Effects of fracture geometries on well production in hydraulic fractured tight oil reservoirs

Abstract

Tight oil production is emerging as an important new source of energy supply and has reversed a decline in US crude-oil production and western Canadian light-oil production. At present, the combination of the multistage hydraulic fracturing and horizontal wells has become a widely used technology in stimulating tight oil reservoirs. However, the ideal planar fractures used in the reservoir simulation are simplified excessively. Effects of some key fracture properties (e.g., fracture-geometry distributions and the permeability variations) are not usually taken into consideration during the simulation. Oversimplified fractures in the reservoir model may fail to represent the complex fractures in reality, leading to significant errors in forecasting the reservoir performance. In this paper, we examined the different fracture-geometry distributions and discussed the effects of geometry distribution on well production further. All fracture-geometry scenarios were confined by microseismic-mapping data. To make the result more reliable and relevant, a geomodel was first constructed for a tight oil block in Willesden Green oil field in Alberta, Canada. The simulation model was then generated on the basis of the geomodel and history matched to the production history of vertical production wells. A horizontal well was drilled in the simulation model, and different fracture-geometry scenarios were analyzed. Results indicated that the simulation results of simple planar fractures overestimated the oil rate and led to higher oil recoveries. In addition, if the secondary fracture can achieve the same permeability as the main fracture, a hydraulic fracture with branches can increase the well production (e.g., Scenario 2 under the conductivity ratio of 1:2) because of a larger effective contact area between matrix and fracture. Secondary fractures with low permeability can decrease the well productivity compared with wells with biwing planar fractures. Furthermore, the effect of hydraulic-fracture geometries on the cumulative production of the wells with higher main-fracture conductivity was more significant compared with those with lower main-fracture conductivity.