Petrel TIPS&TRICKS from SCM

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1 Petrel TIPS&TRICKS from SCM Knowledge Worth Sharing Holiday Tree Facies Model It s that time of year again time for a TIPS&TRICKS with a twist. This article highlights facies modeling using the Truncated Gaussian with Trends method. It is often used to model depositional systems where there is a natural transition through a sequence of facies as in carbonate environments, progradational sequences and shoreline deposits. The Truncated Gaussian with Trends method allows a stochastic distribution of the facies based on a given ordered sequence and a trend direction. The trends are converted into probabilities and the model is run using the standard truncated Gaussian technique which allows you to specify global fractions for each facies. The trend shape and direction are set interactively in the dialog and a range given for the variogram. The twist is that the end result in this example will be a model resembling a holiday tree. If you are new to facies modeling, a facies is defined in geologic terms as the overall characteristics of a rock unit that differentiates it from the other units around it. These characteristics are directly related to fluid flow (i.e. Porosity) in modeling hydrocarbon reservoirs. Similar facies may have similar porosity distributions and trends in a given area. Facies modeling in Petrel is the process of building discrete rock-type facies distributions three-dimensionally in a model grid. Rock-types can be based on lithology (sand/shale), fluid flow (net/non-net) environment of deposition (fluvial/marine) or geologic association (channel/margin). Facies modeling is an essential step in the modeling workflow for proper reservoir description. Attempting petrophysical property modeling without a facies model is risky, sort of like taking a journey without a map or compass. 1

2 Creating the Holiday Tree Facies Model Step 1: The conceptual model The first step in the facies modeling workflow should be to develop a conceptual model. You must have an idea or picture in your mind of what the result should look like, and then apply the tools available, often times in innovative ways, to accomplish the task. In this example, we will use a conifer tree as an analog. We start with a picture of a forest as a visual analog. Next, we break down the tree analog into simple geometric terms for modeling Side View Plan View 2

3 Step 2: Create a simple 3D grid for modeling The next step in creating the tree model is to build a simple 3D grid. We will create constant z-value planar grids at regular intervals to be used as input to the Make simple grid process. The zones created will be used to model facies that represent the tiers of a conifer tree. 1. Use Make/edit surface to create grids to be used as input to the Make simple grid process. Choose the Artificial algorithms method to create grids of constant Z for the top and base of the model as well as intermediate layers for the individual tiers in the tree. The author used grids in 200 foot intervals from 0 to Set the X/Y limits to Min = -1000, Max = Use the Make simple grid process with the constant z value grids as input surfaces. Set the X and Y limits to Min = -1000, Max = 1000, and the grid increment to 10. 3

4 3. Run the Layering process with the parameters set as shown below. Step 3: Model the foliage facies The next step is to model the foliage of the individual tiers / zones. 1. Create a discrete property template that defines the background, foliage, trunk, and each color desired for the lights by copying the Facies template and editing as shown below. 2. Model the foliage for each zone using Truncated Gaussian with trends method. a. Start the Facies modeling process. 4

5 b. In the Zone settings, select Zone 1 and unlock it. Select the Truncated Gaussian with trends method. In the Facies tab, select the Foliage and Background facies in the order shown below. c. In the Geometry tab, select Point source and Retrogradational as the trend type. Set the Radius to center of grid to 0. d. Activate the Edit lines option. Click on the Select and move lines icon. Click on the lower contact of the background property and expand it past the limits of the model area. A dashed line represents the facies contact at the bottom of the zone and a solid line represents the facies contact at the top of the zone. You can zoom in and out by placing the cursor in the trend editing area and pressing the shift key while clicking and dragging on the left mouse button. At this point it is a good idea to copy the zone 1 settings to zones 2 through 8. You will need to re-lock each zone after using the Paste settings to all zones function to avoid running all zones together. 5

6 e. Adjust the upper contact of the Foliage facies so that it converges almost to a point. You will need to zoom in. Notice the white area in the center of the figure below. You will need to adjust these contacts as well. f. Zoom back out and adjust the lower (dashed) contact of the Foliage facies. Move the lower contact inward just a bit towards the center. This will form the top tier of the tree. Remember, we will create several tiers that increase in radius as we move down. Once you have the lower contact radius adjusted to your liking, click on the Select and move points icon. Click and drag about every other point and move it in towards the center to form lobes. Go to the Settings tab and enable the Make trend only (Discrete) option active. Run the modeling process on just the first zone with the filter applied and check the results. As with every facies model, QC and adjust to your liking. 6

7 g. Repeat the process above for each zone one at a time. This example has 7 tiers or zones of Foliage facies modeled, each with increasing radius and depth. Move the upper contact of the Foliage facies towards the center to form a taper from top to bottom. Make sure you re-lock the already modeled zones as you proceed to the next zone to avoid unnecessary computations. Tip: As you move down zone by zone, model each zone as a simple conical shape without the lobes first. View the results in a 3D window with the already modeled zone above it. Adjust the top contact radius using the line edit mode to fit flush facies in the zone immediately above it. Adjust the lower bottom contact as needed also. When you are satisfied with the fit, model the lobes using the point edit mode. 7

8 h. The final zone 8 forms the trunk. It is modeled the same way as the upper zones using Truncated Gaussian with trends, but the trend is a simple tapered cylinder. Step 4: Model the lights The next step is to model the lights. We will use facies modeling again, only this time will we use the Object modeling (stochastic) method. We will nest these facies in the background of the Foliage facies. 1. Select the same property created above as the Existing property and keep the filter option in the Common settings on to avoid modeling the background. 8

9 2. Select Object modeling (stochastic) as the method. 3. Create a number of ellipse objects corresponding to the number of different colored lights by clicking on the Add a new geometric body icon. This example uses 5 different colors. 4. For each ellipse object representing a colored light do the following: a. Click once on the object in the Facies bodies tab to activate it. b. Go to the Settings tab in the lower half of the proper color facies from the drop down list. c. Set the fraction to some small number, 5 for instance. dialog window and select the d. Go to the Geometry tab and set Ellipse as the Body shape. e. Set the Minor width to Uniform, Min = 10, Max = 10. f. Set the Maj/Min ratio to Uniform, Min = 1, Max =1. g. Set the Thickness to Uniform, Min = 1, Max = 1 and put a check mark in the box labeled Fraction of width. 9

10 h. Go to the Rules tab and put a check mark in the box next to Insert ONLY in the following facies and enter 1. i. Activate the Replace ONLY the following facies radio button and enter 1. j. Go to the Background tab and select the Constant option and select the Foliage facies previously modeled. k. You must set and use the property filter for this step to run correctly. i. Open the Settings for the model properties and go to the Filter tab. ii. Click on the box next to Use value filter to place a checkmark there. iii. Select the facies for the Value filter. iv. Click in the box next to Use filter to place a checkmark there. v. Filter out the background property as shown below and click on OK. 10

11 l. Go to the Common settings for the facies modeling dialog and click on the box next to Use filter to place a checkmark there. m. Copy and paste the settings to all of the zones (zone 1-7) with the Foliage facies and run the model. Skip the last zone (zone 8) containing the trunk. 11

12 Step 5: Workflow for blinking lights The light facies can be made to appear to blink by using a simple loop statement in a workflow to change the active discrete property template. 1. Copy the original discrete template used for the tree once for each color of light to blink and rename appropriately. 2. Edit each template so that one color of light is the same as the foliage facies. 12

13 3. Create a simple workflow with a loop that sets each template as the active one in a sequence as in the figure. The lights will appear to flash on and off when the workflow is run. 13