Abstract

This paper presents three examples of reservoir data collection under challenging operational conditions in carbonate and sandstone reservoirs in the Al Shaheen Field offshore Qatar. The examples demonstrate how Formation Pressure Testing and Fluid Sampling can provide early and often decisive information for field development.

Logging operations in the Al Shaheen Field are often performed in wells with horizontal sections in excess of 20,000 ft in thin, unconsolidated sandstone reservoirs. To accommodate these conditions, which are far outside the normal operating envelope of the logging tools, new procedures and techniques have been developed to address 'extended reach logging' and to mitigate potential problems with unconsolidated sand. These procedures and techniques are discussed along with the three field cases.

The first field case describes how in-situ hydrocarbon mobility was determined, and how it justified immediate continuation of an appraisal program. The second field case explains how a fluid contact in a very thin sand was confirmed by fluid sampling, and how it eliminated the need for a horizontal sidetrack. The third field case describes how determination of in-situ fluid properties improved saturation modeling and allowed real-time optimization of the data collection program.

Introduction

The Al Shaheen Field, Block 5, offshore Qatar consists of multiple carbonate and sandstone reservoirs. The reservoirs are laterally extensive, but relatively thin and consequently the field is optimally developed with long horizontal wells. Wells drilled in the sandstone reservoirs are up to 22,000 ft while wells drilled in the carbonate reservoirs exceed some 30,000 ft. Production is currently ongoing from five reservoirs, while water injection is taking place in the three main reservoirs.

In thin laterally extensive reservoirs like those present in the Al Shaheen Field, flow continuity can be affected by lateral facies variations and faulting. Detailed pore pressure information from long horizontal wells therefore provides essential data for understanding and managing reservoir dynamics.

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