bluuebunny/crossref_metadata_2025 huggingface dataset:
A Review Of Fracture Detection With Well Logs
Authors: Shanks R.T. , Kwon B.S. , DeVries M.R. , Wichmann P.A.
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers Inc.

Most systems in use today for fracture detection still employ measurements of acoustic amplitudes. Presentations may vary but basic format includes Presentations may vary but basic format includes recording an acoustic travel time curve and photographically recording an oscilloscope displaying photographically recording an oscilloscope displaying an acoustic wave train in various modes.

Evaluation of the amplitude measurement is complicated because many factors other than a fracture system can cause attenuation and/or distortion of the wave train.

The acoustic amplitude measurements covered by this paper are records of the attenuated signal of paper are records of the attenuated signal of compressional and shear wave studies.

A technique for reducing an attenuation factor through reduction of transmitter to receiver spacing is described. Actual field examples will illustrate transmitter/receiver spacings varying from four feet to less than one foot. The latter spacing, incorporated in an unique sidewall acoustic logging instrument, has much sharper interface resolution than that obtained from classical acoustical logging devices; and produces a cleaner wave form with an easier defined shear wave. Examples are shown of acoustic logs made under various conditions and results are discussed.

Fractures or fracturing characteristics of various formations may be determined from rock moduli logs utilizing compressional and shear travel times with bulk density from density logs. Formation strength parameters as derived from these logs are shown. parameters as derived from these logs are shown. Other types of well logging devices, resistivity and porosity, depict their own worth as fracture detectors porosity, depict their own worth as fracture detectors or as a complement to acoustical devices. Included is an illustration of the field results of a natural gamma ray Spectralog showing a uranium anomaly in fractures.

A newly developed log analysis technique is offered for low permeability, but often partially fractured, carbonate reservoirs. The concept allows an identification of potential pay zones first; then, detailed information on reservoir rock properties, such as: total porosity and secondary porosity. Basic log data required for this type of analysis includes Combination Induction - Electrolog/BHC Acoustilog/Gamma Ray/Caliper; followed by Dual Neutron Lifetime, Log. Recent field results are analyzed for converting log measurements to reservoir parameters. parameters.

Introduction

During the past fifteen years, considerable work has been done toward developing logging and interpretive techniques to locate possible hydrocarbons in formations having fracture systems.
Performance History and Operation of Two Minnelusa Reservoirs - West Semlek Field, Crook County, Wyoming
Authors: Tholstrom Kendell V.
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers Inc.

The West Semlek Field, operated Terra Resources, Inc., consists of two separate Minnelusa reservoirs of nearly equal size as shown on Fig. 1. A natural water drive is present in the southwest reservoir. A fluid expansion/ solution gas drive controlled primary from the northeast reservoir which was unitized in 1972. A polymer flood was started in this NE segment during September, 1973.

Minnelusa produced water from the southwest reservoir is used for supply by the Unit. The Semlek West Unit is the only Minnelusa polymer project in Wyoming out of seven currently in operation which uses produced water for injection. Recent studies show that the ultimate recovery efficiency for both reservoirs will be about the same. The polymer program has been convincingly successful in improving flood performance and total oil recovery. performance and total oil recovery.

FIELD DISCOVERY

The West Semlek Field is located in Crook County, fifteen miles northwest of Moorcroft, Wyoming, see Fig. 2. AMAX Petroleum and partners drilled the discovery well in October, 1963. The Dunning Gov't 28-1 was completed for an initial pumping potential of 337 BOPD and 7 BWPD from the Minnelusa Sand. Several subsequent wells were drilled in defining the field with two of the structurally low wells on the west side going quickly to water. Initial development drilling was completed by November, 1964.

GEOLOGICAL AND RESERVOIR CHARACTERISTICS

The Minnelusa formation in north-eastern Wyoming's Powder River Basin contains rocks ranging in age from early Pennsylvanian to the Wolfcamp Series of Permian age. Oil and gas production is obtained mainly from production is obtained mainly from Permian rocks in the Upper Minnelusa. Permian rocks in the Upper Minnelusa. These rocks consist of shallow marine and eolian sandstone, carbonates and evaporites. The top zone is an erosion surface overlain by impervious red shale of the Opeche formation. A variety of traps exist.
Enhanced Oil Recovery with High Pressure Nitrogen Injection
Authors: Mungan Necmettin
Published: December 2007

