Abstract:
A fluid squeeze monitor downhole tool and a method of monitoring formation squeeze features a tool body that can be placed downhole at a desired elevational location to produce a controlled, localized reduction of pressure head and measure the resultant inward displacement of the borehole wall. The reduction in head is accomplished by draining the fluid in a bladder (or collapsible container) located on the tool body into a reservoir &#34;sump&#34; that is incorporated into the downhole tool.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to exploration well downhole tools, and more particularly relates to a formation squeeze monitor that can be utilized with downhole exploration well equipment, such as wireline test equipment and procedures for collecting data on the squeezing characteristics of salt formations and the like. Even more particularly, the present invention relates to an improved method and apparatus for monitoring and collecting of data on squeezing characteristics of salt formations and the like wherein a downhole tool body (lowered, e.g., on a wireline into the well bore) produces a controlled localized reduction of the pressure head and measures the resultant inward displacement of the borehole wall. The reduction in head can be accomplished by draining the fluid in a bladder or collapsible container located on the tool body into a reservoir or sump that is incorporated into the downhole tool body. 
     2. General Background 
     Several types of rock formations exhibit &#34;squeezing&#34; characteristics. However, rock salt is especially well-known for its tendency to squeeze into wells (manifested as borehole closure). Salt squeeze can collapse casings in deep wells, and also can cause significant volume losses over time in storage caverns constructed in salt formations. 
     A need exists for a downhole exploration well tool that can be used to obtain site specific data on the closure characteristics of boreholes in rock salt formation. This information is desirably obtained using existing downhole equipment, such as wireline test equipment, for example. This data provides a basis for estimating values of minimum &#34;back pressure&#34; necessary to avoid damage due to excessive closure of deep wells and storage caverns in salt. The data could also be analyzed to gain basic information on in situ stresses and properties of salt formations. Site specific data could be used to select adequate, but not excessive, mud weights to stabilize wells and caverns in salt formations; and this would result in more efficient operations. As examples, wells could be safely drilled through deep salt formations without using overly dense drilling muds, and compressed natural gas (CNG) caverns could be designed to operate such that desired storage volumes were retained without using excessive amounts of &#34;cushion&#34; gas. The accumulated data on site specific squeezing properties of deep salt formations would furnish a basis for an analysis of regional effects that could be related generally to salt tectonics in a particular basin. 
     Borehole closure monitoring has been previously proposed and utilized as a field test method for obtaining the squeezing properties of salt formations. In an article published in 1984 and entitled &#34;Interpretation of a Long-Term In Situ Borehole Test In a Deep Salt Formation&#34; (see table below), Fernandez and Hendron (1984) described a related study that was performed in a deep bedded salt formation in Canada. A test well was cased down t o the depth of interest such that the pressure &#34;head&#34; on the formation could be controlled by varying the density and level of fluid in the well. Hole closure was estimated by monitoring the amounts of fluid subsequently displaced during the test. The data obtained were used in designing natural gas storage caverns that were later constructed at the site. 
     Nelson and Kocherhans authored an article in 1984 entitled &#34;In Situ Testing of Salt In a Deep Borehole In Utah&#34; wherein they described &#34;unloading geotechnical drill-stem tests&#34; performed in anticlinal salt in the Paradox Basin. They measured salt squeeze resulting from reducing the pressure in test intervals isolated by straddle packers that were suspended on drill stems. They also estimated hole closure in their deepest test (4,865 ft.) on the basis of fluid displaced from the test interval while subjected to reduced pressures. The hole closure data were then used to analyze the in-situ creep properties of the salt formation. These tests were conducted over relatively short time periods ranging from 0.6-1.1 days, and it is reasonable to speculate that the daily cost of a &#34;rig&#34; (necessary to handle drill stem) had an effect on the duration of these tests. 
     In salt domes the heights of storage caverns usually extend over several hundreds (or thousands) of feet, and thus open-well tests cannot be used effectively. That is, accumulated volume changes of fluid cannot be clearly identified with closure of specific depth intervals of salt within a well. In this case, the use of straddle packers, as used by Nelson and Kocherhans also appears necessary to isolate particular intervals of interest for testing. 
     Wireline downhole test equipment has been used to perform hydraulic fracturing (hydrofrac) studies in Gulf Coast salt domes (Thoms and Gehle, 1988). This equipment incorporates a cable and a single high pressure hose to connect the downhole test unit (including a straddle packer) to surface controls and pump. Other wireline hydraulic fracturing test systems have been developed by Haimsor in about 1984, and by Baumgartner and Rummel in 1989 (see References). Haimson&#39;s equipment employed a cable and two pumps and hoses to service the downhole unit. 
