Experimental Study On Increasing Oil Recovery In Mid - Late Stage Of Development Of Qiudong Condensate Gas Reservoir

The development of condensate gas field occupies an important place in our country or even in the world because of its substantial reserves and high economic worth. Currently quite a number of condensate gas fields in our country have gone into middle-and-later stage and mostly been in a state of low yield due to the seriously retrograde condensation damage, so how to enhance condensate oil recovery has become the important goal in the middle-late period of condensate gas field development. In this thesis, researches are funded by CNPC with the project "the mechanism and technical feasibility of enhancing condensate oil recovery in middle-later period of condensate gas reservoir". It plays an important role in guiding to develop the middle-later period of condensate gas reservoir effectively.Qiudong condensate gas reservoir has gone into middle-and-later stage with a very low condensate oil and gas recovery, which is medium condensate content and low permeability gas reservoir. In order to study the extraction rules of injected gas under the condition of different injection medium and different injection pressure This paper adopt the typical formation fluid to carry out gas injection swelling experiments; after that, Conducting the long-core displacement test in laboratory by using the true cores which simulates the differences in enhancing condensate oil recovery under the condition of different injection fluid and mode during the middle-late period of condensate gas field development and also simulates the effect of gas injection caused by physical differences so that the optimal are obtained combining with the practice; besides, the effects of gas injection caused by physical differences are quantitatively analyzed. The following conclusions and understandings are obtained:(1) The gas injection expansion tests show that the ability of extraction is strongest by injecting CO2under the current formation pressure, followed by dry gas, and N2is weakest. The higher the injection pressure is, the stronger the extraction effect is.(2) The long-core displacement tests of different injection fluid show that condensate oil recovery can reach to66.14%by injecting dry gas, and the injected amount is the least (2.6HCPV), so consider dry gas as the preferred medium to replenish energy.(3) The long-core displacement tests of different injection mode show that condensate oil recovery can reach64.96%by using pulse gas injection, but the injection volume is as high as4.51HCPV. The next is cyclic gas injection, whose condensate oil recovery and injection volumes are38.68%and2.04HCPV respectively. Thus as far as Qiudong condensate gas reservoir is concerned, the method of cyclic gas injection is recommended. Pulse gas injection also can be chosen if there is sufficient gas supply.(4) The inter-layer interference experiment show that the condensate oil recovery of high permeability layer is greater than the low. Compared with Stratified gas injection, the condensate oil recovery of general gas injection is less5.77%at the same gas injection rate when injecting1.48HCPV gas.