Disequilibrium Compaction, Fluid expansion and unloading effects: Analysis from well log and its pore pressure implication in Jay Field, Niger Delta

Disequilibrium compaction, sometimes referred to as under compaction, has been identified as a major mechanism of abnormal pore pressure buildup in sedimentary basins. This is attributed to the interplay between the rate at which sediments are deposited and the rate at which fluids associated with the sediments are expelled with respect to burial depth. The purpose of this research is to analyze the mechanisms associated with abnormal pore pressure regime in the sedimentary formation. The study area “Jay field” is an offshore Niger Delta susceptible to abnormal pore pressure regime in the Agbada –Akata formations of the basin. Well log analysis and cross plots were applied to determine the under compacted zone in the formation since compaction increases with burial depth. It was observed that porosity and permeability of the deeper depth (3700 m to end of Well) are higher than those of the shallow part (3000 – 3700 m). This is against what is expected from normal compacted sediment, demonstrating disequilibrium compaction in deposition. Furthermore, it reveals that sedimentation rate was high, making it unable for the sediments to expunge its fluid as expected. Density and acoustic wave increase with depth in normal compaction trend. However, the reverse that was identified in the mapped interval is attributed to disequilibrium compaction, unloading, clay diagenesis, and fluid expansion. The cross plot divulges sediments at the deeper depth had lower density and acoustic wave value with increased porosity when compared to those at shallow depth. This forms the basis that the sediments from this mapped interval experienced disequilibrium and unloading traceable to clay diagenesis during and after deposition, respectively.

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Porosity and Permeability Measurements Integration of The Upper Cretaceous in Balad Field, Central Iraq

Iraqi Geological Journal ◽

10.46717/igj.54.1b.3ms-2021-02-21 ◽

2021 ◽

Vol 54 (1B) ◽

pp. 24-42

Author(s):

Fawzi Al-Beyati

Keyword(s):

Image Analysis ◽

Log Analysis ◽

Core Analysis ◽

Well Log ◽

Reservoir Properties ◽

Thin Sections ◽

Core Samples ◽

Porosity And Permeability ◽

Well Log Analysis ◽

Porosity Range

The corrected porosity image analysis and log data can be used to build 3D models for porosity and permeability. This can be much realistic porosity obtainable because the core test data is not always available due to high cost which is a challenge for petroleum companies and petrophysists. Thus, this method can be used as an advantage of thin section studies and for opening horizon for more studies in the future to obtain reservoir properties. Seventy-two core samples were selected and the same numbers of thin sections were made from Khasib, Sa`di, and Hartha, formations from Ba-1, Ba-4, and Ba-8 wells, Balad Oilfield in Central Iraq to make a comprehensive view of using porosity image analysis software to determine the porosity. The petrophysical description including porosity image analysis was utilized and both laboratory core test analysis and well log analysis were used to correct and calibrate the results. The main reservoir properties including porosity and permeability were measured based on core samples laboratory analysis. The results of porosity obtained from well log analysis and porosity image analysis method are corrected by using SPSS software; the results revealed good correlation coefficients between 0.684 and 0.872. The porosity range values are 9-16% and 9-27% for Khasib and Sa’di in Ba-1 Well, respectively; 10-21%, 9-25%, and 16-27% for Khasib, Sa’di and Hartha in Ba-4 Well, respectively; and 11-24% and 15-24% for Khasib and Hartha in Ba-8 Well, respectively according to petrographic image analysis. By using the laboratory core analysis, the porosity range values are 12-26% and 17-24% for Khasib and Sa’di in Ba-1 Well, respectively; 6-28% and 14-27% for Sa’di and Hartha in Ba-4 Well, respectively; and 17-19% and 15-24% for Sa’di and Hartha in Ba-8 Well, respectively. Finally, the well log analysis showed that the porosity range values are 11-16% and 7-27% for Khasib and Sa’di in Ba-1 Well, respectively; 4-18%, 21-26%, and 16-19% for Khasib, Sa’di and Hartha in Ba-4 Well, respectively; and 9-24% and 15-23% for Khasib and Hartha in Ba-8 Well, respectively. The permeability range values based on laboratory core analysis are 1.51-8.97 md and 0.29-2.77 md for Khasib and Sa’di in Ba-1 Well, respectively; 0.01-24.5 md and 0.28-6.47 md for Sa’di and Hartha in Ba-4 Well, respectively; and 0.86-2.25 md and 0.23-3.66 for Sa’di and Hartha in Ba-8 Well, respectively.

