Liquid Petroleum Gas Fracturing Fluids for Unconventional Gas Reservoirs

Abstract

Unconventional gas reservoirs, including tight gas, shale gas and coalbed methane, are becoming a critically important component of the current and future gas supply. However, these reservoirs often present unique stimulation challenges. The use of water-based fracturing fluids in low permeability reservoirs may result in loss of effective frac half-length caused by phase trapping associated with the retention of the introduced water into the formation. This problem is increased by the water-wet nature of most tight gas reservoirs (where no initial liquid hydrocarbon saturation is, or ever has been, present) because of the strong spreading coefficient of water in such a situation. The retention of increased water saturation in the pore system can restrict the flow of produced gaseous hydrocarbons such as methane. Capillary pressures of 10 to 20 MPa or higher can be present in low permeability formations at low water saturation levels. The inability to generate sufficient capillary drawdown force using the natural reservoir drawdown pressure can result in extended fluid recovery times, or permanent loss of effective fracture half-length. Furthermore, use of water in subnormally saturated reservoirs may also reduce permeability and associated gas flow through a permanent increase in water saturation of the reservoir. Secondary costs, such as rig time for swabbing, can add to the negative economic impact. Gelled liquid petroleum gas-based fracturing fluids are designed to address phase trapping concerns by replacement of water with a mixture of liquid petroleum gas (LPG) and a volatile hydrocarbon fluid. Once the well is drawn down for flowback, some of the LPG portion of the fluid may be produced back as a gas, dependent upon temperature and pressure. The remaining LPG remains dissolved in the hydrocarbon fluid and is produced back as a miscible mixture using a methane drive mechanism. By eliminating water and having LPG as up to 80 - 90% of the total fluid system, cleanup is greatly facilitated, even in wells having very low permeability and reservoir pressure. The effects of fracturing fluid retention on gas flow in the fracture face can be as important as fracture conductivity when designing a treatment. It is possible to have a conductive fracture with good half-length in the desired productive zone and still not realize economic or optimum gas production if phase trapping and/or relative permeability effects are restricting gas flow. Description Gelled LPG-based fracturing fluids are a unique hydrocarbon-based fracturing fluid system designed for gas well stimulation. They use up to 100% gelled LPG for the pad and flush. The sand slurry stages use a mixture of up to 90% LPG with the balance of the volume being a volatile hydrocarbon-based fluid. All chemicals and proppant are added to the base fluid at the blender. LPG, which composes the balance of the downhole fluid volume, is injected at the wellhead where it forms one miscible mixture with the base oil. It is important to note that under pumping pressures, this is a single-phase gelled fluid system, similar to gelled oil in rheology, friction pressures, proppant transport and leakoff control.

Groundwater Protection and Unconventional Gas Extraction: The Critical Need for Field‐Based Hydrogeological Research

“…Similarly, 7700 to 38,000 m 3 of fluid (2-10 million gallons) is used to fracture each horizontal deep well in the Marcellus Shale in the northeastern United States (Kargbo et al 2010). Because water used in hydraulic fracturing can imbibe into the host rock's matrix and reduce gas relative permeability (and hence gas production), nonaqueous based fracturing fluids (Table 1; e.g., Lestz et al 2007) provide an alternative approach that also assists with water supply and gas recovery issues. Hydraulic fracturing is conducted sequentially in "stages" or perforated sections of the horizontal production casing (Figure 2), and involves the injection of fluids (gases, liquids, foams), with a mix of additives (discussed below), at elevated hydraulic pressures around each "stage" to produce and propagate fractures.…”

Influence of Cryogenic Liquid Nitrogen on Petro-Physical Characteristics of Mancos Shale: An Experimental Investigation

“…Nowadays, 90% of the wells undergo fracturing for production of commercial gas by using the hydraulic fracturing technique. , However, this procedure causes significant environmental problems such as groundwater contamination, wastewater treatment, air pollution, and clay expansion. Hence, there has been a conscious effort by the oil and gas industry to improve the fracturing process and find an excellent alternative for the water-based fracturing fluid. − Thus, several literature reports − have demonstrated the role of water-free fracturing technologies such as cryogenic fracturing, nitrogen foam fracturing, supercritical CO 2 fracturing, and liquefied petroleum gas fracturing using liquid nitrogen (LN 2 ) .…”

Waterless fracturing technologies for unconventional reservoirs-opportunities for liquid nitrogen

“…As a fracturing fluid, gelled LPG has several desirable properties, such as improved viscosity, low interfacial tension, and high solubility with hydrocarbons. Also, the flow back of LPG, unlike other foreign gases, does not need to be flared (Lestz et al 2007). Similar to methanol, LPG has potential safety risks.…”