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Description
Previous studies on movable fluid saturation have primarily used centrifugal experiments combined with nuclear magnetic resonance (NMR) to characterize sandstone samples. However, this method only provides the overall saturation of the movable fluid, failing to reflect the distribution of the fluid within specific pores and throats, thereby hindering detailed reservoir evaluation. This limitation has long hindered deeper research in this field. To address this technical gap, this study developed an integrated multi-method framework combining experimental measurements, statistical analysis, and mathematical computation to precisely quantify movable fluid saturation in different pore-throat units of sandstone samples. The proposed method exhibits strong generalizability and can be extended to evaluate fluid mobility in sandstone reservoirs across various regions, while also addressing the critical gap in current research regarding accurate characterization of displacement volumes in distinct pore-throat units.
The experimental procedure is outlined as follows: 1. Sample Preparation and Fluid Saturation: Core samples from a target water-bearing reservoir were saturated with heavy water and centrifuged at 12,000 rpm. The residual water film retained on the rock surface was regarded as bound water, simulating subsurface conditions. After centrifugation, the samples were re-saturated with distilled water to establish coexisting bound water and movable water phases. 2. Gas Displacement Experiment: Methane gas was used to displace water from the saturated cores. Since bound water cannot be displaced, the heavy water remained intact. Movable fluid saturation in connected pore throats was calculated based on weight measurements of dry, water-saturated, and post-displacement cores. 3. NMR Characterization and Parameter Extraction: NMR measurements were conducted before and after displacement to obtain NMR-derived movable fluid saturation. Based on a segmented pore-size model, the NMR movable fluid saturation within the pore radius range of Rᵢ to Rᵢ₊ₖ was calculated. 4. Error Correction and Relative Movable Fluid Saturation Calculation: To account for inherent NMR measurement errors, a relative comparison method was applied to determine the relative movable fluid saturation from displacement experiments within the Rᵢ–Rᵢ₊ₖ pore-size interval. 5. CT Scanning and Pore-Throat Volume Quantification: CT imaging was used to quantify pore and throat volumes within the Rᵢ–Rᵢ₊ₖ range, and their volume fractions were computed. Given that displacement experiments reflect the overall response of connected pore throats, pores and throats were approximated as fully water-saturated, allowing derivation of relative movable fluid saturation for pores and throats in the specified interval.
Results showed a movable fluid saturation of 51.20% within the 1–100 nm pore-size range, with pores and throats contributing 62.4% and 37.6%, respectively. In the 100–1000 nm range, the saturation was 38.70%, with pores accounting for 79.1% and throats for 20.9%. The integrated multi-method framework developed in this study serves as a reliable tool for predicting movable fluids and optimizing development strategies in sandstone reservoirs.
| Country | China |
|---|---|
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