Non-Darcy flow in oil accumulation (oil displacing water) and relative permeability and oil saturation characteristics of low-permeability sandstones

Abstract

Hydrocarbon resources in low-permeability sandstones are very abundant and are extensively distributed. Low-permeability reservoirs show several unique characteristics, including lack of a defi nite trap boundary or caprock, limited buoyancy effect, complex oil-gas-water distribution, without obvious oil-gas-water interfaces, and relatively low oil (gas) saturation. Based on the simulation experiments of oil accumulation in low-permeability sandstone (oil displacing water), we study the migration and accumulation characteristics of non-Darcy oil flow, and discuss the values and influencing factors of relative permeability which is a key parameter characterizing oil migration and accumulation in low-permeability sandstone. The results indicate that: 1) Oil migration (oil displacing water) in lowpermeability sandstone shows non-Darcy percolation characteristics, and there is a threshold pressure gradient during oil migration and accumulation, which has a good negative correlation with permeability and apparent fluidity; 2) With decrease of permeability and apparent fluidity and increase of fluid viscosity, the percolation curve is closer to the pressure gradient axis and the threshold pressure gradient increases. When the apparent fl uidity is more than 1.0, the percolation curve shows modifi ed Darcy fl ow characteristics, while when the apparent fluidity is less than 1.0, the percolation curve is a "concaveup" non-Darcy percolation curve; 3) Oil-water two-phase relative permeability is affected by core permeability, fluid viscosity, apparent fluidity, and injection drive force; 4) The oil saturation of lowpermeability sandstone reservoirs is mostly within 35%-60%, and the oil saturation also has a good positive correlation with the permeability and apparent fl uidity.

Report on Hydrologic Flow in Low-Permeability Media

“…This may imply the existence of a universal relationship between I and permeability, although some degree of fluctuation exists in Figure 2. Similar power-law relationships have also been reported in the literature of petroleum engineering (e.g., Zeng et al, 2010). Note that for unsaturated flow, k in Eq.…”

“…They argued that this is because increased temperature may weaken the bounding between water molecules and the clay surface. Recently, Zeng et al (2010) also reported an experimental investigation into temperature impact on oil flow processes in initially watersaturated low-permeability sandstone samples. They performed tests at two temperatures (70 o C and 90 o C) and found that observed threshold pressure gradient, in terms of oil mobility (or the ratio of permeability to temperature-dependent oil viscosity), does not depend on temperature.…”

“…However, their results are consistent with the argument of Miller and Low (1963) in that the weakened liquid-solid interaction should correspond to a low effective viscosity. Thus, as a first step, we hypothesize that the finding of Zeng et al (2010) can be applied to water flow in clay materials.…”

Waterflooding Huff-n-puff in Tight Oil Cores Using Online Nuclear Magnetic Resonance

“…Because of the very low permeability and non-Darcy flow in tight oil reservoirs [5][6][7], a starting pressure gradient exists during waterflooding development, which leads to difficulties during injection, a rapid production decline [8][9][10], and insufficient formation energy challenges [11]. The development of tight oil reservoirs has mainly focused on the combination of horizontal wells and volume fracturing [12][13][14].…”

“…Because of a lower fluid content inside the tight oil core, the experimental results of the common huff-n-puff in cores have large measurement errors that are influenced by the change in the external temperature [5]. During the huff-n-puff process, the distribution of fluid in different pores inside the core cannot be obtained in time.…”