An Application of Chemical Tracers In Monitoring Injection In Vertical Hydrocarbon Miscible Floods

Abstract

Chemical tracers have been utilized to effectively monitor injected fluid movement in two vertical hydrocarbon miscible floods in the Rainbow Field, Alberta. By placing small slugs of chemical tracers, consisting of sulphur hexafluoride (SF6) and chlorinated fluorocarbons (CFC) or halocarbons within the injectants, the spreading and development of chase gas and solvent banks were monitored, and in some cases, reservoir flow channels identified. In addition, geological units were confirmed and well workover planning improved, resulting in increased cost effectiveness in operating the miscible floods. The chemical tracer program commenced with the first field application conducted in the Rainbow Keg River "A" (R.K.R.A.) Pool secondary miscible flood on January 31, 1991, where chase gas injection into two wells was traced. Subsequently a program of tracing chase gas and solvent was initiated at one well location in November, 1991 in the Rainbow 1 Keg River "B" (R.K.R.B.) Pool tertiary miscible flood, and later at six additional chase gas and solvent co-injection wells. This paper presents the design of the tracer programs, the significance to the operation of the miscible oil recovery schemes and alternative tracers considered for the future. Introduction Husky Oil operates seven mature secondary and three tertiary miscible flood enhanced oil recovery projects in the Rainbow Field of northwest Alberta (Figure 1). Cost effective operation of these floods requires that solvent and chase gas sweep a significant extent of the reservoir without being produced at high rates. If miscible solvent bypasses large portions of the reservoir due to channeling, recovery efficiency will be lower than expected. Maintaining cost effective operation of hydrocarbon miscible flooding has required the development of extensive tracer programs designed to track and optimize solvent distribution in the reservoir as well as detect breakthrough at the very early stages. Previously, Husky had used radioactive tracers to monitor solvent bank placement in the R.K.R.B. Pool(1). Following the successful conclusion of this program and others in Rainbow Lake, other tracers were researched with the expectation that more of the analysis could be conducted on site and with reduced cost. More recently, Husky has used several Freon" haIocarbons and SF6 as chemical tracers to monitor chase gas and solvent injection in both the R.K.R.A and B Pools. FIGURE 1: Field location map. Illustrations available in full paper. Tracing injected chase gas and miscible solvent is used to identify the distribution of these fluids, both regionally and vertically, in the miscible floods. This enabled identification of the source of early solvent and chase gas breakthrough due to reservoir channeling, and allowed for early remedial action. Tracers less expensive than radioactive tracers, both from an initial cost and a per sample analysis cost basis were sought. They had to be detectable and accurately measurable at extremely low concentrations in the field lab and be readily handled by the field operations group. Finally, they could not be native to the oil reservoirs or have adverse rock or fluid adsorption or partitioning characteristics.

Sequestration of Carbon Dioxide in Coal with Enhanced Coalbed Methane RecoveryA Review

“…These results indicate that migration and adsorption of some tracers is not a problem during subsurface applications. Similarly, Carr et al have used SF 6 and several freons to monitor chase gas solvent injection during a miscible flood at two fields in Alberta, Canada. , They concluded that SF 6 and several freons “have low adsorption on reservoir rock and partition sufficiently to solvent and gas phases in the reservoir to make excellent tracers on an interwell reservoir scale.” They also found that partitioning of the tracers into the oil phase was more pronounced for higher boiling tracers. The physical properties of some of the more common tracers are shown in Table .…”

Extended Brigham Model for Residual oil Saturation Measurement by Partitioning Tracer Tests

“…Brigham's model has been widely adopted in the industry for designing and interpreting tracer tests. 18,19 Fig. 2 exemplifies a typical application of the model for the design of a tracer test in a single-layer reservoir.…”

“…Extrapolation of tracer production curve to completion will introduce a large uncertainty in moment calculation, 14 and therefore in S orw determination. The semiempirical Brigham's homogeneous five-spot model, [15][16][17] which is a common tool in the industry for tracer design 18,19 and data interpretation for its simplicity, lies between these two extremes. However, it should be noted that in spite of its frequent use, the applicability of the model to patterns with significant deviation from the aforementioned assumptions has not been rigorously proved.…”

Extended Brigham Model for Residual Oil Saturation Measurement by Partitioning Tracer Tests

“…Bingham's model has been widely adopted in the industry for designing and interpreting tracer tests 17,18 . Figure 2 exemplifies a typical application of the model for the design of a tracer test in a single-layer reservoir.…”

“…The semi-empirical Brigham's homogeneous 5-spot model [14][15][16] , which is a common tool in the industry for tracer design 17,18 and data interpretation for its simplicity, lies between these two extremes. The original Brigham model can only handle nonpartitioning tracer and its functionality is expanded in this paper to include partitioning tracer for S orw determination.…”