The quest for in-situ water pressure inside a hydrocarbon column

In producing hydrocarbon reservoirs, the oil-water contact (OWC) continuously shifts as field developmentprogresses, yet its exact position over time often remains uncertain. By monitoring pressure variations inboth the oil and water phases, it is possible to estimate the distance to the OWC. Pressure data from production wells typically represent the highest recorded pressure, corresponding to the oil phase, while the pressure in the water phase remains unknown. Measuring the water phase pressure requires a method that selectively accesses the water phase (i.e. water film) within the reservoir rock. This study presents laboratoryexperiments performed with a hydrophilic probe to determine in-situ water pressure in pre-drained coreplugs from Berea sandstone and Mons chalk outcrops to initial water saturations. The plugs were pre-drainedunder varying oil pressures using Isopar oil at ambient conditions. Additionally, some tests were conductedafter aging at 80oC temperature with North Sea reservoir crude oil to achieve the desired wetting conditions.The tests on pre-drained chalk and sandstone plugs demonstrate that it is possible to use the hydrophilicprobe to connect to the water film at oil overpressure of 8.0 bar. During the entire measurements, waterproduction was monitored at the outlet end indicating that the water drainage process was continuing to aneven lower water saturation while measuring the water pressure. Some of the laboratory experiments wereinterpreted using a numerical simulator to better understand the pressure and water saturation distributionduring the water pressure measurements and to identify critical variables for reliable predications for fieldscale applications. The pressure difference between oil and water provides valuable insights into the hydrocarbon column height in a newly discovered field. Detecting changes in the hydrocarbon – water pressuredifference could serve as an early warning system for water approaching in the producing well. In addition,understanding the hydrocarbon column height can accelerate the appraisal processor guide infill drilling,reducing both costs and time. This, in turn, minimizes environmental impact by decreasing the number ofwells required.