bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Dispersion on Local Displacement Efficiency for Multicomponent Enriched-Gas Floods Above the MME
Authors: Johns R. T. , Sah P. , Solano R. 
Published: December 2007

Abstract
Research on four-component one-dimensional displacements has shown that enriching the gas above the minimum enrichment for miscibility (MME) can substantially increase oil recovery for certain systems. Research has further shown that the oil recovery increase can be very sensitive to the level of dispersion at the enrichment chosen.
The main focus of this paper is to extend the research on four-component systems to displacements of multicomponent oils and gases where the recovery is affected by dispersion and enrichment. We consider here a twelve-component oil displaced by solvents enriched above the MME. For this case, the increase in recovery (displacement efficiency) above the MME can be as large as 15% OOIP depending on the level of mixing. The methodology outlined can be used as a screening tool to identify if a significant benefit may exist and further 2-D and 3-D studies are warranted.
A secondary focus of the paper is to examine in detail how dispersion affects recoveries and displacement mechanisms for the four and twelve-component systems. We show that for the case of the four-component model the displacement mechanism changes from a combined condensing/vaporizing displacement (CV) to a strictly condensing one as enrichment increases above the MME. We also show how to quantify the percentage of the CV displacement that is vaporizing or condensing by calculating the compositional distances between key tie lines identified from "dispersion-free" theory.
Why Oilwells Leak: Cement Behavior and Long-Term Consequences
Authors: Dusseault Maurice B. , Gray Malcolm N. , Nawrocki Pawel A. 
Published: December 2007

Abstract
Oil and gas wells can develop gas leaks along the casing years after production has ceased and the well has been plugged and abandoned (P&A). Explanatory mechanisms include channelling, poor cake removal, shrinkage, and high cement permeability. The reason is probably cement shrinkage that leads to circumferential fractures that are propagated upward by the slow accumulation of gas under pressure behind the casing. Assuming this hypothesis is robust, it must lead to better practice and better cement formulations
Integration of 3D-Seismic With Reservoir Simulation for Reservoir Characterization and Assessment of Alternative Exploitation Schemes of Field Development - A Case Study
Authors: Singh C. S. , Borgohain B. , Borgohain D. 
Published: December 2007

Abstract
This paper deals with a study where integration of 3D-seismic survey and reservoir simulation has aided in reservoir characterization which in turn have led to better and effective implementation of reservoir development schemes. Shalmari, one of the major oilfields in Assam-Arakan geological province of North-East India was discovered in 1986 and the initial field development was carried out on the basis of then available 2D-seismic data. During the course of initial field development, the area of major concern was the rapid decline of reservoir pressure. A detailed simulation study was carried out in 1994 for assessment of the pressure maintenance requirements and field development.
A 3D-seismic survey was carried out in 1994 in this area to obtain additional information on the reservoir geometry and structural configuration. The processing and interpretation of 3D-seismic data resulted in identification of additional faults thus bringing about a change in the structural configuration of the reservoir. The presence of identified faults was corroborated by pressure transient surveys. This necessitated in carrying out of another detailed reservoir simulation study by building up a geological model based on 3D-seismic data.
The basic objective of the study was to carry out a more accurate and reliable reservoir characterization apart from identifying the prominent direction of aquifer support and reassessment of the hitherto planned reservoir development scheme including ongoing pressure maintenance scheme. The results of the study carried out in 1997 also indicated possible increase in gross ultimate recovery as a result of water flooding. The financial analysis of the development schemes envisaged in this study was also found to be attractive.
Cross-discipline integration of data expertise and study has helped in accurate mapping of the minor faults and has provided a better insight into fault transmissibilities in the fluid flow simulation.
Production Impairment and Purpose-Built Design of Hydraulic Fractures in Gas-Condensate Reservoirs
Authors: Wang X. , Indriati S. , Valko P. P. , Economides M. J. 
Published: December 2007

