How was the deepest well on land in Asia created?

Workers at Tarim Oilfield are working on the project. Photo provided by Tarim Oilfield

The 8,882-meter Luntan 1 well is 8,882 meters deep, even deeper than the altitude of Mount Everest. It has become the deepest well on land in Asia and also marks a major breakthrough in the ultra-deep exploration of the Cambrian subsalt strata in the Tarim Basin, proving that primary oil reservoirs and high-quality reservoir-cap assemblages still exist in the Tarim Basin at depths of more than 8,200 meters.

A deep well has brought so many surprises to the world. And these surprises were created in the Tarim Basin, where geologists generally agree that the geology has been "broken and trampled on".

On January 19, 2020, the China Petroleum risk exploration well Luntan 1, located in Kuche City, Aksu Prefecture, Xinjiang, produced 133.46 cubic meters of crude oil and 48,700 cubic meters of natural gas per day after acid fracturing test. In the words of Yang Xuewen, secretary of the Party Working Committee and general manager of Tarim Oilfield Company, the purpose of drilling Lunshen 1 is to explore the oil and gas content of ultra-deep Cambrian sub-salt dolomite, overcome new theoretical problems of oil and gas, and accelerate the exploration process of ultra-deep carbonate rocks in new areas.

Oil and gas fields below 8,000 meters exist not only in scientists' minds

Tang Yangang, 39, is the chief geologist of the Tarim Oilfield Exploration and Development Research Institute. "The geology of the Tarim Basin is completely different from that of other places in the world. In the words of our predecessors, the geology of the Tarim Basin is a place that has been 'broken and stepped on'. The various underground geological layers are completely disrupted, and there is no complete geological belt at all. For petroleum geology, only when the theoretical support of oil and gas is first discovered from geology can oil and gas fields be developed."

The practice of oil and gas exploration in the world shows that the world's large oil and gas fields are mainly developed under salt. After 31 years of development, the geological conditions of the shallow layers of the Tarim Oilfield have been understood, and the geological conditions of the deep layers over 6,000 meters are also basically understood. But what about the geological conditions of the ultra-deep layers, that is, below 8,000 meters? Tang Yangang and his team still have some knowledge.

"The main reason for the lack of understanding is that the seismic reflection wave method we use now only lasts for 7 seconds, and to clearly understand the geological conditions below 8,000 meters, the reflection wave requires at least 10 to 12 seconds. From the geological structure, we infer that there should be large oil fields below 8,000 meters in the Tarim Basin." Tang Yangang said firmly.

How to prove this new theory that exists in our minds has become a world-class problem that needs to be overcome in the development of the Tarim Oilfield.

Shallow exploration and development from 1989 to 2003 supported the construction of the 5 million ton Tarim Oilfield and made them realize that a large oil and gas field is like a large bowl, and there must be a lid on it. The geological conditions below 8,000 meters in the Tarim Basin are: there is a thick salt layer on the upper layer, just like the lid on the oil and gas bowl. Is there really a rich oil and gas field underneath it?

The policy of bringing in and going global attracted a group of world-class experts to the Tarim Oilfield. However, after seeing the complex geological structure of the Tarim Basin, these experienced experts all shook their heads and said that they had never seen such a world problem and had no way to solve it.

Tang Yangang and his group of young scientists did not believe that they could not solve this problem. They went to the site, carefully understood the drilling conditions, and seriously analyzed the geological structure data, and finally overcame one technical and theoretical problem after another.

Talking about this process, Tang Yangang said with deep emotion: "In the beginning, we were indeed afraid of ultra-deep wells. Because it has to pass through sandstone layers, and ultra-deep wells will inevitably encounter complex conditions such as high temperature and high pressure. Poor control will bring a series of problems and may even lead to huge losses. But we are not willing to give up. We are engaged in geological exploration. It is both fortunate and unfortunate to encounter such complex geological conditions as the Tarim Basin. Unfortunately, no one in the world has encountered such a situation. Fortunately, we have encountered it. Isn't it a feeling of 'a great mission sent by God'?"

With this fighting spirit, the scientific research team of Tarim Oilfield used existing technical means, structural modeling, and constantly updated theoretical knowledge, and actually discovered three ultra-deep and rich oil and gas fields, laying a solid foundation for the Tarim Oilfield's oil and gas production equivalent to exceed 30 million tons this year.

