bluuebunny/crossref_metadata_2025 huggingface dataset:
Microseismicity Mechanism Investigation of Stochastic Microcracks Rock Model and Application in Hydraulic Fracturing
Authors: Li Wenjing , Zhao Wenyang
Published: December 2014

For the studies on hydraulic fracturing (HF), reservoir formations with natural fractures and their interaction with hydraulic fractures are more concerned. Stochastic Microcracks Rock Model is the microscopic numerical geo-model, which applies the Monte Carlo simulation of stochastic microcracks using Distinct Element Method (DEM). This model compiled in dynamic modeling codes presents more realistic behavior of the rock formations. For characterizing rock mass, the microseismic events are wildly regarded as the indicators of shear slip, and for unconventional reservoir, the induced microseismicity (MS) by HF can be applied in creation more flowing paths to increase very low permeability. Therefore, it is essential to investigate the MS source mechanisms in the rock mass, and with the effect of pre-existing fractures. In this paper, a modified analytical model of microseismicity is derived and verified with numerical simulations coupling Discrete Element Method by Particle Flow Code (PFC3D). The results show that there are the correlation between shearing microseismic event and interaction between hydraulic fractures and natural fractures; and fracture fluid could also contribute to the shear failure during stimulation. This combined numerical modeling provides a unique alternative method for understanding the controlling factors of MS gen-eration and its effect on stimulation. In addition, microseismic events possess the potential to characterize the fracture geometry qualitatively, to evaluate the fluid behavior in fractured formation, to predict fracture propagation, and ultimately to optimize stimulation design.
Less is More: an Objective/Cost-Driven Approach to Reducing Uncertainty in the Appraisal of the Lam Reservoir, Central Yemen
Authors: Sellar Christopher , Zabalza Isabelle Amaya , Miguel Karina
Published: December 2014

This paper presents a cost versus knowledge-gained appraisal strategy for reducing uncertainty in a tight sandstone reservoir within a short timeframe. More uncertainty should not necessarily demand more data acquisition, rather an approach that focuses on answering the big questions first.

In the Shabwah Basin of central Yemen, sands from the Upper Jurassic Lam Member form fine-grained turbidite lobes. These tight sands, encountered while drilling to the Block S2 Basement reservoir, are currently undergoing appraisal as a potential unconventional oil resource. The presence of oil on surface correlates well with direct and indirect indications of natural fractures during drilling and wireline logging. In contrast, fluid sampling of thin hydrocarbon-bearing sands identified by magnetic resonance tools have so far been unsuccessful. Two possible production mechanisms have been identified in this sandstone reservoir: production from natural fractures and/or production from tight sands by hydraulic fracturing.

The carefully risked appraisal strategy will target the key reservoir uncertainties, productivity and production mechanism, using three kinds of well re-completions: testing production from a well with natural fractures (with or without frac’ing), frac’ing and flowing a well with hydrocarbon-bearing tight sands and, drilling a slanted sidetrack well to increase exposure to natural fractures, with or without frac’ing.

The appraisal approach is objective driven, not a wide-ranging data acquisition programme. There are many unknowns in the reservoir but this project focuses on reducing uncertainty efficiently by prioritising answers to the key objectives which are productivity and the production mechanism.

A decision-tree based appraisal strategy has been developed with clearly defined exit points to control the cost of appraisal versus the value of information gained from the re-completion and drilling activities. This innovative, business-driven approach to reservoir appraisal maximises early uncertainty reduction by the most cost effective methods and can be used as a model for appraisal and early development projects in the industry.

Introduction

The Lam Member is an appraisal target for a hydraulic fracture campaign in Block S2 Yemen. The exploitation of this poor quality reservoir faces many challenges, which are approached in a carefully risked way to maximise the value of information gained while minimising financial exposure to stakeholders.

Geological background

The Lam Member of the Madbi Formation was deposited within the Shabwah sector of the Sab’atayn Basin on the southern part of the Arabian Plate during the late Jurassic (Figure 1).
The Application of Very Large Numbers of Pseudo-Wells for Reservoir Characterisation
Authors: Connolly Patrick , Hughes Matthew
Published: December 2014

We describe a method to invert seismic data by matching to large numbers of pseudo-wells. Pseudo-well construction is based on lithofacies micro-layering constrained by a model for the vertical statistics. Elastic properties are derived from a rock physics model. We match either to single or multiple angle-stacks using synthetics based on extended elastic impedance. This is a joint inversion process as it simultaneously accounts for both elastic parameters and reservoir properties. Both localised means and standard deviations of reservoir properties are estimated.

We do not include priors for lateral statistics but instead we envisage this process forming the first step of a two stage workflow with the output providing constrains for geostatistical modelling in the second stage. With no constraints on lateral correlation the first stage can operate in 1D greatly decreasing computational requirements.

