| Popis: |
One of the major issues with the development of unconventional ultratight shale-gas reservoirs is related to concerns about underdisplacing or overdisplacing hydraulic proppant-fracture treatments in multiple-zone completions in horizontal wells. In recent years, a very large number of multistage propped-fracture treatments in horizontal wells in ultratight shale-gas reservoirs have been overdisplaced to obtain a clean wellbore and avoid problems with the hardware (especially pump-down plugs) used for rapid multizone completions. Because cleanout treatments can usually be avoided by these overdisplacements, multiple treatment stages can be performed more quickly, which saves time and minimizes other added costs. However, this practice might result in poor communication between the propped fractures placed in the reservoir and the wellbore. In some situations, such as when the rock strength is sufficient to prevent closure of nonpropped fracture areas, overdisplacing a treatment could result in a very high conductivity region at the wellbore. There is certainly a limit to the length of an unpropped fracture that could stay open for a significant time. This mechanism is similar to what has been seen in some wells with proppant production, where well productivity has increased following proppant production. Proppant production might create some open channels in the proppant pack near the perforations that remain open. This paper discusses current overdisplacement practices and tries to address if and when overdisplacing fractures in shale- or tight-gas reservoirs could have a net positive or a negative effect on production. |