"Compared with other areas at home and abroad, the carbonate rocks in the Tarim Basin are the most complex, with deep burial depth, strong heterogeneity, and complex oil-water relationships, which are definitely world-class problems. However, our scientific research team has carried out key research on carbonate rock sequence stratigraphy, reef-shoal bodies, and paleokarst, confirming the existence of bioherms in the Yijianfang Formation and Lianglitage Formation of the Ordovician System in the Tarim Basin, innovatively establishing the sedimentary model and karst model of the reef-shoal complex, revealing the law of the lens-shaped superimposed and continuous distribution of the reef-shoal karst reservoir along the platform margin, and forming an exploration idea for drilling reefs along the platform margin. Based on this, China's first large reef-shoal condensate gas field, the Tazhong I gas field, was discovered, which was rated as one of the world's major discoveries. We found that there were "beaded" karst reservoirs along the unconformity surface in the thick carbonate rocks, so we formed an exploration idea of ​​drilling interlayer karst reservoirs along the unconformity surface, and discovered the ultra-deep large oil and gas field with an area of ​​5,000 square kilometers in the Halahatang oil and gas field, opening up a new field of carbonate rock exploration in the platform basin area. Carbonate rocks, which have been an unknown supporting role for nearly 20 years, have become the main force in crude oil. "Tang Yangang said excitedly.

How to drill oil and gas fields below 8,000 meters

Under the guidance of geological innovation theory, deep oil and gas fields such as Keshen Gas Field, Tazhong, and Halahatang have been discovered one after another, laying a solid foundation for the West-East Gas Transmission Project. However, most of the rich oil and gas fields are buried below 8,000 meters, which is difficult to explore and requires high technology. How can we develop oil and gas fields?

Wang Chunsheng, deputy manager of the Tarim Oilfield Exploration Division and safety director, believes that the successful drilling of the Tarim Oilfield's ultra-deep wells should be attributed to the modernization and localization of equipment.

Wang Chunsheng said: "When I first started working, if there was a drilling rig that could drill 7,000 meters, the well team would be very powerful, and they were all imported. With the development of the country's manufacturing industry, 8,000-meter and 9,000-meter drilling rigs have been manufactured, which ensures the possibility of drilling ultra-deep wells."

"We have now started using air drills, and the drilling speed is getting faster and faster. We can drill 2,500 meters in less than 100 days, which is dozens of times faster than in the past. In the past, it took 80 days to drill 1,000 meters, but now with the use of air drills, it only takes 20 days," said Wang Chunsheng.

Shen Biao is currently the director of the exploration project department of the platform basin area of ​​the exploration division of the Tarim Oilfield Company. He is only 37 years old. "We started drilling the Luntan 1 well on June 28, 2018 and completed it on June 18, 2019. It took us 361 days to drill the 8,882-meter deep well. From the beginning of drilling to the drilling of more than 2,000 meters, it can be described in one word: it was very enjoyable and the drilling was very smooth. But suddenly one day, the drilling tool broke."

Faced with this situation, Shen Biao stayed at the wellhead for more than a month and tried every possible way to solve the problem, but was unable to do so. The final result was that the broken drilling tools were not salvaged, so they could only bypass this place and continue drilling downwards.

"The most dangerous moment was when we drilled to 8,882 meters. Early in the morning, I suddenly received a call that the drill was stuck. I was anxious at the time and immediately drove to the wellhead. During the two and a half hour journey, I kept making phone calls to understand the situation underground and discuss solutions with the technical staff of the exploration company." Shen Biao recalled.

The drilling tool got stuck, and this ultra-deep well that had been drilled for more than 300 days might have to be scrapped. This made Shen Biao unable to eat or sleep, and he kept thinking of solutions for more than 20 hours. "First, we must ensure the integrity of the drilling tool and take measures within the range of tensile and compressive resistance. We first moved the drilling tool up and down, but it didn't move at all. Not long after the jamming machine was installed, I saw the weight indicator began to move little by little. Suddenly it jumped up and actually moved." Shen Biao said with a smile.

During the 361 days, Shen Biao was very nervous. In his words, this ultra-deep well represents the level of the Tarim Oilfield, the drilling level of China's oil industry, and the level of Asia. He always had a sense of mission and a strong sense of responsibility. Among them, careful and standardized operation is the guarantee of success.

"When I accepted the task, I was mentally prepared for two things: good and bad. Drilling requires a sense of responsibility. We drillers may seem rough, but we must be careful and attentive at work, and be meticulous in our work. After I resolved the stuck drill bit in Luntan 1 well, I felt a sense of pleasure and accomplishment in my heart, which is something that most people cannot experience. It is an unforgettable event and something that I will remember for the rest of my life," Shen Biao said with a smile.

The Keshen gas field was discovered in June 2008. It is a rare ultra-deep and ultra-high pressure fractured tight sandstone gas reservoir in the world at that time. Drilling here faces a series of world-class technical challenges. To this end, the Tarim Oilfield Company has continued to carry out engineering technology research, vigorously strengthened original innovation, integrated innovation, and introduction, digestion, absorption and re-innovation, and formed ten major drilling and completion technology series with Tarim characteristics, which greatly improved the deep and ultra-deep well drilling capabilities of the oilfield.

Tarim Oilfield has mastered the core technology of exploration and development of ultra-deep and ultra-high pressure tight gas reservoirs at depths of 7,500 to 8,000 meters, realizing the large-scale development of such gas reservoirs and laying a technical foundation for the oilfield to advance into exploration in the field above 8,000 meters. The success of Luntan 1 well is not only to drill a "Mount Everest" underground and the first deep well on land in Asia, but also to mark that Tarim Oilfield Company has reached the world level in the field of exploration and development.

