Difficulties and solutions for deepwater cementing projects

Difficulties and solutions for deepwater cementing projects

Blog Article

Deepwater cementing is the core technology of deepwater oilfield drilling. In order to achieve the development and application of deepwater cementing technology, the difficulties of deepwater cementing projects are analyzed, and targeted solutions are proposed to optimize deepwater cementing projects and improve economic and social benefits.

During the construction of marine drilling projects, if the water depth exceeds 500m, it belongs to the deepwater category. Deepwater drilling is to carry out drilling operations in sea areas with a water depth of more than 500m. With the increasing cost of deepwater drilling operations, how to complete drilling projects efficiently and safely has become the key point of current deepwater operations. Cementing, as a part of drilling, also plays an important role. Considering the characteristics of deepwater operations, deepwater cementing projects also face various difficulties, but it is the objective existence of these difficulties that has promoted the development of deepwater cementing technology to a higher level and higher technology.

Challenges in Deepwater Cementing Projects

Low Temperature

Generally speaking, sunlight can only reach the surface of the seawater, or due to the effects of wind, waves, and ocean currents, the heat exchange of seawater is caused, but it is limited to the range of 100-400m below the sea surface. However, in the depth range below 400m, the temperature tends to decrease, that is, the thermocline. In the lower part of the thermocline, the seawater temperature is extremely low; the temperature from the thermocline to the seabed decreases with increasing depth. For deepwater cementing projects, the seabed is located within or below the thermocline, so the temperature is very low. Generally, the seabed temperature in deepwater areas is about 2-6℃.

Low Efficiency of Cement Slurry Application

In deepwater cementing projects, the application efficiency of cement slurry is poor, which can be mainly analyzed as follows:

1. The wellbore structure is unreasonable, which makes it difficult to center the casing.
2. For the softer strata on the surface, they will be affected by the high-pressure sand layer or shallow "water-gas" flow during drilling, which will affect the wellbore structure, increase the friction resistance of the fluid, and make it difficult to achieve turbulent displacement.
3. In the deep-water seabed, the surface layer is mostly in a soft state without cementation. In addition, there is a narrow "window" phenomenon between the fracture pressure and the formation pore pressure, which makes it difficult to achieve turbulent displacement or graded gradient displacement.
4. Due to the complex casing structure, the gap between the surface casing and the wellbore is large, while the gap in the downhole position is reduced.

Shallow "Water-Gas" Flow

The shallow "water-gas" flow problem is mainly caused by the existence of shallow gas, high-pressure layers or gas hydrates on the seabed, which cause unstable decomposition. The shallow "water-gas" flow phenomenon may cause excessive flushing of the wellbore, causing deformation of the wellbore diameter, making it difficult to clean the silt, affecting the interface effect of cementing, and easily causing gaps. In addition, if the application design of cementing slurry is unreasonable, when the shallow "water-air" fluid condenses, cement slurry may invade, resulting in honey flow problems and micro-narrow grooves. The existence of gaps or micro-narrow grooves will affect the annular isolation effect of cement, affect the normal operation of the riser and blowout preventer, and be detrimental to drilling safety.

High Cost

As we all know, the cost of deepwater cementing is significantly higher than that of land cementing. The main reasons are as follows:

1. In general, in order to improve the low temperature environment and avoid the problem of shallow "water-air" flow, special materials and technical measures are used, which increases the cost of cement slurry system and operating expenses.
2. With the increasing development of low-carbon economy, the requirements of the Marine Environmental Protection Law are becoming more and more stringent. Therefore, the cleaning of ancient well equipment must meet "zero" emissions; and requirements are put forward for the environmental performance of the admixtures used in cementing.
3. As the water depth of deepwater cementing projects continues to increase, higher adjustments are required for logistics work, and the costs of various operations have risen accordingly.
4. The current utilization rate of deepwater drilling equipment is as high as 100%, and the cost has also increased, which has increased the construction cost of deepwater cementing operations.

