bluuebunny/crossref_metadata_2025 huggingface dataset:
Fully Coupled Geomechanics and Fluid-Flow Analysis of Wells With Stress-Dependent Permeability
Authors: Chin L. Y. , Raghavan Rajagopal , Thomas L. K.
Published: December 2007

A fully coupled geomechanics and fluid-flow model is developed to analyze pressure-transient problems in stress-sensitive reservoirs with nonlinear elastic and plastic constitutive behavior. For hydrocarbon reservoirs with stress-dependent permeability (stress-sensitive reservoirs), the coupled interaction between geomechanics and fluid production may significantly influence both the stress state and the fluid flow in the reservoir. Therefore, in general the coupling effect cannot be ignored when analyzing stress-sensitive reservoir problems. Detailed model formulations and the numerical implementation are presented. Practical applications illustrating various aspects of well behavior of stress-sensitive reservoirs are also demonstrated in this article.
Neural-Net Identification of Flow Regime With Band Spectra of Flow-Generated Sound
Authors: van der Spek Alex , Thomas Alix
Published: December 2007

Multiphase production log interpretation requires that the flow regime along hole in the wellbore is known. Flow regime is the cased-hole analog of lithology. Knowledge of the flow regime will help to interpret tool signals, will help to evaluate the flow rate on a per phase basis, and will reduce post-processing load. The flow regime can be classified correctly by a neural net in up to 87% of all cases using 1/3 octave band spectra of flow-generated sound plus the pipe inclination angle. Without the inclination an 88% correct classification can be achieved. A neural net trained on commercially available tool data (noise cuts) appears to be too sensitive to the wellbore inclination. Hence, application of automated neural net interpretation of noise logs requires a new generation of noise logging tools.
Modeling Porosity Distribution in the A'nan Oilfield: Use of Geological Quantification, Neural Networks, and Geostatistics
Authors: Wang L. , Wong P. M. , Shibli S. A. R.
Published: December 2007

A'nan Oilfield is located in the northeast of the Erlian Basin in North China. The porosity distribution of the oil-bearing stratum is primarily controlled by complex distribution patterns of sedimentary lithofacies and diagenetic facies. This paper describes a methodology to provide a porosity model for the A'nan Oilfield using limited well porosity data, with the incorporation of the conceptual reservoir architecture. Neural network residual kriging or simulation is employed to tackle the problem. The integrated technique is developed based on a combined use of radial basis function neural networks and geostatistics. It has the flexibility of neural networks in handling high-dimensional data, the exactitude property of kriging and the ability to perform stochastic simulation via the use of kriging variance. The results of this study show that the integrated technique provides a realistic description of porosity honoring both the well data and the conceptual framework of the geological interpretations. The technique is fast, straightforward and does not require any tedious cross-correlation modeling. It is of great benefit to reservoir geologists and engineers.
Ejectors for Boosting Low-Pressure Oil Wells
Authors: Villa Marco , De Ghetto Giambattista , Paone Francesco , Giacchetta Giancarlo , Bevilacqua Maurizio
Published: December 2007

The first field installation of a multiphase surface ejector was successfully accomplished in the Villafortuna oilfield (Italy) in 1996. The ejector increased the oil production rate by 30% and demonstrated the viability ofthe system as a reliable low cost-small size boosting system that had minimal impact on existing facilities, and is suitable for applications in existing fields or for new development both onshore and offshore.

The article describes the main steps ofthe R&D project, developed in collaboration with the University of Ancona, as well as the testing process in which different ejector geometries were extensively tested with crude oil and gas in the Agip's multiphase loop of Trecate.

The article describes the installation in the Villafortuna field as well as other studies under development.
Fracturing Horizontal Wells in Gas Reservoirs
Authors: Soliman M. Y. , Hunt J. L. , Azari Mehdi
Published: December 2007

The fracturing of horizontal wells has recently gained wide acceptance as a viable completion option to maximize the return on investment. This is especially true in the case of tight gas formations.

Horizontal wells have unique rock mechanics and operational aspects that affect fracture creation and propagation and control fracture orientation with respect to the horizontal well. It has been well documented that fracture orientation greatly affects the productivity and well testing aspects of the fractured horizontal wells. Depending on stress orientation relative to the wellbore, the fractures may be transverse or longitudinal.

This paper presents a model for fractured horizontal wells operating under constant pressure conditions. This condition is most suitable for producing tight gas reservoirs. The model considers the presence of either transverse or longitudinal fractures.

In this paper, we examine the factors involved in determining the optimum number of transverse fractures for both finite and infinite reservoirs. For a group of transverse fractures, the rate distribution for each fracture is presented and analyzed. The effect of uneven fracture length is briefly presented.

The performance of a longitudinal fracture is examined and compared to a fractured vertical well and a transverse-fractured horizontal well. A comparison of longitudinal versus transverse fractures from reservoir and operational points of view is presented. Also included is a short discussion of field examples.

