bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Model for the Accurate Prediction of Critical Liquid Removal Based on Energy Balance
Authors: Tan Xiao-Hua , Li Xiao-Ping , Liu Jian-Yi , Zhao Jia-Hui , Zhang Ji-Qiang , Tang Chuan
Published: February 2015

In order to selecting artificial lift technologies and optimizing technology parameters, the critical gas velocity and flow rate for liquid removal are important reference indexes. The conventional models of critical gas rate proposed by several scholars are obtained by stress analysis of droplets in a wellbore and subsequent empirical adjustment. Due to different empirical parameters adopted, there are tremendous variances among different model's predictions. Based on the balance relation between total droplet surface energy and gas turbulent kinetic energy, a new model without empirical parameters is proposed in this paper which adopts Turner's basic concepts, while taking into account influence of droplet diameter. Considering that the gas flow influences the diameter of droplets carried by gas, sequentially influences the efficiency of liquid removal, the new model achieves the purpose of accurately predicting the critical gas velocity and rate by calculating the droplet diameter. By comparison of case calculations using different conventional models, we find out that each model can only accurately distinguish the liquid loading situation of gas wells in a given range of liquid production rate. This explains the reason of the differences among critical gas rates calculated by different models. Well data from Li's paper are used to verify the proposed model; the distinguishing results of the new model are coincidence with the field data. In addition, the predictions of Turner's, Coleman's, Li's and the proposed model are compared with the well data collected from four gas reservoirs in China. In high production gas/water ratio (GWR > 1×104m3/m3) conditions, the deviation of the predictions of Turner's and Coleman's model is higher; in low production GWR (GWR < 1×104m3/m3) conditions, the deviation of the predictions of Li's model is higher. However, good agreement between the new model's predictions and the actual field situations is obtained in different GWR conditions. The result shows that the proposed model is superior to three former empirical models, and has the characteristics of strong adaptability and high accuracy. The new model of the critical gas velocity and flow rate for liquid removal proposed in this paper can accurately distinguish whether the gas well is liquid loading.
Chemical EOR Produced Water Management at Malay Basin Field
Authors: Najamudin Khairul Ezani , Halim Nor Hadhirah , Salleh Intan Khalida , Chai Ching Hsia Ivy , Yusof M Yusri , Sedaralit M Faizal
Published: February 2015

This paper examines the requirements, mechanisms and mitigation options for management of produced water from chemical EOR field. As the application of Chemical EOR at Angsi field, the produced water is expected to contain some levels of injected chemicals such as surfactant and polymer.

A key concern is the potential impacts on marine environment in which current field facilities design is not cater for the produced chemicals management. A detail laboratory studies were conducted such as toxicity assessment on local marine fish, grouper indicated the polymer is practically nontoxic with LC50>500 mg/L, and the surfactant is relatively toxic with LC50=1.23 mg/L. The polymer also poses significant environmental concern as it has low biodegradation property with less than 20% are biodegradable in 28 days.

Complicating this situation, alterations of produced fluids physical and chemical properties are also demonstrated. Laboratory analyses of ASP produced fluids predicted higher fluids viscosities, with stable and higher emulsion formed (increment up to 40%) which contributed to higher basic sediments and water (BS&W) percentage. Even minimal scale issues is predicted, mentioned conditions had already contributed significant impact on existing facilities and chemical dosage efficiency and requirements.

The complexities in the conditions render managing ASP breakthrough required defined EOR produced fluid management. In view of current facilities limitations, the study was focused in identifying suitable chemicals and mechanicals mitigation options to treat and manage surfactant and polymer residues toward Angsi Chemical EOR implementation. Recommended solutions were based on laboratory studies, current facilities configuration, technical and regulatory acceptance and economic viability as the actual impacts varied depending on fluids composition and characteristic of the receiving environment.
Fatigue Analysis of OCTG Premium Connections: Theory, Laboratory Testing and Application
Authors: Jordan G. Rodriguez , Merliahmad M. , Grittini S. , Mazzaferro G.
Published: February 2015

The paper describes the additional design considerations on top of standard design criteria for casing or tubing strings when subjected to cyclic loads. In addition, this paper chronicles comprehensive laboratory testing programs that have been carried out to analyze and quantify the fatigue limit of various semi-premium and premium connections.

OCTG connections are being increasingly used in drilling environments as an alternative to conventional drill pipe. Furthermore, OCTGs are commonly rotated into place in horizontal and ERD wells. During the drilling and running of OCTG in deviated sections, the combination of the resultant bending of the string and its rotation generate alternating stresses in the pipe body and connections, creating the conditions for potential fatigue damage.