Miscible displacement with high pressure nitrogen injection has been selected as an enhanced oil recovery process for a naturally fractured thick carbonate reservoir containing light oil underlain by an aquifer. The objectives are to maintain the reservoir pressure and increase the ultimate recovery. The giant reservoir, containing twelve billion barrels of original oil in place, has only produced one billion barrels after fifteen years of primary production, during which period the reservoir pressure declined from the initial value of 11,500 psi to 4,100 psi and is rapidly approaching the bubble point pressure of 3,750 psi. Over this same period, daily oil production rate has declined from the peak value of 150,000 barrels/day to about 22,000 barrels/day. The costs of nitrogen extraction from air, compressors and compression for a field-wide application, and the additional facilities required to separate nitrogen from produced oil and gas will likely be $1.5 billion U.S. in terms of 1999 dollars. Cost was the strongest reason to pilot test the process first. Pilot testing may take up to three years. Production from high gas/oil or water/oil ratio wells will be curtailed during pilot testing to prevent the reservoir from reaching the bubble point pressure. In this paper, high pressure miscible nitrogen injection pilot test is described.
Swept Volume Calculations and Ranking of Geostatistical Reservoir Models Using Streamline Simulation
Authors: Idrobo Eduardo A. , Choudhary Manoj K. , Datta-Gupta A.
Published: December 2007

Geostatistical techniques are increasingly being used for modeling reservoir heterogeneity and assessment of uncertainty in performance predictions. Although a large number of stochastic reservoir models or realizations may be generated, in practice only a small fraction can be considered for comprehensive flow simulations. This can be done through a ranking process. Several papers have been published in the literature on ranking of realizations. However, a consistent and generally applicable set of criteria for model ranking still remains unclear.

In this paper we propose a connectivity criterion based on the streamline time-of-flight and use this criterion to rank geostatistical realizations for detailed flow simulation purposes and risk assessment. Because time-of-flights reflect fluid front propagation at various times, the connectivity in the time-of-flight provides us with a direct measure of volumetric sweep efficiency for arbitrary heterogeneity and well configuration. We show that the proposed connectivity criterion exhibits strong correlation with waterflood recovery and thus, can be used for ranking stochastic reservoir models. Unlike permeability connectivity which is a static measure independent of the flow field, the time-of-flight connectivity rigorously accounts for the interaction between the flow field and the underlying heterogeneity.

Our proposed approach has been applied to synthetic as well as field examples. Synthetic examples are used to validate the sweep efficiency calculations using the streamline time-of-flight connectivity criterion by comparison with analytic solutions and published correlations. These examples also demonstrate the superiority and effectiveness of the ranking criterion over existing methods. The field example is from the North Robertson Unit, a low permeability carbonate reservoir in west Texas. Our example includes multiple patterns consisting of 27 producers and 15 injectors and illustrates the feasibility of the approach for large-scale field applications.
Poroelastic Effects of Cyclic Steam Stimulation in the Cold Lake Reservoir
Authors: Walters D. A. , Settari A. , Kry P. R.
Published: December 2007

The heating of bitumen reservoirs by cyclic steam stimulation (CSS) requires high pressures and temperatures that disturb the soil matrix. This disturbance results in a dilation of the soil matrix creating regions of enhanced permeability and porosity impacting both the injection and production cycles of steam stimulation as well as affecting porous zones not hydraulically connected to the reservoir. The volumetric strain changes reach far beyond the region of injection and include areas of both expansion and compression. The magnitude of the volumetric strains may result in significant displacements and strains being transferred to porous zones outside the reservoir. This can result in observable pressure changes in an otherwise hydraulically static system.

Pressure data at an observation well drilled to monitor aquifer pressures showed a significant response to the CSS process occurring in the reservoir about 300 m below the aquifer. Coupled geomechanical and reservoir modeling and an analytical calculation both show that this pressure behavior is attributed to the poroelastic response of the aquifer due to the CSS process occurring in the reservoir. This paper describes the field data, the methodology of the coupled reservoir and geomechanical modeling, and the result of the analysis of the field data with the coupled model. The analysis shows clearly that the aquifer response is not due to a hydraulic communication with the reservoir. It also shows the capabilities of coupled modeling, as this type of a problem could not be analyzed with conventional reservoir simulation tools.
Steamflood Strategies Using Alternating Injection Method
Authors: Terez Ivan E. , Temple Richard C.
Published: December 2007

Staggered scheduling of injection has been addressed in several patents and papers. The staggered injection or checkerboard scheme was implemented in the Kern River field.

A simulation study was initiated to assist in the checkerboard development of the Kern River field. The study was carried out using a symmetry model with nine patterns using a nine-spot injection scheme. Two checkerboard development schemes were evaluated and compared with various base case scenarios. This study concluded that during checkerboard development, the cumulative oil recovery and production were not sensitive to the checkerboard switch time. It was concluded that the checkerboard scheme was superior to the base development scenario in terms of ultimate oil recovery and SOR. The production peak in the checkerboard scheme was smaller and delayed in comparison with the base case. A hybrid case consisting of implementing a checkerboard scheme after conventional steamflood breakthough provided the most promising scenario in terms of ultimate oil recovery and steam-oil ratios.