Because performance of a highly conductive longitudinal fracture is almost identical to that of a fractured vertical well, the existing solutions for fractured vertical wells may be applied to longitudinal fractures with a high degree of confidence. This approximation is valid for moderate to high dimensionless conductivity. In the case of transverse fractures, the outer fractures outperform the inner fractures. However, in most practical cases, more than two fractures are necessary to efficiently produce the reservoir. A simplified economic analysis supports this conclusion.
Formation Evaluation of Some Limestone Reservoirs With Particular Reference to Well Logging Techniques
Authors: Finklea Ernest E.
Published: December 2007

Introduction

Evaluation of carbonaceous rocks as to their productive possibilities was for many years virtually impossible from electrical logs. True, many carbonaceous formations had sections of sufficient homogeneity and thickness that methods of interpretation normally associated with sands could be used with a fair degree of success. Unfortunately, the formations having the proper characteristics for such methods were the exception rather than the rule; hence, the log found little use except as a correlation tool.

In recent years many new logging tools have been presented to the industry with the result that under proper conditions it is often possible to arrive at a satisfactory interpretation of the carbonaceous beds traversed by the drill bit. The so-called "proper conditions" are the key to a successful approach to any logging program or interpretation. However, it is not to be concluded that in every instance the conditions can be controlled or anticipated to the extent that the logs obtained will lend themselves to a simple interpretations Too often the combination of Mother Nature and the limitations of even the latest well logging equipment will result in a log from which the logging experts can do little more than make an educated guess as to its interpretation.

The theory of the various logging devices and quantitative interpretations has been amply covered in the literature. This discussion will concern itself with the more common type of carbonaceous reservoir rocks and approaches that may be made toward their evaluation by means of various logging techniques.

Viewed strictly from a logging standpoint, the depth, lithology, porosity, fluid content, borehole diameter variations, and formation dips are the parameters that may be determined. Those that cannot be determined are permeability and, to a degree, the depth of invasion of the mud filtrate and the physical characteristics of the rock. All of these have been discussed in numerous papers; however, their importance to carbonate formation evaluation is such that it is felt time will not be wasted in reviewing some of the more salient points as related to the examples to be discussed.
A Decline-Analysis Technique Incorporating Corrections for Total Fluid-Rate Changes
Authors: Masoner Lance O.
Published: December 2007

Decline analysis inherently assumes a constant total-reservoir-fluid rate in contrast to constantly varying rates in actual field operations. This paper provides an approach for determining decline constants under varying total fluid rates for secondary or tertiary oil recovery processes. It further enables forecasting oil and nonoil production performance under different total fluid rate strategies. The technique helps identify pseudosteady state flow periods when decline analysis techniques are valid. It distinguishes incremental from accelerated oil responses when a recovery process change, operating practices, or workover activity causes a total fluid rate change.
Analysis and Interpretation of Water/Oil Ratio in Waterfloods
Authors: Yortsos Y. C. , Choi Youngmin , Yang Zhengming , Shah P. C.
Published: December 2007

An important problem in water control is the identification of the dominant reservoir or production mechanisms. Recently, Chan (Chan, K.S.: "Water Control Diagnostic Plots," paper SPE 30775 presented at the 1995 SPE Annual Technical Conference and Exhibition, Dallas, 22–25 October) postulated that a log-log plot of the water/oil ratio (WOR) produced vs. production time may be used to diagnose these factors. In this paper we provide analytical and numerical results for a variety of waterflood conditions to explore this possibility.

We show analytically that the late-time slope of the log-log plot can be related to the well pattern and the relative permeability characteristics, specifically the power-law exponent in the kro − Sw relationship or the reservoir heterogeneity. Analytical results are provided for the behavior immediately following water breakthrough. In certain simple cases (mobility ratio equal to 1, layered systems), analytical type curves can be derived. In the general case, we use numerical simulation to provide numerical type curves.

The results are summarized in terms of the various power-law scalings in different time regimes and by a catalog of numerical type curves. They confirm the potential of WOR-time plots as diagnostic tools for reservoir analysis and characterization.
Performance Evaluation and Formation Damage Potential of New Water-Based Drilling Formulas
Authors: Argillier J. F. , Audibert Annie , Longeron Daniel
Published: December 2007

