The objective of this project is to construct a 1D mechanical earth model for the prospective geological sequestration of carbon dioxide (CO2) into carbonate formations. The study sustains a pivotal role in analyzing the possible wellbore instabilities for drilling deep injection wells. Besides, the developed model can be essentially used to evaluate the caprock integrity for long-term CO2 storage and provide the primary analytical assessment of fault slip potential.
This paper describes the extensive construction of a geomechanical model to achieve three ultimate goals. A variety of petrophysical interpretations, shear wave velocity modeling, and Mogi-Coulomb failure criterion are initially established to deliver a safe drilling mud weight window for overpressure ramps in the Delaware basin, a sub-basin of the Permian. Using the dependable outputs of rock properties and strengths, top seal quality is subsequently determined by calculation of the brittleness index and critical pressure of tensile failure. Finally, pore pressure, shear stress, friction angle, and in-situ stresses are integrated to predict maximum sustainable injection pressures for preliminary fault slip analysis in deep aquifer carbonate rocks.
Two distinct overpressured zones of Wolfcamp and Barnett Shale are identified for wellbore instability based on pore pressure and fracture gradient prediction. These pressure ramps have a lower compressive strength, which causes the collapse pressure to exceed the pore pressure and serve as the lower bound of drilling mud weight. The wellbore stability simulation also shows low brittleness indices and high threshold breakdown pressures for Woodford shale caprock. It implies that the caprock may be more resistant to fracture growth and failure, indicating an effective top seal above the injected reservoirs. Meanwhile, close observation may be purposefully monitored to assess the fault slip potential in Devonian and Silurian formations once the critical injected fluid pressure approaches the projected threshold from the analytical computation.
The findings from this study will be useful in further understanding wellbore stability under drilling practices and CO2 sequestration. The appropriate application can support optimizing the casing and drilling mud weight design while also modifying the injection fluid pressure. Furthermore, the estimated rock properties, formation pressure, and principal stresses will be significant elements in building a hydrodynamic simulation of gas plume distributions after certain injection years.