bluuebunny/crossref_metadata_2025_split huggingface dataset:
Production Optimization Under Uncertainty
Authors: Nogueira Pedro De B. , Schiozer Denis J. 
Published: June 2009

Abstract
This work presents a methodology that gives more accuracy to the handling of uncertainty in optimization process of production strategies. In this methodology, pessimistic, intermediate and optimistic realizations for the geological model and the economic environment can be considered. Differently from other methodologies, this consideration is made simultaneously during the optimization process. The process is guided by the expected monetary value (EMV) of project. It gives a greater adaptability to the optimized production strategy.
An algorithm that carries out the EMV of a production strategy for each step of the optimization was developed. This algorithm performs the interconnection between flow simulation and economic analyses, necessary to calculate the EMV of a production strategy. It is called at every time where the optimization process requires the objective-function evaluation. In this work the methodology proposed by Nogueira and Schiozer, 2009 for production strategies optimization based on genetic algorithms is utilized.
The performance of the proposed methodology is compared with the performance of a conventional methodology of production optimization under uncertainty. A case with three geological models and three economic scenarios is studied. The optimized strategy presents more adaptability to the possible variations, showing a good performance in all adopted contexts. Although the proposed methodology represents a more accurate process than the conventional methodology, there is a decrease in the number of flow simulations required to optimize the production strategy. The proposed methodology is shown as a viable alternative for handling of uncertainties for optimization process of production strategies.
Integration of NMR and SCAL to Estimate Porosity, Permeability and Capillary pressure of Heterogeneous Gas Sand Reservoirs
Authors: Hamada G. M. 
Published: June 2009

Abstract
Analysis of heterogeneous gas sand reservoirs is one of the most difficult problems. These reservoirs usually produced from multiple layers with different permeability and complex formation, which is often enhanced by natural fracturing. Therefore, using new well logging techniques like NMR or a combination of NMR and conventional open hole logs, as well as developing new interpretation methodologies are essential for improved reservoir characterization. Nuclear magnetic resonance (NMR) logs differ from conventional neutron, density, sonic and resistivity logs because the NMR measurements provide mainly lithology independent detailed porosity and offer a good evaluation of the hydrocarbon potential. Integration of NMR logs, other open hole logs and SCAL minimizes uncertainties in the determination of formation porosity, permeability and capillary pressure curve.
This paper focuses on determination of three petrophysical parameters of heterogeneous gas sand reservoirs which are Determination of DMR porosity, fDMR, it is deduced from NMR porosity and density porosity; NMR permeability, KBGMR, it is based on the dynamic concept of gas movement and bulk gas volume in the invaded zone and Capillary pressure, it is derived from relaxation time T2 distribution.
Oil Recovery Improvement Using CO2-Enriched Water Injection
Authors: Riazi Masoud , Sohrabi Mehran , Jamiolahmady Mahmoud , Ireland Shaun , Brown Christopher 
Published: June 2009

Abstract
CO2 injection is increasingly considered as having potential applications as a possible enhanced oil recovery (EOR) process for oil reservoirs. However, poor sweep efficiency has been a problem in many CO2 floods and hence, the injection strategies like WAG (water-alternating-gas) injection have been proposed and applied in the field as a way to mitigate the problem. An alternative injection strategy is CO2-enriched (carbonated) water injection (CWI).
This paper presents the results of an integrated experimental and theoretical study on the application of CO2-enriched water flooding for enhanced oil recovery. Direct flow visualisation experiments were carried out using high-pressure transparent porous media. The results of our visualisation experiments demonstrate that CWI, compared to unadulterated water injection, improves oil recovery. The additional oil is recovered as a result of an improved sweep efficiency, due to the oil swelling, viscosity reduction and coalescence of the isolated oil ganglia as a result of CO2 diffusion. This injection strategy is particularly attractive in waterflooded oil reservoirs in which high water saturation adversely affects the performance of conventional CO2 injection methods. CWI can also be carried out in combination with reservoir depressurisation carried out subsequent to CWI or in a cyclic manner in which carbonated and plain water cycles are injected in succession.
The results of a mathematical model are also presented which honours our experimental observations and simulates the dynamic process of oil swelling and shrinkage due to CO2 transfer during Carbonated water and plain water injection.
Automated characterization of fracture conductivities from well tests inversion
Authors: Bruyelle Jérémie , Lange Arnaud 
Published: June 2009

