bluuebunny/crossref_metadata_2025_split huggingface dataset:
Root-Cause Identification and Production Diagnostic for Gas Wells with Plunger Lift
Authors: Singh Ajay 
Published: September 2015

Abstract
The paper presents an application of the regression tree technique as a root-cause identification and production diagnostic tool, and presents case studies for gas wells using the plunger-lift system. The regression tree model is data-driven and easy to construct, and does not require all of the parameters that a first principle-based model often requires. Thus, these models are quite useful in cases where real-time data or the required data for a detailed analysis are unavailable. To improve prediction capability, a cross-validation technique was used to optimize tree size. A total of 8–10 variables that could potentially impact the gas production rate were considered, with case studies conducted on actual field data. Questions, such as which group of wells are performing well or poorly, are quickly answered. Regression tree analysis, when applied at the field level, can identify a group of wells that underperform compared to other wells. As a result, an asset team can prioritize wells identified as poor performers. Further, a statistical analysis helps to gain insight into understanding the causal relationship between the gas production rate and various operational variables. Based on this analysis, recommendations are also provided to improve the gas production rate of poorly performing wells. Individual well models were also constructed to identify the root causes for high or low gas production based on operational changes made over a certain period of time. Only a few of the variables were found to have a significant impact on gas production. The interpretation of the decision tree indicated that additional operational variables, such as production time and pressure build-up time, should be included in the regression tree analysis to improve the diagnostic process. This paper summarizes these conclusions and recommends future work to improve the prediction capability of the regression tree analysis.
Sourceless Porosity and Anisotropy While Drilling Using Nuclear Magnetic Resonance and Azimuthal Acoustic LWD Tools Drilling Technology: A Case History
Authors: Azim Shaikh Abdul , Turky Huda A , Thakuria Nabajyoti , Khesroh Sawsan , Abdulkarim Anar , Saukova Olesya , Samie Mohamed , Aki Ahmet 
Published: September 2015

Abstract
A combination of nuclear magnetic resonance (NMR) and azimuthal acoustic tools was recently run in a logging-while-drilling (LWD) tool combination. This tool combination was used for the first time in Kuwait as a part of the bottomhole assembly (BHA), in addition to conventional tools, to acquire porosity without using radioactive sources.
A deviated 8.5-in. borehole section of a well was planned through sand-shale sequences with a borehole inclination ranging from 0 to 90°. This geological section is typically crucial from a borehole stability point of view. Borehole deterioration and significant variations in pore pressure can create a high risk of becoming stuck-in-hole. The use of conventional porosity tools in a LWD BHA with installed radioactive sources would significantly elevate the risks to an environmental-hazard level. And, even retrievable based sources become problematic for successful extraction in high angle wells.
LWD NMR and azimuthal acoustic tools, free of radioactive sources, were run for the first time in a LWD tool combination, with the primary objective to measure porosity, pressure prediction, and possible anisotropy using a centralized four-axis acoustic caliper.
Previous experiences in the same geological setting encountered borehole enlargements by approximately 5 in. after only 15 to 16 hours. LWD helped bypass this issue and acquire high-quality data before borehole enlargement occurred. Additionally, indications of the presence of possible rock anisotropy were observed. The results were then correlated and matched to offset well data as well as with existing field geomechanics knowledge.
This paper presents the planning, design, and execution of using LWD NMR and azimuthal acoustic tools in this well. It also discusses the viability, integrity, and robustness of logged data as well as interpreted results. Optimization of real-time drilling operations and petrophysical data acquisition requirements are also investigated to improve future field development and overall reservoir management strategies.
Integrated History Matching Workflow to Parameterize and Characterize the Uncertainty Features of a Carbonate Reservoir
Authors: Thomas Tony , Bejaoui Riadh , Al Khoori Ahmed Abdulla 
Published: September 2015

