Dear Ahmed: if you are talking about gravity striping (just one "p") in the sense of footprint acquisition noise due the flight line direction, even aerial or satellite surveys, the answer is Yes!

We use the technique that I try to explain to you in detail, but not only to gravity data, but also to magnetic ones. My experience applying this techniques also are involved the 3D seismic when you load the grids in the grav-mag software such as Geosoft Oasis Montaj.

The procedure is relatively simple if you have the Oasis Montaj softwares modulus for grav-mag interpretation. DECORR GX

Extract Noise and Microlevel at OasisMontaj implement a procedure called microlevelling which removes any low-amplitude component of flight line noise still remaining in airborne survey data after tie line levelling.

Microlevelling calculates a correction channel and adds it to the profile database. This correction is subtracted from the original data to give a set of levelled profiles, from which a final levelled grid may then be generated.

Microlevelling has the advantage over standard methods of decorrugation that it better distinguishes flight line noise from geological signal, and thus can remove the noise without causing a loss in resolution of the data. To microlevel data, first run Extract Noise, then Microlevel.Extract Noise offers two options for the grid of the channel to be microlevelled. If a grid prepared from this channel already exists,it may be specified, and when prompted to overwrite, the user should answer no.

If you as user wishes to prepare a new grid of the channel to be microlevelled, the Minimum Curvature Gridding algorithm is applied. The advanced button provides access to the standard minimum curvature gridding parameters. Once the gridding is completed, Extract Noise applies a directional high-pass filter (see below) perpendicular to the flight line direction, in order to produce a decorrugation noise grid. (The default grid cell size is 1/5 of the line spacing. The user may specify a different cell size if desired. A smaller cell size will give a more accurate result, but a larger cell size will make the dialog run faster and use less disk space.)

The noise grid is then extracted as a new channel in the database (default name is "dcor_noise"). This channel contains the line level drift component of the data, but it also contains some residual high-frequency components of the geological signal. Microlevel applies amplitude limiting and low-pass filtering to the noise channel in order to remove this residual geological signal and leave only the component of line level drift, which is then subtracted from the original data to produce a levelled output channel (defult name is "miclev"). Extract Noise calculates default amplitude limit and filter length values for use in Microlevelling, but the skilled user may be able to set better values for these parameters based on an inspection of the noise grid. (The microlevelling process is broken up into two separate dialogs in order to enable you to do this.) Flight line noise should appear in the decorrugation noise grid as long stripes in the flight line direction, whereas geological anomalies should appear as small spots and cross-cutting lineaments, generally with a higher amplitude than the flight line noise, but with a shorter wavelength in the flight line direction. You can estimate the maximum amplitude of the flight line noise, and set the noise amplitude limit value accordingly.

Similarly you can estimate the minimum wavelength of the level drift along the flight lines, and set the low-pass Naudy filter width to half this wavelength. The defaults are to set the amplitude limit equal to the standard deviation of the noise grid, and to set the filter width equal to five times the flight line spacing. There are two types of amplitude limiting modes that can be applied, clip and zero. In clip mode any value outside the limit is set equal to the limit value. In zero mode any value outside the limit is set equal to zero. The clip mode makes more sense intuitively, but it has been found in practice that the zero mode may reject geologic signal better, depending on the particular data set. As a rule the zero mode works better on data sets in which the noise grid contains a lot of high-amplitude geological signals (e.g. shallow basement areas). For data sets in which the noise grid contains mainly flight line noise (e.g. sedimentary basins), the clip mode works better. Microlevelling applies a level correction to the traverse lines only. If it is desired to grid the tie lines together with the microlevelled traverse lines, then it may be necessary to also apply a level correction to the tie lines so that their values agree with the microlevelled traverse lines at the intersections.

This may be done as follows:

1- Copy the tie line values to the microlevelled channel.

2- Use the Intersection menu option to find cross-difference values for the microlevelled data.

3- Use Load Correction menu option to load these cross-difference values to the tie lines. 4- Apply the Full Level menu option to the tie lines. The output will be a set of tie lines that matches the microlevelled traverse lines at all intersections.

5- Copy the microlevelled traverse line values into the same channel as the corrected tie line values.

Please, check the file that I add to your illustration. I hope the answer wil be useful for you and colleagues. If you have any question, please, answer back.

