Africa (Sub-Sahara) Sahara Group discovered hydrocarbons in three wells drilled in Block OPL 274, located onshore in Nigeria's Edo State. Olugei-1 was drilled to a measured depth of 4537 m and encountered five hydrocarbon zones, with 33 m of net pay. Oki-Oziengbe South 4 was drilled to a measured depth of 3816 m and encountered 64.3 m of net pay in 13 hydrocarbon-bearing zones. Oki-Oziengbe South 5 was drilled to a measured depth of 3923 m and encountered 91 m of net pay in 19 reservoirs. Sahara Group (100%) is the operator. Asia Pacific Sino Gas & Energy Holdings (SGE) flowed gas (coalbed methane) from its first horizontal well in the Linxing production sharing contract (PSC) in China's Shanxi province.
Summary In the past decades, many exploration wells have drilled into igneous rocks by accident because of their similar seismic expression to the common intended targets such as porous carbonate mounds, sheet sands or deepwater sand-prone sinuous channels. In cases where sedimentary features such as channels or fans cannot be clearly delineated, the interpretation may be driven primarily by bright spot anomalies, and a poor understanding of the wavelet polarity may compound this problem. While many wells that are drilled into igneous rocks were based on interpretation of 2D seismic data, misinterpretation still occurs today using high quality 3D seismic data. We propose an in-context interpretation workflow in which the interpreter looks for key clues or parameters above, below and around the target of interest to confirm the interpretation. Introduction Using modern 3D seismic surveys, significant work has been achieved over the past two decades in accurately imaging the geometry of igneous bodies (Hansen and Cartwright 2006; Holford et al., 2012; Jackson et al., 2013; Magee et al., 2014).
Summary Concepts for the relation between faults and folds in an extensional regime have revealed the importance of detailed mapping of fault zones, particularly in combined structural-stratigraphic traps. We show in a case study from the Australian North West Shelf that extensional fault zones are composed of several individual faults. Depending on the depth within the faulted interval, the individual faults may be interrupted by relay ramps. Additionally, release faults perpendicular to the main faults may introduce further potential breaches of the fault seal. Understanding the faults within the reservoir at this level of detail will assist in better understanding the fault seal risk for combined structural-stratigraphic traps.
ABSTRACT: The ability of shale formations to deform and seal the annulus around the casing has been documented in publications and industry presentations. Moreover, development of such natural seals (barriers) in the annulus has been utilized in Permanent plug and abandonment (PP&A) operations as an alternative to conventional PP&A methods and materials. It has been reported that this in fact facilitated the PP&A operations and resulted in considerable cost savings. The objective of this paper is to present the work done to assess the potential of the Gearle formation in the Griffin fields in the southern Carnarvon Basin in Western Australia with respect to its ability to provide a barrier during the PP&A operations. For this purpose, we identify first and second order factors controlling the creep deformation of shales/mudstones. In turn, we compared the material and mechanical properties of Gearle formation with the formations forming seal at NCS and also with other measurements completed on other shales globally. In addition, we have utilized simple numerical creep models to assess the creep potential of Gearle formation to form a barrier around the casing. Later during PP&A operations, we acquired IBC-CBL-VDL logs in the wells and observed evidence of bonding. We, finally, present the cement log bond interpretations in the intervals we observed casing-formation bonding.
Permanent plug and abandonment (PP&A), as common industry practice, is performed by setting a number of cement plugs inside the casing strings. In certain cases, annular seal, traditionally provided by annular cement, may not fulfil the abandonment requirements and rather costly remedial cementing, milling or cut and pull of casing has to be performed in order to complete the PP&A of a well. However, certain rock types, i.e., shale and salt, have the potential to satisfy the requirements for PP&A and can therefore be used as well barrier elements as long as they can be proven to have the required strength and seal around the casing over a sufficient interval. In particular, the ability of shale to deform and seal the annulus around casing to form a barrier has been documented with the experience of operators in the Norwegian Continental Shelf (NCS) in the North Sea -providing ease of operations and cost savings (Carlsen, 2012, Williams et. al, 2009).
