Ecrin v4.30 Update Notes

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Ecrin v4.30 Update Notes

Ecrin v4.30 is expected to be the last major Ecrin release under Generation 4, before the replacement of Ecrin by KAPPA Workstation. Ecrin v4.30 is above all a technical release, with major modeling additions such as the ‘wiggly well’ in all Ecrin numerical modules. This version also incorporates the necessary links to the Generation 5 products recently released, KAPPA Server (replacement for Diamant Master) and KAPPA VIZ (3D collaborative environment)

The Figure above describes the communication between Ecrin and the KAPPA Server thanks to the new KAPPA Client. Note that the Diamant module of Ecrin remains available in v4.30. These notes will provide the Ecrin v4.20 user with an exhaustive list of the additions/modifications in v4.30, and a quick reference to use them. The content found herein is also present in the on-line help. New Guided Sessions can be followed that cover some of the major additions. The first section of these notes describes ‘Analysis/Models’ additions benefiting to Saphir, Topaze, and Rubis. It is followed by sections on the modules themselves. Finally a last section covers some ‘Generic’ additions.

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1. Analysis / Models ‘Wiggly’ well (Saphir – Topaze –Rubis) This is actually the main addition in Ecrin v4.30: the ability to grid and model not only slanted wells, but wells with any arbitrary geometry. In Saphir, Topaze and Rubis, this enables us to: - Model slanted wells, let them be fully penetrating, partially penetrating the formation, or with multiple perforations - all this in single layer or multi-layer reservoirs - Model ‘true’ horizontal wells, i.e., wells not being constrained by the reservoir stratigraphy – a well may now intersect several layers - Model arbitrary trajectories, i.e. ‘wiggly’ wells For achieving the desired goal, we had to abandon the comfort of stratigraphic gridding, in which a well module is nicely embedded in a given layer. This modification, combined with the constraint of precise simulations at all time scales (from pressure transient analysis to history matching) using a ‘reasonable’ amount of grid cells, encouraged us to investigate a few options, the first two attempts being schematically represented below:

Octrees: successive Cartesian grid refinement. Very fast grid generation, but too many cells on large slants

Tetrahedra: using a third party library. Would work for all well shapes, but slow gridding process, ending up many cells, and too many of them with a very bad shape ratio.

Note that the two first attempts cited above did give correct simulations, in spite of the (quickly mentioned) issues they were bringing along. We finally could square the circle with a Voronoi solution, combined with the use of generalized transmissibility corrections (more on this below):

3D Voronoi This method, developed internally, consists in carefully defining a set of points around the wellbore. A purely 3D Voronoi grid is then generated using this set of points. Sub-grids are next generated for each layer with additional constraints on the horizons. The background grid is then merged with all the sub-grids to generate a final 3D grid that respects the horizons.

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This strategy has the advantage of being fast and results in a grid with a relatively limited number of cells; it is however not conformal to a pure 3D Voronoi grid anymore and therefore requires proper transmissibility corrections. We will come back to the generalized transmissibility corrections in a few pages, but let us insist at this stage that combining those corrections with this new gridding strategy enables us to account for x-y-z anisotropy in a seamless manner. How to create a slanted / wiggly well in Saphir – Topaze

In the 2DMap well dialog, you may either set the well as slanted by checking the corresponding box, or set the well as ‘wiggly’:

In the first case (slanted checkbox), the well will be turned into a fully penetrating slant being controlled by a unique additional parameter: the well deviation (note that the well can be turned into a limited entry by checking the corresponding box in the interface). The gridding and simulation will be conducted ‘as usual’, but the (projected) well trajectory will not be visible in the 2DMap (except for its influence on the resulting grid, of course):

Slanted well in Saphir – Topaze: the well is fully penetrating by default (right); the well trajectory is not visible in the 2D plot (left). You may remember that this first interface (slanted checkbox) already existed in Ecrin v4.20, but the well was then gridded vertically and a geometrical skin (computed analytically) was added to the simulation. This approximation has been completely replaced by the new gridding scheme.

