Study On The Researvoir Characterization And CO₂ Migration Underground In The Shenhua CCS Demonstration Project Site

As global climate change has been a serious threat to our environment,reducing CO₂ emissions is great challenge for all the countries to develop sustainable.Carbon Capture and Storage?CCS?has been recognized as one of the most effective technologies to deal with global warming.Reservoirs characterization,site geological modeling and numerical simulation of CO₂ migration are the most important tasks for feasibility verification and safety assessment of the CO₂ geological storage project.However,for CO₂ geological storage,the pressure should be higher than 7.38 MPa,and the temperature should be higher than 31.1?,which means the reservoirs for CO₂ storage should be deeper than 800 m theoretically.Complicated geology,conditions of high pressure & temperature experiment,numerical simulation plans,and accuracy of geophysical monitoring technologies,et al.,all affect the results of geological modelling and numerical simulation of CO₂ migration.Shenhua CCS Demonstration Project is located in Yijinhuoluo County,Ordos City,Inner Mongolia,which is the only one CCS project of CO₂ storage in deep saline aquifers.Shenhua CCS Demonstration Project started CO₂ injection on 9th May,2011 and finished in April,2015 by injected 30.2×104 t total.The results of continuous CO₂ ?underground – surface – atmosphere? monitoring show that there is no CO₂ breakthrough the caprocks and leak into the atmosphere.Therefore,using the Shenhua CCS Demonstration Project as a case study,the author collected and studied the geology and experimental data,carried high resolution sequence stratigraphic correlation and logging constrained seismic inversion for geological modeling.The author also carried out displacement experiment of high pressure & temperature using undisturbed drilling cores and saline to obtain CO₂-water relative permeability and capillary pressure of main saline aquifers.Finally,the author carried out numerical simulation to predict CO₂ migration corrected by the time – lapse Vertical Seismic Profile?VSP?monitoring data.The methodologies of reservoir characterization,site geological modeling and numerical simulation of CO₂ migration could provide guidance for underground utilization and risk assessment on actual CCS projects.The main contents of this paper are as follows:?1?On basis of regional geology,geophysical survey,drilling,logging and other experimental data,the site characterization and geology are studied in detailed.The studies show that the geostructure is gentle,no faults and very few historical earthquakes near the injection well in the site where could store CO₂ safety for a long time.Besides,in the depth of 1600 – 2500 m,the underground water flows very slowly in the thick sandstone saline aquifers of Shanxi,Shihezi,Shiqianfeng and Liujiagou formations,almost hydrated with high total dissolved solids?TDS?.In addition,the Triassic Heshanggou and Zhifangzu could be good regional caprocks for these potential CO₂ reservoirs.?2?The reservoirs and caprocks for CO₂ geological storage in the demonstration project site were divided further using high resolution sequence stratigraphy.Because of differences between the geological survey and other data,and the strong heterogeneity of terrestrial clastic rocks,it is very difficult to predict the reservoir flow units for CO₂ migration and storage.On the basis of data of geology,geophysical survey,drilling,logging and experiment,the author identified the long-term,short-term and medium-term base-level cycles in turn to establish the high resolution sequence stratigraphy hack of Zhifang formation to Majiagou formation.Meanwhile,combined with general standards of CO₂ reservoir selection and perforated intervals in the injection well,five saline aquifer groups were recognized as suitable reservoirs for CO₂ geological storage.Aluminous shale in the bottom of Benxi formation could be good seals for Majiagou carbonate aquifers,similarly,the thick mudstones and silty mudstones of the upper Shihezi formation and middle of Shiqianfeng formation may have sealing effect too.For all these CO₂ reservoirs,the mudstonds or silty mudstones of the upper Liujiagou formation and Heshanggou formation are the caprocks for preventing CO₂ leakage.?3?Combined with CO₂ perforated intervals in injection well and three times VSP monitoring data,the lithology,porosity and permeability of reservoir flow units for CO₂ was predicted,also the historical CO₂ migration and saturation.Three times VSP were implemented to monitor the CO₂ migration underground in 2011 before CO₂ injection,2013 and 2014.The lithology,porosity and permeability of reservoir flow units for CO₂ were predicted using L1 profile?2011?,L2 – L4?2013?profiles and logging constrained seismic inversion method.Furthermore,using the L1 profiles?2011,2013 & 2014?and fluid displacement forward modeling method,the historical CO₂ migration and saturation were predicted.On the basis of drilling,logging,VSP and other experimental data,the time – depth relation and wave group characteristics of geology-seismic data are established by well seismic calibration;then petrophysical analysis was carried out,the pseudo acoustic curves were synthesized first to predict the lithology using logging constrained seismic inversion method.The porosity is predicted using synthesized pseudo acoustic curves,while the prediction of permeability is based on relation fitting of porosity and permeability.Generally,the sandstones are thick in Liujiagou formation interbedded with thin mudstones.As the depth increases,the