bluuebunny/crossref_metadata_2025 huggingface dataset:
Wellsite Interpretation of Multicomponent Induction Log Data in Anisotropic Media
Authors: Kriegshäuser B. F. , Fanini O. N. , Yu L. , Gupta P. , v. d. Horst J.
Published: December 2007

Electrically anisotropic reservoirs are encountered frequently in hydrocarbon exploration. For accurate saturation estimation and optimum hydrocarbon recovery from these reservoirs, it is essential to detect and properly describe their electrical properties. For example, in laminated sand/shale sequences or sands with different grain size distributions the resistivity parallel to the formation bedding is usually smaller than the resistivity perpendicular to the bedding. Conventional induction logging tools with transmitter and receiver orientation parallel to the borehole axis provide insufficient information to accurately evaluate hydrocarbon saturations in anisotropic reservoirs. These reservoirs usually show low resistivities from conventional induction logs, where the hydrocarbon content can be economically significant and are called "low resistivity pay." Under the sponsorship of Shell Technology EP, Baker Atlas developed and field-tested a new induction logging tool that comprises three mutually orthogonal transmitter-receiver configurations yielding all necessary data to derive the horizontal and vertical resistivities of an anisotropic formation.

Interpretation of these measurements is complicated because the magnetic field responses of horizontal induction coils are more sensitive to shoulder bed and borehole effects than conventional, vertical induction sensors. To provide a fast, yet reliable, interpretation of the formation parameters, we developed an enhanced apparent parameter estimation procedure that also applies shoulder bed corrections to the measured field data.

We match the data acquired at each logging depth with responses of an anisotropic, whole-space model optimizing both horizontal and vertical resistivities in a least-squares sense. This process incorporates information about formation dip and azimuth as well as borehole trajectory and tool rotation. Then, we integrate both horizontal and vertical resistivities over layer intervals derived from the horizontal magnetic field data. After that, we apply shoulder bed corrections to the measured data, based on the synthetic layered host model response and the corresponding whole-space responses. Finally, we match the shoulder bed corrected data at the center of each layer with synthetic responses of an anisotropic, whole-space model. These newly derived resistivities in both horizontal and vertical direction are then used to refine both, the layered earth model and the shoulder bed corrections. The process comprising whole-space response matching and refining shoulder bed corrections is repeated until convergence is achieved. This interpretation scheme developed with synthetic data and tested with field data has proven to be fast and efficient, thus allowing us to provide reliable estimates of both horizontal and vertical resistivities at the wellsite.
Application of Array Resistivity Measurements in Horizontal Wells
Authors: Frenkel M. A. , Geldmacher I. M. , Georgi D. T. , Mezzatesta A. G. , Rabinovich M. B. , Tabarovsky L. A. , Meyer W. H. , Fidan M.
Published: December 2007

When interpreting array resistivity measurements in horizontal wells, the objectives are quite different from traditional data interpretation in vertical or near vertical boreholes. While the emphasis for the latter is put on resolving the invasion profile and "true" formation resistivities, the former measurements are aimed at the identification of any nearby geometry, e.g., cap rock or oil-water contacts in the vicinity of the wellbore. In order to accomplish this, new algorithms have been developed ranging from real-time "geosteering" applications to sophisticated inversion-based processing.

Early resistivity tools were complex devices that utilized bucking coils and guard electrodes to "focus" the measurement onto a particular region in the formation, for example, shallow and/or deep. These analog focusing methods were designed for and worked well in quasi-horizontally layered formations penetrated by a near vertical well. In the last decade array tools offering a multitude of electrode or coil arrangements have been introduced. By combining data from different electrodes or receiver coils and transmitters, it is possible to mathematically focus in on a particular formation area, such as illuminating the invasion profile and obtaining a better estimate of the formation resistivity. In horizontal and highly deviated wells, the array data still can be used to characterize the invaded zone, but, more importantly, the array data can be used to probe the layered structure above and below the well. Interpreting the response of today's array resistivity tools in these situations is critical to the drilling and formation evaluation process. In horizontal wells, the response of resistivity tools in even a simple layered formation is complicated and may differ significantly from our vertical well-based intuition. However, forward modeling of the expected formation earth model and inversion techniques, from the simplest to the most sophisticated approach, can assist both the driller and the petrophysicist in extracting required information.