Abstract
Hydraulic fracturing has been the stimulation/completion method of choice for the vast majority of gas reservoirs throughout the world. There is no fundamental difference in the design of hydraulic fractures in reservoirs of any permeability. However, for low-permeability reservoirs, obtaining the indicated length of the hydraulic fracture has been the key element in the execution of the stimulation treatments; for high-permeability reservoirs increasing the fracture conductivity (width multiplied by fracture permeability) is important. For the latter, "tip screen-out" treatments have been developed.
Damage to the fracture, which causes a reduction in the well performance, has manifested itself in two ways, 1) reduction of the proppant-pack permeability because of polymer residue, choking of the near-well region and over-displacement and 2) damage to the fracture face, i.e., reduction to the reservoir permeability normal to the fracture, because of polymer leakoff during the fracture execution. Both types of damage affect primarily higher-permeability formations, the first reducing the much-desired large fracture conductivity and, the second, providing an impediment to flow, which becomes important because of short fracture lengths. For long fractures and short penetrations of fracture-face damage the reduction to the well performance is insignificant.
In gas-condensate reservoirs a situation emerges very frequently that is tantamount to fracture-face damage. Because of the pressure gradient that is created normal to the fracture, liquid condensate is formed which has a major impact on the reduction of the relative permeability-to-gas. Such a reduction depends on the phase behavior of the fluid and the penetration of liquid condensate which, in turn, depends on the pressure drawdown imposed on the well. These phenomena cause an apparent damage, which affects the performance of all fractured wells irrespective of the reservoir permeability (including very low-permeability values). Well testing of such wells would invariably calculate much shorter apparent lengths than actually placed.
We are presenting here a model that predicts the fractured well performance in gas-condensate reservoirs, quantifying the effects of gas permeability reduction. Furthermore we present fracture treatment design for condensate reservoirs. The distinguishing feature primarily affects the required fracture length to offset the problems associated with the emergence of liquid condensate. Also, guidelines for the calculation of the appropriate pressure drawdown during production to optimize well performance are provided.
Simultaneous Propagation of Multiple Hydraulic Fractures – Evidence, Impact and Modeling Implications
Authors: Weijers L. , Wright C. A. , Sugiyama H. , Sato K. , Zhigang L. 
Published: December 2007

Abstract
Multiple hydraulic fractures have been observed in numerous field settings1–9. Direct evidence for the simultaneous growth of multiple hydraulic fractures has emerged over the last decades by coring through propped hydraulic fracture treatments in reservoirs; mineback experiments; intersection of multiple fracture (planes) through offset wells; multi-planar fracture propagation observed in micro-seismic fracture mapping and tiltmeter fracture mapping; and laboratory experiments showing complex fracture growth. The simultaneous growth of multiple hydraulic fractures beyond the near-wellbore area is therefore probably more the rule than the exception, especially when fracturing from a large perforated interval or in naturally fractured formations.
A comprehensive and consistent approach to approximately quantify and model multiple hydraulic fractures growth using observed fracture pressure feedback has provided significant insight into the mechanism of multiple fracture growth. A simplified concept of "equivalent" (equal sized) multiple fractures "competing" for fracture opening and leakoff has been used to approximate this complex phenomenon. This concept is very useful for quick, real-time fracture treatment analysis, and modeling results have also been calibrated by direct fracture diagnostic technologies to limit potential modeling solutions within reasonable bounds.
Long-Term Performance of Hydraulically Fractured Layered Rich Gas Condensate Reservoir
Authors: Al-Hashim H. S. , Hashmi S. S. 
Published: December 2007

Abstract
Compositional simulator has been used to investigate the effect of hydraulic fracture on the performance of a layered rich gas condensate reservoir. The reservoir consists of five layers having permeabilities ranging from 0.08 to 115 md with about 68 % of the gas reserve located in the lowest permeability layer. The fracture is assumed to penetrate all layers.
The results of this investigation show that hydraulic fracturing is effective in improving the productivity (PI) of the gas condensate wells both above and below the dew point pressure by about three folds as compared to the non-fractured wells. Hydraulic fractures are also found to delay the dew point pressure and consequently extend the production plateau above the dew point pressure. The results also show that as the dimensionless fracture conductivity increases, the long-term performance of the gas condensate reservoir is improved, and the improvement is more pronounced for longer fractures. It is also observed that once the dew point pressure is reached, the flowing bottom hole pressure drops sharply to the specified minimum flowing bottom hole pressure in the fractured and non – fractured cases. However, the drop is less severe in the fractured case. This sharp drop in the flowing bottom hole pressure results in dropping the productivity of the gas condensate wells.
At early times after reaching the dew point pressure the highest condensate saturations along the fracture faces are found to be in the highest permeability layer. However, at late times (after reaching pseudo steady state) it decreases and stabilizes at certain level above the critical condensate saturation.
Finally, formation cross-flow is found to improve the productivity of the fractured and the non-fractured wells. However, the improvement is more pronounced in the fractured cases.
Acidizing High-Pressure Water Injection Wells Using a New Low-Damage Acetic/HF Acid System
Authors: Wang Baofeng , Jiang Weidong , Liu Xihua , Feng Puyong 
Published: December 2007

