Seismic Attributes used for Reservoir Simulation: Application to a Heavy Oil Reservoir in Canada

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1 Seismic Attriutes used for Reservoir Simultion: Appliction to Hevy Oil Reservoir in Cnd Crmen Dumitrescu* Sensor Geophysicl Ltd, Clgry, AB nd Lrry Lines University of Clgry, Clgry, AB, Cnd Summry Cold hevy oil production with snd hs ecome one of the min non-therml schemes for developing hevy oil reservoirs in Cnd. One chllenge in modeling the fluid flow in the reservoir simultion studies is reservoir heterogeneity. Severl seismic ttriutes were used to estimte the porosity (rnging from % to %) t the Plover Lke oil snds reservoir in Cnd. First, the top nd the se of the reservoir were mpped sed on severl seismic ttriute volumes tht include the density. From petrophysicl nlysis we lerned tht density is key physicl property in differentiting etween snd nd shle within the oil snds. Proilistic neurl network (PNN) nlysis ws used to derive the reltionship etween density log dt nd externl ttriutes (PP nd PS migrted stcks, AVO ttriutes nd inversion results). Secondly, we used geosttistics to estimte porosity mp within the reservoir. The study is sed on set of porosity logs t well loctions nd severl seismic ttriute mps. Kriging, cokriging, kriging with externl drift (KED) nd multittriute nlysis for mps plus KED, were tested in order to improve the results. The KED with porosity from multittriute nlysis is the most relistic, honoring the wells nd the seismic. Introduction The Plover Lke oil snds project, conducted y Nexen Inc., is locted in Ssktchewn, Cnd. Oil snds of the Devonin-Mississippin Bkken Formtion re found in NE-SW trending shelf-snd tidl ridges tht cn e up to 30 m thick, 5 km wide nd 50 km long. Overlying Upper Bkken shles re preferentilly preserved etween snd ridges. The Bkken Formtion is discomformly overlin y Lodgepole Formtion crontes (Mississippin) nd/or clstics of the Lower Cretceous Mnnville Group (Mgeu et l., 2001). The 3D-3C seismic dtset ws cquired y Verits DGC using the VectorSeis digitl multicomponent recording system over n 8 squre kilometer surfce re. On the project, out of 100 logged wells, only 29 hd sonic, density, porosity nd GR logs. The migrted structure stcks 508

2 for the PP (verticl) nd for the PS (rdil) component were produced y Sensor Geophysicl Ltd. s prt of CHORUS (Consortium for Hevy Oil Reserch y University Scientists) project t the University of Clgry. To chieve n optiml estimtion of density, pre- nd post-stck seismic ttriutes (PP nd PS stcks, AVO ttriutes nd inversion results) were used in the proilistic neurl network (PNN) nlysis. The estimted density volume ws used for mpping the top (Upper/Mid Bkken) nd the se (Lower Bkken) of the hevy oil reservoir t Plover Lke. Figure 1: Mp showing the Plover Lke re, Ssktchewn, Cnd. Once we hd the top nd the se of the reservoir, we mpped porosity within the reservoir using severl geosttisticl methods such s kriging, cokriging, kriging with externl drift (KED) nd multittriute nlysis tht were compred in terms of ccurcy. The estimted porosity mp will e used in susequent effort, for reservoir simultion t Plover Lke. Method Prt A: Mpping the top nd the se of the reservoir From petrophysicl nlysis, we lerned tht density is key physicl property in differentiting etween snd nd shle within the oil snds. Therefore, hving density volume ville over the Bkken Formtion would e very useful for mpping the top nd the se of the reservoir. PNN nlysis ws used to derive the reltionship etween ttriutes of the seismic dt nd density log dt. The PNN nlysis used s input the PP nd PS stcks, the AVO ttriutes nd the inversion results, discussed in previous ppers y Dumitrescu et l. (2006 nd 2007). PNN nlysis, hs four steps: (i) perform multittriute step-wise liner regression nd its vlidtion, (ii) trin neurl networks to estlish the nonliner reltionships etween seismic ttriutes nd reservoir properties t well loctions, (iii) pply trined neurl networks to the 3-D seismic dt volume, (iv) vlidte results on wells withheld from trining. Prt B: Mpping Porosity The dvntge of using geosttistics is tht we cn oth honor the primry dt vlues t the well loctions s well s honor the spirit of the dense dtset wy from the wells. In this project, we tested three different wys of ringing in secondry dtset: (i) cokriging, (ii) KED, nd (iii) multittriute nlysis for mps plus KED. The multittriute nlysis involves comining multiple mp ttriutes to predict reservoir prmeter such s porosity, y trining t the well loctions. 509

