Recovery of Penn-Grade Crude Oils by Steam

Abstract

Experiments conducted on ten Penn-Grade crude oils under isothermal conditions in Berea sandstone cores revealed that, on the basis of one pore volume of steam injection into a waterflooded core, the oil recovery was highest (61 percent) for the Venango First Sand crude oil. Introduction Considerable interest has been shown recently in steamflooding oil reservoirs in the Pennsylvania-New York area, chiefly on account of the low ultimate recovery of about 40 percent at abandonment. Steam has also been found to increase the injectivity of the tight formations containing highly paraffinic crudes found in these reservoirs. This investigation is a first attempt to evaluate experimentally the response of selected Penn-Grade crude oils to steamflooding, and to compare the oil recovery performance using the method proposed by Willman et al. The basic objectives of the experimental work wereto obtain the viscosity and thermal expansion data for the 10 crude oils tested, andto conduct steam-floods using these oils in consolidated Berea sandstone cores. The runs were conducted under isothermal conditions (i.e., core temperature was equal to the injected steam temperature), with the core initially containing irreducible water saturation, or residual oil saturation. Fluid production histories and steamflood residual oil saturations were determined in each case. It is recognized that under actual field conditions, the steamflood residual oil saturations as well as displacement efficiency in each case would be determined by the specific rock permeability, porosity, mineral content, etc. However, it is hoped that the use of Berea sandstone in all cases a situation dictated by the unavailability of actual rock sampleswould provide useful information on the relative steamflood behavior of the crude oils tested. Experimental Investigations of Steamflooding Willman et al. published the results of a comprehensive laboratory investigation of oil recovery by steam injection. They employed crude oils ranging in API gravity from 12.2 degrees to 37 degrees, and refined oil mixtures having predetermined distillation properties. Nonisothermal steamfloods conducted in properties. Nonisothermal steamfloods conducted in consolidated and unconsolidated porous media gave oil recoveries ranging from 75 to 92 percent of the oil in place. The chief recovery mechanisms defined were viscosity reduction, thermal expansion, and steam distillation. Silberberg and Caudle reported the residual oil saturations achieved after steaming small sandstone cores containing waterflood residual oil saturations. The oils consisted of 10 to 55 percent volatile components. The residual oil saturations ranged from 8.2 to 11.4 percent PV. Ozen and Farouq Ali reported the results of an experimental investigation of the recovery of the Bradford crude oil by steam injection. Residual oil saturations ranging from 12.0 to 15.4 percent were found for isothermal steamfloods at 200 psia in Berea sandstone cores. In the case of unconsolidated cores, the corresponding saturations ranged from 3.3 to 6.0 percent under nonisothermal conditions. percent under nonisothermal conditions. JPT P. 705