Decline Curve Analysis

With decline curve analysis (DCA), you can best fit a decline curve to your data and your parameters update automatically. These parameters can then be used for additional analysis. Both the Rate vs. Time and the Rate vs. Cumulative plots can be used as they are synchronized.

The data stream and decline curves (displayed in both plots) may appear differently even though the plots are synchronized. This is expected behavior, and both plots are valid.

When you first open DCA, all of your data points are selected in the Rate vs. Cumulative plot (default setting), and an oil decline curve is displayed with an initial best fit in both plots using operated / average rates. If oil production data is not available, gas or other fluid data is plotted.

DCA automatically fits (best fits) your decline curve based on:

recent trends.
rate data. It is able to handle shut-ins, and exclude these data points from the best fit.
If you have anomalies in your data, a local outlier factor algorithm is used to determine which data points are considered outliers to be excluded from the initial best fit.

In order for the auto-fit algorithm to work, at least six months of data is required. If there is not enough data, all of the data points are selected, and a decline curve is generated based on the data that is available. DCA automatically selects the best subset of your data for an initial best fit.

Each fluid type gets its own color: gas is red; water is blue; oil is green. Note that when you switch fluid types, or between rates, your point selections and decline curves in both plots are retained, even though the display changes.

To adjust the portion of your production data used to generate a decline curve (your history match), best fit your decline curve, which updates your forecast.

Basic functionality

Basic functionality is outlined below:

To auto-fit your plot to your window size, double-click it, or click the Auto Scale icon ().
To switch between wells, select or open a new well in your application, The title for each of the plots displays the currently selected well or group.
To identify your decline curve in the main pane, hover over the plot to see which line is displayed in bold.
To quickly zoom in or out, scroll your mouse wheel.

Changes you make inside the Decline control (properties, parameters, what decline to show, etc.) are discarded when you choose a different item (Well, Pool, etc.) in the Data Navigator pane or close the DataCard.

Show on y axis pane

In this pane, click the data set check boxes you want to display in the Rate vs. Time plot. As you deselect data sets, the corresponding y-axes are hidden from view. The Rate vs. Cumulative plot displays the fluid selected for decline analysis.

A Decline icon () is displayed beside rates and volumes. To change where the decline curve is applied, click the Decline icon for the data set you want displayed, and notice that the decline icon changes to an active state (). Note that you cannot apply a decline curve to multiple fluids at the same time.

You can select the following data sets from this pane:

Calendar rates — the volume of fluid produced or forecast over a period of time divided by the number of days in the period, regardless of actual on-time. For example, if a well produced 300 barrels of oil in a 30-day month, but was only flowing for 15 days, then this rate = 300 bbls / 30 days = 10 bbls / day.
Average rates — the volume of fluid produced divided by the producing time in the period. For example, if a well produced 300 barrels of oil in a 30-day month, but was only flowing for 15 days in the month, then this rate = 300 bbls / 15 days = 20 bbls / d.
Cumulative production — the total amount of fluid produced up to the current period from the start of production for the well.
Volumes — the total amount of fluid produced in a period.
Total fluid — the aggregate of oil, water, and condensate production volumes.
Time on production — the amount of time in a period that the well is flowing. This excludes any time the well is shut in as part of its operations or maintenance, etc.
Ratios — the proportion of one fluid volume to another. Usually, the primary fluid will be contrasted to secondary products, such as the gas-oil ratio for an oil well.

To hide this pane, click the left arrow (<) at the top. The pane displays as a tab on the left-side of the screen.

Properties pane

In this pane, you can customize how your y-axis and x-axis are displayed. To hide this pane, click the down arrow (ᵛ) at the top. The pane displays as a button on the bottom of the screen.

There are three tabs in this pane.

Data set

This tab has the following items:

Line Style — select dotted, dashed, or solid decline lines for your currently selected data set.
Line Thickness — select your line thickness for your currently selected data set.
Line Color — select your color from the color swatches for your currently selected data set. Note that the bottom rows in the color picker represent the default colors for various fluids.

The specific data set selected in the tree structure is displayed at the top of this tab (unless the parent node is selected), so that it is very clear which data set properties are being changed.