     There is thus a need to develop equipment and methods to collect borehole closure data that can be related directly to squeeze effects in deep salt formations. Such equipment should be operable in open, uncased wells, and not require a standby rig. In general it would desirably be more cost effective than existing methods for gathering similar data. Furthermore, predictions of deep well and cavern behavior should then be based directly on these site specific data and the accompanying analyses. 
     Table 1 lists in summary, references that relate generally to deep salt formations, and/or the behavior of salt including formation squeeze. 
     TABLE 1 
     References 
     Baumgartner, J., and F. Rummel, 1989. Experience With &#34;Fracture Pressurization Tests&#34; As A Stress Measuring Technique In A Jointed Rock Mass, Int. J. Rock Mechs. and Min. Sci., V. 26, N. 6, Dec., p. 661-671. 
     Fernandez, G. G., and A. J. Hendron, 1984. Interpretation Of A Long-Term In Situ Borehole Test In A Deep Salt Formation, Bull. of Assoc. of Engr. Geologists, Vol. XXI, No. 1, p. 23-38. 
     Haimson, B. C., 1984. Development Of A Wireline Hydrofracturing Technique And Its Use At A Site Of Induced Seismicity, 25th U.S. Symp. On Rock Mechs., Northwestern University, Evanston, Ill., Rock Mechanics In Productivity And Protection, SME of AIME, p. 194-203. 
     Nelson, R. A., and J. G. Kocherhans, 1984. In Situ Testing Of Salt In A Deep Borehole In Utah, The Mechanical Behavior Of Salt, Proc. of First Conf., Hardy, H. R., and M. Langer (eds.), Trans Tech Publs., p. 493-510. 
     Thoms, R.L., and Gehle, R.M., 1988. Hydraulic Fracturing Tests in the Rayburn&#39;s Salt Dome, Report No. 88-0001-S for the SMRI (as above), 53 pp. 
     Hydraulic Fracture Tests In a Gulf Coast Salt Dome, 28th U.S. Symp. on Rock Mechs., University of Arizona, Farmer, et al, (Eds.), Balkema, Rotterdame, p. 241-248 (1987). 
     Borehole Tests To Predict Cavern Performance, 6th Symp. on Salt, 1985. Salt Institute, Inc., 206 N. Wa. St., Alexandria, Va., 22314, p. 27-33. 
     Thoms, R. L., M. Mogharrebi, and R. M. Gehle, 1982. Geomechanics of Borehole Closure In Salt Domes, Proc. Sixty-First Annual Meeting, Gas Processors Assc., 1812 First Place, Tulsa, Okla., 744101, p. 228-230. 
     SUMMARY OF THE INVENTION 
     The present invention thus provides an apparatus for monitoring formation squeeze in a well borehole having a borehole wall. The apparatus includes an elongated tool body with a sump or reservoir on the tool body for containing a volume of fluid. 
     Centralizing portions of the tool hold the tool body centrally within the borehole. A plurality of bladders (or collapsible containers), each inflatable with the source of fluid are provided on the tool body and the bladders are deflatable to provide a controlled localized reduction of pressure head at a position adjacent the bladders so that a resulting inward displacement of the borehole wall can be induced and measured. 
     The tool body carries a conduit for transmitting fluid between the various bladders and the sump or reservoir. 
     The tool body is in the form of an elongated work string that can be lowered into the well with a plurality of joints or on a wireline. 
     A fluid transmitting line is provided for communicating between the well surface area and the tool body so that fluid can be supplied via the conduit to the tool body. 
     The bladder is preferably in the form of a plurality of vertically spaced, expandable and generally deformable bladder elements. 
     Calipers are provided on the tool body for measuring displacement and/or diameter of the borehole wall before, after, and during testing. 
     Valves are provided in the tool body for controlling fluid flow between the reservoir or sump and the various bladders as well as between the fluid dispensing conduit that communicates with the well surface area. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a further understanding of the nature and objects of the present invention, reference should be had to the following detailed description, taken in conjunction with the accompanying drawings, in which like parts are given like reference numerals, and wherein: 
     FIG. 1 is an elevational schematic view of the preferred embodiment of the apparatus of the present invention illustrating a lowering of the apparatus into a borehole; 
     FIG. 2 is an elevational schematic view of the preferred embodiment of the apparatus of the present invention illustrating a setting up of the apparatus in a borehole; 
     FIG. 3 is an elevational schematic view of the preferred embodiment of the apparatus of the present invention illustrating the performing of tests in a borehole or well; and 
     FIG. 4 is an elevational schematic view of the preferred embodiment of the apparatus of the present invention illustrating a lifting of the equipment out of the borehole or well after testing is completed. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention provides an apparatus 10 for monitoring formation squeeze in a well borehole 11 having a borehole wall 12. The apparatus includes an elongated tool body 13 having an upper end portion 14 and a lower end portion 15 The upper end portion 11 includes an attachment at 16 for forming a connection between the tool body 13 and conductor cable 17. The apparatus 10 is thus adopted to be lowered into well bore 11 to a desired elevational test position. Cable 17 is preferably a conductor cable that connects to a surface controller and recorder at the well head or well surface area. 
