whitson^X — Well Test Certification

1. Introduction

Complete the steps below to become a Well Test-certified whitson^X user. The certification involves performing three analyses: a Chow Pressure Group (CPG) test, a diagnostic fracture injection test (DFIT), and a Devon Quantification of Interference (DQI) test. You can learn more about each test in the manual, which covers most of the theoretical fundamentals:

1. CPG - Chow Pressure Group Test
2. DFIT - Diagnostic Fracture Injection Test
3. DQI - Devon Quantification of Interference

Certified users have the software skills necessary to complete most CPG, DFIT, and DQI evaluation projects in tight unconventional reservoirs.

Need Help?

Send an email to x@whitson.com.

1.1. Before Starting

Make sure you have watched these three videos in the Getting Started section of the manual:

• Log In (1 min)
• Overview of important basics (3 min 30 sec)
• Zoom Plots (3 min)

1.2. Create a Project

1. Go to the Projects module in the navigation panel.
2. Click ADD PROJECT in the upper-right corner.
3. Name the project Your Name - whitson Certificate - Well Test.
4. Click SAVE.
5. All steps are shown in the GIF above.

1.3. Upload Required Data

You can download the files required for each test individually and upload them using the Mass Upload dialog box on the Wells page, as shown in the sections below.

Alternatively, all the data required for this exercise have been bundled into a file that is ready to upload from the MASS UPLOAD → EXAMPLES section.

1. Click MASS UPLOAD in the upper-right corner.
2. In the pop-up window, select EXAMPLES.
3. Search for Well Test Certificate Wells and click UPLOAD.
4. All the data will be uploaded to the project. You can then close the Mass Upload pop-up window.
5. All steps are shown in the GIF above.

2. CPG Workflow

You can analyze the Chow Pressure Group for the monitoring well by navigating to the Chow Pressure Group feature under the Well Testing dropdown.

2.1. Before Getting Started

2.1.1. Recommended Data Size for CPG Tests

CPG datasets may be sampled at a much higher frequency than needed. Sampling intervals can range from one second to tens of seconds throughout the test. High-frequency datasets can be difficult to handle and can make the numerical derivative calculation unwieldy.

Rather than uploading high-resolution data, we recommend resampling the dataset externally using pressure increments of 5 to 10 psi. This reduces file size and improves performance. For best results, keep the number of uploaded data rows between 30,000 and 40,000. To learn how to resample your data within whitson^X, see the resampling section here.

2.1.2. Data Truncation

The Truncate Data feature in the Well Test modules (CPG and DQI) allows users to remove unwanted portions of the dataset and focus the analysis on a specific time range. This is useful for excluding early-time noise, late-time operational changes, or any data outside the period of interest.

Truncation Methods

1. Date-Based Truncation
   Users can manually define the truncation window by selecting a truncate start date and truncate end date using the calendar controls. All data outside the selected range is removed.

   
   

2. Visual Truncation
   Users can visually select the data range to retain directly on the plot. A black dotted line marks the start of the retained data, and a blue dotted line marks the end. Data before the black line and after the blue line will be deleted.

   
   

Data Size

For these certificate steps, there is no need to worry about data size.

2.2. Chow Pressure Group Analysis

2.2.1. Pressure Difference Plot

1. Go to the Chow Pressure Group section in the Well Testing module in the navigation panel.
2. On the upper-left Pressure Difference plot, move the CPG fit line (the dashed yellow line) to match the pressure-difference data before the well's put-on-production (POP) date.
3. You can adjust the slope by:
   1. Manually move the fit line on the plot by dragging its endpoints.
   2. Change the constant and exponent of the power-law fit line directly in the input fields.
   3. Use the lasso tool to fit the pressure data before POP and automatically adjust the fit line.
4. Adjust the gray dashed vertical line along the monitoring-well data to the date and time when the offset production well is put on production.
5. The difference between the CPG fit and the data is plotted with its derivative on the \(\Delta p, \Delta p'\) vs. Time plot in the lower-right corner. Observe how this plot changes as the fit line is adjusted.
   
6. All steps are shown in the GIF above.

2.2.2. \(\Delta p, \Delta p'\) vs. Time Plot

On the lower-right \(\Delta p, \Delta p'\) versus time plot, you can switch between the derivative-calculation techniques by selecting an option from the Derivative Function dropdown list.
Notice how switching between the methods and window sizes in the GIF above changes the derivative shape and, consequently, affects the calculated CPG values.

Note

The Bourdet Derivative and Weighted Central Difference methods provide additional options for modifying the smoothing window as a log-cycle fraction or step size, respectively. Both methods are more accurate than using the Central Difference method with a fixed step size.

2.2.3. Plot Integral Function

Use the Plot Integral icon in the plot options to recalculate the pressure as an integral and recompute the derivative based on the derivative function selected above. You can also use the LOWESS Filter toggle with an appropriate smoothing window in log cycles to smooth noisy pressure data.

