Use of External Casing Packers for Zonal Segregation in the Wilmington Oil Field
Authors: Sampson N.N. , Staub H.L. , Wright A.C. 
Published: December 2007

External casing packers have been used with great success in more than 500 development and injection wells in the Wilmington oil field to segregate zones, to exclude wet sands, and to include more than one producing zone in a common wellbore. The use of these packers has saved the Long Beach Unit considerable money by reducing the number of wells required to develop the field.

Introduction
The Wilmington oil field, located in the southwestern portion of Los Angeles County, Calif., is composed basically of seven productive zones consisting of more than 60 different horizons or sands that have varying characteristics. The major zones are the Tar, Ranger, Upper Terminal, Lower Terminal, Union Pacific, Ford and 237 (Fig. 1). Four sand and fluid Pacific, Ford and 237 (Fig. 1). Four sand and fluid characteristics that have a notable influence on production and waterflooding are permeability, oil production and waterflooding are permeability, oil gravity, zonal pressure and gas saturation. The absolute permeabilities vary between 1,500 and 500 md within the Ranger Zone alone, and API oil gravities vary as much as 12 degrees from flank to crest. When the older portion of the Wilmington field was being developed, zonal pressures were essentially at hydrostatic; however, within the Long Beach Unit area, initial pressures encountered in the Ranger zone varied from pressures encountered in the Ranger zone varied from 50 to 95 percent of hydrostatic and as much as 25 percent between subsands of the completion interval. percent between subsands of the completion interval. As a result of the different degrees of pressure depletion, significantly different production GOR's were observed. Water injection was started originally in the Wilmington oil field in May, 1953, with pilot floods in several areas and zones. These pilot floods were extended to major waterflood operations in 1958 upon unitization of the field and as a major subsidence control measure. From the beginning, wide variations in the characteristics of the sands caused serious overflooding and fingering. The original wells were not specifically drilled and completed for future waterflooding, so control of the flood front depended on such major remedial work as redrilling. As a result of the economic success of the waterflood operations of the older portion of Wilmington, as well as their success in halting subsidence, the unit agreement for the Long Beach Unit required that development drilling be followed immediately by injection to maintain reservoir pressures and to avoid subsidence. This, coupled with the provision that the Long Beach Unit be developed from a limited number of drillsites contained within given limited areas, posed the problem of how to fully develop the field, posed the problem of how to fully develop the field, keeping the number of drilled wells to a minimum, maintaining complete control over water injection, and isolating gassy stringers. Several methods of segregation were considered: cementing, using plastic, setting through and milling out, etc. However, each had its disadvantages. In a review of various methods in use, the inflatable external casing packer was recognized as one of the more effective tools, with the added advantage that no foreign material was required that might damage the formation. In Sept., 1965, the first Long Beach Unit well to be equipped with inflatable external casing packers was successfully completed. The packers were used in this well to isolate intermediate packers were used in this well to isolate intermediate water.
JPT
P. 1101