bluuebunny/crossref_metadata_2025 huggingface dataset:
Reconstruction of Microstructure of a Cavernous-Fractured Reservoirs by Scattered Seismic Waves
Authors: Cheverda Vladimir A. , Lisitsa Vadim , Reshetova Galina , Merzlikina Anastasiya , Shilikov Valery , Pozdnyakov Vladimir
Published: May 2016

The interaction of seismic waves with cavernous/fractured reservoirs is analyzed on the base of finite-difference simulation with grids locally refined in time and space. The necessity to use such grids is caused by significantly differing scale of heterogeneities in the background (coarse grid) and reservoir (fine grid). Computations for each subdomain are carried out in parallel. The data exchange between each subdomain within a group is implemented using nonblocking iSend/iReceive MPIcommands in order to guarantee high scalability of the algorithm. The data exchange between the two groups is donecommands in order to guarantee high scalability of the algorithm. The data exchange between the two groups is done.

Over the last decade the use of scattered waves won a significant place among the wide range of seismic techniques. But so far the main area of application of scattered waves is narrowed to spatial localization of micro heterogeneities clusters, likecracked and fractured areas, cavities and so on. In other words these waves are using just to say "yes" or "no" to the presence of a microstructure. At the same time more detailed knowledge about fine structure of hydrocarbon reservoirs, likeorientation of fracture corridors and fluid saturation of micro heterogeneities (especially cavities) is extremely important in the design phase of deep and horizontal wells. In order to be able to predict this microstructure one must possess a detailed knowledge of the particular features of interaction of seismic waves with cavernous fractured reservoirs, manifestation of fluid saturation especially.

We have developed justified, verified and implemented for supercomputers with parallel architecture the reliable instrument for the studying complicated processes of waves' propagation in realistic 3D heterogeneous multiscale models of geological media – the special finite-difference method with local mesh refinement in time and space. On this base is possible to deal with realistic models and acquisitions and take into account both small scale heterogeneities of a reservoir and mesoscale variations in overburden.

This software was applied for simulation of seismic waves' propagation through realistic digital model developed on the base of all available data for some East Siberian oil field. We have found that orientation of fracture corridors and fluid saturation of reservoir microstructure has very specific impact in synthetic images of scattered waves which can be used as predictive criteria in real life data processing and interpretation. These criteria are verified by comparison of predictions with well log data (fracture orientation) and permeability (fluid saturation) of a collector by test results.
Optimization of Development Well Locations in T Gas Field, Malay Basin; Key Seismic Learnings from Phase 1 Drilling Program
Authors: Abu Samah Mohd Irwan , Lye Yue Choong , Jaynes Scott R.
Published: May 2016

Description

The T gas field, located approximately 200km from Peninsular Malaysia, was discovered in 1979 and streamed in 2013. Gas is present in Lower to Middle Miocene fluvio-deltaic sands (Group X) and tidal flat/channel sands (Group Y). Six wells were drilled during the exploration phase and a 3D survey acquired in 2004 was re-processed in 2010. The Field Development Plan comprises fourteen wells drilled in two phases from two production platforms. The initial development wells targeting multiple zones were successfully placed using a range of re-processed seismic cubes, offering important seismic based learnings for Phase II drilling and for similar field developments in the Malay Basin.

Applications

Pre-drill EOD and hydrocarbon resource density prediction to accurately guide well placement included utilization of new near/mid/far/full seismic cubes and in particular, an inverted VpVs cube. Gamma Ray trends at Pre-Drill locations were subsequently generated from the inverted VpVs cube. Exploration wells were used to calibrate seismic amplitude response in the VpVs inversion process.

Results and Conclusions

Post-drill results indicate that of the various techniques utilized, net pay and EOD predictions based on the inverted VpVs cube most closely match actual well results. There is good correlation between rock quality and VpVs response in the group X and Y reservoir intervals, particularly above the GWC. The use of this technique allowed accurate placement of well trajectories to maximize reservoir quality and thickness in these stacked intervals. The enhanced seismic dataset allowed accurate stratigraphic predictions from single cycle and multi-cycle seismic facies, including a significant, previously unrecognized, fluvial channel cut containing stacked point bars in the Y-1 reservoir interval.

Technical Contributions

Based on the increased confidence in the re-processed dataset, a seismically conditioned geological model build is underway. The use of VpVs responses offers further development optimization opportunities in the field and has applications in similar field developments in the area.
Fast-Track Rock Properties From Broadband Seismic Data
Authors: Geisslinger Axel , Salleh Azim
Published: May 2016

Introduction

Brunei Shell Petroleum acquired 7000 km2 of broadband seismic data during 2012 and 2013, in support of its strategy to "Rejuvenate and Grow". Exploration growth is a key component of this strategic direction and the broadband data is seen as a key enabler. The new seismic data not only delivers far better structural definition but also allows for streamlined QI support to identify new prospective areas. Weeks after the final migrations are available, we delivered a full bandwidth Acoustic Impedance and a Fluid Cube for the entire 3D data space. The swift delivery of these inversion products forms a corner stone in pursuit of Brunei Shell Petroleum's exploration objectives.