In this paper we demonstrate the use and effectiveness of the array resistivity tools in horizontal and near-horizontal wells. We focus on the use of the array data collected by the logging-while-drilling (LWD) Multiple Propagation Resistivity (MPR) tool as well as the wireline or pipe-conveyed driven High-Definition Induction Log (HDIL) and High-Definition Lateral Log (HDLL). For each tool the interpretation process is illustrated with field examples.
Full Tensor Upscaling of Geologically Complex Reservoir Descriptions
Authors: Wen X. -H. , Durlofsky L. J. , Lee S. H. , Edwards M. G.
Published: December 2007

The upscaling of geostatistical models characterized by oriented layering is considered. Such models are representative of a broad class of geologically complex reservoir characterizations as they display full tensor permeabilities on both the fine and coarse scales. The significant errors that result from the improper numerical treatment of the full tensor permeability are demonstrated. The application of existing upscaling approaches to these oriented systems is shown to lead to coarse models of lower accuracy, for both flow and displacement calculations, than in the case of models with horizontal layers. Two alternate upscaling procedures are presented in an attempt to improve the accuracy of these coarse scale reservoir descriptions. The first technique involves the use of a border or "skin" region, while the second approach entails the use of a rotation procedure, in which the gridblock permeability is computed in a coordinate system approximately aligned with the principal directions of the upscaled permeability tensor. Both methods are shown to generally result in improved accuracy in displacement calculations, though the rotation procedure appears to be the more accurate overall. The approaches presented here can be used in conjunction with sophisticated gridding techniques to achieve more accurate and robust coarse scale models.
Calculation of Convective and Dispersive Flows for Complex Corner Point Grids
Authors: Sammon Peter H.
Published: December 2007

Complex corner point grids are often encountered in reservoir simulation. Such grids can be severely faulted and the corner point cells near faults, and elsewhere, can be distorted. Also, extensive refinements may be used. Since such grids are usually presented without specific information regarding inter-cell contact, it is up to the reservoir simulator to decide when to connect blocks together to permit fluid flow, and also, in many cases, how to build the more extensive computational template required to model dispersive fluxes. The latter can be particularly complicated since directions both perpendicular to, and parallel with, the usual flow directions have to be resolved. Nevertheless, dispersive mixing is often a required feature, such as when modelling gas storage reservoirs where cushion gas and fuel gas commingle, or when examining convective mixing as a primary drive mechanism, such as for the VAPEX process.

A corner point grid cell starts with eight points, and can be described as the volume contained within surfaces that are stretched across the corner points associated with each of its six faces. Face contact (or near-contact) can be specified as the requirement for flow to occur from cell to cell. The contact can be full (the four face corner points are shared by each cell), or partial. The first case is easy to detect, while the latter is more complicated, breaking down into sub-cases that will be described in this paper. Once contacts are established and overlap areas are determined, suitable transmissibilities can be defined.

Refined grids need to be seamlessly incorporated into all of the above. These can be difficult to work with if several layers of refinement are present.

Once connectivities have been determined, an extended computational molecule has to built around each cell to allow for the computation of dispersive fluxes to take place. Since directions have to be resolved both parallel with, and perpendicular to, the Darcy phase velocities, an enlarged template is required. An algorithm will be described for processing lists of cell contacts to devise a suitable template for resolution of parallel and perpendicular flows. Once the template has been built, a method for computing the required longitudinal and transverse dispersive fluxes will be given.

Results of computations made using the above algorithms for building flow connections will be described. In particular, the effects of longitudinal and transverse dispersion will be shown.
Phase Behavior of Gas Condensate/Water System
Authors: Kokal Sunil , Al-Dokhi Mohammad , Sayegh Selim
Published: December 2007

Gas condensate reservoirs are an essential part of Saudi Arabia's hydrocarbon resources. A good understanding of the effect of water on the phase behavior properties of these hydrocarbons is essential for carrying out accurate forecasts of the performance of these reservoirs using numerical simulators. In addition, the scaling and corrosion tendencies of the produced water are strongly influenced by mass transfer with the hydrocarbon phase.

This paper presents unique experimental phase behavior data for a typical Saudi Arab gas condensate three-phase (water/condensate/gas) system. The objective of this work is to quantify the effect of water on gas condensate fluid properties.

The results show that appreciable amount of carbon dioxide and methane partition from the gas condensate phase into the aqueous phase. Another important observation was the mass transfer of water into the condensate phase. The mass transfer between the condensate and aqueous phases results in a decrease in the gas/condensate ratio. The carbon dioxide in solution makes the brine acidic, and can dissolve carbonate minerals from the formation, for example, calcium carbonate. In addition, the acidic or sour brine will be quite corrosive. The experimental results are compared with equation-of-state and other correlations published in the literature.
Sand Consolidation Using High-Temperature Alkaline Solution
Authors: Mamora D. D. , Nilsen K. A. , Moreno F. E. , Guillemette R.
Published: December 2007

In the period 1991-1996, sand consolidation using high-pH steam was successfully tested in 13 vertical and 7 horizontal wells in the Wilmington field, California. Savings (for not running gravel-packs) amounted to $90,000 per vertical well and $150,000 per horizontal well.

