Abstract

Deep and ultra deep layers are important replacement areas for increasing oil and gas storage and production. After continuous technological breakthroughs, significant progress has been made in deep and ultra deep well cementing technology, especially in characteristic systems such as high-temperature cementing additives, high-temperature and large temperature difference cement slurries, ultra-high temperature cement slurries, high-temperature preflush technology, key cementing tools, fine pressure control cementing, wellhead progressive pressure suppression, and prestressed cementing.

The domestically independently developed characteristic cementing slurry system and supporting process technology have been promoted and applied in deep and ultra deep well cementing in basins such as Sichuan, Tarim, and Bohai Bay, The application effect is significant on the deepest vertical well Pengshen 6 in Asia, the first "Eight Openings and Eight Completions" Hongxing 1 well in China, and the highest temperature well Qiantan 1 well in Dagang Oilfield.

Due to the increasingly complex goals of oil and gas exploration and development, deep and ultra deep well cementing still faces new challenges. We need to continuously strengthen research on the basic theories of deep and ultra deep well cementing, key materials for high-temperature cementing, working fluid systems, functional cementing tools, and supporting processes, in order to provide strong technical support for deep and ultra deep oil and gas exploration and development.

39% of the remaining onshore oil and 57% of the remaining natural gas in China are distributed in deep layers. Deep and ultra deep reservoirs have become an important strategic replacement area for increasing oil and gas reserves and production, and are also a key focus for increasing reserves and production in the coming years.With the continuous increase in exploration and development efforts and the rapid development of oil and gas well engineering technology, a series of deep and ultra deep well drilling and completion technologies have been formed, helping ultra deep wells to reach a new level of 9000 meters.

Cementing is a key engineering technology that ensures the safe production and efficient development of "well assets" throughout their entire lifecycle. However, engineering challenges such as deep (burial depth, ultra deep), high (ultra-high temperature, high pressure), narrow (narrow pressure window, small annular space gap), and difficulty (complex multi pressure system, high drilling fluid pollution, and low displacement efficiency) during the cementing process pose serious challenges to the key technologies of deep and ultra deep well cementing. Therefore, this article focuses on the technical requirements for deep and ultra deep well cementing, focusing on the development of key additives, characteristic cementing fluid systems, series of functional cementing key tools, and new supporting technologies for deep and ultra deep well cementing at home and abroad. This article briefly describes the application effects of key cementing technologies for deep and ultra deep wells in key fields and wells in China, and puts forward suggestions for tackling key problems in cementing technology for deep and ultra deep wells. This is of great significance for the development of cementing technology for deep and ultra deep wells in China and the exploration and development of deep and ultra deep oil and gas resources.

1. High temperature resistant cementing additives and cementing fluid systems for deep and ultra deep wells

1.1 Key additives for high-temperature cementing

Under ultra-high temperature conditions, the cement slurry system faces a series of problems such as insufficient temperature resistance, failure of setting adjustment, prominent contradiction between settlement stability and rheological properties, serious pollution of the reservoir due to liquid phase filtration, decline in mechanical strength of cement stone, poor adaptability, and difficulties in on-site mixing, which seriously affect the safety and long-term sealing quality of deep and ultra deep well cementing operations.

Cementing materials are important foundations for ensuring the comprehensive performance of the cement slurry system, ensuring the safety of deep and ultra deep well cementing construction, and cementing quality. Among them, high-temperature cementing fluid loss agents, retarders, suspension stabilizers, and cement stone strength decline inhibitors are the key to solve the above problems of the ultra-high temperature cementing slurry system.

1.1.1  High-temperature Cementing Fluid Loss Agents

Fluid loss additive is one of the main additives used to improve the fluidity and stability of cement slurry, reduce liquid phase filtration to the formation, and ensure the overall performance stability of the system. It is crucial to ensure the safety and quality of deep and ultra deep well cementing operations.

After more than 40 years of continuous technological research in China, a series of products have been formed that can meet the cementing requirements of domestic oil and gas wells. Among them, 2-acrylamide-2-methylpropane sulfonic acid (AMPS) copolymer fluid loss additives have become a hot research and application topic both domestically and internationally due to their excellent temperature and salt resistance and molecular structure designability.

Our company Zoranoc produces ZOC-G86L/ZOC-G86S high-temperature AMPS fluid loss agent, which can withstand temperatures of 230 ℃;

ZOC-G80L/ZOC-G80S sulfonic acid based fluid loss additive, ZOC-G87S-A/ZOC-G87S-B solid fluid loss additive, can withstand temperatures of 180 ℃. These fluid loss additive products can be used in freshwater and saline cement slurry systems.

1.1.2  High-temperature Cementing Retarders

The retarder is one of the most important additives for oil well cement, which is particularly important for ensuring the safety of oil and gas well cementing operations and directly determines the success or failure of cementing. 

Since the 1950s, research and use of retarders have been carried out both domestically and internationally to improve the performance of cement slurries, gradually forming a series of retarders such as lignin sulfonates, sugars, cellulose, hydroxycarboxylic acids, organic phosphonates (salts), polymers, inorganic salts, and complex compounds. These retarders can basically meet the technical requirements of domestic oil and gas well cementing, and gradually develop towards environmental protection and intelligence.

Polymer retarders have become a hot research topic both domestically and internationally due to their controllable molecular structure, diverse functional monomers, excellent performance, and stable structure.

Our company Zoranoc produces ZOC-H50L/ZOC-H50S high-temperature AMPS retarder, which can withstand high temperatures of 260 ℃ and effectively extend the thickening time of cement slurry. They can bring good thickening curve with right angle and no influence on strength development. Both retarders have good compatibility with various additives. ZOC-H42L/ZOC-H42S high-efficiency retarders, with a temperature resistance of 190 ℃, suitable for a wide temperature range, and has little impact on other properties such as cement slurry strength, and has no special requirements for the water quality.

1.1.3  High-temperature Stabilizer

Stabilizer is one of the important additives for improving the settling stability of cement slurry and ensuring the comprehensive performance of the system. It is particularly important for ensuring the safety and quality of deep and ultra deep well cementing operations.

The commonly used stabilizers are mainly inorganic materials and organic polymer substances. Among them, synthetic polymer stabilizers have become a research hotspot in cement slurry suspension materials both domestically and internationally due to their ability to be prepared through molecular structure design, selection of suitable functional monomers, and special processing techniques according to product technical requirements.

Our company's ZOC-J20L latex stabilizer is a sulfonated surfactant complex, suitable for temperatures ranging from 35 to 150 ℃. It can effectively stabilize latex cement slurry to avert demulsification of latex.

1.1.4  High-temperature resistant cement stone strength decline inhibitor

Under ultra-high temperature conditions above 200 ℃, the mechanical strength of silicate oil well cement is prone to decline, which affects the long-term sealing quality of cement sheath in deep and ultra deep wells.

A large amount of research has been conducted both domestically and internationally to improve the mechanical strength and stability of cement stone under ultra-high temperatures, mainly by adding quartz sand and increasing the silicon calcium ratio to suppress the mechanical strength decline of silicate oil well cement stone. However, the problem of strength decline above 200 ℃ is still prominent. 

Halliburton's Microblock additive (liquid silicon) is suitable for use at 30-240 ℃ (BHST), which can prevent the strength decline of high-temperature cement stones; Brandl et al. [30] added an appropriate amount of silica and multifunctional additives to the cement slurry system to achieve a temperature resistance of 241 ℃.

Our company also has products such as silicon powder. For specific information, please search the product details page in Cementing Additives.