bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of Residual Oil Saturation by Use of Enhanced Diffusion
Authors: Akkurt Ridvan , Marschall Dave , Eyvazzadeh R. Y. , Gardner J. S. , Mardon Duncan , Dunn K. J. 
Published: December 2007

Summary
The enhanced diffusion method (EDM) exploits the diffusion contrast between oil and water separating their respective nuclear magnetic resonance (NMR) signals. Unlike standard NMR logs acquired with short interecho time (TE), measurements, EDM data are acquired using long TE accentuating diffusion. Fundamentally the EDM establishes an absolute upper bound for the T2 of water, thus any T2's greater than this limit unambiguously indicates that oil is present.
The EDM's best application is with intermediate viscosity oils (approximately 1 to 50 cp) complementing other NMR hydrocarbon-typing applications designed for lighter hydrocarbons (i.e., the differential spectrum method). While expanding the viscosity range of NMR hydrocarbon-typing applications, the EDM also provides a method by which to determine residual oil saturation (ROS), which is the main focus of this article.
The potential use of NMR as a direct indicator of hydrocarbon saturation via techniques such as the differential spectrum method (DSM) has generated significant interest in the petrophysical community in recent years. Although originally developed for applications involving natural gas, the DSM has also been used successfully in light hydrocarbon environments. However, success has been limited to the low end of the viscosity spectrum because of the T1 separation requirements between the brine and hydrocarbon phases.
The T1 separation requirement imposed on diffusion applications in higher viscosity oils can be eliminated by using the EDM, where diffusion is turned into the dominant relaxation mode for the wetting brine phase. Given that brine is more diffusive than the hydrocarbons, the longest apparent T2 from the brine phase can be made short enough to cause separation between the two phases in T2 space, thereby eliminating the need for T1 separation. Wait time manipulation can then be used to quantify hydrocarbon volumes when the two phases are separated in the T2 domain.
In this article we focus on determination of the residual oil saturation using the EDM, while also providing guidelines for job screening and acquisition parameter selection. Several case histories that are provided are used to illustrate the basic concepts and different methodologies available.
Air Injection LTO Process: An IOR Technique for Light-Oil Reservoirs
Authors: Ren S. R. , Greaves M. , Rathbone R. R. 
Published: December 2007

Summary
The paper describes an air injection improved oil recovery (IOR) process for the recovery of residual oil from light-oil reservoirs. Unlike the air injection technique applied in heavy-oil reservoirs, the main concern for a light-oil reservoir is to remove the oxygen from the injected air by some kind of spontaneous reaction between the oil and oxygen. In-situ combustion in heavy oil reservoirs is a very effective reaction pathway to achieve complete oxygen consumption, as well as to generate heat for enhanced oil recovery. For deep light-oil reservoirs, in-situ combustion is not necessary and may not be readily sustained. More likely, so-called low temperature oxidation (LTO) will prevail. In this study, the potential for LTO reactions to consume oxygen, the reaction rate, and the reaction pathways are investigated. A simplified LTO reaction model has been established based on experimental data obtained from a batch reactor experiment. The model was validated against high-pressure flow displacement experiments in an oxidation tube. A scoping simulation study on a reservoir scale has enabled a sensitivity assessment of the process to be made. The effect of air injection rate, reservoir dip, oil viscosity, formation permeability, numerical grid size, and reservoir temperature on oil recovery and the thermal effect were investigated. Compared with what is normally understood to be conventional air injection (insitu combustion), the air injection LTO process is flexible in terms of injection rate, stable because of spontaneous reaction (if the reservoir temperature is high enough), and also an economic alternative to hydrocarbon, nitrogen, or carbon dioxide gas. It can also be used as a secondary recovery method in reservoirs that are not suitable for water injection.
Utilization of Mud Weights in Excess of the Least Principal Stress to Stabilize Wellbores: Theory and Practical Examples
Authors: Ito Takatoshi , Zoback Mark D. , Peska Pavel 
Published: December 2007

SummaryIn this paper, we address the theoretical possibility of drilling with mud weights in excess of the least principal stress for cases of particularly high pore pressure or severe wellbore instability. Because lost circulation caused by hydraulic fracturing is to be avoided, we consider three critical wellbore pressures, pfrac, plink, and pgrow. Tensile fractures initiate at the wellbore wall at pfrac, link up to form large axial fractures that are subparallel to the wellbore axis at plink, and propagate away from the wellbore at pgrow. It is obvious that lost circulation cannot occur if the wellbore pressure during drilling is below pfrac. However, even if pfrac is exceeded and tensile fractures are initiated at the wellbore wall, fracture propagation (and, hence, lost circulation) will be limited as long as the wellbore pressure is below plink. Finally, if the wellbore pressure is greater than plink, the fractures will not grow away from the wellbore (and significant lost circulation will not occur) if the wellbore pressure is below pgrow, which must exceed (if only slightly) the least principal stress. In general, our modeling shows that pfrac and plink can be maximized by drilling the wellbore in an optimally stable orientation, and pgrow can be maximized with noninvading drilling muds that prevent fluid pressure from reaching the fracture tip. We apply the model that uses in-situ stress data collected in real fields, such as the South Eugene Island field in the Gulf of Mexico and the Visund field in the northern North Sea.
New Model of Acid-Fracture Conductivity Based on Deformation of Surface Asperities
Authors: Gong Ming , Lacote Stephan , Hill A. D. 
Published: December 2007

