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Continuous, Thin-bedded Sandy Deepwater Lobe Deposits −a Case Study from the Lower Permian Dean Formation, Midland Basin, West Texas


Permian fine-grained siliciclastic intervals in the Permian Basin often contains large basin floor submarine fans. Typical strike width of depositional lobes of Brushy Canyon formation in Delaware Basin ranges from 150 to 5,000 m. However, the depositional lobes in the Dean Formation in the southern part of the Midland Basin, with individual sandstone bodies ranging from 1 to 4 m thick, can be traced for more than 120 km in dip direction and 80 km in strike direction. The Dean Formation is composed of mudstone, siltstone, and very-fine grained sandstone. Two core groups (7 cores) and more than 2,000 wireline logs were used to infer Dean depositional systems. Group 1 cores (4 cores) are located in the northern part of Permian Basin. Fifty-one thin (3 cm to 30 cm), sandy beds of the Upper Dean interval in one core can be correlated from lithology and structure characteristics with two other cores (3 km away). However, Group 1 core shows that lithology varies significantly for the most of the Dean intervals, suggesting that the Dean in the northern part of Permian Basin contains deep-water channel levee complexes. Thirteen sandstone bodies are identified and are inferred to be continuous with Group 2 cores (3 cores) in the south of the Midland Basin. Each sandstone body can be traced up to 120 km in the dip direction and 80 km in strike direction, extending through the middle and south parts of the Midland Basin. These sandstone bodies are interpreted as distal-lobe deposits based on morphology and sandstone thickness pattern. For most of the sandstone bodies, the transitional zone from narrow feeder systems to lobes occurs in the middle of Midland Basin. Although previous exploration activity for Dean Formation has been mainly focused in the northern part of the Midland Basin, especially in Dawson and Martin Counties because of high net-sandstone thickness, sandstone beds in the middle and southern parts of the basin can also be the potential exploration targets because of laterally continuous sandy lobe deposits and greater number of sandstone beds within these aggradational-lobe successions.