Abstract: A method is disclosed for recovering hydrocarbons from underground formations by a series of sequenced steps, involving (1) injecting steam of a relatively high quality into the formation and (2) about the time of steam breakthrough, reducing the quality of the steam being injected to a quality between about 25% and about 50% while simultaneously increasing the rate of steam injection so as to maintain a constant rate of heat injection into the formation. Optionally, hot water having a temperature between about 120.degree. and 180.degree. F. may be injected following the injection of about 0.5 pore volumes to about 2.5 pore volumes of reduced quality steam.

Abstract: A method is disclosed for recovering hydrocarbons from heavy oil and tar sand formations by a series of sequenced steps, wherein the production wells are initially steam stimulated. Thereafter, about 0.6 to about 1.2 pore volumes of steam of a relatively high steam quality are injected into the formation through the injection wells. An additional quantity of steam is then injected wherein the steam quality is decreased to a relatively low quality. Water injection and wet in situ combustion conclude the method.

Abstract: The viscosity of a heavy oil such as a crude petroleum oil is reduced by subjecting the oil to a visbreaking treatment in the presence of a chain transfer agent and a free radical initiator.

Abstract: Steam breakthrough at the updip outcrop of a steeply dipping heavy oil reservoir is prevented by the injection of a hot water bank above the point at which the steam is injected into the heavy oil reservoir.

Abstract: The vertical conformance of a steam drive process is improved and steam override reduced by penetrating the zone between one injection well and one producing well, with an infill well which is in fluid communication with the bottom half or less of the formation, and producing petroleum from the infill well after steam channeling has occurred at the production well; then converting the infill well from a producer to an injector and injecting steam into the lower portion of the formation via the infill well and recovering fluids from the production well. Two separate communication paths are established, one between the surface and the upper half or less of the formation, and one between the bottom half or less of the formation in the producing well, or in the infill well, or injection well, or combination of two or more thereof.

Abstract: Polymer flooding is an effective means of increasing the sweep efficiency of a displacement process for recovering petroleum from a subterranean, petroleum containing formation; however, most polymers suitable for use in flooding operations hydrolyze or otherwise decompose at temperatures above about 150.degree. F to 200.degree. F, and the temperature of many subterranean petroleum-containing formations is in excess of 150.degree. F-200.degree. F. Polymers may be employed in tertiary recovery in formations whose temperatures are greater than the temperature stability limit of the polymer if the formation temperature is first reduced by introducing an aqueous fluid such as water at a temperature substantially below the temperature limit of the polymer into the formation for a period of time sufficient to reduce the formation temperature to a value at or below the temperature tolerance level of the polymer.