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Petrel 2012.1 Hydraulic Fracturing Modeling

Contents Table of Figures ............................................................................................................................................. 2

Acronyms ...................................................................................................................................................... 2

1. Introduction .......................................................................................................................................... 3

2. Correlation Technique .......................................................................................................................... 3

3. Tartan Gridding Technique ................................................................................................................... 6

4. LGR Technique ...................................................................................................................................... 7

4.1 GSG format export ........................................................................................................................ 8

4.2 GRDECL format .............................................................................................................................. 9

5 Convergence Issues ............................................................................................................................. 12

6 Recommendations .............................................................................................................................. 14

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Table of Figures Figure 1) the settings for the Hydraulic Fracture event\Fracture properties ............................................... 3

Figure 2) the settings for "global completions | Hydraulic Fracture" or “Hydraulic Fracture" event to

Customize for a specific event ...................................................................................................................... 4

Figure 3) SCHEDULE section and at the event time ...................................................................................... 5

Figure 4) Make local grids for the HFs .......................................................................................................... 7

Figure 5) Dropping LGR set in DSC ................................................................................................................ 8

Figure 6) Advanced grid export type selection ............................................................................................. 8

Figure 7) SCHEDULE section exported keywords for GSG format ................................................................ 9

Figure 8) GRID section of exported deck for GRDECL grid type .................................................................. 10

Figure 9) SCHEDULE section exported keywords for GRDECL format ........................................................ 11

Figure 10) Results are the same for different formats and also the performance ..................................... 11

Figure 11) LGRLOCK is automatically added by Petrel to the SCHEDULE section for Eclipse100 cases ..... 12

Figure 12) The performance issue due to LGRLOCK ................................................................................... 13

Figure 13) The effect of managing LGRs by LGRON and LGROFF keywords ............................................... 13

Acronyms DFS: Define simulation case

HF: Hydraulic Fracture

PI: Productivity Index

LGR: Local Grid Refinement

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1. Introduction There are different approaches for Hydraulic Fracturing modeling in Petrel 2012.1. This document is to

discuss each technique and the expected Eclipse keywords which Petrel exports to the data deck; then it

should ease the process of quality checking of the HF modeling. There are also some recommendations

to enhance the performance of the simulation run.

2. Correlation Technique In order to apply correlation technique, the Use correlation in the settings for the Hydraulic

Fracture\Fracture properties should be toggled on (Figure 1). In this technique rather than modeling

fractures explicitly, based on a Schlumberger correlation, Petrel calculates the transmissibility

modification of the grid blocks and a multiplier for well productivity index. The methodology of

obtaining the correlation and the original form of the correlation are available in InTouch

Documentation #4570027.

These transmissibility modifications and the well PI multiplier would be applied to the model at

the hydraulic fracturing event time in SCHEDULE section and depending on the settings for "global

completions | Hydraulic Fracture" it can be shifted to Previous report date, Next report date or just the

same specified event date (Figure 2).

Figure 1) the settings for the Hydraulic Fracture event\Fracture properties

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Figure 2) the settings for "global completions | Hydraulic Fracture" or “Hydraulic Fracture" event to Customize for a specific event

To observe the effect of HF definition in simulation data deck, the well with HF should be used in a

Development strategy and then this Development strategy should be added to a Define simulation

case and the case should be exported. In SCHEDULE section and at the event time (or at the previous

report or next report) there are WPIMULT, BOX, MULTX, MULTY, MULTZ and ENDBOX keywords (Figure

3). Regarding the range of the cells in the BOX keywords, refer to InTouch Solution # 4924790.

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Figure 3) SCHEDULE section and at the event time

As Eclipse Technical Description manual 2012.1 (page 1295)explains: ECLIPSE 300 provides an additional

formula to calculate the connection factor for cases where a vertical fracture penetrates the full width

of the cell in the x- or y- direction. Thus, for Eclipse 300 and the horizontal wells, one might try to

provide the Skin factor and modify COMPDAT (item 13), to use FX and FY rather than X and Y

penetration direction. If FX or FY is specified, the keyword FWELLS and HWELLS must be included in the

RUNSPEC section.

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3. Tartan Gridding Technique For description of this technique refer to InTouch Solution # 5390812. This technique is applicable to

single well modeling in which HF happens at the start of simulation. Therefore, as described in the

InTouch one can define Perm/Porosity of the fractures at the GRID section.

