Bagheri, Mohammadreza (Research Centre for Fluid and Complex Systems, Coventry University) | Shariatipour, Seyed M. (Research Centre for Fluid and Complex Systems, Coventry University) | Ganjian, Eshmaiel (School of Energy, Construction and Environment, Built & Natural Environment Research Centre, Coventry University)
The fluid pressure, the stress due to the column of the cement in the annulus of oil and gas wells, and the radial pressure exerted on the cement sheath from the surrounding geological layers all affect the integrity of the cement sheath. This paper studies the impact of CO2-bearing fluids, coupled with the geomechanical alterations within the cement matrix on its integrity. These geochemical and geomechanical alterations within the cement matrix have been coupled to determine the cement lifespan. Two main scenarios including radial cracking and radial compaction, were assumed in order to investigate the behaviour of the cement matrix exposed to CO2-bearing fluids over long periods. If the radial pressure from the surrounding rocks on the cement matrix overcomes the strength of the degraded layers within the cement matrix, cement failure can be postponed, while on the other hand, high vertical stress on the cement matrix in the absence of a proper radial pressure can lead to a reduction in the cement lifespan. The radial cracking process generates local areas of high permeability around the outer face of the cement sheath. Our simulation results show at the shallower depths the cement matrices resist CO2-bearing fluids more and this delays exponentially the travel time of CO2-bearing fluids towards the Earth's surface. This is based on the evolution of CO2 gas from the aqueous phase due to the reduction in the fluid pressure at shallower depths, and consumption of CO2 in the reactions which occur at the deeper locations.
A new LWD ultrasonic imager for use in both water- and oil-based muds uses acoustic impedance contrast and ultrasonic amplitude measurements to obtain high-resolution structural, stratigraphic and borehole geometry information. Following extensive testing in the Middle East and the US, this paper presents results from the first European deployment of the new 4.75-in. high-resolution ultrasonic imaging tool.
An ultrasonic transducer, which operates at high frequency, scans the borehole at a high sampling rate to provide detailed measurements of amplitude and traveltime. A borehole caliper measurement is made, based on the time of arrival of the first reflection from the borehole wall. A second measurement detects formation features and tectonic stress indicators from the change in signal amplitude. The amplitude of the reflected wave is a function of the acoustic impedance of the medium. Resulting impedance maps have sufficient resolution to detect sinusoidal, non-sinusoidal and discontinuous features on the borehole wall.
Breakouts, drilling-induced fractures, and tensile zones were used for stress direction determination. Breakout identification was obtained both from amplitude images and oriented potato plot cross sections derived from traveltime measurements.
The orientation of natural fractures is parallel at the maximum stress direction, indicated by drilling-induced fractures and tensile zones. The World Stress Map confirms the maximum stress direction determination.
It was also possible to detect certain key-seat zones and investigate borehole conditions to prevent issues during the subsequent casing job.
The new LWD ultrasonic imaging technique represents an important alternative to density and water-based mud resistivity imaging, which has several limitations. Unlike the resistive imaging LWD tool that is very sensitive to standoff, the higher tolerance of the ultrasonic imaging tool enables the amplitude and traveltime ultrasonic images to contain fewer unwanted artifacts.
Recent drilling results have highlighted the potential for the development of Jurassic source rocks of southern England as a shale oil play. Sustained natural oil flows have been reported by UKOG (2015) from the tight, Lower Kimmeridge limestones in the Horse Hill-1 well. According to the operator, this discovery is naturally fractured and can be produced without hydraulic fracture stimulation.
The occurrence of shale gas in the UK has been known of since the nineteenth century, but development of this resource attracted very little interest until recent years (Selley, 2012; Andrews, 2014). The first exploration well in the United Kingdom that was specifically drilled for shale gas was Preese Hall-1 in northwest England in 2010. This well was hydraulically fractured in the Bowland Shale, but operations were suspended following reports of repeated seismicity caused by the injection of fluid during hydraulic fracture treatment (Green et al., 2012). Assessments of the Carboniferous shale gas potential of northern England and Scotland and of the Jurassic shale oil potential of southern England have been published by the BGS/DECC (Andrews, 2013, 2014; Monaghan, 2014). These studies listed the various criteria for evaluation of shale plays and provided broad descriptions and resource estimates for the Carboniferous and Jurassic shale plays in the United Kingdom.
