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Technical Paper: Comprehensive Workflow for Wireline Fluid Sampling in an Unconsolidated Formations Utilizing New Large Volume Sampling Equipment

Society: Other
Paper Number: WHOC11-343
Presentation Date: 2011
 

Abstract

Wireline formation testers (WFT) are well established in the industry, with many applications ranging from pressure profiling and PVT sampling to interval pressure transient testing and stress testing. This paper outlines how the latest WFT technologies are used to address key sampling limitations: acquiring PVT and especially large volume samples in the wells drilled with oil based mud (OBM) in unconsolidated formations. Such samples are very critical for flow assurance studies and production facilities design. While sampling from unconsolidated reservoirs, small solid sand particles can be produced from the formation. Depending on the pressure drawdown and level of the rock weakness, such sand production can lead to tool plugging before representative samples are taken. Cleaning action is then required which is time-consuming and results in interrupted flow periods. This makes filtrate clean up very difficult and it is particularly disruptive for large volume sampling. Technology developments used to address this problem include slow rate pumps, focused and large area probes and filters. New large volume sample chambers have also been developed. Successful utilization of these technologies, particularly in unconsolidated formation requires a comprehensive workflow. This paper describes such a workflow including an example of sampling in highly unconsolidated sand, saturated with biodegraded fluid. Several PVT sampling stations were required. Conventional well-testing was not planned, so about 70 liters of low contaminated oil were needed for various fluid studies. To obtain such a sample in an OBM well a long and uninterrupted flow period is needed. The first WFT configuration attempted included an ultra slow pump for PVT sampling. One of the acquired PVT samples was used for the on-site filtrate contamination analysis. This analysis helped to design the next run, which resulted in the first successful large volume sampling in OBM environment with the new WFT chambers.

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