Finite Element modeling of natural sealing of wellbores in salt using advanced, laboratory-based salt creep laws

Abstract

Using the natural sealing potential of rock salt caprock formations is potentially an economically attractive and safe option for well plugging and abandonment (P&A). Rock salt has excellent sealing capabilities and can be used for P&A by forming a permanent sealing barrier across reamed-out well sections or perforated wells. However, the application of natural sealing by rock salt formations as an abandonment option is not yet common practice; a better understanding of the creep behavior and sealing capacity of rock salt and a quantitative estimate of the timescales required for the wellbore to be fully plugged are needed. In this study the timescales for closure of a reamed-out well section in rock salt are evaluated using finite element modeling, following methods outlined by Orlic et al. (2019). Salt creep is modeled by a two-mechanism steady state creep law, composed of a dislocation and pressure solution branch. Model results show that dislocation creep is dominant in the near-well field and dominates wellbore closure times, whereas pressure solution creep becomes increasingly important for stress relaxation after wellbore closure and in the far-field. Stochastic analysis shows the dislocation creep parameters and temperature to have the largest effect on wellbore closure timescales, and that in many cases wellbore closure occurs within weeks or months.