Abstract
A significant loss of injectivity was observed in some of the high-pressure water injection wells on the Chunhua Oilfield the east of China due to severe formation damage, believed to be caused by fines and clay. This paper details the results of matrix acidizing treatments carried out in Chunhua sandstones, using a new low-damage acetic/HF acid system. The new low-damage acetic/HF acid systems, which will be referred to as "LDA-1", can coordinate aluminum fluoride complexes and buffer the spent HF fluids. The coordination of aluminum fluoride complexes helps alter the aluminumfluoride equilibria, which minimizes the amount of AlF3 in solution and forces the HF reactions to lower F/Al ratios. This system increases the effectiveness of the treatment and overcomes the damaging precipitation of aluminum fluorides during the HF reactions.
A series of laboratory short-core and long-core flow tests has been fully analyzed. Coreflood results showed that the core permeability increased after the treatment. Permeability ratio(final/initial)of reservoir cores exponentially increased with the acid injection rate. Acidizing returns in coreflood were analyzed to better understand the chemistry involved in HAC/HF acidizing. Returned samples were analyzed with inductively coupled plasma (ICP) and 19F nuclear magnetic resonance (NMR) spectroscopy. The combination of ICP and 19FNMR determined fluoride distribution on silicon and aluminum in the samples and the extent of HAC/HF fluid reactions.
The case historie included in this paper is treatment carried out on one formation in Chunhua Oilfield. The field test results shows that LDA-1 mixture is able to generate several fold increases in the injectivity of the wells. They include remedial treatment carried out on zones which had experienced detrimantal results due to poorly-designed conventional HF acid stimulations.
The treatment of CHC23–22 well was monitored with a real-time monitoring program, that showed that the skin factor has dropped from about 13 to –0.21. Following the treatment, injectivity of this interval increased from 0m3/d to 100 m3/d. The real-time monitoring plot shows that the skin has dropped continuously during the injection of preflush and LDA-1, what has proven to be effective for deep damage removal. The LDA-1 system treatment was able to increase the injectivity and sustain it for more than 6 months.
A Study of Fluid Leakoff in Hydraulic Fracture Propagation
Authors: Yew C. H. , Ma M. J. , Hill A. D. 
Published: December 2007

Abstract
A pressure dependent fluid leakoff (PDFL) model and a constant fluid leakoff model (CRFL) model are incorporated into a 3D fracture simulator for studying the effect of fluid leakoff on propagation of a hydraulic fracture. In order to make a meaningful comparison, the leakoff coefficient used in the CFL model is calculated by equating its final fracture area to that predicted by the PDFL model. The propagation behavior of a hydraulic fracture based on these two fluid leakoff models are assessed and evaluated by comparing the calculated time histories of the bottom hole pressure, fracture opening width, and proppant distribution inside the fracture.
Although the agreement between the predicted results from these two fluid leakoff models are good, detailed features in the calculated time histories of BHP and fracture opening width are very different. The difference is large during the fracture growth period, but starts to decrease when proppant packing begins. The results from this study suggest that a more accurate information on propagation of a hydraulic fracture can be obtained by taking the pressure dependent fluid leakoff into consideration.
Computer Simulation of Multilayer Hydraulic Fractures
Authors: Gu H. , Desroches J. , Elbel J. L. 
Published: December 2007

Abstract
When a hydraulic fracturing treatment is carried out in a layered formation, multiple fractures may propagate simultaneously in different layers. It is important to determine whether the multiple layers can be effectively stimulated in one treatment or if a multi-stage treatment is a better solution. Present fracturing models are mostly adequate to design and evaluate multiple stage treatments. In this paper, a computer simulator of multi-layer fractures is presented with the view of designing and evaluating simultaneous fracturing treatments in layered formations. The simulator rigorously calculates the flow rate distribution into multiple fractures based on mass conservation and pressure continuity principles. The fracture in each layer is treated as a pseudo-three-dimensional (P3D) hydraulic fracture model that allows height growth into adjacent layers. The multiple fractures are inter-related not only by the hydraulics through the wellbore, but also by the mechanical interaction through the rock formation, which is important when the stress barriers between layers are weak and fractures grow close to each other. The fracture growth behavior observed from other geomechanics studies is applied in this model. The results from this simulator and a previous one based on the PKN model are compared and discussed. The importance of fracture height growth on flow rate distribution and propped fracture geometry is demonstrated. Tip screenout and near-wellbore screenout in one or more fractures are simulated, showing flow rate diversion into other fractures after screenout occurs in one fracture. Simulation results also show that perforation erosion may have an undesirable effect on the ratio of slurry volume to pad volume in each fracture. Measured data of pressure and flow rates from a field test are compared with the simulation results and good agreement is observed. Based on the results of the simulator, recommendations on the design of simultaneous fracturing treatments of multiple pay zones are presented.
Numerical Simulator for the Combination Process of Profile Control and Polymer Flooding
Authors: Yuan Shiyi , Han Dong , Wang Qiang , Yang Hua 
Published: December 2007