We show examples of application to two fields; one offshore Angola and the other offshore West of Shetlands. These demonstrate the quality of the algorithm which provides laterally stable results, high signal-to-noise modelling of the seismic and accurate blind well predictions.
A Novel Methodology for Estimation of In-Situ Relative Permeabilities from Wireline Formation Tester Data in an Abu Dhabi Carbonate Reservoir
Authors: Cig Koksal , Kristensen Morten , Thum Sebastian , Ayan Cosan , Mackay Eric , Elbekshi Amer , Naial Radwan
Published: December 2014

A multilayer carbonate reservoir, having medium to low permeabilities with distinctive oil-water contacts, is in an appraisal stage. Large data gathering including rigorous coring is underway in the field. It is identified that the slowest part of the data evaluation is generally SCAL analyses due to its laborious workflow. A new approach is proposed by introducing a wireline formation tester (WFT) multiphase flow analysis to obtain relative permeabilities. The WFT tool is commonly used in this field to measure pressures and collect samples. In this paper we present a novel methodology for estimating in-situ relative permeability curves with the help of available WFT multiphase flow data and its numerical optimization.

During drilling of a well the formation is exposed to mud filtrate invasion. The invasion displaces oil in the vicinity of the wellbore, much like a small water flooding experiment in the case of immiscible mud filtrate and formation fluid. A WFT sampling operation in a multiphase flow environment provides an opportunity for determining related properties by utilizing bottom-hole pressure and water-cut data. A numerical model replicates the mud filtrate invasion and sampling with reservoir properties and WFT tool geometry. The numerical simulation model consists of a proper definition of reservoir properties as well as WFT tool geometry, including size and shape of flow inlets, along with tool storage and fluid segregation effects. The model is embedded in an optimization workflow and relative permeability curves, damage skin and depth of mud filtrate invasion are then estimated by minimizing a misfit function between measured and modeled pressures and water-cuts. The relative permeability curves are parameterized using industry accepted models. The optimization workflow uses a distribution function of response parameters where the entire parameter range is included in the numerical runs, thus ensuring that a global optimum is found. Initial parameter estimates are determined from open hole logs, such as resistivity, dielectric, magnetic nuclear resonance and from pressure transient analysis.

The methodology developed in this paper is validated by application to a synthetic dataset with a known solution, and it is subsequently demonstrated on actual field data from a WFT sampling operation. The results of this paper demonstrate that it is possible to reliably estimate multiphase flow properties from WFT sampling data. The key contributions of this study are to show the capability of estimating a variety of multiphase flow properties from routine WFT cleanup data and to establish an automated approach, including a novel inversion methodology, to reduce the turnaround time.
New Frontiers for the Prevention Of Major Accidents and Catastrophic Oil Spill Release: a Successful Synergy of Consolidated Approaches and Innovative Methodologies to Enhance Oil Spill Preparedness and Emergency Response
Authors: Petrone A. , Scataglini L. , Buffagni M. , Aiello G. , Cianfanelli M. , Di Muzio D. , Borello L. , Sordini E. , Faraoni G. , Salvador C. , Giusto M. , Catalano R. , Cherubin P. , Antico L. , Bonuccelli M. , Bandini R.
Published: December 2014

The Oil and gas industry is a risky business: e&p activities have the potential to give rise to major accidents such as Blow Out events, as well as hydrocarbon leaks and also catastrophic pipeline/ riser release leading to fire and or explosion. These dramatic events can result in loss of human lives, severe pollution to the environment, damage to the asset and production disruption, and in additional to the emotional and ethical impact can seriously compromise company reputation.

On top of that, in recent years another critical challenge is posed by e&p activities in sensitive and hostile environment that represent the new frontier of development: in fact the increasing hydrocarbon demand pushes operators towards unconventional deposits and higher-risk and remote areas characterized by social and environmental sensitivities where the emergency response and the oil spill preparedness become particularly difficult.

This paper describes the successful synergy of some consolidated methodologies and new initiatives undertaken within our Company to foresee consequences of major accidents and enhance emergency response and oil spill preparedness in e&p operations: –a new procedure for the evaluation and prevention of the exposure to pollution of e&p wells that foresees the identification of exposure to pollution classes (High, Medium, Low EtP), for different typologies of wells;–the development of SMART GIS project, a web application to acquire data source information to support emergency management and oil spill preparedness;–the combination of in house Short Cut Model (SCM)iiiiii in BART tool for an expeditive estimation of Blow Out consequences;–the development of an expeditive semi-quantitative methodology to assess risk of release from pipeline combined with a Bow tie approach for the identification of preventive and recovery barriers to reduce frequency of hazardous event or mitigate their consequences.
Transition Zone Behaviour: The Measurement of Bounding and Scanning Relative Permeability and Capillary Pressure Curves at Reservoir Conditions for a Giant Carbonate Reservoir
Authors: Spearing M. C. , Abdou M. , Azagbaesuweli G. , Kalam M. Z.
Published: December 2014