1 - Regional Full Bandwidth Impedance Data

Broadband seismic delivers lower frequencies in the seismic spectrum and, through application of the latest imaging techniques, also delivers higher frequency content in the migration velocities. These 2 components can be merged seamlessly, creating an acoustic impedance volume, without having the need to estimate information in the range of ~1.5 to 8 Hz. With conventional seismic this gap needs to be filled with more or less substantiated interpolations of rock properties, based on time consuming interpretation efforts.

We developed a robust workflow to generate regional full bandwidth Acoustic Impedance (AI) data, that essentially relies ona) signal shaping and subsequent coloured inversion to appropriately reflect the earth's AI spectrum,b) the derivation and application of a single calibration factor to obtain band-limited AI andc) subsequent merging of this band-limited AI data with low-frequency AI data that is directly obtained from the imaging velocities. Well tests indicate the quality of the match of well log data against the final impedance volumes (Figure 1).
Geologic Framework of the Laurel Formation, Canning Basin
Authors: Elkhalgi Muftah , Rezaee Reza
Published: May 2016

The main geological and geochemical characteristics of the Tournaisian Laurel Formation across the Fitzroy Trough and Lennard Shelf in the northern regions of the Canning Basin are described in this article. From there it continues to the Laurel Formation, referred to as the total shale section, which are the shale facies thatwere assessed in this study. The Lower Carboniferous Laurel Shale is believed to be the source rock of the oil and gas reservoirs in the Lennard Shelf and Fitzroy Trough. Although the coring process is highly expensive, the core-based measurements are still considered superior and more reliable in their petrophysical characterisation of shale gas resources. Wireline logging was also studied to characterise the rich organic shale facies in terms of both TOC estimation and lithological identification. A combination of wireline logging and conventional core data was extensively focused on to elaborate the petrophysical and geological study; in particular, the vertical heterogeneity of the shale rock is very high, and drilled wells in the Fitzroy Trough are limed. About 15 cored wells were logged and more than 40 un-cored wells were calibrated to cover the largest possible area for the study. A quantitative X-ray diffraction analysis and Scanning Electronic Microscope study were conducted for five shale samples collected from different intervals in the Laurel Formation. Detailed mineral composition and texture analyses have shown four main lithofacies within the Laurel Shale (excluding the carbonate section). In most of the Fitzroy Trough, the sedimentary strata are thick and deep, and south-east in the Lennard Shelf, the total shale section is more than 400m thick, identified as mature to over-mature in the Fitzroy Trough, and immature to marginally mature in the Lennard Shelf. Measurement and estimations of total organic content (TOC) proved to contain rich organic shale in both areas. The Laurel Shale section yielded up to 5.0 wt% TOC in both the Fitzroy Trough and the Lennard Shelf. In this paper, electrofacies analysis, petrophysical study, rock typing approaches, and vertical and lateral facies distribution have been studied for the Laurel Formation in the onshore Canning Basin.
An Effective Methodology for High Resolution Diffraction Imaging
Authors: Akalin Mehmet Ferruh , Khan Farhan Ahmed , Saleh Ahmad Shahir
Published: May 2016

Effective and efficient diffraction wavefield separation from recorded seismic reflection data is important for ultra-high-resolution seismic imaging of discontinuities and stratigraphic details. Here we demonstrate the results of an effective new methodology to separate diffractions from reflections and give examples on synthetic and real seismic data sets. We use the diffraction wavefield in pre-stack migration to obtain ultra-high-resolution seismic images.

Introduction

After noise and multiple attenuation, seismic reflection data mainly contain primary reflections and diffractions. The conventional imaging approach is to use all upgoing wavefield to construct the image of the subsurface. This approach mainly results in the dominance of specular reflection based imaging which suppresses or attenuates the high resolution information carried by diffraction events.

Reflections originate from impedance contrasts at continuous interfaces between layers of rocks whereas diffractions originate from abrupt subsurface discontinuities, the lateral dimensions of which are in the order of the dominant seismic wavelength or smaller e.g. fractures, faults, sudden lateral stratigraphic changes, channels, rough boundaries. The main difficulty in using diffractions is their energy weakness compared with the strong specular reflection energy in seismic records.

