High-density cement slurry suitable for shale gas cementing and preparation method of high-density cement slurry

Abstract

The invention discloses high-density cement slurry suitable for shale gas cementing. The high-density cement slurry is prepared from the following raw materials in parts by weight: 100 parts of cement, 44-57 parts of fresh water, 15-120 parts of a weighting agent, 0-30 parts of a weighting stabilizer, 30-40 parts of a high-temperature strength stabilizer, 3-5 parts of an elasto-plastic agent, 4-7 parts of a fluid loss agent, 1-2.5 parts of a retarder and 0.5-2.5 parts of a dispersant. The preparation method comprises the following steps of weighing the cement, the fresh water, the weighting agent, the weighting stabilizer, the high-temperature strength stabilizer, filler, the elasto-plastic agent, the fluid loss agent, the retarder, the dispersant and a defoaming agent according to the ratio; mixing the components, and stirring to obtain the high-density cement slurry suitable for shale gas cementing. The high-density cement slurry is easily pulped at normal temperature and is good in high-temperature sedimentation stability, capable of improving the breaking strength, shock resistance and toughness of hardened cement slurry, relatively wide in density adjustable range and capable of meeting various shale gas cementing requirements.

Description

technical field [0001] The invention relates to a high-density cement slurry suitable for shale gas well cementing and a preparation method thereof, belonging to the field of petrochemical industry. Background technique [0002] Shale gas is natural gas that mainly exists in the interlayers of mudstone, high-carbon mudstone, shale, and silty rocks in an adsorbed or free state. Unlike conventional gas reservoirs, shale is not only the source rock for natural gas generation, but also Reservoirs and cap rocks that accumulate and preserve natural gas. The total porosity is generally less than 10%, and the effective porosity containing gas is generally less than half of the total porosity. Shale reservoirs are characterized by low porosity, ultra-low permeability and tight physical properties, and are relatively difficult to exploit. It is often necessary to adopt large-scale staged fracturing, so that the standard requirements for cement stone are more stringent. [0003] At ...

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Problems solved by technology

[0003] At present, shale gas well cementing mainly faces three problems: 1. The mechanical properties of cement stone are difficult to meet the requirements. Shale gas wells generally need large-scale staged fracturing, which requires cement stone to have high strength, toughness and durability. ;2. It is difficult to guarantee the sealing quality of the second interface. Because shale gas wells use oil-based drilling fluid, the formation is in an oil-wet environment, and the oil-based drilling fluid has high viscosity and strong adhesion. Poor cleaning and displacement effects; 3. Poor casing centering in the horizontal section affects displacement efficiency

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