1/23/02: 3-D Seismic

 

First Session

PDW Horizons >Horizon Manager. Under "Formation", all entries are probably "None". For

each horizon with a well top (Wab, Bluesky, etc.), change the entry from None to the well

top name for that horizon. (Close)

Load 3D Seismic Volume:

Open existing 2D project with well ties and horizon interpretations, and close seismic line

windows.

PDW Seismic >3d Seismic Data Manager >Add… In Trace File Name: browse for C:\Documents

and Settings\All Users\Application Data\GeoGraphix\Sample Files\Moosehead\3DX\

Moosehead. (Open). (Next>). (Finish). Close Interpretation Manager window.

Examine map for 3D location. (Zoom) to 3D.

(Open a N-S seismic line), LeftClick on 3D area of basemap. Scroll seismic window, note

that horizon ties from 2D interpretations show up as color coded plus signs. Note 2D tie

line labels at top of seismic section and horizon ties.

To enlarge seismic, RightClick on seismic >Adjust Seismic Display >Scale Settings ->5

tr/cm, -> 15 cm /sec, (Save As Default), (OK). Stretch seismic window.

Move seismic window to show both map and 3D line. Bring map window to front, (Open an

E-W seismic line), LeftClick on 3D area of basemap. Study seismic. Note base map for

seismic line locations.

Another method to select seismic lines: Bring E-W line window to front, (Open a N-S seismic

line), LeftClick on seismic where you want to see the N-S cross line.

Close all seismic sections. (Open an E-W seismic line), LeftClick on 3D area near bottom of

basemap. Up/down keyboard arrows step through east-west 3D lines at 10 lines/keystroke.

Left/right keyboard arrows step through north-south lines. Close seismic line.

Step interval can be adjusted. PDW Seismic >Seismic Display Settings… >Scroll Increment

Inline ->1, Xline ->1, Arbitrary ->1. (OK).

(Open an E-W seismic line), LeftClick on 3D area. Up/down keyboard arrows now step through

east-west 3D lines one line at a time. Left/right keyboard arrows step through north-south

lines. Close seismic line.

(Open an arbitrary seismic line), on the basemap LeftClick, LeftClick, LeftClick, LeftClick,

DoubleClick to open 3D seismic traverse. Move seismic window to show both map and 3D

line. Mouse location on seismic shows up on map. Up/Down and Left/Right keys move this

line as well. Recommendation: Do not interpret anything on arbitrary lines, because if you

want to change an interpretation, you must do it on the Arbitrary Line, and it may be

impossible to recreate it exactly. It is easy to recreate an E-W line or a N-S Line.

Close seismic window.

(Build a 2D/3D Composite Line), (Open a 2D Seismic Line), LeftClick and drag on 2D line,

release, (Open an arbitrary seismic line), back to map to continue on 3D traverse, LeftClick

for intermediate points along 3D line, DoubleClick to finish. PDW Seismic >

(Open Composite Window). Note: You must start with the 2D segment at the beginning

of the traverse only. Also note that the tie between the 2D and 3D lines needs to be adjusted.

Close seismic window.

 

Tie 3D Data to Existing Well Control and 2D Seismic:

(Open an arbitrary seismic line). On the map, select an arbitrary NW-SE seismic line which

passes through Wells 03 and 01.

(Zoom) to the Wab Group seismic/well tie. Examine both synthetic ties and note the time shift.

Examine 2D Wab interpretations [+ signs], and the time shift necessary to place those ties

on the 3D peaks. If the + signs are yellow, you might have to select Wab in the Horizons

window to make it more visible.

The average of all these shifts requires an upward shift of the 3D of about 6 ms.

PDW Seismic >Match 3D Volumes… Accept Moosehead 3D default, (Next >). Static Shift ->-6.

*Make new copy of 3ds file. New Version Name ->Moosehead-6ms. (Preview) and study

result on seismic section. If it looks good, (Apply to 3DS).

Browse to C:\Documents and Settings\All Users\Application Data\GeoGraphix\Sample Files\

Moosehead\3DX. Filename ->Moosehead-6ms. (Save).

PDW Seismic >3d Seismic Data Manager > +Moosehead 3D, Component +Dataset versions. You

should see the original 3D version and the –6ms version. (Set Active Version…),

+Moosehead-6ms, (OK). Close window. If you get a warning window, dismiss it.

The current seismic line uses the original version as shown in title bar, so close it. Create another

arbitrary seismic line through the same wells and zoom in close to examine the tie.

Close all seismic windows.

Autopicking 3D Horizons:

On the basemap, open an E-W [XL 35] and open a N-S [L 50] 3D line near well control. In the

Horizons window, select horizon for WAB Group and Autopick the strong WAB peak on

both N-S and E-W seismic lines.

Bring map to front.

PDW Horizons > Interpolation 3D Autopick: Wab Group. Study map for structure in the SW

corner and the rest of the map for noise. Create some Arbitrary lines across anomalies to see

the cause.