Diffraction separation from upgoing wavefield and imaging has been studied by several researchers. Harlan et al. (1984) separated diffractions and obtained velocity information from them. Landa et al. (1987) and (1998) used common-diffraction-point sections for imaging of diffraction energy and detecting local heterogeneities. Taner et al. (2006) presented the theory and application of the separation of reflections and diffractions using simulated common plane-wave source sections. In this domain, diffracted waves appear as quasi-hyperbolic-shaped events whereas reflections are quasi-linear events. Therefore, the reflection energy can be suppressed by a method known as plane-wave destruction (Claerbout, 1992; Fomel, 2002). Separation, velocity estimation and imaging of diffractions using plane-wave destruction in the post-stack domain are proposed by Fomel et al. (2007). Reflection and diffraction wavefields can also be separated in migrated common-image gathers (CIGs) in the dip-angle domain (Audebert et al., 2002; Landa et al., 2008; Reshef and Landa, 2009; Klokov and Fomel 2012).
Should Lessons Learned be the Blueprint for the Future?
Authors: Gordon Brian J , Wilkinson Peter
Published: May 2016

Do we need a journey through the past to make our future better? Many companies say they have a Lessons Learned processas part of their management system. Whilst the intent is sincere, a review of major accident events suggests this is notworking. Why is there no sense of anxiety around this failure to learn and prevent reoccurrence? From a review of variousmajor incidents around the world, we conclude that all possible lessons have not been learned from preceding events.

In one sense, a failure to learn is understandable. Since catastrophic accidents are not common, it is easy for people to believe that similar incidents won't happen to them. Their rarity also means that the generation who were in proximity to a major incident and were deeply affected by it, will in time move on. Trevor Kletz recognised this issue many years ago in his 1993 book, "Lessons from Disaster" or "How organisations have no memory and accidents recur." (Kletz 1993)

However, is this too pessimistic a view? What can we do about building more risk aware organisations and minimising reliance on active risk mitigation systems? Much work has been done already, mainly in the field of identifying lessons to be learnt. This is not the same as actually learning the lessons, which is more difficult. We discuss the mechanisms at work which causes lessons not to be learned along with the various psychological characteristics and traits at play that can affect our ability to learn.

This paper discusses the following essential features of an effective lessons learnt process:A requirement to look outside the organisation and industry for sharing of lessons to learned;A process which goes beyond identifying the lessons to be learnt but has a method to embed or internalise the lessons and actually minimise the risk or eliminate the defect;A specific organisational capability in making changes with senior management patronage;Measurement to check the organisation is applying the lessons and behaviours and hardware have changed in practice.
Large Scale Seismic Modelling of the Pre-Carbonate Geology, Offshore Malaysia, a Multidisciplinary Approach - “Running the Seismic Method Backwards"
Authors: Chandola Sandeep Kumar , Low Cheng Foo , Akalin Mehmet Ferruh , Alai Riaz , Muhamad Abdul Aziz , Bayly Martin paul , Myers Keith Stuart , Brice Timothy , Nyein Glenn , Hydal Saeeda
Published: May 2016

Despite proven analogues elsewhere in Malaysia, pre-carbonate hydrocarbon targets offshore Sarawak have met with limited drilling success. This has been mainly attributed to the poor seismic imaging beneath complex velocity carbonate reefs and platforms with low signal-to-noise ratio and inadequate illumination. Seismic imaging is challenging due to inconsistent illumination, multiple energy contamination and complex wave propagation. A collaborative study was undertaken to model these challenges and recommend optimum acquisition and signal processing solutions to produce a step change in seismic imaging of the pre-carbonate targets.

The study involved building a detailed anisotropic 3D earth model using borehole and seismic data covering more than 600 km2 area to create a robust synthetic seismic dataset. Geological and petrophysical review preceded seismic interpretation and simultaneous AVO inversion results were used to populate a fine scale model. Testing and validation of the model was performed on a data subset to ensured the kinematics and amplitudes were consistent with the actual seismic response. The model was then used to create over 15 billion prestack traces using an anisotropic finite difference wave propagation modelling algorithm. From this data, different survey designs were extracted including; narrow-azimuth (NAZ), multi-azimuth (MAZ), wide-azimuth (WAZ) and full-azimuth (FAZ) circular shooting streamer geometries.

