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Genetic Units Based Reservoir Characterization Using a Normalized Pore Throat Radius for the Clastic System

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Genetic Units Based Reservoir Characterization Using a Normalized Pore Throat Radius for the Clastic System.

ABSTRACT

Globally, 30–50% of hydrocarbon volumes in silici-clastic reservoirs are contained within the thin-bedded pay. In the Niger Delta deep water assets, over 30% of in-place volumes are found within the complex turbidites.

The presence of multi-pore architecture within such facies makes their description from petrophysics very complex. With the quest for hydrocarbon prospects in frontier deep water settings characterized by such complex rock fabric, detailed reservoir characterization is essential for accurate field management and production optimization.

The focus of this work is to characterize complex reservoir pore systems at core scale based on genetic reservoir unit averages and to provide improved models for petrophysical evaluation using a normalized pore throat radius   approach for

clastic reservoirs. New methods are presented for modelling permeability in rocks with multimodal pore throat size distributions using Niger Delta field as case study.

The statistical significance of the coefficients in the proposed relationships for various genetic reservoir units was verified using α-level of 0.05; and the results indicate that the proposed model is very unlikely to have occurred by chance.

Two methodologies are presented for upscaling from core plug to log scale–genetic unit averages of pseudo normalized pore throat radius as input parameter to the proposed model.

This study also presents improved methodology for generating capillary pressures from NMR T2 relaxation time using a genetic unit based averages of the kappa scaling parameter proposed by Volokitin et al.

The improved methodology is also applicable to conventional geophysical logs for estimating capillary pressure in the absence of NMR T2 data.

Comparative analyses indicate that the proposed methodology is an excellent improvement over existing methods (e.g., Reservoir Quality Index, Leverett J-Function, Stratigraphic Modified Lorenz Plot) for characterizing hydraulic flow units.

Additionally, efficiency of the proposed methodology is demonstrated by comparison of estimated permeabilities versus core permeabilities from four depobelts in the Niger Delta.

Permeabilities were derived from existing methodologies including Genetic Unit Averages of FZI’s, Neural Network Permeability, NMR based Schlumberger Doll Research (SDR) and Coates correlations.

It is concluded that the proposed methodology is a superior and practical tool for reservoir characterization.

TABLE OF CONTENTS

Acknowledgement ……. v
Abstract ……….. vi
Table of Contents ….. viii
List of Figures….. xiii
List of Tables ……… xxvi

Chapter 1 Introduction ……… 1

1.1 Statement of the Problem ………… 1
1.2 Literature Review ………… 19
1.3 Objectives of the Study ……….. 23
1.4 Organization of the Thesis ………. 24

Chapter 2 Overview of the Niger Delta Geology ……….26

2.1 Petroleum Geology of the Niger Delta …………… 26
2.2 Genetic Reservoir Units within the Niger Delta Province ……. 28
2.2.1 Channel Sandstone …… 28
2.2.2 Channel Heterolithic …… 30
2.2.3 Upper Shoreface Sandstone …………… 31
2.2.4 Lower Shoreface Heterolithic ….. 33
2.2.5 Marine Shale ……. 34
2.2.6 Coastal Plain Sandstone ……… 35
2.2.7 Coastal Plain Heterolithic …………. 36
2.2.8 Coastal Plain Shale … 37

Chapter 3 Theory of Capillary Pressure Modelling (CPM) ……….39

3.1 Capillary Curves Measurement Techniques ….. 39
3.2 Capillary Pressure Petrophysical Models ……. 42
3.3 Applications of Capillary Pressure Model to Reservoir Understanding . 46
3.3.1 Exploration and Geological Applications …. 46
3.3.2 Reservoir Engineering ………….. 47
3.4 Capillary Curve Corrections and Conversions .. 49
3.4.1 Closure Correction ….. 49
3.4.2 Stress Correction ……… 50
3.4.3 Clay-Bound-Water or Shaliness Correction ………. 51
3.5 Capillary Curve Fitting and Smoothing ….. 53
3.5.1 J. Leverett Function ….. 55
3.5.2 Thomeer Function ……… 56
3.5.3 Trigonometric Tangent Function ……. 57
3.5.4 Brook’s Corey Function ……. 58
3.5.5 Lambda Function …………………. 59
3.5.6 Entry Height Functions ……… 59
3.5.7 Exponential Function ………………. 60
3.5.8 Hyperbola Function ……….. 60
3.5.9 Polynomial Function ……… 61
3.5.10 Sigmoidal Function ……………. 61
3.6 Permeability Modelling from Capillary Pressures/Saturation Curves …………………. 62
3.6.1 Integrating the Area under the Capillary Curve (Kozeny Methodology) ………. 63
3.6.2 Purcell Parameter …….. 65
3.6.3 Thomeer Parameter …….. 65
3.6.4 Swamson’s Methodology for Correlation with Capillary Curve Data …… 68
3.6.5 Windland’s Empirical Relationship for Permeability Modelling … 70
3.6.6 Pittman’s Methodology for Correlation with Capillary Curve Data ………. 71
3.6.7 Permeability Correlations for the Niger Delta Reservoirs ………. 72

CHAPTER 4 Theory of Nuclear Magnetic Resonance (NMR) ……75

4.1 Theoretical Background .. 75
4.2 Genetic Units Averages of Kappa for Capillary Pressure Estimation from NMR measurements …81
4.3 NMR-Log Interpretation ………. 85
4.4 Lithology Independent NMR Total Porosity ………….. 87
4.5 Construction of Capillary curves (Pc) from NMR T2 distribution … 87
4.6 Estimating NMR-Derived Permeability in Sandstones ………… 90

