Directional/complex wells

Nigerian Case Study Explores Drilling Through Shales Below Depleted Sands

This paper presents the mitigation of drilling challenges encountered in the Niger Delta through a technique that relates shale resistivity to shale porosity and vertical effective stress to predict pore pressure.

Lagos Nigeria Oil Rig
Source: Karo Kes/Getty Images/iStockphoto.

Choosing the right casing depth is a key step in executing high-pressure/high-temperature (HP/HT) wells in the geologically complex Niger Delta. In the wells of Astra East Field, a casing shoe was set in a homogeneous shale of approximately 200 ft vertical thickness located between overlying heavily depleted sand and underlying overpressured sand. The question remained, however, as to what depth the casing shoe should be set to minimize the risk of kicks or wellbore instability and losses. To address this issue, wireline log data and drilling observations from other wells in the same field were analyzed and evaluated.


The Astra East field was planned to provide feedstock gas.

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