The mud filtrate has been always a challenge during formation fluid sampling and this challenge becomes aggravated when drilling in formations with different pressures as mud weight has to be adjusted to the higher pressure. In this case, the formation with low pressure gets exposed to high overbalance pressure and invasion will penetrate deeper and deeper overtime making cleanup during formation fluid sampling longer. This paper will illustrate the impact of mud filtrate on the formation based on a case history and how the technique of formation fluid sampling while drilling improves the process.

This paper discusses a real example for Formation Sampling While Drilling (FSWD). Two samples were collected at the same depth, but with different elapsed time since drilling in order to the evaluate cleanup process. The result showed a significant reduction of pumping time when the sample was collected right after drilling the section. Also, the purity of the samples was improved with shorter pumping time. The result showed that there is a time window for sampling shortly after drilling followed by a critical time of mud filtrate invasion in the formation which made the sampling more difficult.

Formation sampling while drilling (FSWD) was introduced to the industry with the capability to collect samples while drilling which brings a great economic value by saving rig time in reducing pumping hours during formation fluid sampling, and eliminating wireline runs for formation fluid sampling after total depth has been reached. A previous study has discussed this advantage based on theory and simulated model that predict invasion as a function of time, overbalance pressure and other factors. This paper adheres to the idea of fluid sampling shortly after drilling significantly reduces the process of sampling.

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