Injection and hydraulic fracturing in plastic shales can be a complex and problematic operation. Issues that accompany such treatments include shale swelling, plastic deformation, embedment’s and perforation tunnel stability issues. Simulators that model fluid or slurry injection in plastic shale have always overlooked the plasticity issues associated with these formations. The approach has led to erroneous estimation of fracture extent and dimensions. Post injection shale deformation due to pore pressure changes can also lead to detrimental effects on productivity (fracture closure due to creep) and well/casing failure.
The current paper offers clear quantitative insights into the overall effect of injection in plastic shales. The experience is gained through drill cutting injection operations that have been taking place in highly plastic shales in an environmentally sensitive remote location. Fracture and slurry containment have been investigated using state-of-the-art 3D fracture simulator to provide assessment of the injection and to estimate out-of zone growth as well as shale plastic deformations and the effects on fracture vertical growth at different batch volumes. Analysis of historical pressure trends and pressure fall-off tests confirmed results from the 3D Simulation and the injection history. The results provide insights that have implications on the job design and implementation of hydraulic fracturing in plastic shale gas, particularly the Haynesville.
The results from the 3D fracture simulator and pressure transient analysis combine to accurately assess fracture vertical and lateral extents in similar formations, hence, minimizing the risks associated with injection and fracturing in these highly plastic shales.