Techniques and Results of Foam Redrilling Operations-San Joaquin Valley, California
Authors: Essary R.L. , Rogers E.E. 
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.
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Abstract
During the past three years, Standard Oil Company of California has had a very active foam redrill program in several oil fields in the Southern San Joaquin Valley. Approximately 150 shallow zone wells have been reconditioned by replacing liners using foam redrilling techniques so that the wells could be utilized for steam stimulation and steam flood operations. Well bore damage during redrilling has been minimized since the use of foam as a circulating fluid provides very low fluid heads against the objective low pressure oil sands. This paper describe (1) procedures and techniques used by Standard, (2) costs of redrilling, and (3) some typical production results of the work.

Introduction
The use of low density, stable aqueous foam as a circulating fluid for redrilling shallow, low pressure wells has become routine practice for Standard Oil Company of California in the San Joaquin practice for Standard Oil Company of California in the San Joaquin Valley. During the past three years, Standard has replaced damaged, or otherwise unsuitable liners in more than 150 wells using foam redrilling techniques. Preformed stable foam provides a very low bottom hole circulating pressure which minimizes or eliminates formation damage and lost circulation. In addition, this low-density, no solids fluid is excellent for circulating out fill and cuttings at low annular velocities from wells which often could not be circulated with conventional fluids when low pressure, highly permeable sands are exposed. Several papers have been published permeable sands are exposed. Several papers have been published which illustrate the many uses and economic advantages of using stable foam. This paper is an update of Standard Oil Company's experience in foam redrill work in the San Joaquin Valley.

EQUIPMENT
Equipment and materials necessary for foam redrilling work are available from a number of contractors (licensed by Chevron Research Company) which are located in most oil producing areas of the United States and in many areas throughout the world. In California, equipment and materials for redrilling old wells and installing new liners have been standardized as follows.A 90' portable pulling unit with a mast rated at 140,000 – 200,000 pounds capacity equipped with a power swivel and drill pipe or N-80 tubing and a foam circulating head with pipe stripper for control of foam returns from the well. (Refer to Figure No. 1)