gather data for determining the integrity of one or more casing strings and cement in the wellbore. The pulsed neutron log may gather data on gas effect and fluid flow behind and between casing strings. The sonic tool may gather data on the cement bond between the casing and the cement and the cement and the formation. 
     A hybrid tool string  3000  may be assembled by connecting a conveyance string  100  to a gamma ray/casing collar telemetry module  110 ; connecting a flexible sub  300  at first end to a sonic array tool  200 ; connecting a pulsed neutron tool  400  at a second end of the flexible sub. A first memory module  150  may be connected to the pulsed neutron tool  400 . If desired, a second memory module  150  may be connected to the sonic tool  200 . Alternatively, the pulsed neutron tool  400  may be disposed above the flexible sub  300  and the sonic array tool  200  may be disposed below the flexible sub  300 . In operation, the tool string  3000  is lowered into the cased wellbore via the electric mono-cable. The tool string is passed inside the casing across one or more geologic formations outside of the cased wellbore. Data is collected with the sonic array tool and the pulsed neutron tool and all or a portion of the collected data is transmitted via the electric mono-cable to a CPU  510  located at the surface of the earth. A portion of the collected data may be stored in the memory module(s)  150 . The tool string is removed from the wellbore and the collected data is processed in combination with the data transmitted to the surface via the mono-cable to obtain selected rock property data about the one or more geologic formations. The rock properties are selected from the group consisting of Poisson&#39;s Ratio, Young&#39;s Modulus, compressional slowness, shear slowness, minimum horizontal stress profile, porosity, simple mineralogy, matrix sigma, and pseudo density. Additionally, the tool string  300  may gather data for determining the integrity of one or more casing strings and cement in the wellbore. The pulsed neutron log may gather data on gas effect and fluid flow behind and between casing strings. The sonic tool may gather data on the cement bond between the casing and the cement and the cement and the formation. 
     During operations of the combined tool string  1000 ,  2000 , and  3000 , data may be gathered simultaneously in one pass across the geologic formations by the sonic array tool  200  and the pulsed neutron tool  400 . Alternatively, data may be gathered selectively by either the pulsed neutron tool  400  or the sonic array tool  2000  as the tool string  1000 ,  2000 , and  3000  is passed one or more times across the selected geologic formation. 
     During operations of the combined tool string  1000 ,  2000 , and  3000 , data on the casing and cement integrity may be gathered simultaneously in one pass across the casing by the sonic array tool  200  and the pulsed neutron tool  400 . Alternatively, data may be gathered selectively by either the pulsed neutron tool  400  or the sonic array tool  2000  as the tool string  1000 ,  2000 , and  3000  is passed one or more times across the selected casing interval. 
     A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. Accordingly, other implementations are within the scope of the following claims: