A novel preflush to improve shear bond strength at cement-formation interface and zonal isolation

Abstract

The effective removal of filtercake during the oil-well cementing job is of utmost importance for the reduction of well integrity problems during well drilling and production activities. Poor removal of filtercake will lead to a failure in the ability of the cement to provide zonal isolation at the cement-formation interface (CFI), during completion and for the well's lifetime. Several chemical mechanisms (chelating agents, acids, enzymes, and oxidizers) have been widely employed to remove filtercake. Nonetheless, at certain circumstances, these strategies have drawbacks that can adversely impact oil-well productivity.This research introduces a novel preflush (KV-IIA as well as KV-IIB) developed in the laboratory to transform the water-based filtercake at CFI into cement-based materials to enhance shear bonding. KV-IIA solution contained 16% CaCl2, and 1% Alkyl Polyglucoside (APG-1214), while KV-IIB fluid comprised 1% Alkyl Polyglucoside (APG-0810), 12% NaOH, 15% Na2SiO3 and water. Simulated wellbores (SWB) with porosity and permeability of 18% and 150 ′ 10−3 μm2 respectively, were also used.The results showed the Reynold numbers for the preflushes KV-IIA and KV-IIB were 46,509 and 29,660 respectively. Since Reynold numbers are greater than 4000 value, the flow regime in the annulus is turbulent. The reactions among H3AlO42− and H3SiO4− from alkali-dissolved reaction, Ca2+, Na+ and H3SiO4− in the KV-II solution, and Ca2+ and OH− from cement slurry form the natrolite and calcium silicate hydrate (CSH) with different silicate-calcium ratio. Based on that, the wellbore shear bond strength (SBS) and the cementing quality were improved. Analysis of the FTIR demonstrated that the CFI of the specimens tested produced additional cement binder material which resulted in increased bonding strength. The results of this work are anticipated to provide insights into the bond strengthening mechanisms in water-based mud that could help cementing specialists customize the preflushes to enhance the rock-cement bonding for better annular sealing to ensure a long-term zonal isolation.