Logging cased hole
- 1. Cased Hole Logging • Surveillance and by-passed pay
- 2. Cased Hole – Fluid Composition Capacitance, Fluid Di-elect. Fluid type - hydrocarbon vs. water. Fluid Resistivity Fluid type - hydrocarbon vs. salt water. Pulsed Neutron Capture 3-phase ID in well, req. homogeneous formation Gradiomanometers Fluid type - oil and water, looses resolution in high deviation, limited in high rate and high oil cut. Fluid Density Fluid type- oil vs. water, better in high GLR. Temperature Fluid entry (zones/leaks) rate/temp limits. Noise Leak/zone entry. Channel flow behind pipe, depending on rate. Fluid Level Survey Fluid level only, confused by foams, froths and emulsions. Spinners Total flow rates and entry/exit points. Deviated wells are a challenge. Radioactive Tracer Tool Total flow rates and entry/exit points. Not useful in deviated wells. Oxygen Activation Velocity of water phase. Holdup and leak detection.
- 3. Cased Hole – Casing/Cement Inspection Caliper Log Accuracy depends on number of fingers, speed, tool type. Casing Inspection Eddy Current Inner wall investigation. Shows some smaller flaws, measures ID Casing Inspection Flux Leakage Casing body inspection. Id of inner / outer wall, and body casing problems, not in OBM Casing Inspection Ultrasonic Casing body inspection. Affected by fluids, used in thicker wall pipe (>0.2”) Casing Inspection Electromagnetic Phase Shift Casing body inspection. ID and wall thickness, averaging tool may miss small defects Casing Inspection Conventional Acoustic Cement presence. Averaged data, not really useful for most problem identification Cement Evaluation Segmented Acoustic Channels, Bond. 360o, channels and voids, bond under right conditions. Cement Evaluation Ultrasonic Casing and Cement bond. 360o, channels, voids, bond, pipe conditions w/ right application. Cement Evaluation
- 4. Cased Hole – Correlation/Evaluation Gamma Ray Lithology and correlation Inexpensive. No porosity. Correlation Neutron log – single detector Lithology and correlation Inexpensive. No porosity. Correlation Neutron log – dual detector Porosity. RA source needed, accuracy less than OH log. Formation Evaluation Acoustic Porosity. Limited in cased wells, requires good bonds for accuracy Formation Evaluation Pulsed Neutron Capture PNC Water saturation. Does not work in low or changing salinity, or low porosity Formation Evaluation Pulsed Neutron Spectrometry PNS C/O Water saturation. Does not work well in low porosity Formation Evaluation Cased Hole Resistivity Water Saturation. Salinity dependent, stationary reading, relative deep reading Formation Evaluation
- 5. Problem or Information Needed Rec. Logging Tools Procedure/Level of Detail Detection of Crossflow or Underground Blow out Temperature Survey Difference in slope of temperature gradient – will detect flow rates down to 25 BPD if liquid and temperatures of fluids are different. Figures on temperature vs. flow distance help estimate water flow in the annulus. Noise Log Best performance of noise logs is with gas flow. Gas flow to about 10 actual ft3/D (Note – not standard ft3/day). At very low gas flow rates (q<400 actual ft3/D), gas flow can be estimated from millivolts of noise between the 200-Hz and 600-Hz frequencies: q = 0.35 (N200 – N600). Where q is the actual gas flow in ft3 and N = noise log cut at that frequency. Oxygen Activation Survey Open hole or channels behind single string. Accuracy is sharply reduced for investigating channels behind two strings (use temp or noise tools). Detection of Crossflow
- 6. Problem or Information Needed Rec. Logging Tools Procedure / Level of Detail Location of Cement Top Temperature Survey OK if run within 12 to 24 hrs of cement job. Little temperature variation with the formation may make cement top difficult to see. CBL (cement bond log) Best results after 3 days or when cement has developed 70%+ of the compressive strength. These tools may be too large for slim hole wells. Gravel-pack logging (GR) Tool response depends on density difference between cement and annular fluid. Location of Cement Top
- 7. Problem or Information Needed Rec. Logging Tools Procedure / Level of Detail Evaluation of Cement Placement Open hole caliper Accuracy depends on caliper and hole roughness and washouts. Caliper tools with more than 4 arms are needed for hole volume measurement accuracy. Sweeps with markers after running casing Sweeps give decent estimates of hole volume, but sweeps may not reach all of the annular space in uncentralized cased holes. Useful for swept hole % analysis. Temperature Survey OK if run within 12 to 24 hrs of cement job. Little temperature variation with the formation may make cement top difficult to see. Gravel Pack Log Good if fluid density difference greater than 0.3 gm/cc (0.13 lb/bbl). Could run before and after cement for background data. CBL – both regular and segmented Semi-quantitative contact measurement of pipe/cement and cement/formation. Affected by casing pressure and tool calibration. Evaluation of Cement Placement and Bond