Summary
Acid-fracture conductivity is affected by the aperture and contact area of the fracture under closure stress. This, in turn, depends on the surface asperities created by the acidizing process and the mechanical strength of these asperities. Acid contact time, acid leakoff, rock mechanical properties, and formation heterogeneity all affect the creation of hydraulic conductivity of an acid fracture.
We have conducted a systematic experimental study to investigate the mechanisms of the creation of hydraulic conductivity in acid fractures, including characterization of the surface roughness created by acid etching, investigation of the damage to the rock compressive strength by acid, and measurement of hydraulic conductivity under closure stress. Experimental data show that longer acid contact results in rougher fracture surfaces and, in turn, higher hydraulic conductivity. However, acidizing also reduces the rock compressive strength causing the surface asperities to easily deform under stress.
Based on our experimental results, a new fracture deformation model was derived which considers both the surface roughness and the rock mechanical properties. The fracture closure under stress is modeled as plastic deformation of asperities. Finally, a cubic law is used to calculate the fracture conductivity. The prediction of acid-fracture conductivity using this model with appropriate parameters shows good agreement with the experimental data.
Ram/Powell Deepwater Tension-Leg Platform: Horizontal-Well Design and Operational Experience
Authors: Lester G. Scott , Lanier Gary H. , Javanmardi Kaz , Bernardi Tony , Halal Afif S. 
Published: December 2007

Summary
A key focus of the Ram/Powell project is to utilize high-rate (&gt;20,000 BOPD), high-volume wells (i.e., reserves several times greater than that of shelf wells) to enhance project profitability. Completions with large 5½-in. production tubing and horizontal openhole gravel packs (OHGP's) exceeding 2,000 ft in length have been implemented successfully. The horizontal OHGP design, the first implemented in the deepwater Gulf of Mexico (GOM), was selected as a means to improve well reliability over prior horizontal completion designs and sustain high production rates without plugging. A high rate of sand-control failure and plugging have plagued prior GOM horizontal non-gravel-packed completions. Achieving high-quality completions is a major project emphasis. Drilling, completion design, and operational experience of the horizontal wells are discussed.
Production from the Ram/Powell tension-leg-platform (TLP) development, Shell's third TLP, began in September 1997. The TLP is located at Viosca Knoll Block 956 in 3,214 ft of water. Four wells were predrilled prior to TLP installation. Ten wells are completed. Five are horizontal OHGP's, one is a single-zone cased gravel pack, and the remainder are two- and three-zone-selective cased gravel-packed completions. Rig operations concluded in January 2000.
Mud Design To Minimize Rock Impairment Due To Particle Invasion
Authors: Abrams A. 
Published: December 2007

Solids invasion and formation impairment can be minimized by adding bridging materials to drilling muds. Measurement of size distributions of solids in the muds along with calculations of rockpore sizes can be used to design competent muds. Test results of a laboratory mud agree well with published results.

Introduction
Although invasion and formation damage occur with all muds during drilling, it is possible to minimize solids invasion and formation impairment by adding bridging material to the muds. This bridging material is chosen by matching its size to the formation-rock pore sizes. Techniques (particularly the Coulter counter method) are now available for measuring the size distributions of solids in the muds. This measurement, coupled with calculation of rock pore sizes from permeability or capillary pressure data, forms the basis of the matching procedures reported here for the design of competent muds that is, muds that impair to depths normally penetrated by perforations.Two rules are used for selecting the size and concentration of bridging materials.1. The median particle size of the bridging additive should be equal to or slightly greater than one-third the median pore size of the formation.2. The concentration of the bridging size solids must be at least 5 percent by volume of the solids in the final mud mix.Laboratory tests with competent muds show that impairment caused by invasion of mud particles occurred to a depth of less than 1 in., a depth normally penetrated by perforations. Levels of impairment observed do not significantly affect injectivity or productivity of the systems studied. A laboratory mud was tested on 4- to 6-darcy unconsolidated sand in a radial-flow apparatus. Also, a Wasson San Andres field mud was tested in linear flow tests on 5- and 50-md dolomite cores taken from the Wasson field. Where comparisons are possible, these results agree with those for similar tests reported in the literature.

