Development and Evaluation of a Novel Delayed Crosslink, Low Friction, High-Density Brine-Based Fracturing Fluid for Ultra-Deep Fracturing Stimulation

Abstract

ABSTRACT: Using heavyweight brines as a base for fracturing fluids is an effective method for solving the problem of exorbitant surface pressure during the deep well fracturing process. However, higher fluid densities can lead to higher friction pressures, and with the well depth increases, the travel time to the mudline prolongs, resulting in the demand for extended crosslink delay times. Therefore, fracturing fluids that provide flexibility in density, lower friction and extended crosslink times are required for effective stimulation in ultra-deep reservoirs. This paper presents details of laboratory studies to develop and evaluate a novel weighted fracturing fluid. The main additives of the novel system were sequentially synthesized, including modified guar gum, a new weighting agent and an organic boron-zirconium crosslinker. Afterwards, a series of lab experiments were carried out to test the comprehensive performances of the novel system, such as temperature and shear resistance, friction reduction, gel breaking performance and core damage rate. The optimal formula of fracturing fluid was 54.3 wt.% weighting agent + 0.4 wt.% modified guar gum + 1.0 wt.% pH regulator + 0.5 wt.% crosslinker. Results show that the novel weighted fracturing fluid is a good choice for ultra-deep reservoir hydraulic stimulation and hence improving the recovery. 1. INTRODUCTION Advancement of exploration and drilling technologies impel the oil and gas industry to extend the depth for hydrocarbons. Achieving efficient development of deep oil and gas is an important way for China’s recent oil and gas exploration and development (Xu et al., 2022; Lei et al., 2021; Wei et al., 2021). For major high-temperature and ultra-deep reservoirs in West China, hydraulic stimulation is facing some particular challenges. For instance, where the true vertical depth is more than 6000 m, there the rock fracturing pressure is often over 100 MPa and the temperature beyond 150 °C (Zhu et al., 2021; Ma et al., 2022). The traditional fracturing fluid system is difficult to play a role in the high-temperature deep well-fracturing process, and the weighted fracturing fluid system is a potential solution for deep well fracturing stimulation. At present, the formula of the weighted fracturing fluid system is not mature enough, and the upper limit of the density that can be weighted is restricted by economic and environmental protection (Wang et al., 2019; Yang et al., 2020; Qiu et al., 2009). Meanwhile, the weighted fluid system does not possess excellent friction reduction performance and cannot meet the requirements of deeper well fracturing stimulation. Therefore, it is essential to carry out the research on a novel weighted fracturing fluid system with high density, low friction and other excellent performances.