OCTG connections are not as fatigue resistant as tool joints due to its inherent design. Fatigue is a complex process that affects mechanical components that are subjected to cyclic loads. Fatigue failure is a sudden crack, but it comes from a process that involves different development phases until the failure of the component becomes evident; this failure is produced at stress levels far below the static elastic limit of the material. Several factors present in OCTG connections applications including mean stress, stress range, make-up torque, and material grades have been introduced in the full scale testing programs. As a result, robust fatigue life limit curves, used for real cases fatigue analyses, have been developed and are presented in this paper.

Since fatigue damage could lead to the failure of the string based on its weakest link, which in general terms would predominantly be the connections, its resistance to cyclic loading must be thoroughly considered to understand the performance limitations this may impose on the entire drilling assembly.
Kinetic Hydrate Inhibitor Removal by Physical, Chemical and Biological Processes
Authors: Adham Samer , Gharfeh Samir , Hussain Altaf , Minier-Matar Joel , Janson Arnold
Published: February 2015

Hydrate formation is a major flow assurance issue in the production of oil and gas fields. Kinetic hydrate inhibitors (KHI) act as anti-nucleating agents and delay the formation of gas hydrates. These chemicals are more economical than the thermodynamic inhibitors and are added at a low dosage without disturbing the pipeline flow. Globally, different proprietary KHI compounds are used; one type of KHI was investigated in the present work. Considering that produced water containing KHI may have negative impact on the environment and reservoir permeability, efficient treatment solutions to remove KHI are needed. The objective of our investigation was to assess various physical, chemical and biological treatment methods for KHI removal. These methods included membranes, heated centrifugation, advanced oxidation and membrane bioreactors. On a lab scale, KHI removal efficiencies were > 99.9 % and 83% for nanofiltration and ultrafiltration respectively. Heated centrifugation removed 40% and oxidation degraded more than 70% of KHI polymer. Biotreatment efficiently degraded about 70% of KHI when added at 1.5% to brine. To check the effectiveness of each process, the treated KHI solutions were eluted through crushed Sulaiy core for deposition/interaction studies. Three criteria were used to verify the effect on the treated effluent: cloud point, particle size and interaction with the crushed core. The desired values for the treated effluent included a cloud point > 65ºC, a particle size less than 0.5 micron, and a retention magnitude of less than 10% of the polymer on the crushed core. To the authors' knowledge, this is the first work reported in the literature regarding KHI removal using some of these processes. The treatment processes have great potential when implemented by the oil & gas industry for environmental and operational sustainability.
Gas Hydrates Extraction by Swapping-Depressurisation Method
Authors: Gupta Ankit , Aggarwal Avi
Published: February 2015

Gas Hydrate, one of the unexplored domains in the energy sector has a vast potential to quench the future energy demands. Depressurization, Thermal Stimulation, Carbon swapping and Inhibitor injection are a few processes involved in its production. These techniques are environmentally degrading as uncontrolled dissociation of Gas Hydrates takes place. The paper focuses on an unexplored but a sustainable technique to extract gas hydrates. When depressurization along with CO2 swapping methods are used simultaneously in two adjacent wells, then these both methods results in a continuous flow of CH4 in both wells through surface and sub-surface reservoir. They acts as counterparts of each other and diminishes each other's limitations that are being faced when used individually. So, this method could be a future technique to efficiently and economically extract methane from its clathrate. The paper also discusses the well modeling required to implement this technique and simultaneously increasing the amount of methane hydrates exposed, overcoming the permeability issues by using Depressurization method along with CO2swapping through injectors and producers creating a continuous cyclic process of swapping and production. In the proposed method, two adjacent wells are used as producer and injector well, at injector swapping method is employed and at producer well depressurization method is employed. Relevant issues along with well modeling and advantages are also discussed in the paper.
Use of Sequential Downtime Analysis in Planning Offshore Operations
Authors: Ballard E. , Evans M.
Published: February 2015

A sequential downtime analysis method is presented, which is applied to the prediction of the expected duration of a typical offshore installation campaign made up of a series of tasks. Accounting for typical limiting sea states for each step of the installation sequence, it is shown how a sequential downtime analysis using a hindcast metocean time series can be used to estimate the likely duration to complete the series of tasks.

The analysis is based on typical stages in the installation of an FPSO mooring and riser system, including set-up before and re-positioning between tasks, combined with multi-year hindcast metocean data. Each task has a set of limiting sea states associated with it, as well as an expected duration and the likely variation in the duration due to delays. The effect of delays in each task on the duration of the complete sequence of operations is accounted for by a Monte Carlo type method.

The results of the analysis show that a sequential downtime analysis can be used in a number of ways to optimise an offshore installation campaign. Firstly, it can identify the best times of the year at a particular site for wave conditions which will minimise weather related delays. Secondly, by correctly accounting for realistic variations in the duration of each task due to delays, the potential total duration of the offshore operation can be more accurately estimated, along with likely costs. Finally, examples will be presented of how this analysis technique can be used to test the economics of employing more expensive equipment and/or vessels with improved capabilities to increase the limiting wave conditions for particular operations, thereby reducing total cost.

