Distribution rules of remaining oil by bottom water flooding and potential exploitation strategy in fault- controlled fractured-vuggy reservoirs

Abstract

Based on the tectonic genesis and seismic data of fault-controlled fractured-vuggy reservoirs, the typical fractured-vuggy structure features were analyzed. A 3D large-scale visual physical model of “tree-like” fractured-vuggy structure was designed and made. The experiments of bottom-water flooding and multi-media synergistic oil displacement after bottom-water flooding were conducted with different production rates and different well-reservoir configuration relationships. The formation mechanisms and distribution rules of residual oil during bottom-water flooding under such fractured-vuggy structure were revealed. The producing characteristics of residual oil under different production methods after bottom-water flooding were discovered. The results show that the remaining oil in “tree-like” fractured-vuggy structure after bottom-water flooding mainly include the remaining oil of non-well controlled fault zones and the attic remaining oil at the top of well controlled fault zones. There exists obvious water channeling of bottom-water along the fault at high production rate, but intermittent drainage can effectively weaken the interference effect between fault zones to inhibit water channeling. Compared with the vertical well, horizontal well can reduce the difference in flow conductivity between fault zones and show better resistance to water channeling. The closer the horizontal well locates to the upper part of the “canopy”, the higher the oil recovery is at the bottom-water flooding stage. However, comprehensive consideration of the bottom-water flooding and subsequent gas injection development, the total recovery is higher when the horizontal well locates in the middle part of the “canopy” and drills through a large number of fault zones. After bottom water flooding, the effect of gas huff and puff is better than that of gas flooding, and the effect of gas huff and puff with large slug is better than that of small slug. Because such development method can effectively develop the remaining oil of non-well controlled fault zones and the attic remaining oil at the top of well controlled fault zones transversely connected with oil wells, thus greatly improving the oil recovery.