Highly Accurate Prediction of Screenouts in the Eagle Ford Shale with the Screenout Index

摘要

Development of unconventional resource plays, such as the Eagle Ford shale in south Texas, require that complex multiple hydraulic fracture stages be placed in the horizontal section of the wellbore to be economical. Operational complexity is presented during both the completion and the fracturing phases, which are performed in an orchestrated manner by many contributors. A screenout during one of the fracturing stages will place many of the contributors on a standby status, delays the placement of subsequent stages, and causes costs to increase substantially because of standby charges, wellbore cleanout costs, and lost production days. The screenout index (SOI) is an empirical indicator developed by analyzing thousands of rate step-down tests (RSTs) from around the world, including hundreds from the Eagle Ford shale. Development of the SOI involved (1) following a specific four-step RST procedure, which requires the fourth rate change be about two times larger than the first rate change (to distribute measurement error over a larger span), (2) determining the instantaneous shut-in pressure (ISIP) in a specific and consistent manner, (3) calculating pressure gradients DP1 and DP4, (4) applying a rate correction to DP4, and (5) calculating the SOI = Corr. DP4/DP1. The SOI provides an advanced warning of an imminent screenout. This is highly beneficial because it allows modification of the remaining steps of the fracture treatment design and preparation of various decision control options to be executed in the event a screenout occurs or extending the treatment becomes necessary. Often, an SOI value of less than 0.5 indicates that a screenout is unlikely. If the SOI value is between 0.5 and 1.0, the chances of a screenout increase significantly. An SOI value larger than 1.0 signifies that a screenout is probable. The predictive accuracy of the SOI has been greater than 95%. Modification of the design of the completion configuration and/or elimination of certain types of completions and procedures can help minimize and possibly eliminate screenouts.