Surfactant Gel Foam/Emulsion: History and Field Application in Western Canadian Sedimentary Basin

Abstract

Abstract Surfactant gels were introduced into the Western Canadian Sedimentary Basin (WCSB) as fracturing fluids in about 1998.These fluids proved to be successful for propped fracture stimulations in shallow gas wells.About the same time, it was found that surfactant gels could be foamed with nitrogen or emulsified with a high quality (volume fraction) of liquid CO2.Since their inception in the Canadian market, surfactant gel foams/emulsions have been used in coal-bed methane (CBM) and also in the stimulation of deeper, higher temperature applications. This paper will discuss the use of these fluids in the WCSB as well as the chemistry of the fluids, laboratory conductivity measurements which show proppant pack retained conductivities of greater than 96%, and their application in more than 3,100 oil and gas producing zones.The fluids have been used in a variety of formations and in wells with permeability's from 0.1 millidarcies to 10 Darcies, depths in excess of 3000 m (10000 feet) and bottom-hole temperatures up to 100 oC (212 oF).For water-sensitive formations, foamed surfactant gel fracturing costs are significantly less in comparison to hydrocarbon, CO2, or methanol-based fluids. Introduction The use of foamed surfactant gelled fluids has proven to be successful in the Western Canadian Sedimentary Basin (WCSB) since 1998.Application is widespread in oil and gas wells in numerous producing fields and formations in both oil and gas wells. Foams are typically employed in formations that exhibit sensitivity to water-based fluids.Water sensitivity is often described as damage to pore throats caused by swelling clays such as smectite and illite (1).In addition to swelling clays, many producing formations in the WCSB are sensitive to water due to an inherent sub-irreducible water saturation condition (2).Historically, non-aqueous fluids, such as gelled hydrocarbons, liquid CO2, and alcohol systems have been used to help alleviate damage to water sensitive formations. The application of foam fluids to minimize damage during fracturing is not new (3). As Harris pointed out, for deeper and higher-pressure wells, foam stabilizing with base gels and foamers/crosslinked gels was were used. These gels or crosslinkerscreate operational complications or damage to the formation, but these issues are minimized by the using less than 25 volumepercent of water-based fluid, the rest being the energizing medium. The use of surfactant gels were coming into being in the later part of the 90's as clean fluids. Since the introduction of surfactant gels as clean fluidstheir introduction into the WCSB, they were successful in shallow gas applications. These fluids were not wall-building fluids and had very good retained permeability both in the formation and the proppant pack. Foaming the base surfactant gel provides significant increase in both viscosity and leak-off control. The surfactant gel system can be foamed either with nitrogen or carbon dioxide. Due to economicsF, it was common to use nitrogen foamed system for shallower wells, and for deeper wells, CO2 was used as the internal phase in the foam treatments. The authors recognize "foams" containing liquid CO2 as the internal phase can be classified as "emulsions", and either term will be used throughout the manuscript.We will discuss the general properties of the surfactant gel system, the foamed system and their successful application for stimulation of hydrocarbon producing basins. To-date, 2,900341 nitrogen foamed treatments and 26004 carbon dioxide foamed treatments were successful in placing proppant and stimulating formations in the WCSB.