bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Simple Correlation to Predict Wellbore Pressure Drop Effects on Horizontal Well Productivity
Authors: Yildiz Turhan , Ozkan Erdal 
Published: December 2007

Abstract
This study presents a simple correlation to predict horizontal well productivity influenced by wellbore hydraulics. The correlation is developed from a rigorous finite-conductivity analytical solution. An inflow factor concept is introduced as the ratio of the pressure loss inside a solid horizontal pipe to that along a horizontal well. It is shown that the inflow factor may be correlated in terms of the Reynolds number and friction factor based on total well flow rate, wellbore size, and hydraulic well conductivity. The inflow factor is used in a simple empirical equation to estimate the productivity of a horizontal well under the influence of wellbore hydraulics. The results estimated from the empirical equation are within 2% of the results from the rigorous prediction method for most practical applications.
Chemicals and the North Sea Environment: A Challenge for the New Millennium
Authors: Craddock Henry A. , Moorfield John L. 
Published: December 2007

Abstract
This paper will discuss the changing regulation surrounding chemical use and discharge in the North Sea. It will discuss the pros and cons of such regulation and look at some options and scenarios for the 21st Century.
This paper will cover some background on the use of chemicals and the progress made to develop more cost effective and efficient chemicals and chemical management leading to environmental impact of the potential discharge of chemicals in the North Sea from the oil exploration and production industry.
This paper will examine the current situation of increasing controls and regulations, problems with appropriateness of certain test protocols, reliance on hazard assessment and the potential dangers this could pose to the oil and exploration and production industry in the North Sea.
This paper will also look forward to the ‘zero’ discharge scenario which will become the norm in the not too distant future as set out in the Oslo Paris Convention ( 2020) and the interim requirements of harmonisation of controls. It will propose that the way forward is through risk assessment of chemical hazard and overall environmental impact, leading to a mature and sensibly regulated market place that will encourage the development of better products, both in terms of technical efficacy and environmental profile
Effectiveness of a Dry Gas Injection WAG Process in a Previously Waterflooded Chalk Reservoir
Authors: Wegener D. C. , Thomas L. K. , Sylte J. E. 
Published: December 2007

Abstract
Little has been published about the effectiveness of dry gas injection, as part of an immiscible WAG process, at recovering hydrocarbons from a previously waterflooded, light oil reservoir. In a PVT cell where the gas and liquid phases are placed in intimate contact, hydrocarbon vaporization can readily be demonstrated to be an effective mechanism for extracting hydrocarbons from light oils. Less easily demonstrated is the effectiveness of gas injection at recovering hydrocarbons from a low permeability porous matrix with a high water saturation.
This laboratory study investigates the potential effectiveness of gas injection, as part of an immiscible WAG process, at recovering hydrocarbons from the Ekofisk reservoir as it would exist in a post-waterflood condition. Reservoir simulation was used to design the laboratory portion of this study which in turn generated results that improved reservoir simulation. Portland outcrop chalk, similar in porosity and permeability to Ekofisk, was used along with live Ekofisk oil. The experiment was conducted at 125°F and 4000 psig which represents a cooled and partially re-pressured region of the Ekofisk reservoir.
The results of the experimental work indicated that approximately 25 weight percent of the C5+ hydrocarbons, inplace in the residual oil at the start of the gas injection phase of the experiment, were recovered after 1.0 pore volume of gas injection. Estimates of the hydrocarbon recovery attributable to swelling/viscous displacement versus that attributable to vaporization were quantified versus pore volumes of gas injected.
Adverse Effects of Poor Mud Cake Quality: A Supercharging and Fluid Sampling Study
Authors: Sarkar Amit K. , Lee Jaedong , Kasap Ekrem 
Published: December 2007

Abstract
Wireline Formation Testers (WFT) are routinely used at discrete depths of a well to collect reservoir fluid samples and to estimate undisturbed reservoir pressures, near-wellbore formation permeabilities, fluid compressibilities, and saturation pressures. A pressure profile in the vertical direction yields fluid densities and fluid-contacts (GOC and WOC) in the reservoir. Reliable results are obtained when the mud cake isolates the wellbore from the formation. When mud cake cannot provide isolation, mud filtrate invasion continues and supercharging occurs. The issue of sample quality becomes critical when using oil-based muds because the filtrate is also oil and is difficult to separate from the formation oil, a pure sample of which is needed for fluid characterization studies. This study investigated the effects of poor mud cake seal on sample quality and formation test data and its analysis when oil-based muds are used. Modeling studies were conducted using a finite element simulator.
The results of the study indicate that mud cake permeabilities need to be less than one microdarcy and mud cake to formation permeability ratios need to be less than 10−4 to achieve sample qualities higher than 90%. Conditions such as high pumpout rates, low overbalance pressures, and shallow filtrate invasion depths improve sample quality. The presence of a permeability-damaged zone around the mud cake improves sample quality but reduces the sampling pressure. The Formation Rate Analysis (FRASM) technique estimates formation permeability accurately in the presence or absence of supercharging. The formation pressure estimated using the buildup data is the pressure at the mud cake-formation interface. The supercharged pressure must be subtracted from the apparent formation pressure to obtain the true formation pressure. A simple procedure is developed for estimating the mud cake permeability and the supercharged pressure. Supercharged pressure is shown to be a product of the apparent overbalance pressure, mud cake to formation permeability ratio, and an invasion factor representing the distance up to which supercharging extends.
Stability and Flowing Properties of Aqueous Foams for Underbalanced Drilling
Authors: Argillier J-F. , Saintpere S. , Herzhaft B. , Toure A. 
Published: December 2007

