Abstract
Most of the water-drive oil reservoirs in the western South China Sea had stepped in the middle and high water-cut stage. By the influence of reservoir heterogeneity, fault distribution, well pattern deployment and variation of reservoir flow parameters during long-term natural water drive and water flooding, the remaining oil distribution forecast is not accurate enough, increasing the difficulty of making effective adjustment and potential tapping measures. Through years of tackling key technical problems and field practice, the detailed characterization technique of the remaining oil in matured water drive reservoir was presented. Based on water displacement mechanism, variation of relative permeability curves are derived from Zhang’s water-drive characteristic curve during long-term water displacement. In addition, dynamic monitoring data matching was adopted to improve the forecast accuracy of the remaining oil distribution in water flooding oil reservoirs. By combination of flow field, remaining oil saturation field, and remaining oil reserves abundance, comprehensive characterization of water drive dynamic state was realized. The remaining oil enriched areas were quantitatively classified into four levels of potential regions, and corresponding adjustment and potential tapping measures were proposed. This technique had been successfully applied in the middle and high water-cut oilfields in the western South China Sea, with remarkable estimated incremental oil production of approximately 204,000 m<sup>3</sup>.
Highlights
There are 23 natural water drive and water flooding fields in western South China Sea, average water cut has reached 75%
Flow field is divided into four levels [19]: super, strong, medium and weak (Table 1), and fluid movement, potential regions of remaining oil (Figure 6) and corresponding adjustment and potential tapping measures (Table 2) are clearly presented
Dynamic monitoring data was adequately used in reservoir numerical simulation, improving the accuracy of history matching and remaining oil distribution
Summary
There are 23 natural water drive and water flooding fields in western South China Sea, average water cut has reached 75%. Key parameters affecting seepage flow (i.e. permeability, oil displacement efficiency, rock wettability) changed after long-term water drive [1,2,3,4,5,6], especially the change of oil displacement efficiency generated appreciable impact on remaining oil distribution and field development efficiency. The parameters of reservoir skeleton, network, seepage, geostress, physicochemical field and flow field are constantly changing [7]. These changes have further complicated the distribution of remaining oil in high water-cut stage, so it is necessary to carry out detailed characterization of the remaining oil in matured water drive reservoir
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