The powerful "king of soil": the "universal soil" in ultra-deep drilling projects

News reports that my country's oil and gas drilling in the Tarim Basin is about to break through 10,000 meters have sparked heated discussions and attention to deep-earth drilling projects. A mere 10,000 meters is only one-third of the average thickness of the earth's crust, but few countries in the world can explore to such a depth. In the scientific and technological community, there has always been a consensus that "it is not easy to reach the sky, and it is even more difficult to enter the earth." The Chinese have broken records in the field of earth exploration, indicating that the overall technical level of China's drilling projects is in the world's leading position.

Why is deep drilling more difficult than space exploration of the moon and deep-sea diving? This is mainly because the rock layers and lithology that make up the earth's crust are too complex, far exceeding the single resistance formed by the atmosphere or seawater. Every meter of footage after breaking through the conventional drilling depth is a new conquest. There are multiple unpredictable risks lurking in the process of 10,000-meter deep drilling, and irreversible accidents will occur if you are not careful. Without the support of high-precision technology and sufficient financial and material resources, it is a foolish dream to explore the geological mysteries of the 10,000-meter deep layer.

In recent years, with the continuous progress of science and technology, my country has manufactured a complete set of drilling rig equipment that can bear the load of 10,000-meter drilling tools, provide strong power, and automatic and digital control, as well as high-strength drill bits, drilling tools and matching testing instruments. However, this is only one of the necessary conditions for drilling 10,000-meter deep holes. It is also necessary to develop high-temperature resistant, low-friction, and super-stable drilling fluids to circulate cooling and lubricate drilling tools, suspend and carry cuttings out of the well, and at the same time protect the well wall, balance the abnormally high pressure formed by underground oil, gas and water, and prevent stuck drills or blowouts.

In modern drilling construction, drilling fluid is also a medium for transmitting deep geological information and providing driving force for the rotation of the drill bit. It can be said that drilling fluid is the core element related to the safety, speed, quality and even success of the entire drilling project. It has always been regarded as the indispensable circulating blood of drilling projects. The high-tech content in it is no less than that of manufacturing 10,000-meter drilling rigs and drilling tools. Such an important drilling fluid does not look high-end and atmospheric. People who do not understand the drilling industry may not be able to imagine that this multifunctional reciprocating drilling fluid is actually a viscous fluid prepared with soil as the base material. Therefore, it has another common name in the industry, called "drilling mud".

It goes without saying that ordinary soil is not qualified to prepare drilling mud. Only the king of soil with great magical powers and superb functions is the preferred base material. Its scientific name is bentonite, also known as bentonite or bentonite. In some areas, it is also called Guanyin soil by the people. Bentonite is a clay mineral with montmorillonite as the main component. It forms veins in various colors such as grayish white, yellow-green, and yellow-white. It is easy to mine and has low cost. It is widely distributed in the world, and my country has very rich reserves. This mineral has very good adhesion, expansion, adsorption, plasticity, dispersibility, lubricity, and cation exchange. It is divided into two types: calcium-based and sodium-based. The chemical name is layered hydroaluminosilicate. It has a very strong suspension after exchanging with salt-based and lithium-based chemical substances. It has good decolorization after acidification treatment, and its chemical properties are quite stable. It can be used to prepare hundreds of chemical products such as adhesives, adsorbents, plasticizers, catalysts, disinfectants, thickeners, descaling agents, detergents, fillers, enhancers, clarifiers, etc. Due to its extremely wide range of uses, it has earned the reputation of "universal clay".

Given that bentonite has excellent solubility and can absorb a large amount of water, expanding its volume by 10 to 30 times, forming a slippery gel-like liquid, showing excellent suspension ability and low friction resistance, it is naturally favored by the drilling industry and has become the most ideal raw material for preparing drilling fluids. Therefore, since the popularization of mechanical drilling, high-quality bentonite has always accompanied drilling projects from shallow to deep, constantly breaking records.

The extremely difficult deep drilling has very strict requirements on the quality of drilling fluid. It is necessary to be equipped with a scientific research team dedicated to the preparation of drilling fluid. According to the predicted changes in the lithology of the formations that may be encountered, the various optimal parameters of the mud are carefully designed. On the basis of bentonite as the main material, a variety of chemical auxiliary agents are added to adjust and improve the comprehensive performance of the drilling fluid at any time to provide guarantees for safe and rapid drilling. There is a well-known example. At the critical moment when the Iron Man Wang Jinxi discovered the signs of a blowout, he jumped into the mud pool and used his body to stir and add cement to increase the specific gravity of the drilling fluid, thus suppressing the raging oil and gas flow. This widely circulated heroic feat is enough to show the important role that drilling fluid plays in drilling construction.

The petroleum industry is a major consumer of bentonite. Not only does vertical drilling for the exploration and development of oil and gas resources require a large amount of mud, but also the construction of pipelines for transporting oil and gas. Horizontal drilling across rivers, railways, and roads also requires circulating mud as a guarantee. Regardless of the drilling method, the amount of mud used is proportional to the diameter of the wellbore, the depth of the crossing, or the length. In general, the amount of mud used is at least twice the volume of the wellbore. In special cases such as formation leakage, gas invasion failure, and drilling into ultra-high pressure oil and gas layers, the amount of mud used will increase several times.

At present, my country's annual bentonite production is about 7 million tons, ranking first in the world. High-quality mineral veins are mainly concentrated in Sichuan, Inner Mongolia and Northeast China. According to rough statistics, my country's oil industry's demand for bentonite is as high as one million tons per year. When celebrating my country's drilling depth breaking through the 10,000-meter mark, the omnipotent bentonite also played a role.

Author: Gong Ke