EFFECTS OF MUD COMPRESSIBILITY ON WELLBORE CLOSURE AND ANNULAR PRESSURE BASED ON FEM WITH THE INCORPORATION OF FLUID ELEMENTS
D. D. E. F. Melo1; Sergio Augusto Barreto da Fontoura1; Nelson Inoue1; J. D. V. Uribe1; J. L. R. Anjos1
1 GTEP PUC-Rio, Rio de Janeiro
doi:10.20906/CPS/CILAMCE2015-0897
Resumo
In recent years, a significant number of sub-salt reservoirs have been discovered. As a result, wells are required to be drilled through salt layers, which can be thicker than 2000 meter. Salt time-dependent behavior can present a high/slow mobility rate, which may lead to major drilling problems. To predict wellbore effective diameter, Finite Element Analyses (FEA) are commonly used. Generally, FEA estimates the radial displacement based on constant mud pressure described as a distributed load on wellbore surface. Although it is a good approximation for the drilling phase, it can underestimate displacements in confined annular after casing set up. With the incorporation of fluid elements, the present work shows the impact of mud compressibility on the wellbore radial displacement. Based on parametric FEA for different mud compressibility, a significant displacement reduction was observed with the increase of fluid bulk modulus. For nearly incompressible fluids in trapped annulus, radial closure is significantly smaller. Furthermore, it is shown that the incorporation of fluid elements lead to displacement errors on order of 60% on deeper depths. From the results of two salt layers (1000 meters and 2000 meters), minimum casing internal pressure was calculated based on mud weight and annular pressure build-up due to salt creep.
Palavras-chave: Sub-salt reservoirs