Abstract
Methodologies and numerical tools are available (i) to construct geologically-realistic models of fracture networks, (ii) to turn these models into simplified conceptual models usable for field-scale simulations of multi-phase production methods. However a critical intermediate step remains that of validating the geometry of the geological fracture network and characterizing it in terms of flow properties. This characterization step involves the calibration of available field data, e.g. well tests, with simulated data. It is usually an ill-posed problem: available data are insufficient to fully characterize the fracture properties, for instance. Therefore prior estimates of these properties are necessary, but these estimates are usually uncertain, resulting in a wide range for the properties values to be investigated. This paper presents a complete methodology to address this inverse problem: (1) a covariance matrix adaptation-evolution strategy is used to explore efficiently the properties space; (2) the latter optimizer is coupled with a surface response methodology in order to detect several solutions simultaneously, and to estimate the properties global sensitivities to field data during optimization. An application involving a horizontal well test and a fracture network with two sets of systematic joints and one fault set is presented. For a given realization of the fracture network geometry, it is shown that the optimization of fracture conductivities via the present methodology results in the characterization of two distinct, although both data-consistent below a 0.1% error in pressure, sets of solutions for the joints conductivities. The fault set conductivity is shown to have a low sensitivity to the well test data. As sensitivities are estimated during optimization, by using a surface response methodology and the Sobol decomposition technique, it is possible to reduce the optimization cost by eliminating low sensitive parameters during the optimization process. The effectiveness of the methodology to characterize physically meaningful and data-consistent fracture properties is discussed further.
Uncertainty Analysis Applied to Biogenic Reservoir Souring Simulation
Authors: De Siqueira Alexandre Guedes , Araujo Carlos Henrique Vieira , Reksidler Rodrigo , Pereira Marcio de Castro 
Published: June 2009

Abstract
In petroleum industry, uncertainty analysis is frequently used to define the expected probabilistic range of oil, gas and water production profiles. This paper describes a new application, aiming to estimate the probabilistic concentration range of hydrogen sulphide (H2S) in produced fluids. Several oilfields undergo increasing concentrations of produced H2S, typically during seawater injection for secondary recovery. Usually, such toxic and corrosive compound is generated by Sulphate- Reducing Bacteria (SRB). Bacterial activity is not favoured in the reservoir original environment, but can become feasible after water injection, mainly because injected water can have high sulphate contents, can cool certain regions of the reservoir, and can dilute bacterial inhibitory compounds in formation water.
Reservoir souring modelling is useful to anticipate decisions, either by preventive measures or a mitigation strategy, to avoid exposition of people, environment and installations to serious hazards. Inasmuch there are significant uncertainties in various simulation parameters, H2S concentrations presented as a probabilistic range – instead of a deterministic value – can be worthy to fine-tune the acceptable level of risk tolerance in the decision-making process.
Each field development scenario relates to a specific sensitivity to the simulation variables and probabilistic ranges are, in some cases, very wide. Commonly, not only microbial-related parameters are relevant: part of the biogenerated H2S is retained in the reservoir, due both to adsorption/reaction with rock minerals and to partition of H2S in water and oil phases.
Since 2005, the mentioned probabilistic approach is used in Petrobras to base decisions that have a large impact on the field development overall costs.
Case History: A Robust Point-the-Bit Rotary Steerable System with At-Bit Imaging and 3D Geosteering Service Integral to Optimal Wellbore Placement in a Complex Thin Sand Reservoir
Authors: Kok Keng H. , Hughes-Jones Huw , Chavez Ernie , Aziz Khairul Azmee Abdul , Yusof Khazimad , Lambert Mark 
Published: June 2009

Abstract
This paper describes the optimization of a well placement in a 4 m thin complex sand reservoir, using a point-the-bit rotary steerable system, real-time LWD imaging, and 3D geosteering software in well Chermingat A02 drilled by Newfield Peninsula Malaysia Inc. Real-time, at-bit gamma images 1 m from the bit proved crucial in providing early structural interpretation for geosteering decisions. Higher resolution density images further refined the structural interpretation. A geosteering consultancy service, based in the customer's office, provided the subsurface team with guidance throughout the geosteering process, which led to the successful delivery of the well objectives.
The advanced, intuitive 3D geosteering software was used to create a geological model based on offset data and geological surfaces. This local geological model was updated continuously throughout the drilling process, based on the best match between modeled and actual logging-while-drilling (LWD) sensor responses, to reveal local bed dip, bed thickness, and faults. Changes in the well trajectory were seamlessly communicated to the directional drillers on-the-fly by means of a two-way down linking system to the point-the-bit rotary steerable system, while on-bottom drilling ahead continued with no drilling interruptions. This new level of efficiency, using at-bit images immediately integrated into an intuitive geological modeling package with full support from the geosteering advisors, resulted in rapid geosteering decisions with no downtime waiting for a decision from town. The team achieved 500m (1,640 ft) MD of high quality reservoir, thus meeting the objective of the original well plan.
This strategy and operational efficiency resulted in a cost savings of $812,000 (USD). The methodology, lessons learned, and experience gained from this well were applied successfully in the next drilling campaign in East Belumut A02 and in subsequent wells on the East Belumut platform.
Evaluation of Extended Seawater Injections Impact on Waste Injection Pressure Response and Waste Disposal Capacity
Authors: Gumarov S. , Ovalle A. , Shokanov T. , Park G. , Simmons S. 
Published: June 2009

