ABSTRACT
New types of high temperature resistant formation blocking agents were studied. Laboratory techniques are described and results shown which should provide a basis for selection of blocking agents for field applications.
Permeability reductions in tar sands as a function of solution concentration and slug size are shown together with the effects of temperature. Blocking capability of these products in brine and steam floods was demonstrated in simulated heterogeneous models with various permeability contrasts.
Prior to their in-situ gelation, these products were shown to have viscosity close to that of water, have controlled rate of gelation and appear to be capable of permanently reducing the water and steam permeability of highly permeable zones in a controlled manner.
INTRODUCTION
Recovery of oil typically requires operations in contiguous zones which differ in permeabilities. Such differences are induced either by natural faults, fractures, compositional differences in the rock or by the recovery operations themselves. It has often been found beneficial to selectively alter the permeability characteristics of the formation to increase the oil recovery from flooding operations. Many processes have been developed which can change permeability of a portion of a reservoir. These changes can range anywhere from a controllable permeability reduction in the high permeability zone to a complete blocking of any fluid flow through such strata.
It is important to emphasize the difference between the injection of a polymer solution to improve oil to water mobility ratio in a reservoir and an injection of a plugging composition to reduce the permeability of a particularly highly permeable zone without affecting the rest of the reservoir.
A review of the literature published during the last decade and dealing with formation plugging techniques provides a wealth of information, but shows an actual shortage of relevant laboratory data and techniques regarding evaluation of applicability of these products at high temperatures over an extended period of time. Various formation plugging agents and mobility modifiers reported in the literature since 1975, can be classified into several groups.
Several products, such as those based on solutions of lignosulfonate reaction products (1-4), foams (5-8), in-situ polymerized gels (9-10), silica gels (11), polymeric emulsions (12,13) and formation of precipitates (14-17) were described as being particularly suitable for high temperature applications. Many other products were introduced for low temperature blocking and mobility changes. These include various aqueous solution of polymers (18-51), foamed blocking agents (52-53), in-situ polymerized gels (54-58), silica gels (59-63), injections or in-situ formation of emulsions (64-70) in-situ formation of precipitates (71-75) and several other techniques (76-95), some of which are claimed to have only temporary effect (96-101).