These datasets were processed and analyzed to test optimal demultiple and imaging approaches and to understand the relative benefits of different acquisition geometries. The results indicated that acquiring azimuthally rich data improves illumination of the pre-carbonate section. The demultiple testing successfully demonstrates the workflow needed to attenuate both short and long period multiples. Reverse Time Migration (RTM) produced an improved image compared to Kirchhoff pre stack depth migration. This case study demonstrates that large scale 3D finite difference seismic modelling, aimed at addressing specific geological challenges, is an effective tool in understanding the optimum acquisition design and processing workflow prior to beginning a new seismic acquisition. Based on the findings of this collaborative study, PETRONAS has now acquired a new seismic data set in the area targeting pre-carbonate objectives using a 3D full-azimuth circular acquisition.
Adaptive Centroid Frequency Shift Q Tomography
Authors: Xie Yi , Xin Kefeng , He Yi
Published: May 2016

The propagation of seismic waves through visco-acoustic media is affected by frequency dependent absorption which is often described by the quality factor Q where a low Q means more loss of signal strength and bandwidth. Complex variations in attenuation, if not accounted for, can severely compromise both the amplitude and phase of the migrated data. This in turn affects the ability to accurately predict reservoir properties. In this paper we propose a new tomographic approach using adaptive centroid frequency shift (CFS) information from surface seismic data to estimate Q.

By picking the events in the migrated section and ray-tracing back to the unmigrated data domain, the centroid frequency of the unmigrated data can be measured for the picked events in the depth migrated CIG gathers. After applying the correction generated on the fly for the given source wavelet, these adaptively corrected CFS will then be back-projected along ray path to reconstruct the attenuation distribution through our tomographic inversion.

A synthetic test and a real data example will be presented to demonstrate how our approach can accurately estimate a Q model and can be included in the Q compensation process to fully account for the frequency dependent attenuation effects observed on seismic data.

A key element of the CFS method is deciding what analytical function should be used to fit the amplitude spectrum of wavelets before and after passing through visco-acoustic media. However, we found the accuracy of Q tomographic inversion to be sensitive to the accuracy of the fitting and that the fixed wavelet fitting function cannot describe the real source wavelet accurately. An adaptive correction is applied to the observed centroid frequency to account for any deviation from the explicit relationship through tabulating the absorption effect for different accumulated dissipation time. These adaptively corrected centroid frequency shifts improve the stability and the accuracy of the inversion.

Introduction

The propagation of seismic waves through viscoacoustic media is affected by frequency dependent absorption which results in loss of signal strength and bandwidth. Complex variations in attenuation, if not accounted for, can severely compromise both the amplitude and phase of the migrated data. This in turn affects the ability to accurately predict reservoir properties (Best et al., 1994). Thus, there is a need to compensate for the frequency dependent absorption during the processing of the data.
Fracture Detection via Double Beam Focusing and Image Filtering
Authors: Protasov Maxim I. , Cheverda Vladimir , Reshetova Galina V.
Published: May 2016

In this paper, the asymmetric summation is implemented by the double focusing of Gaussian beams. To do this, the special weights are computed by propagating Gaussian beams from the target area towards the acquisition system separately for sources and receivers. The different mutual positioning of beams in each pair introduces a variety of "selective images" that are destined to represent some selected singular primitives of the target objects, such as fractures, cavities, edges and so on. In this way, one can construct various wave images of a target reservoir, particularly in scattered/diffracted waves. Additional removal of remnants of specular reflections is done by means of spectral analysis of the scattered/diffracted waves' images to recognize and cancel extended lineaments.

Numerical experiments with synthetic seismic data simulated for the Sigsbee2a model and some typical structures of the Yurubcheno-Tokhomskoya oil field in East Siberia are presented and discussed.

Introduction

Recently, the construction of a diffraction image is taking an active interest. This is primarily due to the demands for prospecting and developing in a typical environment of carbonate fractured reservoirs. According to various estimates these reservoirs contain 35–48 percent of the world 's oil reserves and 23–28 percent of the world's gas. A scattered component of the seismic wave field carries an essential information about the structure of the medium at a sub-seismic scale, where fractured zones are related to. The processing of a scattered component allows one to localize such geologically interesting objects as decompression zones of rocks and fracture-development zones, internal faults and crystalline arrays containing cavernous fractured zones.

Thus, it can be stated that using of the scattered component can solve one of the major problems associated with the discovery and development of hydrocarbons in the carbonate environment: to localize heterogeneities of sub-seismic scale and to determine their fine structure, like the dominant orientation of fracture corridors. This allows to predict the distribution of main stream fluid flows. In particular, it is worth mentioning here that in many carbonate reservoirs, matrix porosity contains the oil in place but the permeability is mainly provided by fracture corridors. In some carbonate reservoirs the oil in place is essentially contained in karstic caves. Thus, the ability to accurately localize clusters of micro heterogeneities (cavities/cracks/fractures) and to characterize their properties is crucial to ensure the effective follow-up exploration and field development.
Jack-Up Suitability from a Risk Assessment Perspective
Authors: Rohani Muhammad Joehan , M. W. Ismail Wan M , Sha'ari Fatimah Az-Zahra' , A Jalil Azri
Published: May 2016

Geohazard can be described as local and/ or regional site and soil conditions having a potential of developing into failure events causing loss of life or damage to health, environment or field installation. PETRONAS Carigali Sdn Bhd (PCSB) is confronted with various geohazards challenges, both in our domestic and international projects. These geohazards includes but are not limited to different types of soil stratigraphy, shallow gas, shallow channel systems, faults, pockmarks, mudflows, corals etc.

