This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 30437, “Risk Management and Control for CO2 Waterless Fracturing,” by Siwei Meng, Qinghai Yang, SPE, and Yongwei Duan, PetroChina, et al., prepared for the 2020 Offshore Technology Conference Asia, originally scheduled to be held in Kuala Lumpur, 2–6 November. The paper has not been peer reviewed. Copyright 2020 Offshore Technology Conference. Reproduced by permission.
Given shortages and uneven distribution of water resources in China, efforts must be made to develop waterless fracturing techniques. The fluid experiences high pressures and low temperatures during carbon dioxide (CO2) waterless fracturing operations, which can lead to accidents and environmental pollution. In the complete paper, a safety-management approach and a contingency plan for such operations are developed. At the time of writing, this CO2 waterless fracturing methodology has been completed successfully more than 20 times.
Surface Process Work Flow of CO2 Waterless Fracturing
The basic process of a CO2 waterless fracturing operation is shown in Fig. 1. First, several CO2 storage tanks are connected in parallel. The booster, sealed blender, fracturing pump (all mounted on trunks), and wellhead equipment are connected. The measuring trunk communicates with each vehicle to monitor operation status. Proppant is put into the sealed blender, into which liquid CO2 is injected for pre-cooling. Pump testing is conducted on the high-pressure line and the wellhead and the low-pressure liquid supply line is pressure-tested. Operation does not proceed until pressure-testing results are positive. Afterward, liquid CO2 is injected into formations to fracture them and, moreover, extend created fractures. The sealed blender is enabled to inject prop-pants, and displacement begins after the end of proppant injection. Finally, a series of tasks, including well shut-in for soaking and flowback, is carried out successively.
Stimulation and Sequestration Mechanism of CO2 Waterless Fracturing for Continental Tight Oil Reservoirs