Wang Chunsheng said: "The Tarim Oilfield has focused on the problems that restrict the improvement of the success rate of deep and ultra-deep drilling and the shortening of the well construction period. It has continued to carry out integrated geological and engineering research, strengthened technical research and field tests, and formed a speed-up model for different formations and well sections. It has achieved results in promoting the capabilities of deep drilling rigs and supporting equipment, preventing deflection and straightening, deep and efficient rock breaking, and underground complex prevention and control."

With a staff department, there is no need to worry about obstacles

In order to overcome extreme difficulties such as ultra-deep reservoirs, ultra-high pressure and high temperature, Tarim Oilfield has cooperated with relevant units to carry out joint technical research in areas such as increasing drilling speed and completing wells to increase production. The Luntan 1 well has created seven records including the deepest onshore well in Asia and the deepest oil and gas well, indicating that the ultra-deep drilling technology of Tarim Oilfield has reached the world's leading level.

"The development of the Tarim Oilfield over the past 31 years has actually been a long march." Liu Hongtao, deputy director of the Tarim Oilfield Oil and Gas Engineering Institute, said this as soon as we met.

The Cambrian subsalt exploration in the Tarim Basin has a wide range and great potential. The favorable exploration area below 9,000 meters is 23,000 square kilometers. The estimated resource scale is 310 million tons of oil and 3.3 trillion cubic meters of natural gas, with an oil and gas equivalent of about 3 billion tons. It will become a new strategic successor area for accelerating the development of the oil and gas industry in the Tarim Oilfield.

But who knows that if the Tarim Basin wants to become a new strategic successor area for the development of my country's oil and gas industry, it must overcome the obstacle of complex geological strata.

Liu Hongtao remembers that the first task he received when he first came to the Oil and Gas Engineering Research Institute was to sort out the oil and gas engineering development history of the Tarim Oilfield over the past 28 years. This was difficult for the young man who had been engaged in field drilling for six years.

"Although the first draft we worked hard to produce was not approved, I still gained a lot of new insights and experiences from this task. Compared with more than 70 ultra-deep, ultra-high-pressure and ultra-high-temperature oil and gas wells in the world, many geological conditions in the Tarim Oilfield are rare in the world and rare in China. The bride is sitting there, but we just can't unveil her, because there are three obstacles underground waiting for us to overcome one by one. One is the extremely thick gravel layer on the rock, the second is the high layer of composite salt where salt and gypsum sometimes appear at the same time, and the third is the strong salt abrasive layer, even the most powerful drill bit will be worn out quickly." said Liu Hongtao.

The Taklimakan Desert and the Kuche piedmont at the southern foot of the Tianshan Mountains are the main operating areas of the Tarim Oilfield. The two blocks have complex geological conditions and harsh working conditions, which pose great challenges to drilling and completion technology. After tackling these problems, they have developed optimized drilling technology for ultra-deep and complex wells and management and transformation technology for high-temperature and high-pressure wells.

"I often describe the work of our Oil and Gas Engineering Research Institute like this: program design, scientific and technological research, decision support, and production support. To put it bluntly, we are a staff department. We are the staff department for oil field decision-making and a good helper for production units." Liu Hongtao said with a smile.

When danger comes, they are the warriors who rush to the front line. Liu Hongtao clearly remembers that in the winter of 2018, a well encountered abnormally high pressure, and he rushed to the drilling platform to connect the oil pipe. At that time, the oxygen on his back was only enough for 40 minutes. He worked on the drilling platform for 40 minutes and finally connected it. When he got off the drilling platform, his legs were weak. If it was a few minutes later, if the leaking gas was poisonous, the consequences would be disastrous.

"From the initial drilling of wells to the completion of wells now, our thinking has also changed. When designing a plan for each well, we must take into account all possible problems and design plans to solve these problems. In the past, we pursued scientificity and rationality, but now we must also add operability, and each process must have a plan. So what our team advocates is: a wolf-like team and an eagle-like individual. It is not something that can be solved by one discipline alone. It requires the entire team, the collaboration of various departments, and multi-disciplinary and cross-departmental research." Liu Hongtao said.

Liu Hongtao is currently leading his team to write key research and application materials on complex deep-earth oil and gas drilling and completion, and is preparing to apply for the National Science and Technology Progress Award. In his words, drilling and completion represent the level of a country, and the unique conditions of the Tarim Oilfield allow them to undertake this historical mission, which is their honor.

It was already past 10 o'clock when they walked out of their office. Looking back at the buildings of the Exploration and Development Research Institute where Tang Yangang worked and the Oil and Gas Engineering Research Institute where Liu Hongtao worked, many lights were on on each floor. Their mission and responsibility made them forget about time. This may be the driving force behind their ability to overcome global challenges one after another.