Preliminary Experimental Results of High-Pressure Nitrogen Injection for EOR Systems

Abstract

Summary Miscible-displacement processes have generally been recognized by the petroleum industry as an important enhanced oil recovery (EOR) method. Nitrogen flooding has become an attractive method for economical EOR. Since no previous studies have been undertaken to observe miscibility conditions directly during their development in an oil reservoir, a research program was initiated to investigate experimentally the mechanism by which miscibility could be achieved in a reservoir model undergoing high-pressure nitrogen injection. Several experiments were conducted in a low-permeability, consolidated sandpacked stainless-steel tube 125 ft long and 0.435 in. in diameter. The apparatus was designed to allow sampling at selected locations along the core tube enabling researchers to investigate fluid behavior during the process. A more-detailed representation of the nitrogen displacement process is formulated and the graphical chromatographic results are presented to illustrate the nitrogen miscibility in consolidated cores. Introduction Previous researchers have investigated, experimentally and theoretically, the problem of predicting the effects of dry-gas injection into a reservoir. Most earlier experimental studies were concerned primarily with the effects of changing pressure, temperature, and gas solubility on oil recovery during gas injection. Vogel and Yarborough conducted a number of laboratory tests on several different reservoir fluids to determine the effect of nitrogen contact by varying the amounts of nitrogen. They reported that the solution-gas gravity, oil density, and oil viscosity increased with continued contact by nitrogen. No previous studies have been conducted to observe miscibility conditions directly during their development in an oil reservoir. This experimental work was initiated to investigatecompositional changes taking place during displacing of crude oil by continuous high-pressure nitrogen injection,change in properties of the liquid and vapor phases during the nitrogen injection,miscible pressures for nitrogen displacement, anddistance from the injection point at which miscibility would be achieved. Experimental Apparatus and Materials Apparatus The experiment was designed to studyvaporization of oil by high-pressure nitrogen injection,mechanisms of nitrogen multiple contact miscibility displacement, andcompositional changes that take place between nitrogen and in-situ oil during the test. Fig. 1 shows a schematic of the equipment used to perform the experimental study. For the purpose of description, the laboratory apparatus may be divided into three parts: a laboratory oil reservoir model, an injection system, and a production and analytical system. SPEJ P. 339^