# Vertical seismic profiling book

Series | Geophysical References Series |
---|---|

Title | Problems in Exploration Seismology and their Solutions |

Author | Lloyd P. Geldart and Robert E. Sheriff |

Chapter | 13 |

Pages | 485 - 496 |

DOI | http://dx.doi.org/10.1190/1.9781560801733 |

ISBN | ISBN 9781560801153 |

Store | SEG Online Store |

## Contents

## Problem 13.4a

A source is offset 1000 m from a vertical well in which a geophone is suspended, and a horizontal reflector is present at a depth of 2000 m. Calculate the traveltimes for the reflection when the geophone is 800, 1200, and 1600 m deep if the velocity =3000 m/s

### Solution

Using a coordinate system with origin at the source and the -axis positive downward, the image point (see problem 4.1) in Figure 13.4a is at (0, 4000) and the geophone coordinates are (1000, ); hence,

For 800 m depth ; for 1200 m, ; for 1600 m, .

## Problem 13.4b

Repeat for reflectors dipping , where the reflector intersects the well at the same point as in part (a) (see Figure 13.4b).

### Solution

i) __Dip down toward the well__

ii) __Dip down toward source __

Coordinates of image are (, 4170),

Table 13.4a shows calculated traveltimes for , 1200, and 1600 m.

Depth(m) | 800 | 1200 | 1600 | ||

time (s) | 1.09 | 0.97 | 0.86 | ||

time (s) | 1.14 | 1.00 | 0.87 |

800 | 958 | 799 | 1.114 | |

1200 | 937 | 1198 | 0.985 | |

1600 | 916 | 1598 | 0.857 |

## Problem 13.4c

By how much do the values in part (a) change if the well deviates by towards the source (see Figure 13.4c)?

### Solution

Well inclination changes the geophone coordiantes from (1000, ) where the in-hole depth , 1200, 1600, to where

where subscript denotes values for the deviated well. The image point remains at (0, 4000), so the traveltime is

**(**)

Substituting the values of , we get the results in Table 13.4b. is the difference in traveltime from that calculated in part (a).

## Continue reading

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Guided (channel) waves and normal-mode propagation | Effect of velocity change on VSP traveltime |

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3D methods | Specialized applications |

## Also in this chapter

- S-wave conversion in marine surveys
- Equally inclined orthogonal geophones
- Guided (channel) waves and normal-mode propagation
- Vertical seismic profiling
- Effect of velocity change on VSP traveltime
- Mapping the vertical flank of a salt dome
- Poission’s ratio from P- and S-wave traveltimes