Since 1993, about 70 horizontal wells, have been drilled in three different successful projects. These projects were implemented in the mature Algyõ field. A fourth project, consisting of more than 20 new horizontal sections, kicking off existing abandoned wells, has been developed for the thin oil rim present in two high permeability reservoirs with top gas and bottom water The main difference between the two reservoirs is that one has water injection and the other has two layers with strong natural bottom water drive.

The first experimental wells of the 4th project were drilled to minimize the coning effects and to increase the areal recovery efficiency in the initially 9 and 6 m thick oil zones (shrinked to 4 and 3 m in the recent state of exploitation).

To decision about the project implementation was based on reserve re-evaluation. The re-evaluated reserves were determined using results of the experimental wells, a 3D geological model, a full field 3D simulation and horizontal well production matches with JTI software. To define saturation, neutron logs were used to determine for the gas-oil contact and carbon-oxygen logs are used for monitoring the oil-water contact (because of the very low salinity of formation water). The target zone of the horizontal sections is +/− 0.5 m vertically and very detailed information analysis is required to plan proper trajectories.

The recent state of the project, the evaluation, methods and simulation process used for the decision- making are presented in the paper.

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