Abstract
Foam stability and rheology are important parameters for foam used as a drilling fluid in underbalanced drilling. A low density fluid is one way to avoid formation damage or borehole fracturing when the reservoir has a low pore pressure, or is depleted. However foamed drilling fluids are not well understood, their stability and rheology are more complex than a conventional drilling fluid. Rheological data have to be applied to model flowing properties within the drill string and the annulus to predict and control the down hole pressure.
In this work we have studied the physico-chemical properties and the flowing properties of aqueous foams formed with a commercial system. Foam stability has been studied as a function of different parameters, including the presence of electrolytes (mono and divalent salts) and contamination by hydrocarbons. Addition of water soluble polymers to increase the stability of the foam has been studied as well as the influence of the hydrodynamic conditions on foam stability.
Flowing properties have been studied by circulation tests in a laboratory transparent flow loop (4 m long and 1 inch internal diameter). Foam circulation experimental data have been used to calculate pressure losses during foam circulation using software based on a published model (Economides 1995). The effect of the quality of the foam on the accuracy of the model has been shown, thus allowing the estimation of the domain of validity of this model. Different methodologies for rheology measuring have been compared. The influence of other parameters such as polymers concentration or foaming agent concentration have been studied also.
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History Matching Finite Difference Models With 3d Streamlines
Authors: Emanuel Alan S. , Milliken William J. 
Published: December 2007

Abstract
In the past several years, 3D streamline simulation (3DSL) software has become available to the industry through commercial vendors, university coop projects, and DOE sponsored research. This paper describes the use of 3D streamlines to assist in history matching conventional finite difference reservoir simulation models.
One of the most difficult tasks in history matching individual well performance in a finite difference model is the identification of the grid blocks that affect the performance of a well. The task is exacerbated by the progression to large, complex, geostatistical models. This paper describes a technique that integrates, in a simple computer program, streamline and finite difference simulation to identify the grid blocks that affect each well and to effect changes to the model for history matching. Two case studies are presented: case 1 is a thick, stratified 60 well eolian sandstone producing under pattern waterflood and case 2 is a 70 well carbonate anticline producing under partial aquifer drive. The two cases illustrate the efficiency of the streamline-based code and the potential of the process to greatly simplify history matching.
Estimation of Hydrocarbon Viscosity with Multiple TE Dual Wait-Time MRIL Logs
Authors: Chen Songhua , Olima Oscar , Gamin Héctor , Georgi Daniel T. , Minetto J. Carlos 
Published: December 2007

Abstract
In this paper, we report a successful example of using multiple TE dual wait-time (TW) log acquisitions for quantitative characterization of San Jorge Basin reservoir oil viscosity. Previously, dual TW logs have been used to separate gas and oil, while dual TE logs have been used as a qualitative light oil indicator. Although theoretically simple, quantitative determination of viscosity from dual TE logs is complicated by several factors, including poor signal-to-noise ratio, difficulties in separating oil from water, and the uncertainty of internal gradient strength.
We used multiple TE acquisitions of dual TW logs to isolate the oil from the water signal. The values of viscosity of the reservoir fluids can be estimated from three NMR properties: intrinsic T2, apparent T2, and T1. All three approaches have advantages and disadvantages. Since T1estimates are not affected by diffusion, the uncertainty in the internal field gradient has no effect on T1-based viscosity. However, T1 is difficult to estimate because it relies on small differences in the dual TW echo data. In estimation of the apparent T2, we used a model that does not explicitly require knowledge of the internal gradient, thereby minimizing the effects arising from the uncertainty of the internal and tool gradient strengths. Since T1 and intrinsic T2 are estimated independently, the degree of agreement between the two values provides an indication of the reliability of the two estimates.
The method has been used successfully in San Jorge Basin, Argentina. Three values of TE, 1.2, 2.4, and 3.6 ms were used and a dual TW log was acquired for each TE. The data were analyzed without need for other geological information or log data from other logging tools. To complicate the matter, previous NMR core analysis of the core plugs cut from another well in San Jorge Basin showed great porosity and permeability variations. Furthermore, no reliable reservoir fluid measurements were available. Thus, interpretation was based only on the NMR log data. The four zones selected for this study were thought to contain heavy, viscous oil. However, our analysis indicated that the viscosity values of the oil are less than 5 cP. Our predictions have been substantiated by production of light hydrocarbons from the three zones that have been perforated. Further, viscosity measurements on the reservoir fluid from one of the three zones is 2.6 cP, which is in good agreement with the NMR-derived estimate of 3.3 cP.
A New Algorithm for Analysis of NMR Logging Data
Authors: Menger Stefan , Prammer Manfred 
Published: December 2007

