Production logs, or PLs, are run on production or injection wells, with the goal of evaluating the well itself and/or the reservoir performance. Put simply, for producing wells, we need to determine what fluid is coming from which zone, and how much. The PL string may be a relatively simple, conventional configuration run in vertical or deviated wells that, based on the assumption the tool is centralised in the flow, measures the bulk flowrate using a calibrated spinner and then discriminates the fluid type(s) using a suite of tools usually including density, pressure and temperature applied to flow correlations in Emeraude.

With the proliferation of horizontal wells in recent years the PL strings have, by necessity, become increasingly complex. The challenge is to handle segregated flow by various distributed measurements around and across the section of the pipe. Emeraude has kept pace with these developments and offers a choice of calculation schemes and visualisation options to cope with these multiple array tools from any vendor.

New Emeraude v5.12

Emeraude Workflow

  • Document\nInitialization
  • Survey
  • PL\nInterpretation
  • Output

General Data

Open hole logs and deviation surveys are loaded. This data is used to depth match the PLT data, and also to correct some tools’ response and as an input of the multiphase flow correlations.

If saturation and porosity logs are also loaded, Emeraude will automatically create a track displaying the formation’s fluid volumes.

Completion details

The internal diameter, depth of the perforations and reservoir zones, markers, pipe roughness and deviation are loaded in the completion details.

Emeraude will use these as inputs for Zone rates calculations.

Well Sketch

It is possible to create a completion diagram of the well, by selecting completion items (casing, tubing, cement, etc.) from a list.

In Emeraude, the well Sketch is for illustrative purposes only, the diameter and length of the components are not used as an input for the calculation process.

Load PL data

Passes and stationary data are loaded from LIS, LAS and ASCII files.

Automatic tracks are built to give an instant view of the log data, whilst customized views can be created through the use of snapshots and templates, permitting fast navigation through the data.

Editing data

The raw PL data normally requires editing before an interpretation can be performed.

Emeraude contains a broad range of editing options: lateral average, depth stretch, shift, delete data and fill, hide data, merging, splicing, derivative, sampling, user formula module, etc…

PL tool configuration

In Emeraude, the user must specify the type of density tool that is used, so the proper corrections are applied in the calculation scheme. The spinner blade diameter must be entered to compute the velocity profile correction factor. A built-in list of capacitance tools is included for the different vendors, with their respective calibration charts.

Define reference channels

The reference channels will be used to compute the PVT properties and also in the regression during zone rates calculation.

In Emeraude, pressure temperature and any relevant hold-up or density channel need to be defined. If more than one pass is selected, a lateral average will be applied.

Spinner calibration

The spinner measures RPS, but the interpreter needs fluid velocity and rates. To transform spinner RPS and cable speed to fluid velocity, the spinner calibration parameters need to be known. When sufficient passes are available, an in-situ spinner calibration can be performed.

Multiple spinners can be handled simultaneously, particularly for multi-probe tools. Different calibration modes and editing tools are available on user defined spinner calibration zones. The interpolation between calibration zones may be modified, depending on the fluid distribution in the pipe.

Velocity calculation

Once the spinner calibration parameters are known, the apparent velocity is calculated for each pass and each spinner, where applicable.

PVT

PL phase calculation is highly sensitive to the PVT. Consequently, when calculating the rates at downhole conditions, a number of PVT properties are required. Also, to convert the downhole rates to surface conditions, the volume factors need to be known.

Black-oil PVT offers a wide choice of correlations, which can be viewed and matched to user-defined measurements. PVT tables may also be loaded. If the PVT is zoned, properties are redefined for each inflow zone. A steam-water model is available to analyse steam injection wells.

Rate calculation

The rates are calculated in selected intervals of the log, and a continuous profile can be created.

Rate calculation is treated as an optimization problem using nonlinear regression, with full flexibility in the type and number of input measurements. Calculations may be zoned or continuous. The zoned calculation focuses on user defined stable flow intervals. The continuous method seeks agreement everywhere on the logs and the holdups are treated as variables, allowing a possible deviation from the slip models. The zoned method works well most of the time and it is very fast. The continuous method may provide a better answer in complex cases and when attempting to match temperature. The user has the choice.

Global regression

The global regression solves for the contribution of the inflow intervals instead of the selected calculation zones only. Such regression solves for the entire well at once, allowing the user to impose constraints such as the contribution sense, surface rates, etc. It is also possible to fix any particular contribution to a fixed or null value.

Log and reports

The interpretation’s result is presented in the form of a cumulative and contribution profiles with phase rates. This can be at downhole or standard conditions.

