Case History of a Successful Flank Well Curtailment Program in a Peripheral Water Flood

Abstract

This paper summarizes the waterflood performance of the KZWA subpool of the Upper Terminal zone, Fault Block VB, in the Wilmington oil field, Los Angeles County, Calif., following a major reduction in water withdrawals by shutting in flank wells. The program was initiated specifically to improve the net injection rate of the pool. Production and development history of the pool are discussed together with a review of secondary recovery operations. The pool was under gas injection for 7 1/2 years, followed by waterflood operations starting in May, 1958.Field two were run in an isolated area of the pool to establish performance that might he expected under the curtailment program. The paper includes projected economics to he expected under continuation of the program prior to the shut-in and the economics under the existing shut-in program. Criteria for selecting a water flood in which flank well curtailment is applicable are also discussed. The economics to date show that a saving in operating costs due to shutting in wells, and increased stimulation of oil from the net injectivity improvement have already increased operating profits. Introduction Determination of the optimum time to shut in flank producers in a peripheral water flood has long been a source of controversy among petroleum engineers. It is extremely difficult, even in the least complicated floods, to apply a strict set of rules to determine the economic limit of high-volume, high-watercut wells. The purpose of this study is to review a flank well shut-in program in the Upper Terminal VB zone in the Wilmington oil field, Calif. Only the KZWA subpool will be reviewed with respect to geology, reservoir data, development history, water injection history, and pool-wide flank- well curtailment program. The upper two sub-zones (HX and JY) were involved in the flank-well curtailment program, but to a lesser degree. However, examples of interference in individual wells producing from those subzones are reviewed and production from them, together with KZWA pool production, is analyzed. The predicted effect of a curtailment program on pool economics is reported along with the status of the analysis 1 1/2 years later. Location, Geology and Reservoir Data The Wilmington oil field is in the Wilmington and Harbor Districts of the city of Los Angeles and the Harbor District of the city of Long Beach, Los Angeles County, Calif. The location of the Wilmington oil field with respect to other fields in the Los Angeles Basin is shown in Fig 1.The oil-producing structure of the field is an anticlinal fold with its main axis trending in a northwesterly- southeasterly direction. The producing zones are highly faulted. There are six main fault blocks numbered I thru VI, and the large subfault blocks are designated by the suffix A, B and D. The fault block with which this study is concerned is VB. Fault Block V]3 is located in the eastern half of the presently developed area of the Wilmington oil field. JPT