Significant reserves are held in the transition zone of an Abu Dhabi carbonate reservoir, but uncertainty exists in how relative permeability (kr), capillary pressure (Pc) and residual saturations vary with initial water saturation throughout the column. A study has been undertaken to provide an improved understanding of the water flood recovery and remaining oil saturation distribution within the transition zone by better definition of the scanning kr and Pc curves. Primary drainage, and imbibition from irreducible water saturation were measured for both kr and Pc to provide the "bounding" data. Imbibition kr and Pc curves were then measured at three higher initial water saturations up to 0.60PV. The semi dynamic method was used for Pc measurements and steady state method for kr. All tests were performed with live reservoir fluids at full reservoir conditions with in-situ saturation monitoring (ISSM). Drainage curves are often measured in the laboratory with refined oil and then aged with live crude oil at Swirr. This may not truly reflect the reservoir wetting conditions and so in this study both the primary drainage kr and Pc measurements were performed with live reservoir crude oil. During the drainage tests an ageing period was allowed at each progressively higher oil saturation as new regions of the pore space were exposed to crude oil. Transition zones are typically modelled using curves that "scan" from the drainage curve origin to the imbibition curve as water saturation increases. Models typically show a distinct separation between the drainage and imbibition bounding curves, within which the scanning curves are located. The shape of the scanning curve is dependent on the model used and typically retains the characteristic shape of the bounding curve.

Results from this study showed:

little spread in the bounding curves with minimal "hysteresis space" for both the kr and Pc datasets. the water imbibition bounding curve to be of lower relative permeability than the water drainage bounding curve, contrary to many models. no clear relationship of remaining oil saturation to initial water saturation.

These results may have a significant impact on how the transition zone modelling is implemented for this carbonate reservoir. This study adds to the literature data set on a topic where few full reservoir condition laboratory measurements have been published.
Well Testing of Multiple High H2S Reservoirs in an Environmentally Sensitive Area Offshore Abu Dhabi
Authors: Al Ameri F. , Al Kindi M. A. , Kuramata H. , Watanabe Y. , Tominaga N.
Published: December 2014

In 2013, Abu Dhabi National Oil Company and Abu Dhabi Oil Co., Ltd. (Japan), ADNOC and ADOC hereafter, drilled an appraisal well in an environmentally sensitive area located offshore Abu Dhabi, tested three zones and abandoned the well successfully in accordance with ADNOC's requirements. Since the operations were carried out in a marine protected area known to contain significant ecological resources, special measures were put in place to ensure the protection of the area during well testing operations.

In the case that the liquid hydrocarbon was oil, it was planned to recover all oil to surge tanks and subsequently re-inject the oil to the reservoir after each test. Therefore, five surge tanks were prepared and flow lines and a re-injection pump were rigged up so that the liquid in the surge tank could be re-injected to the well via a Test Xmas Tree.

In the case that the liquid hydrocarbon was condensate, it was planned to burn the condensate with burner booms, once precautions had been taken to ensure the condensate would be fully burned without any fallout. A special burner which performs fallout-free and smokeless combustion of liquid hydrocarbons produced during well testing was also prepared.

Moreover, the reservoir fluid was sour and corrosive. Well testing operations included various data acquisitions including separator sampling, bottom hole sampling, gas analysis etc. The tests were carried out using a Surface Testing Tool designed by ADOC and approved by ADNOC, which enables tests to be carried out without nippling down the BOP.

This paper will summarize the various challenges, measures taken and lessons learnt during the well test in the stringent HSE regulations and complex conditions of such challenging environments.
The Use of New Technologies to Maximize Oil Production in a Viscous Oil Field in Arctic Environment: The Nikaitchuq Experience
Authors: Raniolo S. , Mancini S. , Vimercati S. , Gentil P. , Simeone D. , Buchanan A.
Published: December 2014

The paper presents the experience of an accurate reservoir Development and Management for a viscous oil field and its benefits in terms of production.

The Nikaitchuq field is located in the North Slope of Alaska. The production start up was in January 2011. The main hydrocarbon reservoir is a Cretaceous sedimentary series developed in a sand lobe environment within the Schrader Bluff formation. The structure is a monocline gently dipping to NE with a gross thickness of about 30-35 ft, the reservoir is composed by two main sand bodies. The oil presents different characteristics varying between 16°-19° API with associated viscosities in the range of 50-200 cP at reservoir conditions.

The oil quality and drilling pad constraints defined a development scheme consisting of a water-flood linedrive with horizontal producers and water injection wells located side by side. Different well designs for producer wells have been implemented in time: single horizontal trajectory undulating between the two sands bodies in counterphase with the related water injectors; fishbone design with main borehole in the lower sand and multiple branches in the upper sand; multilateral counter-phase design with extended reach undulating dual laterals. As a result of the multilateral campaign, well productivity doubled with respect to the average before the intervention.

