Water Flooding Characteristics and Adjustments of a Giant Porous Carbonate Oil Field in Iraq

Abstract

AbstractThe studied field is located in Iraq and is a giant porous carbonate oil field, having produced for nearly 40 years. Although the reservoir thickness is stable and the net-to-gross ratio is high, the vertical heterogeneity of the reservoir is strong and anti-rhythmic. After natural depletion indicated weak aquifer support, water injection development had been employed. Pressure test shows that the reservoir has good connectivity, so vertical wells are used to inject water at the bottom of the reservoir; and vertical and horizontal wells are used to produce oil at the top of the reservoir. By means of physical experiments and numerical simulations, the water flooding characteristics under bottom water injection and top oil producing were studied. It is considered that due to the extremely strong heterogeneity in the longitudinal direction of the reservoir, after water injection at the bottom of the reservoir, the injected water first flows vertically to the top of the reservoir in the near-well area, and then is displaced to the production well. The streamline of water injection has a “T” shape as a whole. So the middle area of the reservoir is poorly water flooded, and the remaining oil will be concentrated in the middle area of the reservoir between injection and production wells. On this basis, technical countermeasures such as adjusting the type of injection wells and increasing perforation in vertical wells were formulated in different regions. Practice had proved that the decline rate of oil production decreased by 3 times in the adjusted water injection well groups, and the development effect had been significantly improved.KeywordsPorous carbonate reservoirVertical heterogeneityReservoir connectivityWater injection methodWater flooding characteristics