Recent studies have revealed a strong correlation between the directionality of reservoir flow in waterfloods and the local orientation of horizontal earth stresses. Field applications are described of a novel technique of determining interaction between wells as an indicator of flow directionality. This technique calculates the Spearman rank correlation coefficient between flow rates at pairs of wells. These applications have demonstrated that the reservoir dynamics associated with correlated rate fluctuations have at least some component coupled to geomechanics. Coupled geomechanical-fluid flow numerical modelling is able to explain some of the observations and so offers an improved predictive tool for planning and managing waterfloods and determining optimal locations for infill wells. Introduction One of the most important parameters in designing the pattern of wells for waterflooding a reservoir is the directionality in horizontal flow; i.e. any preferred lateral direction for fluid flow across the reservoir. Recent studies have revealed a strong correlation between the directionality of reservoir fluid flow and the local orientation of modern-day maximum horizontal principal earth stress (Shmax). Even more surprisingly, this correlation holds equally well for the set of reservoirs which would not normally be described as "naturally fractured" as it does for those that obviously do contain open, conductive natural fractures. It has been conjectured that this correlation is explained by coupled processes in which the conductivities of natural fractures and faults (of which, generally speaking, there is a large population even in "unfractured" reservoirs) are altered by the geomechanical changes induced by the flooding process. According to the concepts of the metastability and self-organized criticality of the lithosphere, perturbation by even minor stress changes is likely. This conjecture was given credence by coupled numerical modelling of the geomechanical, fluid flow and heat flow processes involved in waterflooding; generic modelling of the progress of a flood front around a single injector well gave rise to similar patterns of directionality as observed in the aggregated field data. Coupled modelling therefore provides a potential new tool for improved design of waterfloods and infill drilling projects this will be further demonstrated later in this paper. Directionality The field data which allowed identification of directionality in the correlations with stress derived mainly from tracers, interference or pulse testing, or oil production response to start of nearby water injection. Communication through the reservoir has long been assessed by the strength of the response of oil production to start-up of water injection. However, in a complex schedule of well start-ups, it is often difficult to make unambiguous association between producers and injectors by this means. The technique to be described provides a more rigorous extension of this concept. Rank correlation of rates The basic technique of seeking correlation between well rates to indicate communication in the reservoir has been applied successfully in oilfields of the Former Soviet Union countries for some time.

Résumé -Géomécanique en simulation de réservoir : méthodologies de couplage et étude d'un cas de terrain -Cette publication traite de la modélisation des effets géomécaniques induits par l'exploitation des réservoirs et de leur influence sur les écoulements de fluide dans les réservoirs. Ces effets géomécaniques peuvent être relativement conséquents dans le cas des réservoirs faiblement consolidés et des réservoirs fracturés. Les principaux mécanismes couplés intervenant lors de la production de ces réservoirs, ainsi que les méthodes permettant de les modéliser, sont présentés. Le comportement géomécanique d'un cas réel est ensuite étudié. Un simulateur couplé -ATH2VIS -est utilisé afin de quantifier les effets géomécaniques induits par l'exploitation d'un réservoir carbonaté fortement hétérogène et compartimenté. Ce simulateur met en oeuvre un couplage explicite et gère les échanges de données entre le simulateur de réservoir ATHOS TM développé à l'IFP et le simulateur de géomécanique VISAGE TM (VIPS Ltd. 2001). Le résultat des simulations couplées indique que la modification de l'équilibre mécanique du milieu se traduit par une localisation de la déformation sur certaines failles en fonction de leur orientation et des variations de pression et de température dans leur voisinage. Il est également observé que seule une partie de la faille atteint le seuil de déformation plastique. Au cours de l'analyse couplée, le tenseur de déformation plastique sur les plans de faille est traduit en variation de la transmissibilité de la faille afin d'améliorer la représentation des écoulements dans le réservoir et de faciliter le calage des historiques de production. Abstract -Geomechanics in Reservoir Simulation

