ÇAĞRILI KONUŞMALAR / KEYNOTES Invited Speeches ... - TPJD

Ultra-Deep Offshore Well Casing Design Process
Burak Kayael
Turkish Petroleum Corporation, Drilling Department, Ankara
Drilling an ultra-deep water well is one of the most challenging tasks that an Exploration and
Production Company can undertake. Not only are there technical, logistical and environmental
issues, but the high operating costs makes every aspect of the well planning and execution
process critical. As in any other well delivery process, the casing design is one of the most
important deliverables as this will affect the lead time for procuring equipment, the most likely
time estimate for drilling the well and finally the cost. The first step of casing design involves
coming up with a robust conductor design as this is the main support structure for the well.
Detailed bending studies should be carried out because it will carry hundreds of thousands of
pounds. Secondly any possible shallow flow (shallow water and gas flow) should be considered
which needs to be isolated by an additional casing string. Once initial studies are done for first
two sections, rest of the well design will be mainly limited by pressure gradients (PP and FG).
As rule of thumb in a hole section the pore pressure at section TD should not exceed last casing
shoe’s fracture gradient. If this happens mud losses will occur which could become a costly event
and lead to an influx or kick. To eliminate this risk a detailed PPFG study should be carried out by
geological and geophysical experts, because this study will be the guide for planning engineers
to make casing design. As nature of offshore environment, the higher the water column the
slower the overburden gradient increases as depth increases. This will directly affect the fracture
gradient and make it increase slowly also. In case of having any pressure ramp at pore pressure
the gap between PP and FG will decrease significantly which will cause more casing or liner
strings to be run. In Black Sea region the most complicated casing design up to now had 8 (eight)
casing strings starting with 36” conductor and ending with a 7” production liner. The number of
strings to be run is affected by geological properties of lithologies, pressure profile of the well
and technical limitations. These factors should be examined in detail to make the casing design
effective and suitable for well conditions.
Keywords: Casing Design, Black Sea, Pore Pressure, Fracture Gradient
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