Experimental study on oil based mudcake removal and enhancement of shear bond strength at cement-formation interface

Abstract

Successful removal of oil based mudcake from the wellbore prior well cementing is important for achieving strong shear bond between cement and formation. Failure to proper displacement of mud could result into poor cement bond quality. Both mechanical (water jetting, coiled tubing) and chemical means (acids, oxidizers, chelating agents, and enzymes) have been used for mudcake removal. However, these methods have limitations at certain conditions which can adversely affect well productivity.This work presents a low density and viscosity chemical wash (KV-IA and KV-IB) designed in the laboratory. KV-IA is a mixture of NaOH and Alkyl Polyglycoside (APG-1214). This works as emulsifier to remove the oil based mudcake from the wellbore surface. KV-IB is a blend of SPAN 80 and TWEEN 80 at 9.5 to 10.5 HLB. KV-IB works as a wetting agent to convert the oily-wet surface into water-wet to promote shear bond strength at cement formation interface (CFI).Based on mud removal efficiency and wettability tests, it was observed that KV-IA and KV-IB are efficient oil based mudcake remover and shear bond strength enhancer. The KV-IA solution showed removal efficiency of 80.2% indicating that it can remove oil based mudcake particles in the borehole. The contact angle of l3.3°, showed that KV-IB solution was a good wetting agent enough to change the wellbore surface from oily-wet to water-wet. The FT-IR analysis gives an insight regarding the mechanism of these chemical washes to enhance shear bond strength. It shows higher content of Calcium Silicate Hydrate (CSH) at the interface of treated samples compared to that of untreated samples, high content of CSH resulted to shear bond strength of about four (4) times higher than that of untreated samples.