Formation damage risks are well documented for standard mud formulations but they are poorly analyzed for new types of non-polluting muds. This paper describes extensive laboratory work aimed at evaluating the behavior of these new types of mud formulations. First, static and dynamic filtration experiments were conducted on paper filters and rock slices. Examination of mud cakes by means of cryo-SEM has permitted correlation of filtration behavior with the structural characteristics of both external and internal mud cakes. Then, the simulation of the full process of mud invasion in oil-bearing reservoirs was achieved by performing static and dynamic filtration experiments in a specially designed core-holder cell containing 40 cm long sandstone core samples. Cumulative filtrate losses and pressure drops across six sections of the core, while circulating the mud and back flushing the oil, were continuously monitored to evaluate the permeability damage. Damage arising from overbalanced conditions has been evaluated in terms of cake permeability, fluid loss characterization and reduction in oil permeability after mud exposure. For the three mud compositions tested here, the filtration process in high permeability sandstones is mainly controlled by external mud cakes. Damage is severe but an additional damage due to the trapped aqueous filtrate phase can strongly affect the oil relative permeabilities. This approach has given a complete behavior understanding of new water based drilling fluid formulations including evaluation of their performances, limits of use at high temperature and assessment of risks for different operational conditions.
Field Hydraulic Tests Improve HPHT Drilling Safety and Performance
Authors: Isambourg Patrick , Bertin D. L. , Brangetto Martial
Published: December 2007

For the Elgin-Franklin UKCS fields, drilling of the high pressure/ high temperature (HPHT) phase is critical due to the narrow margin between formation pore and fracturation pressures. This problem is accentuated by the extreme temperature (up to 205°C— 400°F) and pressure (up to 1,200 bar—17,400 psi). A new generation of down-hole pressure while drilling (PWD) tools allows a better real-time monitoring of the bottom-hole pressure, but cannot withstand the extreme temperature of the entire HPHT phase. Furthermore, down-hole and surface pressures are dependent on complex hydraulic phenomena which make predictions challenging. Consequently, it was decided to perform hydraulic tests before drilling the HPHT section of the well 22/30c-G4 (first Elgin development well), in order to quantify the surface and down-hole pressures and temperatures on several operating conditions: circulating (with and without pipe rotation), tripping and flow check. Gelation tests, trapped pressure as well as pressure transmission tests were also performed. Objectives of these tests were to better understand some complex down-hole physical phenomena, to prepare practical guidelines, before drilling HPHT sections, to check reliability and accuracy of new real-time PWD tools, and to collect accurate well data for further hydraulic software packages validation or improvement. These procedures led to great benefits, both in terms of safety and performance, when drilling the HPHT phases of the well: results were considered as highly positive. This paper details down-hole measurement procedures and results, operational guide lines, tools performances, lessons learnt, and explains how to cope with sources of possible discrepancies between actual values and software predictions.
Evaluating the Transport of Solids Generated by Shale Instabilities in ERW Drilling
Authors: Martins A. L. , Santana M. L. , Campos Wellington , Gaspari E. F.
Published: December 2007

The problem of cuttings transport in the inclined sections of extended reach wells (ERW) is a major concern in the oil-well drilling industry. This article presents an innovative time-dependent mathematical model, along with a computer implementation of it, which is based on the well-known two-layer model approach. An innovative feature of this model consists in the consideration of the added amount of solids that comes from the crumbling and cave-in of the wellbore. The unstable effects of this added amount of solids is taken into account through a variable representing the added volume of cuttings per unit time and length. A finite volume approach is used to solve the system of differential equations. The paper represents a first step on the integrated analysis of cuttings transport and wellbore stability problems.
Field Applications of ERD Hole Cleaning Modeling
Authors: Hemphill A. T. , Pogue Tom
Published: December 2007

With the ever-increasing measured depths and horizontal displacements in extended-reach (ERD) wells, good hole cleaning remains a major challenge. Recently a hole cleaning model for fluids in laminar flow was presented to the industry. Since its introduction, the model has been used on many occasions to characterize hole cleaning efficiency in post-well analysis, evaluate fluid performance during the drilling of ERD wells, and to predict fluid rheological properties and pump output levels for optimum cleaning in prewell planning. In this paper, four field applications of the hole cleaning modeling in ERD and deviated wells are discussed. In these cases, the hole cleaning model was used to predict intervals of hole cleaning problems and identify certain ranges of fluid rheological properties that promoted good cleaning.
A Simplified Pore Size Distribution Apparatus
Authors: Bucker H.P. , Felsenthal M. , Conley F.R.
Published: December 2007

Introduction

In the intensive analysis of core samples from oil reservoirs, there is a recognized need for pore size distribution data. Such data, if collected with adequate precision and in sufficient quantity, should contribute to a better interpretation of fluid flow phenomena than is now possible from a knowledge of permeability and porosity data alone. It is hoped, for instance, that pore size distribution data may eventually provide a useful aid for predicting whether a water flood, or other secondary recovery methods, will be successful in a given reservoir.

