Effects of Fluid Confinement on Poor Quality Cemented Wellbores through Salt Formations
DANIEL DUQUE ESTRADA FERNANDES DE MELO MELO1; SERGIO AUGUSTO BARRETO FONTOURA1; JUAN DAVID VELLILA URIBE1; NELSON INOUE1; JOREL LOPES RODRIGUES ANJOS2
1 PUC-RIO; 2 PETROBRAS
Resumo
Wells drilled through salt formations are a big challenge in oil industry. Due to Salt time dependent behavior, loads can significantly modify during long term production. In deep wells, high temperatures and high pressure lead to great deformations on annular volume due to well closure. In the annular above cemented region, uniform loads on casing are expected. In the cemented region, its quality must has a major role on wellbore integrity though. As reported in literature, the presence on non-uniform loads can significantly reduce critical pressure of the pipe. Thus, if cement present any fault, non-uniform loads can be enough to reach casing collapse pressure, leading to casing failure that may result in the loss of the well. Thus, to evaluate effects of cement quality on casing failure, two scenarios must be considered: 1) Trapped cement defect, where drilling mud is confined and no fluid scape to the rest of the annular; and 2) Cement fault connected to the whole annular, where fluid can migrate to annular above top of cement. The present study consist on a parametric finite element analysis of critical defects on cemented annulars based on a plane strain analysis. For the simulation, both fluid compressibility and thermal expansion are computed with the use of fluid elements. In the model with connected cement fault, a fluid pressure is determined based on its density and the annular volume deformation of Salt zone above top of cement. For the confined cement defect, pressure increase is only determined based on casing and salt deformation over the defect volume. Then, a parametric study of critical defect was conducted for spans from 5% to 50%. Results show that the span of cement fault on connected annular has a significant impact on casing failure. For defects lower than 15%, casing stresses do not vary much. As defects increase, non-uniformity of load lead to significant casing deformation, especially when the defects are connected to the annular above. If cement faults are confined, the fluid compli
Palavras-chave: ANNULAR PRESSURE; CEMENT QUALITY; CASING INTEGRITY