Abstract
In the past few years, oil companies have ventured more frequently into deepwater areas in the search for hydrocarbons. This trend is likely to continue, or even accelerate, in the next few years and, if anything, we are likely to see ever-greater water depths.
There are several aspects of deepwater wells that make them particularly challenging, from an engineering perspective, through all phases of the process – construction, production, intervention and abandonment. This paper, however, focuses on the issues surrounding deepwater well cementing, primarily during the well construction phase.
This has been an area of intense interest in recent years, due to industry realisation that the deepwater environment had one or two surprises for drillers. Most notable amongst these is the problem of shallow water flows that can easily wash out the weak, unconsolidated sediments, resulting in seabed subsidence and loss of the hole. Other issues include the presence of shallow gas and gas hydrates, strong subsea currents and extremely low fracture gradients, with the ever-present risk of lost circulation or wellbore collapse. The low seabed temperature, which can be below freezing, also depresses the normal geothermal gradient to a variable depth, depending on the thermal properties of the strata.
None of this is good news for cement, which is required to have short thickening time, rapid development of mechanical properties, a fast liquid:solid transition and low permeability to provide casing support, cope with the risk of influx and provide a long term hydraulic seal, amongst other things. This has driven the development and marketing of a host of proprietary cementing systems that claim to address some, or all, of these problems.
This paper reviews the deepwater cementing issues, in detail, and examines the physical and mechanical properties of various cement systems to assess which parameters are truly critical to success. It combines laboratory data with field case histories and working practices in several parts of the world, to help engineers decide on the best formulations for cementing deepwater wells.
