Understanding Permanent Plug-and-Abandonment Cementing Technology in Changqing Oilfield

Abstract: Permanent plugging of oil wells is a critical phase in oilfield development and production activities. Research into plugging technology will further promote the development and production of oilfields. This paper focuses on analyzing the main operational procedures at permanent plugging construction sites and applies new downhole tools, such as cement retainers, to form a complete construction plan to guide the plugging operations.

Keywords: Oil well permanent plugging, cement retainer

Over time, some oil wells become depleted and have no remaining oil or production potential. Once fully developed, these wells have no further production value and pose ongoing risks to the surrounding environment and people’s lives. Therefore, permanent plugging becomes particularly important. Among the methods used, the most common is the squeeze cementing technique to block perforated zones and the entire wellbore. Especially in recent years, the successful application of cement retainers has significantly improved the efficiency and quality of plugging operations.

1. Preparatory Work

  1. Cleaning the Wellbore
    • Cleaning the wellbore is one of the most critical steps before squeeze cementing. A clean, oil-free wellbore not only facilitates the bonding of cement but also enhances the reliability of downhole tools. A clean wellbore ensures complete adhesion of cement to the inner wall of the casing, thoroughly blocking the path for oil and gas migration along the casing wall, thus ensuring the quality of the plugging operation. The workover team first runs a casing scraper that matches the inner diameter of the casing to clean the wellbore, ensuring there is no sand accumulation or debris at the bottom of the well. Then, they use a scraper to scrape the wellbore walls, with particular attention given to the retainer position, which should be scraped repeatedly five times or more. Finally, a sharp cone is run to flush the wellbore with fresh water at a high flow rate until the water color is consistent both entering and exiting the well, ensuring the wellbore is clean and free of scale, providing favorable conditions for subsequent operations.
  2. Testing the Casing String
    • These oil wells have been in production for a long time, and the casing might have deteriorated due to corrosion by formation fluids, posing risks during squeeze cementing operations, leading to potential stuck pipe incidents. After confirming the wellbore cleaning, the workover team performs a pressure test on the casing string using a packer. Taking a typical test string structure for 139.7 mm production casing in Changqing Oilfield as an example: one piece of 73 mm N80 external heavy-duty tool pipe + Y221-114 packer + ball seat (connected directly to the packer without a ball). The construction unit must prepare various emergency plans in advance and arrange for emergency materials according to emergency requirements. The on-site construction team must conduct emergency drills based on the content of the emergency plan. Prior to construction, the construction unit must survey the site and surrounding environment, observing whether there are villages, residents, forests, major stations, bodies of water, power transmission facilities, or lines nearby. They should carefully investigate the terrain, transportation, communications, and residential conditions around the wellsite, taking into account geological data and weather conditions to implement safety and environmental protection measures against fire, explosion, toxic gas poisoning, flood prevention, collapse, and adverse weather. Emergency plans must be prepared based on these investigations within a 500-meter radius. During construction, risk assessments must be conducted based on the specific procedures and content of the well’s operations and the surrounding environment, and risk mitigation measures must be established. Risk mitigation measures must include environmental protection measures. Strictly adhere to the new “Environmental Protection Law of the People’s Republic of China” and the new “Occupational Safety and Health Law of the People’s Republic of China.”

2. Environmental Protection Requirements

  • The construction site should be equipped with waste liquid recovery tanks. Construction residual liquids, waste fluids, and fluids discharged from the wellhead must be collected in the waste liquid recovery tanks and not discharged randomly. The wellsite should be covered with qualified anti-seepage mats to prevent contamination of the ground surface by construction fluids and crude oil. There should be protective dikes around the wellsite and drainage channels within the wellsite to divert rainwater or fresh water into the effluent pond. The effluent pond must have anti-seepage, anti-backflow, and anti-spill measures. Effluents from the pond can only be collected by tanker trucks and treated at designated locations; they cannot be discharged randomly. It is strictly prohibited to excavate effluent ponds near slopes prone to collapse near the wellsite. The construction area and living quarters within the wellsite must be clearly demarcated and effectively isolated. Solid wastes such as oily sludge generated during construction should be properly collected and disposed of at designated locations; they cannot be discarded randomly. Waste bags, drums, and residues from chemical materials must be recovered and properly disposed of.

Conclusion:

  1. For permanent plugging operations, preparing the wellbore condition is crucial. It not only verifies the construction process but also investigates construction risks. It is essential to rigorously implement measures such as casing scraping, wellbore cleaning, and pressure testing, ensuring accurate data that can guide subsequent squeeze cementing operations.
  2. Before cement is introduced into the well, thixotropic testing must be performed. Plugging with cement plugs is a high-risk operation that requires strict standards for both cement slurry properties and construction equipment to ensure construction safety and cementing quality.