Abstract
The drilling fluid loss or lost circulation via fractures is one of the critical engineering problems in the development of deep oil and gas resources. The conventional treatment is to introduce granular lost circulation material (LCM) into the drilling fluid system to plug fractures. In this work, a method incorporating the fracture surface scanning technique and coupled Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) numerical simulation is proposed for the first time to investigate how the LCM particles plug rough fractures. The rough fracture model is built utilizing a high resolution and high precision measurement system. The LCM particle transport and plugging process in rough fractures are captured in the CFD-DEM numerical simulations. The results show that the local fracture aperture has a significant influence on LCM particle transport and the distribution of the plugging zone. The drilling fluid loss rate will decrease, and the drilling fluid pressure will redistribute during the accumulation of LCM particles in the fracture. The fracture plugging efficiency of nonspherical LCM is improved as a result of formation of multi-particle bridges. This study provides a novel approach and important theoretical guidance to the investigation of LCM particle transport in rough fractures.
Highlights
For the further exploitation of deep underground natural energy, such as geothermal energy and natural gas, massive drillings have been conducted
The purpose of this work is to disclose the potential of fracture surface scanning and Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) simulation to investigate the transport of lost circulation material (LCM) in rough fractures
The CFD-DEM numerical simulation can capture the LCM particle transport and plugging process in a rough fracture. It demonstrates the change of drilling fluid loss rate and drilling fluid pressure redistribution in the fracture with the injection of LCM particles
Summary
For the further exploitation of deep underground natural energy, such as geothermal energy and natural gas, massive drillings have been conducted. The drilling fluid balances the pressure between the borehole and the formation and cleans the borehole. Drilling fluid loss or lost circulation via fracture is a critical problem in drilling (Figure 1a), as it increases non-productive drilling time and risks, which leads to additional problems such as reservoir damage [1]. In the Gulf of Mexico, the lost circulation problem has given rise to an expenditure of an additional 1 billion dollars each year, and 10–20% of the total cost of drilling high-temperature and high-pressure wells has been expended on drilling fluid losses according to the U.S Department of Energy [2]. The most common treatment for this problem is to introduce granular lost circulation material (LCM) into the drilling fluid system to plug fractures. It is especially important to, based on an in-depth understanding of how the LCM plug the fracture, design and select an effective LCM formula to save drilling cost and improve drilling safety
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