| Popis: |
Sand production is becoming increasingly problematic due to the exploitation of poorer quality reservoirs and depletion of existing reservoirs. Cased hole frac-packs (CHFP) combine reliable sand control with potential for high productivity, and have become the completion of choice in many provinces. However, CHFP completions manifest in limited flow entry area into the well. This may cause two problems; a loss of productivity and potential screen erosion. In CHFP designs it is common to perforate the casing with high shot density big hole charges, but due to shot orientation and phasing, only a relatively few perforations connect with the fracture. Entire well production therefore originates from 4spf or less. Detailed modeling shows that this will not cause productivity impairment if the proppant pack is undamaged. Predicted skins for undamaged CHFP should be slightly negative, but field observations in one particular region show typical skins of 2 to 5, but with skins above 10 also reported. This tends to suggest that proppant permeability is being reduced in-situ. By contrast, productivity of open hole frac-packs (OHFP) is significantly less impacted by proppant damage and they also greatly reduce screen erosion risk. The productivity enhancement is revealed through detailed inflow modeling and laboratory experiments. However, it is difficult to engineer multi-zone OHFP completions, and wellbore stability issues complicate implementation. These limitations can be resolved by setting field-proven expandable completion liner (ECL) in the openhole section, prior to running the inner sand screen completion and frac-pack tools. Experiments on large scale samples show that ECL stabilizes the borehole. ECL slot geometry also results in 3-5 fold increase in fracture connection area compared to CHFP. ECL technology can also be combined with a number of different zonal isolation packer technologies, such as expandable, mechanical, swell and combo packer designs, to segment zones. This gives ECL frac-packs (EFP) the functionality of a multi-zone CHFP, but mitigates productivity impairment through proppant plugging and also screen erosion risk. The EFP completion concept also removes a casing string and eliminates perforating, and so also reduces HSE risks. It also has the potential to accommodate larger screen sizes, slim well designs and to reach deeper targets. The EFP completion concept also relies on integration of existing technologies, while offering the potential for a step change in well performance. |