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When the well is defined as ‘wiggly’, the different checkboxes are replaced by an Edit button leading to a Rubis like cross-section view of the well and of its perforations:

The well trajectory may be edited by adding / moving / deleting nodes with the mouse in the geometry view. Double-clicking on the trajectory leads to the following edition dialog:

In the above, the reference point is the (0,0) coordinates of the 2DMap for the X and Y axes, whereas the reference depth (z=0) is the reservoir top. The Load option allows importing a complete well trajectory from an ASCII file; in order to keep the Voronoi grid within a reasonable size the loaded trajectory is limited to 100 points, keeping in mind that more complex trajectories may be reduced with the Simplify option, as shown below:

In this example, the initial trajectory of 654 points is reduced to 15 control nodes, in both horizontal (left) and vertical (right) directions:

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In turn, the perforations may be added / deleted / modified in an edition display à la Rubis – note the table brought up (right) when the user double clicks on any perforation:

One important side consequence of this ability to load complex geometries is that, in some situations, the trajectory displayed in the 2DMap may not go through the well icon ( ) anymore, as displayed in the small example below:

Note also that you can edit and move the well nodes directly in the 2DMap view – keeping in mind that the nodes being displaced will keep the same depth after a displacement in the 2DMap. How to create a wiggly well in Rubis There is no distinction between the ‘simple’ slanted well and the ‘complex’ wiggly well in Rubis: all wells are defined as wiggly. Creating a wiggly well is possible in the 2DMap, through the icon. The editing of the trajectory and perforations is similar to what is available in Saphir / Topaze. Here again, you may remember that a ‘Deviated well’ checkbox was available in Rubis v4.20 in the vertical well geometry dialog: in this situation Rubis was gridding the well vertically and adding a geometrical skin (computed analytically) at run time. This option is rendered obsolete by the new gridding capabilities and has been removed.

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Some simulation examples This first set of simulations shows a comparison in Saphir between the analytical slanted well solution (test designs = markers in the plots below) and its numerical counterpart (displayed as lines) for a range of deviations:

Fully penetrating slanted well, 10° deviation, no vertical anisotropy. 3224 grid cells, 0.5% maximum deviation between analytical and numerical.

Fully penetrating slanted well, 25° deviation, no vertical anisotropy. 3098 grid cells, 0.3% maximum deviation.

Fully penetrating slanted well, 60° deviation, no vertical anisotropy. 3058 grid cells, 1.9% maximum deviation.

Fully penetrating slanted well, 85° deviation, no vertical anisotropy. 3961 grid cells, 1.2% maximum deviation.

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Fully penetrating slanted well, 85° deviation, kz/kr=0.05. 5057 grid cells, 2.5% maximum deviation.

The second example we will show is a Rubis diphasic (oil and gas) example with a ‘true’ horizontal well intersecting three layers, among which the thinner middle layer has a higher permeability; in this example a gas cap lies just above the perforated intervals:

Wiggly well in Rubis: initial geometry definition (left), and corresponding 3D grid (right) This particular case can be gridded with slightly less than 6,000 cells in Rubis, and simulated in a few minutes. Not surprisingly, the simulation shows gas coning taking place through the middle (more permeable) layer:

Initial saturation field:

Final saturation field (after 180 days of production):

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Oil and gas production logs – note the gas breakthrough towards the end of the middle perforation:

