Infill-Well Fracturing Optimization in Tightly Spaced Horizontal Wells

Abstract

Cost-effective production from unconventional reservoirs relies on creating new reservoir surface area where fractures are extended into and produce from undepleted zones. Field observations indicate that infill-well fractures could propagate toward nearby producers and depleted zones. This communication between infill and producer wells has been seen to cause casing collapse, and negatively affect current production levels. In this paper, an integrated reservoir/geomechanics/fracture work flow 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, and (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 bottomhole pressure (BHP), and Biot’s constant. A fracture-propagation model, coupled with the altered in-situ stress field, is used 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 yield the most-likely fracture geometries (taking into account uncertainties in a shale formation). Resulting infill-well fracture geometries are imported into a reservoir simulator to quantify the production and to identify the optimal design parameters.

The coupled work flow (reservoir/geomechanics/fracture) 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 useful in guiding when to drill infill wells before the altered-stress state negatively affects production outcome.