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Marine Carbonate rock is widely distributed, old, deep buried, high temperature, high degree of rock densification, and high sulfur content in some areas. The reservoir space is generally a composite reservoir space composed of karst caves, fractures, and karst pores, and the spatial distribution of the reservoir is uneven. The basic characteristics can be summarized as follows：

• The reservoir is deeply buried and mostly exhibits characteristics such as high temperature and high pressure.
• High levels of H2S and CO2 in natural gas result in severe corrosion.
• The porosity and permeability of the matrix are low, and the reservoir space has significant heterogeneity.
• The law of oil and gas accumulation and complex reservoir lithology.
• Difficulty in reservoir reconstruction of horizontal/highly deviated wells.

The Carbonate rock reservoir is generally modified by acid fracturing technology. The key to improving the effect of acid fracturing is to obtain longer acid etched fractures and higher fracture conductivity. Its main technical ideas are: use efficient retarded acid and supporting materials to slow the acid rock reaction speed, reduce acid fluid filtration, and increase the effective distance of acid fluid; Optimize the acid fracturing process to achieve uniform distribution of acid and non-uniform etching of the formation, and improve the conductivity of acid etched fractures; Using clean, low damage and environmentally friendly materials to reduce the damage of acid fracturing to the formation.

1. An acid system for improving the effective action distance of acid in high-temperature deep wells.For high-temperature formations, using slow acid to reduce the impact of high temperature on the acid rock reaction rate and increasing the effective action distance is the key. Currently, slow acid, mainly composed of hydrochloric acid, is commonly used to increase the length of acid corrosion fractures. Its slow down mechanism mainly includes: ① controlling the acid rock reaction equilibrium to achieve slow down – such as aluminum salt slow down acid system; ② Control the mass transfer coefficient of H+to achieve slowing down – such as adding high-performance thickeners or gelling agents to the acid solution to form gelling and cross-linking acids; ③ Control the dissociation speed of H+to achieve slow speed – such as high-temperature delayed acid; ④ Create a barrier layer between the rock surface and the acid solution to achieve retardation, such as surfactant acid; ⑤ The application of acid wrapping technology to realize slow speed – such as foam acid, emulsified acid, micellar acid, solid acid, etc. In addition, in recent years, clean, green, friendly acid system has also become a new trend in the development of acid system in high-temperature Carbonate rock reservoirs.
2. Clean Self -Diverting acid system.Clean self diverting acid is a heterogeneous formation acidizing fluid system developed in recent years. This system uses special Viscoelasticity surfactant to control the viscosity of the acid fluid system by using the physical and chemical effects of acid rock reaction products. The viscosity change of the acid fluid mainly depends on the change of the surfactant morphology, which is initially in the form of monomer, and the viscosity of fresh acid is low; With the progress of acid rock reaction, the pH value increases and generates cations such as Ca2+, Mg2+, etc. The Viscoelasticity surfactant in the acid fluid changes from monomer form to rod micelle form, forming viscoelastic body, increasing the viscosity of the liquid, effectively diverting the unreacted acid fluid to other fractures, cavities and formations; After acidification, the produced oil and gas contact with the rod micelle form of Viscoelasticity surfactant, which makes the rod micelle change into spherical micelle, thus significantly reducing the viscosity of acid, and the residual acid can be smoothly and thoroughly discharged.
3. Friendly acid system. The key component of this system is extracted from natural amino acid L-glutamic acid, which has excellent chelating, adsorption and self degradation capabilities. It has significant characteristics and advantages for Carbonate rock reservoir acidification: ① it can effectively produce acid etching wormholes in Carbonate rock; ② It can effectively chelate calcium and magnesium salts at different pH values, reducing the risk of precipitation of high valent metal ions; ③ Good thermal stability, still having good stability at 175 ℃; ④ Showing stronger ability to improve core permeability than other chelating agents; ⑤ The acid rock reaction has directionality and has a long effective action distance; ⑥ Low corrosiveness, with a lower corrosion rate compared to other chelating agents and organic acids. Only a small amount of corrosion inhibitor needs to be added to meet the on-site corrosion inhibition requirements; ⑦ Friendly acid is an environmentally friendly acid solution system with good biodegradability and no toxicity, making it more environmentally friendly.