Comparison of Oil Displacement by Water Between Naturally Fractured Reservoir and Vuggy Fractured Reservoir Based on Streamline Technique

The differences between naturally fractured reservoir and vuggy fractured reservoir are apparent in the aspect of oil displacement by water. In fractured reservoir, the oil displacement by water is the governing recovery mechanism known as capillary imbibition, which allows the recovery of matrix oil that cannot be reached by the externally applied pressure gradients of waterflooding. The main difficulty is the problem of choosing the well pattern. While oil displacements in the vuggy fractured reservoir are dependent on the single well huff-and-puff because of its higher permeability and the nonexistence of the coning, thus its displacement is to inject water by production well, and the mechanism is to complement formation energy and replace rather light oil with water by gravity segregation. In this paper, the displacement models of naturally fractured reservoir, which are based on streamline numerical simulation method, are developed and discussed on the well pattern, well type, recovery rate, injection rate, injection cycle, etc. The result shows that design of well pattern plays a dominating role in the waterflooding, followed by the optimization of injection rate. While for the vuggy fractured reservoir, injection cyclic deserves prior consideration. The other factors such as critical recovery rate, critical injection rate, injection opportunity, aquifer, etc. are also taken into account in the study, which make the development scenario of vuggy fractured reservoirs more reasonable and economic. In the end, an example of comparison between Fuyu oilfield(naturally fractured reservoir) and Tarim oilfield (vuggy fractured reservoir) is presented to illustrate the differences of the displacement, and scenarios suited for the reservoir are put into implementation. The study provides an important technical support for similar reservoirs development, especially when confronted with the problem of oil displacement at the secondary recovery stage.