Wellbore cleaning is a vital link between drilling operations and well completion to secure the massive time and money invested to drill the hole intervals by removing drilling fluids residues, pipe dope, and other debris from the wellbore. The well production can be sustained in the long-term by properly accomplishing this step, promoting technical and operational efficiencies. This paper presents an effective customized treatment design and successful execution of a wellbore cleaning case study.
The Wellbore cleaning process is a combination of both mechanical and chemical means, a cleanout string of scraper, brush, magnets, and pill train of surfactants, and solvents are expected to retrieve debris and displace mud residues leaving the wellbore water wet, whose efficiencies can be judged through return fluids Nephelometric Turbidity Unit (NTU) and Total Suspended Solids (TSS). Since different wells vary in geometry, depths, and mud components, a custom design for the wellbore cleaning process is mandatory to guarantee satisfying treatment outputs, the design includes cleanout string parts and spacing, besides solvents and surfactants pills train additives, and volume.
Extensive lab testing was performed to customize the proper wellbore cleaning design to remove inverted emulsion fluids (IEF) residues from casing and tubing in the studied challenge gas well. The casing pickling was executed with 150 barrels (bbl) of solvent and surfactant chemical cleaning Spacers containing 630 gallons (gal) of locally manufactured solvent and 378 gal of locally manufactured surfactant displacing the wellbore water with clean water.
The water returns NTU and TSS of 47 and 0.03 % Solids respectively were achieved at 179 bbl after the high viscosity tail spacer of the casing pickling. The Cleanout Bottom Hole Assembly (BHA) was subsequently pulled out of the hole free from IEF residues and water wet, demonstrating the good cleaning performance of the locally formulated Chemistries. Similarly, the Tubing Pickling was executed with 54 bbl of Chemical cleaning spacer containing 990 gal of solvent. The water returns NTU and TSS of 38 and 0.02 % Solids respectively were achieved at 168 bbl after the high viscosity tail Spacer of the tubing pickling. In a conclusion, the low NTU and TSS values confirmed the effective wellbore cleaning design and treatment.
In this paper, we will be presenting a custom treatment design and successful execution of a wellbore cleaning case study from a chemical perspective, using 100% locally developed chemistries, that are environmentally friendly and readily available in-country, adding the value of lead time and optimized cost to drilling operations, where selected treatments could achieve targeted return fluids NTU and TSS within competitive displacement volume for both casing and tubing.