Challenges and Good Practices for Fluid Sampling on Wireline in Gas Condensate Reservoirs

Abstract Obtaining high-quality representative reservoir fluid samples in gas condensate reservoirs is challenging, regardless of permeability. Formation mobility and pressure overbalance limit pump-out volumes and extend station times, increasing the risk of equipment failure and differential sticking. The complexity of gas condensate phase behaviour further complicates sampling, often resulting in non-representative samples. This paper highlights the importance of utilizing innovative downhole sampling technologies to overcome these challenges and advocates for their broader implementation in gas condensate reservoir fluid sampling. A thorough overview of the challenges associated with fluid sampling in gas condensate reservoirs in varying mobilities will be carried out, including both miscible and immiscible contamination cases. These challenges include ensuring sample cleanliness, maintaining single-phase conditions, managing low pumping rates, and addressing prolonged station times that may lead to differential sticking. This will be followed by an in-depth review of recent innovations in wireline-conveyed fluid sampling technologies—such as extra-large diameter probes, dual-inlet multi-probes, and large-area focused sampling probes—is presented, along with case studies demonstrating their effectiveness in overcoming these issues. This study focuses on low- to intermediate-permeability gas condensate reservoirs, where formation mobilities range from 2 mD/cP to 84.5 mD/cP. These wells, drilled with both water-based mud (WBM) and oil-based mud (OBM) systems, present distinct sampling challenges due to differences in filtrate miscibility. Capturing representative downhole fluid samples requires achieving very low levels of mud filtrate contamination—especially with OBM, where the filtrate is miscible with liquid hydrocarbons. Older technologies, such as the standard probe, require long station times and large pump-out volumes for cleanup, increasing financial costs and operational risks. In contrast, focused sampling probes significantly reduce pump-out volume requirements. The challenges become more pronounced at lower mobilities, where sampling with standard probes result in low pumping rates and fail to capture representative samples. These flow rates are vastly improved with the deployment of new, larger-diameter probes, such as the dual-inlet multi-probe. Additionally, selective slug sampling helps minimize station times by isolating cleaner samples, particularly in cases of immiscible contamination. The implementation of these novel technologies has resulted in cleaner sample acquisition at lower mobilities, a feat previously unachievable. At higher mobilities, they have significantly reduced operation time compared to conventional methods, ultimately lowering both operational risks and financial costs for operators.