Abstract
This paper presents a three-dimensional, three-phase, nine-component mathematical model that can be used as a practical tool for the simulation study on the combination process of profile control and polymer flooding (CPPCPF). This model considers the major mechanisms, principal physico-chemical phenomena and important influence factors during the complicated process, such as the gel formation, mobility performance, blockage characters, gel movability in porous media and various effects caused by gel system as well as the factors involving in the process of polymer flooding. Based on the model, the corresponding numerical simulator is developed subsequently, which can be used for simulating primary production, water or polymer flooding, crosslinked profile control, in-situ permeability modification, low concentration flowing gel (LCFG) injection and any combination of above processes. The simulator has been applied to simulate LCFG experiments with the good consistency between laboratory and simulation results. Effects of various factors on displacement mechanism and oil recovery have been studied based on multi-serial simulating results. Several oilfield pilot tests according to the simulation studies and injection designs have been carrying out with encouraging preliminary results. The applications have shown the powerful capability of the simulator, which is very useful for CPPCPF mechanism study and oilfield performance prediction.
Development of FEM Reservoir Model Equipped with Effective Permeability Tensor and Its Application to Naturally Fractured Reservoirs
Authors: Park Y. C. , Sung W. M. 
Published: December 2007

Abstract
The numerical simulation of naturally fractured reservoirs is commonly based on the continuum dual-porosity model. However, the model needs to assume that the fractures form very regular patterns, different from field observations. In order to overcome this problem, this study proposed a method that considers the characteristics of the real fracture system, and developed a two-phase transient FEM model being able to implement effective permeability tensor. For the permeability of natural fractures assigned to the numerical grid, Darcy’s law in matrix and cubic law in fracture were adopted for considering the flowing characteristics in discrete fracture network (DFN) approach. The developed model was applied to paludal sand reservoir of MWX (multi well experiment) site to demonstrate the validity and the applicability of the model for the naturally fractured reservoirs. The estimated average permeability in the MWX is almost identical compared to the results of the welltest analysis. Then the numerical simulation with the FEM model was performed by using the transient pressure recorded from gas well test on the MWX #1. From the results of BHP and pressure distribution within the system, it was noted that the model with effective permeability tensor generated almost identical results against DFN model in the aspects of the behavior and the direction of fluid propagation with pressure decline, and therefore, the proposed model is considered to be more efficient in terms of the computation time as well as the required storage capacity. Also from the upscaling study, it was shown that even with fewer numbers of gridblocks the developed model can effectively describe the directional flow caused by the fracture characteristics such as orientation and density of the fracture.
Clinton Well Performance Predictions Based On Flow Tests - A Well Study
Authors: Slider H.C. 
Published: December 2007

Introduction
The objective of this paper is to demonstrate methods of testing and predicting the behavior of very tight gas wells that must be tested under nonideal conditions and that result in data that does not conform to the ideal radial flow concepts. Isochronal testing using constant production rates and bottom hole pressure guages is well understood by most engineers. Interpretation of radial flow isochronal data to obtain the gas well performance when it reaches pseudo steady state flow is also well defined. However, it appears that the flow of gas from a very tight reservoir with a "large" artificial fracture at the well has not been treated in a practical manner.
It will be shown that such a well tends to flow under linear unsteady state infinite acting conditions for relatively short periods of time. Then the well gradually changes to a radial flow geometry. An understanding of these flow conditions can lead to an approximate prediction of the gas well behavior with the accuracy depending upon the length of the flow tests and the accuracy of the "guesstimate" of the drainage area of the well. The treatment of the subject is based on a flow test of a gas well producing through the annulus while water production is being pumped through the tubing. Only surface pressures were measured during the flow tests.

CONSTANT RATE DRAWDOWN AND ISOCHRONAL TEST THEORY
Very tight low permeability reservoirs are generally completed by hydraulically fracturing the well during completion. A long vertical fracture and very low permeabilities permit the well to exhibit linear flow characteristics for very short periods of time. This is demonstrated in Fig. 1. The very low permeability means that the disturbances in the reservoir caused by initiating production will move at a relatively slow rate through the reservoir. Since the effect of the disturbance will move outwardly from the long fracture it means that except for the relatively small amount of the reservoir near the ends of the fracture the flow will be linear. Of course the longer the fracture is the less will the flow into the ends of the fracture cause the overall behavior to deviate from a linear flow geometry.
As the affected volume of the reservoir increases with the production time, the fixed length of the fracture becomes smaller in relationship to the affected volume of the reservoir until substantially radial flow will exist throughout most of the drainage area. Thus, for small producing times, t, we would expect the pressure behavior of a well being produced at a constant rate to be governed by an equation for the constant rate infinite acting linear flow behavior in a reservoir.