1. Introduction to Drilling & Completion Fluid

Due to the damage of drilling & completion process to oil and gas layer, oil exploration is confronted with decreased production. In recent years, some progress on reservoir protection has been made in the drilling & completion of oil and gas layer, drilling & completion fluid technology plays a vital role in the protection of oil and gas layer. This article focuses on the developing status of analyzes pros and cons and applicability of different drilling & completion fluid systems in reservoir protection.

2. Progress of Drilling Fluid Technology

A main factor often causing formation damage is drilling & completion fluid, which continues to invade reservoir under positive pressure. Therefore, the research and reasonable application of drilling & completion fluid is a main way to protect reservoir in drilling & completion process. In recent years, a variety of reservoir-protective drilling & completion techniques have been developed at home and abroad.

2.1 Water-base Drilling & Completion Fluid

Water-base drilling & completion fluid is the most commonly used technique at home and abroad. In recent years, a number of oil exploration and scientific research institutions carried out research on new drilling & completion fluid depending on the characteristics of different oil and gas reservoirs. Jiangsu Oilfield selected zwitterionic polymers and cationic polymers and optimized drilling & completion fluid system according to the characteristics of low permeable reservoirs, achieving improved drilling speed, reduced completion time and soaking time and effective reservoir protection.

2.2 Oil-base Drilling & Completion Fluid

Currently, water-in-oil emulsion drilling & completion fluid is the most widely used technique at home and abroad. In the development of Norwegian North Sea oil field, water-in-oil emulsion drilling & completion fluid was successfully applied in order to protect reservoir and stabilize well wall. This drilling & completion fluid has minimal damage to the reservoir and realized a stable increase of productivity together with reservoir protection. In recent years, all-oil drilling technique has gradually become a hot research. American Baroid Company made use of the reasonable particle size distribution of bridging agents in all-oil drilling fluid to form low-permeable thin mud cake in drilling & completion process. The thin mud cake can effectively prevent the invasion of filtrate and solids into reservoir, achieving good protective results.

2.3 Gas Drilling & Completion Fluid

Gas drilling & completion fluid is to artificially contain gas into drilling fluid. Among them, foam drilling & completion system is the currently best applied system. This system has made success in Xinjiang, Erlian, Changqing, Baise, Jidong and Shengli oilfields.

3. Developing Tendency of Drilling & Completion Fluid

3.1 ‘Low, Deep & Hard’

In recent years, more and more attention was paid to oil and gas layer protection, and great progress has been made in drilling & completion method as well as drilling & completion fluid. With the increased difficulty in oil & gas exploration, low-permeable reservoirs, deeper wells and various complex situations become more and more, which put forward higher demand for drilling, completion and transportation. Consequently, how to develop new drilling & completion techniques to deal with a ‘low, deep and hard’ situation would be the focus of future research in oil & gas industry.

3.2 High & Ultra-high Temperature

With the development and use of hydrocarbon resources, the focus of oil & gas exploration has been turned to deep layers. To meet the special demand of deep reservoir protection, completion fluid also confronts with higher requirements on thermal stability; the applicable temperature is shifting from low temperature to high & ultra-high temperature. Some researchers optimized

the formulation of completion fluid and obtained a system with high thermal stability, resistance to temperature and salt and low pollution to reservoir.

3.3 Environment-friendly Drilling & Completion Fluid

After drilling, completion fluid and the waste will eventually be discharged into the natural environment, bringing some pollution to the ecological environment. As environmental awareness increases, environmental regulations became stricter on the use of completion fluid. Therefore, to develop non-toxic, low toxic and biodegradable environment-friendly completion fluid would be the developing trend of future oil industry.

4. Conclusion

With the rapid development of world oil industry, the development of reservoir-protective drilling & completion fluid technology becomes increasingly important. Drilling technology put forward a higher requirement on drilling & completion fluid. Especially with the restriction of environmental policy, laws and regulations, a new fluid system meeting the demand of both drilling engineering and environment protection at the same time seems to be more necessary. This paper argues that, the application of nano-materials and other advanced technologies in the field of oil & gas layer protection can significantly increase oil and gas production, with environmental protection and high efficiency, and has broad application prospects which is worth further study.

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