Fracturing With a High-Viscosity, Cross-Linked GelContinuous Fracturing Technique

Abstract

Introduction Highly viscous fracturing fluids that could be pumped at relatively high rates with acceptable friction pressure were first introduced 18 years ago. This viscous fluids were oil-water dispersions that created some problems because they required special mixing and pumping techniques. The fluids did, however, prove their value by creating wide, deeply penetrating fractures and by carrying high concentrations of propping agents. Since then, other high viscosity fluids have been introduced and their properties and effectiveness reported. Such fluids now properties and effectiveness reported. Such fluids now are used commonly in all areas. Because there is some variation in fluid requirements of different areas and formations, several types of fluids have evolved. All can be classed as viscous fracturing fluids. While these fluids have been used successfully, most have the same primary disadvantage: they must be batched mixed before use. Batch mixing requires that all water gelling agents be premixed in fracturing tanks before pumping. Often this premixed in fracturing tanks before pumping. Often this leads to additional rig-time expense for the operator and additional rig-time expense for the operator and additional equipment time and man hours for the service company. Also, if the procedure is not completed as planned, there can be considerable expense in preparation planned, there can be considerable expense in preparation of fluid that is not used. These expenses can become prohibitively high on large jobs, such as the prohibitively high on large jobs, such as the "massive-fracturing" type treatment. To overcome the disadvantages of batch mixing, specially prepared materials for gelling water have been developed that can be mixed continuously as the fluid is pumped down hole. These materials, first prepared from guar gum polymers, have been in use for 3 years and have proved polymers, have been in use for 3 years and have proved highly successful. More recently, lower residue guar derivatives have been used successfully. Cross-Linked Guar Gels Very high viscosities can be achieved by cross-linking the guar gels. However, preparation of cross-linked guar gels at the well location on a large volume basis has been troublesome and time consuming in the past because of the required batch-mixing technique. That is, the guar gelling agent and cross-linker are premixed in the fracturing water. Adjustments of the fluid's pH are often necessary and present problems in achieving a uniform pH in large fracturing tanks. The guar gelling agent hydrates and produces a high-viscosity solution. JPT P. 119