New (Faster!) time stepping for numerical models (Topaze – Rubis) In Ecrin v4.30, many changes have progressively been made in the numerical system and in the non-linear loop, in order to stabilize and speed-up simulations. Among the main changes, we may cite: (a) Numerical precision has been modified to better handle absent phases (e.g., water defined in the PVT but Sw=0). This improves convergence and speeds-up simulations with absent phases. (b) System variables - unknowns - have been reorganized. This improves each linear system resolution in a multiphase context. (c) In Rubis, the default value of the ‘time step growth ratio’ has been increased to 2 similarly to Topaze - in order to decrease the number of iterations per constraint step. (d) For a well constraint in steps, constraint values may now be relaxed when time steps drop below the input ‘minimum’ value. This intends to reduce the number of restarts at very small time steps for problematic cases. (e) Several internal thresholds regarding time step growth or restarts have been modified, further reducing the overall number of iterations per simulation. (f) In the past, well constraint gauges ‘in points’ were always implicitly treated as gauges ‘in steps’ in the numerical model. This has been modified and the eventual ‘in points’ nature of a gauge is now systematically honored, with very important consequences in terms of time stepping, as detailed below. (g) An option was introduced to force the numerical simulation stepping to follow the gauge stepping. In this case, the ‘time step growth ratio’ setting is completely ignored, and only the minimum number of time steps is performed. Among these modifications, points (f) and (g) have the most important consequences and will be detailed in this section. Let us consider a simple history with 3 constraint steps (either pressure or rate).

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In order to honor the ‘in steps’ nature of the constraint, time stepping in the numerical kernel is handled as follows: - At the beginning of each new constraint step, the time step is reduced to a small value (‘dt new’ in the figure below). This value is referred to as the ‘minimum time step’ in the interface of Ecrin. - After each converged simulation step, the duration of the next time step is increased, following the input ‘time step growth ratio’. Note that this growth is limited by the maximum allowed variations of pressure and saturations in the reservoir during a time step. - The end of the current constraint step is strictly honored. As a consequence, the simulation typically follows the path below:

Note that for each constraint step, many actual simulation steps may be required. Let us now consider a more complex history, where the well constraint is a pressure gauge in points. This gauge contains 172 points (with, in average, one point every 180hr):

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In Ecrin v4.20 any such constraint gauge ‘in points’ would actually be internally treated as a gauge ‘in steps’, each step being centered on the corresponding original point. Hence, the actual simulated history would be:

Since this history ‘in steps’ is simulated using the algorithm described above, many numerical time steps are required per constrain data. For this particular example, we ended up with 1709 numerical time steps, for a total simulation time of 16 seconds. In Ecrin v4.30, we implemented a new time stepping algorithm, in order to honor the ‘in points’ nature of the constraint gauges. In order to illustrate the new approach, let us consider a simple history with 13 constraint points (either pressure or rate):

The new algorithm proceeds as follows: - Only the first time step of the simulation is set to ‘dt new’ (input ‘minimum time step’). - The time step growth is driven by the input ‘time step growth ratio’. - This growth is limited by gauge points (that are actually simulated).

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This growth is also limited by the maximum allowed variations of pressure and saturations in the reservoir during a time step. Constraint values are linearly interpolated between two gauge points.

As a consequence, the simulation typically follows the path below:

We see that this algorithm requires much less time steps than the former ‘by steps’ approach, since we do not come back to the smallest time step duration after each constraint gauge point. Using this approach on the previous example (with the 172 points pressure gauge), we end up now with only 310 numerical time steps using Ecrin v4.30, for a simulation time of 8 seconds. This corresponds to an x2 acceleration compared to Ecrin v4.20. CPU improvements by a factor of 5 can easily be observed for larger gauges. Further CPU reduction can even be achieved, by using the new option ‘follow gauge’ in the run settings:

Topaze settings

Rubis settings

When this option is checked, the time step growth ratio is simply ignored and the simulator tries to go through gauge points only (provided numerical convergence is achieved). This further reduces the total number of simulated time steps when the gauge sampling is irregular.

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Finally, let us mention that in Rubis, this option can also be activated for ‘all gauges’. In this case, target gauges in steps will automatically be converted in points, and simulated using the faster approach previously described.

Parallel initialization (Saphir – Topaze – Rubis) In order to speed up gridding and initialization, several computationally intensive functions have been parallelized in the kernels. The number of processors available for distribution is automatically detected. Parallelized steps currently include: -

Construction of the 3D vertices from the 2D grid (during 3D Grid construction). In particular, this includes interpolation and discretization of horizons for complex multilayer geometries in Rubis. Initialization and construction of the 3D well ‘sub-grids’ (during 3D Grid construction). Here, the parallel distribution is based on the number of wells, but also on the number of fractures when multiple fractures horizontal wells are used. Derivation of the connections and transmissibilities (during model initialization phase). Numerical integrations for the generalized transmissibility corrections (see next section).

