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Reservoir Quality and Fractures System Assessment of Meramec and Osage Limestone by Using Advanced log Analysis Method

Abstract

The Stack play is one of the most prolific unconventional plays in the United States midcontinent region. Meramec and Osage limestones are their primary target, which are characterized by low porosity and permeability. However, they show significantly higher porosity and permeability in fractured intervals. To understand the fracture system and its influence on the reservoir quality, a detailed log interpretation including mineralogy, NMR, borehole image log and deep shear wave image (DSWI) are conducted.

Reservoir quality, typically defined by storage capacity and deliverability, is variable. Some zones in Meramec and Osage are observed with higher porosity and permeability, due to extensive fracturing in the more brittle cherty limestone, whereas other low porosity zones are characterized by cemented and healed fractures. Open natural fractures are served as storage space for oil and gas, sourced from underlying Woodford shale, and also contribute to rock permeability.

Our study area located at the west side of Nemaha uplift. A complete suite of open-hole logs is available from 2 vertical wells and 1 horizontal well. In the vertical pilot section, image facies, fractures characterization and chert indicator were established based on borehole Image logs. The DSWI was important in terms of identifying far field fault and fracture zones up to 150ft from the well bore. The integrated NMR and Mineralogy analysis were used to determine the porosity and fluid type. This information enabled selection of optimal kick-off and landing point for the horizontal well. Mineralogy, borehole Image logs and DSWI were repeated in the lateral section to record variations in lithology and fractures intensity. The approach of integrating borehole Image and DSWI allowed for a detailed structural analysis, revealing a change in bedding dip azimuth, and a potential intricate fracture and fault network away from the wellbore. Reservoir quality characterization of the entire lateral section was used to improve well completion and stimulation design. Multi-well analysis established the petrophysical properties which were important to drive the reservoir performance.