Early-strength low-hydration heat evolution cement paste system applicable to deepwater shallow cementation

Abstract

The invention discloses an early-strength low-hydration heat evolution cement paste system applicable to deepwater shallow cementation. The system is prepared from 100 parts of cement, 5-10 parts of phase-change heat absorption materials, 10-30 parts of a density reducing agent, 8-15 parts of suspension materials, 0.5-1 part of a drag reducer, 0.3-0.55 part of retarder, 0.7-1 part of a fluid loss agent, 0.7-1 part of a defoaming agent, 0.06-0.1 part of an early strength agent and 68.2-82.3 parts of water. The cement paste system has the good early strength property at low temperature, is small in hydration heat evolution amount and good in thickening property, flowing property and sedimentation stability, has right-angle thickening property and small water loss, and meets on-site construction requirements. According to the system, surface cementation in the deepwater hydrate layer can be achieved, operation time and cost can be saved, and a technical support is provided for mining of oil and gas resources in the deepwater hydrate layer.

Description

technical field [0001] The invention relates to an early-strength low-hydration exothermic cement slurry system suitable for deep-water shallow layer cementing, which is suitable for deep-water low-temperature and deep-water hydrate layer cementing operations, and can also be used for permafrost zones in land high latitude regions Shallow and surface section cementing belongs to the field of oil and gas well cementing engineering. Background technique [0002] As the global demand for energy increases, people begin to exploit resources in extremely challenging environments, such as: deep waters, high-pressure and high-temperature formations, etc. In recent years, oil and gas exploration and exploitation in deep water (water depth 400-1500m) and ultra-deep water (water depth more than 1500m) have become the focus of development in developed countries such as Europe and the United States. From 1990 to 1999, 36% of the giant oilfield reserves discovered in the world were distr...

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Problems solved by technology

[0004] The complex geological environment in deep water and shallow layers has brought many challenges to cementing operations, such as low temperature (generally around 4°C, the lowest can reach 0°C), resulting in low early strength of cement that cannot meet the needs of rapid solidification. The problem of channeling is likely to occur under low pressure conditions, and at the same time prolong the well construction period and increase the well construction cost; low formation fracture pressure, under the conventional density cement slurry density, it is easy to leak the formation and pollute the marine environment; the coexistence of high pressure and low formation fracture pressure leads to solid The density of well cement slurry is difficult to adjust, and the low-density cement slurry system cannot be hardened quickly; the hydrate contained in the formation decomposes and releases a large amount of natural gas under the requirement of rapid hydration and condensation of cement, which causes the diameter of the wellbore to expand, gas channeling, and affects mud replacement. Efficiency and other issues will ultimately affect the quality of cementing

In addition, the decomposition of natural gas hydrate will also cause abnormal high pressure, resulting in blowout or even well kick accidents

In serious cases, it will induce earthquakes, tsunamis and other accidents in Haiti, which will cause irreparable losses. It is a great safety hazard for deepwater cementing

However, the existence of hydrates in deep-water formations has not attracted enough attention.

[0005] At present, the cement system used in deepwater well cementing includes (1) G-grade cement mixed with reinforcing material system. Sun Xiaojie et al. developed the lightening reinforcing material S1 and optimized the high-efficiency composite early strength agent CA-5S to improve the cementing performance of Portland cement. Hydration ability at low temperature can promote the development of early strength of cement stone. BXF-500S is preferred as fluid loss reducing agent, but the minimum density of this system can only reach 1.40g / cm 3 , and the system only has a better early strength effect in an environment of 30°C, and the operating temperature is quite different from the deep cement line temperature of 4°C. In addition, the cement slurry does not consider the heat of hydration, so the stability of deep-water hydrate cannot be guaranteed; ( 2) Particle-graded cement system. DeepCRETE developed by Schlumberger uses the principle of particle grading and adds non-retarding dispersant and coagulant to shorten the waiting time of cement slurry. The density at 18°C ​​is 1.50g / cm 3 The cement slurry system exhibits good early strength characteristics under certain conditions, but the operating temperature and density of the cement slurry system are related to the mudline temperature of the deep water environment at about 4°C and the low formation fracture pressure has a significant effect on the cement slurry density of 1.20g / cm 3 There is a big difference between the left and right requirements, and the cement slurry does not consider the influence of hydration heat release on the stability of natural gas hydrate; (3) High alumina cement slurry system, the aluminum silicate cement slurry system studied by BoncanVG et al. Adding activated aluminum silicate to cement, adding accelerators such as fast-setting gypsum, polyvinyl alcohol fluid loss reducer, calcium chloride, etc., the cement slurry can quickly develop static gel strength, but the cement slurry system does not take into account The heat of hydration of high-alumina cement slurry is relatively high. Studies have shown that in a closed environment at 20°C, the temperature generated by the heat of hydration of high-alumina cement slurry can reach above 100°C. The stable existence of hydrate is extremely unfavorable; (4) foam cement slurry system, which can use G-grade cement or aluminate cement, wherein Raghava develops high-alumina cement, which is filled with nitrogen, and sodium lignosulfonate is Retarder, calcium chloride as coagulant accelerator, polypartic acid as dispersant, prepared with a density of 1.32 ~ 1.44g / cm 3 The cement slurry is cured at 10°C for 24 hours, and the highest compressive strength is 2.64MPa. The early strength performance of the cement slurry is not very good. The high daily rent of offshore drilling equipment requires that the cement slurry has good early strength performance at low temperature; (5) fast Concrete gypsum cement slurry, the cement slurry has good early strength characteristics in the environment of about 15 ℃, but the density of the cement slurry is 1.50g / cm 3 Or so, the density of the cementing system used in deep water is high, and the early strength performance of the fast-setting gypsum cement slurry is poor in the environment where the mud line temperature is about 4°C, so it is not suitable for deep water cementing

The above-mentioned cement slurries used in deepwater well cementing all have their own defects, and these cement slurries have not considered the destructive effect of the exothermic heat of hydration reaction on the stability of natural gas hydrate

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