In order to address these Geohazard issues, PCSB has developed a comprehensive Geohazard Assessment Model (GAM) for institutionalization within the company a governance process to manage geohazard risks. The aim of Geohazard Assessment Model is to:Provide a comprehensive integrated geohazards risk assessment framework to ensure geohazards risks are identified and management is given advance recommendations on the mitigation solutions andEnsure all requirements for the Geohazard Analysis such as technical; pre, during and post operations and health, safety and environmental (HSE) are within code compliance and assets are being safeguarded at all times.

The importance of GAM can be reflected in terms of monetary, time, quality and HSE whereby substantial cost savings can be achieved via a risk assessment perspective. GAM utilizes an integrated approach requiring expertise in geotechnical, geophysical and geological disciplines to rationally identify, assess, quantify and mitigate these geohazards for the eventual selection of final field development concept, optimum asset sitting and approaches.

This paper shall present how jack-ups suitability are studied from a risk assessment perspective using GAM. The importance of proactive measures to mitigate geohazards are also elaborated on projects undertaken by PCSB. Adopting a systematic approach to quantifying geohazard risk can minimise time and cost impacts upon any field development.
Maturing Opportunities in a Multi-Layered Waterflooded Reservoir
Authors: Mohamed Isa Amzani Faisal , Nadarajan Sangeetha , Gray Joy Whitney
Published: May 2016

Description

Economic development of multi-layered reservoirs in the 1970s and 1980s resulted in pattern waterfloods where many zones were vertically commingled in both producers and injectors. Infill drilling in the 2000s revealed that there was still relatively high oil saturation in some zones indicating variable conformance of injected fluids and incomplete vertical sweep.

To improve recovery, alternative completion technology to access high oil saturation zones and improve vertical conformance is planned. There is uncertainty in the location of remaining oil saturation with a horizontal water displacement in a multi-layered reservoir. Limited measured data on zonal conformance at water injectors and zonal production contribution at producers, results in significant challenges to history matching a reservoir simulation model. Analytical techniques, in addition to simulation studies, were used to assess and quantify the opportunities.

Applications

This paper demonstrates the use of analytical techniques to assess oil production and reserve opportunities in a multi-layered waterflood, where zonal information is sparse.

Results and Conclusions

Limited zonal contribution information results in a history matched model with significant uncertainties. Evaluation of the range of saturation uncertainties and their impact on opportunities would take significant effort and time. This paper shows that analytical techniques can be effectively used to quickly assess these types of opportunities in a fit-for-purpose manner to facilitate risked business decisions.

Technical Contributions

This paper will aid in finding opportunities in existing fields with multi-layered reservoir description. Alternate technique to reservoir simulation may find opportunities more quickly. The paper describes the value of using upgraded completion technology in older fields.
Implementation of a Fit-for-Purpose Cementing Technology for the First Gas Hydrate Production in Japan
Authors: Taoutaou Salim , Ashraf Shameed , Takahashi Ushio , Ikawa Terumichi , Yamamoto Koji
Published: May 2016

JOGMEC (Japan Oil, Gas and Metals National Corporation) was planning for the first offshore production test of methane hydrates in the eastern Nankai Trough off of Japan. The test needs one production well and three temperature monitoring wells to study the dissociation performance of methane hydrate formations. Cementing these types of wells needed to have a specific cementing technology fit for deepwater shallow unconsolidated formations subject to subsidence and methane hydrate-bearing formations.

A project was initiated in 2011 with the objective being to design and qualify a cement slurry system fit for deepwater shallow unconsolidated formations subject to subsidence and methane hydrate-bearing formations. Based on extensive laboratory and full-scale testing, a cement technology was qualified by the service company and approved by JOGMEC to be the optimum solution for this unique project.

This paper will describe the full-scale and extensive laboratory testing used to qualify the cement technology fit for this application and the different stages that create sufficient wellbore stability for the drawdown during the production test. In addition, real-time temperature data interpretation will be presented showing the cement hydration in these wells after placement. Case histories of the three wells will be presented.

Introduction

One of JOGMEC's corporate objectives is to overcome the constraints resulting from limited resources by investigating the next-generation energy resources, which includes research on methane hydrates. Methane hydrates (MH) available within Japan's territorial waters may well be able to supply Japan with its natural gas needs.

