Abstract

A brief review of 33 Pennsylvanian Age, Cisco Series water floods operated by Cities Service Oil Co. in three North Texas counties is presented. Total injection of slightly more than 99 million bbl of water during the 16 years prior to 1965 has resulted in the recovery of 8.06 million bbl of secondary oil from these projects.

Experience acquired by Cities Service during this period led to certain conclusions which are presented for use by future operators of Cisco Series water floods. In addition to conclusions concerned with the evaluation of these projects, it is shown that the profitability of a Cisco Series water flood can be generally correlated with depth, with the more profitable zones occurring below 1,800 ft.

Introduction

As of Jan., 1965, Cities Service Oil Co. had recovered 8,060,878 bbl of Company-interest waterflood oil from Cisco Series horizons in the County Regular fields of Archer, Wichita and Wilbarger Counties. This amount was recovered through the injection of 99,016,267 bbl of water and represents some 91.8 per cent of the total amount recovered by Cities Service in the North Texas District by water flooding.

In order to evaluate the performance of these Cisco Series water floods, data from 33 projects or zones on twelve leases operated by Cities Service were assembled. The leases in question are located in an area extending from nine miles south of Vernon, Tex., to Electra, Tex., to 14 miles southwest of Wichita, Falls, Tex. [see Fig. 1]. The ages of the projects range from 2.5 to 16 years and the nominal depths of the zones from 370 to 2,500 ft. These Cisco series water floods reached their peak production of 3,036 BOPD in 1958 and have been on a decline since. The pay-out of the projects covers a variety of values as shown in Table 2.

GEOLOGY

The location of the Pennsylvanian-Permian contact is a subject of controversy in North and North-Central Texas. Deposition of Permian sediments occurred in a sea occupying approximately the same position as that occupied in Upper Pennsylvanian time. Since no discernable break in sedimentation separates the Pennsylvanian and Permian beds in this area, the exact limit of the two systems has not been determined. It is generally accepted that the sands above 700 ft are Wichita Series, Permian Age and those below are Cisco Series, Pennsylvanian Age. In North and North-Central Texas, about 40 per cent of the surface beds are of Permian Age. For the purpose of this discussion, and to maintain simplicity, reference to the Cisco Series of Pennsylvanian Age will include those formations from approximately 200 ft in depth to the top of the Landreth lime.

The Red River uplift is directly responsible for the accumulation of oil and gas in the County Regular fields of North Texas, the greater percentage of which consist of Cisco Series horizons. The uplift itself is not one continuous high, but is divided into three individual highs, the largest and most important of which is the Electra Arch. This arch extends across Wilbarger, Wichita and northern. Clay Counties, with a nose pushing into the northern half of Archer County. The Electra Arch is responsible for accumulations of oil and gas in all these counties, including the formations to be discussed here.

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