# Pacific Section of AAPG

Abstract

Geology of the Northern San Joaquin Basin Gas Province, 1997
Pages 29-48

# Exploration and Development of the Blewett Trend, Northern San Joaquin Basin, California

## Abstract

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 Ranch 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′ of gross gas sand in the top of the Blewett Formation, at a depth of 6520′ 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 low relief anticlinal closure. 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′ 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.

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