关键词: 非常规油气资源, 页岩革命, 系统优化钻井, 建井成本

Abstract: Compared with North America, the exploration and development of unconventional oil and gas resources in China began relatively late. Shale gas exploration and development started at the beginning of the “12th Five Year Plan” period. The exploration and development of tight oil, tight gas and shale oil started at the beginning of the “13th Five Year Plan”, and developed rapidly during the “13th Five Year Plan” period. In particular, development of shale gas in Sichuan and Chongqing, conglomerate oil field in the Mahu sag, and shale oil reservoir in the Jimsar sag in the Junggar Basin, have entered the stage of large-scale development, becoming the most important field for oil and gas production increase at the end of the “13th Five Year Plan” and into the period of the “14th Five Year Plan” of CNPC. Compared with conventional oil and gas, unconventional oil and gas resources have poor reservoir conditions, which require large-scale “horizontal well + volume fracturing” to achieve effective development. However, due to limitations of rig equipment and performance of horizontal well drilling tools, and especially shortcomings in concepts and methods, issues of low drilling efficiency and long well construction periods are common in unconventional horizontal wells in China. Generally, the drilling period of a horizontal well is 60-90 days, with a vertical depth of 2,000-3,000 m and a horizontal section of 1,500-2,000 m. In North America, the drilling period of a horizontal well can basically be controlled within 15-25 days, with a vertical depth of 2,000- 3,000 m and a horizontal section length of 2,000-3,000 m. A drilling rig in China can only drill 2-3 horizontal wells a year, while in North America a drilling rig can complete 15-20 horizontal wells a year. With the large-scale development of unconventional oil and gas resources in China, the challenge of drilling rig shortage is increasing. Drilling efficiency has become a bottleneck problem which seriously restricts the rapid and large-scale production of unconventional oil and gas resources in China. There are two advantages which support the great improvement of drilling efficiency of horizontal wells in North America: management and technology. In technology, there are five main aspects: the first is the continuous upgrading of supporting capacity of drilling rig; the second is improvement of the reliability and stability of downhole tools; the third is large-platform factory operation; the fourth is remote real-time support and decision-making systems, and the fifth is the application of the concepts and methods of systematic drilling optimization. In 2018, Strait Energy cooperated with K&M drilling engineering consulting company of the United States to introduce internationally-advanced concepts and methods for systematic drilling optimization. Pilot testing of drilling speed increase in horizontal wells was first carried out by Changning Shale Gas Co., Ltd. in the Sichuan and Chongqing area, and in the conglomerate oil field in the Mahu sag in Xinjiang, which greatly shortened the well construction period and verified the feasibility of systematic drilling optimization methods in the development of unconventional oil and gas resources in China. In order to further promote this, testing of speed increase in the whole block was carried out in the conglomerate oil field in the Mahu sag in 2019, which also achieved remarkable results. This further proves that the concepts and methods of systematic optimized drilling speed increase are scientific, universal and replicable, which is an important shift in practice from experience-based drilling to scientific drilling, and shows very promising prospects for popularization and general application.