Improving Long-Term Pay Zone Isolation Using New Cementing Technologies to Overcome Difficult Wellbore Conditions in Shallow-Water Wells Offshore Mexico

Abstract

Abstract In shallow water wells in the Gulf of Mexico, running and cementing the production casing are considered some of the most complex and critical operations, due to challenging wellbore conditions, 3D trajectories and heterogenous formations with different pressure regimes in the same section. To ensure an appropriate pay zone isolation, alternative, enhanced and more efficient cementing solutions are required to overcome the consequences of having far-from-ideal cementing conditions. This paper will describe a successful implementation of combined cementing system technologies solutions to ensure best-in-class zonal isolation in tough conditions in offshore tertiary wells. In the Shallow Waters Gulf of Mexico, the production zone in tertiary wells is drilled in a 12¼" hole with complex trajectories that combines changes in direction and high deviation angles. To ensure a high-quality cement job and good zonal isolation, it requires, among other parameters, good hole cleaning for proper drilling fluid removal, as well as a proper casing standoff. However, these ideal conditions are not always achievable well by well. Historically, due to concerns about wellbore stability events in the field, and based on torque and drag simulations, the operator limits the number of centralizers ran on the casing strings, where the strategy is focusing the string centralization across the pay zone and the riskiest intervals only. The solution implemented is composed of two innovative cementing technologies, which consist of an engineered chemistry spacer and a drilling fluid-sealing slurry system, looking to deliver a reliable solution that optimize the available resources, and achieve the well integrity aimed. The engineered scrubbing spacer improves non-aqueous fluid (NAF) removal with the mechanical action of scrubbing fibers, providing the best conditions for the cementing job to increase the cement-to-casing bonding. The drilling fluid-sealing slurry limits the detrimental effects of mud channeling by reacting with the NAF remaining in the hole, increasing its rheology, reducing its mobility, and limiting channel permeability. After introducing the new cementing strategy in the subject fields, the cementing operations achieved outstanding results in every application, considering that in majority of the cases the open hole was over-gauged with multiple washed-out intervals and difficult tripping conditions with the drilling bottom hole assemblies (BHAs). The cement bond logs have given very low amplitude values and strong formation signals consistently across all the open hole, even where no centralization was available and aforementioned local enlargements were expected. These results allowed to perform further intervention operations with clear zonal isolation, in both production and injection wells. The use of the innovative cementing technology strategy was standardized in the subject area for all 9⅝" production casing strings. As well, it was expanded to the other Tertiary and even Mesozoic wells in different fields both offshore and onshore, obtaining the same successful results in cement evaluation logs, becoming the primary slurry design across the pay zone.