This paper presents the results of an integrated petrophysical and geological assessment of the Jurassic sequence in the south of England. The study area stretched from the Weald and Vale of Pewsey Basins in the north to the onshore parts of the Portland–Isle of Wight Basin on the Dorset coast in the south (Figure 1). The evaluation focused on the Kimmeridge Clay Formation, the Oxford Clay Formation, the Downcliff Clay Member, Charmouth Mudstone Formation and the Blue Lias Formation.
The stratigraphic framework used for the study is based on the extrapolation of the well-known outcrop stratigraphy on the Dorset Coast to the study wells. Wireline log data and new sedimentological core description results were used to constrain facies mapping. Detailed sedimentological core description was carried out on three of the twelve study wells. From the trends observed in the wireline log data, the lithofacies and level of oxygenation, 14 initial facies associations were assigned over the cored intervals ranging from restricted shallow marine through shoreface to shelfal environments. These facies associations were grouped into seven combined facies associations which were used as input for the electrofacies analysis and facilitated the extrapolation of facies to intervals that lacked core data Additionally this workflow provided a useful template for estimating Total Organic Carbon TOC from logs using the CARBOLOG® equation and this resulted in a significant improvement in the correlation between the laboratory measured TOC values and the log-based TOC estimates. Results from the mineralogical analysis of core and cutting samples were utilised to calibrate and improve the petrophysical interpretations and to assess the elastic properties of the rocks in the intervals of interest. The petrophysical data, elastic properties and the facies interpretations were used to evaluate and map the development potential of the Jurassic source rock intervals as unconventional reservoirs.
An extensive geochemical database was combined with new analyses to characterise the source rocks. This data was integrated into 1-D basin models to identify and map effective source kitchen areas. The organic matter in the analysed interval is dominated by Type II kerogen, with significant input of Type III kerogen towards the London-Brabant Massif. The Upper Jurassic Kimmeridge Clay and the Oxford Clay are within the early oil window, while the Lower Jurassic Downcliff Clay Member, Charmouth Mudstone Formation and the Blue Lias Formation have reached peak oil maturity in the deeper parts of the Weald Basin. The source richness and kerogen types were combined with the maturity maps to create generation risk maps.
The risk for ground water contamination from hydraulic fracturing was also evaluated. These results were combined with the reservoir and generation risk maps to produce common risk segment maps in order to identify the sweet spots in the study area.
The reservoir characterisation of lacustrine carbonates is currently challenging, as historically they are not common as major carbonate reservoirs and therefore have been less studied in terms of reservoir characterization. The giant discoveries of the Pre-Salt of the South Atlantic Margin in Brazil have introduced lacustrine carbonates as a major target for exploration and development and are driving new research.
Lacustrine carbonates are formed in lakes which are particularly sensitive to salinity, pH, water level and sediment supply variations. This variability results in a wide range of primary fabric types and associated porosity types, likely formed by the interaction of microbial and chemical processes. Lacustrine grainstones can be formed from spherulites or coquinas and stromatolites and stromatolite bioherms can form cavities and laminated pore systems. Shrub morphologies are found that can form complex pore networks. These fabric types can be affected by a series of diagenetic processes that can both enhance and occlude porosity.
In this paper, we review how porosity in these systems may be characterised in thin sections and using micro-CT and how permeability and resistivity might be determined in the laboratory or by 3-D modelling. We also address how rock types may be determined by analysis of capillary pressure data, to determine relative permeabilities for different rock types. This paper addresses some classical reservoir characterisation issues that are likely to be important in these reservoirs. The approach considered here emphasises an integrated link between petrography, facies analysis (outcrop studies) and porosity description in a petrophysically-based rock typing framework appropriate for geomodelling, upscaling and calibration with dynamic data. This reservoir characterisation workflow methodology is applicable to all carbonates, however, it is recognized that lacustrine carbonates present some special challenges.