An experimental study was carried out to better understand and optimize the process. The apparatus consisted of a vertical 18 in. long aluminum cylindrical cell with an ID of 1.5 in. into which loose Wilmington Tar Zone sand was tamped. The top half of the cell was thermally insulated while the bottom half was cooled by means of a cooling jacket. Steam was injected at the top of the cell and fluids produced at the bottom of the cell. Temperatures along the cell axis, and inlet and outlet pressures were measured. The cell contents were removed after each experiment and analyzed to determine if sand consolidation occurred. Thin sections of samples before and after the steam treatment were analyzed using an electron microprobe to determine any change in shape, size, and composition of the sand grains. Steam at 250-260 °C and 700800 psig was injected at rates of 5 cc/min and 20 cc/min. Steam with pH of 7 and 12 were used, the latter obtained by addition of sodium carbonate to the feedwater.

Results showed sand consolidation did not occur for steam with pH of 7. However, for steam of pH 12, the sand was consolidated particularly at the top part of the cell in only 3-4 hours. Photomicrographs showed both needle-like and equant crystals of sodium aluminum silicate being formed between the consolidated sand grains. Contrary to the previous postulate that precipitation of dissolved quartz or feldspar "cements" the sand grains, the results indicate that the mechanism of sand consolidation is probably more complex. Further research is being undertaken to fully understand and optimize the process.
Measurement of Waxy Crude Properties Using Novel Laboratory Techniques
Authors: Karan Kunal , Ratulowski John , German Philip
Published: December 2007

Transportation and production of waxy crude oils poses a variety of challenges including wax deposition, increased viscosity and pressure drop at temperatures below the cloud point, and high re-start pressure for gelled oil in the pipeline at temperatures below the pour point.

The driving force for this study is an investigation of live oil transportation through a 600 km long sub-sea pipeline where ambient temperatures range from 0 to 5°C and pressures up to 3000 psia. The design and operation of such a system warrants unique set of input data. Measurement of such data involves the development of novel experimental techniques.

In this paper, newly developed experimental techniques and apparatus used for measuring key waxy crude properties is presented. A novel experimental apparatus was used to visually determine live oil pour points at pressures up to 3000 psi. The gel strength measurements for pipeline restart pressures for both dead and live oils were conducted using a model pipeline test (MPT) apparatus. Measurements of the live oil wax appearance temperature (WAT) were performed using a state-of-the-art High Pressure Cross Polar Microscope (HP-CPM) and a laser-based solids detection system.
Reliability Qualification Testing for Permanently Installed Wellbore Equipment
Authors: Veneruso A. F. , Hiron S. , Bhavsar R. , Bernard L.
Published: December 2007

Reservoir monitoring and intelligent completions require installation of permanent downhole equipment for use by operations personnel to monitor and control wells with flow-control devices. Reliability qualification testing (RQT) is essential for the success of these systems. This equipment is permanently installed in the severe downhole environment; it is rarely retrieved to surface for analysis, and it is impractical to run long-duration laboratory and field tests to qualify the system for its long lifetime before installation.

RQT helps achieve overall system reliability by closing the loop from equipment design, component qualification, and testing to personnel training and field operations. A mission profile provides a realistic basis and framework for the specifications and testing. The challenge is for the entire system to achieve an operational reliability of at least 90% during 5 years or more in the hostile downhole environment at temperatures as high as 150°C and pressures that reach 15,000 psi. Reliability testing identifies weak links, measures progress, and builds confidence to avoid risks and surprises. However, designing and building the special test facilities requires a significant investment and a long-term commitment to run and maintain them.

Case histories illustrate the challenges and benefits achieved with the RQT approach. Examples from more than 10 years of experience with downhole safety valves and permanent gauge installations show surprisingly similar reliability and testing problems to those experienced in automotive and aerospace applications. These examples demonstrate how RQT provides an objective set of techniques to develop and deploy reliable long-life systems.
Start-up Automation of a Petroleum Offshore Platform
Authors: de Campos Mário César , Satuf Eduardo
Published: December 2007

It is difficult to control and manage the start-up of a petroleum offshore platform. In order to solve this problem an intelligent system can play an important role, since available qualified operator and design knowledge can be easily implemented to assist the operator during start-up. This paper describes a system applied to the start-up of a petroleum offshore platform. The intelligent system has many heuristic rules to implement the automation of procedures, like the opening of many on-off valves while simultaneously monitoring process variables. This system can shorten the start-up time by 30%. This intelligent system is operating since June 1999 in the Petrobras’ P-19 platform, the Brazilian Oil Company, in Campos Basin, Brazil. This paper follows reference [1] that presented the operating interface of this intelligent system.
East Texas Hydraulic Fracture Imaging Project: Measuring Hydraulic Fracture Growth of Conventional Sandfracs and Waterfracs
Authors: Mayerhofer Michael J. , Walker Ray N. , Urbancic Ted , Rutledge James T.
Published: December 2007

