Progress, Main Challenges and Future Prospect of Shale Gas Exploration and Development in China
Since PetroChina and New-field Oil Company of the United States signed the first cooperation agreement, Weiyuan Area Shale Gas Joint Research, on the shale gas development in 2007, shale gas development in China has made remarkable achievements. Three national-level shale gas demonstration areas, Chongqing Fuling, Sichuan Weiyuan - Changning and Zhaotong, have been successfully built. The proven shale gas geological reserves and the production capacity are 900 Bcm and 10 Bcm, respectively. The annual production in 2017 is about 9.0 Bcm. Through the technical cooperation and self-innovation, it rapidly established a series of applicable, mature main engineering technology and supporting equipment for shale gas exploration and development with the burial depth shallower than 3500 meters, which effectively supports the shale gas production and construction work. In terms of resource evaluation and reserves. The Marine shale gas resources are identified as high-quality reserves and are the main targets of large scale production. Southern Ordovician Wufeng Formation - Silurian Longmaxi black shale is deposited in the deep water shed environment. It contains graptolite, algae and other enrichment in silicon, calcareous paleontology, and vertical "dessert section" (TOC> 2.0%) thickness up to 30-50 meters. The thickness of Wufeng - Longmaxi organic-rich shale is about 30 to 120 meters. The thickness of Yangtze River area organic-rich shale is more than 30 meters, and the distribution area is more than 80,000 square kilometers. Other formations, such as marine terrestrial, continental and continental transitional shale gas, have not achieved a real breakthrough and are still in the stage of resource exploration and small-scale trial test. In the target position, fine stratification. Through the combination of theoretical research and production practice, it reveals that the target of shale gas horizontal well is located at the bottom of Wufeng-Longmaxi formation. Fuling and Changning’s best targeting position is the bottom of Wufeng – Longmaxi formation. It deposited in the retention of hypoxia environment, deposited in the oxidation environment of the Guanyinqiao section. Weiyuan’s best target is located in the bottom of Longmaxi formation, and the thickness is only 3-8 meters. In order to further analyze black shale, by combining the chronostratigraphy, lithology, electricity, unified regional stratification comparison standard, we can determine the "sweet spot section", which provides the guidance for horizontal well implementation. It already gets the production approval by using graptolite fossils as the basis of precise stratification. In terms of technical policy and development technology. Horizontal well trajectory orientation and maximum horizontal principal stress or natural fracture direction are intersected by large angle. The horizontal well spacing and the length of the horizontal section are determined to be about 200 ~ 500 meters and 1500-2500 meters, respectively, by integrating micro-seismic monitoring and dynamic monitoring results. We need to carry out different production methods and understand the mechanisms of shale gas decline and fracturing fluid flow-back of each block of oilfield. For example, in Changning, the pressure dropped quickly in the first three months, and the pressure stabilized afterward and the production declined quickly; In Zhaotong, since the production and pressure were controlled deliberately, the production and pressure declined steadily; In Weiyuan, due to open production, the pressure and production quickly declined; In Fuling, the production utilized the above three production methods. The fracturing fluid flow-back rates in demonstration areas varied largely, and the average flow-back rate can be as high as 40%. The Fuling block has overall low flow-back rate with the average flow-back rate less than 10%, and the Weiyuan block has a high flow-back rate. Compared with the United States, the burial depths of Fuling, Changning and Zhaotong blocks are comparable and the single well EUR is also comparable. The burial depth of Wei Yuan block is too deep and the single well EUR is low. By the end of 2020, China's shale gas production is expected to achieve more than 20 Bcm based on preliminary prediction. Meanwhile, the future development of China's shale gas is facing some challenges: such as non-marine shale gas potential has uncertainties; marine shale gas production reserve area is insufficient; core technology and equipment for 3500m and deeper resource have not made a breakthrough; the environmental pressure has been increasing. As a next step, it requires to strengthen the evaluation of deep formation, to explore new areas, to encourage the technology innovation for shale gas demonstration area (up to 3500 meters deep). It is important to upgrade development technologies, focus on optimizing the development of technology policy. For 3500-4500m shale gas resources, it is necessary to capture key engineering technology and continue to support the development of China's shale gas. In addition, it is important to strengthen environmental protection and to build green, sustainable, and intelligent shale gas field.
AAPG Datapages/Search and Discovery Article #90333©2018 AAPG Middle East Region, Shale Gas Evolution Symposium, Manama, Bahrain, December 11-13, 2018