Drilling fluid water loss and mud cake adjustment

Drilling fluid fluidity mainly refers to viscosity, including funnel viscosity, apparent viscosity, plastic viscosity, static shear force, and dynamic shear force. The maintenance of drilling fluid fluidity performance is mainly aimed at viscosity maintenance, and various flow patterns change with the change of viscosity. The viscosity of drilling fluid must maintain an appropriate value, otherwise it will cause some adverse consequences.

1. Disadvantages of excessive viscosity
① Large flow resistance and high energy consumption. Low water power. Slow drilling speed:

② Unfavorable for solid phase control and cannot give full play to the effectiveness of solid control equipment. Causes complicated situations underground:

③ The drill bit is prone to mud packing, and the underground pressure is high, which is easy to cause underground blowout, leakage, collapse, and jamming faults:

④ When oil and gas invade, it is difficult to degas, which affects gas measurement and causes gas invasion:

2. Disadvantages of too small adhesion and cutting
① The ability of drilling fluid to carry drill cuttings is weakened, and the wellbore purification is poor, which is easy to cause complicated situations underground:

② Flushing the well wall aggravates the instability of the well wall and easily causes well collapse faults;

③ The cuttings cannot be brought out of the ground in time, and are ground underground, affecting geological logging;

④ It is easy to cause sand settling and drilling jam faults;

3. Adhesion and cutting maintenance method
The change of adhesion and cutting is closely related to underground pollution. It must be carefully analyzed, the cause of the change must be found, and the symptomatic treatment must be carried out.

① Clay invasion, large amounts of slurry in the formation cause increased viscosity, and the method of dilution with clean water and inhibition of dispersed coating flocculation should be used;

② For different types of drilling fluids, select viscosity reducers to reduce viscosity;

③ Strong dispersion of cuttings causes increased viscosity, and strong inhibitors should be used to enhance the ability of drilling fluid to inhibit hydration;

④ Soluble salts invade and cause increased viscosity, and salt-resistant and calcium-resistant viscosity reducers should be used for treatment. At the same time, calcium removers (soda ash, organic phosphates) can be used to precipitate calcium ions.

⑤ To improve viscosity, polymer organic thickeners can be used, such as high-viscosity CMC or composite ionic polyacrylates. Sometimes bentonite (freshwater drilling fluid) and salt-resistant soil (brine, saturated brine drilling fluid) are also used to improve viscosity.

⑥ Add soluble salts (calcium chloride, gypsum, mirabilite, water glass) to improve viscosity and prepare plugging thick slurry.

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