--> Pressure Testing while Drilling in Unconsolidated Sediments Offshore Angola, by Francois Rodot, Enrique Chiapello, Fabrice Cantin, Matthias Meister, Roland Chemali, Joerg Markwart, and Emmanuel Penna; #90037 (2005)

Datapages, Inc.Print this page

Pressure Testing while Drilling in Unconsolidated Sediments Offshore Angola

Francois Rodot1, Enrique Chiapello1, Fabrice Cantin1, Matthias Meister2, Roland Chemali3, Joerg Markwart2, and Emmanuel Penna1
1 Total E&P Angola, Luanda, Angola
2 Baker Hugues Inteq, Germany
3 Baker Hughes INTEQ, Houston, TX

Formation pressure and near well bore mobility are key parameters for reservoir description. This data has been acquired with wireline formation testers upon reaching section or well TD. In high angle deepwater wells, this is a time-consuming operation, as the tools have to be conveyed by drill-pipe. It has now become possible to acquire formation pressure and mobility data during short breaks in the drilling process. Apart from the traditional applications of such data for gradient and fluid contact determination, real-time knowledge of pore pressure can also be used to dynamically optimize the drilling process, assess reservoir connectivity, optimize casing plans, and help in geosteering.

Two of the greatest challenges facing wireline formation pressure testing are large variations in pressure and mobility in a given interval and achieving reliable measurements in soft, unconsolidated formations. An additional challenge confronting formation pressure while drilling tools is the limited bandwidth of mud pulse telemetry, which severely restricts user interaction from the surface. This issue has been addressed by incorporating a sophisticated logic based on Formation Rate Analysis, which allows this LWD tool to actively analyze and "learn" from pressure drawdown and build-up data to perform further drawdown experiments in the most time-efficient manner for formation pressure and mobility verification.

The paper will present the design and operation of a new formation pressure while drilling tool and review the successful application of this tool in the unconsolidated, high permeability sandstones encountered off-shore West Africa. A detailed review of the pressure drawdown and build-up profiles will allow an assessment of the "self-learning" process crucial to successful and time-efficient pressure testing while drilling.