A New Acid for Extending the Lifetime of Wireline Cables with Spearhead Applications
Authors: Rabie A. I. , Prabhu R. , Benavides J. D. , Daeffler C. 
Published: September 2024

Acid spearheading is a known practice in both vertical and horizontal hydraulic fracturing operations. The practice became very common during horizontal well completion aiming at dissolving acid-soluble material in the near-wellbore area, cleaning perforation tunnels, lowering the initiation breakdown pressure, and enhancing injectivity. Low- to mid-strength hydrochloric acid with additives is the commonly applied fluid. However, acid incompatibility with perforating guns and wireline tools mandates separating the perforation creation and tunnel cleaning stages, resulting in longer completion time and additional wellbore fluid to be used. Although "compatible" acids have been recently introduced to perforate-in-acid, their ability to effectively protect wireline cables is questionable. The repetitive use of the wireline leads to significant corrosion, which significantly impacts the cable integrity to the point of mechanical failure. Wireline cable armors are galvanized (zinc-coated) plow steel, which is particularly challenging to protect against corrosion. The zinc layer is approximated at 4 to 5 wt% of the wire armor. A new acid utilizing a specially designed corrosion inhibitor (CI-A) was able to provide an excellent protection to zinc and maintain the protective layer. As a result, less maintenance and substantial increase in the lifetime of the wireline cable are anticipated.

The effectiveness of the new acid was investigated in corrosion testing on pure zinc coupons and wireline armors and compared to a benchmark standard industry "modified" acid (BMSA) at a temperature up to 190°F. Testing duration varied from 2 to 24 hours and optimum load was determined for two HCl concentrations: 5 and 7.5 wt%. Mechanical integrity of the cables was assessed through ductility "wrapping" testing after exposure to the acid under test. Two types of wireline cables were tested, conventional and jacketed cables. Corrosion testing on L-80 and P-110 tubular materials was also conducted. Microscopic imaging was utilized to better visualize the deposited layer on the wireline surface.

The new acid utilizing corrosion inhibitor CI-A showed rapid and excellent deposition on the zinc surface resulting in a weight loss between 0 and 0.5% based on the testing duration, temperature, and acid concentration. Repetitive exposure of the same wire to the inhibited acid showed a negative weight loss indicating excellent deposition and longer lifetime expectations. On the other hand, the BMSA acid failed with 5 to 7% weight loss indicating a complete loss to the protective zinc layer and significant corrosion to the steel beneath it. Wire armors exposed to acid inhibited by CI-A passed all ductility testing successfully. Armors exposed to the BMSA acid broke within the first wrapping cycle. Both acids provided an adequate protection to casing metals, which cannot be the sole criterion for a compatible spearhead acid during perforation.

The new acid with the proposed corrosion inhibitor allows using hydrochloric acid with wireline cables without the risk of corrosion or impacting the wireline mechanical integrity, resulting in a longer lifetime. Moreover, with perforating-in-acid, additional time is saved per stage, wellbore fluid volume is reduced, and pumping time and, hence, emissions are reduced.