Peripheral Water Flood as a Supplement to Gas Injection Pressure Maintenance

Wiliamar West field has been operated with a crestal gas injection program for several years. The analysis and its results which led to the decision to water flood the field are discussed. Economics based on this analysis appear to be favorable for the simultaneous application of both gas and water injection. Introduction Willamar West is a field in which a successful gas injection pressure maintenance program, started during the primary life of the reservoir, is to have a peripheral water flood imposed also, the two to operate simultaneously at opposite sides of the oil column. The Willamar West unit's working interest owners have only recently agreed to water flood the Willamar pay zone; consequently, only the theoretical considerations leading to that decision can be shown at this time. History of Unit Willamar West field is located in east Willacy County approximately 12 miles east of Raymondville, Tex. The Willamar structure is separated by faults into three main producing areas. These areas (Fig. 1) have been designated Willamar West field, Willamar North Graben field and Willamar field by the Railroad Commission of Texas. The Willamar field was discovered by Pan American Production Co.'s Willamar Community Well No. 1 in March, 1941. Subsequent drilling resulted in the discovery of Willamar West reservoir by the completion of Pan American Production Co.'s Kent No. 1. The field was developed very slowly during World War II. However, development was more rapid after 1944, and the field was completely developed for all practical purposes by 1947. The allowable was initially 103 B/D/well, and all of the three Willamar producing areas were considered as having one field MER. As a result of plummeting bottomhole pressures and a rising field GOR, this MER was reduced in 1949 to permit more efficient use of the expansive energy of gas caps and aquifer (particularly the caps). Because of a growing concern over pressure decline and the flaring of casinghead gas, the Willamar Engineering Committee was formed which, with the help of consultant's studies, investigated the advantages of gas injection.