If the autopicks are unacceptable, erase with PDW Horizons > Erase 3D Autopicks: Wab Group.

Your seed pick interpretation on the N-S and E-W and 2D lines will remain, and you can

interpret more lines to refine your interpretation.

Do not click PDW Horizons > Erase Horizon: Wab Group or you will loose your 2D and 3D

interpretations. You should usually erase old Autopicks before autopicking again or else

there will be no change.

Try a different autopicking algorithm. PDW Horizons > Correlation 3D Autopick: Wab Group.

Study map for differences. The colors may look very different, but on a strong event like

the Wab, the autopicks differ little.

During the Interpretation Break, study the Autopicked differences between the two methods.

Adjust the picking parameters to see if you can make improvements.

Autopick Second 3D Horizons:

Interpret another horizon [Fort Vermilion] on the N-S and E-W seismic lines.

Then autopick: PDW Horizons > Interpolation 3D Autopick: Fort Vermilion. Study the resulting

time structure map. Note the structural highs and their correlation to the three wells. Do

you suspect that the location of these wells had something to do with these structures?

Chances are that the 3D was shot at this location to improve the seismic resolution of these

producing structures.

To improve the map, smooth the horizon using PDW Horizons > Smooth Horizon: Fort

Vermilion… ->3 and ->3, (OK). We can do this to some extent because we know that a

single anomalous value is most likely noise. The Fort Vermilion horizon is near the "reefs"

we were speculating about last week. It appears that the 3 wells have tested the 2 best

opportunities. If they were very successful, we can see several other opportunities to

pursue.

Undo the smoothing using PDW Edit > Undo.

Erase 3D autopicks with PDW Horizons > Erase 3D Autopicks: Fort Vermilion.

Go back to Fort Vermilion horizon on, place cursor on the Fort Vermilion troughs and study

amplitudes posted at the lower right hand side of the screen. Estimate the maximum negative

amplitude [about –6000]. On the interpretation, RightClick > Pick Parameters -> 7 in Guide

Window Len, -> about 70% of that maximum trough amplitude in Absolute Threshold

window [use positive value not negative, about 4200], *Amplitude Test. (OK). Return to

map and 3D Autopick horizon again.

Note missing interpretation on the map. This is probably an indication of stratigraphic changes,

only troughs greater that a certain value have been interpreted away from our seed

interpretations on the seismic lines. Imagine if you are interpreting channel sands in a

shale formation. If the sand were thick enough and filled with gas to the point seismic

showed a "bright spot", you could interpret channel on one line, select a threshold

sufficient to include only the strong trough, and use the software to autopick the channel.

There are many similar applications for stratigraphic interpretation.

Return to Fort Vermilion Pick Parameters, turn off Amplitude Test, and 3D Autopick horizon

again.

Interpretation Break: 40 Minutes

Experiment with 3D Autopicking and Evaluation

Study seismic volume on 3D E-W lines, 3D N-S lines, and Arbitrary 3D lines.

Scroll through the 3D lines to study the fault on the SE corner and other seismic structures and

character.

You can change the location of a seismic line you are studying by returning to the map and dragging the

line to a different location. The new traces are displayed on the seismic sections. This even works

on Arbitrary Seismic Lines.

Try to Autopick a "troublesome" horizon such as the Muskeg Formation. Adjust autopicking

parameters to improve the structural interpretation.

Study bad autopicks on seismic lines to determine the cause.

Second Session

Close seismic sections

Timeslices:

A Timeslice is a horizontal seismic section through a 3D seismic volume.

To create a 3D Timeslice, there are 2 methods: first method, PDW Seismic > Open Timeslice. In

Time(ms) -> 508, (OK). Click (Yes) to SeisVision Warning. Note fault "X" on map from

last week’s interpretation and how it lines up with the edge of a major color transition.

Remember, black is seismic peak, red is seismic trough.

Up/down arrows will step through seismic volume. Time of slice is displayed at top of window.

The second method for opening a timeslice is to do it from a seismic data window. Click (Open

a seismic timeslice) button from the top toolbar, then LeftClick on the seismic data at the

time you desire. Note how a current timeslice is represented by faint dashed line on seismic

data.

Fault Interpretation:

Timeslices are one of the best methods for interpreting fault locations. We can interpret faults on

the timeslice, and the fault will be projected onto every seismic section which crosses it.

Enlarge the Timeslice window by dragging the bottom right-hand corner. Scroll to Timeslice

0.508. Note existing fault location and the colors near the "X". To interpret a fault on the

timeslice, you want to have the fault pass through the "X" and parallel the fault trend on the

timeslice.

In the Faults window, (Fault1). (Segment Pick Mode). On the Timeslice, use the same method as

you used for drawing the fault on the seismic sections: LeftClick, move, LeftClick, move,

LeftClick, move, DoubleClick to terminate fault. (Point Select Mode) in Faults window to

move points. On fault point RightClick >Delete Point to remove. We will interpret more of

these during the Interpretation Break.

