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Classification and Characterization of Barrier-Intercalation in Sandy Braided River Reservoirs of HE Oilfield, Sudan

Abstract

HE oilfield is located in Muglad basin, Sudan. The main oil bearing zones are composed of Cretaceous massive braided reservoirs dominated by medium-coarse sand, which are buried at depth of 1,600 to 1,900m. HE oilfield has been developed with commingle production by natural drive since 1996. After nearly 20 years of development, the recovery factor reached 34%, while the water cut reached 95%. It is predicted that 6–9% of OOIP can be more produced by horizontal wells and production techniques. Barrier-intercalations in sandy braided river reservoirs are diverse in types, different in shape and scale, and complex in spatial distribution. Quantitative characterization on barrier-intercalations is crucially important for the further understanding of reservoir architecture and remaining oil distribution. Based on comprehensive analysis of core data, well logs and outcrops, three hierarchies of the barrier-intercalations are developed in the sandy braided reservoirs in the study area, including barriers between the two single layers, intercalations between the two single sandbodies and intercalations within channel bar which, accordingly, are composed of flood shale, abandoned channel shale and shale between accretion bodies. The barriers are delineated by well correlation referring to the abandoned channel location, which are 700–1,500 m wide and 1,000–2,000 m long. Base on empirical formulae by Mr. Kelly and the measurement of 15 modern braided rivers by Google Earth, the relations of channel width vs channel bar width and the length vs width of channel bar are created to estimate abandoned channel shale which are 170–350 m wide. Intercalations within channel bar with the width of 100–400 m and the length of 300–800m are determined according to the scale of accretion bodies which are defined by an empirical equation by Kelly and well correlation. Based on the understanding of barrier-intercalation, the geological model which accurately delineates different types of barrier-intercalations is built by facies-control and stochastic modeling method. The results provided a reliable geological base for horizontal well deployment and water shut off operation.