In addition to these ‘initialization’ functions, it is worth mentioning that during non-linear numerical iterations, calls to the PVT flash calculations have also been parallelized when the simulation context is compositional isothermal (more on this below).

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As an illustration of all this, the small sketch below indicates on a few examples the speedup (as a ratio, with Ecrin v4.20 as reference) that a user may now expect during the gridding and initialization steps – this speedup naturally depends on the number of available CPU cores:

Generalized transmissibility corrections (Saphir – Topaze – Rubis) This option is actually fulfilling two roles in Ecrin v4.30: (a) Its use in the slanted / wiggly well gridding scheme could allow us to obtain accurate models while keeping the number of cells (relatively) low. (b) In the particular case of fractures flowing in shales (let them be connected to a vertical well or to a multi-fractured horizontal well), the high transient pressure gradient in the immediate vicinity of the fracture(s) would drive our existing gridding algorithm to its limits. In essence, linear numerical simulations would show irreducible discrepancies with the corresponding analytical models. Those discrepancies are not huge by any means (< 3% in the most extreme situations), but they do exist. The introduction of generalized transmissibility corrections addresses those two issues. This computation is described at length in a paper we recently posted on KAPPA website [*], but we will attempt to summarize it in a few sentences: Let us consider two adjacent cells in a homogeneous reservoir:

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The flux between the two cells is classically written as a function of the pressure drop through the use of a constant transmissibility Tij:

Qij 

1





Tij Pi  Pj



Where Pi and Pj are the two average pressures in each cell. When the pressure field between the two cells is assumed to be linear, the problem can be solved relatively easily to obtain an expression of the transmissibility in terms of the reservoir permeability, the distance between the cell centers Lij, and the surface Fij. The problem is that this linearity assumption is proven wrong in the extreme cases mentioned above (very complex gridding scheme and/or extreme permeability situations). Then, we have no other means but to rely on some external ways to calculate the overall pressure field, in order to integrate it in space and obtain the desired Tij value:



Tij  k

 P  dS Fij

1 / vi   Pdv  1 / v j   Pdv Ci

Cj

We found that using an analytical pseudo-steady state solution based on Green’s function representation is, indeed, providing good calculation results. Here is for instance the analytical potential field calculated around a limited entry slanted well which can be used as a base for the computation of generalized transmissibilities in that case:

Of course, all this comes with a price: a CPU overhead which, even though it does not significantly impacts the overall simulation time, is noticeable enough not to use it systematically – read: even in (most) situations where it does not bring any additional added value. In Ecrin v4.30, the generalized transmissibility corrections are systematically used whenever a slanted / wiggly well is simulated. They are also available as an option as soon as a fractured well (or multi-fractured horizontal well) is being simulated.

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You may access this option at several locations depending on the module:

In the numerical settings (Settings button in the standard numerical dialog, or Run Settings button in NL dialog) in Saphir and Topaze:

In the Numerical Settings page of the Simulation – Run Settings dialog in Rubis:

[*] Transmissibility Corrections and Grid Control for Shale Gas Numerical Simulation, Vincent Artus & Dorian Fructus.

