Report on Developing a US-China Joint Project on CO2-Based Fracturing Techniques:
There are several types of hydraulic fracturing methods that have been investigated in the past decades that use little or no water. The criteria for selecting an optimal hydraulic fracturing fluids are many, and no single fluid can meet all the desired characteristics. Developing a set of technologies by using different fracturing fluids can better meet individual geologic, economic, and environmental needs. CO2 as an alternative of water for hydraulic fracturing has its unique place among all other fracturing fluids, and can meet both economic and environmental objectives under certain circumstances. There are three main categories of CO2-based fracturing fluids, simple liquid CO2 (LCO2), directly thickened LCO2, and CO2-foams/emulsions. Although LCO2 has many advantages, critical disadvantages arise due to its high operating pressure, low viscosity, poor proppant-carrying capacity, and generation of shallower fracture networks. To date, techniques for direct thickening of LCO2 to overcome these limitations have proven ineffective. To increase the apparent viscosity of CO2, we propose to further develop CO2-foam (and emulsion) fracturing techniques. While CO2-foams have long been used in EOR, the required properties for hydraulic fracturing are different, and relatively few peer-reviewed publications and field test reports are available regarding their applications in fracturing, and the surfactants and additives used are often proprietary This report describes a brief state-of-the-art analysis of CO2-based hydraulic fracturing methods and then discusses a joint plan for a long-term R&D collaboration to advance the most promising CO2-based hydraulic fracturing techniques as part of the U.S.-China Clean Energy Research Center, Water Energy Technology (CERC-WET). The objective of this U.S.-China joint research project is to design and laboratory test a CO2-foam fracturing fluid system, and then conduct pilot field-tests on them in China’s Jilin Oilfield. This joint research project will benefit both U.S. and China for advancing their shared goal of developing better technologies for CO2-based fracturing. The Chinese CERC-WET has two teams joining the project, one from RIPED, responsible for aboveground infrastructure design and construction. Another team from the Jilin Oilfield will be responsible for the field test design and conducting the test. The U.S.CERC-WET team at LBNL will be responsible for providing the CO2-foam formulations and their rheology parameters to be tested in the field (a challenging task and a key to success); participating in the equipment design and field test design; assisting in analyzing field data; and reporting to U.S. DOE and CERC-WET.