Deposits of methane hydrates have been reported in marine sediments of the Nankai Trough off the Pacific coast of central Japan, where the water depth is more than 500 m (Fig. 1). Some estimates indicate that the methane hydrate reserves correspond to a 100-yr supply of natural gas for Japan, making it an important potential energy source. The Japan National Oil Corporation (JNOC) began research work on methane hydrates in 1995, and JOGMEC has overseen the project since the restructuring of JNOC.

The 16-yr exploitation project extending from 2001 to 2016 is being led by METI (Ministry of Economy, Trade and Industry) as one of the Japan national projects. The three-phase project consists of the following steps:· Phase 1—2001–2008– Perform fundamental R&D for exploration, basic properties, and laboratory investigation– Select MH resource fields and assess the amount– Verify production methods through onshore testing· Phase 2—2009–2015– Perform fundamental R&D for production and environmental impact assessment– Verify production methods through offshore testing
Multi Frac in Horizontal HT Wells: Plug and Perf Technique Application on Sandstone Gas Reservoir, Onshore Pakistan
Authors: Mittiga Vincenzo , Martocchia Francesco , Carpineta Gabriele , Maccarini Giorgio Ricci
Published: May 2016

In the last decades, the increasing use of Hydraulic Fracturing as a stimulation technique made possible to unlock reserves that were not economically producible until that moment. This has been possible due to the advances in horizontal drilling and to the improvements in completion technologies which made possible to cut down the costs associated to stimulation of low permeability reservoirs.

The technological improvements of composite bridge plugs resulted in faster operations for deployment and post frac milling: this caused the Plug and Perf technique to be widely used on multi stage fracturing operations in the US during the "Shale Gas Revolution".

This paper will describe a successful experience of exporting the Plug & Perf technology on a multi stage frac performed on a horizontal gas well, Sandstone reservoir, Southern Pakistan. The treatment consisted in six stages of propped hydraulic fracturing using a High Temperature frac fluid system and achieving zonal isolation by using composite bridge plug deployed with coiled tubing. All of the operations were performed rigless. Focus will be on the design, execution and post job analysis of this multi stage fracturing treatment with particular attention to the completion strategy and the operation sequence from the bridge plug setting to the milling operations and well clean up.

Introduction

The target reservoir has been reached with a 6" horizontal drain of about 1000 m length and completed with a 4½", 15.1ppf P110 cemented liner. A total of 6 stages were pumped to create transverse fractures across the entire pay in order to achieve an effective coverage of target layer. Plug and perf technique using E coil was used to complete with a single run the plugging of the early stimulated zone and perforating the next zone to be fractured. To allow production in commingle from the different stimulated intervals, a 3.5" OD milling motor was M/U and RIH on CT as it is described in the Fig. 1.

Based on the experience gained on unconventional plays, the well has been designed 'toe up' to help the water unloading: in this configuration, the bulk volume of liquid accumulation is occurring downstream of the productive interval, providing more gas velocity to sweep the liquids and therefore allowing an easier and faster water flow back.

The wireline logs recorded in the pilot hole and along the drain shown a reservoir permeability ranging from 0.01 to 0.1 mD, and an average porosity of 13 % with a water saturation of 70 %.

The Reservoir Model in FracPro PT chosen is "Lithology Based description". The initial mechanical properties for the interested levels were estimated from the available data from the offset wells and have been calibrated after the diagnostics injection tests.
Benchmarking Power Distribution System to Plant Capacity and Potential Revenue - Finding the Most Cost Efficient Option to Distribute Power
Authors: Firdaus Eddie , Setiadi Andhika Herlambang
Published: May 2016

Oil and gas production plants are dependent on the reliability and availability of a power system. Power is distributed to electrical loads through a distribution system which can be chosen from several types, such as radial, primary selective, or secondary selective system to achieve greater availability. This greater availability results in a higher investment cost, but frequently this is overlooked due to the existing best practice on how to build a power system to provide the greatest availability and support production.

Designing a power system for the sole purpose of providing the greatest availability without considering the plants to which it is connected to will lead to an overdesign, which could reduce the overall profitability of the plant itself. This research aims to benchmark each type of power system, specifically for power distribution, to plant capacity and plant life in order to generate a set of reference or rule of thumb which will give early information on what type of power distribution system is best suited in terms of cost efficiency, whilst still providing the optimum support for production. The data for this research will be taken from North Hamada Project and Block-A Project to reflect the most actual and recent price. BlockSim was used to create a model of each type of power distribution system and calculate the related availability.

