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PIONEERING APPLICATION OF EMERGING TECHNOLOGIES TO THE CHALLENGE OF SAMPLING NEAR-SATURATED FLUIDS IN TIGHT RESERVOIRS

Openhole oil sampling in the tight Middle Cretaceous reservoirs of Alaska can be challenging due to the proximity of the reservoir pressure to the fluid’s saturation pressure. Existing focused probe technologies commonly used in other conditions have limited application in these conditions because their small flow area means slow pumping rates, high drawdowns, and nonrepresentative fluid samples. Nonfocused inlets, such as 3D radial probes and straddle packers, are mostly used to sample in these reservoirs, but deep invasion and slow pumping rates mean using these alternatives leads to long station times. A new wireline formation testing platform has been field tested in three wells since 2018. The objectives included the evaluation of the platform’s abilities to pump at controlled speeds to keep flowing pressures always above the fluid’s expected saturation pressures. A new inlet was tested for focused sampling and higher flow rates with the intention of cutting operating time and improving sample quality. Also, increased sample container capacity enabled the collection of required sample volumes in fewer bottles, which resulted in a shorter and lighter sampling string configuration. A legacy pressure tool was added to the bottom of the new platform for pressure testing benchmarking. During the operation, the tool was positioned at target depth, and an automated routine inflated the inlet assembly to contact the formation. This automation cycle enables the tool to be ready for pumping in less than 15 minutes. In contrast, technologies used in previous operations required 30 to 45 minutes setup time before fluid cleanup could commence. Fluids were then flowed through the tool’s sample and guard lines with a sequence of commingling and focused pumping periods using two simultaneous pumps while assessing fluid quality with a downhole fluid analyzer. Strict control of the 1-cm3/s selected rate for both pumps provided fast cleanup in focused mode with less than 100-psi drawdown. This has never been achieved before in these reservoirs. First hydrocarbon breakthrough was observed less than an hour into the pumping period. Previous operations reported 4 hours or more for first hydrocarbon breakthrough. Three stations were performed, and 10 single-phase samples were collected in as many bottles. Thin-bedded interval testing was possible given the ability of the new platform to collect samples with either the sample or guard lines. Total operating time to complete the program was 30 hours. Comparison with data from similar operations in previous campaigns shows a decrease of 50% in operating time, faster rig- up and rig-down, and decreased cable tension. These latter two aspects add to operational efficiency and mitigation of risks. This case study summarizes several pioneering aspects of the new generation of wireline formation testing platforms. It was the first time a combination of the new and legacy technology was deployed and the first time that high-volume multiphase sample bottles were used during a field test. It was also one of the first applications of this new technology in North America.