Abstract
This paper details the history matching workflow that was used in calibrating and hence parameterizing the key uncertainties in a carbonate reservoir. Multiple uncertainties in the reservoir model, inability to draw conclusions from data obtained, and how to effectively integrate data from different sources (cores, logs, geological model, well test and production data) were the challenges. Steps were taken to overcome these challenges, to recognize the key uncertainty parameters, using an integrated workflow approach resulted in improved well and reservoir characterization. The details of this workflow are presented in this paper.
This paper provides an integrated workflow for dynamic reservoir characterization and improved matching of reservoir behavior. It involves:Analyzing and incorporating dynamic data (well tests, pressure transient interpretation, saturation logs and pressure versus depth),Parameterizing key uncertainties impacting dynamic well and reservoir behavior,Characterizing the key uncertainties and incorporating them into the dynamic model, andValidating the dynamic model with geological information to corroborate the uncertainty findings.
This integrated workflow provided an uncertainty parameterization loop by enabling identifying the key uncertainty parameters that have the biggest impact on the dynamic behavior. This then enabled to narrow down the focus on these key parameters from a multitude of different factors. In carbonate reservoirs the dynamic history matching with the aim of understanding and modeling the key parameters through integrating existing dynamic information is not well defined. This workflow enables this integration and identifying the key parameters that can then be integrated into the modeling of the reservoir for improving the model behavior and predictability.
An integrated approach and workflow towards reservoir characterization and modeling resulting in improved well and reservoir modeling is presented. Data integration from multiple sources, identification of key uncertain reservoir parameters and their impact on the modeling and production prediction are highlighted.
Uncertainty Quantification of Top Structures in 3D Geocellular Models
Authors: Bansal R. S. , Vargas-Guzmán J. A. 
Published: September 2015

Abstract
Building a stochastic structural 3D geocellular model for a reservoir in a new field is a challenge because of insufficient well data. Structural heterogeneity due to folding, faulting and/or associated erosional unconformities may not be completely captured by low resolution seismic and limited well data. This could lead to significant structural uncertainty. Hence, quantification of uncertainty capturing structural heterogeneity requires a comprehensive methodology incorporating seismic interpretation, well data and tectonic information. Experimental discrepancies between predicted and measured depths of horizons in newly drilled wells reveal strong drift, which require a nonstationary model. The physical way to create such nonstationary model is by using numerical paleo-geomechanical deformation algorithms to reconstruct the folding phenomena (e.g., finite elements). Such proposition requires a thorough understanding of rock parameters, and boundary conditions. Another plausible alternative is to use nonstationary geostatistics, because it does not require boundary conditions, or rock deformation parameters. Nevertheless, representing finite differences of order-k, which are required for geostatistical modeling, may be unachievable with insufficient well data. After revisiting the theoretical aspects of the problem, this paper shows a fast approach to quantify the structural uncertainty range for the depth of horizons accounting for spatial drift. The approach is illustrated with an example for a real clastic reservoir.
An Integrated Approach to Quantify the Impact of Geological Heterogeneity on Connectivity in Deep-Water Reservoirs
Authors: Gonano Giacomo , Catanzaro Massimo 
Published: September 2015

Abstract
The purpose of the study was to quantify and evaluate the impact of geological heterogeneities on connectivity in channelized turbidite reservoirs. The main technical objectives of the project were: the identification of the architectural elements of the deep-water system under analysis, the development of different geological models, the quantification of reservoir heterogeneity and the evaluation of reservoir connectivity and the outline of an early appraisal strategy.
An integrated approach was applied, using different frameworks, to two eni's deep-water assets: the first, an exploration asset in the Mediterranean, and the second, a West African field in development. This methodology was based on an earth models construction phase (reservoir characterization and reservoir modeling) and on a dynamic simulations phase (streamline simulations and well test simulations).
Reservoir characterization was performed by interpreting 3D seismic data using a high precision 3D seismic interpretation software. Key surfaces were interpreted in the reservoir interval. Furthermore, deep-water elements and architectures, mainly stacked channels and distal lobes, were duly identified through the interpretation of seismic sections and amplitude maps.
Reservoir modeling consisted of Object-Based and Multi-Point Facies Simulation (MPFS) approaches. A sensitivity analysis was carried out to define critical parameters and their ranges in order to fully capture geological uncertainties and realize different static models. The selected parameters were: seismic conditioning in the MPFS (amalgamation), facies volume fraction, channels shape and shale drapes content.
To quantify heterogeneity and analyze connectivity, streamline simulations were carried out using a Streamline Simulator. For each geological model, a Dynamic Lorenz plot (storage capacity vs. flow capacity) and its related coefficient (standard measure of heterogeneity) were determined using an in house code. It resulted that all the selected parameters, except channels shape, impacted considerably on connectivity.
To outline an early appraisal strategy, well test simulations were performed using an hypothetical exploration well and a standard Dynamic Simulator. Well test simulation was found to be an interesting qualitative tool to identify heterogeneities, especially shale drapes content, and condition further appraisal decisions.
Considering the promising results, this approach will be further developed to effectively reduce the range of uncertainties, mitigate the associated risks and guide appraisal strategies in future deep-water prospects.
A comprehensive approach for CO2 Miscible Injection Piloting in a Giant Carbonate Reservoir in Middle East
Authors: Aissaoui Karim , Pradhan Akshaya Kumar , Jasser Majdolin 
Published: September 2015

