Search found 625 matches

by GuyM
Sat Nov 21, 2020 2:57 am
Forum: Oil and Gas Exploration
Topic: Flat and floating datum corrections, why and when?
Replies: 3
Views: 88

Re: Flat and floating datum corrections, why and when?

So, the smoother the topography, the more closer the two corrections using flat and float datums, right? Um, not quite - it's not just how rough the topography is but the how much it varies from the highest to the lowest point that counts. That's what gives the size of the static shift. A linear ra...
by GuyM
Thu Nov 19, 2020 9:21 pm
Forum: Oil and Gas Exploration
Topic: Flat and floating datum corrections, why and when?
Replies: 3
Views: 88

Re: Flat and floating datum corrections, why and when?

They key thing here is we are trying to use vertical static shifts on traces to "fix" the elevation corrections, when the ray-paths we are dealing with are not vertical. So statics are a bit of an approximation. If the static shifts are small, this is not too bad. It certainly gets us closer to the ...
by GuyM
Mon Nov 02, 2020 1:30 pm
Forum: Oil and Gas Exploration
Topic: procedure for PSTM velocities?
Replies: 3
Views: 212

Re: procedure for PSTM velocities?

There's a balancing act between the accuracy/complexity of the actual migration approach used, the model, and the residual moveout. You can't (for example) remigrate the data to deal with raypath bending or anisotropic effects if those are not part of the migration algorithm and/or model in some way...
by GuyM
Fri Oct 30, 2020 11:27 pm
Forum: Oil and Gas Exploration
Topic: procedure for PSTM velocities?
Replies: 3
Views: 212

Re: procedure for PSTM velocities?

Yup - preSTM, reverse NMO and repick is one approach; some packages will let you read in the "flattened" preSTM gathers and PreSTM velocity and work from that (they have usually have an RMO processing module that will read the both velocity fields and apply a residual) The other approach is to rever...
by GuyM
Wed Oct 28, 2020 1:33 pm
Forum: Oil and Gas Exploration
Topic: Bouncing back from a layoff in oil and gas is harder than it used to be
Replies: 1
Views: 590

Re: Bouncing back from a layoff in oil and gas is harder than it used to be

Prediction is hard, especially about the future. Just reviewing what I posted here back in 2013; a few quotes: That said, as with all careers, I would suggest that ensuring your round out your "hard skills" development with good, transferable "soft skills" is always the best career plan. A narrow an...
by GuyM
Fri Oct 16, 2020 2:12 pm
Forum: General Geophysics and Geoscience
Topic: Work life - what do a geophysicist do in the oil and gas industry?
Replies: 1
Views: 634

Re: Work life - what do a geophysicist do in the oil and gas industry?

That's kind of open-ended. You'll find geophysicists on field crews, in processing centres, and in oil companies. Some will be checking data quality. Some will be processing it to make a structural image. Others will be processing it to extract rock and fluid properties. Others will be interpreting ...
by GuyM
Mon Sep 07, 2020 11:37 pm
Forum: General Geophysics and Geoscience
Topic: Diffraction sensitive to velocity
Replies: 4
Views: 1014

Re: Diffraction sensitive to velocity

What is the difference between time and depth when it comes to diffraction and sensitivity to velocity ? Well you'd never normally depth convert a stacked (normal ray) section, so it doesn't really come up. Or rather, I'd be asking what your goal is when you do it(!) Mostly depth conversion is for ...
by GuyM
Sun Sep 06, 2020 7:17 pm
Forum: General Geophysics and Geoscience
Topic: Diffraction sensitive to velocity
Replies: 4
Views: 1014

Re: Diffraction sensitive to velosity

Is this question tied to depth conversion at all? One of the approaches you can use is: - interpret horizons in two-way-time on a pre-stack time migration - develop a layer based interval velocity model using the V(rms) velocities from Pre-stack time migration and well control - depth convert layer ...
by GuyM
Sun Sep 06, 2020 6:06 am
Forum: General Geophysics and Geoscience
Topic: The Kirchhoff migration
Replies: 3
Views: 599

Re: The Kirchhoff migration

Well - I'm mostly pointing you to the SEG Wiki, which is mostly Oz Yimaz's book. If you can get hold of a copy it will be a big help.
by GuyM
Sun Sep 06, 2020 4:30 am
Forum: General Geophysics and Geoscience
Topic: The Kirchhoff migration
Replies: 3
Views: 599

Re: The Kirchhoff migration

The SEG Wiki Pages may help : https://wiki.seg.org/wiki/Kirchhoff_summation "The diffraction summation that incorporates the obliquity, spherical spreading and wavelet shaping factors is called the Kirchhoff summation, and the migration method based on this summation is called the Kirchhoff migratio...
by GuyM
Sun Sep 06, 2020 2:24 am
Forum: General Geophysics and Geoscience
Topic: lateral velocity variations
Replies: 1
Views: 392

Re: lateral velocity variations

It's how fast the velocity varies horizontally. If you had very boring geology - just horizontal, flat layers, deposited and compacted normally - then you would see a vertical variation in seismic velocity, but no lateral variations. On the other hand, when you have those same flatish layers overlyi...
by GuyM
Fri Sep 04, 2020 7:52 pm
Forum: General Geophysics and Geoscience
Topic: Particle Swarm Optimization (PSO) CODE
Replies: 3
Views: 458