Abstract
Nuclear magnetic resonance (NMR) logging has become an important input to formation evaluation. T2 spectra calculated from pulse-echo trains are the basic building blocks for further analysis. This paper discusses the influence of acquisition parameters such as inter-echo spacing, echo train length, and noise on T2 resolution.
The latest generation of pulse-echo logging tools allows to simultaneously record different NMR data for optimized wellsite efficiency. A new method is presented to merge these different raw echo trains into a single combined echo train. The result is a data set that is optimized with respect to T2 resolution. This echo train can be processed in an efficient way.
This paper presents laboratory and field-test data, recorded with a new generation, multi-volume NMR logging tool, demonstrating that the new algorithm is fast, stable, and yields accurate results.
More Oil with Less Water Using Downhole Water Sink Technology: A Feasibility Study
Authors: Shirman Ephim I. , Wojtanowicz Andrew K. 
Published: December 2007

Abstract
The paper reports on recent R&D progress in the Downhole Water Sink (DWS) technology resulting in an establishment of a joint industry/LSU project - DWS Initiative. Presented are recent case histories of DWS design and successful field trials. The results are then analyzed comparatively in view of the superiority of DWS over the single conventional completions. The analysis shows that, although DWS increases production of oil, its potential for reducing production of water is unknown and remains a controversial issue among operators.
The case history analysis is followed by results from the authors' theoretical and experimental study on water cut suppression with DWS. The study was performed by comparing WC development in the single (conventional) and dual (DWS) well completions for a broad range of oil reservoirs with bottom water columns. These theoretical results are supported with experiments conducted using a laboratory physical model of a dual/single completed well - reservoir system. The results, included in this paper, demonstrate the persistence and irreversible nature of WC in conventional wells compared to its flexibility and easy control in DWS completions. Defined is the range of production rates where DWS may give a sizable, up to 40%, reduction of WC. It is also shown, with calculations, how to determine the expected WC reduction for a given reservoir and well- completion design.
P. 215
Quasi K-Orthogonal Streamline Grids: Gridding and Discretization
Authors: Edwards Michael G. , Elf Regis Agut , Aziz Khalid 
Published: December 2007

Abstract
A new grid generation technique based on streamlines and equi-potentials is developed for reservoir simulation. The natural property of streamlines provides a grid that has a concentration of grid lines in high velocity regions of the flow field thereby optimizing nodal placement. Results computed with the new streamline-potential grids demonstrate a significant improvement in accuracy when compared with conventional Cartesian grids of similar resolution. Streamlines and equi-potentials are shown to be K-Orthogonal. This fundamental observation has major implications for reservoir simulation. A comparison between a two point flux approximation and a full tensor flux approximation is presented for the K-Orthogonal streamline-potential grid systems. P. 373
Problem Identification and Improved Treatment Method of a Thief Zone in a West Texas CO2 WAG for Profile Modification
Authors: Dalrymple E. D. , Creel P. , Hirth J. B. 
Published: December 2007

Abstract
During a field's pilot evaluation of a CO2 water-alternating-gas (WAG) injection into the San Andres formation in a central west Texas unit, a problem was identified: Profile information and no offset response showed the CO2 and water injections were being lost into an upper high permeability layer. This problem was allowing one of the pilot injectors to communicate into a temporary abandoned injection well 2¼ miles away.
To remedy the situation, a chemical treatment was needed that would account for such factors as continual injection of CO2, degradation of the material caused by bacterial growth, deep penetration into the thief interval, development of sufficient strength to withstand pressure extrusions, intermixing, and possible removal.
A diagnostic analysis of selected injection wells was accomplished through multirate injectivities combined with profiled entry analysis; this technique established other criteria for the solution. The solution was governed by two conditions: (1) injection had to occur at a precise rate without significant pressure resistance so that entry would occur only in the problem interval, and (2) the treatment had to be placed deep enough to prevent the CO2 WAG from re-entering the thief interval.
One of the pilot injectors selected for treatment indicated 100% of the inj ection was being lost through a 10-ft interval in the upper portion of the payzone at a determined rate. After the application, the thief zone had been shut off, and the injection was reaching the remaining reservoir. Because this action required fluid entry into more restrictive permeabilities, an increase in pressure was necessary to flood the payzone effectively.
This paper discusses the optimal treatment selection and the laboratory investigations regarding the chemical resistance to CO2. It also discusses the placement techniques chosen and provides field results, which indicate a modified injection profile.
A Computationally Efficient, Transient-Pressure Solution for Inclined Wells
Authors: Ozkan E. , Raghavan R. 
Published: December 2007

