This paper presents solutions and analysis of mathematical model of skins due to completions in gravel packed oil and gas wells. The models can bedivided into three cases:
Open Hole gravel packed well
Cased-holeperforated gravel packed well
Collapsed perforation tunnel gravel packed well.
The skins due to completion include damaged skin, restricted entry skin, liner skin, gravel packed sand skin, slanted well skin, perforation geometry skin, crushed zone skin, non-darcy skin and the skin in the perforation tunnel.
The results obtained from the calculation in open hole gravel packed show that the skin in damaged zone decreases as the damaged zone permeability increases. For the cased-hole perforated gravel packed oil and gas well, the results show that increasing the perforation radius, perforation length and crushed zone permeability result in the decrease of crushed zone skin for both darcy and non-darcy flow, the perforation geometry skin and skin in the perforation tunnel for both darcy, and non-darcy flow for a given shot density. For the collapsed perforation tunnel gravel packed oil and gas well, the results show that the increasing perforation radius results in the decrease of hemispherical flow geometry skin and skin in the perforation tunnel for both darcy and non-darcy flow for a given shot density.
The solutions of each gravel packed skin model is used to analyze field and experimental data in order to estimate the skins and the decrease or increase in productivity ratio due to completions in gravel packed wells.
Gravel pack is a common sand control technique used in many formation with unconsolidated or poorly consolidated sands. As a sand control treatment gravel pack has been used to exclude sand from the production well and hence the produced fluid in the Gulf of Mexico for over 50 years. Sand production can often be readily achieved by proper sizing of the gravel with respect to formation sand size using well established rules. Sometimes well consolidated formations can produce sand and hence gravel pack is employed in such formations for sand control.
Gravel pack completions are normally of three types namely:
cased hole and
The open hole gravel pack is used when the completion is in a consolidated single sand. or when multiple consolidated sands can be produced without fear of gas or water production. The cased hole and collapsed tunnel gravel packed completions require perforation and are often used in unconsolidated and poorly consolidated sands or when multiple sands are produced through tubing string.