The formation of oil-water emulsions presents a major challenge for the petroleum industry. Emulsions in wells and flowlines cause higher viscosities and lead to larger pressure drops, reducing production performance. The empirical modelling of emulsion viscosity as a function of water cut is presented. Measurement techniques for emulsion viscosity in a laboratory are explored and their use in a multiphase flow simulator to predict well and flowline pressure drops is explained. The reverse of this methodology can also be used with field data to back calculate the ostensible emulsion viscosity curve. Using the BHP Billiton operated Pyrenees oil development as a case study, this paper contrasts the laboratory derived and reverse engineered viscosity curves generated across a number of wells that have produced to the point of natural emulsion inversion. A possible mechanism for the differences between the two is proposed. In the latter part of 2014, a campaign of downhole demulsifier dosing across the Pyrenees fields was intiated with considerable success. The impact of this chemical injection on emulsion viscosity modelling is also explored in detail.
The Exmouth Plateau is a subsided, stretched and rifted continental platform that forms the northern part of the Northern Carnarvon Basin off Western Australia's northwest coast. The plateau is bound on three sides by oceanic crust and consists of more than eight kilometres of Palaeozoic to Mesozoic sediments (
Structural interpretation from seismic data is one of the most important steps in understanding the subsurface. Geoscientists spend a considerable amount of interpretation time picking faults and horizons from seismic data to understand the subsurface structure. A traditional interpretation workflow, commonplace in the oil and gas industry, is to consecutively investigate separate 2D sections and subsequently combine the interpretations to build a 3D picture. This limits the understanding of the subsurface geology in highly faulted, structurally complex areas.
This study involved the application of a new workflow for producing a structurally validated interpretation on 3D seismic data from the eastern part of the Exmouth Plateau. This workflow incorporates seismic preconditioning, fault framework modelling, structural reconstruction and structural analysis techniques to validate the interpretation ( A new workflow to produce structurally validated interpretations in structurally complex regions.
A new workflow to produce structurally validated interpretations in structurally complex regions.
The framework model also becomes the foundation for geo-cellular modelling and further detailed analysis of dynamic behavior. This ensures the verified structural interpretation is carried throughout the entire exploration and production lifecycle.
Imaging faults is a complex process, which requires a combination of various approaches. Methods based on the gradient vector field, obtained from the seismic 3D cross correlation, is sensitive to any local variation. Deriving the vector field to local dip, curvature or oriented filters such as variance, is used extensively to enhance structural discontinuities. By analyzing the maximum of variance, a new attribute depicts the probability of fault occurrence. Although it shows a skeleton of the fault network, it remains difficult to use it for automatic extraction.
Another method consists in using derivatives of a relative geological time model, obtained during a comprehensive interpretation process. In such case, the fault image is directly related to the vertical throw and provides a high level of detection even where the seismic variance is limited due to a low signal to noise ratio. To increase the precision of the detection, surface attributes for each relative age are computed in the flattened space and then converted to the seismic domain.
With such technique, the calculation of the extrema values of the deepest descent gradient shows the fault break points at a sub seismic accuracy and is related to the vertical throw. It becomes a complementary attribute to the variance and the fault probability. Applied to the Exmouth data set, located on the North West Australian margin, these various types of attribute were used to interpret complex faulted deposits in the reservoir level.
Presentation Date: Monday, October 17, 2016
Start Time: 4:35:00 PM
Presentation Type: ORAL
The petroleum industry in Australia has an important role to play in minimising the spread of marine pests by contributing to the effective management of biofouling on contracted vessels, rigs and immersible equipment. The introduction of Invasive Marine Species into sensitive coastal waters has the potential to cause significant social, economic and environmental impacts. Woodside Energy Ltd (Woodside) has developed and implemented a systematic risk-based approach to the management of marine biofouling within Australian waters. Most recently, the risk management process has been reviewed and expanded for application to Woodside's expanding international portfolio.
The risk assessment methodology assesses the likelihood that a vessel, rig or immersible equipment has been infected by invasive marine species of concern by evaluating its prior operational and maintenance history. A semi-quantitative scoring system is used to determine whether further management measures such as inspections, cleaning or treatment of internal seawater systems are required.
The approach simplifies the management of invasive marine species into a standardised toolkit including a management plan, risk assessment tool, inspection procedures and a contractor information pack. The fit-for-purpose process is embedded in Woodside's systems, procedures and contractual requirements and is consistently applied to all marine operational activities.
Since implementation of the process in 2009, 230 risk assessments have been carried out on a range of vessels, rigs and other immersible equipment using Woodside's methodology. Verification of the effectiveness of the tool has also been undertaken by proactively inspecting all 20 vessels used for the offshore Western Australian North Rankin Complex Redevelopment Project, in parallel to using the risk assessment tool. The data from this project verified the methodology is delivering excellent marine biosecurity and environmental outcomes, whilst targeting effort and resources to areas of greatest concern.
