ABSTRACT:

Increasing formation pressure during fluid or gas injection might cause reactivation or instability of existing faults. Effective in-situ stresses evolve with changes in pore pressure which is called coupling effect. Understanding this effect is important during hydrocarbon field development to assess the fault reactivation risks during reservoir depletion and injection processes. Utilizing the poroelasticity theory and applying analytical solution of Biot’s diffusion equation is helpful when investigating the coupling effects on various states of in-situ stresses and formation pore pressures. This paper focuses on the horizontal stress and pore pressure coupling effects on a fault stability study during cushion gas injection in a gas storage field in the Netherlands. To do so, initial field stresses were estimated using field data. Thereafter the poroelasticity theory and diffusion equation were implemented to estimate the injection-induced stresses at different time-steps caused by pore pressure changes. In this paper, the sensitivity analysis was performed to explore the influences of injection time and fault distance on the induced instabilities. The results of this study showed relatively good agreements of injection-induced stresses obtained from the analytical method with corresponding values from complex finite element simulations. Moreover, the results indicated that the injection point could be located closer to the central fault.

1. INTRODUCTION
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