Downhole Oil-Water Segregation in Production Wells: Review, Design, Simulation and Field Trials

Sagyndikov M. Gussenov I. Shakhvorostov A. Melis Y. Salimgarayev I. Shilanbayev B. Khoramian R. Imanbayev Z.
December 2025 Engineered Science Publisher

Engineered Science
2025 #38

Excessive water production increases lifting costs and shortens well life, yet existing control methods remain inadequate—chemical treatments are short-lived, mechanical systems costly, and cyclic operations disruptive. To overcome these issues, this study presents a Downhole Fluid Segregation workflow that exploits gravity-driven phase separation in the wellbore to selectively produce oil while retaining excess water in the reservoir. Calculations showed single oil blobs rose through a water column within 1-16h, with transit time decreasing as droplet size increased. Analytical scaling indicated that stabilization time increases sharply with reservoir thickness but decreases with vertical permeability. For instance, for a 13-m-thick reservoir with a vertical permeability of 400 mD, full rebalancing required 193 days. Reservoir simulations of a 15-month shut-in increased oil saturation in upper intervals from 0.2-0.4 up to 0.6. Restarting production at moderate rates provided the best balance between oil recovery and water control, while high rates caused early water breakthrough. Field pilots in Western Kazakhstan confirmed feasibility: watercut fell to <1% even in a well producing 8,500cP oil, while medium-viscosity wells showed increased oil output and watercut decline from 95-98% to <1%. Limitations include fractures, low kv, and fluid-stability constraints. Future work targets full automation and multiwell pilot verification.

Downhole fluid segregation , Enhanced oil recovery (EOR) , Field pilots , Water production , Watercut control , Wellbore gravity oil–water separation

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Institute of Polymer Materials and Technology, microdistrict Atyrau 1, 3/1, Almaty, 050019, Kazakhstan
Researching and Development LLP, microdistrict 29, b.4, Aktau, 130000, Kazakhstan
Satbayev University, 22a Satpaev Street, Almaty, 050013, Kazakhstan
School of Mining and Geosciences, Nazarbayev University, 53 Kabanbay Batyr Avenue, Astana, 010000, Kazakhstan
Republican Public Association (RPA) Veterans of the Oil and Gas Complex (VOGC), 19 Kabanbay Batyr Avenue, Astana, 010000, Kazakhstan

Institute of Polymer Materials and Technology
Researching and Development LLP
Satbayev University
School of Mining and Geosciences
Republican Public Association (RPA) Veterans of the Oil and Gas Complex (VOGC)

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