RELATIONSHIPS AMONG IN-SITU STRESS, FRACTURES AND FAULTS, AND FLUID-FLOW - MONTEREY FORMATION, SANTA-MARIA BASIN, CALIFORNIA

We used borehole televiewer (BHTV) data from four wells within the ons hore and offshore Santa Maria basin, California, to investigate the re lationships among fracture distribution, orientation, and variation wi th depth and in-situ stress. Our analysis of stress-induced well-bore breakouts shows a uniform northeast maximum horizontal stress (S-H max ) orientation in each well, This direction is consistent with the S-H max direction determined from well-bore breakouts in other wells in th is region, the northwest trend of active fold axes, and kinematic inve rsion of nearby earthquake focal plane mechanisms, In contrast to the uniformity of the stress field, fracture orientation, dip, and frequen cy vary considerably from well to well and within each well, With dept h, fractures can be divided into distinct subsets on the basis of frac ture frequency and orientation, which correlate with changes of lithol ogy and physical properties. Although factors such as tectonic history , diagenesis, and structural variations obviously have influenced frac ture distribution, integration of the in-situ stress and fracture data sets indicates that many of the fractures, faults, and bedding planes are active, small-scale strike-slip and reverse faults in the current northeast-trending transpressive stress field, In fact, we observed l ocal breakout rotations in the wells, providing kinematic evidence for recent shear motion along fracture and bedding-parallel planes. Only in the onshore well do steeply dipping fractures strike parallel to S- H max Drill-stem rests from two of the offshore wells indicate that fo rmation permeability is greatly enhanced in sections of the wells wher e fractures are favorably oriented for shear failure in the modern str ess field, Thus, relatively small-scale active faults provide importan t conduits along which fluids migrate.