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Compositional isothermal (Saphir – Topaze – Rubis) As you may know, a compositional thermal model has been available in Rubis since the Ecrin v4.20 release. In addition to this full model, the fluid properties may now be defined as compositional isothermal by checking the ‘EOS (Peng-Robinson)’ option in the PVT definition interface:

This option is naturally available in Rubis, but also in NL analyses of Saphir and Topaze. When the EOS option is selected, clicking on the icon gives access to the fluid composition and properties, as illustrated in the following screenshots:

Allowing the compositional model to be constrained to isothermal has enabled us to parallelize the most CPU intensive part of the simulation – the flash calculations, ending up with compositional models significantly faster than in the complete EOS thermal case. When the PVT is compositional, the initial conditions may be expressed in several ways: the input of the fluid initial saturations, the fluid bubble point or dew point pressure, or the direct initial composition of the mixture. All combinations are possible in Ecrin:

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Note that when the ‘composition’ input is selected, the fluid initial composition is set to be the fluid composition defined in the PVT. When the input is set to saturation or saturation pressure, the sample fluid composition defined in the PVT dialog is modified in order to meet the desired condition. Note that this modification might not always be possible: if, for instance, the input saturation pressure is outside the convergence pressure envelope of the set of components, we have no other choice but to display an error message stating that the desired equilibrium condition could not be met. Explicit import / export of KEG files (Saphir – Topaze – Rubis) The KEG format stands for “KAPPA Export Grid”. It is an internal format containing the current 2DMap geometry (including well trajectories and faults/fractures paths), the Voronoi grid and eventual result fields in an XML + binary transcription. KEG files may be imported in Rubis (as an alternative to GRDECL in the ‘Init from Geomodeler’ option), in K-Viz, or in third party products. Any numerical model simulated in Saphir and Topaze can be exported as a KEG in the Export dialog; any model (simulated or not) built in Rubis may be exported as a KEG in the similar Rubis Export option. Analysis dropdown menu (Saphir – Topaze) A Saphir or Topaze document containing a large number of analyses (>10) induces a large number of tabs (one for each analysis), and switching analysis becomes difficult. To solve this practical issue, the Ecrin v4.30 analysis toolbar now contains a dropdown menu enabling the user to perform this operation more easily:

(Note that this addition was not required for Rubis, as switching from one run to the other was already performed via a dropdown menu). Miscellaneous  Leaky fault analytical solution (Saphir – Topaze): the leakage value can now be greater than 1.

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2. Saphir Minifrac analysis for Gas The minifrac analysis is now opened for gas tests, following the publication SPE100578 [*]. To be more precise, the minifrac option is available for gas if the two following conditions are met: (a) the reference extracted flow period is a fall-off; (b) the previous period is a water injection period. If those two conditions are met, the analysis can be conducted as for the oil case. [*] SPE100578: “Application of a New Fracture-Injection/Falloff Model Accounting for Propagating, Dilated, and Closing Hydraulic Fractures”, D.P. Craig, Halliburton, and T.A. Blasingame, Texas A&M U. Oval probe for formation test analysis In the ‘Tool infos’ dialog of the Formation Test analysis, it is possible to define the active probe as an oval probe. In that case the usual probe radius Rp describes the probe width; it is completed by the probe height named Hp:

The rest of the analysis can be conducted as for the radial probe case, with the noticeable exception that the multi-layer model option is disabled when an oval probe is used. This new probe geometry is naturally also available for the test design option – as an illustration you will find below the comparison of a series of test designs conducted on an oval probes with a range of probe heights varying from 1 inch (in which case the probe is radial) to 10 inches; the left-hand side plot shows the active probe response, whereas the right-hand side plot shows the simulated pressure response 10 ft away from the active probe:

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Use equivalent total bottomhole rate to simulate linear gas+water problems In Ecrin v4.20, it is possible to define a gas interpretation containing both gas and water productions, but the linear models (let them be analytical or numerical) are then disabled – clicking on Generate triggers the following message:

In other words, only diphasic nonlinear numerical models can be simulated in such a situation. This limitation is bypassed in Ecrin v4.30: linear models may be simulated in gas+water situations now that an equivalent total bottomhole rate is used as production history. This modeling is naturally an approximation and cannot replace the full diphasic nonlinear model, but simplifies the analysis workflow by inserting a first diagnostic step using simplified (and faster) models. Larger pressure gauge dropdown menu in the analysis toolbar The size of the pressure gauge dropdown menu has been increased in size, in order to present greater visibility when large gauge names are used: Ecrin v4.20: Ecrin v4.30: Modifications in the ‘Create rates from slug pressures’ option The ‘Create rates from slug pressures’ option in the Saphir Edit Rates tab now offers the following options: - A total cumulative production may be manually entered to constrain the rates reconstructed over the calculation interval. - A ‘Positive rates only’ flag is available; when checked the calculation will ensure that only positive rates are obtained, by setting zero rates during the injection intervals and by modifying the total rate history accordingly. - Fluid density and tubing I.D. are now stored in the document (and not reset to default between two consecutive calls as before).

