Wireline formation fluid sampling in weakly consolidated, heavy oil reservoirs has been unsuccessful in appraisal wells in the Bohai Bay area, offshore China. Poor sampling and prolonged testing time were unacceptable from both operational and formation characterization points of view. The challenges involved the production of solids during fluid sampling, contamination as well as poor and unreliable pressure testing.

An integrated study was conducted to build a fit-for-purpose geomechanical model for the study field using drilling data, well logs, formation and drill stem testing data and sanding observations in several offset wells. An analytical sanding evaluation methodologywas used and calibrated with the observed sand production in the study wells. The calibrated model was then used in a near-real time basis for new wells to optimize the sampling depth points and drawdown pressures to avoid sanding while sampling and also to speed up the sampling time to reduce operation time and costs. The aim was to use higher drawdowns and faster testing while also avoiding intervals where sand-free drawdown may not be possible.

Using the workflow in new wells has resulted in sand-free sampling at higher drawdownsas well as faster sampling speeds. In contrast, in wells where the rock mechanical aspects of fluid sampling and the root cause of sanding while sampling were not incorporated into the logging and formation testing operations, the sampling failed again due to sanding issues despite the moderate drawdown and slower sampling rate.

Real-time integrated geomechanical and formation evaluation analysisresulted in delivering sand-free fluid samples, saving 30% rig time, and more successful and reliable pressure and fluid sampling for accurate reservoir and fluid characterization.

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