Solutions to Deepwater Cementing Projects

Compared with land operations, the seabed where deepwater cementing operations are located is relatively soft, the fracture pressure is small, the terrain conditions are relatively complex, and fluid migration is very likely to occur; in addition, the temperature of the seabed is low, which is not conducive to the hydration process in oil well cement. Therefore, how to enhance the performance of cement slurry and ensure the smooth implementation of deepwater low-temperature operations has become a problem that must be considered in current deepwater cementing. In response to the various construction difficulties mentioned above, the following countermeasures can be considered:

Optimizing Cement Slurry Performance

In order to improve the operating environment of deepwater cementing and avoid the impact of low temperature, shallow laminar flow, narrow safety window, etc. on the project, it is necessary to select a cement slurry system with low temperature, early strength and reasonable density. Therefore, the cement slurry design in deepwater cementing projects should meet the following characteristics:

• Control the cement slurry density.
• Improve stability.
• Reduce transition time.
• High compressive strength.

To gain a deeper understanding of these methods, resources like Oil and Gas Simulation can provide valuable insights into the technologies shaping the industry.

Avoid Shallow Water Channeling

At present, the shallow "water-gas" flow problem that is common in deepwater cementing projects can be solved through the theoretical experience of "preventing gas channeling". In fact, water and gas are two elements that are very different in terms of physical and chemical properties, such as compressibility, density, viscosity and other characteristics. Since the density of gas is small and the compressibility is strong, pressure is the main factor affecting gas movement; however, pressure has no effect on cement hydration. Only because gas moves in cement in various ways (percolation, cracks, bubbles, etc.), it will affect the structure of cement stone and then affect the solid layer. However, when the formation water enters the cement slurry, in addition to its properties affecting cement hydration, it will also affect the water-cement ratio, thereby changing the coagulation time and coagulation strength of the cement slurry. Therefore, it is imperative to strengthen the research on shallow water channeling, combine the principle of shallow water channeling, and take targeted measures to avoid shallow water flow problems.

Drilling Fluid-Cementing Fluid Integration

In view of the various difficult problems faced by the current deepwater cementing project, improvements have been made through the drilling fluid-cementing fluid integration technology. For the application of drilling fluid-cementing fluid integration technology, if different types of drilling fluids can be combined to optimize the degree of influence on the hydration performance of cement slurry, improve the polymer molecular structure, or use materials with relatively small cement hydration heat to achieve compounding technology, then the application performance of drilling fluid admixtures can be improved and the smooth implementation of drilling operations can be ensured. In addition, the formed filter cake or filter membrane will also produce chemical reactions with cement slurry, which not only effectively avoids the crossflow channel of micro-annulus, but also ensures the bonding strength between the formation and cement stone. For the filter cake or filter membrane that has not been completely removed, it can also be used to ensure the strength of the soft seabed formation and better avoid the crossflow phenomenon of shallow "water-gas" during deepwater cementing.

Optimization of Deepwater Cementing Technology

The application of cementing technology mainly transforms indoor experiments to deepwater sites. With the continuous development of deepwater cementing projects, on the one hand, the development of miniaturized, high-performance mixing devices and precise measurement systems is accelerated, and advanced computer information technology is applied to support the realization of automatic control; on the other hand, the development of cementing technology is accelerated. For example, when cementing in the deepwater area of the Mississippi River Canyon, liquid admixture systems, nitrogen systems, etc. are used, and they are connected to the computer system to form a construction whole. The entire cement injection process is displayed on the computer screen to achieve remote control.

As can be seen from the above, due to the decreasing terrestrial oil and gas resources, deepwater drilling will inevitably become a trend of future development. However, due to the particularity of the deepwater natural environment and geological environment, if deepwater oil and gas exploration is to be successfully completed, water temperature, safety, cost and other problems must be improved. At present, foreign deepwater oil and gas exploration has made certain progress and achievements, promoting the rapid development of drilling technology. Drawing on successful experiences at home and abroad, in the future development of drilling technology, my country will definitely make breakthroughs in deepwater cementing, overcome complex operating environments and geological conditions, and improve drilling operation efficiency and quality.