Cement paste system for well cementation

Abstract

The invention relates to a cement paste system for well cementation. The cement paste system is prepared from the following raw materials in parts by weight: 100 parts of oil well cement, 20-45 parts of micro-silicon, 20-50 parts of active lightening material, 2.5-3.5 parts of a fluid loss agent, 0.5-1 part of a dispersing agent, 0.9-1.8 parts of a retarder, 1.5-3 parts of an early strength agent, 1-1.5 parts of a de-foaming agent and 112-250 parts of water. The cement paste system has the advantages that the active lightening material is added into the cement paste system, so that the cement paste density is reduced, and meanwhile, the active lightening material can chemically react with and is integrally fused with cement hydration product, so that the early strength of low-density set cement can be promoted, and the problem of high probability of breaking of floating beads under high-pressure fast stirring conditions can be solved; the retarder is a compound ionic retarder and has a temperature self-adaption characteristic, and under a low-temperature environment, the molecular chain is curled, and adsorption groups are under a bound state, so that the adsorption to cement grains is reduced and the retarding property is weakened; under a high temperature condition, the molecular chain is unfolded, more adsorption groups are exposed and the retarding property is enhanced.

Description

technical field [0001] The invention relates to the technical field of deep well and ultra-deep well cementing, in particular to a cement slurry system for well cementing. Background technique [0002] At present, most shallow oil and gas resources in China are close to depletion after long-term exploitation, and recoverable and easy-to-recover reserves are limited. In order to increase crude oil production and support the development of the national economy, exploration and development work has begun to expand to deep oil and gas reservoirs, especially in recent years. The discovery of a large number of deep wells and ultra-deep wells has brought people gratifying oil reserves, but also brought great challenges to cementing operations; [0003] The existing cement slurry has a high water-solid ratio, and its own stability is poor. Due to the great disparity between the density of the lightening material and the cement particle, it is easy to cause the slurry to settle due t...

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Problems solved by technology

[0003] The existing cement slurry has a high water-solid ratio, and its own stability is poor. Due to the great disparity between the density of the lightening material and the cement particle, it is easy to cause the slurry to settle due to gravity separation. For example, the commonly used floating beads (ρ≈0.7 g / cm 3 ), it is very easy to float up, making the stability of the slurry worse. What's more, due to the poor shear resistance and compression resistance of the floating beads, it is easy to shear and break, or rupture in the high-pressure environment at the bottom of the well, causing cement slurry The actual density is higher than the design density, and there is a risk of formation leakage

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