Apparatus for measuring pore size distribution by mercury injection at pressures ranging from 0 to 2,000 psi have been described in the literature. All of these apparatus are somewhat complex and fairly expensive. Furthermore, the calibration of some of the apparatus is not always easy. Great difficulty, for instance, was experienced in obtaining reproducible pressure-volume correction data for the mercury pump shown in one of the references. An apparatus was therefore developed which was less complicated and less expensive than those of previously described designs. This apparatus is, in some respects, an improved version of a previously described low pressure apparatus (maximum pressure 150 psi) which did not employ a mercury pump but instead used a precision bore glass tube for measuring the injected volumes.

Tests were performed with the apparatus from vacuum to 2,000 psi and it was observed that the apparatus furnished reproducible pressure-volume correction data. In addition, it was noted that the maximum correction was small, precision of measurement was high, and operation of the entire apparatus was relatively easy. Although the apparatus was designed exclusively for samples of 1 in. diameter and 1 in. length or smaller, it could be modified without much difficulty for larger samples, if desired.
Efficient Technique for Inversion of Reservoir Properties Using Iteration Method
Authors: Chu Lifu , Komara Moussa , Schatzinger R. A.
Published: December 2007

In light of the inverse solution theory, an efficient solution procedure has been developed to generate reservoir descriptions conditioned to statistics for rock properties, hard data, and dynamic data. The technique yields realizations for wellbore skin factors at each active well and porosity and permeability which honor a priori information and dynamic production data. The technique invokes inverse solution theory to construct the objective function and uses the gradient method to generate the maximum a posteriori estimates.

Differing from the previous works, we derived and implemented a two-loop iteration method to perform the minimization. By using Krylov space-based methods to solve the linear part involved in the minimization, the explicit construction of the sensitivity coefficient matrix is avoided. Complexity analysis and computational results indicate the new algorithm is more efficient than several available methods due to the decrease of the number of the nonlinear iterations demanded for convergence.

We also developed a modified procedure for computing realizations using the Chebyshev approximation of the decomposed a posteriori covariance matrix. In this way, the expensive computational cost of the construction and decomposition of the a posteriori covariance matrix is substantially reduced. When estimating multiple categories of parameters, which is the case in this study, our new procedure produces much more accurate results than the conventional Chebyshev method.
In-Situ Sand Consolidation by Low-Temperature Oxidation
Authors: Osman E. A. , Aggour M. A. , Abu-Khamsin S. A.
Published: December 2007

Low-temperature oxidation (LTO) of crude oil has been investigated for its potential as a sand consolidation technique. Loose sand (20/30 mesh) saturated with crude oil (18 to 20° API) and brine was subjected to air injection at a low temperature (100 to 150°C) for a period of time (6 to 18 hours). The sandpacks developed compressive strengths ranging between 375 and 1,264 psi. The permeability loss due to consolidation was between 4.5 and 22%.

It was found that higher oxidation temperatures reduced the consolidation time and increased the compressive strength; but had no effect on the magnitude of permeability loss. Heavier oils required less oxidation time, caused slightly larger permeability losses, but had an insignificant effect on compressive strength. The presence of clay enhanced the LTO reactions by shortening the oxidation time and increasing the amount of residue deposited on the sand grains. This greatly increased the compressive strength, but at the expense of larger permeability losses. When interstitial water was present with clay, the permeability loss was increased further while the compressive strength was slightly reduced. Acid treatment had no effect on the residue deposited on the sand grains.

Experimental testing as well as two predictive models showed that this technique provides sufficient compressive strength to withstand sand-free, high-flow velocities and results in much smaller permeability losses compared with plastic consolidation.

It is planned to test the consolidation process in one of the fields in the Middle East. Work is in progress to optimize the process parameters for the conditions of this field to be able to test the process on the first well by December 2000.
Application of Wavelet Transforms to Reservoir-Data Analysis and Scaling
Authors: Panda M. N. , Mosher C. C. , Chopra A. K.
Published: December 2007

General characterization of physical systems uses two aspects of data analysis methods: decomposition of empirical data to determine system parameters and reconstruction of the system attributes using these characteristic parameters. Spectral methods, involving a frequency-based representation of data, usually assume stationarity. These methods, therefore, extract only average information and, hence, are not suitable for analyzing data with isolated or deterministic discontinuities, such as faults or fractures in reservoir rocks or image edges in computer vision.

Wavelet transforms provide a multiresolution framework for data representation. They are a family of basis functions that separate a function or a signal into distinct frequency packets that are localized in the time domain. Thus, wavelets are well suited for analyzing nonstationary data. In other words, a function or a discrete data set when transformed into a time-scale space using wavelets shows how it behaves at different scales of measurement. Because wavelets have compact support, it is easy to apply this transform to large data sets with minimal computations.