Re: Particle Swarm Optimization (PSO) CODE

Ah - you misunderstand, I just found this library : https://pyswarms.readthedocs.io/en/latest/ and this thread on research gate: https://www.researchgate.net/post/Is_it_easy_to_implement_Genetic_algorithm_and_Particle_swarm_optimization_on_Python My observation was that we tended to find better main...
by GuyM
Fri Sep 04, 2020 6:04 pm
Forum: General Geophysics and Geoscience
Topic: Particle Swarm Optimization (PSO) CODE
Replies: 3
Views: 458

Re: Particle Swarm Optimization (PSO) CODE

Well, no, but you might want to consider making the leap to Python at some stage. A quick google shows a bit more activity on PSO in terms of open libraries in that community. More or less anything we looked for we found very quickly in Python. Even stuff like single-click outputs of Powerpoint file...
by GuyM
Fri Sep 04, 2020 5:31 pm
Forum: General Geophysics and Geoscience
Topic: huygens' principle
Replies: 3
Views: 517

Re: huygens' principle

I used to have a nice powerpoint slide illustrating this; it was animated and added in more and more circles centered on the same straight line until a new "wavefront" formed; that's back when I used to run seismic processing training courses :-)
by GuyM
Fri Sep 04, 2020 5:29 pm
Forum: Oil and Gas Exploration
Topic: North Carolina sues over federal decision on seismic testing
Replies: 4
Views: 881

Re: North Carolina sues over federal decision on seismic testing

Hmm - I'm not sure how critical this one area is to the industry survival; WesternGeco have no boats, and I'm prepared to wager the other companies are all in the "data library" game as well. They like new real estate (ie under explored areas) for the speculative potential, rather than the actual po...
by GuyM
Fri Sep 04, 2020 4:55 pm
Forum: General Geophysics and Geoscience
Topic: diffraction-in seismic
Replies: 4
Views: 627

Re: diffraction-in seismic

Not come across that term but it seems to be used when there's complex back-scatter patterns. Back-scatter is another way of saying diffractions. Where you have a rough surface - for example a seafloor that has a small amount of soft sediment over a steeply dippling, uplifted, harder and layered roc...
by GuyM
Fri Sep 04, 2020 11:17 am
Forum: General Geophysics and Geoscience
Topic: diffraction-in seismic
Replies: 4
Views: 627

Re: diffraction-in seismic

What will happen for diffraction? You get a curve shape on an CDP gather; this can be "flattened" using NMO, but the velocity needed to flatten the diffraction will be higher than the true stacking velocity that flattens the reflections. Not that diffractions and reflections can appear at the same ...
by GuyM
Thu Sep 03, 2020 5:20 pm
Forum: Oil and Gas Exploration
Topic: North Carolina sues over federal decision on seismic testing
Replies: 4
Views: 881

Re: North Carolina sues over federal decision on seismic testing

Seismic testing uses powerful airguns that blast sounds at the ocean floor repeatedly for months at a time. Marine experts say these sounds can harm marine and coastal resources – and could have significant impacts on the state’s fishing and tourism industries. After a lot of R+D it looks like effe...
by GuyM
Thu Sep 03, 2020 3:01 am
Forum: General Geophysics and Geoscience
Topic: coherent event
Replies: 1
Views: 325

Re: coherent event

Coherence is how similar two traces are to each other.
There's a few ways of calculating this (or terms it can mean) : https://wiki.seg.org/wiki/Coherence
by GuyM
Thu Sep 03, 2020 2:57 am
Forum: General Geophysics and Geoscience
Topic: grid in geophysics
Replies: 3
Views: 530

Re: grid in geophysics

A surface in a sub-surface modelling package can be multi-valued; like the top of a salt dome, that can bend over. Or a thrut fault. By multi-valued, I mean that at give X,Y coordinates the surface is present in the model more than once. With a grid, you have an z, y and z value. There's only one z ...
by GuyM
Thu Sep 03, 2020 2:53 am
Forum: General Geophysics and Geoscience
Topic: meaning of redundancy
Replies: 4
Views: 609

Re: meaning of redundancy

Well - I have run a written and run a few seismic processing courses in my time ;-)
by GuyM
Tue Sep 01, 2020 3:15 pm
Forum: General Geophysics and Geoscience
Topic: meaning of redundancy
Replies: 4
Views: 609

Re: meaning of redundancy

Oh - thank you for asking these questions! I've stepped back from geophysics after >25 years in seismic and while I'm very happy with my new career direction, it is also nice that all of the stuff that I have learned over the last quarter of a century is not sitting in my head not helping anyone :-)...
by GuyM
Tue Sep 01, 2020 3:11 pm
Forum: General Geophysics and Geoscience
Topic: meaning of redundancy
Replies: 4
Views: 609

Re: meaning of redundancy

When you have lot of seismic data containing the same information. For example, modern marine seismic is often collected at a 2ms sample interval, and with a receiver group interval of 12.5m This would allow for frequencies up to 250Hz (Nyquist) and a CMP bin spacing of 6.25m Given the filtering eff...
by GuyM
Sat Aug 29, 2020 8:06 pm
Forum: General Geophysics and Geoscience
Topic: nmo eq
Replies: 7
Views: 867

Re: nmo eq

How do you relate the NMO equation to Pythagorean theorem? In the picture, you have a right angled triangle formed by : - half the source receiver distance; ie from the source to the mid point - the vertical depth of the reflector below that midpoint - the ray-path from the source to the mind point...