Treating method of drilling fluid used for high salt-gypsum content formation block

Abstract

The invention provides a treating method of drilling fluid used for a high salt-gypsum content formation block. Drilling is conducted by means of fresh water polymer drilling fluid. The treating method comprises the following steps that (1) the fresh water polymer drilling fluid is utilized for dissolving salt in a formation, and the chlorine ion content of the formation is kept at 50,000-70,000 mg / L in an under-saturated state; (2) a PH value conditioning agent is added into the drilled salt-gypsum formation, so that the PH value of the drilling fluid is kept at 9-10; (3) PSC is added into the drilled salt-gypsum formation to control the viscosity at 30-45 s; (4) while the salt-gypsum formation is drilled, the density of the drilling fluid is kept at 1.17-1.22 g / cm<3>; (5) while the salt-gypsum formation is drilled, the content of bentonite is kept at 40-50 g / L; and (6) an anti-sloughing filtrate reducer is added, and the mass content of the anti-sloughing filtrate reducer is kept at 0.4-0.5%. The low-viscous-shearing and high-water-loss drilling fluid is adopted for drilling the salt-gypsum formation, so that the mechanical drilling speed can be increased; furthermore, the adding amount of the anti-sloughing filtrate reducer is decreased; and the drilling fluid has good fluidity, the scouring capability of the drilling fluid to the well wall is enhanced, a certain expanded diameter of a well is formed, and the phenomenon that drilling slacking-off is caused by creeping and diameter-reducing of the salt-gypsum formation is reduced.

Description

Technical field [0001] The invention belongs to the field of drilling fluid processing, and in particular relates to a method for processing drilling fluid for high-salt gypsum layer blocks. Background technique [0002] The salt-gypsum layer is a layer with salt or gypsum as the main component. It is a layer often encountered during drilling. For example, the Tertiary formation of construction wells in the west of Tuha Oilfield such as Shenquan, Shengnan and Yanmuxi blocks contains a lot of Salt gypsum, pure salt layer, gypsum mudstone layer. The salt-gypsum block has serious pollution to the conventional drilling fluid during the drilling and construction. The salt-gypsum intrusion makes the drilling fluid thicken rapidly, and the gypsum mudstone absorbs water and expands or deforms plastically, resulting in the coexistence of diameter reduction and well collapse, forming candied gourd boreholes. There have been complicated downhole situations such as serious jamming or jammin...

AI Technical Summary

Problems solved by technology

When drilling in the salt-gypsum layer, the conventional drilling fluid is seriously polluted. The salt-gypsum invasion makes the drilling fluid thicken sharply, and the gypsum mudstone absorbs water and expands or plastically deforms, resulting in diameter shrinkage and well collapse. Underground complex situations such as severe jamming or pipe stuck accidents, resistance in electrical testing, cementing pump failure, etc.

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