This paper presents detailed analyses of hydraulic fracture microseismicity and engineering data created during the joint operator Cotton Valley Hydraulic Fracture Imaging Project in East Texas. The project was a joint operator consortium with the goal of evaluating hydraulic fracture growth of conventional "sandfracs" and waterfracs with very low sand concentrations. A variety of fracture diagnostic tools were used on ten fracture stages in three wells including microseismic and downhole tiltmeter fracture mapping, fracture modeling, stress tests, radioactive tracers, pressure transient well tests, and production logging. We also introduce a methodology that uses full triaxial waveform analysis of the microseismic signals to obtain seismic source parameters, which characterize failure modes during hydraulic fracturing. This information could potentially be used for a detailed description of fracture geometry, growth and complexities and may give some indications about created versus propped fracture lengths. The paper compares the microseismic created lengths and propped lengths with those from frac models.
Experimental Study on Fracture Initiation by Pressure Pulses
Authors: Yang David W. , Risnes Rasmus
Published: December 2007

A new testing device has been developed which can be utilized to study the dynamic fracture initiation by pressure pulses. Instead of using propellant gas, the device employs a falling weight to impact on the piston that compresses the borehole fluid and transmits a dynamic pressurization to the simulated wellbore. The device is instrumented to measure the pressure pulses in the simulated borehole and in the confining chamber. The fracture pattern can directly be observed and examined. A systematic work has been done to calibrate the set-up and to identify the factors for controlling the pressurization rate.

Altogether 63 tests with commercially available or artificial rock samples have been conducted by using the developed setup. The transition from the hydraulic-fracture pattern to the multiple-fracture pattern has been observed. Three series of tests have been conducted to confirm the transition and determine the relation between the transition and rock strength.

Besides presenting the experiment results, the paper also briefly discusses how to use the data in designing the dynamic fracturing treatments for enhancing well productivity or injectivity.
CONTROL: PCP – An Intelligent System for Progressing Cavity Pumps
Authors: Carvalho P. G. , Morooka C. , Bordalo S. , Guilherme I.
Published: December 2007

This paper describes an intelligent system for the management and control of petroleum wells operating with progressing cavity pumps (PCP), named CONTROL: PCP.

The purpose of CONTROL: PCP is to maintain the operational conditions of PCPs within the established limits, reduce the operational costs, maximize the useful life of the equipment, and, consequently, increase the profitability of the petroleum wells. The architecture of the system involves expert knowledge for handling an existing database.
Interpretation and Application of Acoustic and Transient Pressure Response to Enhance Shale (In)Stability Predictions
Authors: Tare Uday A. , Mese Ali I. , Mody Fersheed K.
Published: December 2007

The main objective of this work is to discuss the initial results of an ongoing experimental study. The study has investigated the role of chemical potential of drilling fluids on transient pore pressure, acoustic, static properties, and strength of shale formations subjected to compressive confining stress. The motivation behind this study is to develop real time wellbore (in)stability logging capability.

Wellbore (in)stability in shales is a major problem costing the petroleum industry, according to conservative estimates, $700 million annually. Understanding and modeling mechanisms of shale (in)stability is an ongoing industry effort. Drilling a hole into a formation in equilibrium induces stress concentration near the borehole. A chemical interaction will occur if parameters such as chemical potential, ionic concentration, etc., of the drilling fluid and the shale formation fluid are not in equilibrium. Any differences in these parameters will alter the near wellbore pore pressure which in turn will influence the borehole equivalent stress-state and the shale mechanical strength thus affecting wellbore (in)stability. Tests conducted at compressive uniaxial and triaxial stress conditions in the past have indicated the strong influence of these chemical parameters on shale strength.

In this study, transient pressure, compressional and shear wave velocities, deformation and strength of shale cores were measured as a function of time when exposed to a drilling fluid. The experiments were conducted under conditions simulating a borehole portion under geostatic stress and the wellbore surface exposed to a circulating drilling fluid.

The uniqueness of this study comes from the fact that the mechanical property, acoustic velocity and transient pressure for each sample are measured simultaneously as a function of time during the experiment. This eliminates the anisotropy-associated differences obtained when different samples are used to determine the relationship between these characteristic parameters of shale formations. This comprehensive testing program will enhance our understanding of the relationship between acoustical, mechanical and chemical properties of shale as a function of time when exposed to a drilling fluid.

