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Abstract

An alkaline flooding system has been designed for application in the Main Zone reservoir of the Joughin Unit in the Torrance Field. The flood will encompass the major portion of the Unit (Section B) and will consist of twelve inverted nine-spot patterns. With a caustic injection rate of 38,000 BPD (6042 m3/d), this flood will be the largest alkaline flood ever attempted in the world to date. In 30% pore volume preflush injection, which consists of softened fresh preflush injection, which consists of softened fresh water, began on June 30, 1981 to reduce the divalent ion content and salinity of the reservoir. A 16% pore volume caustic slug consisting of 1.2% sodium orthosilicate is scheduled to begin in early-1985. Caustic injection will require approximately two years.

Extensive laboratory studies have been conducted to verify the viability of the alkaline slug process in this reservoir. Interfacial tension measurements demonstrated that extremely low interfacial tensions can be achieved with a dilute solution of sodium orthosilicate in softened fresh water and reservoir brine. Furthermore, core floods utilizing sodium orthosilicate solutions of 0.8% and 1.2% resulted in reductions in the residual oil saturation of up to 9.4%% Vp over waterflooding alone. This data along with the caustic consumption laboratory data were utilized in a chemical flooding simulator to scale results to the field and to make oil recovery predictions. The study indicates that the injection predictions. The study indicates that the injection of a 16% Vp slug of 1.2% sodium orthosilicate will result in a incremental oil recovery of 1875 MBO (298,125 m3) or 1.75% OOIP in Section B. Results of the laboratory studies, reservoir engineering work, and the computer simulation study to optimize the process are presented.

Introduction

The Torrance Field is located between the cities of Redondo Beach and Wilmington in Los Angeles County, California (Figure 1). The center of the field is about seventeen miles south and four miles west of the center of Los Angelas. The Joughin Unit covers 1,107 acres (4.48 × 10 m2) of the Torrance Field. The oil produced in the Joughin Unit varies from a minimum gravity cc 12 degrees API (0.9861 gm/cc) to a maximum of 27 degrees API (0.8927 gm/cc). The average gravity produced from Section B of the Main Zone is 21 degrees API (0.9279 gm/cc) and the average oil viscosity is 17 cp (.017 Pa-s) at reservoir temperature. Sections A, B, and C of the Joughin Unit are delineated in Figure 2.

Production started in the Joughin Unit in 1923 Production started in the Joughin Unit in 1923 when the Sentinel Oil Company completed the Joughin No. 1 for an initial production rate of 1200 BOPD. (191 m3/d). The peak oil production rate for all the leases that currently form the Joughin Unit was reached in 1924 with an average production rate of 8100 BOPD (1288 m3/d) (Figure production rate of 8100 BOPD (1288 m3/d) (Figure 3). By 1964, with a cumulative production of 28,400 MBO (4,516,000 m3) from Sections A, B, and C, production had declined to 740 BOPD (118 m3/d). The most prolific portion of the Unit was Section B. The ultimate primary recovery for Section B was estimated at 31,000 MO (4,929,000 m3) or 29% OOIP. The recovery mechanism was pressure depletion and limited water encroachment. pressure depletion and limited water encroachment. On September 1, 1964, the Joughin Unit was formed in order to conduct a waterflood operation in the Main Zone reservoir. Prior to the waterflood, the reservoir pressure had declined from an original 1620 pc (11,162 kPa) to approximately 235 psi (1,619 kPa).

Water injection started in December, 1971, with fresh water being injected in a peripheral pattern arrangement at approximately 43,000 BWPD (6837 m3/d) into 16 wells with an average surface injection pressure of 1600 psig (11,127 kPa). It a result of the flood, the Main Zone production rate increased from 461 BOPD (73 m3/d) in 1971 to 1980 BOPD (315 m3/d) in 1977 (Figure 3). Also, the gas-oil ratio declined from a Preflood average of 900 SCF/STB (160 m3/m3) to an estimated 150 SCF/STB (27 m3/m3).

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