The success of a gravel-pack completion depends on placement of gravel in the perforation tunnel area and the screen-casing annulus. Wellbore deviation is one of the predominant factors affecting gravel placement. As wellbore deviation increases, the gravitational forces and carrier fluid limitations may result in gravel settling (duning) and an incomplete packing of much of the perforation tunnel area, as well as a premature screenout of the screen-casing annulus.
A completion technique is introduced that eliminates problems associated with gravel settling. The technique uses buoyancy forces to counter the gravitational forces on the gravel particulate. Particulate settling is minimized by decreasing the ratio of the particulate density (Dp) to the base fluid density (Dc). Verification of the concept includes test results from a gravel-pack model. The model is 18 ft long with an inside diameter (ID) of 6.2 in., a screen and blank pipe size of 2-7/8 in., and a working pressure of 1,000 psi. The blank pipe length is 6 ft and the screen length is 12 ft. There are 20 perforations that include a chamber to simulate a void space behind the casing.
Test results include gravel-pack efficiency for variations in base fluid properties, wellbore deviation up to 90° (horizontal) and particulate density/ base fluid density ratios (Dp/Dc) from 2.65:1 to 0.8:1. Recommendations for a treatment technique and low-density particulate specifications also are included.