programming work

programming work

programming work

pYTHON pROJECT fOLD CALCULATION

pYTHON pROJECT fOLD CALCULATION

TU12 ADVANCED SEISMIC INTERPRETATION

TU12 ADVANCED SEISMIC INTERPRETATION

TAPIA Pedro

TAPIA Pedro

Start

General Information

Part 1: Land Acquisition Fold Calculation

Part 1: Marine Seismic Acquisition

Part 1: Acquisition Proporsal

Part 2: Seismic Imaging Excercise

Index

Part 2: Prestack and Postsack

Conclusions

General Information

Objectives

Introduction

This project focuses on implementing Python code for seismic data acquisition and processing, including fold calculation for both land and marine seismic acquisition. As a practical application, a seismic acquisition proposal will be developed for the Isle of Wight monocline, which was explored during the Wessex course earlier this year. Additionally, key seismic processing concepts will be applied, including NMO correction, DMO, prestack time migration, poststack migration, and basic geometry construction. This project integrates theoretical knowledge and practical implementation to design a seismic acquisition plan.

Develop and implement Python code to perform fold calculations for both land (onshore) and marine (offshore) seismic acquisition based on acquisition parameters.

Apply key seismic processing techniques, such as NMO correction, DMO, and prestack - poststack migration, to reinforce theoretical knowledge through practical implementation.

Design a seismic acquisition proposal for the Isle of Wight monocline, considering appropriate acquisition parameters and methodologies based on the calculations and processing techniques applied in the project.

Land example

Part 1: Land Acquisition Fold Calculation

To define the 2D acquisition line, considerations such as layer depth, a constant velocity (meaning no variation in the rock medium), different receivers, layer thickness, and instrument spacing were established.

It is important to be noted that in a 2D onshore acquisition with horizontal layers, the CDP (Common Depth Point) and CMP (Common Midpoint) coincide at the same point, as there are no significant distortions in the wave propagation

The following parameters are established:Geophones: 16 Geophone spacing: 5 meters Sources: 2 Depth: 6m

Part 1: Marine Seismic Acquisition

MARINE EXAMPLE

Considering the previously mentioned principles, a marine acquisition line should be established where there is 1 source and a streamer with 80 receivers. Each receiver should be spaced 12.5 meters apart. The source and the first receiver should be separated by 60 meters. The SP spacing is twice the RC spacing.

to calculate the Fold in this case its necesary to apply the next formula:

To clarify and ensure accuracy in the calculation of fold we consider the parameters to apply in the formula: Receiver Spacing (RC Spacing): 12.5 meters Number of Receivers: 80 SP Spacing (Source to Receiver spacing): 25 meters Fold calculation = (12.5 m X 80) / ( 2 X 25) Fold = 20

Part 1: aCQUISITION PROPOSAL

The Isle of Wight Monocline is a major geological fold in southern England, formed during the Late Cretaceous to early Cenozoic as a result of the Alpine orogeny. It represents a significant flexure in the sedimentary layers of the Hampshire Basin, with steeply dipping Chalk and older Mesozoic strata. This structure controls the island’s topography, influencing cliff formations and coastal erosion patterns. The monocline is key to understanding regional tectonics, basin development, and hydrocarbon potential in southern England.

In the area, there are zones of various deformations affecting Cenozoic strata. The presence of continuous Chalk sequences or layers generates moderate to high amplitude reflections, which allows for the establishment of continuity in areas close to anticlines. However, there are variations that may be due to lithological characteristics or fractured zones, which could pose challenges during data interpretation.

a customer wishing to image the structure of the Isle of Wight. we propose the diferent acquisitions to succed in terms of structural interpretation.

Proposal

Part 2: Seismic Imaging Excercise

SIMPLEST IMAGING ASSUMPTION NMO ASSUMPTION

bASIC GEOMETRY AND SEISMIC REFLECTION RAYPATH

Theoretical NMO point (P*) below M In purple (Apparent travelpath using NMO assumption (SP*R)

L=SP=P*R d=MP*

Part 2: Prestack and Postsack

Poststack migration

Prestack time ellipse

Points identified with true dippong geometry (P) and NMO assumption (P*) Draw possible reflecting points in surface in both sides of the midpoint

The Circle does not correctly image the reflector at any point.and its related with the not accurate application of the process for dipping reflectors. Its not giving a certain result compared with non dipping layers.

geometrical interpretation of the migration ellipse is that the half-width of the x-axis is L and the half-width of the z-axis is d.

Part 2: Prestack and Postsack

partial prestack time migration (dmo correction)

POSTSTACK MIGRATION AFTER DMO

The DMO operator is an ellipse passing through the NMO corrected value (P* point), the source S and the receiver P points. Keeping in mind the full prestack ellipse, this leads to the following equation for the DMO ellipse:

With h the distance between S and M (or between M and R), equivalent to the half of the offset. The half-width of the ellipse on the horizontal-axis has been changed from L to h but the vertical half-width has been kept to d.

We apply poststack migration centered at N and circles intersects with reflector providing a better result

Conclusion 1

Conclusion 2

Conclusion 3

thank you

References: Russell, Brian. (1998). A simple seismic imaging exercise. The Leading Edge. 17. 885-889. 10.1190/1.1438059. Evans, D. J., Kirby, G. A., & Hulbert, A. G. (n.d.). New insights into the structure and evolution of the Isle of Wight Monocline. British Geological Survey.

SEISMIC ACQUISITION FOLDS

By considering standard acquisition parameters, this approach provides a practical method for estimating fold calculations in both land and marine seismic acquisition. While not deeply focused on Python implementation, the methodology enhances the understanding of subsurface folds and supports practical applications in seismic survey planning. This contributes to more efficient and informed decision-making in geophysical exploration.

SEISMIC IMAGING CONCLUSION

In this simple graphical exercise, we’ve connected three key imaging concepts: NMO, DMO, and prestack time migration.This concepts worked well in this case because we assumed a constant velocity Earth and a single dipping reflector. As we see, if we vary paramethers the excersice becomes more complex, and these assumptions break down, requiring advanced prestack time and depth migration techniques

Same line with shift measure

Total Acquisition Line Distance: 1000 meters Distance between Streamer and Source: 60 meters Shift of 50 between each source

The seismic lines will allow for the possible definition of structures depending on the area and the purpose of the analysis. To stablish a more certain structural identification we propose this considerations

The proposals could be mixed to define onshore and ofshore subsurface. Both will obtain the structural characteristics of the area

Geofones: 80Spacing: 40 Line spacing 200Number of lines 25 Fold: 8 Total Distance: 3.2 km

Geofones: 125Spacing: 40 Line spacing: 80Number of lines: 10Fold: 31.25 Total distance: 5km

SEISMIC ACQUISITION PROPOSAL

The seismic acquisition proposal for the Isle of Wight Monocline incorporates both onshore and offshore acquisition options to enhance the understanding of the area's structural characteristics. By considering appropriate acquisition parameters and methodologies, the proposal aims to optimize data quality and resolution, providing valuable insights for geological interpretation and further exploration.

In this graph, the corresponding fold is highlighted, where the yellow areas represent zones with the highest incidence of reflected waves.

To obtain coverage and identify the fold, 15 sources are positioned along 80 meters, located at the midpoint of each geophone. The reflected wave trajectories define the CMP and CDP at the surface of the layer, indicating the fold.