Remaining Oil Distribution and Potential Tapping During High Water-Cut Stage in Offshore Bottom Water Fault Block Reservoirs

Abstract

Abstract CFD oilfield is an offshore structural bottom water reservoir located in the Bohai Bay basin. The oilfield is developed by horizontal wells. After the high water cut of the oil wells, all oil producing wells are converted into reinjection wells to meet the needs of the production of the oilfield group. After more than 10 years of high intensity water injection, the injection volume has exceeded 20 times of geological reserves. In order to understand the distribution law of water-flooded and remaining oil in this reservoir, we introduced the relative permeability time-varying characterization into the reservoir numerical simulation on the basis of large-scale physical simulation experiments, quantitatively described the evolution process of water ridge shape below the horizontal well and its internal oil displacement efficiency with time and injection volume during the production and water injection process of the bottom water reservoir, and finally predicted the current residual oil distribution law. According to the research results, when the injection volume of a single well is 5 times, 10 times and more than 20 times of the well control reserves, the radius of the water ridge below the horizontal well is<200m, 250~350m and>450m respectively. This conclusion is confirmed by several passing wells and the current distribution of remaining oil is basically consistent with the research prediction. Under the guidance of research conclusions, we have developed an overall plan for inter-well infilling to tap the potential again and have achieved excellent results. During the implementation of this plan, many wells have achieved high production of more than 300 m3/day at the initial stage. It is predicted that the recovery efficiency of this reservoir will increase by 11 percentage points.