Abstract
The injection of drilling generated waste into a selected subsurface formation has evolved into the most preferred waste disposal technology in terms of environmental compatibility and cost effectiveness, especially for remote and environmentally sensitive areas. The main principle of waste injection (WI) is the initiation of hydraulic fracture and the placement of solids within the created fractures through the high-pressure pumping of slurry batches. The fracture propagation is governed mainly by in-situ stresses. As injection progresses solids accumulation in the fracture leads to an increase of in-situ stresses within the injection zone causing a build-up of injection pressure. As allowable injection pressure is often limited by equipment, the undesirable or rapid injection pressure build-up could jeopardize the operational life of an injection well and limit its waste disposal capacity.
This paper introduces a new approach to a regular seawater injection by investigating the relationship between pressure behavior and seawater injection. Displacement of slurry from the tubing by seawater over flush is carried out routinely in WI operations worldwide. However, never before it was considered as a pressure maintenance tool. The authors describe the impact of continuous seawater injection on injection pressure through the lifetime of three waste injectors. The injection pressure behavior before, during and after continuous seawater injection was reviewed using downhole measured data. It was noticed that regular seawater over-displacements during the continuous time periods between slurry injections reduced injection pressure considerably. Consequently, a thorough evaluation was initiated to investigate the impact of extended seawater injection on in-situ stresses and its potential advantage in maintaining the injection pressure within lower limits. 
Considering the novelty and value of study for expanding worldwide WI operations, this paper presents the new approach to seawater injection as an injection pressure and disposal capacity maintenance tool.
Natural and Conventional Tracers for Improving Reservoir Models Using the EnKF Approach
Authors: Huseby Olaf , Valestrand Randi , Nævdal Geir , Sagen Jan 
Published: June 2009

Abstract
Natural tracers (geochemical and isotopic variations in injected and formation waters) are a mostly unused source of information in reservoir modeling. On the other hand, conventional inter-well tracer tests are an established method to identify flow-patterns. However, they are typically underexploited, and tracer-test evaluations are often performed in a qualitative manner, and rarely compared to simulation results in a systematic manner. To integrate natural and conventional tracer data in a reservoir modeling work-flow, we use the ensemble Kalman Filter (EnKF) that has recently gained popularity as a method for history matching. The EnKF includes online update of parameters and the dynamical states. An ensemble of model representations is used to represent the model uncertainty. In this paper we include conventional water tracers, as well as natural tracers (i.e. geochemical variations), in the EnKF approach. The methodology is demonstrated by estimating permeability and porosity fields in a synthetic field-case, based on a real North Sea field-example. The results show that conventional tracers and geochemical variations yield additional improvement in the estimates, and that the EnKF approach is well suited as a tool to include this information. The principal benefit from the methodology is improved models and forecasts from reservoir simulations, through optimal use of conventional and natural tracers. Some of the natural tracer data, scale forming ions and toxic compounds, e.g., are monitored for other purposes and exploiting such data can yield significant reservoir model improvement at a small cost.
Ant Colony Optimization for History Matching
Authors: Hajizadeh Yasin , Christie Mike , Demyanov Vasily 
Published: June 2009

Abstract
This paper introduces a new stochastic approach for automatic history matching based on a continuous ant colony optimization algorithm. Ant colony optimization (ACO) is a multi-agent optimization algorithm inspired by the behaviour of real ants. ACO is able to solve difficult optimization problems in both discrete and continuous variables. In the ACO algorithm, each artificial ant in the colony searches for good models in different regions of parameter space and shares information about the quality of the models with other agents. This gradually guides the colony towards models that match the desired behaviour – in our case the production history of the reservoir. The use of ACO history-matching has been illustrated on a reservoir simulation case for Gulf of Mexico which showed that Ant Colony optimization can be used to generate multiple history-matched reservoir models.
Faster Convergence in Seismic History Matching by Efficient Parameter Searching
Authors: Sedighi F. , Stephen K. D. 
Published: June 2009