The methods presented in the paper are considered to represent a significant improvement over typical methods for planning and costing offshore operations. By allowing the likelihood and magnitude of potential delays to be better quantified, informed decisions on the potential benefits of using more capable vessels and/or equipment can be made and costs connected to the duration of the operation better predicted.
Finite Element Approach to Predict the Effect of Annular Pressure Buildup on Wellbore Materials
Authors: Jandhyala Siva Rama Krishna , Chiney Abhinandan
Published: February 2015

Annular pressure build up (APB) is caused by thermal expansion of wellbore fluid enclosed in an annulus experiencing cyclic thermal loads due to production and injection. This may lead to significant damage to the cement sheath causing zonal isolation issues and may also cause casing collapse/burst. This work focuses on using an engineered approach based on finite element modeling to analyze the cement sheath response to APB loads for the life of the well. Actual field data of pressure build up and bleeding rates are used in our analysis.

The present study provides a methodology to analyze cement systems for their ability to survive APB conditions. A proper knowledge of response of wellbore materials (cement and casing) to APB can be helpful in design of better cement systems and in selection of appropriate casing materials which can withstand the APB conditions.

It has been observed from our comparative study of two cement systems that the stresses in the elastic cement are less than those in conventional cement. A parametric study has also been performed to analyze the effect of different cement properties. The results are quantified in terms of stresses experienced by cement sheath and casing.

This study is based on fundamental principles of structural mechanics, thus providing more reliable predictions. It helps in deciding the appropriate cement system for a predetermined production/injection rate or can give a recommendation of production/injection rates for a given cement system such that damage to the cement sheath can be avoided.
Foundation Integrity: Shallow Gas Mitigation Using the XPP Monitoring Tool - An Offshore Malaysia Case History
Authors: M.J. Rohani , A.R. Azam , T. Lunne , J.M. Strout
Published: February 2015

Gas migration along wells from reservoir formations to shallow sub-seabed strata was identified to occur at a field, offshore Malaysia. Since 1993 numerous shallow gas kick events had occurred in the vicinity of the platform designated in this paper as Platform DB, at gas charged layers of 60m and 90m below mudline. The occurrence of shallow gas kicks is a concern as it relates to the development of excess pore water pressure in soil which in turn can potentially impose detrimental effect to foundation integrity.

Due to the dynamic nature of shallow gas migration at various depths around the subject platform, the foundation integrity of the platform complexes needs to be monitored to ensure that possible progressive increase in excess pore pressure can be identified and reduced to maintain foundation integrity.

This paper describes the efforts undertaken by Petronas Carigali Sdn Bhd (PCSB) to install the XPP@TM monitoring tool to measure the magnitude of the excess pore pressures. This paper also discusses the studies undertaken to understand the extend of the shallow gas migration and the mitigation plans that are put in place to monitor the foundation integrity at the designated Platform DB. Equipment design and operational procedures are also presented to record the efforts undertaken by PCSB engineers to ensure that XPP@TM Monitoring Tool is robust and fit for purpose.
An Experimental Study on Vertical Oil Storage System
Authors: Cai Zhonghua , Wang Jin , Li Zhe , Wang Deyu
Published: February 2015

A new vertical oil storage system based on oil-water exchange method for a deepwater floating production system was investigated experimentally. The system mainly consists of a storage tank, water tank, upper tank, lower tank, oil pumps and pipes. Two kinds of oils (light oil and heavy oil) were investigated in the experiment. 12 oil/water exchange tests and 18 dynamic tests were carried out. The Oil/water exchange test simulates oil-water exchange progress. A special oil/water separation device was designed to separate stored oil from the water by the use of density difference between oil and water. The oil content in the discharged water at different locations was measured in terms of PPM. The cycle time of oil/water exchanges was also investigated. The aim of the dynamic test is to find out if there is significant disturbance or sloshing at the oil/water interface due the motion of the floater. The storage tank was placed on the 3-DOF sloshing equipment. Sloshing tests were done for 50% and 75% filling level. During the experiment, the oil/water separation device was set on the oil/water interface to reduce the disturbance.

Main finding from the experiment are:The oil content of in the discharged water is less than 50ppm, which meet the oily wastewater discharge standards of offshore petroleum development industry (GB 4914-85).Compared with light oil, the oil content in the water seems larger for the heavy oil in the oil/water exchange tests.The device of upper and lower tanks can reduce the oil content in the water.In the dynamic tests, no matter there is oil/water separation box or not, there is no significant disturbance at the oil/water interface.
Ultimate Gas Recovery by Use of Full Field Simulations in Concept Selection Phase
Authors: Irmann-Jacobsen Tine Bauck , Headridge Barry
Published: February 2015

This paper presents a simulator that has been developed for the full production system from reservoir to receiving facilities including a subsea boosting station. Thus, the simulator provides a powerful tool to screen design alternatives to identify the optimal field solution in a cost efficient way at an early stage. The objective of the screening is to expose the system to all possible operational scenarios over the life of field so as to answer technical feasibility, maximum recovery and select the optimal business case.

