Summary

Cost-effective production from unconventional reservoirs relies on creating new reservoir surface area where fractures are extended into and produce from un-depleted zones. Field observations indicate infill well fractures could propagate towards nearby producers and depleted zones. This communication between infill and producer wells has been seen to cause casing collapse and negatively impact current production levels. In this paper, an integrated reservoir-geomechanics-fracture workflow is established to optimize infill well treatment schedule and to minimize fracture communication between wells. In particular, the paper presents: (i) numerical evaluation of depletion induced stress changes between tightly spaced producers, (ii) hydraulic fracture curving in a perturbed stress field, (iii) hydraulic fracture communication between wells, and infill well treatment design optimization to maximize production.

A systematic study of depletion effects and the key parameters that control fracture curving allows us to improve the infill well fracture design by minimizing the communication between wells while maximizing the hydraulic fracture extent. Depletion perturbs the in-situ stress tensor in the formation around fractured horizontal wells. The analysis shows that the perturbed stress field is a function of stress/formation anisotropy, fluid mobility, pore pressure, operating bottom-hole pressure, and Biot's constant. A fracture propagation model, coupled with the altered in-situ stress field is utilized to predict the hydraulic fracture propagation path(s) and their radius of curvature (i.e., if the stress state dictates that the fractures should curve). The analyses are performed for different infill well treatment schedule(s), and output the most likely fracture geometries. Resulting infill well fracture geometries are imported into a reservoir simulator to quantify the production and to identify the optimum design parameters.

The coupled workflow (geomechanics-fracture-reservoir) is then applied to a field example to demonstrate the feasibility of its application at the reservoir scale. The results show that (a) infill well fractures between tightly spaced horizontal wells can intentionally be curved and (b) communication between wells and fracture coverage area can be controlled by adjusting stimulation parameters to maximize recovery. Forward coupled modeling can be effective in advising when to drill infill wells before the altered stress state risks a commercial outcome.

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