Hydraulic fracturing has remained a fundamental technique for stimulation of oil and gas reservoirs for enhanced or economic recovery of hydrocarbons from tight formations for more than 60 years. Transporting proppant downhole without any interruption and then to obtain maximum recovery of fracturing fluids are two important criteria for successful hydraulic fracturing. To achieve such objectives, the fracturing fluid should demonstrate good viscosity and complete cleanup of gelling agents. Because wells are exploited at both shallow and great depths in environments of moderate to very high temperatures and pressures, fracturing fluid selection is fundamental. Fracturing fluids prepared by crosslinking guar, guar derivatives, and other naturally occurring polymers with borate or metal crosslinkers often exhibit instability at very high temperatures. The primary reason for instability of the fracturing fluid is because strength of the bonds between the polymer chain and crosslinker decreases sharply in addition to breakdown of the glycosidic bonds between monomer units of the polymer chain beyond 375°F. Additionally, metal crosslinked bonds are prone to shear degradation, creating doubt for a successful stimulation treatment in high-temperature extended-reach wells. To address these issues, a synthetic gelling-agent-based fracturing fluid that can work at temperatures greater than 400°F was developed. The gelling agent is a terpolymer, which can be crosslinked with a zirconium-based crosslinker. This paper discusses evaluation and performance of an extreme temperature fracturing fluid. This fracturing fluid system has sufficient proppant carrying viscosity and provides efficient post-treatment cleanup using delayed oxidized breaker. Analysis of fluid viscosity stability and delayed oxidizing breaker usage is presented in addition to performance parameters such as regained permeability and fluid loss. The study illustrates performance of the synthetic gelling-agent-based fracturing fluid at temperatures ranging from 380 to 440°F.
Hydraulic fracturing has remained a fundamental technique for stimulation of oil and gas reservoirs for enhanced or economic recovery of hydrocarbons from tight formations. Transporting proppant downhole without any interruption and maximum recovery of fracturing fluids are two important criteria for successful hydraulic fracturing. To achieve such objectives, the fracturing fluid should demonstrate good viscosity and complete cleanup of gelling agents. As wells are exploited at greater depths in environments of higher temperature and pressure, fracturing fluid selection is key. Fracturing fluids prepared by crosslinking guar, guar derivatives, and other naturally occurring polymers with borate or metal crosslinkers often exhibit instability at very high temperatures. The key reason for instability of the fracturing fluid is because strength of the bonds between the polymer chain and crosslinker decreases sharply in addition to breakdown of the glycosidic bonds between monomer units of the polymer chain beyond 375°F. Additionally, metal crosslinked bonds are prone to shear degradation, creating doubt for a successful job in high temperature long reach wells.To address these issues, a synthetic gelling-agent-based fracturing fluid that can work at temperatures greater than 400°F was developed. The gelling agent is a terpolymer, which can be crosslinked with a zirconium-based crosslinker. This paper discusses evaluation and performance of an extreme temperature fracturing fluid. This fracturing fluid system has sufficient proppant carrying viscosity and provides efficient cleanup using delayed oxidized breaker. Analysis of fluid stability and delayed oxidizing breaker usage is presented in addition to performance parameters, such as regained permeability and fluid loss. The study illustrates performance of the synthetic gelling-agent-based fracturing fluid at temperatures ranging from 380 to 420°F.
Trapped gas within the matrix and fractures of source rock shales is termed as "shale gas." Geologically, the shale-gas-bearing formations are fine-grained, organic-matter-rich (0.5 to 25%), porous, but impervious sedimentary strata with natural gas trapped in the pores, natural fractures, and/or adsorbed onto the clay surface. The primary factors related to the geology and geochemistry of the formation that govern shale gas production potential would be porosity, permeability, natural fracturing, their original hydrocarbon-generating potential, and the amount of gas still present in the formation. Hydrocarbon-generating potential includes the amount of organic matter originally deposited or the total organic carbon content (TOC), types of source organic matter or kerogen type, thermal maturity and hydrocarbon-generating capacity or gas yield, and the extent of conversion of source organic matter to hydrocarbon. These factors again depend largely on the availability of organic matter, depositional environments, depth of burial, local geothermal gradient, and degree of metamorphism. Hydrocarbon-producing potential further depends on the network of natural fractures, microporosity, adsorption, etc. The impervious nature of shale gas formations requires extreme natural or artificial fracturing (fracture stimulation) to recover commercial quantities of gas. Hydraulic fracturing and horizontal drilling are successful techniques recently used for commercial shale gas production, which depend on geomechanical properties, such as mineralogy and brittleness/ductility of the formation. However, selection of drilling and stimulation methodology requires knowledge of other geological parameters, such as the arrangement of the bedding planes, stratigraphy, natural fracture porosity and intensity, clay content, shale-water absorption, fluid-water sensitivity, shale capillary, shale fractal pattern, shale hydration, gas-shale fracture conductivity, relation of geological features of the formation with regional geological settings, and spacial and temporal variation of reservoir parameters. These parameters govern the direction of fracture propagation, gas recovery rate, and wellbore stability of the drilled well, and also aid in determining base-fluid salinity and fluid-type selection for a fracturing treatment. The aim of this paper is to elucidate the geological processes related to shale gas formations for the development of the proper technology to aid hydrocarbon recovery.
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