scope:

FLOWS

This document is the compilation of technology and practices used by many operators drilling wells in deep water. In a number of cases, there is not a single way of performing a speciÞc operation. In some cases, several options may be listed, but in others there may be practices which are successful, but which are not listed in this document. This document is not meant to limit innovation.

In wells drilled in deep ocean waters, water ßows from shallow formations can compromise the hydraulic integrity of the tophole section. Modes of failure include: (1) poor isolation by cement resulting in casing buckling/shear; (2) pressure communication to other shallow formations causing them to be overpressured; and (3) disturbance of the seaßoor due to breakthrough of the shallow ßow to the mudline. Such damage can and has resulted in the complete loss of drilling templates containing previously cased wells. Additionally, such shallow ßow can result in changes in the state of stress in the tophole section, possibly resulting to damage to existing casings in the present or adjacent wells later in the life of the well.

Flows from these shallow formations are frequently a result of abnormally high pore pressure resulting from undercompacted and over-pressured sands caused by rapid deposition. Not all flows are the result of these naturally developed formation geo-pressures. Hydraulic communication with deeper, higher pressure formations is another cause for abnormal shallow pressures. Some of the observed shallow ßow problems have been due to destabilization of gas hydrates or induced storage during drilling and casing and cementing operations. Although minor compared to geo-pressured sands, ßows due to induced storage may still cause damage from sediment erosion or mining, breakthrough to adjacent wells and damage to the cement before it sets. These problems can worsen with each additional well when batch setting shallow casings. Although most of the discussion in this text is focused on shallow water ßow (SWF), shallow ßows can be mixtures of water, gas and formation Þnes. In most cases the concepts are similar and can be employed with minor modiÞcations, depending on the type of flow.

Flows allow production of sand and sediments resulting in hole enlargement which can increase the ßow potential and make it more difÞcult to control. The enlargement may also cause caving of formations above the flow interval. The ßow of water and formation material from these zones can result in damage to the wells including foundation failure, formation compaction, damaged casing (wear and buckling), reentry and control problems and sea ßoor craters, mounds and crevasses (OTC 11972, IADC/SPE 52780).