Abstract
This work provides an efficient algorithm to compute transient pressure responses of inclined wells. The solution is derived in the Laplace domain and cast into computationally efficient forms for all inclination angles. The algorithm allows the computation of pressures and derivatives at the wellbore as well as at observation points. Short- and long-time approximations for the evaluation of pressure responses are also provided. The long-time approximation is used to derive a general pseudoskin expression that is applicable for all inclination angles. Example computations are presented in the forms of tables and figures to display the efficacy, accuracy, and the practical use of the algorithm.
P. 343
Pressure-Transient Behavior of Multibranched Wells in Layered Reservoirs
Authors: Larsen Leif 
Published: December 2007

Abstract
Analytical methods are presented to determine the pressure-transient behavior of multibranched wells in layered reservoirs. The computational methods are based on Laplace transforms and numerical inversion to generate type curves for use in direct analyses of pressure-transient data. Any number of branches with arbitrary direction and deviation can in principle be handled, although the computational cost will increase considerable with increasing number of branches. However, due to practical considerations, a large number of branches is also unlikely in most cases.
Productivity Correlation for Horizontal Sinks Completed in Fractured Reservoirs
Authors: Sato Kozo 
Published: December 2007

Abstract
When completed in fractured reservoirs, horizontal sinks (hydraulically fractured wells or horizontal wells) are believed to intersect several fractures and outperform their vertical counterparts. Based on the numerical experiment outcomes, productivity correlations are developed with horizontal-sink length and fracture parameters as the correlating parameters. The correlations are of use in predicting the expected value and the most-likely minimum value of productivity for a horizontal sink parallel or perpendicular to fractures.
Analyzing the developed correlations enables us to quantify the individual contributions of a sink itself; distributed fractures, and sink-intersecting fractures to the horizontal-sink productivity. Fractures tend to yield a significantly magnified contribution to the productivity when they intersect the horizontal sink. The advantage of completing a horizontal sink perpendicular rather than parallel to fractures is attributed largely to such fractures.
P. 357
Estimation of Production Forecast Uncertainty for a Mature Production License
Authors: Jensen Trond B. 
Published: December 2007

Abstract
A comprehensive effort to estimate the range of uncertainty in the long term forecast for the mature Ekofisk and surrounding fields (Eldfisk, Embla and Tor) located in the Norwegian sector of the North Sea is presented. Even for this mature production license (PL018) which has been on production for more than 25 years we experience significant discrepancies between actual and forecasted production. This prompts the need for estimating the range of uncertainty in the reservoir production prognosis. Decision tree analysis formed the basis for our methodology in which each branch on the decision tree is coupled with a full field 3D numerical reservoir model. A large number of full field, numerical simulations were run to forecast the different realizations. Reservoir, operational and facility uncertainties were considered. These results were coupled with straightforward statistical techniques to allow estimation of probabilistic forecasts. Individual fields production forecasts were aggregated into a single license production forecast using Monte Carlo simulation.
P. 331
Acidizing in the Teak Field: A Comprehensive Approach
Authors: Gdanski R. , Jurai V. , Mohan R. , Chung R. 
Published: December 2007

Abstract
Even though reasonably successful acidizing treatments have been performed in the Teak Field for a number of years, many of the treated wells returned to the pretreatment production rate within 4 to 5 months.
A comprehensive approach was therefore undertaken in 1997 to improve production from damaged wells in the Teak Field. Using new techology and relying on historical perspectives and experience, a stimulation team set out to identify the causes of damage, recommend damage removal treatments, verify treatment effectiveness, and determine methods to prevent damage.
To accomplish these goals, team members had to establish the formation mineralogy, the damage mechanisms, the type of HF blends to use, the acid volumes to use, the amount of diverter to use, and which wells to acidize. After the acidizing jobs were performed based on these specific recommendations, the treating charts and flowback returns from these treatments were analyzed.
When these results were combined with available mineralogical and production data, the damage mechanism for each particular sand body could be determined, and these bodies were categorized into four groups. Stimulation designs could then be tailored to treat the specific type of damage that appeared in a given category.
Damage prevention strategies were also developed, which reduced the number of stimulation treatments required. The outcome of this approach has been a 37% increase in incremental production over the previous year, and an increase in estimated reserves of about 1 million barrels of oil, even though fewer acidizing jobs were done, and the jobs were begun later in the year. This paper describes how this improvement was achieved in just 1 year.
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