Abstract
Seismic history matching is the process of modifying a reservoir simulation model to reproduce the observed production data in addition to information gained through time-lapse (4D) seismic. The search for good predictions requires that many models are generated particularly if there is an interaction between the properties that we change and their effect on the misfit to observed data. In this paper we introduce a method of improving search efficiency by estimating such interactions and partitioning the set of unknowns into non-interacting subspaces. We use regression analysis to identify the sub-spaces which are then searched separately but simultaneously with an adapted version of the quasi-global stochastic neighbourhood algorithm. We have applied this approach to the Schiehallion field, located on the UK Continental Shelf. The field model, supplied by the operator, contains a large number of barriers that affect flow at different times during production and their transmissibilities are highly uncertain. We apply history matching by modifying the model. We find that we can successfully represent the misfit function as a second order polynomial dependent on changes in barrier transmissibility. Firstly, this enables us to identify the most important barriers and, secondly, we can modify their transmissibilities efficiently by searching sub-groups of the parameter space. Once the regression analysis has been performed we reduce the number of models required to find a good match by an order of magnitude. By using time-lapse seismic to effectively condition saturation and pressure changes in history matching we have gained a greater insight into reservoir behaviour and have been able to predict flow more accurately with an efficient inversion tool. We can now determine unswept areas and make better business decisions.
Optimum Logging Programs in Tight Sands
Authors: Tchambaz M. 
Published: June 2009

AbstractHigh potential of tight sands (quartzitic sandstones) makes these non-conventional reservoirs a priority for oil companies during next decades. Due to numerous formation evaluation challenges in tight sands, conventional logging does not allow reliable and comprehensive investigations that are essential for exploration and development.Classical logging techniques/measurements are frequently affected by significant uncertainties, leading sometimes to erroneous evaluation results.New technology has brought advanced logging methods improving accuracy and reducing uncertainties of reservoir evaluation and characterization. Efficient implementation of these techniques is explained considering resolution/precision and limitations of measurement physics.Best practices for logging in this type of formation are recommended with guide-lines and examples. Depending on well category (exploration, semi-exploration, appraisal or development), appropriate and optimum logging programs can be designed and sequentially performed to acquire full set of necessary data/information.Latest generation of logging tools, in sonic, nuclear magnetic resonance, accelerator-neutron, formation-tester and analysis-sampling techniques, which offer significantly better evaluation, are proposed in integrated and optimized methodology. All of advanced logging tools may not be needed systematically for all types of wells; selective criteria are analyzed according to defined objectives/needs, reservoir particularities or/and sequential investigation results.Data/information provided by tool answers-measurements are linked to key equations that will be accurately solved in different workflow implemented within the framework of formation evaluation, reserves estimation, completion selection, stimulation design and enhanced production projects.This approach could be considered as guide lines for preparation of specific tool combinations and adequate logging programs fundamental for tight sands potential assessment and important management decisions.
An Improved Method for Total Mechanical Skin Calculation for Perforated Completions
Authors: Kabir Akim H. , Salmachi Alireza 
Published: June 2009

Abstract
Computation of total mechanical skin for perforated completions and comparison of various completion options is a challenge faced by Engineers involved in completion design/optimization. The topic of total mechanical skin calculation has been investigated by various authors. Karakas-Tariq (1991) proposed a method which is widely accepted by the industry for its simplicity, ease of use and a good theoretical basis. However, this method has a serious drawback in that it fails to give consistent, reasonable & continuous results if a parametric study is done on perforation length or invasion damage depth.
A review of Karakas-Tariq perforation and total mechanical skin model has been conducted and their shortcomings have been identified. The calculated total mechanical skin is discontinuous and illogical as the perforation length crosses the damage boundary (for a fixed damage depth) or as the damage boundary crosses the perforation tunnel tip (for a fixed perforation length). Various techniques have been tried to solve this problem. An ideal solution should honour the Karakas-Tariq model for perforation tunnels terminating some distance away from the damage boundary and should give reasonable and continuous results as the perforation tunnel reaches or extends beyond the damage boundary. The proposed solution, developed using analytical equations, achieves this desired outcome. Flow has been split between a stream which passes through the damaged zone and the stream which goes directly into the perforation tunnels. The resulting modified Karakas-Tariq method has been extensively scenario tested with synthetic & published well completion data and results are encouraging. This improved method now can be incorporated in any comprehensive perforation/inflow modeling software for comparing various completion options.