     A fluid line 18 transfers high pressure fluid to and from control valve assembly 22. The tool body carries a pair of spaced apart packer sleeves 19, 20 including an upper packer sleeve 19 and a lower packer sleeve 20 adjacent lower end 15 of tool body 13. Control valve assembly 22 controls fluid flow between fluid supply line 18 and each of the packer elements 19, 20 as well as controlling the flow of fluid to each of the spaced-apart collapsible containers or bladders 23, 24, including upper bladder 23 and lower bladder 24. Reservoir 25 serves as a sump for containing fluid 34 that is to be transmitted from the collapsible containers or bladders 23, 24. Multi-conduit flow line 26 communicates with control valve assembly 22 and with reservoir 25 at outlet port 27 and with tool body 13 at inlet port 28. The multi-conduit flow line 26 thus communicates fluid under pressure to and from control valve assembly 22, to and from sleeves 19, 20, to and from collapsible containers or bladders 23, 24, and to reservoir 25. 
     Cable 17 communicates with caliper unit 30 via caliper line 29 so that caliper position readings can be transmitted to the surface area for recording by a surface controller and recorder. The caliper 30 gives well borehole wall 12 position information, such as during a controlled collapse of the borehole wall 12 inwardly at the test interval area 21 which is the area below upper packer 19 and above lower packer 20, as shown in FIG. 2. The caliper assembly 30 includes multiple caliper arms 31, 32 that can extend outwardly and contact the wall 12 as shown in FIG. 2. Such caliper are commercially available. The packers 19, 20 function to centralize the tool body 13 in the borehole 11. 
     Tool body 13 below reservoir 25 is in the form of a mandrel section 33 which is a central pipe stem portion of a straddle packer assembly that includes the packer sleeves 19, 20. The bladders 23, 24 are preferably in the form of slip-on packers that are filled with fluid prior to testing and later &#34;bled off&#34; into the reservoir 25 to maintain a specific pressure in the isolated test interval 21. The initial reservoir pressure is at atmospheric. The caliper arms 31, 32 are expanded to contact the well bore wall, as shown in FIG. 2, at the initiation of the test. Caliper arms 31, 32 displace inwardly monitoring displacements in well borehole wall 12, the displaced borehole wall being designated by the numeral 12A in FIG. 3 wherein some displacement of the borehole wall has occurred. 
     Caliper arms 31, 32 are displaced inwardly as the wall 12A at test interval 21 displaces inwardly as shown in FIG. 3. The expanded packer sleeves in FIG. 3 illustrate the creation of the test interval 21 below packer sleeve 19 and above packer sleeve 20. The collapsible bladders 23, 24 are illustrated in FIGS. 1 and 2 at the filled size, namely, the size of the bladders just prior to inflating the packer sleeves. In FIGS. 3 and 4, the bladders 23, 24 have been &#34;bled off&#34; into reservoir 25 to maintain a specific pressure in the isolated test interval 21. In FIG. 4, the packers 19, 20 have been collapsed to the original position as shown in FIG. 1 so that the entire assembly 10 can be removed from the borehole 11. The caliper arms 31, 32 are also collapsed, as shown in FIG. 4, for removal of the entire apparatus 10. In summary, FIGS. 1-4 are sequential views illustrating a lowering of the apparatus 10 into a borehole 11 (FIG. 1), a setting up of the packers to form the test interval therebetween (FIG. 2), performing of the test in the borehole 11 by a controlled collapse of the bladders and a measurement of borehole wall 12A displacement using caliper assembly 30 (FIG. 3), and a lifting of the apparatus out of the borehole 11 after testing is complete (FIG. 4). Table 2 below lists the part numbers and descriptions as used in the written specification and on the drawings. 
     
                       TABLE 2______________________________________PARTS LISTPart Number     Description______________________________________10              formation squeeze monitor11              well borehole12              borehole wall13              tool body14              upper end15              lower end16              attachment17              conductor cable18              fluid line19              packer sleeve20              packer sleeve21              test interval22              control valve assembly23              upper bladder24              lower bladder25              reservoir26              fluid line27              outlet port28              inlet port29              caliper cable30              caliper assembly31              caliper arm32              caliper arm33              mandrel34              fluid______________________________________ 
    
     Because many varying and different embodiments may be made within the scope of the inventive concept herein taught, and because many modifications may be made in the embodiments herein detailed in accordance with the descriptive requirement to be interpreted as illustrative and not in a limiting sense.