Optimum Hydrocarbon Fluid Composition for Use in CO2 Miscible Hydrocarbon Fracturing Fluids and Methods of Core Evaluation

Abstract

Previous studies (1)(2)(3)(4) described the theory and application of CO 2 miscible hydrocarbon fracturing fluids for gas well stimulation. These fluids are ideally suited to gas reservoirs susceptible to phase trapping resulting from high capillary pressures when water-based fluids are used. Gas reservoirs particularly prone to phase trapping are those with in situ permeability less than 0.1 mD, those with initial water saturations less than what would be expected from normal capillary equilibrium (subnormally water saturated) and those that are under pressured. Such reservoirs represent a growing proportion of the market. This, combined with increased gas prices, creates a strong need for an optimized gas well fracturing fluid system.Hydrocarbon-based fracturing fluids present an ideal solution to phase trapping concerns associated with water-based fluids provided the hydrocarbon fluid can be effectively and quickly removed from the formation after the fracturing treatment.This paper investigates in more depth what constitutes an ideal hydrocarbon-base oil for this application. This involves consideration of many factors including cleanup mechanisms, safety, cost and capability to be gelled and broken.In order to meaningfully evaluate fluid clean up, regained core permeability evaluations must be conducted by accurately duplicating downhole conditions. This paper presents testing methodologies designed to achieve this goal.To illustrate the need for these methodologies, the applicable phase behaviour and fluid displacement mechanisms by which these fluid systems operate are discussed. Topics covered will include:• Methane drive fluid recovery mechanism involving the use of CO 2 with hydrocarbons and resulting effect on interfacial tension (IFT). • Secondary recovery mechanism based on vapour pressure of light hydrocarbons resulting in their being produced back in the gas phase with methane. • Application of these concepts to address phase trapping in low-permeability gas reservoirs and how these effects are accentuated in formations that may be subnormally water-saturated, have low reservoir pressure or have low permeability.

Organogels with Complexes of Ions and Phosphorus-Containing Amphiphiles as Gelators. Spontaneous Gelation by in Situ Complexation

“…We demonstrate that the gelation efficiencies depend mainly on the nature of substituents attached to the phosphorus atom. This research complements and expands upon our previous studies, , exploring the gelation abilities of complexes between 1 − 3 and a Fe(III)-based surfactant agent (which has not been completely characterized) as well as those of several other groups . The paramagnetic nature of the Fe(III) agent precluded some NMR analyses from being performed on its gels.…”

“…General Considerations. The preparation and spectroscopic properties of 1 − 3 have been reported previously 23 in conjunction with paramagnetic Fe(III) complexes and their gels. , …”

“…These studies demonstrate that the properties of the gels can be modulated by careful choice of the structural variables in the phosphorus-containing latent gelators. For example, the analogous gelators with Fe(III) as the complexing agent have found uses in hydraulic fracturing. , The results presented here provide an interesting class of two-component gelators that can be made from freely flowing solutions by mixing the components at room temperature, even without perturbations from enzymatic catalysts, radiation, or sonication. − …”