Deeper water, longer flowlines and the demand for increased recovery have lead to the development of more complex subsea systems. A " right design first time" strategy has great impact on the subsequent phases in terms of implementation and cost. Early phase selection is particularly challenging when a Subsea Boosting Process is introduced in a large network of wells and flow-lines. The physical parameters that affect the solution increase in numbers which means increased uncertainty and risk. When evaluating the use of subsea processing on an existing or a new field, it is of crucial importance to investigate how the process will perform in the total production system from reservoir to topside.

The simulator gives the opportunity to efficiently investigate huge amounts of data and parameters. For any possible combinations of input parameters and production targets, bottlenecks in the system are revealed and challenged. Thus, all design elements that affect the conditions upstream and downstream the gas compression station are considered. The simulator uses mechanistic field proven models for all flow components (wells, pipelines and process equipment) giving realistic system responses. If a system is designed to work in balance with the natural system responses from the beginning, complicated process control can be minimized.

In this paper, optimal Subsea Gas Compression design simulation results for specific fields are presented. In addition is shown how Flow Assurance strategies for hydrate and liquid management are integrated as a part of the total system design. It is shown that using a full field simulator in the concept selection phase ensures robust and optimized field design.
An Integrated Sediment Mobility and Scour Assessment: Characterisation, Calibration and Mitigation Studies for a Pipeline in the South China Sea
Authors: O'Leary L. , Spinewine B. , Haneberg W. , Clare M. , Thomas S. , Wu H.
Published: February 2015

We present an export pipeline case study in the South China Sea in water depths between 200 m and 600 m. Several types of sediment bedforms and variations in seabed roughness were identified at seafloor; hence the requirement for a sediment mobility assessment. Data types acquired include seafloor and sub-bottom geophysical data, geotechnical samples, in situ tests, geological analyses, hydrological testing and metocean measurements. The outcome of the testing determined sections of pipelines requiring burial.

A phased approach was taken from a qualitative, geomorphological assessment, to a quantitative determination of a morphological baseline. This approach is applicable to scour assessment for cable, pipeline routes and other seafloor structures and ensures that unnecessary effort is not wasted at early stages of assessment.

A review was initially performed of regional present day and past metocean regimes and a geomorphological assessment of features characteristic of sediment mobility. A geometrical characterisation identified the superposition of small, younger bedforms on megaripples. A targeted sampling programme acquired cores for detailed sedimentological and geochronological analysis to validate these interpretations. Critical shear stress values for mobility were determined from theoretical relationships (classical Shields curve) and from erosion function apparatus (EFA) testing performed in the laboratory on site-specific samples. The local sediment flow conditions were plotted on bedform regime diagrams for oceanic flows identifying that not all of the observed bedforms could be considered in equilibrium under present day near-bed current conditions. A predictive relationship for bedload sediment transport was used to assess sediment transport rates over the bedforms. An active bedform field was identified, with predicted migration rates of up to 1.8 m during one year extreme background conditions. This was mitigated by using a spectral decomposition approach to identify the amplitudes of mobile versus immobile bedforms and obtain probabilistic estimates of a morphological baseline.

Assessments of sediment mobility and scour need to be geologically credible, temporally relevant, and well calibrated. An assessment of sediment mobility from just one of the methods may provide either over- or under-conservative design solutions. This study demonstrates the importance of full integration and the added benefit of inputs from multiple different disciplines.
Two degrees of freedom CFD Simulation of Vortex Induced Vibration of Two Circular Cylinder in Tandem Arrangements
Authors: Jamei S. , Maimun A. , Ghazanfari S.A. , Tofa M. , Ahmed Y.M.
Published: February 2015

Many researchers have studied on the flow around a steel riser for the vibration and fatigue analyses that are the principal challenges in riser design and fabrication. It is a demand to enhance our knowledge about vortex-induced vibration effects (VIV) on the risers in deep-water for oil extraction.

VIV is the main factor to predict the long life of the risers. In this study, the fatigue estimation of steel riser in deep water will be numerically investigated, and then design parametric study respect to some design parameter such as mass ratio and aspect ratio of riser will be done.

The motion of the riser and flow pattern around it will be examined in detail. This fluid structure interaction (FSI) problem will be solved by commercial code ANSYS. Reynolds-averaged Navier-Stokes equations (RANS) and some turbulent models will be employed in computational fluid dynamics (CFD) for force calculation and finite element (FM) method will be used for structural analysis. For validation purpose, the numerical results will be compared with other research works. Next, the effect of design parameter on vibration and fatigue life of steel riser will be explored.

