Reasonable Design of Underbalance of Reactive Shaped Charge

Abstract Static and dynamic underbalance perforation techniques can significantly enhance the cleaning efficacy of perforation tunnels. The crux of static underbalance perforation lies in precisely formulating the optimal underbalance to ensure that the wellbore pressure subsequent to perforation is lower than the formation pressure, thereby facilitating the influx of formation fluids into the wellbore and achieving effective perforation cleanup, while concurrently averting sand production or damage to downhole tools. Dynamic underbalance (DUB) perforation attains an ideal cleaning outcome by enabling the rapid ingress of wellbore fluid into the gun body after the perforation tunnel formed by shaped charges, generating a rapid pressure drop and establishing a transient underbalance state within several tens of milliseconds. DUB perforation can effectively operate irrespective of whether the initial condition is overbalanced, underbalanced, or balanced. To optimize the design of DUB perforation, it is typically necessary to employ multi-parameter comprehensive software for simulation analysis. Unlike conventional shaped charges, reactive shaped charges primarily differ by integrating reactive substances into their inert metal liners. Once the perforation tunnel is formed, reactive substances promptly release secondary energy within the tunnel, loosening or eliminating the crushed zone and generating clean perforation tunnels, thereby significantly ameliorating perforation performance. For hard and brittle formations, on account of their low permeability, static or dynamic underbalance techniques sometimes struggle to provide adequate flow to achieve the desired perforation cleanup effect. In contrast, reactive shaped charges can instigate secondary implosion within the perforation tunnel, expelling rock cuttings and leaving behind clean perforation channels. Nevertheless, the utilization of any single technique independently is prone to fall short of achieving the optimal perforation cleanup effect. Hence, for hard and brittle formations, the combination of reactive shaped charges and underbalance techniques constitutes the optimal approach to achieve ideal perforation cleanup. Laboratory investigations have indicated that conventional shaped charge perforating charges induce a dynamic underbalance effect persisting for several tens of milliseconds subsequent to detonation, whereas reactive shaped charges engender a dynamic overbalance effect. Currently, within the industry, when designing the static and dynamic underbalance of reactive shaped charges, this disparity is frequently overlooked, leading to suboptimal perforation cleanup outcomes. Consequently, this paper puts forward a novel design theory for the static and dynamic underbalance of reactive shaped charges, with the aim of providing more scientifically rigorous guidance for perforation practices.