Interpretation of static and dynamic rock properties utilizing acoustic velocity data as a function of the transient pressure of shales under identical stress state will facilitate real time wellbore (in)stability predictions using MWD/LWD information. Thus, this application provides better real-time management of (in)stability problems in the field.
Bidding Strategy: Reducing the "Money-Left-on-the-Table" in E&P Licensing Opportunity
Authors: Tavares Mario J. D.
Published: December 2007

When the results of Licensing Opportunities are analysed, one of the main features observed is the amount of "money left on the table". This is the difference between the highest (winning) and the second highest proposal presented in one specific tender. The objective of all investing companies should be to minimise this excess of money paid to win the tender, as it does not bring any benefit to the winner. An analysis of the Gulf of Mexico deep-water Lease Sales from Mar/97 to Mar/2000 revealed that companies left an excessive high amount of money on the table: an average of 42 to 63%. The 3rd Licensing Round in Venezuela and the 1st Licensing Round in Brazil were also assessed, revealing, respectively, 25% and 51% as the average money left on the table. Another important feature revealed in all these Licensing was that the money left on the table reduced as the number of competitors increased. By analysing all these issues, this paper proposes a strategy to increase the trade-off between thecapital invested to acquire areas and the overall expected value of the areas acquired. By following this approach, companies should avoid the excessive amount of money paid to win the tenders and still be able to acquire more area in the Licensing Round, if applicable.
Production Data Integration in Sand/Shale Reservoirs Using Sequential Self-Calibration and GeoMorphing: A Comparison
Authors: Wen X. -H. , Tran T. T. , Behrens R. A. , Gómez-Hernández J. J.
Published: December 2007

The stochastic inversion of the spatial distribution of lithofacies from multiphase production data is a difficult problem. It is so even for the simplest case addressed here of a sand/shale distribution and under the assumption that reservoir properties are constant within each lithofacies. Two geostatistically-based inverse techniques, sequential self-calibration (SSC) and GeoMorphing (GM), are extended for such purpose and then compared using synthetic reference fields. The extension of both techniques is based on the one-to-one relationship existing between lithofacies and Gaussian deviates in truncated Gaussian simulation. Both techniques attempt to modify the field of Gaussian deviates while maintaining fixed the truncation threshold field through an optimization procedure. Maintaining a fixed threshold field, which has been previously computed on the basis of prior information of lithofacies proportion data, well data, and other static soft data, guarantees preservation of the initial geostatistical structure. Comparisons of the two techniques using 2-D and 3-D synthetic data show that the SSC is very efficient in producing sand/shale realizations matching production data and reproducing the large scale patterns in the reference fields, although it has difficulty in reproducing small scale features. GM is a simpler algorithm than SSC, but it is computationally more intensive and has difficulty in matching complex production data. Better results could be obtained with a combination of the two techniques in which SSC is used to generate realizations identifying large scale features, then these realizations are used as input to GM for a final update to match small scale details.
Effect of Pore-Lining Chlorite on Petrophysical Properties of Low-Resistivity Sandstone Reservoir
Authors: Durand Claudine , Cerepi Adrian , Brosse Etienne
Published: December 2007

Chlorite bearing sandstones usually give low resistivity signals, and are thus erroneously identified as non pay zones, even if they exhibit good preserved porosities at depth. The purpose of the paper is to provide petrophysical and mineralogical laboratory measurements, that help improving the log interpretation in these sandstones.

The main results, obtained on a selection of reservoir cores, for sandstones having an amount of chlorite between 3 and 11 wt-%, are (1) the cementation index and saturation exponent (m and n) have values lower than the common 2 values, n frequently around 1.5. These low values have been carefully checked in order to avoid experimental artefacts. (2) Cationic Exchange Capacities (CEC) and Specific Surface Area (SSA) have low values, as expected from the clay structure. (3) the distribution of pore throats is bi or tri-modal, with a large contribution of microporosity.

The interpretation suggested by these results is that the amounts and distribution of microporosity associated to pore lining clay is the key of the chlorite sandstones electrical behavior. The values of CEC or SSA are too low to fully explain the low values of saturation index n.

Use of these low values in log interpretation has the effect of increasing the evaluation of oil in place. Advantages of a multi-disciplinary approach for better evaluation of such complex argillaceous sandstone reservoirs is highlighted.
Correcting for Wettability and Capillary Pressure Effects on Formation Tester Measurements
Authors: Elshahawi H. , Samir M. , Fathy K.
Published: December 2007

Conventional formation tester interpretation techniques have long assumed that the measured tester pressure is identical to the pressure of the continuos phase in the virgin zone of the formation. As such, a series of pressure measurements at different depths would be expected to consistently yield a pressure gradient corresponding to the density of the formation fluid. Recent work by the authors of this papers as well as by others has shown that the formation testers will actually measure the pressure of the continuos phase present in the invaded region, typically the drilling fluid filtrate. The measured tester pressure is, thus, different from formation pressure by the amount of capillary pressure. This capillary pressure has been shown to be a strong a function of the wetting phase saturation. The effects of the rock wettability and capillary pressure on wireline formation tester measurements are manifested as pressure gradient changes and/or fluid contact level changes on many logs, particularly those recorded with oil-based mud in the borehole.

