The enhancement of performance and imbibition effect of slickwater-based fracturing fluid by using MoS2 nanosheets

Abstract

Slickwater-based fracturing fluid has recently garnered significant attention as the major fluid for volumetric fracturing; however, lots of challenges and limitations such as low viscosity, poor salt tolerance, and possible formation damage hinder the application of the conventional simple slickwater-based fracturing fluid. In addition, nanomaterials have proven to be potential solutions or improvements to a number of challenges associated with the slickwater. In this paper, molybdenum disulfide (MoS2) nanosheets were chemically synthesized by hydrothermal method and applied to improve the performance of conventional slickwater-based fracturing fluid. Firstly, the microstructure characteristics and crystal type of the MoS2 nanosheets were analyzed by SEM, EDS, TEM, XPS, and Raman spectroscopy techniques. Then, a series of evaluation experiments were carried out to compare the performance of MoS2 nanosheet-modified slickwater with the conventional slickwater, including rheology, drag reduction, and sand suspension. Finally, the enhanced imbibition capacity and potential mechanism of the nanosheet-modified slickwater were systematically investigated. The results showed that the self-synthesized MoS2 nanosheets displayed a distinct ultrathin flake-like morphology and a lateral size in the range of tens of nanometers. In the nano-composites, each MoS2 nanosheet plays the role of cross-linking point, so as to make the spatial structure of the entire system more compact. Moreover, nanosheet-modified slickwater demonstrates more excellent properties in rheology, drag reduction, and sand suspension. The nanosheet-modified slickwater has a higher apparent viscosity after shearing 120 min under 90 °C and 170 s−1. The maximum drag reduction rate achieved 76.3% at 20 °C, and the sand settling time of proppants with different mesh in the nano-composites was prolonged. Spontaneous imbibition experiments showed that the gel-breaking fluid of nanosheet-modified slickwater exhibited excellent capability of oil-detaching, and increase the oil recovery to ∼35.43%. By observing and analyzing the interfacial behavior of MoS2 nanosheets under stimulated reservoir conditions, it was found that the presence of an interfacial tension gradient and the formation of a climbing film may play an essential role in the spontaneous imbibition mechanism. This work innovatively uses two-dimensional MoS2 nanosheets to modify regular slickwater and confirms the feasibility of flake-like nanomaterials to improve the performance of slickwater. The study also reveals the underlying mechanism of enhanced imbibition efficiency of the nano-composites.