Abstract

Laboratory studies have indicated that foamed anhydrous methanol may be an effective stimulation technique for the sands and shales of the Appalachian Basin and the Eastern Overthrust Belt. These formations are characterized by low pressures, low permeabilities, and sensitivity to injected water. Conventional aqueous fracturing foams pumped into these formations result in fluid pumped into these formations result in fluid retention, clay swelling, and migration, along with capillary pore blockage. To forego such problems, some operators instead pump strictly problems, some operators instead pump strictly nitrogen (N2) gas or liquid carbon dioxide (CO2) as the stimulation fluid. Such treatments minimize formation damage but are incapable of transporting appreciable quantities of proppant for the created fractures. Laboratory studies were conducted to determine a more effective stimulation fluid. Results indicate that foamed anhydrous methanol may be such a fluid because it is nonaqueous and capable of transporting proppant. proppant

Introduction

Spanning from northwestern New York down through northern Kentucky and possibly as far east as North Carolina, the Devonian shales have been active hydrocarbon producers for the greater part of this century. With matrix permeabilities part of this century. With matrix permeabilities to gas of less than 0.01 md, it is generally acknowledged that the majority of hydrocarbon production results from flow through natural production results from flow through natural fractures. For this reason, drilling designs and completion methods are premised on technologies that maximize the efficiency of these unusual reservoirs. Besides possessing a high density of natural fractures, the Devonian shales have characteristically been susceptible to water damage. This water damage is apparent from the observed low returns of treatment liquids (water, acid, etc.). The reasons for liquid entrainment are not exactly known, and considerable speculation exists on whether it is a result of clay swelling and migration or of capillary forced pore blockages resulting from high liquid surface and interfacial tensions. Furthermore, with location variations in rock and fluid properties, the specific cause of water entrainment may also be a variable. Stimulation design in this shale formation, for reasons of formation sensitivity to aqueous fluids, minimize water. Because of the low flow capacity of the Devonian shale matrix, stimulation treatments usually require hydraulic fracturing to increase formation conductivity.

At present, a common stimulation technique for the Devonian shales is composed of only gaseous nitrogen and/or liquid carbon dioxide. These systems, when pumped at very high rates (approaching 100,000 scf/min), have proved effective at inducing new fractures, opening and connecting natural fracture networks, and being for all practical purposes nondamaging. Because the system typically purposes nondamaging. Because the system typically incorporates no proppant however, post-fracturing production decline is rapid as the induced fracture production decline is rapid as the induced fracture heals. The advent of placing sand with nitrogen or liquid carbon dioxide should theoretically prolong fracture conductivity; yet sand placement prolong fracture conductivity; yet sand placement with these systems is relatively low (approximately 10,000 lb).

The predecessor to the purely gaseous fracturing treatments without proppant is the foam fracturing system. Typically incorporating treated water (2% KCl brine) in liquid volumes of 15 to 30 percent, the system is capable of creating substantial percent, the system is capable of creating substantial fracture widths and maintaining excellent sand transport abilities, low leak-off and subsequent high sand placement (approximately 60,000 lb). However, production results are sometimes less than expected and liquid retainment unfortunately high.

LABORATORY INVESTIGATION

Because of the rapid production decline associated with strictly nitrogen or carbon dioxide fracturing systems and the assumed formation clay and pore throat damage arising from aqueous foam systems, a major void existed in successfully stimulating the Devonian Shale. As a result, several different analyses were conducted to understand the existing problems better, substantiate present theories, problems better, substantiate present theories, and present a solution.

p. 161

This content is only available via PDF.
You can access this article if you purchase or spend a download.