A Framework to Study Geomechanical Impacts of Thermochemical Re-Pressurization for Fracture Hit Mitigation

Abstract

Infill drilling and hydraulic stimulation of child wells are used to maximize recovery in tight formations; however, these practices can lead to frac hits where child well fractures extend into the pressure-depleted zone of the parent well and result in extensive well interference. The exothermic reaction of Ammonium Chloride and Sodium Nitrite was previously identified as a means to reduce the possibility of frac hits. The present work introduces a framework to study the evolution of the state of stress around the parent well as the reaction takes place. We also examine the likelihood of generating secondary fractures and how it affects the interference. This framework simulates the coupled thermo-hydro-mechanical-chemical (THMC) processes resulting from downhole expansion of generated Nitrogen gas, steam, and heated native fluids against representative rock types for major tight formations, to calculate the resulting pore pressure buildup and subsequent geomechanical effects. Additionally, we evaluate different downhole reaction control strategies to identify the optimal operating conditions that prevent premature formation of secondary fractures around the parent well. This study presents examples on producing a barrier that persists for several days post treatment. Application of this framework to four major tight plays shows that heat is the main provider of the support. It is also noted that near-saturated reagent loading results in excessive stress, up to four times the desired limit, which necessitates the inclusion of reagent saturation as a design parameter. Additionally, effective normal stress inside the heated region were observed to increase, indicating that the treatment stabilizes natural fractures against shear slip rather than promoting it. These results allow us to formulate a set of best practices for maximizing the efficiency and effectiveness of the thermochemical re-pressurization of the parent wells to prevent fracture hits.