Objective The aim of the project is the validation of high resolution borehole seismic techniques dedicated to the hydrocarbon reservoir description. These techniques are the crosswell seismic surveys between two boreholes (or between one borehole and a shallow core-drill). They offer a higher frequency bandwidth than the surface seismic techniques and therefore a better spatial resolution (of about 1 m). These techniques require a specific acquisition system (downhole source and receivers) and specific processing (transmission tomography, filtering of tube waves, migration...). The aim of the project is to validate these different aspects : acquisition, processing and interpretation in a test site with a very well known structure and to evaluate the different technical possibilities available today.High resolution crosswell tomography and reflection imaging were implemented on a test site. The tomography survey resulted in an image of the subsurface between two wells distant from 80 m with a 5 m resolution. The velocity field was updated following these results and utilized for migrating reflection data obtained between two 220 m distant wells. The migrated section shows little faults with throws of 5 and 2 metres respectively, fitting the log data. The vertical resolution is estimated to be 2 meter.The test site is a mine of uranium which belongs to COGEMA. This company has drilled many wells, sometimes 20 meters apart, in order to recognize the small faults which affect the sedimentary overburden. The depths of the wells is about 600 m. A 2D section has been selected which prevents a few small faults recognized by previous wells.The project has five phases:- Additional calibration of the site- P wave transmission tomography- Shear wave cross well reflections- P and Shear wave cross well reflections- SynthesisPhase 1 includes the drilling of two wells down to 600 m and of a core-drill down to 80 m, the acquisition and interpretation of logs and VSP in the three wells and of one offset VSP in order to eliminate the structure between the wells with a conventional seismic resolution. It includes also the analysis of an offset VSP recorded in the well with a Sparker source located in the core-drill.Phase 2 corresponds to the acquisition and processing of a P wave tomographic experiment which is operated with a Schlumberger cross-well equipment. The tomographic inversion will be done with different methods and in particular will take account the eventual anisotropy of the layers.Phase 3 corresponds to the acquisition and processing of a Shear wave reflection experiment which is operated with a weight drop source developed by IFP and with a hydrophone streamer. This source has a lower frequency bandwidth and a higher energy than the previous one and it is hoped to have strong shear reflections. A special acquisition design and processing is sought in order to enhance these reflections and obtain a mini section between the two wells.Phase 4 corresponds to the acquisition and processing of cross well data recorded with a non axisymetrical source. Phase 5 includes :- the integrated processing of all acquisitions in order to obtain one consistent image of the underground with all techniques,- a comparison of the values of velocities and anisotropyto core measurements, a comparison of mapped faults with known existing faults,- a comparison of the three different techniques and the evaluation of their benefit for reservoir description. Programme(s) ENG-THERMIE 1 - Programme (EEC) for the promotion of energy technology in Europe (THERMIE), 1990-1994 Topic(s) 5.4 - GEOPHYSICS AND PROSPECTING Call for proposal Data not available Funding Scheme DEM - Demonstration contracts Coordinator GERTH EU contribution No data Address 232 AV. NAPOLEON BONAPARTE 92500 Rueil Malmaison France See on map Total cost No data