Miscellaneous  Perrine: initialize kro to 1 and krw to 0 when there is no water production  Perrine option is renamed “Linear Multiphase Well Testing”  Radius of investigation and tested volumes are not output anymore when no model is present.

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3. Topaze Time dependent well intake This option has been implemented to primarily address the needs of production analysis in unconventional reservoirs, where time dependent completion is systematic. In Ecrin v4.30, a new ‘Time dependent’ checkbox is available in the well intake dialog:

When this option is checked, and when no prior well intake exists, the user is prompted to define the first well intake step, with the very same options and possible input choices. When this definition is completed (or when a prior well intake already exists), the following display shows up:

As can be seen above, the previously defined well intake is split into two (identical) steps which may be edited with the button; the start time of the second well intake step is defaulted to one month after the document reference date, and may naturally be modified as needed. Note that more than two well intake steps may be defined, and that deleting all well intakes (but one) gets you back to a unique well intake definition applied to the whole data duration (and to the usual interface).

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The example below illustrates a typical result obtained when this option is used – in this case, a well intake correction named ‘Casing’ has been applied until the beginning of May, 2009, then followed by another well intake step named ‘Tubing’. The plot superposes the uncorrected surface pressure gauge (in green) to the ‘Casing’ and ‘Tubing’ corrections applied over the whole time interval (orange and purple curves); finally the time dependent well intake correction using both models is displayed in black:

A few precisions to finish this quick description: -

As this option is not available in Saphir or Rubis, only the first well intake step will be copied by the drag & drop of a Topaze document or well intake to those modules. For the time being, the rate forecast option is limited to the input of sandface pressures when a time dependent well completion has been defined.

Maximum rate for analytical and linear numerical models In Ecrin v4.20 it was already possible to define a maximum flowing bottomhole rate in the q(p) simulations by setting its value in the 2DMap well dialog, as illustrated below:

This value was then only taken into account in NL numerical models. What is new is that in Ecrin v4.30 this maximum rate is honored in all situations: all numerical models - including the linear ones, and all analytical models – in which case a full mixed p(q) + q(p) superposition is performed in the model (we do not just truncate the simulated rates, in other words).

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Linear flow plot for oil The linear flow plot is now available when the analysis reference phase is oil – it used to be restricted to gas in Topaze v4.20. Note as well the addition of the line slope in the results. This extension was mostly made for the analysis of shale oil production data. Arps power law loss ratio (Ilk) for oil For the very same reason (shale oil), the power law loss ratio option of the Arps plot (added for gas interpretations in Topaze 4.20) has been extended to oil cases. As a side effect, this option has been renamed from ‘Use tight gas/shale gas decline (Ilk)’ to ‘Power law loss ratio (Ilk)’ in the plot right-hand side menu. Allow the control of reference rate in loglog and Blasingame plots A reference rate has always been used in Topaze in order to obtain loglog and Blasingame plots with a pressure scale (instead of p/q) on the Y scale. As you may know, this reference rate was a constant hidden value fixed at 0.001 m 3/sec (or 543.44 STB/D). This value can now be accessed and modified through the option ‘Reference Rate…’ in the loglog and Blasingame plots menus:

Productivity index plot As a special client request, a Productivity Index plot was added to Topaze – it displays the following quantity:

Where q(t) is the imposed or simulated well rate (imposed in case of p(q) model, simulated otherwise), pwf(t) the imposed or simulated bottomhole pressure, and p average(t) the simulated reservoir average pressure. This result is available in all Topaze analyses, as soon as a model with a simulated paverage is available. In theory, PI should converge towards a constant when the reservoir undergoes pseudo-steady state flow. The objective of the additional plot is to check that it is the case, and therefore to detect potential deviations caused by the model. This is limited to a very specific situation of long time declines inverted from Laplace space. Display model as points in the loglog and Blasingame plots As a (small) side effect of the current KURC developments, we introduced (in the plot toolbar and the plot menu) the possibility to use points rather than lines for the model display in the loglog and Blasingame plots – with the only intent to reduce the background noise caused by the material balance time – see next.