This paper summarizes the effects of wettability and capillary on wireline formation measurements and investigates in detail the possible techniques for recognition and estimation of and correction for those effects. The older techniques rely on the use of core capillary pressure data log-computed flushed zone saturations, but they can often yield inconsistent results. Amongst the more innovative techniques suggested in this paper is the use of NMR measurements to estimate the magnitude of capillary pressure effects and hence correct the measured tester pressure. Also discussed in the use of the pump-out capability of the Modular Dynamics Tester (MDTTM) to estimate the capillary pressure effect by making measurements before and after the removal of drilling mud filtrate. This allows accurate correction for capillary pressure effects, or better still, the elimination of the need for the correction altogether.
Design, Implementation, and Analysis of Multilayer Pressure Transient Tests in White Rose Field
Authors: Coskuner Gökhan , Ramler Leon B. , Brown Murray W. , Rancier D. Wayne
Published: December 2007

The White Rose field is located in the Jeanne d’Arc Basin, lying some 350 km off the east coast of Newfoundland. The basin has proven to be the only area off the East Coast of North America with established major oil accumulation potential. The discovery well in the south area of the structure, the E-09, was drilled in 1988 encountering some 300 m continuous sand interval with an oil column of 135 m. Although there was a potentially significant amount of oil distributed in several fault blocks, the productive capacity of future development wells was uncertain based on the five conventional pressure transient tests conducted.

Following a 3D seismic program, a delineation program commenced in 1999 and three delineation wells were drilled geologically confirming over 600 MMSTB oil in place in the south. The wells were extensively cored and logged. Two sand intervals in the first well, the L-08, were tested using the conventional pressure transient testing technology. However, it was decided that a multilayer test (MLT) could be employed in the second well, the A-17, leading to significant cost savings when compared with conventional testing.

The A-17 well was logged to evaluate the formation as well as the cement bond. Four distinct pay intervals were observed and it was decided that the properties of these layers could be measured by conducting an MLT while also measuring the flow profiles with a Production Logging Tool (PLT). The test was successfully conducted and analyzed. Consequently, the rig time to test the well was reduced by at least 16 days, yielding savings of C$8 million. Given the success of the technique in the second well, the third delineation well, the N-30, was also tested using the MLT technique, again with significant cost savings. This paper discusses the design, implementation and the analysis of MLT's conducted in the A-17 and N-30 wells.
New Well-Testing Methods for Rod-Pumping Oil Wells — Case Studies
Authors: Guoynes John C. , Azari Mehdi , Gillstrom R. , Friend B. L. , Fairbanks M. D.
Published: December 2007

A new well testing method that provides high-resolution bottomhole pressure measurement has been developed for use with rod pumping oil well completions. This new well testing technique is conducted by running a high-resolution downhole pressure gauge in a specially designed carrier assembly with the downhole pump. The gauge assembly is run on the rod string without pulling completion packers or tubulars. Using the new method, a downhole pressure system is in place while the well is flowing during the entire well test. High-resolution downhole pressure data can then be recorded during all flow and shut-in periods of the well test, which provides more accurate pressure data and enhanced capability for reservoir analysis.

Traditional techniques use wireline-conveyed pressure gauges, tubing-conveyed pressure recording devices, and surface pressure monitoring systems with advanced fluid-level measurement to record data from pumping well completions. These methods are limited in their capability to provide accurate test results when low-pressure conditions prevail. The new method allows operators of low-pressure oil well completions to use advanced well-test analysis software to analyze actual pressure data to obtain reservoir properties and quantify skin damage. Data can be acquired from many types of rod-pump completions, including wells with downhole gas separators. Excellent pressure resolution has been obtained with this new testing technique using either of two downhole assembly designs, depending upon the completion configuration.

The results and the ensuing well test analyses in several pilot pumping wells will illustrate that the new process permits more flexibility in well testing and allows for greater accuracy and better interpretation of data in low-pressure rod-pumping oilwells.
Fast and Robust Algorithm for Compositional Modeling: Part I – Stability Analysis Testing
Authors: Firoozabadi Abbas , Pan Huanquan
Published: December 2007

Given pressure, temperature, and composition of a fluid, one desires to determine whether the single phase state is stable. This problem is, in principle, much simpler than phase-behavior calculations. For certain applications such as compositional-reservoir modeling, stability testing can be the most important item for efficient phase-behavior calculations.

In this paper, we use the tangent-plane-distance (TPD) in the reduced space to perform stability analysis testing. The results reveal that there are major advantages in the reduced space. One interesting feature of the transformation is that the TPD surface becomes smooth and has one minimum. The combination of a single minimum and the surface smoothness contributes to a remarkable robustness in calculations.
Guidelines for Choosing Compositional and Black-Oil Models for Volatile Oil and Gas-Condensate Reservoirs
Authors: Fevang Øivind , Singh Kameshwar , Whitson Curtis H.
Published: December 2007

This paper provides specific guidelines for choosing the PVT model, black-oil or equation of state (EOS), for full-field reservoir simulation of volatile/near-critical oil and gas condensate fluid systems produced by depletion and/or gas injection.

