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Counter-Current Spontaneous Imbibition in Different Geometries and Its Impact On Early- and Late Time Recovery Behavior
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, IOR+ 2023, Oct 2023, Volume 2023, p.1 - 19
Abstract
Solutions are investigated for counter-current spontaneous imbibition in dimensions between 1D and 3D for samples of different shape. The dimension and characteristic length of the sample are calculated based on relations with area per volume and derivative of area with respect to volume. This correctly produces linear, radial and spherical flow as special cases for symmetrical plugs, while for rectangular or cylindrical core plugs, a continuous range of dimensions are produced. This results in a novel characteristic length different from the traditional (Ma et al) as it accounts for flow conditions: imbibition into a cylinder is ∼1D if the height-to-radius ratio is small, ∼2D (radial) if the ratio is large (reproducing analytical limits) and ∼3D if the ratio is near 1.
The differential equation for counter-current imbibition in N-D is derived and investigated. The solutions are described by the same self-similar saturation profile at early times (when the imbibition front has not traveled very far). At later times the saturation profiles shape depends on distance from the inlet and the dimension. When the deviation from self-similarity at the inlet is affected by either the distance traveled by the front or the late time interaction with the closed boundary, the recovery profile will start to deviate from a stable early time behavior. During this early-time, recovery is proportional to square root of time, regardless of geometry, as long as imbibition occurs inwards. This is validated by literature and in-house experimental data with different geometry.
Deviation from self-similar behavior occurs sooner when the dimension is higher, as the imbibing saturations interact more strongly. The early time behavior can be calculated semi-analytically and permit scaling of all solutions without limiting assumptions on saturation functions. An approximate analytical solution is derived describing imbibition into the core plug as a piston-like displacement to demonstrate the effect of geometry (e.g. linear vs spherical) on recovery behavior. The impact of geometry on the advancing front and recovery profile is derived and captured in a new time scale. It is shown both generally and by the simple solution that early time recovery in N-D is N times faster than in 1-D when the system characteristic length is the same.
Counter-current experiments are among the most common multiphase experiments being performed and although the samples are rarely designed to give linear flow, they are modeled and interpreted based on mathematical descriptions assuming linear flow.