Simulating the Life of Hydraulically Fractured Wells Using a Fully-Coupled Poroelastic Fracture-Reservoir Simulator

Manchanda, Ripudaman (The University of Texas at Austin) | Zheng, Shuang (The University of Texas at Austin) | Gala, Deepen (ExxonMobil Upstream Research Company) | Sharma, Mukul (The University of Texas at Austin)



Horizontal well fracturing is an established practice to improve the recovery of hydrocarbons from oil and gas reservoirs. To simulate fracture propagation, fracture closure during production and fracture reopening during fluid re-injection, it is essential to combine three important aspects of the problem: multiphase flow, geomechanics and fracture propagation. Current simulation software utilize separate models for these processes. Our objective in this paper is to present a streamlined workflow that we have developed to integrate these highly coupled processes into a single computationally efficient simulation model.

A fully coupled 3-D geomechanical reservoir simulator has been developed to perform multi-cluster hydraulic fracturing and reservoir simulations. The model (Multi-Frac-Res) uses coupled fluid and proppant transport in the fracture with multi-phase reservoir flow and reservoir stresses, in one system of equations. It also accurately models fluid and proppant distribution between multiple perforation clusters in the wellbore. Fracture closure during shut-in or production requires the use of implicit contact models and these models account for the impact of proppant embedment on fracture conductivity. The coupled system allows for seamless transition between fracture propagation, fracture closure, reservoir production and re-injection. This is done in one streamlined workflow without the need for inefficient transfer of information between different simulation software.

An effective hydraulic fracturing treatment aims at maximizing the EUR while maintaining high hydrocarbon production rates. The integrated model allows us to directly evaluate the impact of cluster spacing, frac fluid injection rate, proppant volume, and drawdown on the effectiveness of a hydraulic fracturing treatment. Simulation results are presented that show the relative importance of all the above parameters during the lifecycle of a typical horizontal well. We show how smaller cluster spacing can cause more interference between fractures and hamper the EUR. Larger proppant volume is shown to improve the conductivity of the created fractures and improve the productivity. Faster drawdown is shown to cause faster depletion and faster closure of the fracture but also helps in producing more fluid. Changes in the stress field around the fracture are presented and are shown to impact the growth of fractures in in-fill wells as well as the performance of refracturing treatments. These poroelastic effects are also shown to play a very important role in the growth and reorientation of fractures in injection wells during waterflooding.

Current simulation software utilize separate models for these processes leading to inefficient data transfer between several models that can cause loss of data. This study showcases an integrated model that can simulate the lifecycle of hydraulically fractured wells all the way from creation of the hydraulic fractures to production and reinjection and allows for a holistic comparison between scenarios by comparing productivity numbers and EUR estimates.