Geologic materials' response to shaped charge penetration

A comprehensive experimental effort was recently conducted to evaluate the penetration performance of oilwell perforating charges into stressed and unstressed Berea sandstone cores. Rock confining pressure (Pc) and pore fluid pressure (Pp) were varied from ambient to 10,000 psi, to simulate downhole stress environments typically experienced by subterranean reservoir rock. Experiments yielded a generally inverse correlation between penetration depth and effective stress (σeff). However, a new definition of effective stress is proposed. Historically, the perforating community has defined σeff = Pc − Pp, but a new treatment (σeff = Pc − aPp; a = 0.5) better fits both present and published historical penetration results. These findings culminate an initial application of combined penetration mechanics and rock mechanics analyses to the investigation of shaped charge penetration into geologic materials. Future work will address different rock types, additional poroelastic quantities, and dynamic effects as they contribute to pressure-induced strengthening of target rock.