Abstract
The performance of the micellar/polymer flood conducted in the Sloss reservoir did not follow predictions by a streamtube model. The model assumed that micellar flood displaces oil and water in a piston-type miscible manner with a final oil saturation of 5 % PV, and sulfonate retention based on short-term laboratory adsorption tests. This paper, in conjunction with a complementary paper,1 describes process mechanisms needed to model the flood performance.
The results of laboratory studies show higher sulfonate retention caused by ion-exchange effects, which result in partitioning of sulfonate into the oil phase and higher adsorption caused by long contact times. Long-term aging of the Sloss micellar fluid at the high reservoir temperature (93.3°C [200°F]) does not reduce oil recovery. The results of laboratory studies also show that the final oil saturation after micellar flooding is capillary-number dependent. A higher final oil saturation can be the result of reduced injectivity /productivity, increased interfacial tension (1FT), and/or decreased viscosity.
This paper demonstrates that ion exchange, hardness, and sulfonate partitioning can significantly affect micellar-flood performance. The paper presents an experimental plan that provides information for optimizing the design of micellar/polymer floods. This plan, when applied to a specific flood, allows an investigator to examine effects of adsorption, ion exchange, hardness, and partitioning on flood performance. Specifically, phase studies and sulfonate requirements must encompass effects of in-situ-generated calcium ions as a result of sodium/calcium ion exchange. Sulfonate itself can increase the calcium content of the fluids because of a calcium/micelle association. High calcium concentrations can increase sulfonate requirements. Sulfonate adsorption requirements for micellar flood design are sensitive to the experimental procedures employed. The paper outlines improved procedures encompassing ion exchange and time effects and demonstrates that a favorable ion-exchange process can be used to reduce adsorption requirements.
Introduction
Interpretation of micellar-flooding pilots is essential to the development of a predictive model for commercial demonstration and fieldwide micellar floods. To interpret field micellar-flood performance, process variables (e.g., compositional effects) must be separated from field variables (e.g., reservoir description and operational difficulties), and the process mechanisms must be identified.
This paper describes experimental procedures for use by industry to identify effects of composition changes during micellar flooding. The paper describes application of these procedures to determine the effects of composition changes on the displacement mechanisms of the micellar/polymer fluids injected in the Sloss field, Kimball County, NE.2 The results enhanced our mechanistic understanding of the micellar-flooding process. This understanding is required for interpretation of pilot performance.
This paper discusses the first portion of the mechanism studies for the micellar/polymer system used in the Sloss reservoir. Results of the second portion of the mechanism research were published in 1982.1 A separate paper discussed results of the Sloss pilot posttest evaluation well.3
Pilot Performance
The streamtube model with classical miscible-immiscible displacements was used to obtain preflood predictions.1 This model assumed sulfonate retention (by adsorption) of 3.42 kg active Mahogany AA sulfonate/m3 contacted PV [1.20 lbm/bbl PV], a final oil saturation of 5 % PV in the micellar swept zone, and mobility control. The preflood predictions and pilot performance were in excellent agreement during the early stages of the project.2 However, the observed performance later deviated from the preflood predicted performance.2,4 Postflood predictions by the same model more closely matched total pilot performance by assuming an increased sulfonate retention and a higher final oil saturation.
Process Mechanism Studies
Detailed laboratory studies were initiated to enhance our mechanistic understanding of the process. These studies needed for interpretation of the pilot performance included:phase behavior,compositional effects on oil displacement,propagation of the oil and micellar banks,ion-exchange behavior,sulfonate retention,time effects on sulfonate adsorption, andeffect of micellar fluid aging on oil recovery.
Evaluating compositional effects on the laser-induced combustion and shock velocities of Al/Zr-based composite fuels
