InterPore2025

Interpretation of an Interwell Partitioning Tracer Test in a Multi-layer Carbonate Reservoir

21 May 2025, 12:50

15m

Oral Presentation (MS06-A) Physics of multiphase flow in diverse porous media MS06-A

Speaker

Samuel Fontalvo (King Abdullah University of Science & Technology)

Description

Interwell Partitioning Tracer Test (IPTT) estimates remaining oil for economic evaluation of reservoir operations. It involves waterflooding and co-injection of two chemicals: one that is water-soluble (conservative) and another that also partitions into the oil phase. The downstream concentration of injected chemicals yields concentration history (CH). Cooke's interpretation of CH estimates remaining oil from tracer arrival times. Complex reservoirs need extra interpretation effort. This study reanalyzes IPTT data from a giant Saudi Arabian reservoir, as published by Sanni et al. (2016).

We introduce the following complexities of an oil reservoir: multi-layer structure, mass-transfer resistances, and stagnant zones. We combine them in a physically reasonable way to capture the first-order effects.
We use the well-known advection-dispersion equation (ADE) with extra terms for each of the complexities. Partitioning tracer transport is modeled with an ADE and mass-transfer resistance to the stagnant oil phase in each layer. The oil phase is continuous and allows for partitioning tracer communication between the layers. The conservative tracer follows classic ADE in both layers. The system of differential equations is solved numerically with COMSOL.

Remaining oil saturation presented in Sanni et al. (2016) was $\sim$ 0.2, while missing half of the partitioning tracer mass. The model shows a good fit of partitioning tracer at early times, and notably lower quality fit at late times. This result was obtained using a non-mass conservative analytic solution fitted to the data independently for conservative and partitioning tracers thus ignoring continuity of physical properties of the formation.
Conversely, our model preserves such continuity by fitting only one dual-layer mass-conservative model with partitioning tracer transport between the layers. Consequently, our model accounts for all recovered mass for both conservative and partitioning tracers. The oil saturation obtained by our model is 0.17 in the first layer and 0.2 in the second layer. The saturation in the two layers indicates microscopically trapped oil that reached residual saturation. While the oil saturation in two layers is similar to the original result, the existence of an extra oil rich layer explains the late time data much better than the original model. Figure 1 shows the breakthrough curves with the IPTT data, the original report model (blue dotted line), and our proposed model (blue dashed line), both for partitioning tracer.

For the first time, we interpret IPTT data for a multi-layer reservoir with stagnant zones, inter-layer oil communication, and slow partitioning tracer diffusion in oil phase. Our analysis reveals hydrocarbons in a second layer, missed in the original report. This study demonstrates proper physics-based test interpretation and provides guidance on essential data collection to improve IPTT analyses.