A challenging horizontal reach/depth step-out ratio between 6.0 to 6.5 has been achieved, the lateral section lengths stand between 6,000 up to 18,000 ft. The completion string was equipped to provide the capability of integrating a complex reservoir monitoring plan including distribute temperature surveys, inflow control devices and polymer tracers. Nikaitchuq is a "Digital Oil Field" and a full set of monitoring activities are performed in real time from remote.

With the aim to maximize production a set of future actions have been established: Intrawell tracers campaign for a comprehensive understanding of reservoir communication; EOR technologies to improve sweep efficiency.

At present production is sustained by 23 producers and 18 injectors. The multilateral design is now standard practice for the remaining producers. Since the multilateral campaign started up the fieldwide production step-change was evident with a doubled oil rate in a six month timeframe.
Integrated Seismic Feasibility Workflow: Elastic Modeling Approach In A Complex Near Surface Area
Authors: Mattonelli V. , Brega F. , Buia M. , Ferla M.
Published: December 2014

The objective of this study is to assess the most appropriate seismic acquisition parameters and processing workflow in a complex near surface area characterized by presence of extreme topography, boulder-strewn canyons and shallow fracture systems. Proper simulation of this harsh topographic and geological environment, through an elastic modeling approach, is implemented into an integrated feasibility study to identify the main effects in the seismic response.

The consequent evaluation and analysis reproduce the main issues related to processing, useful to identify reliable acquisition template and processing key-steps able to support better imaging for explorative targets in the area. The scope of elastic modeling is to simulate the effect on seismic of a system of aligned fractures, areal scatterers and canyons, located in the near surface of the future survey area. Anisotropic elastic modeling was accomplished through a finite difference (FD) code, generating the possible seismic response in terms of vertical and horizontal components (P-wave and PS-wave seismic data). The parameters and the geophysical model, input to the modeling exercise, were defined on the basis of in-place data measurements and observations (logs, outcrops, vintage seismic, etc.).

Synthetic seismic was then carefully analyzed in order to infer considerations about the geophysical problem generated by such an environment, with particular attention to surface wave generation, scattered and mode converted energy, anisotropic behavior. Denoise tests were implemented in order to identify the most effective acquisition parameters and a possible future processing strategy. The integration of the achieved results demonstrated that seismic data and the quality signal are strongly affected by the presence of canyons, in terms of diffractions and scattering; the fracture system amplifies the noise in the data, increasing the scattering effect.

An appropriate acquisition template is then proposed to reduce the noise level in the recorded data. Processing steps are also recommended to face the geophysical issues in such surface and near-surface complexities.
Digital Architecture, Infrastructure and Cultural Development in the Information Age Using 3D Animated Video Manuals for Attracting, Engaging and Enriching Future Workforce
Authors: Sanakam Sreenivasa Rao
Published: December 2014

This paper discusses the practical use of information management in workplace safety concentrating on current and future generation work force technical and safety training, utilizing Multimedia, Social Media, Mobile Devices and Digital Technology. Impending baby boomer retirement is creating a need for younger workers. Organizations can use multimedia tools to develop younger workforce competency and to transfer knowledge across generations immediately. Animations appeal to a technologically savvy workforce, retain subject matter expertise within organizations, transfer technical information across generations of workers, convey industry best practices effectively and can do all of the above on a global basis in multiple languages. So continuous, informal and formal ongoing flexible education techniques in compliance, processes, mandatory, crisis response training procedures will help organizations build their employee competency through animated video manuals, interactive animations and educational gaming techniques. The combination of Industry experts or (SMEs) and accomplished technical animation designers allow organizations to develop safety and technical related information that is visually engaging, precise, cost effective and superior to other alternatives. Providing a format that allows for visual learning, that helps clearly demonstrate intricate and detailed steps that is readily accessible, can be utilized anywhere employees can carry combustion proof smart phones, tablets or a computer with access to Internet or downloadable apps. Adding evaluation techniques that assess the trainee knowledge improves understanding and accuracy. Employee engagement is enhanced with mobile/digital devices. With a finger click on subjects such as field guides, risk related decision support tools, industry best practices and procedures, lessons learned and pre-job/checklists, contextualized learning, augmented learning and simulations can be provided. Animations have the ability to withstand technology changes over time without costly redesign or reconfiguration and can be used in multiple applications to assess situations, identify hazards, recognize industrially accepted procedures and implement appropriate solutions to reduce human errors on critical tasks and critical elements. In conclusion 3D animated video manuals can provide effective and inexpensive tools for training technicians on protocols and safety rules, which include best practices to convey information from experience personnel and industry experts.
From a Standard to a More Rigorous Development Framework for Unconventional Reservoirs
Authors: Colombo I. , Spelta E. , Giamminonni D. , Russo S. D. , Rotelli F. , Rotondi M.
Published: December 2014

During the last years, oil Majors have been struggling trying to make the unconventional business profitable. Indeed, the strategy to build an unconventional portfolio by means of merges and acquisitions is not giving enough return of investment. This is mainly due to internal processes, which contrary to Independents, are customized on a very different business model.