Hopefully, new findings of the current study can be useful for riser research and design.
Short-Term Variability of Wind Measurements in South China Sea
Authors: Muyau Joel , Ewans Kevin , Jonathan Philip
Published: February 2015

Good understanding of the wind characteristics is essential in offshore structural design and operational activities. The short-term variability of wind is captured in design codes with prescribed forms for the wind spectrum and for the ratio of mean wind speed maxima for given durations to the one hour mean. Relationships are also prescribed for scaling these wind speeds between different elevations, essentially defining the wind profile in the turbulent boundary layer. All of these are based largely on measurements made in mid-latitude regions during extra-tropical storms or hurricanes; but these measurements will not be representative of the wind field during squalls, which are not stationary, and possibly not representative of the wind field during general monsoonal conditions. Several years of continuous recordings of wind speed and direction, sampled at 1Hz, at several South China Sea locations allow us to examine the short-term variability of wind in squalls and monsoonal conditions, and allow comparison with expressions given in design codes. We investigate the variability of the stationarity of the winds, the wind spectrum, the mean wind speed, and the wind profile, for the South China Sea measurements. The premise for the short-term variability prescriptions is that the wind field is stationary. Accordingly, we first report our evaluation of this assumption, and based on this, our evaluation of the relevance of the various prescriptions in the codes for describing short-term variability is developed.
Improved Numerical Simulation for Shale Gas Reservoirs
Authors: Guo Chaohua , Wei Mingzhen , Chen Haowei , He Xiaoming , Bai Baojun
Published: February 2015

Producing gas from shale strata has become an increasingly important factor to secure energy over recent years for the considerable volume of natural gas stored. Unlike conventional gas reservoirs, gas transports in shale reservoir is a complex process. In the organic nano pores, slippage effect, gas diffusion along the wall, viscous flow due to pressure gradient, and desorption from Kerogen coexist. In the micro fractures, there exists viscous flow and slippage. Also, with pressure depletion, gas viscosity will decrease. The porosity will increase when the gas desorbs from the pore wall. However, factors such as viscosity decrease and porosity increase have not received enough attention in existing mathematical models. It is important to construct a unified model considering all known mechanisms.

In this paper, based on dual porosity continuum media, mass balance equations in matrix and fracture were constructed using dusty gas model. In the matrix, Knudsen diffusion, Fick diffusion and viscous flow were considered. Gas desorption was characterized by Langmuir isothermal equation. In the fracture, Forchheimer flow was considered. Porosity increase was calculated by the equivalent volume increase due to gas desorption from the pore wall. Gas viscosity was characterized as a function of Knudsen number. Later, equivalent integral weak forms were derived based on constant pressure boundary. And model got solved using finite element method. Finally sensitive factors of shale gas production were analyzed. The results show that considering gas viscosity change increases cumulative gas production by nearly 12% under given reservoir conditions. Considering porosity increase will obtain higher production than without. The matrix and fracture permeability increase with time during production. Ignoring one of these factors such as Knudsen diffusion, slippage effect, desorption, viscosity decrease and porosity increase will obtain less cumulative production. For more accurate shale gas production prediction, it is crucial to incorporate these factors into the model.
Centrifuge Model Study on Vertical Pullout Behavior of Square Plate Anchors in Normally Consolidated Clay
Authors: Chen J. , Tho K.K. , Leung C.F. , Chow Y.K.
Published: February 2015

As oil and gas extraction has reached increasingly deep water in recent years, floating platforms are now more widely used than conventional facilities. The mooring of floating systems can be problematic since significant vertical loading is imparted to the foundation systems. Consequently many different types of anchors have been developed to resist the pullout forces, and compared with conventional anchors SEPLA (suction embedded plate anchor) is more widely used because of its lower cost and shorter installation time.

The vertical uplift capacity of plate anchors has been studied extensively. However most of the studies were based on theoretical and numerical analysis or tests in 1g conditions. In the present paper, 50g and 100g centrifuge model tests are performed to analyze the pull-out behavior of plate anchors in normally consolidated soft clay and the soil flow mechanism during the uplift process.

The anchor is idealized as square in shape. Load-displacement curves and vertical pullout capacity are obtained in a series of wish-in-place tests. The contributing factors are also examined, with special attention paid on the anchor embedment ratio (H/B). Half-anchor tests are performed to study the soil movement patterns surrounding the anchor during the uplifting process, by using PIV (particle image velocity) method and the close range photogrammetry technique. Results are presented in the form of capacity factor (Nc) and are also compared with previous numerical and empirical solutions. Full-flow mechanism (soil flows around the anchor with local failure in shear) is observed in the half-anchor tests.

