Research On Enhanced Recovery Of Super-heavy Oil Reservoir By HDCS Flooding Technology

For super-heavy oil reservoirs with deep depth and thin thickness,the methods of conventional steam injection or SAGD development are difficult to play an effect exploitation.At china and abroad there is no successful development experience yet.For extra-heavy-oil reservoirs,the crude oil is with high viscosity,high steam injection pressure,small sweep range of steam,large heat loss and low oil recovery.Shengli Oilfield effectively has developped this kind of reservoir using HDCS method,which is a kind of strengthening production technology.In this paper,enhanced oil recovery technology for the extra-super-heavy oil reservoirs was researched through laboratory tests,physical simulation and numerical simulation method.In late stage of conventional steam huff and puff stimulation,liquid production and crude oil production may decrease,and steam flooding development mode after multiple rounds of HDCS can recovery formation pressure,and supplement the formation energy in some extent.Therefore,the HDCS flooding after HDCS is very important to improve the final oil recovery of the extra-super-heavy oil reservoir.In the study of the production process of the steam huff and puff and steam flooding,the effect of viscosity reducer and CO₂ in the whole simulation process on the properties of crude oil and CO₂ and steam on viscosity reducer diffusion effects were researched using three-dimensional physical model.During the experiment,the oil production,liquid production,and water cut were analyzed.Through the three-dimensional physical model real-time pressure and temperature at different positions of the reservoir were detected,and reservoir temperature and pressure changes at different stage were accurate monitored.For the first time the conversion time for deep layer of super heavy oil reservoir stimulation flooding was given,that the water cut is more than 85%and reservoir pressure is 3⁵MPa.At the same time,the crude oil nature at different flooding stage of the cycle huff and puff was researched.The analysis of the results shows that,after injection of viscosity reducer,liquid volume flowing into the finger tip of horizontal well is fewer than that into the heel end.The viscosity reducer has more significant effect on the oil near the wellbore.The asphaltene content and molecular weight of the ultra heavy oil have been effectively reduced because of the viscosity reducer.The viscosity reducer distribution is very irregular,and the nature of the recoveried crude oil is relatively different.Under the condition of injection viscosity reducer ony,the diffusion is slow.The injection of CO₂ can significantly improve the viscosity reducer diffusion velocity,and the viscosity reducer scope has been expanded.In addition,the viscosity reducer distribution is more uniform.After the injection of steam,the flow of crude oil is better,and the nature of the crude oil is more balanced.In the actual site production,crude oil viscosity will increase with the same soak period.Viscosity reducer dissociation effect will be weakened with the increased cycle.In the process of thermal recovery by steam injection,injection of steam and formation fluid density difference will lead to"steam override"phenomenon.Because injected steam and formation fluid mobility is much greater than heavy oil in the reservoir,which will not only reduce the steam in the reservoir area affected due to the high mobility ratio caused by steam channeling,but also affect the oil recovery of super heavy.For solving this problem,an enhanced foam under high temperature is developed in this paper.The influence factors of reservoir temperature,salinity of formation water on sealing performance of extract and alkali lignin enhanced foam system were studied by dual parallel drive for indoor physical simulation experiment.Experimental results show that the synergistic effect was found in both foam and gel system.The gel strengthened foam can carry more gel into the high permeability layer,so as to realize good profile control.The three-dimensional physical simulation results show that,the two kinds of system can enhance the oil recovery and greatly reduced moisture content.The tannin extract foam system with steam flooding can enhance oil recovery by about 20%than that of pure steam injection,and alkali lignin foam system can increase the oil recovery by 11%.Through the introduction of Zheng-411 block’s current state of development analysis,the development effect of extra-super-heavy oil reservoir numerical simulation study.Numerical simulation results show that for reverse nine spot well network production,reasonable steam injection rate is 200m³/d on the basis of the recommended injection ratio of greater than 1.2,reasonable injection quantity for oil soluble viscosity reducer for single well is 250m³⁵00m³,reasonable injection quantity of CO₂ for single well is 20000m³.The reasonable injection method of oil soluble viscosity reducer and CO₂ in steam flooding stage is divided into five slug injection.