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Well‐log analysis of pore pressure mechanisms near a minibasin‐bounding growth fault at South Eugene Island field, offshore Louisiana

10.1190/1.2147906 ◽

2005 ◽

Author(s):

Matthew M. Haney ◽

Ronny Hofmann ◽

Roel Snieder

Keyword(s):

Pore Pressure ◽

Log Analysis ◽

Well Log ◽

Growth Fault ◽

Well Log Analysis

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Pore pressure prediction in Niger Delta high pressure, high temperature (HP/HT) domains using well logs and 3D seismic data: a case study of X-field, onshore Niger Delta

Journal of Petroleum Exploration and Production Technology ◽

10.1007/s13202-021-01264-5 ◽

2021 ◽

Vol 11 (10) ◽

pp. 3747-3758

Author(s):

Abdulquadri O. Alabere ◽

Olayemi K. Akangbe

Keyword(s):

High Pressure ◽

High Temperature ◽

Pore Pressure ◽

Niger Delta ◽

Seismic Velocity ◽

Sedimentary Basins ◽

Geothermal Gradient ◽

Pore Pressure Prediction ◽

Fracture Gradient ◽

High Temperature High Pressure

AbstractFew wells targeting high temperature, high pressure intervals in most tertiary sedimentary basins have achieved their objective in terms of technicalities and cost. Since most shallow targets have been drilled, exploration focus is drifting into deeper plays both onshore and in deep offshore areas. To ensure safe and economic drilling campaigns, pore pressure prediction methodologies used in the region needs to be improved. The research aims at generating and testing a modification of Eaton’s equation fit for high temperature, high pressure intervals on a field. The evolution of pore pressure in the field was established from offset well data by making several crossplots, and fracture gradient was computed using Mathew and Kelly’s equation. Eaton’s equation parameters were then calibrated using several wells until a desired field scale result was achieved when compared with information from already drilled intervals i.e., kicks and RFT data. Seismic velocity data resulting from high density, high resolution velocity analysis done to target deep overpressured intervals were then used to predict 1D pore pressure models at six selected prospect locations. Analyses reveal depths shallower than 3800 m TVD/MSL with geothermal gradient 3.0 °C/100 m and pressure gradient less than 1.50sg EMW are affected mainly by undercompaction; depths greater than 3800 m TVD/MSL with geothermal gradient of 4.1 °C/10 m and pressure gradients reaching 1.82–2.12sg EMW are affected by unloading with a narrow drilling margin for the deep highly pressured prospect intervals. Eaton’s n-exponent was modified to 6, and it proved accurate in predicting high overpressure in the first prospect wells drilled.

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Formation Pore Pressure Variation of the Neocomian Sedimentary Succession (the Fahliyan Formation) in the Abadan Plain Basin, SW of Iran

Geofluids ◽

10.1155/2017/6265341 ◽

2017 ◽

Vol 2017 ◽

pp. 1-13 ◽

Cited By ~ 4

Author(s):

Bahman Soleimani ◽

Mohammad Hassani-Giv ◽

Iraj Abdollahi fard

Keyword(s):

Pore Pressure ◽

Middle Part ◽

Burial Depth ◽

Pressure Data ◽

Pressure Step ◽

Data Points ◽

Sedimentary Succession ◽

Pressure Regime ◽

Formation Pore Pressure

The Neocomian Fahliyan Formation is one of the important oil reservoirs in the Abadan Plain Basin, SW of Iran. To evaluate the pore pressure regime of the Fahliyan reservoir, 164 in situ pressure data points (MDT, XPT, and RFT) were analyzed from seven wells belonging to six oilfields. The pressure versus depth plot revealed that the Fahliyan reservoir is highly overpressured in all fields. The formation was characterized as a multilayered stacked reservoir with different pore pressure decreasing downward in a step-wise manner. Also, there is a major pressure step in the middle part of the reservoir, suggesting the presence of a regional efficient seal dividing the reservoir into two stacked compartments, where the upper compartment is more overpressured than the lower one. The stepped pressure pattern of the Fahliyan Formation is a regional phenomenon controlled by a factor governed regionally, the depositional condition, and facies lateral changes during the deposition of shallowing upward sequence of the Fahliyan reservoir. In addition, direct relationship is observed between the reservoir pressure and burial depth. This matter could amplify the initially generated overpressure state more possible due to dewatering of sediments and by-pass product of oil migration from Garau source rock to the Fahliyan reservoir.

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Estimation of overpressures from porosity based method : a theoretical approach applied to the central/coastal swamp depo-belts of the Niger delta basin

International Journal of Advanced Geosciences ◽

10.14419/ijag.v6i1.8547 ◽

2017 ◽

Vol 6 (1) ◽

pp. 14

Author(s):

Ubon Mkpese

Keyword(s):

Bulk Density ◽

Pore Pressure ◽

Theoretical Approach ◽

Niger Delta ◽

Sonic Velocity ◽

Pore Pressure Prediction ◽

Formation Resistivity ◽

Pressure Regime ◽

Niger Delta Basin

The Depth-dependent compaction theory that variations in certain geophysical properties with depth; bulk density, formation resistivity together with sonic velocity being a reflection of the pressure regime is the basis for pore pressure prognosis study. Pore pressure prediction (PPP), when done accurately can be used to avert disaster and helps in safe drilling. A porosity-based model has been applied to predict overpressured zones in an onshore environment of the Niger delta basin. Zones with hard overpressures greater than a magnitude of 0.7 psi/ft are generally within 10000ft and below. Top of overpressures for studied wells ranges between 7000ft and 10000ft. Porosities in shale are of typical values ranging between 0.05 to 0.46. A robust concordance between PPP and MPP profiles for each of the wells validates the results here and confirms suitability of model to the studied area.

