Numerical Study on Influencing Factors of Breakdown Pressure in Perforated Horizontal Wells in the Mahu Tight Reservoir

Abstract

ABSTRACT: In this paper, a numerical method was used to study how breakdown pressure varies with different factors and how to lower the breakdown pressure in hydraulic fracturing of perforated horizontal wells in the Mahu tight reservoir. The research shows that the breakdown pressure is the lowest with a perforation angle of 0° relative to the maximum horizontal principal stress. When the perforation depth varies between 5 cm and 33 cm, the breakdown pressure decreases remarkably with depth increase. The diameter beyond 12 mm of the perforation hole has a small impact. The acid pretreatment has a significant influence on the breakdown pressure. The acid-rock reaction dissolves the minerals, significantly increasing the porosity and permeability of the rock and reducing the tensile strength of the formation so it can effectively reduce the breakdown pressure. The quality of cementing also has an impact on the breakdown pressure. High cementing quality increases the difficulty of initiation. The breakdown pressure can be lowered by reasonably optimizing parameters up to 11 MPa. 1. INTRODUCTION The Mahu Oilfield in Xinjiang, China, was discovered in 2017. It has one billion tons of reserves and contains rich oil and gas resources (Qin et al., 2023). The tight reservoirs in the Mahu depression have low porosity and permeability, with poor physical properties and undeveloped natural fractures (Zhuo et al., 2023). Due to the high breakdown pressure in hydraulic fracturing of perforated horizontal wells in the Mahu tight reservoir, significant difficulties are increased in the fracturing treatment (Zhang et al., 2023). Many scholars have investigated the influencing factors of formation breakdown pressure through theoretical, physical experiments and numerical simulation. Regarding theoretical research, Li conducted a theoretical analysis to calculate breakdown pressure for horizontal wells based on elastic mechanics and tensile strength theory (Li, 2009). Recent years have witnessed a spurt of progress in computational mechanics; numerical simulation techniques have gradually been implemented in the investigation of fracture initiation mechanisms and breakdown pressure. Li et al. used finite element numerical simulation technology to analyze the influence of perforation parameters on breakdown pressure (Li et al., 2009). Zhu et al. analyzed and predicted the factors that affect the breakdown pressure under oriented perforation conditions (Zhu et al., 2014). Jia et al. studied the effects of different perforation and acid pretreatment parameters on breakdown pressure using natural outcrops excavated from the Mahu sag through an experimental method (Jia et al., 2023). However, what are the main factors affecting the breakdown pressure and the technology that lowers the breakdown pressure under perforation conditions against the Mahu tight reservoir is still a current research hot spot and aporia.