One of the largest clastic reservoir fields in the Sultanate of Oman has been discovered in 1980 and put on production in 1985. The field produces viscous oil, ranging from 200 - 2000+ cP at reservoir conditions. Over 75% of the wells drilled are horizontal wells and the field is one of the largest producers in the Sultanate of Oman. The field challenges include strong aquifer, high permeability zones/faults. Due to large fluid mobility contrast, the fields have experienced in pre-mature water breakthrough that has resulted in very high-water cuts. The average field water cut for open hole horizontal well after 6-9 months of production is over 94%. This paper details a meticulous journey in qualification, field trials followed by field-wide implementation and performance evaluation of Autonomous Inflow Control Valve (AICV) technology in reducing water production and increasing oil production significantly.

AICV can precisely identify the fluid flowing through it and shutting-off the high water or gas saturated zones while producing oil from healthy oil-saturated zones. Like other AICDs (Autonomous Inflow Control Device) AICV can differentiate the fluid flowing through it via fluid properties such as viscosity and density at reservoir conditions. However, AICV's performance is superior due to its advanced design based on both Hagen-Poiseuille and Bernoulli's principles. This paper describes a comprehensive AICV completion design workflow that was developed across a multi-disciplinary team.

Some of the initial wells completed with AICV has shown the benefit of accelerating oil production of over 30,000 bbls within the first few months of installation. Many wells started with 5-10 % water cut and are still producing with low water cut and higher oil production. The operator has approved AICV technology based on techno-commercial analysis and its positive impact on the project such as accelerated oil production and lower cost of water handling at the surface. AICV also helped in mitigating the facility constraints of handling produced water which resulted in reduce OPEX as allow the operator continued to drill horizontal wells.

At the time of writing this paper, the operator has completed several dozen wells in the field with AICV technology and has an aggressive long term plan to complete several new and old wells.

Finally, this paper also discusses in detail the comparative analysis of AICV wells for different subsurface conditions and share some lessons learned to further optimise the well performance. The technology has a profound impact on improved sweep efficiency and as well plays an instrumental role in reducing the carbon footprint by reducing the significant water production at the surface.

It is concluded that AICV is a cost-effective field-proven technology for the water shut-off application. Due to its ability to autonomously identify and shut off water and gas production, the AICV technology has been approved to use as full fields implementation and in other fields.

Field Background and Reservoir/Production challenges

The operator produces around nine barrels of water against each produced barrel of oil. In general, the water produces to the surface with hydrocarbons contains many chemicals, which are usually not environmentally friendly and required additional treatment which increases the disposal cost. The Operator was looking for a cost-effective and proven technology that can control/shut off water production and improve oil production.

The fields have a strong bottom aquifer and heterogeneous reservoir properties, such as permeability and downhole water saturation profiles. The challenge with matured brownfields, typically newly drilled wells will have pre-mature water breakthrough within few months of production. The fields have a highly viscous oil, with viscosity ranges from 200 cP up to 2000 cp at downhole conditions, thus creating a high mobility contrast between the oil and water, causing water fingering and coning at an early stage of production.

These production challenges cause a significant recoverable oil left in the reservoir i.e. bypassed oil. Furthermore, excessive surface water production affects the integrated production system back pressures and flow, as well as an individual well's dynamics and pump efficiencies. This also has a significant downstream impact, where substantial investment is needed to handle, treat, and dispose of the water. Reducing these water volumes at the surface adds up to a tangible reduction in OPEX for water processing as well as environmentally friendly and assist the reservoir to maintain the reservoir pressure and energy by keeping the water in the reservoir. (Hilal et al 1997, Hassasi et al 2020)

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