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Marlim R3D: a realistic model for CSEM simulations - phase I: model building

Brazilian Journal of Geology ◽

10.1590/2317-4889201720170088 ◽

2017 ◽

Vol 47 (4) ◽

pp. 633-644 ◽

Cited By ~ 1

Author(s):

Bruno Rodrigues Carvalho ◽

Paulo Tarso Luiz Menezes

Keyword(s):

Model Building ◽

Reference Model ◽

Sedimentary Basins ◽

Realistic Model ◽

Complex Model ◽

Well Log ◽

Recent Past ◽

Complementary Information ◽

Geoelectric Model ◽

Calibration Time

ABSTRACT: The marine controlled-source electromagnetic (CSEM) method provides complementary information to seismic imaging in the exploration of sedimentary basins. The CSEM is mainly used for reservoir scanning and appraisal. The CSEM interpretation workflow is heavily based on inversion and forward - modeling for hypothesis testing. Until the recent past, the effectiveness of a given workflow was achieved after the drilling results, as there wasn’t any geological complex model available to serve as a benchmark. In the present paper, we describe the workflow to build up Marlim R3D, a realistic and complex geoelectric model. Marlim R3D aims to be a reference model of turbidite reservoirs of the Brazilian continental margin. Our model is based on seismic interpretation and constrained by the input of available well-log information. The workflow used is composed of seven steps: seismic and well-log dataset loading, well-tie, Vp cube construction, Vp resistivity calibration, time-depth conversion, resistivity cube construction, and quality-control check. As a result, we obtained an interpreted dataset composed by main stratigraphic horizons, pseudo-well logs, and the resistivity cubes. These elements were made freely available for research or commercial use, under the Creative Common License, at the Zenodo platform.

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Predicting Formation Pore-Pressure from Well-Log Data with Hybrid Machine-Learning Optimization Algorithms

Natural Resources Research ◽

10.1007/s11053-021-09852-2 ◽

2021 ◽

Author(s):

Mohammad Farsi ◽

Nima Mohamadian ◽

Hamzeh Ghorbani ◽

David A. Wood ◽

Shadfar Davoodi ◽

...

Keyword(s):

Machine Learning ◽

Pore Pressure ◽

Optimization Algorithms ◽

Well Log ◽

Log Data ◽

Hybrid Machine ◽

Formation Pore Pressure

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Spatial variation in porosity and permeability of the Rupel Clay Member in the Netherlands

Netherlands Journal of Geosciences – Geologie en Mijnbouw ◽

10.1017/njg.2016.28 ◽

2016 ◽

Vol 95 (3) ◽

pp. 253-268 ◽

Cited By ~ 2

Author(s):

Hanneke Verweij ◽

Geert-Jan Vis ◽

Elke Imberechts

Keyword(s):

The Netherlands ◽

Spatial Variation ◽

Clay Content ◽

Burial Depth ◽

Southeastern Part ◽

Boom Clay ◽

The North ◽

Sealing Capacity ◽

Porosity And Permeability ◽

Permeability Data

AbstractThe spatial distribution of porosity and permeability of the Rupel Clay Member is of key importance to evaluate the spatial variation of its sealing capacity and groundwater flow condition. There are only a limited number of measured porosity and permeability data of the Rupel Clay Member in the onshore Netherlands and these data are restricted to shallow depths in the order of tens of metres below surface. Grain sizes measured by laser diffraction and SediGraph® in samples of the Rupel Clay Member taken from boreholes spread across the country were used to generate new porosity and permeability data for the Rupel Clay Member located at greater burial depth. Effective stress and clay content are important parameters in the applied grain-size based calculations of porosity and permeability.The calculation method was first tested on measured data of the Belgian Boom Clay. The test results showed good agreement between calculated permeability and measured hydraulic conductivity for depths exceeding 200m.The spatial variation in lithology, heterogeneity and also burial depth of the Rupel Clay Member in the Netherlands are apparent in the variation of the calculated permeability. The samples from the north of the country consist almost entirely of muds and as a consequence show little lithology-related variation in permeability. The vertical variation in permeability in the more heterogeneous Rupel Clay Member in the southern and east-southeastern part of the country can reach several orders of magnitude due to increased permeability of the coarser-grained layers.

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