The research result is plotted into a chart which displays break even points of each power distribution system when applied to various plant capacity and plant life. It can be concluded that a plant with certain capacity and lifetime will have its most suitable power distribution system to be selected, which is not always necessarily the highest cost one. By having information on the plant design capacity and lifetime, one can already have an early reference on what type of power distribution system to select when plotting it on the chart generated by this research.
Petroleum system, migration and charge history in the Neo- and Meso-Proterozoic series of the Taoudenni Basin, Adrar: Insights from fluid inclusions
Authors: Girard Jean-Pierre , Eichenseer Herbert , Kabbej Amir , Idris Kamil Mohamed
Published: May 2016

Exploring ancient Paleozoic–Proterozoic cratonic basins is a very challenging undertaking because it is often difficult to achieve a good understanding of complex burial/thermal histories and old petroleum systems. As part of an ongoing exploration campaign, two frontier exploration wells were recently drilled in the northwestern part of the Taoudenni basin in Mauritania, targeting Proterozoic clastic and carbonate petroleum plays located at present-day depths between 2.4 and 3.0 km. Both wells were investigated by use of the so-called FIS (Fluid Inclusion Stratigraphy) technique in order to document the performance of a Proterozoic petroleum system in the Adrar sector of the basin. The results permitted to document the existence of 1) petroleum paleo-accumulation and -migration in the Neo-Proterozoic Lower Assabet sandstones and Meso-Proterozoic Atar dolostones, 2) an efficient seal to oil, above the Lower Assabet sandstones, 3) multiple charges of oil of variable maturity in the eastern well (shallower paleo-burial) subsequently lost by leakage, 4) secondary cracking of a primary oil charge, and possibly gas dismigration, in the western well (deeper paleo-burial). This work demonstrates the existence and the functioning of an oil-prone Proterozoic petroleum system, and provides very valuable guidance for future exploration in this area of the Taoudenni basin. It also opens up potentialities to be investigated for Proterozoic gas/oil shale plays.

1. Objectives and context

Frontier onshore exploration is presently being conducted in the northwestern part of the Taoudenni basin, Mauritania, with the objective of investigating very old (450–1500Ma) Paleozoic-Proterozoic plays. This is a very challenging undertaking because this very old cratonic sedimentary basin remains largely under-explored today. Two wells were drilled in the early seventies (1973–1974, Ouasa-1 & Abolag-1) and three in the recent years (2009–2013) in the northwestern part of the basin, but no economical discovery was made so far.

The present study focuses on two of the most recent exploration wells. They are located in the Adrar region, east of the city of Atar (Fig. 1), and are referred to as well A (western well) and B (eastern well).

The Adrar prospective area is characterized by a Proterozoic-Paleozoic sedimentary succession and a Proterozoic petroleum system (Fig. 1). The Meso-Proterozoic series is composed of the predominantly clastics sediments of the Char Group at the bottom overlain by the thick succession of dolomitic carbonates of the Atar Group. The Neo-Proterozoic series is composed of, from bottom to top, the thick Assabet sandstones, the Jebliat glacial deposits and the thick Teniagouri shales. The Paleozoic rocks are essentially clastics of Cambrian (Nouatil sandstones) to Devonian (Tenemouj sandstones) age.
Techniques to Understand Reservoirs Associated with Deepwater Sedimentological Processes, from Basin to Field Scale - A Case Study
Authors: Acevedo Andres , Madhoo Hamechan A , Khramtsov Artem , Noomee Lakkanaporn , Tetzlaff Daniel Matias
Published: May 2016

Over the last decade, there have been several discoveries of significant oil accumulations in deepwater reservoirs. With advances in research and the availability of high-resolution seismic data, their variability and complexity have been well documented. For hydrocarbon exploitation purposes, however, the industry lacks an integrated approach to interpret these reservoirs, using multiple domains, and efficiently consume the available data. This paper describes a series of innovative interrelated techniques, plus observations to help improve the understanding of these reservoir types at three scales:Basin scale: Stratigraphic forward modeling is a useful method to simulate regional geological processes. Using this technique a paleo-basin floor surface reconstructed from seismic can be used to set a series of simulations. By varying several parameters, such as water level and water/sediments coefficients, within a reasonable range of values and comparing results to observed data, plausible models are created. These, considered jointly, provide an integrated understanding of the uncertainty of the occurrence of observed features and sediment properties.Sequence scale: Sinuosity and stacking configurations are critical factors that control local channel-fill patterns. By using seismic sections along channels, coupled with seismic reconstruction, complex paleo-sequence geometries can be resolved. In our case a low-sinuosity channel was identified and a backstepping-fill pattern defined.Reservoir scale: The quantification of net-to-gross is critical in hydrocarbon exploitation. By using training grids and multipoint statistical methods a comprehensive facies model can be built. Training grids, based on fill patterns and channel geometry, are combined with probability properties to condition the overall stochastic distribution of facies. Additionally, uncertainties associated with this process are captured in an uncertainty workflow.