- 8. Problem or Information Needed Rec. Logging Tools Procedure / Level of Detail Detection of casing wear from drilling E-line calipers Multi-arm calipers generally good, but slick line calipers may rotate and “over-report” the bad spots. EM – eddy current tool that measures wall thickness Highly accurate if the hole is filled with a non conductive fluid. Acoustic wall thickness tool Qualitative indicators of wear (thickness numbers are not very accurate) Casing Inspection
- 9. Problem or Information Needed Rec. Logging Tools Level of Detail Detect casing collapse EM – eddy current wall thickness survey Investigation is to 8 to 10” radius. Investigation ability falls off after the first string encountered. Qualitative investigation. Splits are more difficult to see. Gravel-pack (GR – density) Depth of investigation depends on source strength – may range from 4” to 16”. Splits are more difficult to see. Determination of External Casing Corrosion
- 10. Problem or Information Needed Rec. Logging Tools Procedure / Level of Detail Annular Flow Temperature Survey Useful where the well has active annular flow. Can spot flows on the order of 1 bpd (after 24 hrs) if temperature of formation at measurement and source of water is sufficiently different. Two surveys, 12 hrs apart is usually adequate to spot presence of a channel. OA - oxygen activation Accurate, but don’t swap out muds. Migration of fluids in pipe may be seen as “channel”. Noise logging Accuracy depends on channel variations to accelerate flow and change sound. Flow Behind Pipe
- 11. Problem or Information Needed Rec. Logging Tools Procedure / Level of Detail Determine annular flow in injector RA Tracer Survey - inject slug of I- 131 in brine. Track from surface to annulus until slug is completely pumped away. Track any flow that goes behind pipe and moves up. OA- oxygen activation survey Not as reliable as the chemical tracer, due to fluctuations in the injection rate. Temperature survey Three temperature surveys are needed: one before annular injection (base line), one during and one 4 to 6 hours after injection (decay). Borax Log Pumping borax/water solution down tbg into the liner, allowing mix to invade perfs & any channels in casing/formation annuli. Initial pass, before borate injection, is w/ Pulsed Neutron log (no Borax), followed by passes at 20bbls, 40bbls, and 60bbls as borax mix pumped. Borax affects neutron capture, leaving a characteristic signature. Overlays of the Sigma/CNL counts reveal the zones of borax penetration, and identifies channels taking fluid. Determination of Flow Behind Pipe for Injector
- 12. Problem or Information Needed Rec. Logging Tools Procedure / Level of Detail Certification for annular disposal Radioactive Tracer Survey with RA isotope in brine, pumped into annulus while logging with a GR tool in tubing. Can distinguish entry points and limited detail on up or down movement of the inject slug. Oxygen activation survey Not as accurate as RA logging. Fluctuations in rate create problems. Temperature survey Can determine channels and entry points. Needs 3 runs – before, during and after. Borax Log Pumping borax/water solution down tbg into the liner, allowing mix to invade perfs & any channels in casing/formation annuli. Initial pass, before borate injection, is w/ Pulsed Neutron log (no Borax), followed by passes at 20bbls, 40bbls, and 60bbls as borax mix pumped. Borax affects neutron capture, leaving a characteristic signature. Overlays of the Sigma/CNL counts reveal the zones of borax penetration, and identifies channels taking fluid. Location of Annular Leak
- 13. Problem or Information Needed Rec. Logging Tools Procedure / Level of Detail Location of leak to annulus or crossflow behind pipe Temperature survey Relatively accurate at rates of at 1 bpd or more. Need minimum of 2 runs, before and during injection. A third run may help define a qualitative level of leak rate. Run at 1oF/in sensitivity. Will not see small gas leak rates through liquid. Noise log Best for gas leak detection. Run static log and then again during flow or negative test. Upward gas movement (percolation) at actual 10 ft3/D or more should be detectable. Oxygen activation log Can detect flows of 20 to 40 bpd in the annulus of a single string well if the leak is directly opposite the tool. Resolution drops to >200 bpd when two strings are present Borax Log Pumping borax/water solution down tbg into the liner, allowing mix to invade perfs & any channels in casing/formation annuli. Initial pass, before borate injection, is w/ Pulsed Neutron log (no Borax), followed by passes at 20bbls, 40bbls, and 60bbls as borax mix pumped. Borax affects neutron capture, leaving a characteristic signature. Overlays of the Sigma/CNL counts reveal the zones of borax penetration, and identifies channels taking fluid. Location of Source of Annular Leak
- 14. Gamma Ray Tool (Basically a Geiger Counter) • Uses a scintillation crystal and a photomultiplier tube to measure naturally occurring and artificially induced gamma-ray radiation. • The gamma-ray radiation is a signature of the formations in a well – very useful in depth control. Used in open hole or pipe • Also used to spot changes in radiation (NORM scale) and radioactive tracers. • GR is sensitive to logging speed and factors/statistics that govern radioactive decay. • Used as one measurement of shaliness, correlation tool for stacked beds and in shales, seal/barrier location, id of organic rich zones, gross and net reservoir thicknesses.