In the paper we have used a "generic" reservoir from the North Sea containing a fluid system with compositional grading from a medium-rich gas condensate upstructure, through an undersaturated critical mixture at the gas-oil contact, to a volatile oil downstructure.

A component pseudoization procedure is described which involves a stepwise automated regression from the original 22-component EOS. We found that a six-component pseudoized EOS model described the reservoir fluid system with good accuracy and, for the most part, this EOS model was used in the study.

Methods are proposed for generating consistent black-oil PVT tables for this complex fluid system. The methods are based on consistent initialization and accurate in-place surface gas and surface oil volumes when compared with initialization with an EOS model. We also discuss the trade-off between accurate initialization and accurate depletion performance (oil and gas recoveries).

Each "reservoir" is simulated using black-oil and compositional models for various depletion and gas injection cases. The simulated performance for the two PVT models is compared for fluid systems ranging from a medium rich gas condensate to a critical fluid, to slightly volatile oils. The initial reservoir fluid composition is either constant with depth or exhibits a vertical compositional gradient. Scenarios both with saturated and undersaturated GOC are considered. The reservoir performance for the two PVT models is also compared for different permeability distributions.

Reservoir simulation results show that the black-oil model can be used for all depletion cases if the black-oil PVT data are generated properly. In most gas injection cases, the black-oil model is not recommended — with only a few exceptions.

We also show that black-oil simulations using solution oil/gas ratio equal to zero (rs=0) does not always define a conservative ("P10") sensitivity for gas injection processes. If gravity segregation is strong, the incremental loss of oil recovery due to "zero vaporization" is more than offset by exaggerated density differences caused by erroneous gas densities.
A New Rate-Time Type Curve for Analysis of Tight-Gas Linear and Radial Flows
Authors: Chen Her-Yuan , Teufel Lawrence W.
Published: December 2007

This paper presents a new set of Fetkovich type curves for production data analysis. The set extends early-time flow regime to include near-linear up to pure-linear flow, which are lacking in the original set. The proposed set is general but is particularly suitable for tight-gas wells due to the inclusion of the often-observed pure- and near-linear flow behavior. Theory of cross type curves between rate, cumulative production, and time is presented as well as the methodology of cross type-curve matching. Examples are given to show the applicability of the type curves for tight-gas evaluation.
Determination of Formation Properties From Stabilized and Unstabilized Gas-Well-Test Data
Authors: Tureyen Omer Inanc , Satman Abdurrahman , Onur Mustafa
Published: December 2007

In this paper, new explicit analytical equations for stabilized and transient deliverability coefficients in terms of formation/fluid parameters are presented. These equations are derived for fully and partially penetrating vertical wells and for fully penetrating horizontal wells. The proposed equations use the relationship between the empirical (Rawlins and Schellhardt) deliverability equation and rigorous (or Forechheimer’s) deliverability equations for both stabilized and unstabilized (transient) flow conditions. Based on these new equations, we also present new methods for determining not only the performance coefficients, but also formation parameters from stabilized and transient gas deliverability data. Unlike the existing methods, our new methods do not require geometric mean of pressure or rate data. This is a distinct advantage of the methods presented in this paper over the existing methods because determination of geometric mean of pressure or rate data may be quite difficult, and the mean value is quite sensitive to the measurement errors in such data. Thus, the methods given in this paper should prove very useful for determining formation parameters accurately from deliverability tests in vertical and horizontal wells. The accuracy and applicability of the methods given in this study are verified by analyzing two test data published previously in the literature as well as simulated test data. Results are compared with those obtained from the existing methods in the literature and indicate that combination of our new methods with the Hinchman-Kazemi-Poettmann method for isochronal test types provides more information about the formation and reliable deliverability forecasting.
Applying a Decision-Analysis-Based Method to the Evaluation of Potential Risk-Reducing Measures: The Case of a Floating Production Storage and Offloading Unit in the Gulf of Mexico
Authors: Lassagne M.
Published: December 2007

This paper presents an innovative methodology to evaluate risk-reduction measures applicable to an offshore installation, both from an economical and from a technical point of view and to help in choosing among them. The methodology notably addresses some of the most important weaknesses of traditional Cost-Benefit Analysis. Although it requires a more important involvement of the concerned parties than is the case for Cost-Benefit Analysis, we show that it may help to better evaluate and to select risk-reducing measures. After explaining some theoretical aspects, we present an ongoing application to FPSO risks and the expected results of this study.
Optimum Underbalance for the Removal of Perforation Damage
Authors: Walton Ian C.
Published: December 2007

It has been estimated that the permeability of the damaged zone around a perforation tunnel is reduced to approximately 20% of the original rock permeability. Since the perforation tunnel is the conduit for all produced fluids into the wellbore, removal of some or all of this damaged material is critical to the success of a perforated completion. Underbalanced perforating is regarded as the most efficient method of removing this damage.

