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Abstract: Exploration and Development of the Upper Cretaceous Blewett Trend, Northern San Joaquin Valley, California


One of the more active exploration areas of California for the past seven years has been the Blewett trend of the Northern San Joaquin Valley. This deep water sand trend extends from Gill Ranch gas field to Vernalis gas field, over sixty miles in length. Recent exploration activity has been focused in the southern third of the trend where significant reserves of gas have been developed in the upper Cretaceous Blewett Formation, west of Gill Ranch, Moffat and Chowchilla gas fields.

Unocal initiated the interest with the O'Banion #1, located in section 25, T11S/R13E, MDB&M. The well was drilled in July 1989, and encountered approximately 80 feet of gross gas sand in the top of the Blewett Formation, at a depth of 6520 feet KB. The Merrill Avenue discovery confirmed the geophysical interpretation of a seismic anomaly identified on several seismic lines. The gas appears to be trapped on a faulted nose dipping southwest. Additional drilling to develop the field, however, met with limited success. First production began on October 1991, after the construction of a 30 mile pipeline.

McFarland Energy and partners obtained a significant acreage position north of the discovery. McFarland drilled the Wolfson #1-10, in March of 1992, about 3 miles northwest of Unocal's O'Banion #1. The well encountered 54 feet gross Blewett gas sand on water. Additional drilling, based on identification of geophysical anomalies in the Blewett met with a high degree of success in the Merrill Avenue, Mint Road, and Ash Slough gas fields. Production data from all recent wells indicates most wells to have recoveries from 0.5-1.0 BCFG. A few wells have produced greater than 1.0 BCFG, and only the O'Banion #1 has produced in excess of 10.0 BCFG.

Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California