Results of Studies
Results from investigations of the effects of drilling-mud particle invasion on rock permeability can be summarized as follows.1. Invasion and formation damage occur with all muds.2. The depth of invasion and level of impairment can be controlled, to a certain degree, by designing the mud to include bridging material.3. The effectiveness of the bridging material in reducing invasion is a function of the concentration and particle size of the material and of the pore sizes of the formation rock.4. Damage is most likely to occur in higher permeability formations; most muds contain sufficient quantities of particles, including cuttings, in the size range required to bridge lower-permeability rocks.5. Where invasion occurs, backflushing does not remove the impairment.These results are based primarily on tests performed on linear, consolidated cores using fluids that in many instances were not designed to minimize invasion. Although depths of invasion as great as 12 in. have been reported, impairment with competent muds has been found to occur within several inches of the wellbore.
JPT
P. 586^
Effects of Pressure Drop in Horizontal Wells and Optimum Well Length
Authors: Penmatcha V. R. , Arbabi Sepehr , Aziz Khalid 
Published: December 2007

SummaryAs the length of a horizontal well is increased, its contact with the reservoir increases. But at the same time, the resistance to flow in the well also increases, which has a direct negative effect on the productivity of the well. The overall performance of a horizontal well depends on the balance of these two opposing factors. A semi-analytical well model is developed for homogeneous reservoirs which can quantify the effects of both single-phase oil and two-phase oil/gas flow pressure loss in the well on the overall well performance. The model is quite flexible and can incorporate any friction factor correlation. A methodology is developed to show the effects of various reservoir, fluid, and well parameters on well productivity. We demonstrate that ignoring frictional effects could lead to unrealistically higher production estimates and longer breakthrough times for water or gas. As a result of pressure drops in the well, breakthroughs occur first at the heel of the well. A methodology is also developed to calculate the optimum horizontal well length.
Comprehensive Reservoir/Wellbore Model for Horizontal Wells
Authors: Penmatcha V. R. , Aziz Khalid 
Published: December 2007

Summary
Comprehensive, three-dimensional, anisotropic and transient, reservoir/wellbore coupling models are developed for infinite-conductivity and finite-conductivity wellbores to calculate the productivity of a horizontal well placed in a box-shaped drainage volume under single phase flow conditions. The finite-conductivity well model considers frictional and accelerational pressure drops in the wellbore. It also takes into account the effects of fluid inflow into the well. These models are semianalytical in nature and can be used under transient or pseudosteady state flow conditions. The infinite-conductivity well model is compared with the uniform flux model to show the differences in well productivity calculations. The effects of wellbore pressure drop on well productivity are shown using the finite-conductivity well model. These models can provide reference solutions to calculate well indices or to check the accuracy of a numerical simulator. Because of their analytical nature they are easier and faster to use than numerical simulators. Using superposition in space and time, these models can be run under a variety of constraints. We believe that our finite-conductivity well model is more general than any published previously.
Production Logging in Horizontal Wells by Use of Ultrasonics
Authors: Nyhavn Fridtjof , Bang Jon , Øyangen Terje 
Published: December 2007

Summary
This paper discusses technical and practical aspects on the future needs for monitoring of flow conditions in deviated and horizontal production and injection wells. A monitoring technique based on ultrasound has been developed. Examples of measurements in various North Sea wells are presented. The results are promising, and show the potentials of nonintrusive techniques for flow monitoring. It is expected that a combination of several sensor principles would facilitate the interpretation of downhole flow conditions.
Sulfide Removal in Reservoir Brine by Indigenous Bacteria
Authors: Jenneman G. E. , Moffitt P. D. , Bala G. A. , Webb R. H. 
Published: December 2007

Summary
A field test was performed at the Coleville field to evaluate the ability of indigenous bacteria to remove sulfides from reservoir brine. Ammonium nitrate and sodium phosphate were injected continuously at two injectors for nearly 50 days. Sulfide levels at the two injectors declined by 42 to 100% and by as much as 50 to 60% at two adjacent producers. Concentrations of indigenous sul- fide oxidizing, nitrate-reducing bacteria increased at injectors and producers while concentrations of sulfate-reducing bacteria remained unchanged or decreased slightly. Stimulation of indigenous beneficial bacteria has potential application as a costeffective, low toxicity means to remove and control sulfides in reservoir brines.
Natural Downhole Separation and Its Impact on Production Performance
Authors: Asheim H. A. 
Published: December 2007

