In 2010 Qarun Pet. Co. started an extensive infill drilling campaign in Western Desert of Egypt for 9 fields, aiming to improve recovery after water flooding. The well spacing was reduced to half of its original value and all infill wells were producers. Through the course of the paper the authors will conclude some key findings from the success stories and learned lessons from the failure cases.

The fields of Samra, Asala, Diyur, North Diyur, Yomna, E-Bah C, E-Bah D, E-Bah E and E-Bah F were developed by water flooding either from the start of production or after a short period of depletion production. After about 2 years of production, high water production rates were observed although these fields did not achieve their planned recovery. Several analyses were carried out and showed that significant remaining oil existed. Reasons identified for bypassed oil include lateral pay discontinuities, completion inconsistencies, and high level of heterogeneity.

Drilling significant number of infill wells was the key technology suggested to recover bypassed reserves. Initially, the well spacing was about 450m between producer-producer or injector-injector pairs. The well spacing was reduced to maximum 300m to better connect pay intervals especially for Upper Baharyia reservoir, due to its high complexity and heterogeneity level.

After implementing the infill drilling within the 9 main fields, comprehensive monitoring plan was executed to observe the recovery improvement. 6 Fields (i.e. Samra, Asala, Diyur, North Diyur, Yomna and E-Bah D) recorded additional reserves by infill drilling and the other 3 fields (i.e. E-Bah-C, E-Bah-E and E-Bah-F) did not achieve the expected increase. Comprehensive integrated analyses revealed that the heterogeneity level and maturity (age) of the water flood were the main controlling factors in the success of infill drilling.

Five main lessons learnt are presented (supported with data) for successful implementation of infill drilling in low permeability and heterogeneous reservoirs. Analysis workflows are presented for water flood candidate selection and for infill drilling evaluation.

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