Deep Structural Exploration in Zagros, SW Iran, Using Oriented 3-component VSP and Resistivity Borehole Wall Imager

A deep exploration well was drilled down to 5300 m on the top of a surface fold in the mountainous Zagros in order to encounter a deep anticline at the top of Permian reservoir formation expected in the area. Due to poor surface seismic, geological and practical considerations were used for locating the well. The structural interpretation was refined during the drilling operation, using: well logs, borehole resistivity imaging, geological data, a 2D surface seismic and an intermediate VSP recorded using a three component (3C) sensor tool implemented with a Relative Bearing / Roll angle sensor.

The VSP data was processed before drilling the deep interval 5300m to 6130m Total Depth (TD), with the intention to predict any reflection below the intermediate 5300m drilled depth.

Next, the whole borehole data was further analyzed after reaching TD. The main focus was on independent extraction of dip/azimuth information from oriented 3C VSP data and from borehole wall resistivity measurements.

The highly folded structure encountered by the well and the absence of high energy seismic reflectors with substantial lateral extension detected by the VSP are coherent with the blurred results on the 2D surface seismic section in the well vicinity.