Wellbore Stability Analysis for Post- and Pre-salt Drilling in Brazil´s Campos Basin
Research output: Research › Master's Thesis
Wintershall has the intention to develop fields in the Maromba area of the Campos basin, which are part of the BC-20A concession. Petrobras, the national oil and gas company of Brazil, is operator with 70% interest of this concession, divesting 30-35% of their interest. Brazil´s Campos basin is one of the most challenging basins to develop. Close pore to fracture gradients, salt and pre-salt drilling, poor hole cleaning as well as high differential stresses are only some issues, which require not only high development cost, but also well-founded knowledge and innovative technology to bring the wells on stream. The thesis will cover the wellbore stability analysis, in particular of the Maromba area 100 km apart from Cabo Frio and the deep water area of the Campos basin. Data from four different exploration wells have been evaluated. Those wells were drilled in the shallow water of the Santos basin and the deep water of the Campos and Espírito Santo basin. The Santos and the Espírito Santo basin are attached to the Campos basin and located southwest and northwest of it. Beside the analyses of the wellbore stability problems, the pore and fracture pressures as well as the stratigraphic columns are elaborated. Based on the acquired data, recommendations concerning the drilling fluids, casing setting depths, drilling times as well as wellbore instability indicators are made to prevent problems and associated costs. Raising the mud weight is one of the main statements of the read literature to solve wellbore stability problems. However, some of the conclusions move away from this well practiced and industry wide recommended method. Nevertheless, only potential wellbore instabilities could be assumed. For more precise predictions of the wellbore instabilities series of laboratory tests with rock and fluid samples need to be done. Those tests should include stress checks, rock-fluid interaction and the mineralogical composition of all different formations. Moreover, core analyses and logging information of the formations would be of particular importance. Thus, bedding directions, local stress regimes, wellbore behaviors and inhomogeneities could be identified over a long sequence.