We apply wavelet transforms to one-dimensional and twodimensional permeability data to determine the locations of layer boundaries and other discontinuities. By binning in the time-frequency plane with wavelet packets, permeability structures of arbitrary size are analyzed. Wavelets are also applied to scaling up spatially correlated heterogeneous permeability fields.
Time-Lapse Seismic Monitoring and Dynamic Reservoir Characterization, Central Vacuum Unit, Lea County, New Mexico
Authors: Benson R. D. , Davis T. L.
Published: December 2007

This article presents the results of a multidisciplinary, four-dimensional (4D) (time-lapse), three-component (3C) (multicomponent) seismic study of a CO2 injection project in vacuum field, New Mexico. The ability to sense bulk rock/fluid properties with 4D, 3C seismology enables characterization of the most important transport property of a reservoir, namely, permeability. Because of the high volume resolution of the 4D, 3C seismology, we can monitor the sweep efficiency of a production process to see if reserves are bypassed by channeling around lower permeability parts of the reservoir and the rate at which the channeling occurs. In doing so, we can change production processes to sweep the reservoir more efficiently.
A Long Range Lookahead for Oil and Natural Gas
Authors: Hedlund C.J.
Published: December 2007

Introduction

We are living in what might be called the "Age of Mineral Energy". This is an era in which increased use of mineral energy is eliminating the drudgery of yesterday and providing a foundation for the technological progress of today and tomorrow.

We in the oil industry are fortunate to be playing a major role in the development of this significant era. The fluid fuels -oil and natural gas - are the most popular and most convenient all-around sources of energy. During 1955, close to 70 per cent of total energy consumed in the United States was supplied by oil and gas. Oil contributed 44 per cent and natural gas supplied 24 per cent.

Enthusiastic public acceptance of fluid fuels has made possible the rapid growth of the petroleum business. The industry itself has a right to be proud of the vigor and resourcefulness it has displayed in developing new sources of supply, new techniques, and new products. Along with success, however, new responsibilities have fallen upon us.

The industry has important responsibilities to its stockholders, to its employees, and to the public. This paper will treat its responsibility for long range supply. Energy is so basic to economic growth that the assurance of an adequate supply of liquid fuels over the years is one of our most important obligations.

Growth Continues with 1955 a New Record Year

We might first examine the historic growth in consumption of oil and gas to see the magnitude of the problem.

Petroleum consumption in the United States was nearly 8.5 million bbl daily in 1955, an increase of about 70 per cent over the less than 5 million bbl consumed in the first postwar year of 1946. It has exceeded by far the most optimistic outlooks made just after the war.

During the nine postwar years the population of the United States increased around 24 millions or 17 per cent. But in this same period the use of oil was growing by 70 per cent. Clearly, we must look beyond mere population growth to explain oil's expansion. The answer lies in the enormous increase which has taken place in petroleum consuming units such as oil burners and vehicles of all kinds.
Scaleup in the Near-Well Region
Authors: Durlofsky L. J. , Milliken W. J. , Bernath A.
Published: December 2007

Scaleup techniques are commonly used to coarsen detailed geological models to scales more appropriate for reservoir simulation. These techniques typically generate upscaled permeabilities through solution of the local pressure equation, subject to some type of linear boundary condition. In the near-well region, coarse scale permeabilities computed in this manner may not adequately capture key features of the fine scale flow. In this article, we present a general method for computing accurate coarse scale wellblock transmissibilities and well indexes for vertical wells in two and three dimensions. The method is based on the solution of local well-driven flow problems subject to generic boundary conditions. Simulation results for two-dimensional systems indicate that the near-well treatment always provides improved predictions compared to those obtained using standard methods. In some parameter ranges, this improvement is quite substantial. Several three-dimensional models with vertical wells are also considered and improvement relative to the standard approach is achieved in all cases. Extension of the method to accommodate more general well configurations could result in significantly improved coarse scale simulations of nonconventional wells.
An Effective Matrix Diversion Technique for Carbonate Formations
Authors: Saxon Alan , Chariag Belgacim , Rahman M. R. Abdel
Published: December 2007

The removal of formation skin damage from carbonate reservoirs is ordinarily accomplished by stimulation with hydrochloric acid. Uniform coverage of the zone being treated during matrix acidizing stimulations of carbonate reservoirs is an accepted1 requirement for successful treatment. However, the task of achieving efficient diversion and uniform zonal coverage is often difficult because of permeability heterogeneity within the treated interval.

