Acquire formation fluid samples and pressure measurements in a highly deviated wellbore that intersected pressure-depleted zones with increased risk of differential sticking.
Use fluid mapping while drilling to acquire reservoir-representative fluid samples and accurate pressure data to determine formation water salinity and to enhance completion and production planning.
To further develop a field offshore Malaysia, the Hess Corporation needed a complete understanding of the reservoir, particularly fluid properties. Unfortunately, no critical data was available from the existing exploration well. As a result, Hess needed to obtain formation fluid and gas samples and formation pressure measurements from three wells. Because these three wells were highly deviated and the well paths would likely intersect pressure-depleted formations, Hess was concerned about differential sticking during sampling.
Schlumberger recommended obtaining the downhole pressure and fluid samples using fluid mapping to monitor the reservoir fluid properties and cleanup process as fluid is pumped through the flowline. When the pumped fluid meets the operator’s requirements, a downlink can be sent from surface to capture the formation fluid. Multiple sample bottles can be filled at a single sampling station, and as many as 12 fluid samples can be captured in a single run.
Using fluid mapping, Hess collected 4 fluid samples, 2 gas samples, and 21 formation pressure measurements over 12 hours while also avoiding differential sticking. Downhole testing showed the samples were contaminant-free, and later lab results confirmed that the samples were representative of the reservoir. Further sampling of the asset in a second and third well was deemed unnecessary, saving Hess 3 days.
This was the first sampling operation conducted by Hess in this field. With the collected water samples, the operator gained insight into formation water salinity, which is critical to calculating water saturation and optimizing completion design and production planning. The pressure data will help the operator understand zonal connectivity within the field.
Determine capability of new sampling method to optimize sampling and formation pressure testing processes.
Use fluid mapping while drilling to obtain reservoir-representative downhole samples in a wildcat exploration well and provide in situ fluid properties in
Eni US Operating Co. wanted to optimize formation sampling and formation testing processes to save time and money in future wells. The operator conducted a field test while drilling an exploratory well in the Mississippi Canyon area of the Gulf of Mexico in Miocene turbiditic sands. The target zone was located at a water depth of about 5,800 ft with uncertain reservoir characteristics and fluid properties. A new sampling method would need to be capable of acquiring pretests, capturing clean downhole samples and fully describing reservoir pressures at a cost and time savings.
Schlumberger recommended using fluid mapping to acquire samples, analyze them in real time, and measure formation pressures from the exploratory Mississippi Canyon well. This service is added to the downhole drilling assembly and collects reservoir-representative samples while drilling. Traditionally, sampling happens about a day after drilling, which often results in contamination of the reservoir by the drilling fluid filtrate. Fluid mapping while drilling accurately delivers individual compositions from C1 to C5, C6+, GOR, fluid color, hydrocarbon and water fractions, flowline fluid resistivity, temperature and pressure and formation volume factor, CO2—all during drilling.
Fluid mapping was used to collect and analyze six samples downhole in real time, setting an industry first for the transmission of detailed in situ fluid properties. Fluid mapping estimated contamination and cleanup time; performed fluid identification and typing; and measured GOR and fluid composition (C1 to C5, C6+, and CO2).
These results were verified 10 weeks later by lab results, which showed good agreement with field results on every measure. Contamination was estimated in real time to within ±2% of the laboratory-determined values. Pretests, pressure measurements, and fluid gradients were also successfully taken during the operation. A total of 28 pretests were taken—17 while drilling and 11 while pulling out—that provided Eni a full description of the reservoir pressure and fluid gradients.
By delivering lab-quality results while drilling, Eni concluded that fluid mapping is a reliable method of gathering clean samples and good measurements while demonstrating a time savings of about 10 weeks.
Even though it is the early days of the realization of sampling while-drilling (SWD) as a service, a picture of what might be achievable in practice is beginning to emerge.
The while-drilling environment poses several potential challenges to acquiring representative formation-fluid samples; in particular, sampling times are expected to be restricted (perhaps severely) and dynamic filtration conditions are expected to predominate.