If HF does not happen at the start of simulation time which this is the implicit assumption of the InTouch

Solution # 5390812 then basically the model should have the effect of the applied HF in SCHEDULE

section. In Eclipse defining PERM in SCHEDULE section is not possible and the user has to define MULTX,

MULTY or MULTZ. The calculation of these parameters is not straightforward. A possible workflow

would be

Define Perm in a pilot project for the HF fractures

Export the model

Extract MULTX, MULTY and MULTZ

Then by keyword editor, in the HF event time, user can add the MULTX, MULTY, and MULTZ

Repeat the steps for every HF event

It is a tedious workflow and I do not recommend it.

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4. LGR Technique In order to define HF with LGR, one should remove the tick of Use Correlation in the settings for the

Hydraulic Fracture event\Fracture properties (shown in Figure 1)

Then open Make local grids and drop the well with HF event in and specify the required parameters or

just leave them as default (Figure 4).

Figure 4) Make local grids for the HFs

Then drop the created Local grid refinement set into the Grid tab of Define simulation case (Figure 5).

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Figure 5) Dropping LGR set in DSC

4.1 GSG format export

Figure 6) Advanced grid export type selection

If the Advanced grid export type would be the default (.GSG format) as Figure 6, then by clicking Export,

Petrel will export the following relevant keyword:

RUNSPEC Section:

PETOPTS -- Generated : Petrel

INITNNC LGRSIMGD / LGRSIMGD: to inform the simulator about LGR

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GRID Section:

PETGRID -- Generated : Petrel

'HF_LGR.GSG' /

So basically the LGR definition is embedded into .GSG file and user will not be able to observe the details

such as CARFIN keywords anymore.

SCHEDULE section:

At the time of HF event (it is 30 Jun 2012 in this example) for SCHEDULE section, there are COMPDATL,

WPIMULTL keywords for modifying the completion parameters. As many as the HF event sets, at this

particular time, there are BOX, MULTX, MULTY, MULTZ, and ENDBOX keywords (Figure 7).

Figure 7) SCHEDULE section exported keywords for GSG format

4.2 GRDECL format

If the Advanced grid export type would be the GRDECL format, then by clicking Export, Petrel will

export the following relevant keyword which is somehow different from GSG format (Figure 8) but

they are basically definition of the same object with different approaches.

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GRID Section:

There are some CARFIN and ENDFIN keywords to define LGRs, but the fracture properties would be later

on defined in SCHEDULE section.

Figure 8) GRID section of exported deck for GRDECL grid type

SCHEDULE section:

Figure 9 shows the keywords which are exported in SCHEDULE section.

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Figure 9) SCHEDULE section exported keywords for GRDECL format

The results are the same for different formats and also the performance (Figure 10).

Figure 10) Results are the same for different formats and also the performance

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5 Convergence Issues Eclipse 100 only: If the simulation case is Eclipse Black oil, Petrel exports LGRLOCK at the beginning of

SCHEDULE section which sometimes has a serious effect on the performance which is absolutely case

dependent. So I recommend double checking of suppressing/removing LGRLOCK by using keyword

editor and compare the performance and the results before proceeding (Figure 11).

Figure 11) LGRLOCK is automatically added by Petrel to the SCHEDULE section for Eclipse100 cases

Note: If LGRLOCK is removed then as soon as Petrel exports the case again, it adds LGRLOCK but if

LGRLOCK (or any other keyword) is suppressed, then there is no worries for exporting the case again

because Petrel checks the suppressed keyword and will not add it again. Thus, I recommend suppressing

such keywords rather than removing them.

Figure 12 shows although the Gas Production Rate of the Field is almost the same, the case in which

LGRLOCK is removed is much faster than the equivalent case with LGRLOCK. But there are some

evidences that LGRLOCK might be helpful as well.

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Figure 12) The performance issue due to LGRLOCK

Eclipse 100 only: If the user can manage turning off the LGRs on a time before HF event by using LGROFF

and then turning them ON at HF event by LGRON keywords, the performance might be dramatically

boost as shown in Figure 13 whereas the results are the same.

Figure 13) The effect of managing LGRs by LGRON and LGROFF keywords

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6 Recommendations Regarding validity of HF definition and known issues refer to InTouch Best Practice #5637349.

There are some evidences that show the results of HF correlations are over-estimated in some cases

such as InTouch Case Study #4796291 and also there are some cases that show a good match between

using Correlation and making LGR technique such as InTouch content # 4607976.

My conclusion is that the reliability of the HF Correlation approach is case dependent and can be

exercised by a pilot test before proceeding. The advantage of faster simulation runs is obvious for

correlation approach.

Eclipse 100 only: In order to enhance the performance of HF with LGR simulation runs, try to

suppress/remove LGRLOCK, then manage your run by adding LGROFF at the beginning of simulation run

in SCHEDULE section and add LGRON at the HF event report step for the relevant LGRs.

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