Microorganisms for Secondary Cementation: A Promising Solution for Cracks and Microchannels in Oil Well Bore Casings
Authors: Priyadarshan Amit 
Published: October 2023

Abstract
Secondary cementing plays a crucial role in oil and gas well operations by providing zonal isolation and ensuring the integrity of wellbore structures. Secondary cementing is always performed after the primary cementation process to address potential deficiencies encountered during the primary cementing process. The objectives include achieving complete zonal isolation, strengthening wellbore integrity, preventing fluid migration between formations, mitigating potential casing leaks, and also to treat conditions arising after the wellbore has been constructed. In secondary cementing, various methods such as squeeze cementing, plug cementing, and remedial cementing are used to address specific well challenges, such as cementing behind pipe, sealing off unwanted zones, repairing damaged casing, and remedying lost circulation zones [1]. Cement bond logs, temperature logs, pressure tests, and cement evaluation tools are employed to assess cement quality, identify potential issues, and verify the efficiency of the secondary cementation job.
Current Secondary cementing technologies and methods include a plug-back job, where a plug of cement is positioned at a specific point in the well and allowed to set. For a secondary cementing job to be successful, appropriate cement placing methods, suitable mud displacement, optimized cement slurry design, efficient mud removal, and good casing centralization are essential factors. In order to improve cement quality including fluid loss management, gas migration prevention, and setting time optimisation, cementing additives, and new pumping technologies are used [2].
Secondary cementing is a critical operation in oil and gas wells but, the challenges in achieving a successful cementing job are high. Evaluating the quality and integrity of the cement bond is a challenge in the secondary cementing process. For achieving proper mud displacement, complete mud removal is required, which will avoid mud channel formation and inadequate bonding between the casing and formation, which will compromise zonal isolation. Another challenge is the design of cement slurry. To create cement slurries with adequate rheological characteristics and improved durability, consideration must be given to factors such as high temperatures, high pressures, and corrosive environments.
The proposed approach harnesses the natural abilities of certain microbes to produce a biological cementing material, effectively sealing off the undesired pathways. The blended solution, comprising the appropriate microbe type, concentrated nutrition solution, and a carrier fluid, is introduced into the fractured zone, allowing the microbes to consume the nutrients and produce the desired cementing material. The soaking period, typically around 48 hours, allows sufficient time for the microbes to consume the provided nutrients and synthesize the cementing material. Once this period is completed, the well can be brought back to production, resuming regular production operations in accordance with client procedures. This innovative approach holds great potential for sustainable wellbore remediation and zonal isolation enhancement. Utilizing natural processes and minimizing the use of chemicals, it aligns with the industry's increasing focus on environmentally friendly solutions [3]. In this paper, we will explore the feasibility and benefits of this microbial-based cementing solution. We will discuss the underlying microbial mechanisms and the practical considerations for implementing this technique in oil and gas wells. By examining the scientific principles, field application, and potential advantages, we aim to provide valuable insights into this novel sustainable approach for addressing microchannels and fractures in cement and formation.