In this article we describe a technique that has been used successfully to divert treating fluids in carbonate formations.
Enhanced Mechanistic Model and Field-Application Design of Gas/Liquid Cylindrical Cyclone Separators
Authors: Gomez L. E. , Mohan R. S. , Shoham Ovadia , Kouba G. E.
Published: December 2007

An existing mechanistic model for prediction of the hydrodynamic flow behavior in a gas-liquid cylindrical cyclone (GLCC) separator has been enhanced. The main enhancement incorporated is a flow pattern dependent nozzle analysis of the cylindrical cyclone inlet for prediction of the gas and liquid tangential velocities at the GLCC entrance. Four typical field GLCC systems were designed for actual industrial applications using the proposed model. These include multiphase metering loop with both single-phase and multiphase flow meters, and pre-separation and full separation configurations. The field applications demonstrate the cylindrical cyclone capabilities and its potential impact on the petroleum industry.
Experimental Foundation for Relative Permeability Modeling of Foam
Authors: Vassenden F. , Holt T.
Published: December 2007

Optimization of foam treatments requires modeling or simulation of the process using a foam model that is capable of reproducing the critical properties of foam. In this work we present a simple model that is based on the relative permeability concept, and is well suited for simulation of foam processes with conventional or slightly modified numerical simulators. The model can unify understanding of a number of phenomena that characterizes foam flow. The validity of the model is substantiated by experimental data. A consistent interpretation of foam breakdown, shear thinning effects, permeability effects, and effects of system pressure is possible with the model for gas relative permeability in foam presented.
Integrated Characterization and Flow Modeling of a Heterogeneous Carbonate Reservoir in Daleel Field, Oman
Authors: Abbaszadeh Maghsood , Koide Naoki , Murahashi Yoya
Published: December 2007

This article presents applications of deterministic and conditional geostatistical reservoir characterization methods to the heterogeneous carbonates of the upper Shuaiba formation in Daleel field, Oman. High-resolution reservoir descriptions based on the integration of logs, core, pressure transient tests, geology, and seismic data are constructed; and upscaled for use in reservoir simulation models to history match field performance data. Generally, geostatistical techniques combined with geology and proper upscaling of permeability heterogeneity yield best results without artificial alterations in various fluid and rock properties. Although acceptable history matches can be obtained with compromised less-detailed reservoir descriptions, these require modifications to reservoir data beyond reasonable ranges. Only detailed and concise reservoir descriptions result in history matches that are consistent with a variety of measured data sources.
Characterizing the Greater Burgan Field With Geochemical and Other Field Data
Authors: Kaufman R. L. , Kabir C. S. , Abdul-Rahman B. , Quttainah R. , Dashti H. , Pederson J. M. , Moon M. S.
Published: December 2007

This paper describes recent results from an ongoing geochemical study of the supergiant Greater Burgan field, Kuwait. Oil occurs in a number of vertically separated reservoirs including the Jurassic Marrat reservoir and Cretaceous-Minagish, -Third Burgan, -Fourth Burgan, -Mauddud, and -Wara reservoirs. The Third and Fourth Burgan sands are the most important producing reservoirs. Over 100 oils representing all major producing reservoirs have been analyzed using oil fingerprinting as the principal method, but also supported by gravity, sulfur, and pressure-volume-temperature (PVT) measurements.

From a reservoir management perspective, an important feature of the field is the approximately 1,200-ft-long hydrocarbon column which extends across the Burgan and Wara reservoirs. Oil composition varies with depth in this thick oil column. For example, oil gravity varies in a nonlinear fashion from about 10°API near the oil/water contact to about 39°API at the shallowest Wara reservoir. This gravity-depth relationship makes identification of reservoir compartments solely from fluid property data difficult. Including oil geochemistry in the traditional mix of PVT and production logging data improves the understanding of compartmentalization and fluid flow in the reservoir, both in a vertical and lateral sense.

The composition of reservoir fluids is controlled by a number of geological and physical processes. We attempted to identify unique sets of geochemical parameters that were sensitive to specific oil alteration processes. One set of geochemical properties correlated strongly with gravity and is, therefore, related to the gravity-segregation process. A second set of parameters showed essentially no correlation with gravity or depth but established unique oil fingerprints for most of the major producing reservoirs and identified a number of different oil groups within the Burgan and Wara reservoirs. We interpret the presence of these oil groups to indicate reservoir compartments owing to laterally continuous shales and faults which act as seals on a geologic time frame. More tentative is the identification of production time frame barriers from the fluid composition data. The oil fingerprint data have been used to distinguish oils from the major producing reservoirs and evaluate hydrocarbon continuity within the reservoirs.
Development Drilling From a Floating Rig
Authors: Eckerfield R.J. , Soemantri B.
Published: December 2007

A drilling concept using a floating rig to drill development wells has been used successfully offshore Indonesia. The results have been acce-lerated cash flow and more effective use of equipment.

Introduction

In 1973, Union Oil Co. of Indonesia, acting as operator under a production-sharing agreement with Pertamina, the Indonesian state oil company, drilled a discovery well in the Kerindingan field offshore East Kalimantan, using the floating rig Wodeco VI. The company wanted to develop the field and get it on production as soon as possible, but no other rig was available. To accelerate possible, but no other rig was available. To accelerate development, it was decided to develop the field with the Wodeco VI.

The project was successful, and the concept also has been applied in the Sepinggan and Attaka fields.

