To improve hydrocarbon production from unconventional reservoirs, well spacing and completion design optimization are key, yet challenging due to the unknown hydraulic fracture geometry and the uncertainty of reservoir properties. Combining fracture and reservoir diagnostic analysis is an efficient and cost-effective approach to generating realistic fracture geometry, understanding fluid flow behavior, and defining fracture conductivity distribution. This paper describes the development of a rigorous fracture conductivity calculation methodology for integrating fracture simulation with numerical rate transient analysis (RTA), and an integrated unconventional simulation case study validated with diagnostic results to evaluate well spacing and production.
A novel conductivity calculation model was developed based on a series of experimental conductivity measurements of propped and unpropped fractures. Different factors and mechanisms, such as continuous and discontinuous proppant pack distribution, proppant mesh size and type, and net stress were considered in the model. Due to different assumptions of methodology and fracture dimensions between numerical RTA and fracture simulation, an algorithm was developed for handling the integration of fracture simulation and RTA under different well and completion designs by considering the weighted-average reservoir properties.
In a North America unconventional reservoir development, a vertical pilot hole with downhole pressure gauges was designed for monitoring pressure changes in multiple benches during stimulation and production. The downhole gauge responses were used to calibrate the fracture model. The novel in-house fracture conductivity calculation was performed by using a rigorous fracture conductivity calculation methodology based on the fracture model results calibrated by the pressure response from downhole gauges. To integrate with RTA, an algorithm was performed to provide the weighted-average reservoir properties, averaged conductive fracture half-length and height calculations, based on calibrated fracture models and petrophysical inputs. These key parameters were used to set up the RTA model for history matching and production forecast.
By applying the in-house fracture conductivity calculation workflow and the measured pressure response, the calibrated fracture model results show that conductive fractures are aligned with the fracture conductive heights from the diagnostic datasets. After the completions and production histories were matched for six wells, sensitivities regarding well landing, spacing, and completion design were performed. The study shows that, by applying the rigorous in-house fracture conductivity calculation methodology, a calibrated fracture model proves to be an effective and rigorous physic-based workflow for developing a history-matched RTA model for evaluating and optimizing completion designs, well landing, and spacing. This paper also demonstrates how modeled fracture geometry was calibrated using diagnostic datasets, and the novel weighted-average workflow for reasonably calculating the reservoir inputs of numerical RTA models.