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Convert step rates to points in extraction dialog The possibility to temporarily convert the rate gauges loaded as steps to point gauges has been introduced in the extraction dialog, as can be seen below:

Conversely, this option allows treating as steps a rate gauge loaded as points in Topaze (by unchecking the corresponding flag in the extraction dialog). Its whole point is to check and remove potential early-time discrepancies induced by an over-sampling of the rate gauge when defined as steps or as points, which may induce distortion on the semilog derivative in some specific situations.

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4. Rubis Gauge control switch When the user defines a target supported by a rate or pressure gauge, it is now possible to determine the time at which the target will be active, hence allowing the switch from one gauge to the other during a simulation as shown by the example below:

In the above, time input has to be greater than or equal to the gauge starting date. Copy-paste of well controls The Controls dialog contains an option allowing the copy of controls from one well to the other – all gauges used as targets also being copied. The option to copy all controls (and the controls only) is also available upon the copy-paste of a well in the Rubis browser:

Voidage replacement controls Two new controls called ‘Voidage (W)’ and ‘Voidage (G)’ are available for injectors:

In each case, the control is such that Rubis will inject the required amount of gas or water to keep the well bottomhole pressure constant. Below an example in which a gas injector greatly increases its injection rate after 4000 hrs – just when a nearby producer is set active (note the little kink on the producer downhole rate: the production decreases until it feels the injector interferences):

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Gas injector with voidage replacement control

Nearby producer New controls for network option: pressure targets at groups, conditional constraints Simulation controls can be input at the level of (surface) groups linking several wells in the Network option released since Ecrin v4.20. What is new is that it is possible now to input a (surface) pressure target in addition to the different rate targets. Conditional constraints have also been made available:

Aquifer water volume included in initialization results

When a numerical aquifer is connected to the contour, the different volumes of fluid initially present in the aquifer are provided in results at the end of the initialization phase:

Note that if the initial state is such that the aquifer extends above the water level, hydrocarbons eventually trapped in the aquifer will also be provided.

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Dataset edition: allow point selection in plot In the Dataset edition dialog the user may select points in the right-hand side mini-2DMap in order to highlight them in the left-hand side table – the selected points are displayed in white:

Selecting the points in the table will symmetrically highlight them in the 2DMap. Gas condensate initial state: define under-saturated gas caps Even though this new option is also available when the PVT is defined as saturated oil, its main interest lies in the condensate gas case… You may (or may not) know that the main limitation of gas condensate simulations in Rubis was related to the initial state definition. Because of the input parameters (gas-oil contact plus, eventually, a set of dew-point pressures at a given depth), Rubis v4.20 would always initialize the reservoir on the dew-point locus, with always the same characteristics: (a) an oil phase with a constant composition (and a constant bubble point pressure) below the GOC, (b) a gas phase with a dew point pressure equal to the gas pressure above the GOC. Put it another way: the gas-cap would always be saturated, and the Rubis simulation could only start from the points A or C in the diagram below:

This limitation is overcome in Rubis v4.30 now that we have the possibility to directly input a dew-point pressure at the reservoir reference depth, as illustrated below:

Ecrin v4.30 - Doc v4.30.01 © KAPPA 1988-2013

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In the example shown above, the reservoir initial pressure is 1000 psia greater than the dew point pressure; in other words, we are 1000 psia above point A in the P-T diagram displayed in the previous page. And the reservoir pressure can be lowered by this 1000 psia amount before the first drop of oil appears. In fact the ability to define the initial state without the direct input of a gas-oil contact is also available for the saturated oil case (where the GOC input may be replaced by a bubble point pressure or a composition) and for compositional models (where the GOC may be replaced by a bubble point pressure, a composition or a dew point pressure). This alternate initialization procedure brings more degrees of freedom, as illustrated in the small examples below (note that those examples apply to compositional, condensate and saturated oil PVT definitions):

Initial state definition with a GOC and an initial pressure (Pi) at the reference depth In that case the saturation pressure is constant below the GOC, and follows the oil initial pressure above it; hence the gas cap is always saturated.

Ecrin v4.30 - Doc v4.30.01 © KAPPA 1988-2013

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Initial state definition with an initial pressure (P i) at the reference depth, and the input of a bubble point pressure (Pbi) It is implicitly assumed that the reference depth lies in the oil zone. The whole saturation pressure profile is shifted so that it is in agreement with the Pbi input; the GOC contact (if it exists in the reservoir) is the point where Pbi meets the initial oil pressure profile.

Initial state definition with an initial pressure (P i) at the reference depth, and the input of a dew point pressure (Pdi) It is implicitly assumed that the reference depth lies in the gas zone. Hence the saturation pressure is now equivalent to a dew point pressure; it remains constant with depth until it intersects the initial gas pressure profile. The zone above this intersection point corresponds to the saturated gas zone.

Multiple vertical fractures in multilayer reservoirs When the reservoir geometry contains more than one layer, the presence or absence of the fracture may be defined layer by layer for a (vertical) fractured well, hence allowing Rubis to simulate a vertical well intersecting several vertical fractures.

To do so, a fractured well must be created first, and the user must edit the cross-section view of the well geometry dialog, as shown opposite:

Ecrin v4.30 - Doc v4.30.01 © KAPPA 1988-2013

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Once the fracture has been selected in the view ( + click on fracture), a double-click on the fracture plane brings up the following dialog:

Checking the ‘Multiple fracture’ box in this dialog allows specifying whether the fracture is absent or present in each intersecting layer:

Note that in that case the fracture must fully be present or absent in each layer, as opposed to a limited entry fracture when the multiple fractures option is not checked. You will therefore typically end-up with the type of display shown opposite:

It is worth mentioning that the fracture ½ length remains constant (throughout all layers) in this geometry, and that the fracture hydraulic properties (e.g., finite conductivity, etc…) are also uniquely defined. Miscellaneous  Output fields: Psat (saturation pressure) is now available as an output for saturated oil and gas condensate cases.  Target selection for injectors: the oil phase (saturated oil, dead oil, or condensate problems) cannot be injected anymore. Hence the choice of the phase being injected is limited to gas and water.

Ecrin v4.30 - Doc v4.30.01 © KAPPA 1988-2013

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5. Generic Maximum RAM extended to 4 GB Even though this modification is also available in Ecrin v4.20 (≥.07), it is worth recalling that the maximum RAM that may be allocated to Ecrin v4.30 has now been extended from 2 GB to 4 GB. This is available on 64bit OS.

OpenServer: add comments and flag valid analyses in the XML output Since Ecrin v4.20, the main results stored in a Saphir / Topaze / Rubis document are concatenated at the end of the binary file in a specific ASCII format (XML). As a consequence those results are freely accessible if one opens a saved Ecrin document with, for instance, a text processor – see next Figure. This XML block is also used in the OpenServer interface of the KAPPA Server v5.0. In Ecrin v4.30, comments added to the Ecrin document are inserted, as well as the ‘valid’ flag which may be assigned to any Saphir / Topaze analysis, or to any Rubis run:

Modified oil compressibility calculation for saturated oil The oil compressibility calculation for saturated oil now sticks to Martin’s equation [*], and is defined as follows:

[*] Petroleum Reservoir Fluid Property Correlations, William D. McCain, Jr., John S.Spivey, Christopher P.Lenn, p.66 (PennWell editions). [End of Document]