Full Scale Gravel Packing Model Studies

Abstract

Abstract An 18-foot (5.49 m) transparent casing and formation sand chamber were used to study the behavior of slurries and fluids during simulations of existing gravel packing procedures. Gravel packs were established in the casing-liner annulus and against formation sand in a chamber connected to the casing through a 1/2-inch (1.27 cm) ID transparent perforation tunnel. perforation tunnel. The effect of special techniques and devices for increasing packing effectiveness were investigated using water and gelled water as carrying fluids. The simulation of present gravel packing field techniques in the model offered a means for studying the factors that often produce unsatisfactory sand control. These factors included annulus bridging, gravel-formation sand intermixing and mixing of borehole fluids with the gravel slurry. Improvements in the gravel packing process were attempted by selectively altering packing process were attempted by selectively altering treatment techniques and materials. Work in the model studies has shown that a tell-tale screen should not be positioned above the main screen when viscous gel carriers are used. A tell-tale screen below the main screen allowed better compacting of sand in the annulus below the perforations. Tool companies are presently using gravel perforations. Tool companies are presently using gravel packing systems with a lower tell-tale screen. packing systems with a lower tell-tale screen. The tests described in this paper are only a part of an ongoing model studies program. part of an ongoing model studies program. Introduction The process of gravel packing to prevent the production of formation sand from oil wells is one production of formation sand from oil wells is one of the oldest and most economical means of sand control. Previous studies have covered the necessity for properly sizing gravel to specific formation sand, the effects of gravel and formation sand intermixing, and techniques for enhancing the placement of stable gravel packs in the casing-liner annulus in deviated boreholes. The present study employed a full-scale model consisting of a transparent casing with a perforation tunnel and formation sand chamber to examine present gravel packing techniques and fluids. Gravel placement efficiency in a casing-liner annulus and against placement efficiency in a casing-liner annulus and against a highly permeable formation sand were studied under varying conditions including borehole deviation from vertical to horizontal. These model tests are part of a continuing study. Description of the Gravel Packing Model Packing Model The equipment used to perform the tests described in this paper is schematically represented by Figure 1. Fluids and slurries were prepared in the reservoir, and the bypass line allowed circulation through the pump to promote mixing in the reservoir. Valve 1 was operated partially closed during tests to maintain a constant pressure in the system and to provide constant circulation of the reservoir. A pressure gauge (G1) was provided to assist the pump operator to maintain the desired pressure. A pressure transducer (T1) was used to provide a constant strip chart record of pump pressures. A one-inch (2.54 cm) ID rubber hose connected the pump to the gravel packing model through valve 3, which was equipped with an air operator, as were valves 4, 5, and 6. Valves 7 and 9 were used to flush pack sand out of the casing-liner annulus after each test. Valves 5 and 6 were outlets for the liner and wash pipe respectively. The fluids discharged through valve 8 were forced from the formation sand chamber as fluids and slurries were pumped through a transparent, 1/2-inch (1.2 cm) ID perforation tunnel from the casing-liner an annulus. P. 311