Re-fracturing is a common technique to ensure the maximum recovery from low-permeability, unconventional reservoirs. Generally in such reservoir systems, optimal gains are made from treating new areas of the reservoir that were unstimulated during the initial completion. To be successful under such circumstances, diversion away from depleted sections of the wellbore is critical. This paper discusses laboratory testing and subsequent finite element modeling (FEM) of full-length expandable casing patches deployed in several refracturing treatments in the Denver-Julesburg Basin, Colorado.

Short sections of casing patches were deployed in 4.5′, 13.5# casing. These sections included unanchored and anchored patch components. One type of each section (anchored and unanchored) was then perforated with a full-size perforating gun, 4 shot each section, 90° phasing. The perforating took place at the Edgar Mine Testing Facility in Idaho Springs, Colorado. Both the anchored and unanchored, perforated and unperforated, patch/casing sections were then push/pull-tested to determine friction factors and the impacts of the perforating on the patch/casing interface. These results were then incorporated into FEM modeling to determine the ability of the full-size, field-deployed patch to remain stationary and the impact such would have on perforation alignment during treatment conditions.

Both the push/pull tests and the subsequent FEM modeling suggest that the full-length casing patch exhibits only a minimal shift during the application of the forces associated with the hydraulic fracturing process. Some miss-alignment of perforations may occur but not to the level that they negatively impact the treatment success. These results align with the field trials which indicate positive re-fracturing treatment results. This unique project tested the viability of full-length casing patches in the refracturing process and incorporated laboratory testing of the casing-casing patch interfaces under both perforated and unperforated into FEM modeling, with comparison to field results. This process provides a full cycle analysis of the re-fracturing process using this diversion technique.

You can access this article if you purchase or spend a download.