In-Situ Fluid Sampling Technologies for Ultra-Deepwater and Ultra-Shallow Reservoirs

During wireline formation testing and sampling in ultra-deepwater and ultra-shallow weakly consolidated reservoirs, problems such as sand plugging, setting failure, and even borehole wall collapse are prone to occur, severely constraining fluid sample acquisition and fine reservoir evaluation. To address the problems of weak consolidation and fine grain size in the Lingshui 36-1 Block of the South China Sea, core grain-size analysis and sand-production mechanism studies were conducted. An in-situ fluid sampling technology system centered on “active sand control and precise pressure control” was established. The critical sand-production pressure-difference threshold was determined to be 0.345 MPa. An ultra-low-speed constant-flow pump with a minimum flow rate of 0.2 mL/s was developed, enabling fine sand grains to be produced without plugging. Through adaptive modifications of the instrument probe and key modules, along with optimization of precise pressure difference control procedures and operational parameters, the applicable mobility lower limit was extended to 1 mD/(mPa·s). The technology system was applied 55 times in more than 15 wells in the Lingshui 36-1 Block, achieving a 100% operational success rate and significantly improving the success rate of ultra-shallow sampling. The developed sand-control sampling technology for weakly consolidated formations can be extended to other sand-prone reservoirs such as heavy oil reservoirs.