fluid characterization analysis (fca-dwm) -processor guide- · 2020-01-12 · dwm based fluid...

TetraSeis division of TETRALE Group

Fluid Characterization Analysis (FCA-DWM)based on Duplex Wave Migration

(Processor Guide)

ContentsDuplex Wave Migration based ..................................................................................................... 1

Fluid Characterization Analysis (FCA-DWM) ............................................................................... 1

1. Introduction ............................................................................................................................ 2

References .............................................................................................................................. 3

2. Processor Guide ...................................................................................................................... 4

LAp Cubes.................................................................................................................................... 5

Difference Cube Slices ................................................................................................................ 6

Technical notes ......................................................................................................................... 10

DWM based Fluid Characterization Analysis (FCA-DWM) July 2012

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1. Introduction

Recent research indicates that oil filled fracture systems should be expected to producesseismically significant responses as compared to the response of water filled systems (“Slowwaves in fractures filled with viscous fluid”; Valeri Korneev: Geophysics Vol 73). In this paperKorneev discusses the substantial absorption effects that viscous fluids such as oil has onseismic wave energy. Also, interestingly, none viscous fluids such as water are expected to havemuch less absorption effects on the seismic signal.

Figure 1.1 (left and centre pictures) illustrates the DWM response from synthetic datagenerated using two depth models. Both depth models featured a sub horizontal layer and an 8meter wide vertical fracture system. The fracture system in the first model was given the viscoelastic absorption properties of water and the second was given the visco elastic absorptionproperties of oil. It shows the DWM response to these two vertical geo-bodies with the waterfilled fracture on the left and oil filled on the right. The visco elastic attenuation parameterswere selected to be consistent with the poro elastic theory that have been published by ValarieKorneev. Our modelling experiment indicates that phase difference of the DWM response forwater versus oil is approximately 180 degrees.

Figure 1.1 (right picture) illustrates an interesting example of what is an apparently continuousfracture system on a DWM horizon depth map generated using real 3D seismic data. Note thatthe phase of the DWM response rapidly flips by what appears to be approximately 180 degrees.One possible explanation for this observation is that the DWM response may be indicating theboundary of the oil to water contact. These observations lead us to believe that we can useDWM based technology to assist in the characterization of fluid type in a fractured reservoir.

DWM response to synthetic data modelled with water filled fractures (left) and oil filled fractures (center).

The two responses are approximately 180 degrees out of phase.

Figure (right) is a blow up of a linear fracture system on a DWM depth slice generated from real seismicdata with the abrupt apparent phase change of approximately 180 degrees.

DWM based Fluid Characterization in Fracture Systems

Water DWMResponse

Oil DWMResponse


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Using FCA-DWM method allows obtaining seismic images of sub-vertical boundaries which areformed by the waves having the fixed incidence angle ranges (partial DWM cubes), and thencarry out the AVO analysis and classification of relating sub-vertical objects properties.

Figure 1.2

References

G.Dubrova, I.Khromova, A.Kostyukevych, D.Luo, W.Liang, B.Li. Duplex Wave MigrationBased AVO for Determination Properties of Vertical Boundaries. – 73rd EAGE Conference &Exhibition, Vienna, Austria, 23-26 May 2011. – #P311.

Example of the FCA-DWM on a real 3D data set


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2. Processor Guide

Figure 2.1 Dialog-box for correction of a slice dimension parameters *grd

This technology is not considering using any special programs but DWM3D, PostProc, Excel

and Surfer 8 or 9; for visualization and QC Tesseral-Pro is used.

This technology has been tried on such projects as: L-41 (China) and Torovej (Russia), and

partially it was tried on: Nazym-1, West LekeJaga, Jugansk (Bazhen) and Makariha.

This technology is realized in two main stages – obtaining DWM cubes using local

construction apertures (for short – LAp) and then statistical amplitude analysis of a wave

field of these cubes (StAn).


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LAp Cubes

Figure 2.2 DWM cube slices with different apertures (LAp cubes)

In principle, LAp cubes can be built for certain local apertures, but it appears, that frompractical view point, it is better to build cubes for continues apertures starting from maximal,for example, 0-2000. For this aperture time wave fields and DWM cube are calculated. Tobuild images for cubes with shorter apertures, for example, 0-1900, 0-1800 and so on we needto run only migration itself. This is convenient in respect of computation time and for picking ofoptimal aperture for conventional DWM on an object.

