Attic Oil Recovery in the Alvheim Field

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Abstract

Abstract The Boa and Kameleon accumulations in the Alvheim field have thin oil rims developed with long horizontal wells. Several of the latest wells are characterized as attic infill wells, drilled in the remaining oil rim, close to the gas cap, and shallower than the early wells. Autonomous inflow control technology is a key enabler for these wells. This paper describes the design, execution and performance review of a Boa attic well. This well combined passive and autonomous inflow control devices (AICD). The AICDs used were tested with Alvheim fluid in the laboratory. A clear lower completion strategy was essential in the planning and execution of this well, e.g. to use AICD close to the gas cap and to design inflow linked to estimated oil per drainage area. 4D seismic interpretation, pilot wells information and deep resistivity logging while drilling were other critical factors to plan and optimize the well path. Tracers were mounted in the sand screens to monitor clean-up, inflow per zone and the onset of water production. The steady state inflow model was used extensively in the execution and review phases. Pilot wells information and logging while drilling enabled successful geo-steering. During the drilling phase, the steady-state model was updated with the as-drilled information and the lower completion design adjusted to get what was estimated to be an optimal inflow. Tracers sampled during the clean-up indicated good clean-up of the entire well. The initial well performance with no water and low free gas amounts gave a larger pressure drop than expected. A later tracer based chemical PLT gave also slightly different results than expected. Pressure data, tracer data, log data and the effective multi-phase AICD model were thoroughly investigated to derive scenarios, that could explain this discrepancy. The most likely scenario gives a good history match for both pressure and tracers and gives extra insight into key reservoir parameters, zonal inflow and the effective behavior of the AICDs during multi-phase flow. The well has exceeded pre-drill production rate expectations, despite the larger than expected pressure drop. This is partly explained by the autonomous choking on gas inflow along the wellbore. The post-review evaluation enables continuous improvements for Alvheim and similar fields.

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