The primary objective of production logging is reservoir performance evaluation or flow profile evaluation. Production logging is a complex downhole logging technique designed to allow us to determine flowrate, fluid types, and fluid flow distribution in production and injection wells.
Secondary production logging objectives are lift (or completion) performance evaluation and estimations of factors affecting the reservoir performance (leaks and crossflows).
The best known production logging tool is the flowmeter log. There are 3 flavours of flowmeter: continuous or fullbore, diverting, and array spinner flowmeters.
Other measurements are usually needed to aid analysis, including:.
Radioactive tracer log
Focused gamma ray density log
Unfocused gamma ray density log
Fluid capacitance log
Fluid identification log (in high angle wells)
Gradiomanometer (fluid density) log
Pressure sensors for static, flowing, build-up, and draw-down pressures
Gamma ray and collar log for depth control
See links on right-hand navigation menu to access these tool descriptions.
Modern toolstrings include up to one hundred various sensors, and processing techniques utilize probabilistic non-linear algorithms of multiphase flows. The basics are still the same as 40- 50 years ago, but they have been brought into the 21st century..
Production logging is sometimes combined with well integrity logging (multiarm calipers, ultrasonic thickness devices, or serve itself as an indicator with temperature, flowmeter or noise logging sensors) and cased hole formation evaluation logging (multidetector neutron logs, dipole shear sonic logs, pulsed neutron logs with spectrometry capability, natural gamma ray spectrometry logs) in through tubing applications.
Production logging is usually carried out by the cased hole wireline crew of the service company. That is carried on wells of different definitions: production wells (on different stage of the field development), injection wells (with water, gas or steam stimulation), exploration wells and wildcats (in combination with conventional DST), hydrology wells and steam energy (geothermal) wells. When the well is producer the test is known as production logging test, when the well is injector – the test is known as an injection logging test.
The number and sequence of production logging tests performed on a well-managed field is defined by the field development team. A good practice is to run the Production Logs at an early stage of the life of the well, in order to establish baseline that will be used later when things go wrong. Too often Production Logs are run when something has gone wrong as the last resort (to design well interventions and workovers or even to take decision to abandon the well).
PLANNING A PRODUCTION LOGGING PROGRAM
The above example
illustrates 5 PLT surveys being performed (2 in shut in mode and 3
in flowing). Shut in survey (when the
well is closed at the surface) is used for downhole tool
calibration, pressure estimation, and possible crossflow evaluation.
In some cases, (low permeability rocks, shale gas formations, etc), the steady state flow cannot be reached (or requires extremely long time for well stabilizing). In this case, the advanced methods, known as isochronal or optimized isochronal tests are being utilized.
PRODUCTION LOGGING RESULTS
The total Inflow Performance Relationship IPR diagram, which is a
part of well testing steady state flow data interpretation,
reflects the pressure (or dP) as a function of total surface rate.
SIP is extremely useful reservoir engineering tool that provides an opportunity to estimate reservoir pressure, producibility index, possible zone crossflow and depletion for every pay zone and for various fluid phases. To construct the SIP several well flowing regimes (at least two) are required. Well flowing regime means the well is producing with constant (steady state) or close to steady state at surface. During the PLT, the surface multi-phase rates are measured as usual and are used later for matching with downhole data and velocity (flowing) model
PERMEABILITY FROM FLOW RATE
oilfield work, fluid flow from a reservoir into a wellbore is not
linear but radial, so the equation becomes:
estimation should be calibrated with other data sources,
example pressure transient
analysis technique on pressure buildup or drawdown data, or the
geometric average of conventional core analysis data. Some skin-effect assumptions
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