The trap door problem is a useful model for providing a clearer understanding of the stress distribution around civil engineering structures such as anchor plates and tunnels. The passive mode can be used either to compute the uplift force of anchors or any buried structure which may be idealized as an anchor; the active mode can be used to compute the gravitational flow of a granular material between vertical walls or the soil reaction curve for tunnel design. Both modes of displacement are modelled numerically in this Paper using the finite element method. The results are presented in the form of influence charts, which may be used for both the passive and active modes to provide failure loads for a range of geometries and soil properties, using non-dimensional&d parameters. The use of these equations is compared with results obtained from other sources using both physical and numerical models. KEYWORDS: anchor design; finite element analysis; trap door problem; tonne1 design further details, see p. ii.

Empirical field data show a strong correlation between the preferred directionality in many normal IOR floods and the local modern-day state of earth stress. The conjecture that this correlation is due to the activation of natural fractures by changes in the stress state induced by the flood has been tested with coupled modelling of fluid flow and geomechanical deformaton. The results of initial generic modelling incoroporating thermal stresses from cold water injection showed good agreement with the details of the field data, lending strong support to the conjecture. The modelling indicated that directionality trends increasingly towards the major horizontal stress axis as a flood progresses. The new coupled modelling capability provides an improved tool for planning well patterns, infill drilling and flood management.

Dr. NC Koutsabeloulis and Dr. SA Hope, V. I.P.S. (Vector International Processing Systems) Ltd. C0rM9ht 199S. SadOfy of Pdmfmm Enginows, fnc, This pqmr w pfqmrmd fw pfotentdion qt SP&lSRM Eurca+t'9Ehdd In Tr.mdlwhn, Norway, S-10 Juty 199S. This paper was sektod for prcsenfatkm by qn SPE Progr8m Ccmmittaa fatiowing mfiaw of WOrrnalbn Contnfnad h all dldraa mimlitwd~rho WthOr(s). COntonts of Itw Papsr, qs od,fuwl-bunmv!-ved by ttw Sodoty of Pdrdaum Engln..rs and qm wb@ct to cemctkm by ttu q ,ihqs). Tha mdorkf, qs pmsented$ does not n-s-dtv -any -M cd ffw Cicel.ty of Pdmfemn Engineaa, fts oftkcrs, or memlwm. Pmpas pre-md d WE mntings arc sut$sct to @lkxficm reviw by Edftodd Cunmfttoos of ttw Society of Patmtaum Engin..r8. Efoctmnlc rqxcwktion, dlstributbm, or domga of any patt of this papar W ccmmwcial purpascs wilfwul tfw !wfffw m$mt of ttw .5cmdy of Petrdwm Engineeri h p+'chbited. Pannkdcm to ropmduca h pflnt It mstrfdad 10 q abstract of not mom Ifmn S00 b~~fti~nuy not b med. Tfw Sbstract must Cemtarn conspicuous Ickmmktgment of whcro and by w (ha pspar was P+ason!ad, Writ. Librarhn, SPE, PO. SOx 833S36. WefwdsOn, TX 750s3a36 . Ws,h, fax of-iT7z.9s2.04ss. AbstractBoth the mechanical and hydraulic behavior of black oil resemmh is dominated simultaneously by the properties of tie 'intad' rti md the discontinuities within such masses. When inter-connected, these discontinuitiw define individual blcdcs that may become unstable, when subjected to pressure and/or thermal gradients. Studies involving coupled stress, thermal and flow modeling, in reservoir enghmring, using both mechanical and hydraulic proprties for the rcxk fabric and incorporating the stress magnitude and its directiomdity, have demonstrated the ccmept that preferred directionality during waterfhoding is stress related and progressive in time. 2-D and 3-D field applications WMrate that r6wmwirs are both 'reactive' and dynamic in nature and substantial changes to both the hydraulic and mechanical constitutive behavior are taking place during waterflooding operations. April 1990.