Removal Efficiency, Cleanup Mechanism, and Damage Analysis of a Novel Treatment for Oil-Based Drilling Fluid Filter Cake Removal

Abstract

Removing oil-based drilling fluid (OBDF) filter cake is a difficult task. Low removal efficiency of filter cake may result in pay zone damage, including drilling fluid filtrate incompatibilities with reservoir fluids, fines migration, and undesirable change of permeability and porosity. The cost-effective and single-stage application of new surfactant/oxidant system to enhance the removal efficiency of OBDF filter cake and minimize the formation damage and corrosion damage.

Rotational viscometer optimized the formulation of OBDF by regulating the rheological properties. Filter press simulated various high-pressure/high-temperature (HP/HT) well conditions in laboratory to form the OBDF filter cakes and remove them from sandstone disks. Drop shape analysis was performed to illustrate non-ionic surfactant treatment on OBDF emulsion. Inductively Coupled Plasma (ICP) equipment disclosed the cleanup mechanism of filter cake components by breakers. Formation damage was disclosed by experimental results of X-ray Computed Tomography (CT) scan and Coreflood implements. Corrosion rate was tested with L-80 metal to determine the most efficient corrosion inhibitor concentration.

Surfactant used in the new removal system breaks OBDF emulsion and thus expands the contact area between dense filter cake and effective breaker. Coated breaker can be circulated out of wellbore after the removal work, based on its low density and tightly coated property. HP/HT filter cake removal tests indicate the optimized new system can disperse and remove the OBDF filter cake by up to 98 wt% removal efficiency. After 12 hours filter cake removal test, the optimized surfactant/oxidant system results in 4.38 % loss of initial porosity mostly and carried out the retained permeability up to 72.66 %. 1.5 and 2 wt % of 0% coated persulfate with 5 vol % of Rodine 31-a gave an industry accepted corrosion rate of 0.033 lb/ft² and 0.045 lb/ft² , respectively, although pitting was still present on the faces of coupon.

With optimized formulation and soaking time, the cleaning solutions will benefit the oilfield industry significantly by removing OBDF filter cake under challenging well conditions. The new surfactant/oxidant system minimizes the effects of drilling fluids on formation properties, based on its quick removal steps, high removal efficiency, and acceptable formation damage and corrosion damage.