Diagenesis and porous system in Danish Zechstein carbonate reservoirs

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Energy research
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• Publié par: EUROPEAN-COMMISSION-DIRECTORATE-GENERAL-FOR-THE-INFORMATION-SOCIETY-AND-MEDIA-DI
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• Langue: English
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Commission of the European Communities
eneray
Diagenesis and porous system in Danish
Zechstein carbonate reservoirs
/ Commission of the European Communities
Diagenesis and porous system in Danish
Zechstein carbonate reservoirs
P. Frykman, N. Stentoft, K.L. Rasmussen, O.W. Christensen,
P.V. Andersen, F.L. Jacobsen
Geological Survey of Denmark
Thoravej, 31
DK-2400 Copenhagen NV
Contract No EN3C/0030-DK (MB)
Final report
Research funded in part by the Commission of the European Communities
Non-nuclear R&D programme
Optimization of the production and utilization of hydrocarbons
Directorate-General
Science, Research and Development
1989 Published by the
COMMISSION OF THE EUROPEAN COMMUNITIES
Directorate­General
Telecommunications, Information Industries and Innovation
L­2920 Luxembourg
LEGAL NOTICE
Neither the Commission of the European Communities nor any person acting
on behalf of the n is responsible for the use which might be made of
the following information
Cataloguing data can be found at the end of this publication
Luxembourg: Office for Official Publications of the European Communities, 1990
ISBN 92-826-0984-7 Catalogue number: CD-NA-12446-EN
© ECSC-EEC-EAEC, Brussels ■ Luxembourg, 1990
Printed in Belgium ABSTRACT
The aim of the project "Diagenesis and porous system in
Danish Zechstein reservoirs" was to quantify parameters used
in the fields of production optimisation and seismic model­
ling.
The production study reached the following main points:
• Recognition of the facies geometry within a hypersaline
carbonate platform indicates that potential carbonate
reservoirs are likely to form at the platform margin as
ooid-sand shoals.
• The dominant secondary porosity was essentially formed
by an early diagenetic process of dissolution which
developed mostly as oomouldic porosity. During late
diagenesis porosity was destroyed to varying degrees by
precipitation of anhydrite. The final diagenetic process
was hydrocarbon migration and emplacement.
• The pore geometry has been described qualitatively and
quantified by use of image analysis and has been corre­
lated to other flow-relevant parameters. The diagenetic
development of secondary porosity in the carbonates
results in a highly complex arrangement of both connec­
ted and isolated pores. It is particularly important to
evaluate the isolated porosity in order to improve wire­
line log interpretation and estimation of production
characteristics.
• Chemical characterisation of the sediments has shown
that many of the trace elements and REE were re-distri­
buted during diagenesis, and thus that they may repre­
sent an important source of information concerning dia­
genetic processes.
The velocity study reached the following main conclusions :
• Ultrasonic P-velocities (1 MHz) have been measured suc-
cesfully in the laboratory on dolomite, anhydrite and
halite plugs. In order to derive formation relevant
sound velocities, it has been necessary to adjust the
velocity according to measurements under a confining
pressure corresponding to formation conditions.
• The correlation of velocity to porosity has required
adjustment of published equations because of anhydrite
content and porosity types. Similarly, the correlation
between porosity and acoustic impedance seems to have
certain characteristics that are specific to this parti­
cular investigated setting and rock composition. The
presence of anhydrite as a rock component and the devel­
opment of secondary vuggy porosity accentuates the pro­
blems in relating porosity to acoustic impedance. There­
fore, these relationships must be taken into account in
each specific region when seismic modelling is attemp­
ted. TABLE OF CONTENTS
Page
AIMS OF THE RESEARCH IX
INTRODUCTION 1
DESCRIPTION OF THE RESEARCH 2
Description of material
PRODUCTION STUDY 4
Introduction
Depositional model for Zechstein carbonates
Platform environments for the Ca-2 6
. Oolite shoal
. Back-shoal 7
. Lagoons
. Marginal marine
Depositional facies geometryl model for the Ca-2 basinal area 8
Facies in the Ca-2, Løgumkloster-I 9
Comparison to adjacent Zechstein deposits
Diagenesis 10
Diagenetic evolution
Discussion1
Porosity types2
Primary porosity
. Intergranular porosity 1
. Shelter porosity
. Primary vugs3
Secondary porosity
. Mouldicy
. Intercrystalline porosity
. Intracrystalliney
. Fracture porosity 14
Porosity evolution
Textural classification6
Log analysis of Zechstein carbonate sequences 17
Introduction
Regional correlation based on wireline logs
Log response and sedimentary facies8
Relation of porosity and permeability 20
. Ca-2 in the L/gumkloster-1 well1
Re-evaluation of hydrocarbon saturations2
. Core evaluation 2
. Petrophysics3
V . Log processing 23
Discussion of hydrocarbon saturations 24
General conclusions on log analysis5
Comparison of spectral gamma logs7
Introduction
Material
Method8
Results
Discussion and conclusion9
Depth correction of core material 2
Image analysis of pore geometry 30
Introduction
Material and methods1
Image analysis procedure2
. Field related parameters3
. Objectds4
. Measurements
Results 36
. Field parameters
. Objects
Discussion7
Conclusions
Pore investigation by nitrogen volumetric adsorption 38
Introduction
Results
Discussion 40
Conclusion1
Chemistry of carbonates2
Chemical analysis of suite 1ls ofe 24
Sample preparation and analytical procedures 4
Results6
Discussion
VELOCITY STUDY 5
Introduction
P-velocity at surface conditions5
Pressure response of ultrasonic velocities 5
Introduction
Material
Method7
Results8
Discussion9
Conclusion 61
Adjustment of velocities to formation conditions 62
Method
Results
Discussion and conclusions3
- VI Frequency dependence of P-velocity 64
Method 6
Results5
Discussion and conclusion
Attenuation in Zechstein carbonates6
Method
Results and discussion
Correlation of velocities to rock parameters 67
Relation between P-velocity and porosity
Discussion 70
Conclusions2
Acoustic impedance3
Results
Discussion and conclusion4
SUGGESTED FUTURE WORK AND DEVELOPMENTS5
TABLE OF SYMBOLS7
LIST OF REFERENCES 79
TABLES 8
FIGURES 10
- VII -