Experimental study on the effect of oil based filtercake on bonding strength at wellbore second interface

Abstract

The integrity of the oil-gas wellbore is critically depending on the quality of the binding between cement and rock materials. Weak bond between cement and formation may lead to the potential leakage of high-pressure formation fluids through cracks and micro-annulus formed at the interface which results into blowout and groundwater contamination. Failure to properly displace mud prior to cementing can lead to poor bonding at the second interface (SI) of the wellbore. The main purpose of this study is to quantify the impact of oil based-filtercake on the bonding quality at the wellbore Second Interface during the drilling of sandstone reservoir well by using shear bond measurements and material characterization techniques. The results indicated that, the presence of oil based-filtercake at the SI has a detrimental effect on shear bond strength making it as weakest point of adhesion. The tested Blank samples had higher bond strength compared to treated (oil based filtercake) samples. The low bond strength for filtercake system was due to existence of oil based filtercake films which hindered the totally cement hydration process to form a strong bond as the oily film cannot allow the interact with aqueous cement slurry material to complete the hydration process. The FTIR analysis showed that, the lower transmittance (35%) at 1091 cm−1 band (Si–O) of mud treated samples revealed the low content of chemical binder material (Calcium Silicate Hydrate - CSH) at the interface while the blank samples gave 62% at 1088 cm−1 band (Si–O) showing the high content of CSH at the interface which led high bond strength. The results show that oil-based filtercake has a significant detrimental effect on shear bond strength of the second interface.