This study with centrifuge model test provides insightful information on the uplifting pullout capacity of plate anchors as a part of foundation systems of floating platforms, as well as the flow and failure mechanism of surrounding soil.
CO2 Separation from Natural Gas Through Hydrate Formation
Authors: Onn M.S. , Seman A.A. , Kassim Z. , Esa M.A.
Published: February 2015

Presently, the major factor hindering the monetization of high carbon dioxide gas field is the high capital cost for the Acid Gas Removal System (AGRS). Several technologies have been evaluated by the industry so far including the membrane system and phase separation system such as cryogenic distillation. Based on the previous studies on Integrated Coal Gassification Combined Cycle (IGCC), a new model of carbon dioxide removal through the formation of carbon dioxide hydrate is proposed. The concept capitalized on the difference in the phase equilibria of carbon dioxide and the rest of the gas making up natural gas component such as methane, nitrogen and butane. Using this concept, the operating parameters are chosen to be in region of thermodynamic equilibrium of carbon dioxide, while at the same being in the hydrate dissociation region of other gas components by varying the pressure and temperature. The selectivity of carbon dioxide as the main guest molecule for the hydrate encapsulation is further promoted via the optimization of thermodynamic and kinetic properties, including the solubility of carbon dioxide in water and increasing carbon dioxide hydrate formation rate via the optimization of hydrodynamic properties. These variables are assessed in the continuous bench scale where hydrate slurries are formed in the tank reactor, and upon separation from the unreacted gas, is dissociated as the carbon dioxide rich stream. The performance indicator of the system is the amount of the carbon dioxide captured in the outlet stream compared to the feed gas. The paper discussed the separation system and its trending with operating parameters.
CO2 Removal from Natural Gas Using Membrane Contactor
Authors: Chan Zhe Phak , M Yusop Nurida , Abai Mahpuzah , M Shariff Shahidah , Ishak M Adaham
Published: February 2015

CO2 is one of the major contaminants in natural gas streams. Its removal from the natural gas stream is necessary prior to entering downstream units of the gas processing plants due to Health, Safety and Environment (HSE) concern, heating value specification, as well as plant and pipeline corrosion issues. CO2 is conventionally removed using acid gas absorption tower and membrane technologies. Application of these technologies in offshore facilities requires high capital and operating expenses, and large foot print.

The potential reduction in both capital investment and equipment footprint has made membrane contactor technology a compelling solution for the removal of CO2 in natural gas. A membrane contactor is a device that allows gas-liquid mass transfer without direct contact of the two phases which flow at the different sides of the membrane. Recent findings have shown that membrane contactors have several advantages over those existing separation systems, which include smaller footprint, modular, not sensitive to flooding, channelling or back-mixing, and provide larger contact areas for increased mass transfer rate. Realizing its potential, PETRONAS and Dalian Institute of Chemical Physics (DICP) have successfully completed a development study on membrane contactor which can remove CO2 from feed gas containing a range of 70-10% of CO2 down to as low as 1% at the outlet gas stream. The technology could potentially further remove CO2 down to ppm level meeting LNG specifications. A pilot plant to demonstrate its performance on actual plant conditions will be commissioned at PETRONAS Gas Processing Plant in 2013.
Use of Platform Response Measurements from On-Line Monitoring (OLM) System to Verify the Effectiveness of Structural Repairs and Managing On-going Structural Integrity
Authors: Nichols N.W. , Md Harif H.
Published: February 2015

Structural member damage to fixed-jacket offshore platform occurs for a number of reasons including impact damage from vessels and fatigue of ageing jackets. Such structures represent substantial capital assets to operators and therefore it is important to verify the effectiveness of structural repairs in restoring the structural integrity of the platform.

An On-line Monitoring (OLM) instrumentation system at deck level can be used to continuously monitor the structural response due to ambient from wave and on board sources before, during, and after the repair process.

The observed changes in structural response can be compared with those predicted using finite element structural analysis. The outcome from a Pilot study implementing the use of OLM by Petronas Carigali Sdn Bhd (PCSB) has enabled PCSB to effectively identify that the repair was adequate and further demonstrated the applicability for using OLM for Managing Structural Integrity over time in assessing the effectiveness of any future repairs.

The paper also describes details on demonstrating the benefits of using OLM in supporting the ongoing Managing of Structural Integrity due to degradation arising from various sources to assist engineers in making and verifying correct engineering assessment decisions and where appropriate supporting the case for either enhancing safety or reducing inspection/maintenance activities.
Chemical Tracers for the Offshore Determination of Residual Oil Saturation
Authors: Myers Matthew , White Cameron , Heath Charles , Pejcic Bobby , Stalker Linda
Published: February 2015