Integrating these three techniques leads to a better understanding of reservoir-critical factors. The above approach is proven by using a seismic dataset from Campos Basin, Brazil, which contains well-documented reservoirs originally deposited in a deepwater setting.

Introduction

Deepwater clastic sediments form important hydrocarbon reservoirs globally, for example the Atlantic margins of West Africa and Brazil (Weimer et al., 2000), and over the last decade there have been several significant discoveries in these provinces. However, with increasing insight into these deepwater reservoirs as a result of high-resolution seismic data and borehole imaging techniques, more complexities are being revealed than previously anticipated. Furthermore, with higher data volumes there is a growing need to integrate, both across data types and geoscience domains.
Using 4D Seismic Surveys and History Matching to Estimate Critical and Maximum Gas Saturation
Authors: Obidegwu Dennis Chinedu , Chassagne Romain Louis , Macbeth Colin
Published: May 2016

An approach is explored for estimating critical and maximum gas saturation using 4D seismic data from multiple surveys shot during gas exsolution and dissolution in a producing hydrocarbon reservoir. To guide this process, hydrocarbon gas properties and behaviour are studied, and their relation to the fluid-flow physics is understood using numerical simulation and seismic modelling. This understanding is then used to interpret observed seismic data, which has surveys repeated every 12 to 24 months, from a turbidite field in the United Kingdom Continental Shelf (UKCS). Furthermore, the field reservoir simulation model is then history matched to the production data and the gas saturation effects observed on the 4D seismic data. The 4D seismic response is a function of pressure changes, fluid (oil/water/gas) changes and noise. The effects of the gas mechanism are extracted from the seismic data based on its unique relationship to the seismic amplitudes. It is found that these changes can be represented by a binary model (presence or absence of gas) which enables the use of a logical objective function to compute the misfit between the observed data and simulated data, and thus guide the parameterisation process of the history matching exercise. This approach circumvents full physics modelling in a joint history matching workflow that includes conditioning to both production data and multiple time lapse seismic data. It is concluded that for seismic surveys repeated at intervals of six months or more, the gas saturation distribution during either liberation or dissolution exists at two fixed saturations defined by the critical and the maximum gas saturation. From analysing only the 4D seismic data, we find a low critical gas saturation and a maximum gas saturation that is relatively unconstrained. The history matching exercise also gives us similar low values for the critical gas saturation, and highlights the importance of the vertical permeability in getting an extensively corroborated model. This paper explores a direct link between 4D seismic and the fluid flow parameters, a link between the gas saturation distribution and seismic response, as well as a quantitative analysis using multiple 4D seismic surveys for history matching.
FLNG: Technological Breakthrough and Innovative Application of Existing Technologies
Authors: van der Velde Harry , Boekhorst Alexander
Published: May 2016

Shell, with a history in LNG spanning 50 years, has become the world's largest international oil company by equity LNG production with ownership in many liquefaction projects currently in operation or under construction. We believe that floating liquefied natural gas (FLNG) will write the next chapter in the history of the industry. Our FLNG journey started in the 1990s with early stage project development followed by further design work. FLNG technology allows for the production, liquefaction, storage and transfer of LNG at sea, as well as the ability to process and export liquefied petroleum gas (LPG) and condensate. This opens up new business opportunities for countries looking to develop their gas resources and bring more natural gas to market.

Shell's FLNG uses a range of proven technologies in innovative combinations. Examples include the internal turret – selected for its suitability to tie-back complex subsea systems and harsh meteocean conditions, a double wall substructure hosting the product storage tanks, processing equipment such as the absorption columns and main cryogenic heat exchangers that have been modified to allow them to operate efficiently under marine conditions and a system of specially designed cryogenic loading arms. The safety of the FLNG facility has been paramount during its design. The layout of the facility for example has been developed using rigorous process safety standards and evaluation through Quantative Risk Assessments. The layout includes open 20 meter safety gaps across the full width of the barge between the main processing modules and escape routes at both starboard and port side, as well as through the central alley.

Shell's final investment decision (FID) for Prelude in May 2011 was the world's first FID for a FLNG project. Shell is the operator of Prelude FLNG in a joint venture with INPEX (17.5%), KOGAS (10%) and OPIC (5%). The facility is built by a consortium of Technip and Samsung Heavy Industries (SHI), with the Goeje yard in South Korea being a key construction location.

Looking forward, Shell's FLNG philosophy is pursuing standardisation so that subsequent developments can become quicker and more cost effective. Shell has also developed a FLNG solution for leaner gas fields. The so called 'FLNG Lean' can be applied on fields with lean compositions and by optimizing liquid handling and storage facilities, FLNG Lean is able to achieve higher LNG production capacities.