The approach is applicable and transferable to activities beyond the oil and gas industry. Woodside has openly shared its simple methodology and tools with other petroleum companies, regulators and educational institutions. New challenges arise internationally due to the lack of baseline data and knowledge of local species in some areas. Woodside's approach allows for increased flexibility while maintaining the same level of management control and prevention of marine pest introduction.
The effectiveness of Woodside's approach has been formally recognised by receiving the inaugural Western Australian Department of Fisheries Excellence in Marine Biosecurity Award in 2014 and the Australian Petroleum Production and Exploration Association (APPEA) 2015 Health, Safety and Environment Award.
This paper will outline the key drivers for managing marine biofouling and detail Woodside's risk-based approach to preventing the introduction of invasive marine species both in Australia and internationally. The data gathered to verify the effectiveness of the approach, case studies and learnings will also be detailed.
A development campaign offshore Australia, with a total of 15 laterals in a challenging geological environment, has been successfully completed by Quadrant Energy. The main objectives were to geosteer and place the well path at an optimum standoff from the oil/water contact (OWC), while drilling at the interface of the gas/oil contact (GOC), when present, and at 1-1.5m TVD from the reservoir top when not.
The field is characterized by a series of transverse and longitudinal seismic and sub-seismic faults that bisect hydrocarbon-bearing sands which represent the greatest challenges in this development campaign. Evidence from exploration wells showed a thin column of heavy oil and a gas cap in the fault-bonded reservoir. A new multi-disciplinary methodology not only enabled Quadrant Energy to achieve its development objectives, but to develop a full subsurface picture of the Coniston field reservoir.
The use of the Reservoir Mapping-While-Drilling (RMWD) combined with Bed Boundary Mapping Tool (BBMT) and Multi-Function LWD services enabled the laterals to be placed at 1-2m TVD below the reservoir top or gas cap, when present, even in highly faulted sections. In addition to this precise placement the extreme depth of investigation of the RMWD service, in conjunction with the real-time multilayer inversion capability, constantly mapped the OWC at a distance up to 19m TVD below the wellbore. While drilling, different qualities of reservoir sands were identified and enabled the extensions of the wells’ TDs based on reservoir properties. The distance to boundary information, provided in real-time by the RMWD service, was used in real-time by the Quadrant Energy geology and geophysics team to update and validate the seismic model that provided increased confidence in the reservoir model and a more precise planning for future development wells.
This paper will illustrate the use of the latest LWD RMWD technology in a challenging geological environment. The paper will explore the close collaboration, teamwork, and integration necessary to drive innovation and demonstrate the outcomes of this successful campaign which have not only exceeded the development goals, but have also generated a full 3D view of the reservoir.
This study aims to combine a novel global interpretation method, using a relative geological time model and spectral decomposition imaging techniques, into a powerful workflow capable of extracting from seismic data very fine geomorphological features. The workflow was applied to a public domain 3D marine seismic data set covering the Exmouth Sub-basin in Northwestern Australia. The analysis at a sub-seismic scale of horizons stacks allowed the interpretation of complex geo-bodies, which would have remained undetected with classical methods.
The Exmouth Sub-basin is characterized by a complex geology made of various stratigraphic unconformities and a dense fault system. For those reasons, the interpretation of such a region with classical methods remains an intensive task, where only a few horizons could be obtained with many assumptions. The novel global approach presented in this paper was applied to the Exmouth Sub-basin dataset to build a full interpreted volume and better resolve geological ambiguities and identify sedimentary features.
Geological settings and data
The 1,000-km² seismic survey HCA2000A 3D covers the Jurassic and the Cretaceous depocentres of the Exmouth Sub-basin. The Exmouth Sub-basin is part of the North Carnarvon Basin, along the West Australia margin. From the late Paleozoic to the Early Jurassic, the basin evolved as a sag basin. The dense fault system in the lower part was developed by rifting during the Jurassic-earliest Cretaceous, associated with the breakup of East Gondwana (Tindale, 1998). Thick Jurassic syn-rift marine sediments were deposited in the new accommodation resulting from the extension. Uplift and erosion to the South of the basin provided a supply of sediments for the Lower Cretaceous sandstones, which prograded across the sub-basin.
The geological features from the Jurassic and Cretaceous periods represent potential targets for exploration. Previous work on this area has shown proven reservoirs in the Barrow Group and Dupuy Sandstone. The Muderong Shale is a regional seal and the Jurassic-Cretaceous faulted parts represent a good structural trap within the Mungaroo.