| Popis: |
ABSTRACT: Hydraulic fractures propagate when fluid pressure overcomes 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. 1. INTRODUCTION Multi-stage hydraulic fracturing is needed to stimulate production from unconventional petroleum reservoirs due to their extremely low permeability. Hydraulic fractures create new surface area and deliver fluid pressure to pre-existing fractures, causing microearthquakes that increase the area of contact with the rock matrix. Efficient and safe stimulation depends on the ability to control fracture growth and limit stimulation to target intervals. To propagate through or across any stratigraphic layer, the pressure within a hydraulic fracture must overcome the minimum horizontal stress (Shmin). Since pressure cannot be raised above the value of Shmin where the fracture is generated, layers with higher values of Shmin may act as barriers to hydraulic fracture growth. Shmin also determines the frictional failure criterion for pre-existing faults i.e., what populations of faults are well-oriented for slip and how much fluid pressure is required to induced slip. |
