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 v5.20

Emeraude Workflow

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

General Data

Open hole logs are loaded for depth matching purposes and to complement the PL interpretation. Also, a deviation survey is required to correct some tool responses and as an input for multiphase flow correlations.

Apart from the traditional logs, Multifinger calipers, borehole images, Cement logs (CBL, VDL, Impedance maps, etc) and any other array data type (typically DLIS files) can be loaded to supplement the PL analysis.

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. The Well schematic can be shared with other KW modules.

Load PL data

Passes and stationary data are loaded from LIS, DLIS, 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.

Array data type can be loaded directly (DLIS files) or created at the loading stage from individual/multiple LAS or .csv files thus allowing loading of noise, cement or integrity logs as part of the survey 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

Due to the complexity of the flow regimes encountered in highly deviated and horizontal wells 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, GAT and SAT), OpenField FAST, Baker Hughes PAI, Hunter-Probe (AFC, AFR, AFV and AGH) and Spartek probe tools. Moreover, Emeraude allows the definition of any arbitrary multiprobe tool geometry and measurement type, in case the tool to be analysed is not included in the built-in library.

Templates for facilitating the QA/QC of measurements are available for all the 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. 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/DTS

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). If the thermal properties of the fluids, completion and formation are known it is possible to perform quantitative production or injection profiling.

Coupling energy and mass balance equations, Emeraude offers methods for production and injection profiling and annular leak detection. Also, Emeraude incorporates specific formulations for Water Injection Fall-off (warmback) and steam injection.

A simplified Thermal/DTS workflow is available. Visit the Thermal page to learn more about thermal solutions in Emeraude and Rubis.

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.

Pulsed Neutron

Once the well has been completed, it is not possible to use the typical open hole resistivity logs for the determination of formation water saturation. Pulsed neutron logging techniques, based on the decay of the population of thermal neutrons, is the most common way to obtain the water saturation behind casing. Since the capture cross section of the chlorine is much higher than the other elements found in the formation, the saturation of saline water may be determined.

Emeraude incorporates a specific workflow for analysing Pulsed Neutron logs in Sigma (capture) mode. Models for clean, shaly and dual water formations are available. A number of crossplot techniques facilitate the determination of the different component’s sigma values needed for determining the formation water saturation. Once obtained it is possible to display the evolution with time.