Schlumberger

Technical Paper: Advanced Formation Testing and PVT Sampling in Deep Gas Condensate Reservoir: Case Study from Malaysia

Society: Other
Paper Number: 13623
Presentation Date: 2009
 

Abstract

Downhole sampling in gas condensate reservoirs is challenging because of the nature of the near-critical fluids. Fluid properties can change dramatically with slight changes in reservoir pressure and temperature. Accurate, representative PVT data are essential for reservoir fluid modeling and field-development purposes.

This paper presents the first downhole gas condensate sampling in a deep gas condensate field offshore East Malaysia. Samples collected from the previous surface tests showed large variation in condensate/gas ratio, from 50 to 200 stb/MMscf. This resulted in large uncertainty in the dewpoint pressure, condensate yield, reservoir fluid productivity, and also reservoir fluid typing, i.e. rich or lean gas condensate reservoirs. As a result, there are strong needs to acquire high-quality downhole samples to reduce these uncertainties, which may affect the entire field-development plan.

A case study illustrates several key challenges, including tools sticking because of the required minimal stationary time during cleanup. Minimizing oil-based mud contamination and controlling drawdown pressure drop in a low-mobility reservoir were also challenges. The use of new-technology wireline formation testing tools such as a focused sampling probe and in situ fluid analyzer were introduced to ensure that job objectives could be met with the limited time per station.

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