Objective
The project aims at a better exploitation of VSP data for drillhole planning. The interactive operation allows to directly include survey data, log data and VSP data for the decision. The VSP measuring data are directly introduced to develop a subsurface model.
The receiver chain has been successfully tested in boreholes of up to 3000 m. In these tests the capabilities for multi-offset VSP could not yet be fully exploited. The gimbled 3-component element, designed for deviated wells, was successfully tested for dip angles up to 55 deg. C against vertical. The application of the Disco -software system was abandoned in favour of an onsite data processing, based on a personal computer system. The software for modeling and migration has undergone final acceptance tests.
Dip analysis and polarization analysis were successfully applied to field data.
The project consists of two groups of activities : data acquisition and onsite data processing on one side and sophisticated large computer data processing and interpretation on the other.
Data acquisition consists of two groups of elements : the sonde the cable and the seismic sources, and which are lowered into the borehole the recording equipment and onsite data processing computer at the earth's surface. The sonde is designed to meet the environmental specifications, and to reduce the round trip time ( lowering the sonde down to the largest depths and measuring when pulled up back to the surface) to a minimum. For this purpose a 3 -component receiver chain, consisting of up to 5 elements with a predetermined spacing of 25 m was designed. The number of elements allows to reduce the round trip time by recording simultaneously at different depths. For deviated wells with dip angles of more than 30 deg. against vetical, a gimbled 3-component geophone receiver was selected for installations in each of the elements.
The recording time can be appreciably reduced when using multi -source technique. This technique can be preferably applied together with the VIBROSEIS method. Multi-source technique can be applied for multi-offset VSP and for simultaneous P- and S-wave recording. The onsite data processing was designed as part of the quality control of the recording process. It allows to continuously control the data quality and thus minimize recording time without loss of data quality.
The software for large computer data processing enables a careful preparation of the data acquisition by determining the optimum parameter and by combining all available data and the survey data in a straightforward manner for later interpretation. A first way of analyse consists of transferring the seismic results into a 3-dimensional picture of the subsurface in the environment of the well.
This process, called migration, works sufficiently well in all cases where the layer velocities are known and layer spacing is not too small compared to the wavelength of the seismic signal.
For complicated structures, however, these conditions are normally not met. In this case an interactive approach must be made, starting for the subsurface model constructed from the available data before the VSP measurement has been made and then refining this model.
In some cases a dip analysis, made from multi-offset VSP data, can help to analyse difficult structures. A polarization analysis must be made when shear waves areinvolved, especially when polarization effects have to be considered.
Programme(s)
Topic(s)
Call for proposal
Data not availableFunding Scheme
DEM - Demonstration contractsCoordinator
30635 Hannover
Germany