No abstract

Fluids capable of transporting proppant with the least formation and fractures contamination are one of the most relevant areas of the technological development of hydraulic fracturing treatment. In the world in recent years, there has been a tendency to switch from cross-linked guar-based fracturing fluids to synthetic ones. Highly viscous friction reducers find wider application in the new concept of modern industry development. Unlike traditional guar-borate-based fluids, these fluids have a number of advantages - they provide higher residual fracture conductivity, are less sensitive to the mineral composition and temperature of the water source, contain fewer chemical elements in the working formulation and, as a rule, are less demanding of equipping a hydraulic fracturing fleet. Also, in addition to the above features, note the possibility of making changes to an engineering solution immediately in the work process, ensured by the simplicity of fluid making-up and high hydration rate. Despite the obvious advantages in using synthetic fluid systems over standard guar-based systems, until now they have not been widely used in conventional reservoirs. This is supported by poor knowledge of the practical application associated with proppant transport and the absence of selection criteria based on the system rheological properties which significantly affect the hydraulic fracturing success rate. The paper describes a set of rheological studies, including building viscosity and elasticity profiles, as well as an assessment of the fluid system thermal stability. The viscosity behavior was also studied in a wide range of shear rates. The effects of elastic moduli were studied by conducting vibrational-shear tests in a spectrum of various frequencies. Quantitative and qualitative comparative measurements were carried out to study the settling rate of proppant, as well as its viscoelastic properties in a flow. The result of the study is generalized analytical findings on synthetic fluid systems confirmed by practical application in real conditions of conventional reservoirs in West Siberia. This paper will help to understand the key factors affecting the choice of fracturing fluid formulations based on high-viscosity friction reducers and, in the future, may become the basis for creating a methodology for testing synthetic gels.

In the context of a comprehensive search for ways to optimize and reduce operating costs for hydraulic fracturing operations, one of the areas to consider is the use of alternative water sources for making-up hydraulic fracturing fluids such as Cenomanian, mixed or produced water. This solution allows to optimize the speed and quality of work without wasting time and financial resources due to no need for heating and remote transportation. The main goal of the study was to create a stable guar-based hydraulic fracturing fluid system with a borate crosslinker, which allows high-quality treatment using high-salinity water. Much attention is paid to the composition of real saline sources, i.e. produced, mixed and Cenomanian water, which were sampled from the Gazpromneft-Khantos fields. Based on the data ranking by composition, the main groups of mineral components, as well as the cut-off criteria that determine the behavior of a hydraulic fracturing fluid in linear and cross-linked forms, were identified. The main stage of working on the fluid system quality included two areas: screening stabilizing components that meet the criteria for performing hydraulic fracturing operations, and assessing the fluid clogging properties based on flow tests. To study and select the composition of a hydraulic fracturing fluid, both standard and extended rheological tests were performed, which included core tests on real samples from target reservoirs and tests of residual conductivity and permeability of a proppant pack. The sand-transport properties of the fluid were measured both in static and dynamic conditions. The study resulted in the development of a fluid system complex including stabilizing additives and criteria for their applicability at real field conditions, taking into account the features of the existing equipment of hydraulic fracturing fleets. Experiments have shown that standard guar fluids based on water from alternative sources, when using a complex of stabilizing components, successfully replace the basic set of additives for fresh water, and are quite competitive not only in rheological properties and the ability to transport proppants, but also in restoring the permeability of a proppant pack and core samples. Each stabilizing component of such fluid makes its own unique contribution to achieving the required parameters of the fluid without losing its quality. An important achievement is the development of methods and criteria for the applicability of stabilizing components that make it possible to work with any source, whether it is produced, mixed, or Cenomanian water. The solution allows in a short time to adjust the fluid system depending on the actual mineral composition in a stationary field laboratory without the involvement of specialized equipment and expensive research.