In the past decades, water injection development with horizontal wells is seeing more implementations and achieves considerable benefits for carbonate reservoirs in the Middle East. However, significant problems such as early water breakthrough (WBT) and uneven displacement pose great challenges to successful water drive development, and need to be solved urgently. This research focuses on the water-out performance and pattern of horizontal wells in a thin carbonate reservoir with bottom water, so as to investigate efficient water-out management strategies.

In this paper, the main controlling factors of water-out performance for horizontal wells were first determined with the methods of core description, Fullbore Formation Microimager (FMI), and Whole-Core CT Scanning, etc. Then, based on the production performance analysis and sector model simulation, water flood characteristics and water-out regularities were identified. Finally, the typical water-out patterns of horizontal wells were concluded, and the controlling measures were proposed for them respectively according to the specific water-out mechanism and remaining oil distribution characteristics. Results indicate that high permeability layers, fracture zones, high viscosity oil, and well pattern have significant influences on the early WBT and uneven displacement in horizontal wells. The water-out performance are characterized by single point breakthrough, multi-points breakthrough and linear breakthrough, which result in water-out in the local or integral horizontal segments. The proposed four types of typical water-out pattern have intimate relationship with the main influential factors. For example, the water-out pattern A, in which the thief zones dominate the flood performance, shows banded displacement characteristic in the horizontal segments. The vertical and horizontal flow of injected water or bottom water are mainly controlled by vertical fractures and thief zones separately. The water-out pattern can be identified according to the inflection characteristics of derivative curves of water-oil ratio (WOR) and relation between water cut (WCUT) and oil recovery factor (RF).

This paper presents a methodology of identifying water-out performance and pattern for horizontal wells, which helps reservoir engineers to specifically tackle water flood challenges and to propose customized management strategies.

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