Abstract

Shallow water flow (SWF) represents a costly drilling challenge in deep water. Establishing the differential pressure between the sand and the shale beds is the main objective. This is because most of the SWFs take place while penetrating the shale-sand boundaries. During compaction, sand's formation water influxes rapidly upward, whereas shale's dewatering is very sluggish. The differential pressure (ΔP) value ranges from 670 psi (1.2 ppg) to 50 psi (0.2 ppg) at variable depths. All ΔP's show high values at depth between 1000 ft and 3000 ft below mudline at any water depth, which is where most SWF takes place. ΔP noticeably increases near the mudline at greater water depth and can be the reason for the occasional conductor and wellhead sinking in the extra-deep water. Choosing correct mud-up values (ΔP) at depth is essential to combat SWF and avoid loss of circulation. The safe mud weight is calculated at different water depth and below the mudline depth. Algorithm and tabulations are systematically presented. Case histories from the Gulf of Mexico, where the upper Pleistocene-recent depositional fan was and is still active, are utilized.

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