Important Geological Factors Affecting The Sloss Field Micellar Pilot Project
Authors: Basan P.B. , McCaleb J.A. , Buxton T.S. 
Published: December 2007

Abstract
Amoco Production Company is conducting a nine acre five-spot tertiary micellar project in the Sloss Field, Kimball County, Nebraska. Sloss Field, which is in the Denver Basin, produces from the Lower Cretaceous Muddy J Sandstone. The inability to match performance data collected during preflush water injection with mathematical model results suggested that an improved reservoir description was needed. Part of the effort to obtain a better reservoir description was to make a detailed geological study of the southern portion of the Sloss Field where the pilot is located.
The geological update shows at least two genetically related, although different, deposits occurred within the field. Deposit Type I is a rather permeable sand that probably was deposited in a permeable sand that probably was deposited in a distributary channel. These deposits trend southeast-northwest and are relatively homogeneous. Permeability within these deposits is continuous. On the Permeability within these deposits is continuous. On the other hand, deposits of Type II, in which the pilot is located, represent overbank splays and apron sands. Sands in these deposits are discontinuous; consequently, there is a low probability that these sands have good areal and vertical communication with each other. The flow pattern in Type II sands is less uniform and less predictable than flow in Type I sands.

Introduction
The Sloss micellar project is being conducted, in a nine acre normal five-spot pattern, in the southern portion of the field. The four injectors are wells 110, 113, 114 and 115; Well 112 is the central producer (Fig. 1). All of these wells were drilled and cored after the pilot site was selected. All other wells in the southern portion of the field are shutin. Wells 109 and 75 are tested periodically.
Reservoir performance data (primarily tracer data) collected during preflush water injection, prior to micellar injection, yielded results that prior to micellar injection, yielded results that conflicted with predicted flow behavior. The reservoir description utilized in the mathematical model predictions included a preferential permeability in predictions included a preferential permeability in a northwest-southeast direction to account for the flow behavior observed during earlier waterflooding and COFCAW operations. The description also contained the vertical variations that could be deduced from cores and logs in the pilot area. The description, however, did not include any significant variations in rock properties between the four quadrants of the pilot pattern. All four quadrants of the pattern were treated in a basically similar manner. Such a reservoir description would suggest that flow behavior within the quadrants of the five spot also would be similar.
The conflicting tracer results were obtained from a program initiated in February, 1976. Different tracers were injected into each of the four injection wells. Samples were collected at the central producer, Well 112, and tracer concentrations in the produced fluid were obtained. Cumulative recoveries of these tracers, as a function of cumulative production, are shown in Figure 2. As may be seen from the figure, there was considerable difference in performance. The tracers injected at wells 110 and 115 broke through sooner and recoveries were higher than for tracers injected at wells 113 and 114. The performance was not consistent with the reservoir description being used for performance predictions. performance predictions. Changes in the reservoir description were needed. The steps that were taken to obtain a better description of areal and vertical variations in net pay, porosity, and permeability were (1) pulse testing, (2) additional tracer testing, and (3) a detailed geological study. The Sloss pulse test program is discussed in a separate pulse test program is discussed in a separate papers; the additional tracer test also is discussed papers; the additional tracer test also is discussed elsewhere.