Equipment and Procedure

The concept involves two "new" hardware systems: a multislot subsea drilling template that fixes well spacing, and a subsea casing-hanger modification that allows subsequent casing tie-back to the platform.

Similar templates have been used in jack-up drilling operations, where a mud-line suspension system is used to support the casing at the mud line. In the jack-up operation, the template is used only to space the wells. Three such templates have been used with a jack-up to complete development projects in the area.

The floater-type template structure (Figs. 1 and 2) is much heavier than usual because it is designed to support the 30-in. conductors, as well as to space them out.

P. 711
Environmental Aspects of Produced Waters From Oil and Gas Extraction Operations in Offshore And Coastal Waters
Authors: Koons C.B. , McAuliffe C.D. , Weiss F.T.
Published: December 2007

Environmental literature has been greatly concerned with possible detrimental effects of continued produced-water discharges in offshore and coastal areas. This review paper presents results from a number of studies that should relieve some of these concerns.

Introduction

This paper reviews the constituents of produced waters and their effects on both offshore and coastal marine environments. Considerable laboratory and field data were interpreted.

This review paper was prepared to allay certain concerns expressed recently in environmental literature about possible detrimental effects on the marine environment of continued produced-water discharges in offshore and coastal areas.

Petroleum Hydrocarbons in Petroleum Hydrocarbons in Produced Waters Produced Waters Inputs

A recent National Academy of Sciences (NAS) report reviews the input of petroleum hydrocarbons to the marine environment from various sources. This study estimates that the worldwide input of oil to the oceans from all sources is about 6 million metric tons per year and from offshore drilling and production operations only about 0.08 million tons per year. Of this latter total, about 0.06 million tons comes from major spills. The remaining 0.02 million tons is attributed to minor spills (50 bbl or less) plus discharges of oilfield-produced waters during normal drilling and producing operations. Table 1 summarizes the input estimates from the different sources.

Another particularly interesting comparison can be made between the produced-water input and the much higher continuous discharge of petroleum hydrocarbons from submarine seeps, estimated to total 0.6 million metric tons per year. Seeps have been discharging hydrocarbons into the marine environment for millions of years. Petroleum hydrocarbons also are being added continuously to the marine environment by erosion and discharge from uplifted sedimentary rocks containing hydrocarbons generated during burial. Thus, petroleum hydrocarbons are certainly not substances foreign to the marine environment.

The relative amount of hydrocarbons contributed to the marine environment by oilfield-produced waters is so small that any over-all environmental effects from this input should be minimal.

Fate

Water coproduced with oil and gas and separated for discharge retains up to 50 ppm of separate-phase oil as small droplets. The water also may contain up to 35 ppm of dissolved hydrocarbons. These produced waters discharged from offshore operations are diluted with large volumes of moving water, The oil (dispersed and dissolved) immediately undergoes a number of changes that result in changes in concentration and composition. The mechanisms are dilution, evaporation, spreading, emulsification, air-sea interchange, biological degradation, and photo-oxidation. These natural processes quickly lower the actual measured concentrations of hydrocarbons.

JPT

P. 723
Diffraction Theory and Statistical Methods To Predict Wave-Induced Motions and Loads for Large Structures
Authors: Loken A.E. , Olsen O.A.
Published: December 2007

This paper presents the results of computations of wave loads on fixed antifloating structures using three-dimensional, sink-source techniques (diffraction theory). Theoretical calculations are compared with model experiments. Statistical methods are discussed also.

Introduction

Basic contributions to the use of three-dimensional diffraction theory are the studies of Lebreton and Cormault and Garrison and Seetharama Rao. Since their presentations, this method increasingly has become the predominant technique for handling wave-induced loads on large offshore structures of arbitrary form.

However, strip theories based on two-dimensional (diffraction) solutions have been applied in ship design to determine responses in regular waves for some time. The linear superposition technique proposed by St. Denis and Pierson normally is used to determine the responses in irregular seas.

Different computer programs have been developed on the basis of the method proposed by Lebreton and Cormault. This paper presents the applications of a computer program and information gained from experimental program and information gained from experimental results. Computations of short-term responses in irregular seas using different wave-spectrum formulations are included also. This procedure has not been prominent in the design of large offshore structures yet, although it long has been used widely in ship design.

Theoretical Formulation

A review of the basic equations used in the diffraction theory program is presented in the following section.

The Equations of Motions

The motions of a floating structure are derived from the condition of dynamic equilibrium between excitation and restoring and the damping and inertial reactions of the system. Assuming that the system is harmonic, the six coupled linear differential equations of motions may be written as

6 -iwt (mjl + mjl) nl + Wjl nl + Cjl Nl = Fje.

l=1 .................................(1)

Here, mj is the component of the generalized mass matrix (j=l = 1,2, . . . 6) and mjl and Wjl are the added-mass and damping coefficients, respectively. The restoring coefficients Cjl and the complex amplitude of the exciting forces and moments are Fj. The real part should be used in all expressions where e-iwt is part should be used in all expressions where e-iwt is involved. The wave encounter frequency that is the same as the response frequency is denoted as w. Displacements are represented by n. Dots are used to indicate time derivatives.