These methods inherently smooth the pressure response and remove additional noise from the dataset, creating smoother derivative and CPG plots. Because the pressure integral is already smooth, a smaller window size can be used for the derivative calculation.

2.2.4. CPG Value

Lastly, on the Chow Pressure Group plot, you can set the final CPG value in three ways:

1. Move the horizontal dashed line to track the average CPG value after the POP date.
2. You can also adjust it by entering a value for the CPG fit.
   
3. Alternatively, you can select the CPG based on the slope in \(\Delta p\).

The CPG value indicated under Chow Pressure Group (CPG) Fit is the final CPG value, which indicates the level of interference between the production well and the monitoring well.

3. DFIT Workflow

3.1. Before Getting Started

3.1.1. Recommended Data Size for DFIT Tests

DFIT datasets may be sampled at a much higher frequency than needed. Sampling intervals can range from one second to tens of seconds throughout a test, making the data harder to handle and the numerical-derivative calculation unwieldy.

Instead of uploading such high-resolution data, the recommended practice is to smooth the dataset by resampling it using pressure increments of 5 to 10 psi. The DFIT feature further reduces the data using pressure increments of 30 psi to improve the speed of dynamic calculations. However, it is good practice to limit the number of data rows uploaded into whitson^X to between 30,000 and 40,000. To learn how to resample your data within whitson^X, see the resampling section here.

Data Size

For these certificate steps, there is no need to worry about data size.

3.1.2. Required Choices and Assumptions

1. Choose a pre-closure method (G-function or H-function with radial or PKN fractures). The H-function method with radial fracture geometry is recommended.
2. Choose a post-closure method based on late-time impulse-flow signatures (linear or radial flow). Note that the pre-closure fracture-geometry assumption also applies automatically to the post-closure analysis.

Some notes on automated selections in the software

These preliminary steps are performed automatically, but you may still need to review the selections:

1. Shut-in is detected automatically from a zero rate. Instantaneous ISIP is identified as the pressure immediately after the well is shut in.
2. Initial pressure, P_w,init is chosen as the first point in the pressure data.
3. Cumulative injection volume and the maximum sustained injection rate until the shut-in time (characteristic rate) are calculated from the plot. Injection duration is computed automatically from the two values above.
4. The slope of pressure versus cumulative injection on the Wellbore Storage plot is detected to calculate wellbore storage. If rate data are unavailable, enter values for cumulative injected volume, maximum sustained rate, and wellbore storage.
5. Pore pressure is calculated automatically by extrapolating the post-closure linear transient (default) on the inverse-square-root-time plot.
   

3.2. Parameters

1. Go to the DFIT section under the Well Testing dropdown in the navigation panel.
2. Review the automatically selected parameters from the plots, including initial pressure, Literal ISIP, characteristic rate, injected volume, wellbore storage coefficient, and minimum $dP/dG$.
3. Enter the additional parameters relevant to the calculation, including Young's modulus, Poisson's ratio, reservoir-fluid viscosity, and initial total compressibility.

3.3. Physical Assumptions

The pre-closure and post-closure method dropdowns allow you to switch between methods and fracture-geometry assumptions.

1. Selecting the fracture geometry (radial or PKN) in the pre-closure methods applies the same geometry assumption to the post-closure methods.

2. Note that the PKN model requires fracture height as an additional input.

3.4. G-Function Plot

1. Identify the point of minimum $dP/dG$ in the G-Function plot.
2. Identify the point of maximum $G\,dP/dG$.
3. All steps are shown in the GIF above.

These selections automatically determine the effective ISIP, fracture-contact pressure, and minimum principal stress, which are used in subsequent permeability calculations. The resulting values can be overridden manually.

3.5. Late-Time Shut-In Identification

1. Click the slash icon in the upper-right corner of the dp after shut-in plot to add a slope.
2. Determine whether the late-time shut-in data contain post-closure transients.
   • Linear flow has a half-slope signature, while radial flow has a unit-slope signature. Radial flow is rare; beware of false radial signatures in gas wells.
3. Add the interpretation lines if needed. To switch to the impulse radial-flow plot, click the PLOT RADIAL button to the right of the plot.
4. Align the slope with the pressure points near x=0 and extrapolate it to calculate the pore pressure.
5. All steps are shown in the GIF above.

3.6. Permeability Computation

The permeability calculation updates dynamically whenever an input changes. If you have reliable post-closure transients, use the permeability estimates from the post-closure analysis. Correct pre-closure permeability estimates by about 1.5 because they statistically tend to overestimate permeability.

4. DQI Workflow

4.1. Before Getting Started

4.1.1. Recommended Data Size for DQI Tests

DQI datasets may be sampled at a much higher frequency than needed. Sampling intervals can range from one second to tens of seconds throughout a test, making the data harder to handle and the numerical-derivative calculation unwieldy.