After that PostProc (<Difference of 2 similr files>) is used, we create a number of differenceDWM cubes (cubes of local apertures). For step out and increment of 100m – it will be anorder, for example, 2000-1900, 1900-1800, 1800-1700 and so on. Sometimes for stability of

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difference results it is useful to test a row, for example, with step out of 100m and increment of200m (2000-1800, 1900-1700, 1800-1600 and so on); or, in the same sense, different versions.

Difference Cube Slices

The next step is getting difference cubes slices accumulated in Z direction in approximateinterval of 100m above base-boundary using program PostProc (< Two sub-horizontal sections>). Data format - *.txt or *.grd.

It is desirable to do these two steps for whole area which includes all investigated in this senselocal objects.

Local objects of target analysis are determined based on received dynamic slices of cube.Based on our studies we concluded that 100-200m diameter of a local slice size gives usreasonable statistical stability and resolution; but there is a sense to analyze a certain row -from bigger locality to smaller.


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Figure 2.3 Objects for analysis

areaarea well-119+

area

area wells 53+

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area 2 &

2 3+

area

area well-118+

area wells 53+ & 84+ & 59+ & 85+ & 46+

area 2 & area 3 & area3+

area well-101+ & well-24+


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For description of local dimensions of slide and picking required grid points we used options ofSurfer program. Here are the steps for doing this:

1. original cube slice in .txt format (or in .grid, saved in .dat) is again transformed into .grd

format, at the same time in a dialog-box (see pic.1 in DWM_AVO.ppt) correction of

coordinates (and grid spacing) is conducted in conjunction with picked target object, for

example, area around well;

2. file is transforming into text format, and wave field amplitude values are corrected – to

convert them to absolute values (F4 change “-“ for “space”);

3. incorporating program <New Worksheet>, loading received text file and then in option

“data” ”statistics”, where in available menu choosing statistical characteristics which

we consider appropriate for our target; they are saved in table form;

4. parameters choice and their arrangement (in our case, major like <Mean> and

<Median>) for a number of local apertures need to be done manually;

5. then in <Excel> environment built graphs of amplitudes (or field energy) dependency

from local apertures which have been used for image creation;

6. approximate evaluation of aperture values in relation with angles of rays striking near

root part of sub-vertical target object has been done in average velocity assumption

(using straight ray).

It is worth mentioning that in a process of data choosing on a target local object using Surfer,picked area has a rectangular shape with it sides parallel to axis [X, Y]. But it is not alwaysacceptable. Very often we need to pick area with arbitrary orientation such as corridors (alongdefined lineament). Such simple program has been written (Y. Roganov).

an


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Figure 2.4 Combined FCA-DWM graphs

Figure 2.5 Averaged coefficients of well productivity

From figures 2.4 and 2.5 it can be seen that here is apparent correlation between anomalousFCA-DWM effect and production coefficient in wells on these graphs (based on report data).

Loca

lap

ertu

re

wells 53 &84

well 118

Angle

CombinedFCA-DWMgraphs

85° 80° 75° 70° 65° 60° 55°

50°(signs ofproduction)

(wat

erin

flu

x)

Amplitude

Angle 85° 80° 75° 70° 65° 60° 55°

50°


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Figure 2.4 Well productivity charts

Technical notes

DWM parameters (Task.ini) in this application were the same as for a routine DWM on thisobject. Particularly, grid step was 20m; testing grids with step 10 and 5 meters showed thatsuch diligence in current conditions is not necessary.

It is necessary to underline that received in this case relations give in reality only a glimpseabout combined AVO-effect on base and target sub-vertical boundaries. To calculate this effectfor the last one, it is necessary to input certain corrections calculation of which requiresmodeling as well. Such steps have been tried on object L-41 (China).

There is a report on this job and paper (G.Dubrova, I.Khromova, A.Kostyukevych, D.Luo,W.Liang, B.Li. Duplex Wave Migration Based AVO for Determination Properties of VerticalBoundaries. – 73rd EAGE Conference & Exhibition, Vienna, Austria, 23-26 May 2011. – #P311.).

In mentioned above paper topics of AVO prediction were investigated for target sub-verticalobject using AVO analysis data from DWM.

fluid characterization analysis (fca-dwm) -processor guide- · 2020-01-12 · dwm based fluid...

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