content of argillaceous rock increases in the Shiqianfeng formation and Shihezi formation,especially the upper Shihezi formation.Majiagou formation mainly developed carbonate rocks.The porosity of sandstones in the bottom of Liujiagou formation,upper Shiqianfeng formation,middle and lower Shihezi formation are high relatively ranging from 9% – 15% generally,with 18% highest at local sandbodies.However,the permeability of the potential reservoirs is very low ranging from 10 – 20 mD.Historical CO₂ saturation in L1 VSP seismic profile was predicted using fluid displacement forward modeling method considering the difference of seismic wave velocity,the results show that the CO₂ migration and saturation of Liujiagou formation,Shiqianfeng formation & Shihezi formation increased significantly.Because of the smaller sandbodies in the southeast,CO₂ plume from injection well migrated further to the northwest,but the CO₂ saturation increased more significantly in the southeast of L1 profile.In addition,there is more CO₂ in Liujiagou formation because of the larger thickness of sandbodies,while CO₂ migrated further in Shihezi formation because of the average permeability in L1 profile.?4?The CO₂ – water relative permeability and capillary pressure of main saline aquifers are tested in condition of high pressure & temperature of reservoirs underground using undisturbed drilling cores and reprepared saline.The CO₂ – saline relative permeability and capillary pressure are key parameters for reservoir injectivity evaluation and numerical simulation of CO₂ migration.In this paper,using the underground water quality data of main saline aquifers,the author reprepared the similar saline of main aquifers.Then,selected the undisturbed drilling cores to carry out physical displacement experiment to test the curves of CO₂-water relative permeability and capillary pressure which could provide key parameters for numerical simulation of CO₂ migration.The results show that in the same capillary pressure,the water saturation of Shihezi cores are lowest,then the Liujiagou and Shiqianfeng cores,while the CO₂ – water relative permeability of Liujiagou cores are higher than Shiqianfeng and Shihezi.?5?The 3D geological model of Shenhua CCS Demonstration Project site was developed using by corner-point grid and Kriging interpolations methods.Compared with Sleipner Project in Norway,there is a great challenge for geological modeling of Shenhua CCS Demonstration Project because of different geology,geological survey and geophysical monitoring technologies.The author constructed the 3D geological model using PETREL software based on High resolution sequence stratigraphic correlation,time – lapse VSP seismic inversion data and predicted reservoir flow units.The region of the 3D geologicla model covers 5 km×5 km centered on the injection well,which is well – coincident with gelogy understanding and geophysical interpretation,especially the central 1 km×1 km based on the VSP data prediction with high reliablity.?6?Numerical simulation of CO₂ migration was carried out finally corrected by the time – lapse VSP monitoring data.The CO₂ migration and saturation in the saline aquifers involves the safety and risk of CO₂ geological storage project.Because of high cost of the time – lapse technology,small total amount of injected CO₂,long – term storage time and so on,numerical simulation method plays a key role in prediction of CO₂ migration and the stored form of CO₂ in reservoirs at different time scales.On the basis of 3D geological modeling,the model for simulation was optimized further which involves the curves of CO₂ – water relative permeability and capillary pressure,and the pressure,temperature and salt of main saline aquifers.Finally,CO₂ migration was numerical simulated using by ECLIPSE 300,and corrected by the time – lapse VSP and drilling monitoring data.The results of numerical simuation show that CO₂ mainly migrated to Northwest during injection and the CO₂ plume would not spread much more from November 2014 to May 2035.From the topview,CO₂ will migrate furthest in the upper Shiqianfeng Formation after 20 years with a radius of about 1000 m in the NW – SE and 750 m in the NE – SW.Liujiagou and Shiqianfeng Formation have stored more than 80% of total injected CO₂,and the CO₂ saturation droped quickly and will be lower than 55% after 20 years in Liujiagou Formation.During the CO₂ injection,bottom hole pressure changed with time during CO₂ injection coincidently,and will drop along with the CO₂ saturation.As time goes on,about a third of the total injected CO₂ will dissolve in the saline.Meanwhile,there are some innovations in this paper as follows:?1?Using the methods of high-resolution sequence stratigraphy and well logging constrained seismic inversion,the lithology,porosity and permeability of main formations are supplemented,and the reservoirs and caprocks for CO₂ geological storage are divided detailed too.This paper summed up a methodology of CO₂ reservoir flow unit prediction.?2?The CO₂ – water relative permeability and capillary pressure of main saline aquifers are tested for the first time in condition of high pressure & temperature of reservoirs underground using undisturbed drilling cores and reprepared saline.?3?Historical CO₂ saturation in L1 VSP seismic profile was predicted for the first time using fluid displacement forward modeling method considering the difference of seismic wave velocity.?4?A new and more appropriate 3D geological model was constructed to simulate the CO₂ migration characteristics which are concordant with the time – lapse VSP seismic and drilling monitoring data.