Monterey Problems: Enhanced Mud-Logging Techniques Integrated with Rock Mechanics and Geochemistry for a Solution

John MacPherson, Michael Taylor, Ed Guenard, Alan Daly

Miocene Monterey Formation of southern California is an extremely complex lithological sequence. The delineation of producing intervals using wireline analysis is difficult at best as most production appears to occur from fractured intervals. Interpretation is also hampered by the extreme variability in lithological character and in hydrocarbon character (tar to gas).

Recent studies using conventional and enhanced mud-logging techniques, including geochemistry, have demonstrated the applicability of good geological analysis in the delineation of producing intervals in the Monterey. The techniques utilized are based on the integration of surface-acquired geological and engineering data, MWD data, and geochemical data.

Delineation of fractured intervals is accomplished through the integration of drilling response modeling and pulsed Nuclear Magnetic Resonance (pNMR) measurements of porosity on drilled cuttings. Delineation of potential producing intervals is accomplished by detailed hydrocarbon analysis (gas ratios, entrained gas, normalized gas, and geochemistry). In nonfractured intervals, permeability and irreducible water saturations can be estimated using integrated MWD and drilled cuttings (pNMR and sample examination) analyses.

The use of this composite geological technique while drilling is illustrated by several examples. The techniques described can be applied to wildcat wells in the Monterey without the need to develop empirical relationships for specific fields.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.