Vertical to Horizontal Reservoir Characterization, of the Meramec Shale, Oklahoma, for Optimal Well Placement, Completion and Stimulation of Laterals

Abstract The Meramec Shale is a primary target located in the STACK play, Oklahoma, USA. It is a low porosity, carbonate mudstone with a variable reservoir quality. Some zones are characterized by higher porosity, due to extensive fracturing in the more brittle chert and siliceous limestone, whereas other low porosity limestone zones are characterized by a complex distribution of cemented and healed fractures. Identification of open natural fractures and faults is of key importance, as they provide storage space for oil sourced from the underlying Woodford shale and also contribute to rock permeability. Operator strategy is to define the optimal landing depth and then drill horizontally intersecting as many open fractures as possible. Commercial production then requires hydraulic fracture stimulation of these horizontal wells. In the vertical section, NMR and Mineralogy analyses were integrated with Borehole Resistivity and Ultrasonic Acoustic Images as well as Acoustic Deep Shear Wave Images. The integration determined porosity and fluid types in the Meramec zones and characterized fractures intersecting the wellbore and non-intersecting reflectors farther away from it. Following the selection of an optimal kick-off and landing point for the lateral, open hole mineralogy and image logs were repeated in the horizontal section to record lateral variations in porosity, lithology and structure. The vertical well analysis identified extensive non-intersecting events, up to 70 ft away from the wellbore. The strike of these events is consistent with borehole intersecting fractures, leading to interpretation of long vertical fractures in the formations. The presence of chert, or the amount of silica, increases rock brittleness and correlates with the increase in secondary fractured porosity. The borehole image, along the lateral, revealed a change in bedding dip azimuth, from NE to SE, indicating the presence of an intersecting fault, which was confirmed by a correlating discontinuity in parallel beds and bedding dips on the deep acoustic image. Overall, the integration reveals an intricate, open and sealed, fractures and fault network both intersecting and away from the wellbore. Reservoir quality characterization, of the entire lateral, was used to improve the completion and stimulation design. Multi-well analysis established petrophysical properties driving the reservoir performance and the regional variation of these properties.