Residual oil saturation (Sor) is a particularly important parameter for depleted oilfields as it gives an indication to the potential effectiveness of an enhanced oil recovery program. The single-well chemical tracer test using reactive ester tracers such as ethyl acetate has been used extensively to accurately determine Sor. However, these tracers are typically highly volatile and have low flash points presenting a large impediment to their deployment in an offshore environment. We have investigated the behaviour of higher molecular weight diesters and triesters (ethylene glycol diacetate, propylene glycol diacetate and triacetin) as possible alternatives for this test as they are much less volatile and flammable. These compounds are particularly attractive chemical tracers as they are commonly used in the food and cosmetics industries and are generally recognized as have minimal health and safety concerns. The oil/water partition coefficient is a critical property of the tracer that dictates its behaviour and effectiveness for this test. For example, simple chromatography models based on the method of moments suggest that the optimal sensitivity range for the partition coefficient at Sor of 10 % is 4.5 to 13.5, at 20 % is 2 to 6 and at 30 % is 1.2 to 3.5. Through a series of laboratory experiments, we have determined the water/decane partition coefficients at a range of temperatures where decane is a mimic for crude oil. These experiments demonstrate that these diesters and triesters are suitable for a wide range of temperature and residual oil saturation conditions.
ECA of High Pressure and High Temperature (HP/ HT) CRA Pipelines
Authors: Kumar Shashi B. , Chong Steven , Tornqvist Rikard , Tronskar Jens P. , Lai Man On , Loh Wai Lam
Published: February 2015

Deepwater and marginal oil and gas fields are often found to be at high pressure/ high temperature combined with high CO2 concentration in the production fluid. In order to develop the oil and gas fields with harsh environment, C-Mn line pipes is considered to uneconomical / nonviable and CRA Clad line pipes are increasingly selected for such situations. The CRA clad line pipe generally consists of C-Mn backing steel material with 3.0 mm (nominal wall thickness) metallurgically clad layer at the inner diameter made from nickel base alloys 825 or 625 or 316L stainless steel. Often small diameter line pipes (< 10" diameter) is made by joining two (2) 6m pipes using 309 Mo consumables.

These line pipes are typically welded on board the lay barge using 622 or 625 nickel base or 2509 super duplex consumables. The recent research has shown that the tensile and fracture toughness properties which is most important to ensure the integrity of the girth welds is very sensitive to the test temperature, specimen geometry, specimen sampling direction. Moreover due to planned and unplanned lateral buckling design the girth welds may be subjected to high peak strain/stress, sometimes in the range of 0.5 to 1.5% total strain. Engineering critical assessment (ECA) performed according to DNV OS-F101 appendix A is used to derive the weld flaw acceptance criteria for inspection of girth welds by automatic ultrasonic testing (AUT).

There are several challenges associated with HP/HT CRA pipeline such as i) under-matching girth weld as compared to the base metal yield strength, especially at elevated temperatures, ii) small tolerable flaws which are difficult to achieve with practical girth welding procedures iii) high noise level vs. signal during inspection of the girth welds using automated ultrasonic testing due to anisotropic nature of austenitic or austenic/ferritic weldments and CRA layer. Often welding specification requires that no detectable imperfections are present in the root pass and possibly also in the hot pass. The paper l discusses the above mentioned challenges in relation to HP/HT CRA pipelines and provides some solutions and guidelines for ECA of CRA clad lines.
Implementation of a Trans-Horizon Microwave Troposcatter Communication Link
Authors: Jin Wong Hock , Zainudin Abi Sufyan , Khan Mohamad Rizal
Published: February 2015

This paper discussed the implementation of a Trans-Horizon Microwave

Troposcatter

Communication Link between one of the Talisman Malaysia South China Sea offshore platforms and an onshore facility in Malaysia. This communication link replaces an existing VSAT (Very Small Aperture Terminal) system.

The platforms are located too far from any networked asset to be linked by Optical fiber or line-of-sight microwave. Apart from the high operating cost, the VSAT link has a minimum latency of 0.5 second due to the use of geo-stationary satellites and bandwidth is limited to only 4Mbits/sec. Studies have identified Digital Troposcatter as an industry proven technology offering higher data rate and minimal latency. This paper describes how the offshore platform will be used as a communication hub for the adjacent platforms.

Conventional Microwave links are impeded by the curvature of the earth, Troposcatter overcomes the earth's curvature by exploiting the natural scattering of radio signals that occurs in the low atmosphere. The scattered signal may be picked up by a high gain antenna and sensitive receiver. Digital signal processing is used to enhance the received signal and for the Troposcatter link to provide a 20Mbits/sec duplex data with Quality of Service in excess of 99.95%.

This requires the procurement and fabrication of high technology equipment, not commonly found in civilian installations, and the construction of transmitting and receiving facilities onshore and offshore.