Abstract
CO2 flooding is known to be one of the most applied miscible EOR process in E&P industry given its ability to mix with reservoir oil and form a miscible flood at relatively low reservoir pressures. CO2 EOR pilots' locations selection, configurations and design are key for success of an EOR piloting scheme. This goes without withstanding detailed compositional simulation to replicate components exchange under the MCM process as well as potential implications on existing well completions and surface facilities.
A structured workflow was established to rank and prioritize all reservoir units in terms of their suitability for miscible EOR. A thorough scrutiny of pilot locations, configuration as well as pilot design as a whole was undertaken. This was aimed to short-list preferred pilot locations and configurations that address most of remaining uncertainties. It was also intended to establish a list of expected deliverables from the pilots. Numerous pilot configurations were analyzed and ranked based on the size of EOR prize, uncertainties reduction as well as capturing synergies and common objectives across the reservoir units.
Detailed compositional simulation studies are being undertaken. This included one-dimensional models for the purpose of examining the displacement process; 2D mechanistic models to assess the impact of heterogeneity on the displacement process as well as fine grid pilot models for the purpose of optimizing the pilot design. A probabilistic production forecast of each pilot is also considered aiming to capture a range of possible outcomes and identify key uncertainties to be acted upon.
A tailored monitoring program is being designed to acquire key performance data including production and saturations monitoring, fluid sampling and pressures. This will feed inputs to sector model calibration as well as the evaluation of pilot performances.
Results from this study are expected to assist ADCO to plan and implement the EOR road map while accounting for all related issues such as flow assurance and asphaltene deposition, reservoir pressure maintenance, CO2 strip-out and re-injection as well as its impact on existing facilities.
A Novel Compositional Model of Simulating Fluid Flow in Shale Resrvoirs - Some Priliminary Tests and Results
Authors: Cao Yang , Yan Bicheng , Alfi Masoud , Killough John E. 
Published: September 2015

Abstract
Multiple porosity systems exist in shale reservoirs: organic matter, inorganic matter, natural fractures and hydraulic fractures. Accurately simulating fluid storage and flow in this complex environment still remains a challenge. One key is to properly account for the multi-component adsorption and diffusion phenomena occurring in the shale matrix. Most studies conducted in recent years use a single gas phase model or a black oil model to consider these aspects. A compositional model specifically tailored for the characteristics of shale reservoirs is required to properly model all of the physics.
In this paper, such a compositional model is introduced. The model takes the pressure and component molar masses as the primary variables, and applies the IMPEM method (implicit pressure and explicit mass) as the solution technique at the current stage. The multi-component adsorption and diffusion terms are incorporated into the component mass balance equations. Adsorption is described through the Extended Langmuir equation, and multi-component diffusion can be described either through the classical or the generalized Fick's law. The latter has the capacity of accounting for component interactions and the phase thermodynamic non-ideality. Knudsen diffusion can also be incorporated through the concept of an augmented effective diffusion coefficient.
Several preliminary tests have been conducted to validate the model. The influences of the important parameters, such as total carbon content, wettability, and fluid composition, on shale reservoir fluid recovery were also investigated with the new simulator.
A New Coupled Axial-Radial Productivity Model for Horizontal Wells with Application to High Order Numerical Modeling
Authors: Cao Jie , James Lesley A. , Johansen Thormod E. 
Published: September 2015

Abstract
For long, highly productive wells, frictional pressure loss cannot be ignored. The axial flow along the well trajectory in the near-well region must therefore also be considered. A new, fully analytical model for coupled radial well inflow and axial reservoir flow has been developed. The new model will be briefly reviewed and solutions to steady state flow summarized.
A discussion on the usage of the new model in simulation of horizontal wells together with its numerical performance compared to standard finite difference methods will be presented. The new analytical model has been used in the formulation of a numerical scheme for simulation of coupled well inflow and near-well reservoir flow. The analytical model results in a linear pressure distribution in the axial direction and a logarithmic pressure distribution in the radial direction in each near-well reservoir segment. Therefore, the pressure distribution is piecewise linear/logarithmic, contrary to existing piecewise constant distribution resulting from a standard finite difference method. Calculation examples are presented applying both the new method and the standard finite difference method to determine the pressure profiles and flow rates in both the wellbore and the near-well reservoir. Numerical results show that the new method represents a substantial improvement compared to a standard finite difference method, requiring fewer segments to achieve the same accuracy. The new method is more accurate especially near the heel, where accuracy is most important. This numerical scheme has also been proved to be higher order accurate in space discretization than a standard finite difference scheme. Since the axial flow rate is built into the new model analytically, the need for local grid refinements around the well is reduced.
Different Methods of Modeling Tilted Free Water Levels and the Impact on Field Production
Authors: Gao John , Schrijver Bart 
Published: September 2015

