Improvement of Lost Circulation Control While Drilling by Using Managed Pressure Drilling System

Abstract

ABSTRACT: Due to the complex lithology and geological conditions of deep and ultra-deep formations, fractured formations with narrow safety mud weight window are often encountered during drilling, which is easy to cause lost circulation and gas kick. In order to enhance the pressure bearing capacity of fractured formations, lost circulation material (LCM) is usually employed as an effective measure. However, the wellbore pressure fluctuation in conventional drilling can affect the fracture width, which makes LCM difficult to enter into the fracture, consequently, lost circulation occurs frequently. In this paper, we aim to explore the improvement of lost circulation control while drilling by adjusting the fracture width using managed pressure drilling (MPD) system. Firstly, the range of wellbore pressure fluctuations in the process of drilling operation was investigated. Then, the changes of fracture width with dynamic wellbore pressure were calculated and analyzed. Finally, the relationship between fracture width and choke pressure of the MPD system was analyzed, and the proper choke pressure was optimized to enhance the effect of lost circulation control while drilling. The results indicated that with the increase of wellbore pressure, the fracture width gradually increases, and the stronger the nonlinearity of fracture width distribution. The fracture width is highly dependent on the wellbore pressure, and the dynamic wellbore pressure will cause dynamic fracture width. The improper particle size distribution of LCM is difficult to match the dynamic fracture width in the process of lost circulation control while drilling. An appropriate stable wellbore pressure is a useful way to adjust the fracture width, which can make the LCM enter into the fracture to bridge, consequently, the lost circulation control while drilling can be improved by adjusting the fracture width using the MPD system. 1. INTRODUCTION With the development of oil and gas resources of deep and ultra-deep formations, more and more deep and ultra-deep formations with complex lithology and geological conditions will be encountered during drilling (Ma et al. 2016). Due to the deep and ultra-deep formation is generally featured by well-developed fractures, so as to the pressure bearing capacity are significantly reduced by the existing of weak fractures (Liu et al. 2020a). Consequently, the deep and ultra-deep formations usually have a narrow safety mud weight window, and even the caving pressure or pore pressure is much higher than the fracturing pressure (Chen and Ma 2014; Ma et al. 2018, 2019; Liu et al. 2019, 2020b; Zhang et al. 2021). For the drilling operation in such a fractured formation, the conventional drilling operations are prone to a series of downhole conditions and drilling problems, such as lost circulation and gas kick.