In addition, it is becoming clear that unconventional resources cannot be considered and developed as "statistical" ones. Nowadays, several publications are stating that only a small percentage of fractured wells is generating positive return. Even though unconventional reservoirs are considered more complex than conventional ones, less efforts are unjustifiably applied for their understanding. Hence, there is a need to switch from a "drill baby drill" to a "more from less" approach. This implies to address several issues such as: a better understanding of shale gas production mechanism at nano-scale, sweet spots identification, proper fracture placement and treatment, realistic full field simulation of fractured wells.

This paper describes how seismic-reservoir integration, advanced production analysis, accurate nano-scale and 3D full field simulations may address the above issues and help oil Companies to be more efficient in developing their unconventional portfolio. This new approach, based on placing and fraccing wells only where needed, is already providing interesting results in mature plays like the Barnett Shale and will be even more crucial for sustainable unconventional developments outside US.
Integrated Surface Facilities Management: Continuous Production Optimization
Authors: Di Sarra Andrea , Scaramellini Sara , Cerri Paolo , Pellegrini Simone , Viadana Giorgio , Bianco Amalia , Buongiorno Nicola , Masi Silvia
Published: December 2014

Production Optimization is one of the most complex and multi-disciplinary task in the oil & gas industry from an operational point of view. Optimization involves surface asset all along its production life and requires a continuous improvement process. Improvements, modifications, and temporary upsets in surface facilities during operation phase create the necessity to manage and optimize production scenarios with a more tight time-frame.

Technology improvements have enabled a widespread use of integrated simulation models for a better asset management to be fully combined with measured field data. This paper shows a dedicated workflow for surface facilities – gathering system and process plant - production enhancement and management using an advanced optimization technique based on a biogenetic algorithm.

The main feature of the proposed workflow is the ability to control many variables simultaneously according to the system constraints even with complex, conflicting, and non-direct interconnections and objectives to be reached. The workflow and the optimization approach are included in a wider integrated tool for production management, called rabbit™ - Risked Algorithm for Biogenetical Balance Integration Tool. Other features of this tool, such as transient phenomena and risk analysis evaluations, complete the ability of the tool to support the production and operation management. This paper will provide a useful description of how the tool can contribute in definition of field potential, production optimization and planning, minimizing production losses during planned/unplanned upsets as well as supporting debottlenecking activities.

It will provide some case studies of rabbit™ implementations on different oil and gas fields, both on-shore and off-shore, showing benefits on using the integrated workflow.
Monitoring and Confirming Full Activation of Hole-Enlargement-While-Drilling (HEWD) Tool using MWD Real-Time Data. A process developed by the Operation Support Center.
Authors: Al-Saadi Murad , Khambete Shreepad , El-Masri Hassan , Day Tim , Al-Awadhi Farhaad Khaled , Al-Hussieny H. , Karim Hassan Abdul
Published: December 2014

An operator in the Middle East planned to drill and perform a hole-enlargement-while-drilling (HEWD) operation in hard carbonate formations with an unconfined compressive strength (UCS) between 20,000 and 35,000 psi [138 to 241 MPa]. The main concern from the operator was ensuring that the hydraulic reamer was fully activated while drilling ahead.

Downhole logging-while-drilling (LWD) tools that provide real-time caliper data cannot be run above the reamer because of the operational requirements of both the reamer and the LWD caliper tools. The reamer requires a small plastic ball to be dropped through the inside of the drillpipe to activate the reamer and, consequently, placing a real-time caliper tool above the reamer would prevent the ball from reaching the reamer. Additionally, such a configuration would prevent electrical signal communication between the LWD tool and the real-time data transmission available at the measurements-while-drilling (MWD) tool. Hence, it was not possible to use real-time LWD data to confirm the reamer activation, and an alternate method had to be developed.

