JULANDER, DALE R., and PETER F. COWELL, Chevron USA Prod. Co.; HAIQING WU, Chevron Petroleum Technology Co.; and JORG A. ANGEHRN, Chevron Petroleum Technology Co.

Abstract: An Investigation of Subsurface Fracture Distribution in the Monterey Formation, Lost Hills Oil Field, CA using Borehole Image Logs and Whole Core

We are presently investigating the subsurface distribution of natural fractures in the Monterey Formation, Lost Hills Field, California. The first step in the study involves interpretation of fractures from borehole image logs (EMI, FMI, and FMS) in 19 vertical wells and 3 horizontal wells using Z&S Recall software. The fractures are picked by an interpreter and contain information about fracture location, strike, dip, type, and pick quality. These picks are then used to calculate a fracture density curve for each of the wells.

The second step involves characterizing fractures in whole core. Six wells with image data have core available. Emphasis is being placed on analyzing fractures in these wells in order to establish a relationship between fracture density in image logs and core. Cores taken in wells lacking image logs are also being analyzed to augment data from the six image log/core pair wells and to improve aerial distribution of fracture data.

The third step involves variogram analysis for each fracture set (orientation), extrapolating the fracture density data into areas without core or images, and analyzing the densities with respect to structure, stratigraphic position, and diagenetic phase of the biogenic silica (Opal phase: A, CT, or Quartz). Finally, the relationships between fracture density and: (1) production data, (2) pressure data, and (3) hydraulic fracture propagation data will be investigated in order to determine the influence natural fractures have on production within the field.

AAPG Search and Discovery Article #90920©1999 AAPG Pacific Section Meeting, Monterey, California