Model to guide completion/stimulation designs to enhance fracture performance, slash water use
Eagle Ford, South Texas
The precise installation of a cased plug and perf completion requires a debris and proppant-free lateral. Therefore, to clear the way for the toolstring to reach targeted setting depth, operators typically overflush after each fracture treatment by 50 and up to 100 bbl in excess of the initial perforation volumes. This widely accepted practice has long raised concerns about the risks of weakening near-wellbore proppant conductivity and, thus, reducing sustained production. In addition, overflushing requires tremendous volumes of precious freshwater.
To better understand the impact of over-flushing on continuity between the proppant pack in the fractures and the wellbore, STRATAGEN conducted an investigation in the liquids-rich window of the Eagle Ford. The FRACPRO fracture design and analysis software was used to construct a 3D fracture model to simulate stimulation scenarios with various overflush volumes. Fracture modeling confirmed that over-flushing fracture stimulation treatments as low as 20-bbl has a measurable impact on near-wellbore proppant concentration and production. Widely recognized proppant transport and settling and critical velocity equations were then used to develop a new treatment methodology. The new approach uses real-time wellbore modeling, verified with fluid sampling, to monitor the calculated bottomhole proppant concentration, while sequentially reducing over-flushing volumes.
Fracture profiles for flushing to 0 lbm/gal at top perforation
Deepest cluster on left, shallowest on right. Source: SPE 170743 “Minimizing Over-Flush Volumes at the End of Fracture-Stimulation Stages - An Eagle Ford Case Study”
The modeled data was used to calculate flush volume on-the-fly in more than 250 fracture stages, recording a 100% success rate in achieving targeted setting depths. Over-flush volumes were reduced from 20 bbl to nearly 0 bbl without any incidence of plugs sticking during plug-and-gun tool string operations. While the theory does not quantitatively assess the effect of over-flushing on eventual production, the outlined procedures provide valuable insight for use in completion and stimulation design strategies, including fluid type, to enhance proppant pack-wellbore continuity and, ideally, fracture performance. Furthermore, its widespread application promises to conserve tremendous volumes of increasingly limited freshwater supplies. The strategy likewise opens the door for future investigation into whether minimizing over-flushing can increase production.