A new screening method of low permeability reservoirs suitable for CO2 flooding

Since the existing gas flooding reservoir screening criteria lack economic indexes reflecting future dynamic production performances, indexes reflecting economic profits are added into the exiting criteria (related to well oil production rate) to form a new method of selecting low permeability reservoirs suitable for CO2 flooding. Reservoir engineering methods of average well peak oil production rate prediction for gas drive is given by employing the concept of “Oil production rate multiplier due to gas flooding”. Based on the principles of technical economics, the method calculating the economical limit well oil production rate of CO2 flooding is also presented. On this basis, a new screening criterion of reservoirs suitable for CO2 flooding is proposed: if the peak well oil production rate predicted by reservoir engineering method is higher than the economic limit well oil production rate, the target reservoir is suitable for CO2 flooding. Furthermore, a four-step reservoirs screening method is advanced: technical screening, economic screening, fine feasibility evaluation, recommendation of optimal gas flooding blocks. The new screening criteria were applied to evaluate the CO2 flooding potential of seventeen blocks in an oilfield, which ended up with only 32.4% of the original oil in place from conventional method suitable for CO2 flooding. It is recommended blocks suitable for CO2 flooding be selected according to the new procedure to ensure economic success. Key words: CO2 flooding, low permeability reservoirs, screening criterion, oil production rate multiplier due to gas flooding, reservoir engineering method, economic limit well oil production rat

Potential impacts of climate change on the distribution of the relict plant Shaniodendron subaequale

Shaniodendron subeaqualis is a tertiary relict plant unique to China. This species has high greening, ecological, and scientific research value, and has been listed as a national I-level key protected plant. Clarifying the main climatic factors restricting the geographical distribution of S. subeaqualis and predicting the potential geographical distribution pattern of this species can provide a scientific basis for the protection of the germplasm resources of this rare species. Based on 104 S. subeaqualis natural distribution records and 9 climate factors, the MaxEnt software was used to predict the potential suitable areas of S. subeaqualis in different periods (LGM, MH, Current, SSP245-2050s, SSP245-2090s, SSP585-2050s, SSP585-2090s). The results showed that the contemporary AUC predicted by MaxEnt is 0.996, with high simulation accuracy; Precipitation in the driest season (Bio17), the average temperature in the coldest season (Bio11) are main factors affecting the distribution of S. subeaqualis. At present, the suitable area of S. subeaqualis is mainly distributed in Jiangsu, Anhui, and Zhejiang province, with a total area of 11.575 × 104 km2, of which the high suitable area is 1.424 × 104 km2 and the medium suitable area is 3.826 × 104 km2. In the LGM, the area of S. subeaqualis was roughly similar to that of the contemporary period, but there was a southward migration phenomenon in some areas, such as the suitable area in the south of Zhejiang. In order to avoid the influence of ice age, S. subeaqualis moved to nearby refuge places, such as Dabie Mountain area of Anhui province, the west of Tianmu Mountain area of Zhejiang province and mountain area of Jiangsu province. In the MH, the suitable area for S. subeaqualis was reduced and moved northward to a small extent. In the future period, the suitable range of S. subeaqualis will not change greatly, but the overall degree of fragmentation will intensify. If effective measures are not taken, it is bound to bring severe challenges to the survival of S. subeaqualis. In order to protect S. subeaqualis germplasm resources more effectively, it is suggested to dynamically monitor the existing S. subeaqualis population and take various measures actively to reduce the negative effects of climate change on S. subeaqualis