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Zonal Isolation Through Gas Hydrates Offshore Tanzania

Deepwater cementing becomes increasingly challenging as drilling operations move to greater water depths and more-remote locations. Before the first exploration well for an operator offshore Tanzania was spudded, an extensive cementing-operations risk analysis was performed. The risks determined were low temperatures at seabed, unconsolidated formations close to seabed, potential shallow gas, and likely presence of hydrates. To drill further sections successfully, objectives were identified as zonal isolation across the shallow-flow and hydrate zones, cementing back to seabed, and good cement around the casing shoe.

Introduction

Block 2 (Fig. 1) is located southeast of Tanzania’s capital, Dar es Salaam. The water depths in Block 2 vary from 1000 to 3000 m. The target is an excellent-quality sandstone gas reservoir with very large potential. The seabed consists of soft clays and silts with minor sandy intervals. Shallow hazards were identified for this block from seismic data.

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 163462, “Zonal Isolation Through Gas Hydrates Offshore Tanzania,” by J. Vølstad and T. Tveit, Statoil, and P. Aguilar, N. Hurtado, and M. Bogaerts, Schlumberger, prepared for the 2013 SPE/IADC Drilling Conference and Exhibition, Amsterdam, 5–7 March. The paper has not been peer reviewed.
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Zonal Isolation Through Gas Hydrates Offshore Tanzania

01 January 2014

Volume: 66 | Issue: 1

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