Stress Analysis of a Fractured Producer Well in a Poroelastic Medium

Abstract:

It has been observed in the field as well as in laboratory experiments that hydraulic fracture propagation in a reservoir stimulation treatment can deviate from its original plane, typically normal to the direction of the minimum in situ stress, and possibly connect with a neighbouring fractured producer or injector well. It has also been observed that due to the possible stress reversal around a previously fractured well, hydraulic refracturing of a well may lead to new, orthogonal fracture orientation. Previous numerical case studies have illustrated how the poroelastic stress changes due to fluid injection/production from an exiting fractured well can lead to non-trivial new fracture trajectories. In this work, we develop a general plane-strain analytical solution for the perturbed poroelastic stress field around an un-propped fractured well which allows for a more systematic study of the relevant factors / parameters at play. We consider a fractured well produced at a constant rate within a poroelastic homogeneous rock characterized by ambient reservoir pore pressure and far-field mean and deviatoric stresses. The solution for the induced stresses normalized by the characteristic perturbative stress value and the corresponding stress trajectories normal to the perturbed minimum principal stress direction is developed analytically as a function of the position (normalized by the fracture length), dimensionless production time $\tau$ (normalized by the characteristic diffusion timescale) and the normalized far-field stress deviator parameter $S$. Stress field perturbation are minimal at small times $\tau$ and large values of $S$. Parametric analysis of the solution highlighted how different fluid and rock properties and ambient reservoir pressure-stress conditions influence the degree of stress field perturbations and the wholesale properties of the resulting stress trajectories (e.g. the `domain of attraction' of the fractured well). This may be helpful in considerations of re-development of existing reservoirs, whether involving refracturing existing wells or placing new fractured wells.