Identification of well breathing phenomena in HPHT wells and technical solutions to enhance drilling efficiency in the Nam Con Son Basin

Abstract

The Nam Con Son Basin is considered the most technically challenging area for drilling operations in Vietnam and ranks among the most complex globally. Its central region, dominated by high-temperature, high-pressure (HPHT) conditions, accounts for approximately 70÷80% of the basin’s total gas production. This area is geologically characterized by heterogeneous stratigraphy, abnormally high formation pressures and temperatures, and a narrow margin between pore pressure and fracture gradient-commonly referred to as the “narrow pressure window.” Under such conditions, even minor variations in mud weight can lead to wellbore instability or formation damage. One of the most critical drilling challenges in this environment is wellbore breathing - a transient loss and subsequent return of drilling fluid-typically observed in formations within the Miocene formation. These formations exhibit low porosity, low permeability, and elastic rock behavior, which can result in misleading well control indications, non-productive time, and potential well control incidents if not identified and managed appropriately. This study presents a novel diagnostic framework for recognizing and managing wellbore breathing in HPHT wells of the Nam Con Son Basin. It systematically evaluates operational data from recent wells using four key indicators: (i) loss circulation behavior during circulation, (ii) mud-volume return after pump stoppage, (iii) downhole pressure variations, and (iv) changes in total gas and gas-peak composition in returns. The combined indicators reliably identified early breathing onset and severity, distinguishing it from other circulation anomalies. Field validation confirmed the method’s robustness across multiple well sections. Applying the proposed framework, along with mud-weight optimization, real-time monitoring, and wellbore strengthening, reduced non-productive time and minimized well-control false alarms. These outcomes demonstrate significant practical value for improving safety, integrity, and efficiency in complex HPHT drilling environments worldwide HPHT.