SPE 166416 Petroleum Engineering Curricula: Is it Better to Enhance Geographical Diversity or to Standardize International Education? Copyright 2013, Society of Petroleum Engineers This paper was prepared for presentation at the SPE Annual Technical Conference and Exhibition held in New Orleans, Louisiana, USA, 30 September-2 October 2013. This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied.
Nguyen, V.H. (IFP Energies nouvelles, Universite de Cergy-Pontoise, Geosciences & Environnement Cergy) | Gland, N. (IFP Energies nouvelles) | Dautriat, J. (IFP Energies nouvelles) | Guelard, J. (IFP Energies nouvelles) | David, C. (Universite de Cergy-Pontoise, Geosciences & Environnement Cergy) | Wassermann, J. (Universite de Cergy-Pontoise, Geosciences & Environnement Cergy)
A multidisciplinary approach to shale characterization in a variety of North American gas- and liquids-rich shale plays has lead to improved understanding of the bulk physical, chemical and mechanical properties of these deposits and their geologic history. This effort is leading to successful exploitation of these enigmatic resources. Microfacies analysis of mudrocks provides a platform for upscaling from the "nano?? to the regional scale, and results in comprehensive mudrock characterizations.
Microfacies analysis of mudrock types within a select stratigraphic interval in a basin leads to the recognition of mudrock lithofacies. Lithofacies identification allows for calibration of petrophysical models, documentation of basinspecific variations in mudrock composition and microfabrics, the distribution of organic-rich members of these intervals, definition of the mechanical stratigraphy for completion design, and provides the litho-stratigraphic building blocks for predictive sequence stratigraphic models.
Successful exploration and exploitation of mudrocks as resources can be advanced when the recognition of mudrock lithofacies provides a methodical means to tie together the geologic, chronostratigraphic, geochemical and petrophysical data from a diverse spectrum of physical scales and technical disciplines.
It is now possible to relate most oil and gas reserves to six stratigraphic black shale formations which include the majority of the world's oil and gas source rocks (Ulmishek and Klemme, 1990). From 1997 the US Dept of Energy attempted to predict the activity of NORM and other factors which may affect the activity and / or occurrence of NORM in E&P production operations (Chriss 2002). Black shales are the source rocks for petroleum trapped within Uranium deposits (IAEA 2009).
According to current ideas kerogen† is the organic constituent of sedimentary materials that is associated with petroleum formation. Kerogen is considered by petroleum geologists as being of two different varieties: humic kerogen associated with poor oil sources and sapropelic‡ kerogen, related to subaqueous sediments and associated with rich oil sources. Oil and gas is formed by the thermal cracking of organic matter (kerogen) trapped in sedimentary rock.
Two hypotheses regarding NORM in E&P production operations need to be considered. The first hypothesis is that NORM is produced by locally high U and Th concentrations in the reservoir rocks. If this is generally true, NORM scale will be largely controlled by the geological formation and lithology. The second hypothesis is that NORM is released from ordinary geological media during normal geological processes. If this is generally true, the potential for NORM scale
precipitation may be predicted largely from basin setting and history.
A worldwide survey comprising a comprehensive review and detailed analysis of reported NORM activity in oilfield scales has now determined which of these hypotheses prevails. For the first time management will now have the ability to predict the magnitude of NORM in E&P facilities worldwide.
Time series analysis has been performed for the first time on the Cenomanian-Turonian sequence in Central Tunisia in order to shed light on its Milankovitch-like cyclicity. This analysis was tested and applied on two foraminiferal species: the biserial Heterohelix, an oxygen minimum zone (OMZ) dweller, and the triserial Guembelitria, a eutrophic surface dweller. Average sedimentary rates and the duration of the second Oceanic Anoxic Event OAE-2 in each studied section were estimated. Alternatively, the fluctuations of these two opportunistic species can be related mainly to both precessional (23-19 ka) and eccentricity (414-106 ka) cyclicity suggesting that changes in surface water fertility were linked to the Milankovitch parameters.
Keywords: Time series analysis; Heterohelix spp; Guembelitria spp; Milankovitch cyclicity; cyclostratigraphy; Cenomanian-Turonian boundary.