Y axis

This tab has the following items:

Axis — when the Rate vs Time plot is in focus) select the data set you want to display on the y-axis.
Axis Min — type your minimum value for the y-axis. If the Rate vs Time plot is in focus, the axis for the data set specified in the Axis field is updated. If the Rate vs Cumulative plot is in focus, the currently displayed axis is updated.
Axis Max — type your maximum value. If the Rate vs Time plot is in focus, the axis for the data set specified in the Axis field is updated. If the Rate vs Cumulative plot is in focus, the currently displayed axis is updated.
Grid Lines — click this check box to display grid lines. If the Rate vs Time plot is in focus, the grid lines apply to the Axis selected from the drop-down list. If the Rate vs Cumulative plot is in focus, the grid lines apply to the currently displayed axis. Select solid or dotted grid lines from the drop-down list.
Axis Title — click this check box to display a title next to the y-axis closest to the plot.

X axis

This tab has the following items:

Axis Start Date — when the Rate vs Time plot is in focus) select your start date by clicking the down arrow ().
Axis End Data — when the Rate vs Time plot is in focus) select your end date by clicking the down arrow ().
Axis Min — when the Rate vs Cumulative plot is in focus) type your minimum value for the x-axis.
Axis Max — when the Rate vs Cumulative plot is in focus) type your maximum value for the x-axis.
Grid Lines — click this check box to display grid lines. Select solid or dotted grid lines from the drop-down list.
Axis Title — click this check box to display a title at the bottom of the plot.

The x-axis is automatically scaled based on your well data.

Rate vs. time plot

In this plot, you can display multiple production data sets (including their axes) by clicking their check boxes from the tree structure on the left. As you hover over the plot, the decline curve is displayed in bold, so you can easily identify it.

Click one of the Decline icons () to automatically apply a decline curve to your data.

Best fitting is done the same way in both plots. Afterward, you can use the parameters displayed on the right-side for additional analysis.

Rate vs. cumulative plot

In this plot, click one of the Decline icons () to view rate vs. cumulative volume, and automatically apply a decline curve to your data.

Best fitting is done the same way in both plots. Afterward, you can use the parameters displayed on the right-side for additional analysis.

If you do not apply a decline to any of your data sets, this plot is blank.

Icons

The DCA interface has the following icons:

/ Maximize / Minimize — toggle between maximizing your plot to the full window size, and reducing / minimizing your plot to the default size. If you click the Maximize icon, you can switch to the other plot by clicking its tab.
Rectangle Zoom — visible after you click the plot, and draws a rectangular region to zoom in to.
Auto Scale — visible after you click the plot, and scales the plot, so that all data and analyses are displayed.
Tooltips — click this icon to display tooltips for your data set's rates on both plots. Times are displayed as x-axis tooltips in the Rate vs Time plot, and cumulative volumes are displayed as x-axis tooltips in the Rate vs Cumulative plot. Click the icon again to hide tooltips.
Rotate control — visible after you click the decline curve or the Manipulate Decline button, and enables you to rotate your decline curve. You can also slide the rotate control along the decline curve. As you hover over the rotate control, its line is displayed in bold, so you can easily identify it.
Decline — click the Decline icon in the Show on Y Axis pane to apply a decline curve to your plots. The icon changes state after its been clicked .
Pan — visible after you click the decline curve, and enables you to move your decline curve.
b value — visible after you click the decline curve, and enables you to change the b value (curvature) of the decline curve.
Left / right resizing — visible after you click the decline curve, and enables you to adjust the Rotate control's anchor point.

Decline parameters pane

In this pane, you can manually enter values in the white parameter fields, or you can adjust the decline curve and the parameters are automatically updated. To shorten your decline curve, you can enter an appropriate value in the q_f field. Grey parameter fields are automatically updated when you move the decline curve.

If you manually edit these parameters: b, q_i, q_f, or a_i, your data points are deselected in the plots.

You can also change your start date by clicking the Start Date down arrow () and selecting a date from the calendar.

If you do not apply a decline to any of your data sets, this pane is blank.

Analysis pane

In this pane, there are two buttons that impact both plots, as well as drop-down lists that enable you to customize how your decline curve is displayed (that is, by selecting your line style, thickness, and color from drop-down lists). The buttons are described below:

Manipulate Decline — after you click this button, the Rotate icon () appears. Reposition your decline curve to manually best fit your production data.
Re-Initialize Decline — after you click this button, the plots are reset back to their original auto-fit settings.
Select Data Points — after you click this button, the Data Selection icon () appears. Draw a box around the data points you want to be included in an automatic best fit.