## 6 Advantages and Disadvantages Analysis and Prospect of Non-Condensate Gas Injection
### Future Prospects  
(1) Non-condensable gas prospect  
However, injecting CO\({}_{2}\) into heavy-oil reservoirs can improve oil recovery, and it can also realize the geological storage of CO\({}_{2}\), which can improve environmental pollution and climate change to some extent. In recent years, foreign scholars have proposed CO\({}_{2}\)/N\({}_{2}\) composite gas EOR technology [100; 101]. Although domestic scholars have carried out a lot of studies on EOR by gas injection, most of them focus on a single-gas injection medium such as CO\({}_{2}\) and N\({}_{2}\). Recently, a new type of heat carrier (MTFs, multiple thermal fluids) has been introduced into the heavy-oil recovery process [102; 103]. As a new heat carrier, MTFs are different from the traditional mixed gas of steam and non-condensate gas. The non-condensate gas in MTFs is a mixture of N\({}_{2}\), CO\({}_{2}\), CH\({}_{4}\), and CO. Therefore, the MTF-based process can also be considered as a steam-solvent-gas co-injection process. In addition, non-condensate gas can also be applied to heavy-oil reservoirs with water at the bottom [104]. Water cone has always restricted the effective development of heavy oil reservoirs. In order to prevent or slow down the occurrence of water cone, non-condensate gas or non-condensate gas foam can be used. After use, the rise of aquifer can be effectively controlled to some extent.  
(2) New technique prospect  
The main difficulties in the development of heavy-oil resources at the present stage are to improve the recovery of heavy-oil reservoirs in the late stage of thermal recovery and to efficiently develop the hard-to-use heavy-oil reservoirs after a long period of steam injection development. Serious formation pressure loss and the development of cross-well channeling channels have become the main factors restricting the development effect of heavy-oil thermal recovery. Steam-non-condensable gas, steam-chemical agent, and steam-organic solvent combined thermal recovery to enhance oil recovery technology can effectively solve the problems faced in the late thermal period. The key to the implementation of this technology is to select the appropriate additive types from non-condensate gases, solvents, and chemicals. At the same time, it is the focus of the attention of oil companies to seek efficient and low-cost additives. At present, it has been proved in field applications that the thermal composite development method will be the key technology to realize the late stage of steam thermal recovery of conventional heavy oil and the efficient development of hard-to-use heavy-oil reservoirs.  
In contrast to waterflooded light-oil reservoirs, an EOR process for heavy-oil resources is more challenging. Common technologies include an in situ combustion process, a thermal-solvent process, a thermal-NCG (non-condensable gas, such as N\({}_{2}\), flue gas, and air) process and thermal-chemical (such as polymer, surfactant, and geland foam) process. The offshore multi-component thermal fluid injection process and the thermal CO\({}_{2}\) and thermochemical (surfactant and foam) processes of onshore heavy-oil reservoirs will be some opportunities in the next decade. In addition, the new electrical method, in situupgrading (such as ionic liquids, and the addition of catalyst and steam nanoparticles) and novel wellbore configuration have also attracted some attention [105]. The effective development of heavy-oil reservoirs in the whole life cycle is a process of continuously improving oil recovery. It is the most important task to evaluate the performance of effective new technology and select the best process, not only from the laboratory experiment, but also from the field.