Application of Comprehensive Optimisation Strategy for Waterflooding Development Using Horizontal Wells in Thin Carbonates

Abstract

Carbonate reservoirs in Middle East are strong heterogeneous with great reservoir physical property difference vertically, water breakthrough easily caused by high permeability streaks and some dissolution vugs when the reservoirs start water injection. How to successfully implement horizontal well waterflooding with high well productivity and long plateau period for complex carbonate reservoirs face great challenges. K reservoir of B oilfield, as a case study in the paper, has been put into production by horizontal wells and subsequently revealed production problems of unbalance of injection and production, rapid water breakthrough and production decline in the early stage of water injection.The paper put forward integrated modular workflow to optimize horizontal well waterflooding for the major K reservoir. The workflow includes main controlling factors analysis, real-time production performance monitoring and diagnosis, waterflood parameters optimisation and strategy proposal, waterflood effect assessment and potential prediction, and technology strategies and pilots.Based on seismic interpretation, well logging, geological model, dynamic model, production data and engineering, water breakthrough mechanism has been studied to clarify high permeability “thief zone” and partially dissolution vugs are the main controlling factors for water channeling of horizontal producers. Multiple indexes diagnosis modular for horizontal water flooding has been established, of which classification charts for horizontal well with different changing law are used to divide three type of “burst rising, fast rising, and slowly rising” for water breakthrough producers, and typical simulation models have been run to determine injection and production parameters limits. Production optimisation strategy modular has been established to propose key injection and production parameters and production measures for the early and middle water injection stage to improve the waterflood effect for the reservoir. Production characteristic curve method has also been put forward in the paper to evaluate production performance and predict potential of horizontal producers when optimisation measures are implemented. Real-time analysis and optimisation for horizontal well waterflood have been under cycling in turn to improve the areal and vertical sweep efficiency. Technical strategies have been put forward and gradually executed with pilots.The novel modular optimisation methods have been applied in the oilfield to successfully maintain yearly oil rate with 6 million ton more than for 6 years and restore reservoir pressure above 400 psi. The multidisciplinary study plays an important role to mitigate water breakthrough and production decline. Yearly oil decline rate of the oilfield has reduced from 35% of recent years to 15% in 2019 and incremental cumulative oil has reached above 2 million ton.The study in the paper provides important experience of horizontal well waterflooding to other similar thin carbonate reservoirs with strong heterogeneous in Middle East.KeywordsHorizontal well patternWaterfloodingOptimisation strategyThin carbonates