Evolution law of dominant flow channel of water flooding in partially enclosed fault reservoir

Abstract

A partially enclosed fault reservoir is a common reservoir type. The partially enclosed faults caused by low-order faults lead to different fluid flow and distribution laws of remaining oil between partially enclosed fault reservoirs and completely enclosed reservoirs. Through the existing technology， it is difficult to quantitatively describe the evolution law of the dominant flow channel in the deep part of the reservoir in the whole process of water flooding， which affects the efficient development of this kind of reservoir. Therefore， the physical model of a partially enclosed fault reservoir was designed and fabricated， and the water flooding experiment was carried out. The numerical inversion model was established according to the model parameters and experimental results. The dominant flow channel was quantitatively characterized based on the standardized flow rate algorithm. Then， the numerical inversion model was used to compare with the evolution law of the dominant flow channels in fault-free reservoirs and reveal the evolution law of the dominant flow channel in the physical model of the partially enclosed fault reservoir. The results show that the accumulative oil yield and the oil production rate of the production well in the fault-occluded area were low. The reduction of the flow area in the fault discontinuity led to the earliest breakthrough in the production well. Although the production wells on the other side of the fault had close oil production in the early stage， the blocking effect of the fault on injection water led to a higher flow diversion rate and the highest oil production rate in the late stage in the strongly fault-occluded area. During the anhydrous oil production period， a dominant flow area played a positive role in oil displacement， which developed into a spindle-shaped dominant flow channel at the bottom of the reservoir through vertical equilibrium distribution and “finger-shaped” distribution. After water production in each well， a dominant flow channel was formed from the injection well to the bottom of the production well， except for the strongly fault-occluded area. With the increase in injection volume， this channel developed in the vertical direction and around the production well and played a negative role in oil displacement. Compared with fault-free reservoirs， partially enclosed faults made the development of dominant flow channels lag in strongly fault-occluded areas and difficult water sweep in strongly fault-occluded areas， resulting in significant differences in the distribution of remaining oil in each area， and the remaining oil is concentrated in the upper part of the strongly fault-occluded area and near the faults in strongly fault-occluded areas.

Keywords

• partially enclosed fault
• water flooding
• dominant flow channel
• physical simulation
• numerical inversion