3 This method is n extension of the multittriute pproch pplied to seismic volumes (Hmpson et l., 2001). Results Prt A: Mpping the top nd the se of the reservoir Neurl network nlysis used s trget log the density from 22 wells nd s externl ttriutes seven seismic volumes: P-wve reflectivity, S-wve reflectivity, the Fluid Fctor, the PP nd PS stcks, P-wve impednce nd S-wve impednce. Figure 2 (left) presents cross-plot of Density nd Gmm Ry logs (colored y porosity) with zones defining snd nd shle within the reservoir nd t ll 22 wells. The sme zones re identified on the cross-plot of the ctul nd predicted density logs (Figure 2, right). Gmm Ry (pi) 200 Predicted density (kg/m3) Cross-correltion=96% shle shle snd snd Density (kg/m3) 2000 Actul density (kg/m3) Figure 2: (left) Cross-plot of the Gmm Ry nd Density logs (colored y porosity) nd (right) Cross-plot of the ctul density nd predicted density logs using PNN. A perfect prediction corresponds to the red digonl line. Dt points from the nlysis zone of ll 22 wells. The cross-correltion etween ctul nd predicted logs is 94% showing good prediction of the density log in the Bkken reservoir t Plover Lke. Some oservtions out this reservoir re: (i) from petrophysicl nlysis we know tht density is key physicl property; (ii) the top of the reservoir is Upper Bkken tht is lmost identicl with Mid Bkken in mny wells, (iii) the se of the reservoir is Lower Bkken, (iv) synthetics for severl wells disply the Upper/Mid Bkken s trough nd Lower Bkken s pek, oth very difficult to identify on the migrted stck (Figure 3), nd (v) density volume proves to e quite useful in mpping the top nd the se of the reservoir (Figure 3). 510

4 W MB LB T Density (kg/m3) W MB LB T 2100 Figure 3: () Rp nd inserted synthetic trces for severl wells nd () density results on EW line 37 of the 3D. Inserted in color re the density logs. All the wells tie this line within 60 m projection distnce. (W: Wsec, MB: Mid Bkken, LB: Lower Bkken, T: Torquy). Prt B: Mpping Porosity In this pper, we integrted the wireline logs nd seismic dt to directly predict porosity mp within the hevy oil reservoir. First, we produced porosity mps using kriging (sed only on wells informtion), cokriging (sed on wells s primry vrile nd P-impednce slice s the secondry vrile) (Figure 4) nd KED (Figure 5). Next, we improved the initil fit using multiple ttriutes. The multittriute nlysis result hs produced good prediction of porosity. However, it does not tie ll the wells. Finlly, we used the multittriute nlysis derived porosity mp s secondry vrile for KED (Figure 5). Figure 4: Porosity mps sed on: () kriging nd () cokriging method. 511

5 Figure 5: Porosity mp showing the result of using: () KED nd () KED with porosity from multittriute nlysis result s the secondry vrile. In lrger study, depth converted porosity mps will e trnsferred into the erth model frmework used for reservoir simultion. Conclusions The density volume computed with neurl network nlysis hs een used successfully in mpping the top nd the se of the hevy oil reservoir over the Plover Lke Project re. Those horizons re very difficult picks on the migrted stck. Severl geosttisticl pproches were used for mpping porosity within the reservoir. Porosity mps sed on kriging, cokriging nd KED ll honor the porosity vlues t the wells. We comined multiple mps in multittriute nlysis to get etter prediction of porosity nd then performed second pss of KED, using this porosity mp s secondry ttriute. The new porosity mp is more relistic, honored the seismic dt nd tied the wells. Acknowledgements We cknowledge nd thnk: CHORUS, Nexen Inc. nd Sensor Geophysicl Ltd. References Dumitrescu, C.C., nd Lines, L., 2006, Hevy Oil Reservoir Chrcteriztion using Vp/Vs Rtios nd Spectrl Decomposition; Technicl Astrcts of the SEG Annul Meeting, Dumitrescu, C.C., nd Lines, L., 2007, Hevy Oil Reservoir Chrcteriztion using Vp/Vs Rtios from Multicomponent Dt; EAGE Conference, London Hmpson, D., Schuelke, J., nd Quirein, J.A., 2001, Use of multittriute trnsforms to predict log properties from seismic dt: Geophysics, 66, Mgeu, K.R., Leckie, D., nd Mguire, R., 2001, The Bkken formtion of West Centrl Ssktchewn nd est centrl Alert: A depositionl history, strtigrphy, nd fcies distriution of Bkken shelf snd ridges using the Cctus Lke Field s working model: CSPG Annul Meeting, Clgry, Alert 512