Unconventional Oil - Decline Permeability Multipliers for Model Calibration

Abstract

The unconventional fracture model (UFM) has been routinely used to model complex fracture systems. The UFM generates both geometry and conductivity of simulated hydraulic fracture networks, which can be used to create unstructured grids for production simulation. The production simulation model generated from the UFM must be calibrated with actual production data so that it can be used for production predictions and different sensitivity analyses such as well spacing, landing point evaluation and completion optimization. The calibration of the production simulation model is done by specifying oil production rate and history matching the bottomhole pressure (BHP), gas-oil ratio (GOR), and water cut (WCT) measured from oil production wells. The history-matching process mainly involves modifications of the geometry (height and length) and conductivity (permeability) of the hydraulic fracture system, as well as the stimulated reservoir volume (microfractures) surrounding the hydraulic fractures. Modification of the hydraulic fracture geometry usually requires rerunning of the UFM modeling process, which is time consuming. The modification of the hydraulic fracture conductivity usually requires the use of different permeability multipliers in different fracture regions that are defined arbitrarily. To make these modifications, a consistent and systematic process, a permeability multiplier function, has been developed and successfully used in different projects. The function and its application will be introduced and discussed in this paper. The decline permeability multiplier (DPM) function is defined with three parameters: the permeability multiplier at the initiation point (wellbore) of the fracture, the permeability multiplier at the endpoint (tip) of the fracture, and the curvature of the decline between the two points. By adjusting these three parameters, pressure and production data (BHP, GOR, and WCT) can be reasonably history matched. In practice, the function can be applied to hydraulic fractures and microfractures separately with different parameter values. The function can be used not only to define conductivity distribution inside hydraulic fractures, but also to help initialize water saturation distributions in hydraulic fractures in either structured grids or unstructured grids. An example of water saturation distributed with this decline function to better match the water cut is also presented in the paper.