Abstract
Hydraulic fracture conductivity losses because of proppant embedment, proppant failure and rock damage by nonnative fluid interactions are the leading cause of drops in well productivity. These conductivity losses are strongly governed by the local stress regime in the vicinity of the fracture face and the geomechanical responses of the rock to these stresses. Drawdown management for shale wells seeks to minimize fracture conductivity losses and matrix permeability impairment in order to create conditions for favorable long-term well performance. This is achieved by controlling drawdown to manage near-wellbore and near-fracture stresses to avoid or mitigate proppant embedment and sharp fracture conductivity decline. However, these approaches may also lead to poor initial production trends.
This work focuses on the use of a coupled geomechanical and reservoir flow model for optimizing choke or drawdown management to maximize NPV for liquids-rich shale wells. Geologic analysis, reservoir and fluid properties and completion-related properties acquired from a prominent liquids-rich shale play within the continental US forms the basis of our study. Three different stress sensitive models are used as a proxy for soft, medium and stiff rocks to simulate different degrees of irreversible rock deformation. The geomechanical model considers the effects of hysteresis and choke management strategies developed for a diverse set of rock mechanical properties.
The Productivity Index (PI) along with the cumulative rates are used to evaluate the effectiveness of any chosen choke management strategy. Our results indicate that the most critical time period for optimizing long-term well management is during the initial life of the well. High production rates with sharp declines, typical of shale reservoirs, causes irreversible damage in the vicinity of the fracture affecting its conductivity. Choking back the wells in anticipation of longer term stable production profiles is also shown to be less than optimal. We compare and contrast several different drawdown settings and demonstrate that the choice of a larger choke setting during the initial life of the well coincides with the highest possible NPV and recovery factors over a wide range of reservoir and fluid properties. Our results also indicate that irrespective of the choice of drawdown setting, the losses in fracture conductivity and matrix permeability tend to be very severe in the first few days of production.
