When drilling the East Kameleon structure in the Alvheim field in 2010, two pilot wells proved multiple and stacked hydrocarbon accumulations. The lower oil zone was developed in 2012 with a horizontal MLT well. When drilling the upper zone in 2014, the completion job failed, causing an undesirable zonal crossflow. A reservoir management strategy had to be established to secure long-term area development.

To mitigate undesirable crossflow across the stuck sand screens, the well was filled with cement. A new horizontal producer was subsequently drilled and successfully completed to recover the oil from the upper zone. With potential lower-upper zonal crossflow, the reservoir model was updated to analyse the reservoir management options. Three scenarios were considered regarding zonal crossflow: a) No crossflow due to a successful cement plug, b) restricted crossflow representing mud/cement impairment, and c) fully open-hole crossflow without flow restrictions.

A reservoir management strategy was established in 2015 to monitor zonal pressures and restrict upper zone production to minimize unwanted gas crossflow. Reservoir simulations showed that this was key to secure the oil recovery of the lower zone. The upper producer came on-stream with a high GOR, indicating gas crossflow according to scenario (b). From 2015 to 2020, the upper producer was choked back to low offtake rates. After five years with the lower zone oil recovery optimized, the reservoir management strategy allowed high offtake of the upper zone. Today, the upper horizontal well is one of the best oil producers in the Alvheim area, producing at a high oil rate with a declining GOR trend. The reality and the updated history matched reservoir model support scenario (b) as postulated in 2015. Analysis of recent pressure data has also strengthened the geological understanding of stratigraphical compartmentalization in this turbiditic sand deposit.

This case study can act as an example of how to establish a reservoir management strategy in a complex multiple gas-oil zonal reservoir setting. It can also provide insight into the level of formation impairment when cementing a long horizontal well with stuck sand screens.

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