Addressing Multiple Challenges of Drilling Performance Improvement in HPHT Wells

Abstract

With the continuous growth in demand for oil and gas resources in China, conventional reservoirs can no longer meet developmental needs. Consequently, an increasing number of high-temperature high-pressure (HTHP) formations are being explored and developed. HTHP formations are characterized by high temperatures (typically >150°C), high in-situ stresses, and potential overpressure in localized areas, resulting in a narrow safe mud weight window. During drilling operations in HTHP formations, significant temperature fluctuations at the wellbore surrounding rock occur due to circulating drilling fluids. These temperature changes substantially impact the collapse pressure and fracture pressure of the wellbore, making wellbore instability highly likely. Therefore, quantitative risk assessment of wellbore instability is particularly critical during HTHP drilling. Previous temperature-dependent models for calculating collapse pressure and fracture pressure were relatively simplistic and primarily designed for vertical wells, limiting their accuracy in evaluating wellbore instability risks across different HTHP well types. To address this, this study builds upon traditional collapse and fracture pressure calculation models. It investigates and categorizes different collapse and fracture modes, establishing corresponding temperature-dependent calculation models for collapse pressure and fracture pressure applicable to various well types under these different modes. Based on this foundation, a quantitative risk evaluation model for wellbore instability under different modes is developed. Furthermore, a quantitative analysis and evaluation of wellbore instability risk patterns under various influencing factors are conducted.