My best wishes, Mario E. Sigismondi

Dr. Mario Emilio Sigismondi

Thank you for your detailed answer. Really, I'm taking about "Gravity Stripping" with double "p". Generally, the gravity stripping, as a complex processing and interpretation procedure, evaluates and computes gravity effects of shallow sedimentary strata aiming to derive a new Bouguer gravity map that includes only effects from deeper geological structures.

Dear Ahmed, in the sense that you consider Gravity Stripping, it means that you trying to get from the total gravity anomaly the residual and the regional. I understand that this operation is more simple:

1- from the total response, apply for example UWC (up-ward continuation)

2- the UWC anomaly represent the "regional" effect due to deeper sources

3- Substract the total anomaly - UWC anomaly = residual anomaly.

Of course friend, what do you thinking is deeper geological structures depend of your target-zone study. Maybe the basement?

Best wishes, Mario

Dr. Mario

Thank you again for your answer. Yes, it is nearly similar to UWC.

This is the general procedure of gravity stripping:

1- Calculating density values for the different formations present in a certain basin.The subsurface density data can be derived from different sources.

2- Calculating the gravitational effects for these formations.

3- Subtracting these effects from the Bouguer anomaly map.

2- The result will be a Bouguer anomaly map that includes only effects from deeper geological structures (regional anomalies).

you can use NFG (normalized full gradient ), it is sensitive oil

Dear Tran van Kha

Thank you for your answer. Can you write a short note about NFG for me, please?

can you see

https://doi.org/10.1190/1.1500375 and more other authors

Dear Tran

Thank you for sharing this paper. It is really a good work.

Dear Ahmed, in the sense that you consider Gravity Stripping, the answer is a definite YES for any knowledgeable explorationist. I have a Professional Engineering degree in Geophysics from the Colorado School of Mines, 1958. The technique was taught there. I used it while working on occasional gravity projects for Mobil Oil from 1958 to 1978; and for numerous clients as a Consultant with Emerald Exploration Consultants from 1979 to 2018. The concept is so simple and easy to perform that it seems ridiculous that we are even discussing it.

Thank you Prof. Ernest Berkman for your answer. I know that this method is too old and a good example for it is: Hammer, S. (1963). Deep gravity interpretation by stripping. Geophysics, 28(3), 369-378.‏ I read the full-text of this paper. He introduced the method with examples for oil exploration.

Based on your experience in this field, is there any recent modifications on this method? are there any recent approaches for hydrocarbon exploration using gravity data?

Dear colleagues, I appreciate that you share your experiences and knowledge.

Please, let me share another methodology, that I use in some study-cases: if you have a 3D seismic prestack simultaneous elastic inversion, in some cases, under better conditions, you can estimate three volumes: P-impedance, S-impedance, and density, each one with well-logs control and gathers with the angle range enough.

So, from your seismic interpretation, with the horizons, faults, key-wells and the density volume, is a peace of cake, easier, to substract the gravity influence of each formation. Of course: you need the grav data too.

The limitation, maybe, is that do you need a good prestack information and well control, and the areas of coverage of 3D perhaps are limited by local surveys.

The advantage is the quality and resolution, both vertical and horizontal of the input data for the estimation of the gravity effects. Also, the fact that in the calculations, you will have the lateral changes of density , in a more realistic model. If you have a high-quality S/N in your seismic, I strongly recommend to you to try it.

Best wishes,

Mario E. Sigismondi

I would say that current usage involves computer programs for joint interpretation of seismic and gravity data. One interprets the seismic from shallow to deep and the gravity profile is computed "on the fly" from input velocity/density tables. I believe this has been particularly helpful in structurally complex areas, and areas of "deep salt".

Dear Ernest Berkman: thank you very much for your wonderful answers.

I just wondering if you can send us your recomendation about computer programs both grav and seismic.

Petrel?

Cheers, Mario

Dr. Mario and Dr. Ernest

Thank you for sharing your excellent experience. It is really a great benefit to me.

I agree with Dr. Mario, if Dr. Ernest can send us his recommendation about computer programs both gravity and seismic.

Ahmed, Ernest, and colleagues: I think the idea is something like us: I share this brochure from Petrel's colleagues just a couple of minutes. Just thinking about it.

Best wishes,

Mario

It is Awesome! Dr. Mario. Thank you for sharing.

