Oil recovery from naturally fractured reservoirs by steam injection methods. Annual report, October 1, 1990--September 30, 1991.

摘要

The United States of America has naturally fractured reservoirs containing many tens of billions of barrels of oil. When secondary and enhanced recovery methods are applied, fractures tend to channel injected fluids through the reservoir to production wells, resulting in much of the oil in the matrix blocks being bypassed and not recovered. This results in a low recovery efficiency from fractured reservoirs. Oil recovery by steam injection is a proven, successful technology for non-fractured reservoirs, but has received only limited study for fractured reservoirs. Preliminary studies suggest recovery efficiencies in fractured reservoirs may be increased by as much as 50% with the application of steam relative to that of low temperature processes. The objectives of this research program are to quantify the amount of oil expelled by these recovery mechanisms and to develop a numerical model for predicting oil recovery in naturally fractured reservoirs during steam injection. The experimental study consists of constructing and operating two apparatuses to isolate each of these mechanisms. The first will measure the thermal expansion coefficient for the pore volume of various lithologies and the second will measure the maximum gas saturations that could build up within a matrix block. A third experimental task will be to measure oil expulsion from matrix blocks at low and high temperatures by capillary imbibition alone. Other experimental measurements will be conducted on thermal properties of porous media using existing equipment. The numerical study will consist of developing transfer functions for oil expulsion from matrix blocks to fractures at high temperatures and incorporating them, along with the energy equation, into a dual porosity reservoir simulator. This simulator will then be utilized to make predictions for steam injection processes in selected naturally-fractured reservoirs.