Rather than uploading high-resolution data, we recommend resampling the dataset using pressure increments of 5 to 10 psi. This reduces file size and improves performance. For best results, keep the number of uploaded data rows between 30,000 and 40,000. To learn how to resample your data within whitson^X, see the resampling section here.

4.1.2. Data Truncation

The Truncate Data feature in the Well Test modules (CPG and DQI) allows users to remove unwanted portions of the dataset and focus the analysis on a specific time range. This is useful for excluding early-time noise, late-time operational changes, or any data outside the period of interest.

Truncation Methods

1. Date-Based Truncation
   Users can manually define the truncation window by selecting a truncate start date and truncate end date using the calendar controls. All data outside the selected range is removed.

   
   

2. Visual Truncation
   Users can visually select the data range to retain directly on the plot. A black dotted line marks the start of the retained data, and a blue dotted line marks the end. Data before the black line and after the blue line will be deleted.

   
   

Data Size

For these certificate steps, there is no need to worry about data size.

4.2. PVT

PVT initialization is required to obtain fluid properties, such as compressibility and viscosity, from the black-oil tables. Ensure that the PVT initialization represents the fluid expected between the wells.

1. Go to the Scenarios module in the navigation panel.
2. Initialize PVT with 100% water saturation.
3. Go to the PVT module in the navigation panel.
4. Open the Reservoir Fluid Composition input card.
5. Click SAVE.
6. All steps are shown in the GIF above.

For a DQI test conducted shortly after the initial stimulation of the offset well but before production begins, initialize PVT with 100% water saturation. This is the approach used for the example dataset, as shown in the GIF above.

For tests in which the well pair has been producing hydrocarbons, initialize PVT with the GOR associated with the in-place reservoir fluid.

4.3. Align the POP Line of the Offset Well

1. Go to the Production Data module in the navigation panel.
2. Examine the pressures in the production data to estimate the POP time, which is 1.48 days in this case.
3. Go to the DQI section in the Well Testing module in the navigation panel.
4. Set the offset well POP to 1.48 days.
5. All steps are shown in the GIF above.

You can enter the value or move the vertical dashed gray line on the graph to the point at which the offset well is put on production.

4.4. Align the Line to Pressure Trend Before POP

1. Fit the pressure trend by moving and adjusting the slope line to align with the stabilized pressure trend before the POP time. 1. You can do this manually or use the lasso tool to fit the stabilized pressure data.
2. All steps are shown in the GIF above.

Notice how the pressure and pressure-derivative-versus-time plot after POP is recalculated dynamically as you adjust the prior pressure trend.

4.5. Autofit

Once the prior pressure trend and POP time have been selected, the pressure and pressure-derivative data are plotted.

1. Click the AUTOFIT button in the upper-left area of the page.

2. This fits the analytical model to the pressure and pressure derivative data to determine model parameters:

   1. α (which controls hydraulic diffusivity) affects the timing of the onset of pressure interference.
   2. The κ parameter (which controls fracture conductivity) affects the shape of the curve after interference. Resolving these two parameters allows you to calculate the fracture conductivity, κ, and the maximum possible drainage length along the fracture, L, given W (fracture width or aperture), $dW/dP$ (the change in fracture aperture with pressure), and other parameters.

   Assessing Fit Quality

   The priority is to ensure that the fit matches the initial response—the first tens or hundreds of psi. The analytical solution is not expected to match the transient after the initial response.

3. The Ld is then calculated using the well spacing, y.

4. This value is plotted using the empirical correlation developed to calculate DPI from $L_d$.
5. The resulting DPI should be close to 99%.
6. All steps are shown in the GIF above.

Record α and κ, which, along with DPI, indicate the quality of well-pair connectivity. These values will help you rank well-pair connectivity in large-scale tests involving multiple well pairs.

Do It Yourself

Did you know that the CPG and DQI datasets are both interference tests between different well pairs? This means that the CPG dataset can be used to calculate the DPI for that well pair and the DQI dataset can be used to calculate the CPG value for the other well pair.

Do you want to try this? Use the wells in your project and assess the interference datasets using an alternative technique.

Report the answers in your submission below for some extra kudos!

Want to Learn More?

Schedule a Well Test session with one of our engineers by contacting x@whitson.com.

Done?

When you are done analyzing your Well Tests, please:

1. Send an email to certification@whitson.com.
2. Make the subject: "whitson^X Well Test certificate: [YOUR NAME HERE]".
3. Include the link to your project.
4. Feel free to share any notes, comments, or observations related to the analysis. Feedback on the user-friendliness of the software is also appreciated.

After that, we will provide feedback on your evaluation and issue your whitson^X certificate if everything looks good.