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CO2 flooding technology is an effective technical means to enhance the recovery of low permeability reservoirs. After CO2 comes into contact with crude oil， the asphaltene in the system is deposited in a solid form， which causes a certain blockage to the reservoir， but the dissolution improves the flow capacity of the reservoir as a whole at the same time. The damage of CO2 flooding to low permeability reservoirs under different injection methods is different. The organic scale plugging mechanism， reservoir wettability， and CO2-water solution corrosion evaluation experiments were carried out after continuous CO2 injection and CO2-water alternating injection. The variation characteristics of relative permeability curve parameters were evaluated， and the damage of different injection methods of CO2 flooding to low permeability reservoirs was quantitatively characterized. The results show that the organic scale produced by CO2 flooding would block the pore throat of the rock， but on the whole， the dissolution caused by the reaction of CO2 and chlorite is stronger， which makes the recovery of the low permeability reservoirs effectively enhanced. Moreover， the organic scale blockage caused by CO2-water alternating injection is weaker than that caused by continuous CO2 injection， and the dissolution effect is better. The permeability loss rate is lower. It could achieve a better oil displacement effect in pores with a radius of more than 0.2 μm and increase the pore space and flow channel of the rock so that the recovery of low permeability reservoir could be effectively improved.

Aiming at the large error of power function fitting in traditional methods, a weighted normalization method based on effective reservoir thickness is proposed. It takes into account the heterogeneity of sandstone reservoirs and analyses the proportion of various reservoirs in small formations. The effective thickness of a single well is used to normalize the weights of different types of reservoir. The result is representative of the reservoir. Taking block Zhongqu 43 of Jianghan oilfield as an example, three normalization methods are compared. According to curve shape, characteristic parameters and data standard deviation, the new normalization method is reasonable and effective. It has the highest degree of fitting with the original curve. The new nor-malization method can qualitatively evaluate the production capacity of a single well and production potential of the block from the perspective of microscopic pore structure. It can provide guidance for development. [ABSTRACT FROM AUTHOR]

For the development of CO2 flooding in low-permeability oil fields, due to the strong heterogeneity and viscous fingering, it is easy to form the actual situation of the dominant air channel. To understand the heterogeneity of the reservoir in advance, and to obtain the information of the underground fluid distribution status in time, through the indoor evaluating the experimental study, the two gas-phase tracers QT-1 and QT-5 were optimally evaluated in terms of storage time, temperature, and static adsorption, and the cross-valve gas tracer monitoring was performed on the transferred 29-33 well group. The production dynamics of the test wells in the CO2 drive field was Tracked and evaluated. According to the seeing conditions, migration speed and direction of the gas tracer, and the results of the reservoir connectivity, a comprehensive analysis of the advantages of the gas drive was carried out. The results show that under the condition of reservoir, the gaseous tracers QT-1 and QT-5 coexist and move with gas phase and light hydrocarbon mixed phase with CO2 in the oil reservoir. The migration speed of the tracer in the first-line well is relatively slow, and the velocity of the second and third line wells faster, indicating that the fracture is not developed. The No. 2 small-layer injection and production well of the Qingyi I sands group has good connectivity and there is intra-layer heterogeneity. The production concentration is parallel to the southwest direction of the sand body, indicating that the there are gas-fed advantages in the direction. Different tracer output curve shapes correspond to different reservoir characteristics. A single set of thick sand reservoirs shows "single peak", long time for seepage, and long duration of output peak; multiple sets of thin sand reservoirs show "Multiple peaks," short reagents, output peak duration, and other features. [ABSTRACT FROM AUTHOR]