Drilling fluids: The "blood" of modern drilling engineering and the revolution in polymer technology

In the field of oil and gas exploration and development, drilling fluid is known as the "blood" of drilling engineering, which appropriately reflects its core position in drilling operations. Drilling fluid, also known as drilling mud, is a complex circulating fluid system composed of water or oil, clay, chemical treatment agents and various functional additives. It performs many key functions such as breaking core, carrying cuttings, lubricating and cooling drill bits, balancing formation pressure, and protecting wellbore stability. With the extension of oil and gas exploration to deep, complex and unconventional reservoirs, drilling fluid technology is facing unprecedented challenges and opportunities, and innovative applications of polymer materials are leading this technological revolution.

Traditional drilling fluids are mainly composed of a base liquid (water or oil), a viscosifier (such as bentonite), a weighting material (such as barite), and various chemical treatment agents. Water-based drilling fluids are the most widely used because of their low cost and environmental friendliness, while oil-based drilling fluids perform well in difficult Wells and shale gas development. However, conventional drilling fluid is often unable to cope with complex working conditions such as high temperature and pressure, salt paste layer and fractured reservoir, and is prone to technical bottlenecks such as out-of-control viscosity, excessive filtration loss and wellbore instability. This situation has led scientists to look at polymer materials, through molecular design to give drilling fluids superior performance.

Polyacrylamide (PAM) is the most representative polymer used in drilling fluid. The amide groups on the molecular chain can be bonded with clay particles through hydrogen bonding, and the long molecular chain structure can form three-dimensional network in solution. This unique structural property makes it show a triple effect: when used as a viscosifier, the low concentration of PAM can significantly improve the apparent viscosity of drilling fluid and enhance the rock-carrying capacity; As a filtrate reducing agent, PAM molecules can form a dense adsorption layer on the pore surface of the formation to effectively control filtrate intrusion. When used as a shale inhibitor, the polar groups of PAM can neutralize the surface charge of clay and inhibit hydration expansion. Deepwater drilling in the U.S. Gulf of Mexico has shown that drilling fluids optimized with PAM can increase ROP by more than 20% and reduce hole expansion to less than 5%.

The breakthrough of polymer technology is more reflected in the improvement of environmental adaptability. The emergence of temperature and salt resistant polymers solves the problem of failure of traditional treatment agents in high temperature and high salt environment. For example, AMPS copolymers with sulfonic acid groups can withstand high temperatures above 200℃ and saturated brine conditions; Zwitterionic polymers maintain stable rheological properties in the salt paste layer through the synergistic effect of positive and negative charges. In the application of ultra-deep Wells in the Tarim Basin, China successfully used the self-developed hydrophobic association polymer drilling fluid through multiple sets of complex salt formations, creating the deepest onshore drilling record in Asia. Intelligent responsive polymers take drilling fluid technology to new heights. These materials can sense environmental changes such as downhole temperature, pH or CO2 concentration, and automatically adjust molecular conformation to achieve intelligent behaviors such as viscosity changes and self-healing.

Unconventional oil and gas development has opened up a new battlefield for polymer drilling fluids. In the drilling of shale gas horizontal Wells, the "water-in-oil" emulsion drilling fluid, which is composed of synthetic polymer and natural modified polymer, not only ensures wellbore stability but also minimizes reservoir damage. In the Marcellus shale in the United States, the optimized polymer drilling fluid extended the lateral length to more than 3,000 meters and increased production per well by 35%. Biodegradable polymers, such as polyglutamic acid and chitosan derivatives, can be naturally degraded after completion to avoid long-term damage to the pay zone.

Looking forward to the future, the drilling fluid polymer technology will be developed in the direction of molecular precision design, nano-composite modification, and biomimetic. Graphene-reinforced polymers can improve both mechanical properties and thermal conductivity. The self-healing polymer can automatically repair structural damage during downhole circulation. DNA nanotechnology may even enable "programmed" behavior control of drilling fluids. These innovations will not only break the current technical bottlenecks in deep and deep-sea exploration, but also redefine the role of drilling fluids in emerging fields such as oil and gas stimulation and geothermal development.

The history of drilling fluid technology is, to some extent, a chronicle of polymer material innovation. From their beginnings as natural polymers to today's smart composites, polymers have always been a key driver of breakthroughs in drilling fluid performance. With the development of oil and gas resources toward "deeper, farther and more difficult", drilling fluid as "blood" will carry more missions, and polymer technology will continue to inject new vitality into this "blood" and write a more brilliant chapter of modern drilling engineering