Evaluation of Wellbore Clean Up Fluids by Comparing Laboratory Test Results with Field Production Data

Abstract

Wellbore clean up has become an integral part of well completion operation aiming to maximize well productivity from a near skinless wellbore. The awareness has become more widespread with more and more horizontal and sand packed openhole wells being completed with so-called non damaging Drill-In-Fluids (DIF). Although drill-in-fluids control fluid loss and saturation related damage to a great extent, they tend to leave a sticky filter cake containing polymers and Calcium Carbonate particulates which can severely restrict well flow. Acids, oxidizers, chelating agents and enzymes have been often used as wellbore clean up fluids with mixed success. This article demonstrates laboratory and field evidences on superior efficiency of some recently developed bio-enzymes and explains the reason of their not so satisfactory treatment result in some wells.Simulated Reservoir Condition Core Flow (RCCF) and return permeability measurement was the basis of laboratory evaluation and comparison of various clean up formulations, including inorganic/organic acids, oxidizing agents, various enzymes and combination treatments. Mud filter cake was developed by simulating drilling and reservoir parameters. Cleaning treatments were mimicked as per realistic field operation. Photographic evidences were produced on clean up efficiency and final conclusion was drawn based on return permeability.Well treatment methodologies are discussed and production data from over twenty wells/legs were produced, analyzed and compared. An effort is made to analyze unsatisfactory treatment outcome in some of the enzyme treated wells and to establish the best practice approach for wellbore clean up operations.

Residual Damage, Its Consequences, and Remedial Measures on Post Hydrofrac Well Productivity: Learnt Lessons

“…Enzyme breakers are proteins consisting of a complex structure of amino acids [161]. Enzymes work on a lock and key principle; thereby, an enzyme can attack only a specific chemical bond to facilitate a reaction [162,163]. This site-specific attack effectively breaks guar into monosaccharides or oligosaccharides, thereby avoiding undesirable reactions with the wellbore and downhole equipment [164].…”

Delayed Breaker Systems To Remove Residual Polymer Damage in Hydraulically Fractured Reservoirs

“…When all sites are aligned, the substrate reacts to form an enzyme-product complex that releases the product, leaving the enzyme unaltered for further attachment to a fresh substrate (causing a superior effect at low concentrations). For enzymatic hydrolysis, the process continues until the substrate is depleted or degraded to the depolymerized simplest form where no further reaction can occur. , Figure illustrates the polymer breaking mechanism.…”

“…For enzymatic hydrolysis, the process continues until the substrate is depleted or degraded to the depolymerized simplest form where no further reaction can occur. 21,22 Figure 2 illustrates the polymer breaking mechanism.…”

Development of Hybrid Drilling Fluid and Enzyme–Acid Precursor-Based Clean-Up Fluid for Wells Drilled with Calcium Carbonate-Based Drilling Fluids

“…Furthermore, the wellbore clean-up is another crucial challenge, and the current research indicates that the clean-up solutions composed of a wide range of components such as strong acids, weak acids, enzymes, chelating agents, and oxidizers are used. , The ability of the clean-up solution to remove the deposited filter cake varies significantly based on its content. Strong acids such as hydrochloric and hydrofluoric acids tend to react with downhole equipment and tubulars, causing severe corrosion, and often result in non-uniform clean-up because of the formation of wormholes.…”