For viewing seismic data I use SeiSee for 2D and OpendTect for 3D. Seismic interpretation programs include Petrel, OpendTect, and DownUnder GeoSolutions (DUG) Insight. Petrel has a high license fee: OpendTect has a free version with plugin that can be licensed for short term use at very reasonable rates: and Insight has a moderate license fee. I am a consultant and my level of business does not justify paying monthly license fees, so I use OpendTect. For more information please visit http://www.dgbes.com and/or http://www.opendtect.org.

For gravity I used ARKeX’s Integrated Potential Field Modeling Software (XFIELD) in OpendTect on a few projects but unfortunately ARKeX went out of business in 2015. There still are several YouTube presentations available, https://www.youtube.com/watch?v=iBaS9p7HR1s or check the YouTube index.

I have numerous free standalone gravity and magnetic programs that I have acquired from various sources over the years. I would privately trade information on their sources with interested explorationists. Contact me at [email protected], I’ll send you my company brochure that has a list and descriptions.

Dr. Berkman

Thank you for sharing such a great experience. It is really an excellent discussion with great scientists. I'll contact you on email.

Hi Ahmed, you may want to contact Enrique Hung, a good friend and brilliant colleague who works with a group that as I understand have done a bit of it [email protected]

Prof. Arminio

Thank you for your kind help. I'll contact him.

In answer to your original question the most recent advances are the use of full tensor gradiometry as pioneered by Ark Geophysics (alas no longer extant) but continued by others including CGG. With regard to display of seismic and potential field data, Kingdom is of course excellent and easy to use for seismic and Ascii magnetic and gravity grids can easily be imported and displayed as a layer but it can't be used for stripping exercises.

Preliminary flight testing of our Gravex gravity and gravity gradiometer system suggests that we will be recording one valid gravity point per second at 240 kts flight speed, equivalent to 72 metres / second, so capable of seeing a 140 metre diameter mass. The system uses 3 sensors (shortly moving to 12 sensors) and records true vertical gravity and (over a 14 metre baseline) the gradient, with a noise floor of ~100ng rms for 3 sensors, better than half that with 12.

Dear Adrian and Christopher

Thank you for sharing your experience.

Ahmed, Hi there - saw a reference to Gravity Gradiometry above - CGG fly the Falcon Gradiometer which was specifically develped to be used in airborne exploration for minerals & Oil and gas

https://www.cgg.com/en/What-We-Do/Multi-Physics/Airborne/Falcon-Gravity-Gradiometry

Please follow this link to find out more about this technology - regards James

Thank you James for your answer.

Dear Ahmed,

I believe that a strong statement cannot be made regarding the limitations of gravimetry or magnetism without having evidence or data to endorse and verify them.

It happens many times that the comparison is not valid, because it is clear that seismic is a quintessential tool in reservoir characterization, especially in the case of loans in the domain of prestack elastic inversion, both, for fluid / lithology discrimination.

Such as Naeim said above, the integration of methods is the clue to solve the subsurface geometry.

But both, gravity and magnetic, are not only for Exploration stage (e.g., new frontier areas), but also it is very useful in Development or Reservoir Management: thinking about the case for instance of the 4-D Gravity Survey to characterize fluid contact in boreholes.

Even without this 4-D, gravity and magnetic aerial surveys are critical for example in areas with environmental restrictions, or logistical limitations in the stage of Reservoir Management. Thinking about the use of gravity and seismic for depth pre-salt imaging of complex hydrocarbon systems (Recóncavo Brazil / Gabon-Congo system; Santos-Campos Brazil / Kwanza – Benguela Angola).

Another example of the use of gravity anomalies in Reservoir Characterization is related with the construction of the low-frequency model to run seismic inversion. Remember that for potential method environment softwares, you can export a SEGY file with your gravity inversion, load in the seismic interpretation environment and go on with your low-frequency model previously to run the acoustic-elastic- seismic inversion workflow.

Let me show you two examples of my own experience that I compare the 3D seismic basement imaging with magnetic solutions and be careful of the sizes and the statistics that I show you, you take a better idea about the advantages.

I hope this answer will be useful for colleagues and you.

Mario E. Sigismondi

Thank you Dr. Naeim Mousavi and Dr. Mario Emilio Sigismondi for sharing your experience.