Horizon Slices:

A Horizon Slice is a horizontal seismic section flattened on a horizon in the 3D seismic volume.

You can create a Horizon Slice from a Timeslice window. RightClick >Adjust Timeslice >Flatten

to horizon: +Wab Group, *Show 2d data, *Show Culture, *Display Wells, Time ->518,

(OK). Answer (Yes) to any SeisVision warning. What are we looking at?

Step down into the 3D volume using the down arrow studying the layers. Stop at about Wab

Group +509 msec.

You will begin to see the interpretation of the Fort Vermilion, first near the wells, indicating that

the time between Wab Group and Fort Vermilion is shortest at the wells, therefore a paleo or

depositional high.

Do not interpret faults on Horizon Slices for the same reason you don’t do it on Arbitrary seismic

lines. If you change your mind, it is almost impossible to recreate the Slice and edit the

interpretation.

 

3D Fault Interpretation:

Change from Horizon Slice to Timeslice. RightClick >Adjust Timeslice >Flatten to

horizon: +Datum. Time (ms) ->920.

Interpret fault cut on this timeslice.

Open an E-W seismic line [XL 95]. Step through the seismic lines examining the projected fault

cut. Return to E-W CrossLine 95, and interpret a fault from 0.4 to 1.3 seconds.

Repeat for CrossLines 85, 75, and 105. GeoGraphix will interpolate faults between your

interpretations, but you must eventually complete your manual interpretation in order to

create fault polygons.

Return to the timeslice to study correlation between your fault picks on the crosslines and the

color trends on the timeslice. If you see a major timeslice trend, you might want to interpret

a fault cut on the timeslice, then return to the crosslines to study the result.

Interpreting faults is an iterative process, make several interpretations on timeslices, then study

results on several seismic lines and make interpretations there, then return to the timeslices

to see where the seismic line interpretations show up.

Edit fault locations until you are satisfied. Always try to plan ahead so that you have an evenly

spaced grid of interpretations when you are finished.

3D Fault Polygon:

Create fault polygon for the WAB Group on each crossline [75, 85, 95, and 105]. Open each

line, make sure WAB is selected in the Horizons window, manually interpret WAB horizon

including offset down the fault.

In the Faults window, click (Fault Heave Pick Mode), LeftClick on the upper WAB contact then

on the lower WAB contact for the four lines.

On the basemap, PDW Horizons > Erase 3D Autopicks: Wab Group, (OK). Note location of

the picked lines and the fault polygon.

PDW Horizons > Interpolation 3D Autopick: Wab Group.

Note map color change doesn’t exactly match fault. We will need separate autopicking for

each fault block. At top of map, click (Polygonal subset selection mode), draw polygon for

the northwest block by clicking along fault and then beyond the east, north, west , and

south edges of the 3D. DoubleClick to close polygon.

PDW Horizons > Erase 3D Autopicks: Wab Group.

PDW Horizons > Interpolation 3D Autopick: Wab Group. Click (Polygonal subset selection

mode) to remove subset selection outline.

Do same thing for separate fault block on southeast edge of 3D.

Interpretation Break: Until end of Class

Experiment with Time Slice Fault Interpretations

Warning: Only interpret faults on N-S lines, E-W lines, 2D lines and Timeslices. Do not interpret faults on Arbitrary Lines or Horizon Slices. Once you close an Arbitrary Line of Horizon Slice containing an interpretation, you can only change that interpretation if you re-create exactly the same Line or Slice which is extremely difficult. Interpret using a grid such as E-W Lines 105, 95, 85, and 75. You can always infill for more detail, but try to keep an even spacing between interpretations.

Scroll through Timeslices to study seismic structure. Note additional fault cuts at 0.632, 0.678, 0.780, 0.920, and 1.156 seconds among others. You may choose to interpret fault segments on these timeslices and several others with obvious color contrasts. Remember, these color contrasts represent fault orientation, not the actual fault cut. Your interpretation should pass directly through the "X" fault cut from LBT-201 but only parallel the color contrast. Keep your fault cuts smooth.

You will need to use your geologic common sense to manually pick the Wab Group in the SE fault block. There is a significant degradation of the data here due to diffractions and noise. There are also many other faults in this block if you feel adventurous.

 

Homework Due 1/30 at Beginning of Class:

Interpret the faulting on S.E. corner of the Moosehead 3D every 10 crosslines (east-west lines) from line XL75 to line XL105.

Extend all well horizons previously interpreted on the 2D lines onto these 4 crosslines and across the fault with geologically reasonable offsets.

Manually interpret WAB horizon Fault Heaves across fault, and create a fault polygon for the WAB Group fault.

Hand in a print of the seismic line with your best fault interpretation and reasonable horizon offsets.

Make a 3D autopick map by separating the two fault blocks using "Polygonal subset selection mode". Print and hand in the resulting Wab time structure map.