Wellbore Cleanup in Horizontal Wells: An Industry Funded Study of Drill-in Fluids and Cleanup Methods

Abstract

David B. Burnett Abstract This paper describes the results of a two year study comparing the performance of a number of commercially available drill-in fluids (DIFs) used in horizontal well completions. The project was designed to provide a direct comparison of those fluids by measuring wellbore and formation damage and well cleanup in horizontal openhole completions in consolidated and unconsolidated formations. Thirteen different types of DIFs were evaluated including laboratory prepared and field samples of sized salt DIFs, synthetic base, polymer-carbonate based, and formate based DIFs. Screening tests were performed in single core (consolidated) tests without sand control screens. Later, radial flow-dynamic leakoff tests were performed in a multi-core test cell. DIFs were also tested in core wellbores modified to evaluate filtercake damage caused by production through sand control well screens. Practically all DIFs exhibited low spurt loss and good filter loss control. These DIFs formed external filtercakes on the walls of the wellbore, but with little invasion into the rock. A number of cleanup practices were used to remove these filtercakes. HCl acid washes and soaks, dilute brine washes, solvent soaks, and oxidizer treatments were all evaluated. Two types of internal breakers were incorporated into sized salt systems as well. We found that cleanup was not as effective as expected. Core materials exhibited low regained productivity (permeability) even after cleanup to remove wellbore damage. Low regained permeability was related to the nature of the DIF filtercakes and to the presence of simulated drill solids added to the DIFs. These materials caused the filtercakes to be tighter, more tenacious and harder to remove from the wellbore. Production of filtercake and filtercake residue from well walls also caused significant screen plugging. Polymer- carbonate DIFs showed greater screen damage than sized salt systems. As we learned more about the causes of damage we modified our completion practices to incorporate new DIF formulations and new cleanup practices. As a result the average productivity regained went from 58% regained flow capacity in the first year of testing to 71% in the final year of the program. P. 469