Accurate pore pressure and stress estimation are extremely important for safe and efficient drilling. The objective of this study is to establish robust models for an unconventional shale play to predict pore pressure and stress magnitudes from elastic properties derived from seismic. The pore-pressure magnitudes have often been shown to impact productivity and minimum horizontal stress (Shmin) link directly to ‘fraccability’ of a rock.
Unexpected overpressure is a major cause of drilling hazards, costing the industry billions of dollars and posing a huge potential risk for damage to the environment. Overpressure also has a significant impact on the ability to artificially fracture shale formations as well as increasing the production drive of liquid hydrocarbons and favor higher production rates (Heller and Anantharamu, 2020). The derived volumes of pore pressure and stress can assist in determining "sweet spots" within a play.
To derive the 3D pore-pressure and geomechanical properties, seismic data is crucial. In this case, the data was acquired using high trace density seismic acquisition. This improved the spatial resolution of the seismic and its associated seismic attributes. This enabled the interpretation of structural and stratigraphic geologic frameworks that are less resolved using onshore acquisition methods typical for the late-2000s. The survey geometry collected additional data such as acquisition of more near and far offset traces, finer lateral sampling, higher fold, broader frequencies, and fuller azimuthal sampling. All of these increased the resolution that illuminated fine-scale geology.
Using the above seismic data, we have done an integrated study involving phases 1 and 2. As part of phase 1, a detailed petrophysics and rock physics analysis was performed, then seismic AVO conditioning and finally, seismic AVO inversion was performed to extract elastic properties from seismic angle stacks. Parallelly in phase 2, a detailed pore pressure and geomechanics analysis was performed on a series of wells throughout the study area. 1D calibrated models for pore pressure estimation, stress and failure were constructed based on detailed drilling history reviews of offset wells, formation pressures and fracture closure pressures from DFITs, Image log data and lab rock mechanical tests. Finally, both the phases were combined to estimate the properties in 3-dimensions.