A right-handed coordinate system (x, y, z) fixed with respect to the mean position of the structure with an origin in the plane of the free undisturbed surface is presented. The coordinate z points up vertically through the center of gravity and the coordinate x points in the direction of backward motion. It is assumed that the structure is symmetric about the x-z plane and the center of gravity is located in (O, O, Zc).

JPT

P. 549
Microbial-Induced Corrosion of Subsea Pipeline in the Gulf of Suez
Authors: El-Raghy S. M. , El-Leil H. M. Abou , Ghazal H. H.
Published: December 2007

In mid-May 1996, a leak developed in a 24-in. crude oil line that transfers the untreated crude oil from El-Morgan field in the Gulf of Suez to the onshore process facilities (Fig. 1). The line, a carbon steel API-5L XS-60 seamless pipeline with a wall thickness of 0.75 in., was installed in April 1993. A diving survey was carried out after an oil spill using side-scan sonar survey and a remote operating vehicle (ROV) video. The ROV inspection identified the leak to be the result of internal corrosion in eight joints located at a depth of 240 to 250 ft. After fixing the leaks, a complete ultrasonic survey was performed using a high-resolution intelligent pig. The ultrasonic data, with the sample analysis of the deposits accumulated ahead of the pig, confirmed the mode of corrosion as internal microbial-influenced corrosion (MIC) at the 6 o'clock position.

A comprehensive review of the corroded line history, the available corrosion monitoring data, and the applied corrosion-mitigation program shows the following:

corrosion monitoring using weight loss coupons, electrochemical devices, and/or chemical methods installed in the two ends of the subsea pipelines does not show any sign of a high corrosion rate (average 3 MPY); absence of the frequent pigging in the pipeline resulted in the accumulation of sludge that caused underdeposits corrosion; thermophilic sulphate-reducing bacteria (SRB) were not detected; however, some non-SRB were detected.

This article reviews the pipeline history, corrosion mechanism, inspection outlines, and reservoir souring modeling. We present a plan of action to prevent this leak from happening again, and a brief introduction for mitigation options strategies and economics.
Probabilistic Fatigue Analysis of Fixed Offshore Structures
Authors: Vugts J.H. , Kinra R.K.
Published: December 2007

This paper describes the application of probabilistic techniques to a detailed fatigue analysis of offshore structures. The structural properties are characterized by stress transfer functions in the properties are characterized by stress transfer functions in the frequency domain. Long-term statistics follow by accumulation and fatigue damage is computed using Miner's law. Spectral analysis is used to evaluate short-term stress statistics for each sea state in the wave climate.

Introduction

General Description of Fatigue in Offshore Structures

Failure caused by fatigue in welded structures is related to the variable loads experienced by the structure during its life. Fatigue under random loading conditions, as experienced offshore, is a complex subject. The present state of the art for welded steel structures generally accepts the following as trueWelded connections are most susceptible to the development of fatigue cracks.Small, sharp defects inevitably exist in welds and can cause cracks.Fatigue in offshore structures is predominantly a matter of crack propagation as a result of these defectsIn as-welded connections, stress of yield-strength magnitude in tension exist because of residual stresses.Therefore, stress fluctuations range from tension yield downward and this range of the fluctuation alone is the governing parameter.Consequently, fully tensile stress cycles and partially or wholly compressive stress cycles are equally partially or wholly compressive stress cycles are equally damaging in welded structures.The fatigue strength of welded connections is independent of the yield strength of presently used structural steels.Crack propagation and consequent fatigue damage in an offshore environment will continue at some rate, no matter how small the stress range - that is, no endurance limit is found such as in constant-amplitude, cyclic loading above 2 x 10(6) cycles.Shear stresses may be neglected in fatigue life calculations.

Stress fluctuations normally result predominantly from wave loads. These wave-induced stresses are of variable magnitude and occur in random order. The true time history of the local stresses almost invariably is simplified because it can be described adequately in statistical terms by a reasonable number of stress blocks. Each stress block is composed of a number of cycles of constant stress. Thus, the sequence of variations in the true stress history is lost. The cumulative effect of all stress blocks representing the stress history is estimated by Miner's rule of linear accumulation of damage:

nb ni Fd = -----, ni i=1

where Fd = damage ratio

and

nb = number of stress blocks considered

A fatigue failure is assumed to occur when the damage ratio, Fd, reaches unity. In fatigue analysis, this criterion is considered the definition of a local fatigue failure. This does not necessarily imply an actual failure nor a partial or complete collapse of the structure.

JPT

P. 657