A built-in report can be printed and previewed that includes predefined sections. It is possible to produce a report in MS-Word using the OLE interface of Emeraude. A template MS-Word report is installed and can be customized as required.

Summary table

The output logs provide a visual output of the interpretation. The numerical outputs can be obtained from the summary table, which shows the cumulative and contribution rates, and velocities of each phase, with the PVT properties at the level of each inflow zone.

Exporting output

The user may export the result profiles and part of the data loaded in Emeraude; to third party software.

Emeraude log channels can be exported in LIS, LAS or ASCII format.

Horizontal PLT

Since the 1980s, the number of horizontal wells has increased dramatically. As the flow regime is normally segregated, it is not possible to use conventional tools to obtain the production profile. More complex multiprobe or array tools are used, with distributed measurements around the cross section of the pipe.

Emeraude includes specific treatment for the Schlumberger PFCS, GHOST and FSI, the GE Sondex MAPS suite (CAT, RAT and SAT) and Hunter probe tools. Image views are created and cross sections displayed at any depth, and for any combination of passes. A regression process fits the discrete measurements with the relevant 2D models, contingent on user-defined constraints on segregation, phase presence or other tools. The output can be presented for QA/QC and results compared with the raw data. Average values of phase holdups, mixture velocity, and phase rates are produced and serve as inputs to the final interpretation.

Selective inflow performance (SIP)

In a multirate PLT, the well is logged at different surface rates. For each choke setting, the contribution of the zones and corresponding bottom hole pressures will change. Plotting the bottom hole flowing pressure versus the contributions for each zone, it is possible to obtain an IPR curve for each producing layer, and therefore quantify important reservoir parameters, such as reservoir pressure, productivity index and absolute open flow.

In Emeraude, an SIP analysis can be made with a few clicks. Pseudopressures can be used for gas. An unlimited number of SIP’s can be created and compared. Each zone can be assigned a different model: straight line, C&n or L.I.T. The SIP can use the total rate, a phase rate or the total liquid rate. Data may be downhole or from surface. Pressure datum correction and composite IPR’s are available.

Thermal

Increasingly, wells are completed with fibre optic distributed temperature sensors (DTS). Even in a conventional PL job, the spinner may fail or give an erroneous response under certain circumstances (counter current, high viscosity etc). In such a case the temperature log may be the only source of information about the rates. If the thermal properties of the fluids, completion and formation are known, and if the problem is not undetermined, it may be possible to infer the production profile based on the temperature log.

Emeraude offers a segmented model and an energy model. The analytical segmented model accounts for enthalpy balance in front of inflow zones, and conduction/convection between zones. Joule-Thomson effects are calculated from a user estimated pressure drop. The numerical energy model solves the full energy equation in the wellbore and the reservoir, accounting explicitly for the thermal effects within the reservoir.

Steam injection

When designing a steam injection well, the goal is to obtain the highest quality of steam downhole. That is, to minimize the condensation of liquid water and maximize the volume of vapour that the perforations receive. The variables that can be optimized are the injected rates, pressures and thermal properties of the completion.

This special analysis uses a dedicated 2-phase steam-water PVT for the design of steam-injection tests. The temperature, pressure, holdup and velocity profiles are calculated from surface, to determine the property of the injected fluid in each zone. Relevant slip models are considered.

Apparent permeability (APERM)

Estimation of effective permeability at reservoir scale is fundamental for an accurate reservoir model. In carbonates, the permeability in vuggy or fractured intervals can be dramatically different from the matrix permeability measured in core plugs. The apparent permeability based on PLT data may be the solution for a field-scale characterization.

This method corrects, with the PL interpretation, the open-hole effective permeability. It uses an IPR relationship where the relevant reservoir or perforation parameters are defined zone by zone. The method is implemented for single-phase liquid, liquid mixture, or for gas using pseudopressures.

Leak detection

Leaks represent an extremely dangerous situation for the integrity of the well. Leak diagnostic is normally performed through the use of callipers, spinners and temperature. For very small leaks, the spinner may have insufficient resolution to identify the leak. It may also be missed by the caliper. However, temperature is very sensitive and can provide and easy method to determine the presence of leaks.

The leak option simulates the thermal profile along the tubing and annulus in cases where a tubing leak is suspected. An extra energy equation is added to the system that accounts for energy conservation in the annulus. The balance of energy is then made between tubing flow and annulus flow (accounting for conductive and convective heat fluxes) and in between annulus flow and the reservoir (accounting for conductive heat fluxes).