document preview

Abstract

Taking drilling beyond the continental shelves further into the great depths of water leaves the drilling industry with no option of avoiding reservoirs lying beneath great masses of salt formations. Presently, salt formations trap rich reservoirs in Brazil, West Africa, Gulf of Mexico, North Sea and off the coasts of eastern Canada. The discovery of producible reserves beneath vast, thick sheets of salt formations challenges the regular drilling and completion practices, making every operation a unique experience. Drilling through salt formations can become successful only when the essential properties of salt formations (e.g. halites) that may cause instability are clearly understood.

Instabilities in salt formations arise from the ability of the salt to flow under loading conditions (creep) and the ability to dissolve at certain conditions and elevated temperatures (solubility). This paper presents the checklist of essential contributing properties that must be accounted for in modeling creep- and solubility-induced instabilities in salt formations. These properties are classified under the physical, mechanical and structural sub-headings, and the values of these properties for deepwater subsalt formations are provided for use in creep and solubility predictive models. This paper is based on well design approach i.e. begin  the planning from the depth of location of the salt formation, that is, the salt formation becomes the starting point, working backwards to the surface and forward to the target reservoir. Temperature response, melting point, solubility, thermal conductivity, octahedral shear stress, solubility, creep, anisotropy, density, friction, hardness, strength,  fracture gradient, permeability are some of the properties analyzed in this paper and their influencing parameters in order to develop an all-encompassing model for used in drilling through alt formations.

In addition, this paper examines the application of the essential properties to the geo-mechanical studies of salt formations. The case study of this research is the design of an exploratory well in the Gulf of Mexico where properties of the salt formations: crystal structures, salt dissolution, creep, temperature and pressure response determined the drilling fluid composition, cement slurry, and casing design.