A new process was developed to monitor and confirm the full pad activation of the reamer. When the reamer is not activated, then 100% of the flow passes through the reamer, MWD tool, and drill bit. However, when the reamer is activated, then 20% to 30% of the flow is diverted through the HEWD tool to open the pads and cool and lubricate the cutters. The process ensures activation of the underreamer using the relation between MWD turbine RPM and flow. Alarms built into the monitoring software are triggered under certain conditions to alert the system operator to the expanded or retracted state of the underreamer. The operator can quickly check flow conditions and make adjustments to change the state of the underreamer. The process was used to perform a successful HEWD run with a BHA that included a rotary steerable system (RSS), MWD tool, an underreamer, and a 14.5-in. drill bit. The BHA delivered a high-quality in-gauge borehole and met all directional objectives, holding tangent at 19° inclination and 94° azimuth.
Pipeline Internal Damage Prediction by Deterministic Models and Neural Networks
Authors: Gabetta G. , De Masi G. , Gentile M. , Vichi R. , Scapin M.
Published: December 2014

Internal corrosion is a crucial issue for the safe operation of oil&gas pipelines. Corrosion in pipelines is due to interaction of several mechanisms and parameters, as for instance: electrochemistry, water chemistry, protective scales, flow velocity, steel composition, localized bacteria attacks, and more. The phenomenon is very complex and despite the large number of models proposed in literature, rarely can be reproduced and/or predicted for fit for purpose estimates.

In this paper, available corrosion models were examined and compared with field case data. The need for implementation with more parameters was pointed out, and an attempt to define a comprehensive approach was pursued. An ideal model shall be able to describe the evolution of a corrosion situation in time and in space (along the pipeline).

Fluid velocity and flow regime as a function of pipeline length were taken into account, and available Water Wetting models were also implemented. Model results were compared and calibrated with intelligent pig inspection results, corrosion rate and thickness measurements. To a better understanding and a more accurate prediction of the phenomenon, the implementation of more sophisticated mathematical analysis tools (ANN, Artificial Neural Newtorks) was also suggested. A first case study shows that a ANN based model can outperform the deterministic ones.
Success Case History of Well Pressure Balance Estimation based on Gas Trend in Ultra HPHT Wells
Authors: Tanaka Hisaya , Stuart Colin , Vigor Herve
Published: December 2014

Reducing pore pressure (PP) uncertainties during exploratory drilling operations remains a challenge especially with limited offset information available. Estimation of a pore pressure range while drilling based on gas trend is a recommended method for managing mud weight and to estimate margin of overbalance. Drilled and swab kicks still occur in HPHT wells with alarming frequency. Much can be done to reduce the chances of this occurring and in this paper we discuss some recently applied mud weight management techniques. While Managed Pressure Drilling is a significant advance in managing bottom hole pressure, there are surface equipment limits, and complex operations management controls to be defined. Therefore, in many future HPHT projects conventional overbalanced drilling will still be required. While maintaining attention on PP estimation is the focus of this paper, experience shows that minimum MW for borehole stability can sometimes be overlooked in HPHT wells if the sole focus is on well control aspects.

In the following example HPHT wells where downhole temperature exceeded 400degF and downhole pressure exceeded 10,000psi, drilling operations were carried out successfully by applying well pressure balance estimation based on gas trends. The key points and recommendations for this method are introduced in this paper. In the case study, three examples of gas trend interpretations with example data are described.
Increasing Depth of Penetration by Electrokinetic Driven Low-Concentration Acid IOR in Abu Dhabi Tight Carbonate Reservoirs
Authors: Ansari Arsalan A. , Haroun Mohammed , Rahman Md Motiur , Chilingar George V.
Published: December 2014

Conventional acidizing, though useful in increasing the effective permeability in the near well-bore region, has compatibility and operational issues such as limitation in depth of penetration and HSE issues to handle, transport and injection of high concentration of acid into the well. On the other hand, the application of electrokinetics (EK) has a number of economic and environmental advantages such as reduced oil viscosity, reduced water-cut, and no depth limitation. This paper presents recent research that demonstrates the impact of EK on matrix acid stimulation in carbonate reservoirs with varying acid concentrations and voltage gradients.

Core-flood tests were conducted by saturating core-plugs retrieved from Abu Dhabi oilfields with medium and light crude oil in a specially designed core-flood setup. Initially, EK was applied using acids of varying concentrations up to 1.2% HCl injected at the anode to cathode (producer) at 0.25ml/min. Experiments were also repeated with low concentration HCl stimulation without the application of EK.

Several correlations related to acid concentration, displacement efficiency and permeability enhancement are presented here at ambient and reservoir conditions on aged oil-wet core-plugs. The experimental results have shown that the application of waterflooding on the carbonate cores yields an average oil recovery of 60%. An additional 17-29% oil recovery was enhanced by the application of EK-assisted low concentration HCl-IOR (EK LA-IOR). In addition, EK LA-IOR was shown to enhance the reservoir's permeability by 32% on average across the tested core-plugs. It was observed that low acid concentration with application of low voltage EK, recorded a maximum oil displacement of 81% at reservoir conditions. Furthermore, this technique can be engineered to be a sustainable process in the presence of EK as the concentration and voltage gradient can be optimized to reduce the amount of acid injected and power consumption by 20-41%, further improving economic feasibility.
Optimal Waterflood Voidage Management Significantly Increases Oil Recovery with Minimal Incremental Cost
Authors: Vittoratos E. Steven , Zhu Zhouyuan , West C. C.
Published: December 2014

Empirical data, laboratory experiments, and mathematical simulation methods indicate that for many heavy oil waterfloods the optimal voidage replacement ratio (VRR) is less than one. Many more recovery mechanisms are activated with VRR<1 than with VRR = 1. Some are readily understood with existing conventional reservoir engineering concepts, while others invoke emulsion & foamy oil multiphase flows that are activated under changing reservoir conditions. Not all the consequences of VRR<1 are positive for recovery. In aggregate, however, as displayed in empirical observations, VRR<1 can result in a significant increase in reservoir oil recovery, particularly for the heavier oils.

