Paper: Willard Unit Stimulation History A Case Study

This paper presents statistics for remedial stimulation work performed at the Willard Unit since 1986. It also discloses how stimulation candidates are chosen, what stimulation fluids are used at present, and how stimulation work is tracked. The Willard Unit is a San Andres carbon-dioxide flood located in the north-central portion of the Wasson field near Denver City, Texas. The Unit produced under primary from the mid 1930's until the start of water-flood operations in the mid 1960"s. Tertiary operations commenced in 1985 with the injection of carbon dioxide into approximately two thirds of the unit which is comprised of 340 producers and 260 injectors. The San Andres at the Willard Unit is a dolomite found at a depth of about 5100". Gross pay averages 150", porosity averages 8.5%, and permeability averages 1.5 md. The majority of wells are cased to 1 D and perforated with 15 to 20 holes. Producers have been sand fractured, and injectors have been either sand fractured or gelled-acid fractured.