Limits of Well Deviation to Prevent Screen Erosion in Cased-Hole and Frac-Packed Wells

摘要

For high permeability, loosely consolidated reservoirs, cased hole and frac packed (CHFP) completions have been employed for both sand control and production stimulation. More often than not, these wells are offshore and are drilled deviated or highly deviated from centralized platforms. Because fractures are almost always vertical with a very well-defined azimuth, fractures executed in deviated wells have very inefficient contact with the wellbores. This means only a few perforations are actually connected to the fracture even with the so called halo effect. As a result, a large portion of the total rate bypasses the fracture and enters the well through the perforations that are not in contact with fracture. For example, at 10,000 STB/d with permeability of 50 md, the fractional flow through the fracture is 64% even for a 10° well deviation. It drops to only 30% for a 45° well deviation. This provides different velocities, different erosion C-factors (15.6 vs. 39.2 through the fracture region and 1.4 vs. 1.9 for the rest, respectively) and different sand control characteristics between the two sets of perforations. A limited number of perforations connected to the fracture means that the velocity through them, for a given production rate, is high. This could cause fine movement which would further cause screen plugging and screen erosion. When the screen is partially plugged, it is more prone to erosion simply because the screen inflow area is reduced and therefore (at the same flow rate) the fluid velocity increases. Screen erosion can be more severe at one well deviation angle than another. Here the number of opened perforations in the deviated wells and a range of C-factors for different well production rates (i.e. for different reservoir permeabilities and well deviations) are calculated. These C-factors are compared with published experimental and field data. It appears that they frequently exceed the maximum C-factor of screen erosion. Finally, guidelines on acceptable well deviations that will not lead to screen erosion are offered.