Summary
This article deals with phenomena associated with gravity-induced separation along the completed interval of inclined wells. The model developed computes liquid accumulation and production performance. From the results it is shown that both the overall inflow performance and the gas-liquid ratio observed at the surface are affected by the downhole separation.
It is shown that downhole separation may be constrained by either backseepage to the reservoir or countercurrent flooding along the wellbore. The liquid backflow rate limit due to flooding has been derived explicitly, providing a design parameter for downhole separation devices.
Incorporating Seismic Data of Intermediate Vertical Resolution Into Three-Dimensional Reservoir Models: A New Method
Authors: Behrens R. A. , Tran T. T. 
Published: December 2007

Summary
Three-dimensional (3D) earth models are best created with a combination of well logs and seismic data. Seismic data have good lateral resolution but poor vertical resolution compared to wells. The seismic resolution depends on seismic acquisition and reservoir parameters, and is incorporated into the 3D earth model with different techniques depending on this resolution relative to that of the 3D model. Good vertical resolution of the seismic data may warrant integrating it as a continuous vertical variable informing local reservoir properties, whereas poor resolution warrants using only a single map representing vertically averaged reservoir properties. The first case best applies to thick reservoirs and/or high-frequency seismic data in soft rock and is usually handled using a cokriging-type approach. The second case represents the low end of the seismic resolution spectrum, where the seismic map can now be treated by methods such as block kriging, simulated annealing, or Bayesian techniques. We introduce a new multiple map Bayesian technique with variable weights for the important middle ground where a single seismic map cannot effectively represent the entire reservoir.
This new technique extends a previous Bayesian technique by incorporating multiple seismic property maps and also allowing vertically varying weighting functions for each map. This vertical weighting flexibility is physically important because the seismic maps represent reflected wave averages from rock property contrasts such as at the top and base of the reservoir. Depending on the seismic acquisition and reservoir properties, the seismic maps are physically represented by simple but nonconstant weights in the new 3D earth modeling technique.
Two field examples are shown where two seismic maps are incorporated in each 3D earth model. The benefit of using multiple maps is illustrated with the geostatistical concept of probability of exceedance. Finally, a postmortem is presented showing well path trajectories of a successful and unsuccessful horizontal well that are explained by model results based on data existing before the wells were drilled.
Uncertainty Analysis in Predictive Reservoir Simulation Using Gradient Information
Authors: Lépine O. J. , Bissell R. C. , Aanonsen S. I. , Pallister I. C. , Barker J. W. 
Published: December 2007

Summary
We demonstrate how gradient-based techniques can be used to estimate uncertainty in predictive reservoir simulations made following history matching. We discuss how the gradient calculations can help in finding the parameters that make the largest contributions to the uncertainty, estimating the uncertainty on these parameters, and estimating the uncertainty in predicted quantities by use of a linear analysis. The methodology is illustrated on two field examples, and compared with other methods of uncertainty quantification.
Analysis of Pressure/Flow-Rate Data With the Pressure-History-Recovery Method
Authors: Gilly Patrick , Horne Roland N. 
Published: December 2007

Summary
This study presents a new way to integrate flow rate history and pressure history data in well-test analysis. The method used is an extension of the deconvolution principle to a chosen period of time before the well test. It is based on the recovery of missing parts of the pressure history by taking into account the flow rate history and the available sections of measured pressure history. The method has the advantage of working without making any assumption about the reservoir by using the data itself to define the "model." A real example with 71 pressure points and 70 corresponding flow rate points shows how it is possible to recover the first 20 pressure points correctly considering that only the flow rate history and the last 51 pressure points are known.
The main purpose of this procedure is to have an alternative to treat the problem of flow rate variations both before and during the well test. In such a case, neither the usual deconvolution (only applicable for flow rate variations during the well test, when flow rate and pressure are both known), nor the multirate superposition plots (which assume specific reservoir behavior) can be applied properly. In addition, the principle of the method enables us to extend its use to the analysis of well tests with pressure recording errors or missing pressure recording. Examples show that it is possible to make a good analysis of a well test with missing pressure regions when current methods give only parts of the information.
Numerical Solution of the Material Balance Equations of Compartmented Gas Reservoirs
Authors: Hagoort Jacques , Hoogstra Rob 
Published: December 2007

Summary
This paper presents a robust and rigorous method for the numerical solution of the material balance equations of compartmented gas reservoirs. The method is based on the integral form of the material balance equations and employs an implicit, iterative solution procedure. The proposed method enables extension of traditional p/z analysis of single gas reservoirs to complex, compartmented gas reservoirs.
Example calculations of the depletion of a compartmented reservoir show how the p/z is affected by crossflow, reservoir size, and depletion rate. The depletion behavior can be rationalized by the observation that depletion of a compartmented reservoir at a constant rate tends to develop a semisteady state. A field example is presented that illustrates the capabilities of the extended material balance for the analysis of the past performance of compartmented reservoirs.