This paper focuses on the quantification of the relative importance of the mechanisms activated by VRR<1 in saturated or nearly saturated reservoirs. The absolute value of the VRR<1 depends primarily on the oil quality and its associated properties, whereas the optimal time evolution of the VRR depends on the well spacing and the reservoir heterogeneity of the depositional environment. Numerical simulations have ranged from simple 1D models to a detailed fluvial depositional environment model. The role of relative permeabilities are demonstrated by the 1D model. The 3D field models of increasing geological complexity are useful for quantifying the incomplete waterflood sweep, and the role of VRR < 1 in activating solution gas drive to deplete the ‘cul-de-sacs’ of bypassed oil. We also propose here a numerical model to incorporate emulsion flow behavior into heavy oil water flooding, calibrated using data from a large scale (‘big can’) experimental waterflooding study of a heavy oil prone to emulsion formation. The methodologies developed in this study show that for heterogeneous heavy oil reservoirs the incremental recovery expected from an optimized VRR < 1 process is similar to that of other commercial IOR processes such as polymer flooding, but with very little incremental cost.
Microporosity: Characterization, Distribution, and Influence on Oil Recovery
Authors: Fullmer Shawn M , Guidry Sean A , Gournay Jonas , Bowlin Emily , Ottinger Gary , Al Neyadi Abdulla , Gupta Gaurav , Gao Bo , Edwards Ewart
Published: December 2014

Microporosity is very common in limestone reservoirs globally and is especially significant in many large Mesozoic reservoirs in the Middle East. Despite its common occurrence there is:

Wide variation in its definition, Uncertainty around characterization, genetic controls, and distribution A rudimentary understanding of its influence on reservoir performance and hydrocarbon recovery.

The results of this study, based on a global survey of microporosity and specific Middle Eastern case studies, provide clarity on each of these topics.

One volumetrically significant type of microporosity occurs between micron size subhedral crystals of low magnesium calcite in matrix and within grains. This micro-pore system is very homogenous in terms of pore size distribution with 90% of pores between 1 and 3 microns in diameter. Pore throat radii range between 0.1 and 1.5 microns. Porosity, permeability, and capillarity relationships reflect this homogeneity for rocks dominated by microporosity. Rocks with less than approximately 80% microporosity exhibit a marked increase in pore system heterogeneity.

A pore geometry characterization approach incorporating digital image analyses of petrographic thin-sections was developed and provides a very effective means of rapidly characterizing and quantifying the total pore system, including microporosity.

The lateral and stratigraphic distribution of microporosity is systematically related to the distribution of depositional facies and the regional extent of burial diagenetic processes. Factors that inhibit burial diagenesis, such as hydrocarbon charge, also have a strong influence on the nature and distribution of microporosity.

Remaining oil saturation in microporous limestone, as measured from centrifuge capillary pressure and steady state (SS) core flood experiments, is negatively correlated with the percent fraction of microporosity. Due to the homogenous nature of the micro-pore system, rocks dominated by microporosity have more favorable oil recovery than rocks with mixed pore systems. In the specific cases studied here, water provides more favorable recovery than gas. These results have implications for resource assessment, field development planning and optimization of ultimate recovery in limestone reservoirs with significant microporosity.
Rotating Sand Screens to TD in Korchagina ERD wells
Authors: Valisevich A. , Zvyagin V. , Wilson K. , Bayanova A. , Shapovalov A. , Huseynov M. , Moen T. , Jaruga P. , Hansen S. , Hanley P.
Published: December 2014

To extend areal coverage for maximum reservoir contact from a single offshore platform, Korchagina oil field is developed with Extended Reach (ER) wells with MD up to 8km, TVD 1.5km. The main target of Korchagina field is Neokomian sandstone formation with large gas cap that necessitates field development with horizontal ICD sand screen completions to minimize early gas breakthrough.

In 2011 a task was set to work out set of solutions that would convey ICD sand screens to TD in Korchagina ER environment, with openhole coverage up to 5000m, and to design completion elements around these solutions.

At planning phase industry expertise – completion practices in projects operating in similar ER environment was reviewed, and existing to date technologies to complete ER wells were analyzed.