The degree of underbalance required to generate efficient perforations is still subject to much debate. Several guidelines have been produced in recent years, all of which calculate the optimum underbalance in terms of the permeability of the matrix (and fluid and tunnel parameters). All agree that the optimum underbalance should fall with increased permeability, but there is a great discrepancy in the specific relationship proposed. Most of the data on which the correlations are based and the models are validated comes from experiments on rocks with permeabilities in the 100–200 md range; extrapolation to lower and higher permeabilities is dangerous.

In contrast to published models, we propose in this paper that underbalanced perforating promotes productive perforations by initiating mechanical failure of the damaged zone. A method is developed which predicts the optimum underbalance in terms of the strength of the matrix, the strength and extent of the damaged zone and the imposed stress conditions. Comparison with the results of single-shot perforating experiments lends support to the theory.
Perforation Damage Studies in Unconsolidated Sands: Part II - Baseline Studies and Comparison of Analytical Methods for Quantifying Damage
Authors: Snider P. M. , Benzel W. M. , Barker J. M. , Leidel D. J.
Published: December 2007

Traditional API Recommended Practice 431 Section 1 test of a gun system is focused on determining the perforation characteristics from the point of view of a perforating gun fired into rock of significant unconfined compressive strength. Entrant hole size and depth of penetration are the key parameters measured to demonstrate the gun system performance. These parameters do not tell how the energy of the penetrating jet is dissipated in the formation nor do they characterize flow from the formation through the perforation. The API Section 4 test is a means of producing the information desired, flow characteristics of the rock after perforating. These tests are expensive, long and difficult.

Furthermore, the API Recommended Practice 43 does not include a test method for evaluating perforators used in unconsolidated sand formations, but only simulates perforation in competent rocks. However, in unconsolidated sands, the guns do not produce a "tunnel or cavity" in the sand. Rather, the perforation path is filled with crushed sand and debris that strongly influence the flow properties of the perforation and requires characterization.

Two years ago the authors presented data showing a simple sand filled clamshell target could provide useful information for the development and design of shaped charges for unconsolidated sand. Suggested here is a standardized test method for a target focused on measuring the gun performance from the viewpoint of the formation while retaining the gun system performance parameters and developing a correlation between perforation path damage and perforation flow characteristics.
4D Cause and Effect: What do reservoir fluid changes look like on seismic?
Authors: Khan M. , Waggoner J. R. , Hughes J. K.
Published: December 2007

While most reported 4D effort focuses on 4D processing and interpretation of 4D seismic results, perhaps it is time to look at the problem the other way around. What 4D results are likely to arise from common reservoir depletion and displacement conditions? By better understanding the engineering cause of the geophysical effect, it may be possible for engineers to better contribute to the processing and interpretation of 4D data.

This paper looks at this issue through reservoir simulation studies. The reservoir simulator is a powerful tool to predict how fluid saturations and pressures are distributed throughout the volume of the reservoir over time. This information can be used in conjunction with a properly scaled rock physics model to generate seismic attribute maps that reveal the patterns of 4D results that would be expected under various depletion, displacement, and heterogeneity conditions.

The preliminary findings of this work are that pressure effects do obscure fluid saturation changes and exacerbate the effects of porosity variations in the reservoir. In addition, it is shown that care must be taken to accurately represent the poor vertical resolution of surface 3D seismic to avoid overly optimistic predictions of likely 4D seismic results.
Permeability Determination from Stoneley Waves in the Ara Group
Authors: Qobi Latifa , De Kuijper Andre , Tang Xiao M. , Strauss Jonathan , Munkholm Mette
Published: December 2007

Measurement of continuous permeability profiles on a routine basis has become possible through recent advances in wireline logging hardware and software. Continuous permeability profiles allow geologists, and reservoir engineers to better characterize their reservoirs and to more efficiently complete and manage the production of the hydrocarbon reserves. One of the most promising methods for the calculation of continuous permeability information is the use of Stoneley wave data acquired using a monopole acoustic device.

This paper presents the results of a case study conducted for Petroleum Development Oman (PDO) in which permeability is determined from Stoneley wave data for two wells, namely Sarmad-1H2 (SAR-1H2) and Sarmad-2H1 (SAR-2H1), penetrating the carbonate reservoirs of the Ara group in Oman. The objectives of the study are: To demonstrate the validity of the methodology.To test whether this method can be used on a routine basis aimed at obtaining a continuous permeability index for completion evaluation purposes.

The Stoneley wave derived permeability profile is compared with permeability data from other sources, such as, core data, wireline pressure tests, and interpretation of nuclear magnetic resonance measurements.

The results of this case study clearly demonstrate the great potential of using Stoneley wave for permeability prediction.