Fracturing With Crosslinked Gelled Methanol: A New Approach To Well Stimulation

Abstract

Abstract Recent development of a water-free fracturing fluid has improved stimulation successes in several Alberta formations. Methanol has been used for many years to reduce formation damage caused by swelling clays and capillary blockage resulting from high-fluid surface tension. This paper discusses the development and field application of the gelling and crosslinking of commercially available methanol. The study also details the rheological characteristic of the system under dynamic conditions. The relative effects of both intensity and duration of shear hat is applied during the preparation of the crosslinked gelled methanol system are presented. Several factors that are inherent in the evaluation of a fracturing luid for field application will be discussed. These includeproppant transport capability, fluid leak-off coefficients, compatibility with carbon dioxide and safety in handling a potentially volatile fluid. Data on the zones treated as well as post-frac production results are included. Introduction Greater emphasis today is being placed on well stimulation fluids that can be used to increase production from water sensitive reservoirs. Formations with low permeability, high clay content, or low bottomhole pressure usually experience poor fluid recovery after fracturing with conventional fracturing gels. This poor post-frac performance may be attributed to permeability damage caused by the swelling of clay particles or by the migration of particles and fines(1). Slow clean-up of water in this type of formation may also be caused by gas and water relative permeability effects or by the high capillary pressure in low-permeability rocks(2). Formations containing gas reservoirs with relatively large quantities of migrating-type clays (kaolinite and mica/illite) are common throughout Alberta. Core samples from the Basal Quartz formation have been found to contain more than 20% aolinite on framework grains and in pore throats. Other Alberta gas-producing formations, such as the Viking Sandstone can contain expandable mixed-layer clay, usually illite/smectite or the. highly expandable smectite mineral. Still others contain large amounts of both the migrating type clay and the expanding type clay. An example is the Cardium formation. Methanol, with varying degrees of water and energizing fluids has been used in the past with some success to treat these problems formations. Papers documenting the successful use of methanol/water and CO2 methanol/water-based fracturing fluids have been presented. These include "Experience with CO2 Laden Fracturing Fluid for Stimulating Water-Sensitive Formations" and "The Use of Alcohol-Water Mixtures in Fracture Stimulation of Gas Wells". Recent product and chemical developments enable the use of commercial grade methanol for preparing either a medium viscosity linear gel or a high-viscosity crosslinked fluid for fracturing. With proper knowledge about the rheological properties, the proppant transport capabilities and the fluid loss control properties, a system prepared from only methanol or methanol/ CO2 can be selected to stimulate typically sensitive formations and provide improved clean-up performance. Background The application of methanol in stimulating hydrocarbon reservoirs has been the central issue of technical discussions over the years. Its virtues in fracture stimulation have been well documented and indicate that a pure methanol fracturing fluid would have many benefits in achieving successful production fromvarious reservoirs that are sensitive to other stimulation and/or complet