The reporter learned from the Jianghan Oilfield of Sinopec that recently, in Longtouxi Village, Jiannan Town, Lichuan City, Hubei Province, the Red Page 2HF well was continuously trial production for 15 days, and the Nissan shale gas remained stable. The well is the second shale gas pre-exploration well deployed in the Permian in the Hongxing area of Icheon City, following the Red Page 1HF well, in the Jianghan Oilfield.
"The Red Pages 1HF well successfully completed the trial production, filling the gap in the exploration and development of continental Permian shale gas. The continuous deployment of the Red Page 2HF well and the Red Page 3HF well shows that the oil and gas drilling is good, marking a major breakthrough in shale gas exploration in the region. Guo Zhanfeng, manager of the oilfield exploration management department, introduced that Jianghan Oilfield has successfully submitted the first batch of permian shale gas forecast reserves of 105.103 billion cubic meters in the Red Star Region, which is equivalent to more than 100 million tons of crude oil. The relevant achievements won the special prize of Sinopec's 2021 oil and gas exploration major discovery last month.
From conventional gas production to proposed shale gas extraction
The natural gas exploration of Jianghan Oilfield in Hubei Province dates back to the 1960s and 1970s, when Jianghan Oilfield discovered the Jiannan Gas Field, the only gas field in Hubei Province, in Lichuan.
"The Red Star area includes the Jiannan Block, the Sanxing Block and the LongjuBa Block, and the three wells that are now implemented are all in the Jiannan Block, but the original natural gas is conventional, and now it is shale gas." Guo Zhanfeng introduced.
After the discovery of the Jiannan gas field, Jianghan Oilfield has successively deployed 28 wells in the block, but no major breakthrough has been made.
In 2008, with the success of the North American shale gas revolution, a shale gas exploration boom was set off in China. Jianghan Oilfield refocused its attention here, reviewing the hydrocarbon source of conventional natural gas exploration in the early days of Western Hubei (hydrocarbons are organic compounds composed only of two elements of hydrocarbon - reporter's note), and selecting Cambrian, Silurian and Jurassic as favorable strata for shale gas exploration, of which the thickness of Silurian and Cambrian shales exceeded 100 meters. From 2011 to 2014, the oilfield targeted the shale gas of these two strata, and successively deployed a number of drilling wells in Enshi and other places, but neither of them achieved an industrial breakthrough.
In 2016, on the basis of reviewing the old wells and analyzing the data, the researchers proposed to deploy the Red Page 1HF well in the Permian Formation of the Red Star Area.
Breaking through the "lower limit" begins to find gas in thin reservoirs
The disadvantage of the Permian exploration of shale gas is the thin reservoir. "Prior to this, 30 meters were used at home and abroad as the lower limit for the thickness of the effective gas layer of shale gas." However, in the Enshi Red Star region, researchers found that the Permian shale reservoir was less than 20 meters, far from reaching the "lower limit".
The researchers boldly hypothesized and carefully verified, and carried out a large number of investigations from western Hubei to eastern Yudong, and found that although the Permian shale has a thin reservoir, the total organic carbon content is even higher than that of the Fuling shale gas field in Chongqing.
Breakthroughs in understanding, coupled with advances in engineering technology, enabled the Drilling of the Red Page 1HF well to pass the demonstration smoothly. In November 2019, the well's guide eye well was officially drilled.
After the drilling of the guide eye well, the analysis and evaluation work is very important, which is directly related to whether the horizontal well drilling will be implemented. The drilling of horizontal wells is the key to the success of exploration of new stratigraphic systems. Core sampling, sampling, analytical testing and fine description, a series of research evaluation results confirmed the researchers' prediction: the organic carbon content of shale in the Permian Wujiaping Formation is more than 8% on average, which is nearly double that of the Fuling shale gas field.
"The organic carbon content is the most critical indicator to determine whether there is shale gas, and the higher the content, the stronger the ability to generate oil and gas." Eventually, the Permian Wujiaping Formation shale was recognized by experts as a new shale gas exploration stratigraphy.
"Walking a fine steel wire more than 3,000 meters underground"
Drilling horizontal shale gas wells at depths of up to 3,300 meters is a challenge.
"The horizontal section of the target window is only 6 meters thick." Chen Xiaogang, director of the Exploration and Development Research Institute of the First Gas Production Plant of Jianghan Oilfield, introduced that due to the limited accuracy of seismic data and the thin reservoir, the difficulty of geological guidance in the horizontal section of the Red Page 1HF well is tantamount to "walking a tightrope more than 3,000 meters underground".
During the drilling process, the researchers of Jianghan Oilfield used the gamma measurement system while drilling to conduct reservoir tracking and comparison and model calculation in real time, and adjusted the drilling trajectory in time. In the end, the drilling rate of the well's high-quality shale gas layer reached 95.6%.
"The content of brittle minerals in the underground is as high as 80%-90%, and it is necessary to press the formation to form a 'highway' for shale gas flow, which puts forward higher requirements for the process of reservoir fracturing transformation engineering." In the face of unprecedented problems, oilfield researchers have repeatedly demonstrated, put forward the idea of reservoir transformation process, increased the expansion of long seams and wide seams, and adopted a new fracturing fluid system to form a smooth gas production channel.
At the end of 2020, the Red Page 1HF well completed the gas test. After the breakthrough of the well, Jianghan Oilfield deployed the Red Page 2HF, Red Page 3HF, Red Page 4HF and Red Page Mao 1 well.
Sun Jianfa, secretary of the party committee and senior engineer of the first gas production plant in Jianghan Oilfield, introduced that the first batch of permian shale gas in the Hongxing area is predicted to have a gas storage area of more than 300 square kilometers. The local shale gas storage range is far more than this area. It is estimated that the amount of shale gas resources buried within 4500 meters in the area is more than 400 billion cubic meters, which has broad prospects for commercial development.