Acid Stimulation of a Fractured Shale Zone

Abstract

Honolulu Oil Corp., operator for the Antelope Shale Zone Unit, Buena Vista Hills, initiated a program for oil well acid treatment for the purpose of removing precipitated carbonate scales from production equipment and for well stimulation, Oct. 23, 1956. This program was active through Feb., 1958. In this period 35 wells were acid treated yielding a net increase in oil of 1,390 B/D and gas increase of 3,265 Mcf/D. The total cost of acidizing the 35 wells was $80,000.

Introduction

Acid stimulation of California oil wells has been used to a limited extent, primarily for dissolving precipitated carbonate scales and other plugging agents within or adjacent to the wellbore.

In the Antelope Shale Zone in Buena Vista Hills, some producing wells showed evidence of rapid carbonate scale precipitation on the tubing and rods in early phases of production. Observation of this scale led to the belief that acid treatment of a well might be beneficial both to production equipment and to production rate, if liner and adjacent wellbore were suffering plugging. Initial application of acid to an oil well was made almost solely to clean up production equipment.

History of Development

The Buena Vista Hills field is located in Kern County near Taft. The field is on a large anticlinal structure including two domes and containing several productive sands from about 2,300 to 3,900 ft, and also containing the Antelope Shale Zone which is predominantly a fractured shale. The shallower sand zones were developed over a period from 1909 to the present time. The fractured shale zone has been developed in the last six years and development is still progressing to a minor degree. This report is confined to the East Dome. The upper sands have been acid treated on occasion over a period of years in a spotty manner giving spotty results. A few jobs were quite beneficial, but the majority were of moderate or no success. The predominant basis for treatment of these upper sands was also the observation of precipitated scale on production equipment.