Abstract
Summary
This paper presents a general procedure for estimating the cost of recovering crude oil by surfactant waterflood techniques. The general procedure is illustrated by working through an example in detail. The economics of surfactant flooding is a complex function of many elements, such as surface facilities, well operations, reservoir parameters, and chemical cost. We identify 13 elements, explore the interactions among them, and describe a procedure for estimating the wellhead price a producer must receive for surfactant flooding to be economical.
Three actual reservoir stratifications were simulated with surfactant-front-tracking model. Oil recoveries vs. time vs. surfactant injection were obtained. These data were used to illustrate the effect of injection rate, oil saturations at the beginning of the surface flooding, reservoir properties such as thickness and depth, well workover, infill drilling, fracturing, chemical cost, and the discounted cash flow (DCF) rate of return on the required wellhead prices. We show what favorable combinations are needed for an economical surfactant flood.
Introduction
Surfactant waterflood techniques for recovering crude oil have been explored for more than 20 years. Laboratory work has resulted in a spectrum of techniques for judging the oil displacement effectiveness of surfactant/ polymer systems. Numerous field tests have also been polymer systems. Numerous field tests have also been conducted and some understanding of both potentials and limitations of the technology is available.
It is clear that very large quantities of crude oil-billions of barrels-could be recovered from watered-out fields in the U.S. by this technology. What is not clear, however, is how much of this oil can be recovered at costs that a producer or the nation will be able to afford.
The judgment of affordability is exceedingly complex. This complex judgment can be aided by critical examination of the elements of the surfactant technique, from a physics and reservoir engineering viewpoint and from a field operational and economic viewpoint. The purpose of this paper is to identify these elements, to explore the interactions between them, to outline a general framework for estimating required wellhead prices a producer must receive for surfactant-recovered oil, to illustrate this framework by a reference case study, and to show how required wellhead price depends on many reservoir, field, chemical, and economic parameters.
Although numerous cost analyses have been carried out previously (some superficial and some relatively previously (some superficial and some relatively complete), we believe this is the first attempt to generalize such analyses to provide an overview of the technology.
Reservoir Characteristics Affecting Surfactant Waterflood Oil Recovery
By far the most important parameters that determine surfactant recovery attractiveness are those that derive from the geological history of each reservoir. This can be better understood by examining the reservoir physics of the displacement process.
Oil recovery by fluid injection can be thought of as the product of three efficiencies: displacement, pattern, and product of three efficiencies: displacement, pattern, and invasion. Displacement efficiency is the volume of hydrocarbon displaced from pores divided by the volume of hydrocarbon in the same pores just prior to displacement. Two factors influence the displacement efficiency: mobility ratio and fluid injection rate. Mobility ratio is defined as the ratio of the mobility of the displacing fluid to that of the displaced fluid. Displacement efficiency is higher when the mobility ratio is favorable (i.e., 1) than when it is unfavorable (i.e., 1). Displacement efficiency also increases with the increase in the fluid injection rate. The mobility of the fluid is a function of its viscosity and relative or effective permeability. Relative permeability is a function of factors such as sand-grain-size distribution, clay content, and shape of the grains. Thus mobility ratio and, in turn, displacement efficiency are functions of the physical properties of the fluids and the reservoir. Relative properties of the fluids and the reservoir. Relative permeability is, of course, also strongly affected by the permeability is, of course, also strongly affected by the surfactant.
Pattern sweep efficiency is the hydrocarbon pore space enclosed behind the injected fluid divided by the total hydrocarbon pore space of the reservoir. Pattern sweep depends on the shape of the displacement front, which is a function of the gross geometry of the reservoir, reservoir heterogeneities, and mobility ratio.
Gross geometry includes the shape of the reservoir boundaries, the location of the injection and production wells, and the relative magnitude of flow rates associated with these wells. In actual reservoirs, formation properties vary with location.
JPT
P. 208