Why is this happening? You could always run expensive diagnostics to find out. But the evidence you uncover may not be useful in preventing future deformation.
Good news: we have some answers—and tips for avoiding future deformation. In our experience (and the experience of respected researchers), casing deformation most often happens for one of four reasons:
1. Tubular Envelope
The use of tubular structures are common in soft-sediment formations. Drilling the holes necessary for these structures can cause “liquefaction or fluidization; reverse density gradation; slumping or slope failure; and shear stress” (Mills, 1983). There’s not much you can do to fix your rock. That said, knowing this is a considerable factor in proper cementing is the first step.
2. Improper Cementing & Isolation
Properly cementing a well ensures the distinct geological zones are isolated and the casing is properly supported when it comes time to frac (over and over again). But if it’s not done right… well, plug slippage is the least of your worries. Start thinking ahead during the cementing stage and identify ways to guarantee perfect isolation. For example, according to one study of horizontal wells with laterals measuring over 10,000 feet, you’ll see better results if you rotate casing while cementing (Turner et al., 2019).
3. Geological Formations
Some geological areas are more prone to seismic induced or frac induced casing deformation due to the types of rock layers and formations present. One example is the Montney Formation, where the shale layers are prone to splitting. In situations where geological complications can cost you extra time and money, “the key to solve casing deformation failure is the reasonable spacing design of multi-stage fracturing” (Lian et al., 2015). Other studies indicate proper wellbore isolation (including frac plug efficacy) reduces the risk of cyclic stresses inducing casing ovality.
4. Operational Practices
It’s not easy to hear, but sometimes plug slippage is the unfortunate result of operational practices. As an example, the inherent process of multi-stage hydraulic fracturing includes repetitive pressure cycles that can create loads exceeding the production casing’s failure envelope (Barreda et al., 2018). Furthermore, crimping and ovality in wellbores nearby to active fracs can sometimes be avoided by solving for near wellbore frac-hits .
When plug slippages happen, investigate to see if one of these four causes is to blame. It’s also a good idea to work with your frac plug provider to see how they can help. You might find that a different type of plug—not a different brand—can do the trick for your specific well.
Interested in Repeat Precision’s downhole solutions? Contact us today and add the industry’s favorite frac plug to your completion.
Sources:
- Mills, P. C. (1983). Genesis and diagnostic value of soft-sediment deformation structures—a review. Sedimentary Geology, 35(2), 83–104. https://doi.org/10.1016/0037-0738(83)90046-5
- Turner, W., Adam, D., Cowan, K., Tellez, D., & Willis, J. (2019). Casing Rotation for Improved Cement Quality in Unconventional Horizontal Wellbores. 10.2118/196232-MS.
- Lian, Z., Yu, H., Lin, T., & Guo, J. (2015). A study on casing deformation failure during multi-stage hydraulic fracturing for the stimulated reservoir volume of Horizontal Shale Wells. Journal of Natural Gas Science and Engineering, 23, 538–546. https://doi.org/10.1016/j.jngse.2015.02.028
- Barreda, D., Shahri, M. P., Wagner, R., & King, G. (2018). Impact of cyclic pressure loading on well integrity in multi-stage hydraulic fracturing. Proceedings of the 6th Unconventional Resources Technology Conference. https://doi.org/10.15530/urtec-2018-2902463