Existing technologies and practices did not provide sufficiently robust and flexible solutions for Korchagina ER environment. Hence, innovative solution was proposed – Rotating sand screens to TD, with contingency to run in stages if rotation limit is expected to be exceeded based on drilling results.

Further, design of completion equipment was reviewed to accommodate high torque and rotation capability: direct wrap sand screen media with proven sand retention performance in high torque; integral centralizers, to transfer rotational motion at contact points to reduce drag; high torque connections. Paper discusses in details the solutions proposed and design of completion equipment.

In 2 years 11 ERD wells were completed with TD reaching 7996m MD at 1565m TVD and openhole coverage up to 4700m. Of these 11 wells, in 3 wells actual friction factors came low enough to allow completion run conventionally, in 8 wells rotation was required at 800m-3000m off TD. The results are presented in the paper.

Based on successful results of application, rotation is set as requirement for completion design for all the wells of current Korchagina field.
Journey of a Technology from Lab to Readiness for Field Application: Enzymatic CaCO3 - A Novel, Environment-friendly System for Conformance and Sand Consolidation
Authors: Bansal B. , Morkved M. , Javadi M. S. , Dorthe P. , Monberg J. , Bähring S. , Nielsen T.
Published: December 2014

Long horizontal wells are hydraulically fractured or acid stimulated to economically develop chalk reservoirs in the North Sea. To separate the zones and ensure conformance, each fracture or zone is separated by isolation packers and flow is controlled with a sliding sleeve. With time, conformance control capability of the lower completion may be lost if the sliding sleeve is stuck open or holes are eroded or corroded in the lower tubing. If a shortcut has developed between an injector and producer, either during stimulation or operation of the well, the consequence of losing conformance capability of the lower completion is more severe. Another scenario with serious consequences occurs when the well has been hydraulically fractured with proppant and the proppant is back-produced without a possibility to close off the zone.

To mechanically fix this conformance issue, it would require working over the well and replacing the lower completion. In an old (30-40 years) well, this is a challenge. A better solution is to solve the problem chemically by consolidating the sand in the fracture or plugging the fracture connecting the injector and producer. Recovery from the reservoir will then be optimized and the solution is likely to be cheaper than working over the well.

Enzymatic CaCO3 technology is a novel chemical system that can be used for plugging fractures and consolidates sand in propped fractures in horizontal wells. All chemicals used offshore in the North Sea need to be compliant with OSPAR regulations; the Enzymatic CaCO3 system is classified as environment-friendly. It also has predictable chemistry and is completely reversible. This paper discusses the process of maturing the technology from concept to readiness for field implementation covering lab testing, IP protection, chemical procurement strategies, environmental impact evaluation, and quality assurance process during field application.
Dolomitization of the Lacustrine Carbonates of the Toca Fm. (Kambala Field, Offshore Cabinda) and Quantitative Diagenetic Modeling
Authors: Frixa Alfredo , Maragliulo Chiara , Consonni Alberto , Ortenzi Andrea
Published: December 2014

Hydrothermal dolomitization is one of the main diagenetic processes potentially affecting the petrophysical characteristics of carbonate reservoir rocks.

It's effect on Barremian lacustrine carbonates of Upper and Lower Toca Formations has been investigated through an integrated diagenetic study and simulated through a quantitative diagenetic modeling (RTM TOUGHREACT software), in order to understand the behavior of dolomitizating fluids in the carbonate reservoir rock. This approach is also useful in carbonate marine contexts.

Among the analyzed core samples, the best reservoir facies are represented by coarse Mollusk Coquina limestone and hydrothermal dolomite, which is the subject of this study.

Two types of dolomite have been recognized. A finely crystalline, likely early diagenetic dolomite, shows low reservoir properties, and a coarsely crystalline, likely late diagenetic zebra dolomite, with very good reservoir properties.

Dolomitisation is associated with strong silica precipitation in the Upper Toca Formation, pointed out by mineralogical and chemical analyses that also document, the presence of detrital palygorskite, typical of lacustrine environments under arid conditions and, in the Lower Toca Formation, of talc replacing ooids and indicating strong hydrothermal conditions.

The integration of different investigation techniques allowed to hypothesize a mechanism of dolomitization by hypersaline fluids probably mixed with modified hypersaline and fresh waters, interacting with crustal rocks, as pointed out by Strontium isotope analysis. High homogenization temperatures registered in fluid inclusions (100 to 140 °C) could be due to crustal thinning, while the hypersaline fluids (20 to 25 NaCl eq. %) could be migrated from the Aptian Loeme Fm. salt or be originally present in the deep water lake sediments.

The RTM TOUGHREACT software simulations pointed out that an important control on the results is exercised by the permeability field of the rocks. Dolomitization is directly proportional to the flow intensity, while temperature seems to exert less influence. From the sensitivity analysis water composition is very important for the process.