Abstract

The Synrift sequence in the Bantumilli Graben, Krishna-Godavari (KG) Basin, was deposited during the rifting of the Indo-Antarctic plate in the Late Jurassic to Early Cretaceous period. Synrift sedimentation began under a half-graben configuration, with the depocenteres in the grabenal part. These half-graben settings are exemplified by the Gudivada Graben/KazaKaikalur High and the Bantumilli Graben/Bantumilli High. Core data studied from the Synrift section in various wells across the Bantumilli Graben indicate massive sandstones with minor shale intercalations. Laboratory studies show that these sandstones are medium to coarse-grained. The blocky character of the gamma ray (GR) logs, along with fining-upward trends in some intervals, suggest a fluvial depositional environment. By integrating core data, log character, and tectonic interpretation, a geological model for the Synrift sequence has been developed. This model demonstrates that rift-related sediments were derived from the erosion of adjacent basement highs and deposited as alluvial fan or fan delta systems in a fluvial to marginal marine environment. Globally, significant hydrocarbon discoveries have been made in Synrift plays located on the rising flanks of half-graben systems. The Malleswaram Field of KG Basin, situated on the updip portion of the rising flank of the Bantumilli half-graben, contributes significantly to hydrocarbon production, approximately 29% of total oil output from the Rajahmundry asset. The understanding is further supported by the recent Yandapalli New Oil Field discovery, which has yielded commercial oil production from the Synrift play and opened a new corridor for future exploration.