Impacts of variations of the minimum horizontal stress on hydraulic fracture growth and microseismicity

Hydraulic fractures are created by increasing fluid pressure over the minimum horizontal stress. Variations of the minimum horizontal stress with depth determine where hydraulic fractures can grow and what orientation of faults will slip. Here, we use a stress model and field data from the Hydraulic Fracture Test Site-1 to simulate hydraulic fracture growth in different landing zones along the length of horizontal wells. We found that strata with lower stress allow for significant lateral growth while strata with higher stress act as barriers to vertical growth. When stimulation occurred in a higher stress zone, the fracture grew both upwards and downwards, whereas in the lower stress zones, fracture propagation was limited by higher stress layers. Although high and low stress layers show characteristic differences in microseismicity, we found no clear relationship between the distribution of microseismic events and the fracture areas. Our results emphasize that the minimum horizontal stress is the primary control on hydraulic fracture growth and must be sufficiently and accurately measured to predict patterns of stimulation.