The flux-leakage devices measure, by means of pad-conveyed coils in contact with the pipe wall, the induced currents that result from magnetic field lines that escape at abrupt changes in metal-wall thickness. Both types of tools make indirect measurements that are then related to metal loss through calibration. The last two categories, monitoring of fluid contacts in formations and selection of recompletion zones, use the cased-hole nuclear logs such as:.
Please refer to the nuclear logging page for information on these logs. Quality control is paramount, and careful attention must be focused upon three parts of the logging operation:. Just like openhole-logging tools, production-logging tools should be run in complementing suites so that one log can be compared with another. Seldom does a single log identify a problem sufficiently to prescribe a remedial action.
Table 1 lists the more common tool combinations used to diagnose problems and allocate flow. The Class A tools respond to flow either inside or outside the pipe containing the sonde and are usually employed for initial evaluation of a production problem. Class B tools respond to flow past the sensor and are used for detailed flow allocation from multiple entries into or exits from the pipe containing the sonde. The resolution of some of the Class A tools is actually better than some of the Class B members.
Production logs should be interpreted in a consistent fashion that first identifies normal or expected features. The abnormal portions can then be examined to determine which parts are pertinent to the problem and which parts are irrelevant. It is these irrelevant features that so often confound novices to the point that they delay or forego appropriate remedial action. Once these three myths are set aside, the requisite skills, listed next, can be developed for use of production logs.
The effective user must be able to:. The tools referenced in Table 1 are each described in greater detail in separate articles.
A dead weight sinker bar is necessary to overcome the force of the wellhead pressure acting on the cross-sectional area of the logging cable. The weight shown is just enough to balance the force of the well pressure acting on the wireline. Additional weight above that which is indicated on the graph is needed to realize downward movement of the logging string. As the inclination angle of the wellbore increases, it becomes especially important to increase the sinker bar weight over the value specified by the vertical axis of the figure.
When an inclination angle requires unreasonably long sinker bars, roller centralizers are required. Typical slickline diameters are represented by the group of lines at the bottom of Fig.
The low sinker-bar weight needed to carry out a slickline survey, even at high wellhead pressures, requires only a short lubricator. As a result, slickline services are enjoying a rebirth. New versions of these tools contain sufficient downhole memory to record what is essentially a continuous log. The ends of the tool contact the bottom of the borehole, and its middle touches the top.
With the following equation, the maximum tool length that can pass through a bend can be calculated. While Fig. The expression for L t involves the hole and tool diameters, as well as the inside radius of the bend.
The inside radius can be expressed in terms of the angle of the bend, and the distance to bend through the specified angle see Fig.
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These subjects are covered fully during the Horizontal well PL interpretation course. Toggle navigation. Profile Logout. Production logging toolstring.
This production logging toolstring consists of a fullbore spinner, fluid holdup and bubble count probes, a pipe diameter caliper and centralizer, a relative bearing sensor, pressure gauges, a temperature sensor, a gamma ray tool and a casing collar locator. When engineers run the tool in memory mode, batteries and a data recorder are used. Surface readout tools use a telemetry and power section.
Service companies have developed tools based on a variety of physical principles to obtain fluid density measurements: differential pressure across two ports separated by a known distance Compton scattering of gamma rays pressure gradient relation to density flow vibration relation to density and viscosity.
Figure 2. Production log. This log shows data typically provided by downhole sensors in a production logging survey. Two intervals have open perforations Track 1, red. Engineers make multiple passes at different logging speeds Track 2 ; negative cable speeds represent down passes and positive logging speeds are up passes. Color-coding based on logging speed helps differentiate datasets. Gamma ray data Track 3 provide correlation with openhole logs.
From spinner data Track 4 , engineers identify changes in fluid velocity associated with inflow from production, outflow from thief zones or outflow from injection.
The fluid density data Track 5 indicate water 1. Temperature data Track 6 indicate heating or cooling effects caused by inflow of fluids. Steady well pressure Track 7 is a characteristic of stable flow during acquisition. Holdup data Track 8 indicate water and oil fraction within the wellbore. The software computes incremental and cumulative flow rates Tracks 9 and The two intervals are producing oil; the lower interval is also producing a trace amount of water Track 9.
Flow Regimes To analyze production logging data, production engineers must be aware of downhole flow regimes. Figure 3. Fluid flow. Theoretical work and flow loop experiments have helped engineers understand multiphase flow in vertical, deviated and horizontal wellbores.
The parameters of interest include pipe diameter and inclination and fluid density, viscosity and flow rate. Each case shows the variation in water and oil holdup based on well deviation. Reservoir Surveillance and Management Production logs help engineers diagnose problems that occur during the life of a single well and are also used for management and surveillance of multiple wells or of the entire reservoir.
Lifetime Logging Production logs provide reservoir and production engineers with a diagnostic aid for understanding the downhole wellbore environment. Share This.
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