CHAPTER 5 Material and Methodology ………….92

5.1 Sample Selection and Data Analysis …………….. 92
5.2 Genetic Reservoir Units Definition: Sedimentologic Characterization and Rock Type Definition .106
5.3 Pore Throat Size Histogram Analysis ……. 108
5.4 Pressure Range Setting and Curve Fitting ………….. 111
5.5 Permeability Modelling from Capillary Pressure …….. 113

CHAPTER 6 Data Analysis, Results, and Discussions …… 123

6.1 Introduction …. 123
6.2 Statistical Significance of Model Coefficients for the Proposed Genetic Unit Based Permeability Model.. 124
6.3 Proposed Model Calibration using NMR T2 transversal relaxation time ……………. 127
6.3.1 Capillary Pressures and Pore Throat Distribution from NMR measurement … 127
6.3.2 Flow Unit Based Analytical Methodology for NMR-Pc Calibration . 138
6.3.3 NMR-Pc Calibration: Application to Reservoir Characterization Using the Niger Delta Deepwater Turbidites as Case Study .. 143
6.3.4 Genetic Unit Averages of Pseudo-Normalized Pore Throats and Model Upscaling .. 165
6.4 Statistical Analysis and Uncertainty Modelling in Permeability Derived from the Proposed Model . 184

CHAPTER 7 Improved RQI, Leverett J-function and SMLP Concept using the Normalized Pore Throat (Rtot) 187

7.1 The Reservoir Quality Indicator (RQI) Concept …… 187
7.1.1 Integrating the Rtot with the RQI Concept ………….. 189
7.1.2 Case Study of the Clastic Turbidite Reservoirs .. 190
7.2 The Leverett J-Function ……….. 205
7.2.1 Integrating the Rtot with the Leverett J-Function …… 207
7.2.2 Case Study of the Clastic Turbidite Reservoirs ….. 207
7.3. Improved Stratigraphic Modified Lorenz Plot (SMLP) Concept Using the Proposed Normalized Pore Throat (Rtot) Model .. 215
7.3.1 Methodology for Hydraulic Flow Units Characterization Using the SMLP … 218
7.3.2 Case Study 1 of the Tidal Channel Sandstone Reservoir (Zone 1) …………….. 221
7.3.3 Case Study of the Fluvial Channel Sandstone Reservoir (Zone 2) …………….. 228
7.4 Application of the Normalized Pore Throat Methodology in 3D Reservoir Characterization Studies .233
7.4.1 Field Overview and Location of Study Area… 233
7.4.2 Reservoir and Fluid Characterization of the Study Area … 234
7.4.3 Results and Analysis …… 239
7.4.4 Implication of the based Modified RQI Methodology in 3D Simulation Studies 244

CHAPTER 8 Contribution to Knowledge ….. 253

8.1 Major Contributions …….. 253
8.2 Published research articles ……………. 254
8.3 Publications In-view ……….. 255

CHAPTER 9 Summary, Conclusions and Recommendations …… 256

9.1 Summary and Conclusions …. 256
9.2 Recommendations …………….. 259
Nomenclature ………….. 260
References ……….. 264

INTRODUCTION

1.1 Statement of the Problem

Reservoir characterization has been a major research subject in reservoir engineering and formation evaluation since the 1960s, as a key input linking geology and petrophysics into reserves optimization.

In today’s economic climate with an increasing challenge to find new reserves in frontier basins, it is more important than ever to emphasize the value petrophysics adds to our business.

The most commonly encountered and probably the most challenging task confronting reservoir modelling is arriving at a realistic realization which best describes both the static and dynamic features of the reservoir.

This involves the proper understanding of their insitu petrophysical properties. Detailed knowledge of these properties such as permeability, initial saturation, capillary pressures and relative permeability are crucial to performance prediction and effective reservoir management.

Inaccurate prediction of such petrophysical properties; or nature of their distribution within the turbiditic clastic environment can result in significant cost due to inefficient completions, interventions/work-overs, or reserves exploitation. When a good history-matched model results in a bad forecast, question your petrophysical data (Hani Qutob et al., 2013).

REFERENCES

Hani H. Qutob, Abdelaziz Khlaifat, and Mohamed S. Efnik, “When a Good History- Matched Model Results in a Bad Forecast; Question your Petrophysical Data” (September 2013). SPE 166056.

Nadeau, P.H., Bjorkum, P.A., and Walderhaug, O., (2005) “Petroleum system analysis: impact of shale diagenesis on reservoir fluid pressure, hydrocarbon migration, and biodegradation risk”. Northwest Europe and Global Perspectives – Proceedings of the 6th Petroleum Geology Conference, Geological Society, London, 1267–1274.

Nadeau, P.H., Walderhaug, O., Bjorkum, P.A., and Oelkers, E.H., “Fundamental particle size analysis: Application to hydraulic conductivity models in shales/mudstones”. Conference of the European Clay Groups Association: Cracow, Program Abstracts, p. 115, 1999.

Ejedawe, J.E., Coker, S.J., Lambert-Aikhionbare, D.O., Alofe, K.O., Adoh, F.O., 1984. “Evolution of oil-generative window and oil and gas occurrence in Tertiary Niger Delta basin. AAPG Bulletin 68, 1744–1751.

Knox, G.J., Omatsola, E.M., 1989. “Development of the Cenozoic Niger Delta in Terms of the “Escalator regression” Model and Impact on Hydrocarbon Distribution”. Proceedings KNGMG Symposium, Coastal Lowlands, Geology, and Geotechnology. Dordrecht, Kluwer. 181-202.

Hulea I.N. and Nicholls C.A. (2012) “Carbonate rock characterization and modelling– Capillary pressure and permeability in multimodal rocks – a look beyond sample specific heterogeneity.”AAPG Bulletin, September, v. 96, p. 1627-1642.

 

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