Influence of Viscoelastic Surfactant Fracturing Fluids on Modified Coal Fracture Flow Characteristics

Abstract

Ecofriendly viscoelastic surfactant fracturing fluids (VESFFs) can effectively promote the connection of fractures. These can modify the fracture surface and change the flow capacity at the pressure-holding stage, which affects coalbed methane exploitation. In this study, deionized water (DW) and three common VESFFs which, namely, are the cationic surfactant fracturing fluid (CSFF), cationic–zwitterionic surfactant fracturing fluid (CZSFF), and anionic–zwitterionic surfactant fracturing fluid (AZSFF), were used to modify coal fractures for the first time. To analyze the flow characteristics of coal fractures, a triaxial servo seepage test device was used to conduct the test. The variations in fracture surface morphology were analyzed by a three-dimensional optical topography scanner, an environmental scanning electron microscope, and an X-ray diffractometer. The degree of flow capacity improvement following modification by the VESFF decreased in the following order: CSFF > AZSFF > CZSFF > DW. At a high confining stress (6.1 MPa), DW treatment of the coal fracture decreased the flow rate by 26% and hydraulic aperture by 11.16%. The CSFF modification of the coal fracture increased the flow rate by 18% and the hydraulic aperture by 6.43%. A new friction factor model with the Reynolds number and relative roughness as the variables was proposed, which describes the flow characteristics of the gas from laminar to turbulent flow. VESFFs affected the flow capacity of coal fractures in five aspects: mineral dissolution, mineral precipitation, electrostatic removal of coal particles, reduced degree of fracture engagement, and increased effective fracture connectivity.

Physicochemical Effect on Coal Pores of Hydrocarbon Chain Length and Mixing of Viscoelastic Surfactants in Clean Fracturing Fluids

“…The foam fracturing fluids have some problems such as complicated technology, long construction preparation time, and high construction costs. , Clean fracturing fluids have attracted attention because of their high interfacial activity, high viscoelasticity, and lack of residue after gel breakage . Some studies have shown that clean fracturing fluids can improve the effect of coalbed methane extraction and are environmentally friendly. − Clean fracturing fluids have broad application prospects in coal-seam permeability enhancement.…”

Review on High-Temperature-Resistant Viscoelastic Surfactant Fracturing Fluids: State-of-the-Art and Perspectives

“…To overcome the problems of the traditional polymer-based fracturing fluids, researchers have proposed viscoelastic surfactant (VES) fracturing fluids composed of surfactants and additives. They have significant advantages such as fewer components, easy on-site preparation, low treatment friction, limited damage to proppant pack and formation, and no insoluble residue. − Since the VES fluid was first introduced into hydraulic fracturing for reservoir stimulation as a fracturing fluid thickener by Schlumberger in 1997, , the VES fracturing fluid has been widely used in hydraulic fracturing all over the world and achieved good stimulation effect . A high-temperature well (121–143 °C) in El Tordillo field of the San Jorge Basin in Argentina was stimulated with VES HT fluid, bringing about an increase in liquid production from 7 m 3 /day to 79 m 3 /day with a water-cut rate of 72% .…”

Development and Performance Evaluation of a Novel Silica Nanoparticle-Reinforced CO2-Sensitive Fracturing Fluid with High Temperature and Shear Resistance Ability

“…The hydraulic fracturing technology reduces oil flow resistance and improves oil recovery in tight reservoirs . Therefore, it is very important to develop a suitable fracturing fluid with high efficiency, low cost, strong sand-carrying capacity, temperature resistance, and shear resistance in the process of fracturing construction. − Compared with the traditional natural guar gel fracturing fluid and the synthetic polymer fracturing fluid, a clean fracturing fluid has obvious advantages of simple compositions, residue free after gel breaking, high flowback rate, and low formation damage. − The main driving mechanism for the formation of the clean fracturing fluid is the interaction between viscoelastic surfactants and counterion salts to form a complex three-dimensional network structure overlapped by wormlike micelles. − Under tensile or shear forces, the wormlike micelle network has characteristic rheological properties that allow the clean fracturing fluid to quickly return to its original state after being pumped at high speed.…”