Tight heterogeneous clastic and carbonate formations present great challenges in terms of reservoir fluid characterisation and downhole fluid sampling during exploration phase. The low mobility imposed by the tight clastic formations usually prohibits conclusive formation testing and sampling using conventional wireline formation testers (WFT) with single probe. The small flow area provided by single probe typically does not allow single phase reservoir fluid withdrawal in such low mobility environment due to the high pressure drawdown. In addition, the optimisation of pressure drawdown is critical to ensure single phase and representative downhole reservoir fluid sampling within the allowed station time. On the other side, the heterogeneous nature of the carbonate pore system imposes a significant mobility range, varying from very tight to good permeability intervals. Pinnacle reef carbonates are often naturally fractured. The natural fracture system may cause fluid losses resulting in drilling and data acquisition challenges. Detailed planning and careful consideration on various testing options available is needed to address this high mobility variation and subsequently to maximise the data acquisition at minimum operation cost, time and risks.

This work presents case studies demonstrating a new WFT approach in appraising tight laminated sandstone and carbonate reservoirs in offshore Malaysia fields. An initial attempt with conventional technology did not allow to obtain any conclusive formation pressure measurement, pressure gradients, downhole reservoir fluid identification and sampling. On the other hand, the application of WFT Dual Packer offers limited pressure drawdown range and requires extended station time usually resisted by drillers. Realising the importance of these exploration wells to verify potential reserves from initial geological and petrophysical data, it became crucial to search for an alternative technology to achieve the fluid evaluation objectives in a time-effective manner.

This paper presents a new approach and methodology that was implemented and resulted in reliable reservoir rock pressure, mobility, and sampling while improving operational efficiency. As a result, it was possible to successfully evaluate the reservoirs of interest and meet study objectives.

This work will also provide a proposed best practice, workflow, and recommendations supported by field data examples.

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