Performance of the Lower Pawelek Reservoir, Falls City Field, Karnes County, Texas

Abstract

Abstract This paper presents the initial results of a pressure maintenance by waterreturn project in the Lower Pawelek reservoir of the Falls City Field, KarnesCounty, Southwest Texas. Production is from the Lower Wilcox section at anaverage depth of 6,030'Ft on the downthrown side of a "down to thecoast" fault. Of particular interest is that the reservoir oil is highgravity and low viscosity but far undersaturated with gas at the originalreservoir pressure and temperature. The early pressure and production historyindicated only a partial or limited water drive, and this fact, coupled withthe characteristics of the reservoir fluid and artificial lifting problems, made advisable the water injection program to maintain reservoirpressure. The paper includes a description of the reservoir and reservoir fluids, thepressure and production history, a description of the water injectionfacilities, and the results of reservoir calculations involving Hurst'sunsteady state flow and the material balance equations for calculation of waterinflux and prediction of the pressure-production relationship at various ratesof withdrawal. The reservoir calculations and initial field results indicate that reservoirpressures in excess of 85 per cent of original pressure can be maintained bycontrol of water injection even at very high rates of production. Introduction The purpose of this paper is to report the initial results of a pressuremaintenance by water return program in the Lower Pawelek reservoir, Falls CityField, Karnes County, Texas, and to calculate an empirical relationship betweenpressure and production in this limited or partial water drive reservoir. Discussion Location The Falls City Field (Fig. 1) is located two miles north of the town of FallsCity in Karnes County, Texas, and is approximately 50 miles south-southeast ofSan Antonio on U. S. Highway 181. Discovery and Development The initial block of leases was taken after a surface geological surveyidentified a major east-west fault and closure on the south or downthrownsection. The discovery well, Southern Minerals Corporation's Joe F. Bartosch 1, was completed at 4,650'Ft in the Lower Bartosch sand in December, 1944.Drilling was continuous until December, 1946, and resulted in the discovery of12 oil reservoirs between 4,600 and 6,050'Ft in the Middle and Lower Wilcoxformations. T.P. 2937