Subzone Redevelopment of the Long Beach Unit, Wilmington Oil Field: A Case Study
Authors: Robertson J.A. , Blesener J.A. , Hoo S. Soo 
Published: December 2007

SPE Members

Abstract
A Major program of infill subzone re-development to improve vertical waterflood conformance has been successful in materially improving oil recovery performance in the Long Beach Unit of the Wilmington Oil Field California. The well completions in individual subzones or layers will result in greatly improved future reservoir management opportunities through individual subzone or layer monitoring and control.

Introduction
The Wilmington Oil Field comprises the largest oil producing feature of the Redondo Beach - Wilmington trend, which is one of the numerous such fault oriented oil field trends in the Los Angeles Basin of Southern California (Figure 1). Although production began as early as the late 1930's in the western portion of the field, the majority of the eastern portion, which now comprises the Long Beach Unit (Figure 1), was left undeveloped because it underlayed both the recreational offshore harbor area and the downtown townlot area of the City of Long Beach. An earlier pronounced surface subsidence problem in the western portion of the field was major factor in the environmental concern.
In the early 1960's, legislative and other legal actions cleared the way for unitization and development of the eastern area under highly controlled conditions designed to protect the surface environment. These conditions included requirements for unitization of the entire area, major development being restricted to no more than four environmentally enhanced man-made offshore islands, and replacement of all reservoir fluid withdrawals and maintenance of original reservoir pressures through water injection. Other features of the actions referred to above resulted in rather unique administrative and operational responsibilities. In summary, the City of Long Beach functions as Unit Operator through its Department of Oil Properties and is the majority Unit Participant through its trusteeship for the State owned tidelands tract. The State of California, through the State lands Commission and its staff, must approve the Plan of Operations and Budget, the bottom-hole location of all new wells and redrills, and certain other specific well details. The State also receives the major portion of the net profit revenue from the Unit through its ownership of the tidelands tract, and as a result of the highly competitive net profits retention type bidding on the several contractors agreements. The THUMS Long Beach Company became the Field Contractor for the Unit Operator as a result of this bidding.

INITIAL DEVELOPMENT
Initial development of the Long Beach Unit began in 1965 and continued into mid-1970 with some 590 wells being completed, roughly one-fourth of those being injectors. The restriction to five drilling sites required highly deviated wells with kick-off depths as shallow as 100 to 200 feet and maximum hole angles of 70 to 75 degrees not uncommon. Figures 2 and 3 illustrate the resulting individual well plan view which developed the area and a section view of typical well courses. Because of the necessity for sand control in all but the deepest two reservoirs; gravel packed, slotted liners were the common completion method. With the environmental and space limitations on surface pumping equipment, and the ultimate expectation of large fluid lifting requirements as a result of waterflooding, electric submersible pumping was selected as the major lift method.
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