Abstract
This paper presents and compares the results of the creation of a titled Free Water Level (FWL) from two different modeling methods and the impact on field production.
Worldwide there are examples of oil and gas fields with tilted FWL's. These can be generated by different mechanisms. This paper focusses on the modelling of a tilted FWL associated to a hydrodynamic system. There are several methods of modeling a tilted FWL, most of them emphasize on how to create a tilted FWL but lack the correctness of pressure distribution. Two modelling methods were investigated and their results were compared. One is a static method in which a tilted FWL surface is assigned and the respective water saturation (Sw) values are calculated in the model. The second approach is a hydrodynamic method based on the hydrodynamic principle that a tilted FWL is generated by lateral pressure variation related to a water flow below the hydrocarbon bearing interval. Both methods can generate a correct tilted FWL surface and the associated water saturation distribution, but the pressure distribution shows a significant difference depending on which method was applied. The hydrodynamic method delivers a correct pressure distribution in both the hydrocarbon and the water zone as it captures the physical principals of the tilted FWL and aquifer and therefore the corresponding pressure data. In the field-model a realistic stronger pressure support can be observed, leading to realistic recovery figures. The static method provides a correct pressure distribution in the hydrocarbon zone but not in the water zone, and delivers a nonrealistic weaker pressure support, leading to lower production figures. The fundamental difference in pressure distribution has a signiciant impact on a field production and therefore project economics.
In conclusion, proper tilted FWL modeling should provide not only a correct FWL surface but also pressure distribution. In cases where a tilted FWL is associated to water flow below the hydrocarbon zone, the hydrodynamic method based on the hydrodynamic principle is recommended.
Single Sandbody Stacking Pattern, Calcareous Barrier and Fracture of Tight Low Permeability Oil Sandstone Reservoir and their Impact on Water-flooding - A Case Study of Ansai oil field, Ordos Basin, China
Authors: Li Jiahong , Song Xinming , Tian Changbing , Wang Youjing , Xu Feng , Hui Gang , Wang Ruigang 
Published: September 2015

Abstract
Similar to conventional medium-high permeability reservoirs' water-flooding process, quite a number of tight low-permeability sandstone reservoirs (average permeability&lt;10mD) in China have reached a high water-cut ratio of over 60%, after decades of water-flooding. Despite of the high WC, these reservoirs' recovery remains less than 14%. Heterogeneity caused by matrix and fracture is desperately in need to be characterized to curb the drastic production decline.
A systematic reservoir description workflow of C61 delta-front formation, Ansai oil field, was run, based on outcrop, densely-spaced well cores and loggings. 3 types of single sandbodies and 9 types of single sandbody stacking patterns were recognized and summarized, from the perspective of matrix heterogeneity. Also, hydraulic fractures near producers and dynamic fractures near injectors deriving from fracture reopening by injection pressure accumulation, are descripted. A fine-scale geologically conceptual model embracing information of single sandbody stacking patterns, calcareous barriers and fractures near wells, was then established to quantitatively evaluate the water-displacement differentiation between tight and conventional reservoir, and the impact of stacking pattern, barrier and fracture on tight oil sandstone reservoir recovery.
Simulation results indicate that, (1) water-flooding front in tight sandstone matrix runs slowly but relatively homogeneously compared with in conventional reservoir matrix, especially showing no conspicuous vertical tonguing or fingering; (2) these 9 stacking patterns differ by petrophysical property, barrier frequency and mutual erosion extent, the first 2 factors of which exert dominant controls on water-flooding; (3) calcareous barriers inside composite sandbodies deteriorate vertical displacement homogeneity, and block water-front near erosion interfaces to certain extent; (4) connectivity of these stacking patterns were then evaluated comparatively based on petrophysical property and barrier frequency; (5) heterogeneity derived from fractures, prevailing matrix, triggers oriental flooding along the in-situ maximum principal stress direction.
Fracture, especially the inevitably dynamic fracture in water-flooding, predominates in tight oil sandstone heterogeneity. How to harness fracture with matrix and design compatible well pattern would be the primary issue to be handled for tight oil sandstone water-flooding.