- 15. Multi-sensor caliper (cased hole) • Multi-arm feeler – gauges the shape and smoothness of the casing id. – Corrosion and pit detection – Pipe collapse and deformation – Pipe wear
- 16. Production Logging (PLT) • Spinner or radioactive tracer ejector that is useful for identifying and quantifying fluid entry and exit points in the well. • Challenged by deviated wells if the tool is not in the predominant flow stream.
- 17. PLT in Gas Lift Wells • Very common to run PLTs in gas lift wells – w/ precautions. • W/ fullbore spinners, choke the well back and reduce or shut-in the lift gas to reduce the chance of getting the tool stuck. Make sure the well is stable before logging. • Run in at 50 to 75 ft/min. A pressure / density log may show some gas lift problems that a flowing gradient survey will not. • There is very little chance of getting the PLT stuck in a GLM if a series of gauging runs is made immediately prior to the log (insures full ID). • The fullbore centralizer collapses to the tubing ID and the tool is run with the spinner centralized so the point / bull-nose on the tool does not contact the walls of the tubing. There is a possibility of the centralizer holding up in the mandrel, but picking up and running a little faster should take care of this. • Adhere to the service companies recommendation on minimum tool clearance. Sources: Duane Toth and Franklin Bohla
- 18. PLT Sticking Hazard • Greatest risk of tool hang-up is in the tubing tail (TT). • Also watch the reservoir (may not be able to run a full ID drift gauge) for scale build up. Running a slim hole GR prior to the spinner to look for potential barium scale deposits is a good idea. Other scales and non- NORM BaSO4 scale may require a tool-sized drift. • Lost Tool Experiences (from Duane Toth): – Lost one in Alaska where we didn't shut-in the well before going from the 7" production casing into 2-7/8" tubing. The tool was off center, hung-up on the TT, and the wire came loose. We were able to fish this tool. – The other was in Algeria where we lost the tool across the reservoir section. Believed to be result of excessive barium scale deposition, but fill may have also been a problem. This tool string was never recovered, and since it had the GHOST tool, it was an expensive mistake. Source – Duane Toth
- 19. Cement Bond Tool • Transmitter-receiver tool measures the signal received back from a segment. Helps assess cement presence and bond to the formation and the pipe.
- 20. Temperature Tool • A recording of the wellbore temperature. – Identify fluid entry or exit – Gas channeling – Tubular leaks – Hydraulic frac height – Cement top – Fluid levels – Differential temperature curve
- 21. Down Hole Static Temperature Varies with Depth - Effect of the Geothermal Gradient 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 50 100 150 200 250 300 Temperature, F Depth,ft "cellar effect - temperature normally cools from surface temperature to about 100 ft below surface, then temperature begins to increase with increasing depth. Watch for anomolies. This response is about 2.1o F per 100 ft
- 22. Temperature log – Saaman Well – Trinidad. Leak at packer using annular injection after base line at same rate.
- 26. Gradiomanometer • Measures the differential pressure of a 24” column of fluid – calculates the fluid density. – Determine gas or liquid entry points – Identify static fluid interfaces – Determine exact depth of fluid density change – Assist production logs
- 27. Flow meter • Measures fluids moving past the tool. Moving fluids turn the spinner – To determine fluid entry or exit points – Evaluate perforations – Evaluate cross-flow occurrence – Helps evaluate completion design
- 28. Tension Measurement Device • A component of the tool string that records the tension during logging in various parts of the wellbore. Helps spot increased drag and break free points (tool jumps) that may signal poor logging tool records. • Used for quality control on logs, as an indicator of depleted zones (fluid loss sticking), dog-legs, location of sticking (above or below tool when compared with a surface record).
- 29. Logging Behind Casing • Key Elements: – Understand the condition of the casing – Understand the connection of casing to the formation – cement bond. – Inclination, diameter, geometry
- 30. Information Sought Logging Tools Used Casing Condition USIT, Multi-arm Calipers, Sonic Calipers, Downhole TV Cement Condition Cement Bond Logs (sonic) Saturation Resistivity Tools (CH), C/O Logs, Reservior Saturation Tools, DSS Lithology Gamma Ray, Density, Neutron, Sonic Porosity Resistivity Tools (CH), Porosity (CH), CNL, Dipole Shear Sonic Formation Strength Dipole Shear Sonic, Oil Resistivity, Casing Wall Coring Tools, Gas Neutron and Sonic Tools By-passed Pay Resistivity, O/C Logs, Pressure Casing Wall Coring Tools Partial List of Information Sought and Cased Hole Logging Tools