HORIZONTAL PRINCIPAL STRESS AXES IN SICHUAN BASIN DEDUCED FROM OIL-WELL BREAKOUTS

Schlumberger company conducted well logging service in China's Sichuan oil field. Four-arm caliper logging records at 12 wells are available to us for the purpose of crustal stress study. The logging depths are generally from 2,000 down to 4,500 meters beneath the ground surface,with different logging intervals. The longest interval is more than 1,300 meters.The logging records are digitized,and plotted to get plane projections of the measured well-diameter for the whole logged intervals. Most projections show prominent elongation of the well bores in the NNW-SSE or nearly N-S direction. Following the common explanation that in the direction of elongation lies the minimum horizontal principal stress axis,we get the feature of the stress axis orientations in the Sichuan basin which gererally agrees with the pattern of regional tectonic stress in Sichuan and the surrounding regions obtained from composite focal mechanism analysis.