# US 2014/0191879 A1 · Casing detection tools and methods > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0191879 A1 - Document ID: US20140191879A1 - Status: Published application - Kind: A1 - Application number: 14/239,364 - Filed: 2011-08-18 - Published: 2014-07-10 - Earliest claimed: 2011-08-18 - Assignees: Halliburton Energy Services, Inc. - Inventors: Michael S. Bittar; Hsu-Hsiang Wu - Web page: https://patentgrep.com/patent/US20140191879A1 ## CPC - E21B 47/04: Measuring depth or liquid level - E21B 7/04: Directional drilling - E21B 43/24: using heat, e.g. steam injection - E21B 43/2406: {Steam assisted gravity drainage [SAGD]} - E21B 47/0228: using electromagnetic energy or detectors therefor - E21B: EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS ## Abstract Methods and tools for detecting casing position downhole is presented. The method utilizes electromagnetic. (EM) tools with tilted antenna systems to detect casing position. Sometimes titled antenna designs also increase EM tools' sensitivity to formation parameters, which can lead to false signals for casing detection. In addition, it is very difficult to distinguish measured signals between a casing source and a formation source. The methods presented help to distinguish between the two sources more clearly. The methods and tools presented also help to minimize those environmental effects, as well as enhance the signals from a surrounding conductive casing. The methods herein provide ideas of EM tool's design to precisely determine casing position within a certain distance to casing position. ## Claims ### Claim 1 A downhole logging method that comprises: obtaining formation resistivity measurements from a first borehole; determining an expected environmental signal level for a second borehole at a specified position relative to the first borehole, based at least in part on the formation resistivity measurements; selecting at least one of a transmitter-receiver spacing and an operating frequency to provide a desired detection signal level for the first borehole from the second borehole, the desired detection signal level being greater than the expected environmental signal level; and providing a tilted antenna logging tool having the selected spacing and/or operating frequency in a bottomhole assembly for the second borehole. ### Claim 2 (depends on 1) The method of claim 1, wherein said desired detection level is less than ten times said expected environmental signal level. ### Claim 3 (depends on 1) The method of claim 1, wherein said first borehole is cased before the drilling of said second borehole. ### Claim 4 (depends on 1) The method of claim 1, wherein said tilted antenna logging tool comprises antenna modules that can be separated by a variable number of intervening subs. ### Claim 5 (depends on 1) The method of claim 1, wherein said tilted antenna logging tool has a programmable operating frequency. ### Claim 6 (depends on 1) The method of claim 1, wherein said expected environmental signal level includes an azimuthal signal dependence attributable to formation anisotropy. ### Claim 7 (depends on 1) The method of claim 1, wherein said expected environmental signal level includes an azimuthal signal dependence attributable to a formation fluid interface or a bed boundary. ### Claim 8 (depends on 1) The method of claim 1, wherein said expected environmental signal level includes an azimuthal signal dependence attributable to a borehole effect. ### Claim 9 (depends on 1) The method of claim 1, wherein said determining an expected environmental signal level includes generating a model response based on a tentative transmitter-receiver spacing and operating frequency. ### Claim 10 (depends on 9) The method of claim 9, wherein said selecting includes: finding a model response for a casing detection signal based on the tentative transmitter-receiver spacing and operating frequency; and systematically varying the tentative transmitter-receiver spacing and operating frequency until the modeled casing detection signal exceeds the modeled environmental signal level. ### Claim 11 A casing detection tool designed for use in a high resistivity formation, the tool having: at least a tilted transmitter antenna that emits a transmit signal; and at least a two or more tilted receiver antennas that detect components of an induced magnetic field, wherein the receiver antennas are at least a selected spacing distance from said transmitter antenna, and wherein said transmit signal has at least one frequency component at or below a selected operating frequency, said selected spacing distance and operating frequency providing an expected casing detection signal level greater than an expected environmental signal level. ### Claim 12 (depends on 11) The tool of claim 11, wherein said expected environmental signal level includes at least one of a dependence on formation anisotropy, a dependence on a formation fluid interface, a dependence on a bed boundary, and a dependence on a borehole effect. ### Claim 13 (depends on 11) The tool of claim 11, wherein said expected casing detection signal level is based on a specified detection range and a formation resistivity. ### Claim 14 (depends on 11) The tool of claim 11, wherein said selected spacing distance is greater than about 35 feet and the selected operating frequency is below about 100 kHz. ### Claim 15 (depends on 14) The tool of claim 14, wherein said selected spacing distance is greater than about 40 feet and the selected operating frequency is below about 10 kHz. ### Claim 16 (depends on 15) The tool of claim 15, wherein said selected spacing distance is greater than about 50 feet and the selected operating frequency is below about 1 kHz. ### Claim 17 (depends on 11) The tool of claim 11, wherein said transmit signal has a programmable operating frequency. ### Claim 18 (depends on 17) The tool of claim 17, wherein said casing detection tool has a number of intermediate subs between the transmitter antenna and at least one receiver antenna, wherein the number is variable to provide at least the selected spacing distance. ### Claim 19 (depends on 11) The tool of claim 11, further comprising a processor that collects measurements at multiple transmitter-receiver spacings.