To protect oil and gas reservoirs during drilling, shielded temporary plugging technology has long been the key to oil and gas well drilling operations. Hard ultrafine calcium carbonate (CaCO3) has been widely used to effectively plug the storage, and to remove the plugging in time after drilling and completion effectively. Ultrafine calcium carbonate has the advantages of high strength, adjustable particle size, excellent bridging and plugging effect, and rapid and full reaction with acid. However, the bridging effect of hard particles usually cannot achieve complete sealing. This study intended to use acid-soluble preformed particle gels (ASPPG) as a collaborative plugging material. ASPPG is a soft material that can form deformation filling and self-decomposition. The research results show that the “superfine calcium carbonate + ASPPG” synergistic plugging system can significantly improve the plugging strength of the drilling fluid. In addition, the system can completely react or self-degrade in the process of hydrochloric acid plugging removal, causing very little damage to the formation. Besides, as the ASPPG particle concentration increases or the particle size decreases, the plugging strength will gradually increase. Moreover, the system can also be applied to high temperature (90 °C) formation conditions. The above experimental research results can provide a research foundation for the pilot application of the shielded temporary plugging drilling fluid technology based on the “hard particles + soft particles” synergistic plugging effect.

Aimed on the problem that the Drilling fluids were easily intruded by the saline water in high-pressure salt-gypsum formations, and the properties of the drilling fluid were damaged and accidents easily occur. The mechanism of drilling fluid contamination by the formation brine was analyzed and the capacity limits of the contamination were found out. The results show that small amount of brine invasion causes emulsification while large amount of brine invasion lead to demulsification. Two capacity limitations were proposed. The first limitation is 10% of saline water concentration, below which the performance of the drilling fluid remains relatively good. The second limitation is 30% of saline water concentration, below which the drilling fluid needs to be systematically maintained, and after which the fluid has no potential for maintenance. This proposal has been successfully used in 8 wells in Kuqa foreland area, and the drilling cycle was saved by 35 days on average.

In this paper, an inorganic/organic water-based drilling fluids reducer AM/AA/GO was prepared by using acrylamide (AM), acrylic acid (AA) and graphene oxide (GO) as raw material. Performance evaluation showed that the AM/AA/GO has an excellent filtration loss reduce performance. It has a good salt resistance performance and its temperatures resistance ability was up to 140 °C. The comprehensive results showed that AM/AA/GO is expected to be used in anti-collapse water-based drilling fluids.

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