RESUMO-A técnica Pressurized Mud Cap Drilling (PMCD) tem sido muito utilizada na perfuração de poços altamente fraturados, visto que esta técnica apresenta um controle preciso frente a extremas perdas de circulação e kicks, em comparação com as técnicas convencionais. O PMCD se dá por meio da injeção de um fluido viscoso na região anular e um fluido de sacrifício na coluna de perfuração. Esta operação não possui retorno para a superfície, o que possibilitou a perfuração de poços antes inviáveis. As principais etapas do PMCD, em um poço que sofreu um kick de gás, consistem, em linhas gerais, na migração de gás com o poço fechado e posterior indução deste fluido invasor para a formação rochosa através da etapa chamada de Bullheading. O Bullheading consiste na injeção de um fluido em contracorrente, para forçar o retorno do gás invasor de volta para o reservatório. O presente trabalho tem como objetivo o estudo da operação de Bullheading durante o uso da técnica PMCD, apresentando resultados de simulação e validação através de experimentos.

Drilling highly fractured formations, typically fractured carbonates, often experiences kick problems and severe losses of circulation, resulting in a high nonproductive time (NPT). Pressurized mud cap drilling (PMCD) is the most appropriate methodology for such scenarios, being performed by injecting a sacrificial fluid into the annulus, without fluid return to the surface. When a gas kick is detected, the bullheading operation is executed in order to force gas and cuttings back into the formation, also reducing annulus pressure and sealing fractures. However, for a successful operation, the flow rate must be properly selected in order to push gas back into the formation, without causing well damage. The present work aims to solve a nonlinear constrained optimization problem using SQP (Sequential Quadratic Programming) during bullheading operation, ensuring the successful use of the PMCD technique. Simulation studies were carried out and validation tests were performed by employing an experimental facility, which depicts the main characteristics of the oil well drilling process. As a result, the methodology developed is able to provide proper bullheading flow in order to assure safe operation and effective minimization of annulus gas content for carbonate reservoirs, the majority of world oil reserves, characterized as a drilling challenge due to its complexity and heterogeneity nature and where implementing PMCD is the only safe mode of operation. KeywordsSQP • Kick • Drilling • Fracture • Mud loss List of symbols A Flow area (m 2 ) l Volume fraction of liquid phase (Dimensionless) g Volume fraction of gas phase (Dimensionless) l Density of liquid phase (kg/m 3 ) g * Márcia Peixoto Vega