Effect of Liquid-Liquid Subsea Separation on Production Forecast Considering Integration of a Deepwater Reservoir and Surface Facility Models

Abstract

In this work, we present a case study of the integration of surface facility models and a deepwater reservoir, as well as an engineering evaluation of the implications of liquid-liquid subsea separation (LLSS) on the integration process. For this, a heavy oil sandstone reservoir and several surface facility layouts were computationally integrated using a commercial simulator. A gathering unit, subsea separator, and water disposal unit were added to the surface facility model layouts to support the LLSS system. The term "merge scenario" was used to refer to the quantity of production streams that were gathered and delivered to the subsea separator. To allow the production from the reservoir model, the minimum bottom-hole pressure (BHP) for the producing wells were defined for all the simulations. Our investigation includes fluids produced at platforms, produced water at disposal unit, the pressure drop in the riser in terms of hydrostatic and friction terms, and economic analyses of these investigations. This case study shows that, depending on the merging situation, the reservoir needs 2 to 5 times more injection water than the separated water. Despite efforts to reduce the pressure restriction in the surface facility by increasing the riser diameter, the oil recovery did not change significantly when the number of merging wells was adjusted. This happened because the wellhead was not affected by the production system's pressure disturbance and the surface facility models’ boundary conditions remained unchanged. The economic calculations also indicated that the value of the technology (the highest acceptable price for the technology) for eleven merge scenario was 130 MMUSD and the OPEX and CAPEX can be lowered by 95 and 35 MMUSD (3% and 5% on average), respectively. This economic benefit was due to the lower cost of platform water handling from the produced water separation. In later stages of simulations, when the water cut surpasses 90%, hydrostatic pressure loss overtakes friction pressure loss as the primary contributor to overall pressure losses in the riser for 11 merge scenarios. These tests demonstrated that adding LLSS increases the complexity of the integration process and engineers can apply the engineering ideas of this study to other field designs in development. This work is the first case study of its kind that examines the relationship between the impact of LLS and the integration of a deep-water reservoir and surface facility model. This article's production forecast problem description can be utilized as a starting point to develop a general methodology for simulating complicated offshore production systems using LLSS operations.