The paper will discuss the project justification, the principles of the link and illustrate the design, procurement and engineering challenges.
25Cr Completion Campaign Successfully Meets Unusual, Highly Corrosive Reservoir Conditions - A Case History
Authors: M Noor Adlan Long , b Samad M Elmy Ismail , Osuji-Bells Godwin , b Khalid M Zaidan , Budi Setiawan Trigunadi , Rodhiah Siti , Zol Hamidy Hudzaifah , Paramavathar Sanggeetha , Madi Diana
Published: February 2015

Gas wells often produce sour gas (H2S) along with significant quantities of CO2, and when it is suspected that these conditions will be encountered, corrosion-resistant alloys (CRAs) must be used in completions. This paper discusses an unusual development strategy for an offshore gas cluster off Peninsular Malaysia. The planning for the project had to consider that the environment contained approximately 57% CO2 in addition to H2S. To meet the needs of this project, a dedicated team from the operator and service/engineering company developed a completion strategy incorporating several "firsts" for this area. This paper will discuss the unusual completion strategies selected, why they were used, and the resulting success of the well completions. This was the first usage of 25Cr by this operator in Malaysia. Some of the changes included:Alloy 25Cr was used for all 3–1/2- and 4–1/2-in. completion equipmentThe equipment was rated for 5000psi and 7500psi

The wells were completed without any issues relating to the use of any of the new strategies, and these have become the standard for all future Monobore/Dual completion wells with high CO2 content and low H2S content for both upper and lower completions. The wells have been in operation for more than one year, and production has been as anticipated.

This case history covers the early stage planning (including materials recommendation stage), technical design review, equipment design, CRA handling and equipment preparation onshore, CRA handling offshore, and completion execution throughout the campaign. Results of the operation from a mechanical perspective will also be presented.
ANN Powered Virtual Well Testing
Authors: Aggarwal A. , Agarwal S.
Published: February 2015

Due to the drying up of old oil fields throughout the globe, the age of easy oil is over and the newly discovered fields have reservoirs with complex heterogeneous media. The reservoir parameters are identified indirectly by correctly interpreting well test model which is recognized by the feature of pressure derivative curves. Well testing involves creation of disturbance in fluid flow by injecting liquids and simultaneously recording the pressure transient data. Lost production, equipment and personnel costs turn well testing as highly cost intensive job making it difficult to cover all the important wells in a particular field. But with the advent of artificial neural networks (ANN) it is now possible to generate synthetic pressure transient data. This technique provides a basis to leach out detailed information from the available pressure transient data and it doesn't eradicate the need for actual well tests. This technique can also prove to be very vital in cases where equipment breakdown may have taken place and full set of data couldn't be availed. This simulated well testing involves training of a neural network from pressure transient data obtained from designated wells in the field, which has the potential to generate pressure transient responses at other well sites where no well test has been conducted.

In this paper a 3 layer multi-layer perceptron (MLP) Time Delay Neural Network - NARX model has been designed working on resilient backpopagation algorithm for training. Cubic Spline Interpolation has been used from enriching the data before feeding it to NARX model. A simulated example which highlights the efficiency of NARX model in attaining accurate synthetic pressure transient data has been discussed. The neural network is successful in predicting well test interpretation model. The ANN thus produces expeditious and reliable synthetic data which has the potential to revamp the industry.
Managing Micro-Emulsion and Scale During ASP Flooding for North Sabah Field EOR
Authors: Alwi Noraliza , Borhan Noorazlenawati , B M Ibrahim Jamal Mohamad , Paramanathan Subashini , Bouwmeester Ron
Published: February 2015

Alkaline Surfactant Polymer (ASP) flooding has been identified as one of the best EOR methods to further recover the trapped oil in Malaysian maturing fields. ASP flooding application promises a huge incremental recovery factor based on recent successful implementation on offshore fields in other part of the world. The application of ASP flooding has been identified for pilot in North Sabah reservoir which is currently flooded with seawater since March 2011. Despite the promising recovery factor from the pilot laboratory and simulation study with incremental recovery of >80% above waterflood, the ASP flooding success always comes with risks and challenges.

Two major challenges behind the success of ASP flooding are the formation of scales near wellbore due to the high pH of the alkaline in the injection fluid and the tight micro-emulsion which produced back in separator vessel which contains surfactant breakthrough. The identified pilot North Sabah reservoir which is currently been flooded with seawater is expected to further worsen the scaling effect due to the high divalent cation concentration (i.e. Ca2+ and Mg2+) in seawater. In addition, the high seawater cut causes a very tight micro-emulsion which is very difficult to manage. These challenges cause formation damage which impact injectivity and flow assurance issue to the production facilities as well as impair the crude quality and sellability.

This paper will discuss in great detail on the lab test results which was designed based on the reservoir simulation ASP flooding study in North Sabah reservoir. Based on the in-situ produced water and chemical breakthrough simulated, this paper describes the extent of emulsion and scale severity at various ASP to water ratio, extensive performance tests evaluating the demulsifier and the scale inhibitor and discusses on the challenges in finding the suitable demulsifier and scale inhibitor at the simulated breakthrough condition.