Various sensitivity runs were conducted to investigate the rate effect and an imposed pressure differential across the study area. The results showed no significant effect on the checkerboard performance.
Application of Tiab's Direct Synthesis Technique to Multi-Rate Tests
Authors: Mongi A. , Tiab D.
Published: December 2007

During a pressure drawdown test, it is quite difficult to hold a constant rate long enough to achieve the test requirements. Any change in rate, if not taken into account, can lead to erroneous results. Also pressure drawdown tests are not suitable in sand producing wells. Pressure buildup tests, in high production wells, are uneconomical because of income loss. For these reasons a multirate test is run instead of buildup or constant rate drawdown tests. The conventional analysis of a multirate test requires a type curve matching technique, which is essentially a trial-and-error procedure.

A method is presented to analyze variable rate tests in oil reservoirs. This method, referred to as Tiab's Direct Synthesis. utilizes the characteristic intersection points and slopes of various straight lines from a log-log plot of pressure and pressure derivative data. Direct synthesis technique uses exact analytical solutions to obtain reservoir parameters. The pressure derivative concept is introduced for interpreting multirate tests.

The proposed technique is applicable for the interpretation of either continuously changing flowrate tests or a series of constant rate tests. This technique is illustrated by several numerical field examples for oil reservoirs.
Geomechanical Analysis for Resak's Extended-Reach Drilling - A Case Example
Authors: Ong Seehong , Baim Ahmad Shah , Ibrahim Mohd Zaki , Zheng Ziqiong
Published: December 2007

This paper presents a case example to illustrate how a consistent geomechanical approach and coherent data integration are used to provide the basis for the evaluation of formation mechanical properties, characterization of in-situ stresses, identification of wellbore failure mechanisms, and calibration of a wellbore stability model. The calibrated model is then used in conjunction with the proposed build-and-hold and catenary well profiles to generate the mud weight windows for an ERD well. To provide further insight into the wellbore stability with respect to wellbore trajectories and in-situ stresses, contour plots of mud weights are generated for a critical depth interval. These contour plots delineate potential instability areas and are critical for predrilled well trajectory designs. Additionally, an innovative approach to establish the lower limit of mud weight for wells that cannot be drilled without failure zones (breakouts) forming around the wellbore is presented. This approach enables difficult wells to be drilled, with the lower mud weight reducing the risk of formation damage and increasing the rate of penetration.
Analysis of Extended Reach Drilling Data Using an Advanced Pressure and Temperature Model
Authors: Bjørkevoll K. S. , Anfinsen B.-T. , Merlo Antonino , Eriksen Nils-Harald , Olsen Espen
Published: December 2007

Two North Sea extended reach wells have been analyzed in detail by comparing downhole pressure and temperature measurements with results from an advanced pressure and temperature simulator. Drilling of 12 ¼ in. and 8 ½ in. sections are studied.

Early indications of hole cleaning problems were observed both on temperature and pressure. Calculations predict that downhole temperature is very flow regime dependent, and flow regime depends on eccentricity of the inner string, which therefore is important to take into account. It is also demonstrated that the presence of tool joints may influence temperature dramatically.

Improvements in the planning and modeling of the drilling of extended reach wells are suggested.
Modelling of Transient Cuttings Transport in Underbalanced Drilling
Authors: Doan Q. T. , Oguztoreli M. , Masuda Y. , Yonezawa T. , Kobayashi A. , Kamp A.
Published: December 2007

Underbalanced drilling holds several important advantages compared to conventional drilling technology. These include elimination of formation damage, faster penetration rate, ability for evaluation of reservoir productivity during the drilling process. As underbalanced drilling technology matures, it has also been used more and more. However, many aspects of underbalanced drilling technology remain poorly understood. The model presented in this paper seeks to understand the mechanisms involved in the transport of cuttings in underbalanced drilling.

The model simulates the transport of drill cuttings in an annulus of arbitrary eccentricity, and includes a wide range of transport phenomena including cuttings deposition and re-suspension, formation and movement of cuttings bed. The model consists of conservation equations for the fluid and cuttings components in the suspension, and the cuttings deposit bed. Interaction between the suspension and the cuttings deposit bed, and between the fluid and cuttings components in the suspension, are incorporated. Solution of the model determines the distribution of fluid and cuttings concentration, velocity, fluid pressure, velocity profile of cuttings deposit bed at different times.

The model is used to determine the critical transport velocity for different hydrodynamic conditions. Results from the model agree quite closely, qualitatively and quantitatively, with experimental data obtained from a cuttings transport flow loop at JNOC's Kashiwazaki Test Field in Japan. These results show the importance of slippage in the formation of the cuttings deposit bed. The model is useful in evaluating the minimum flow rate for effective cuttings removal in underbalanced drilling.
Reducing the Risk, Complexity and Cost of Coiled Tubing Drilling
Authors: Portman Lance
Published: December 2007

This paper focuses on arguably the most cost-effective application for coiled tubing drilling. The application is the non-steered extension of an existing well in the underbalanced state. This operation can be very fast and efficient with coiled tubing. However, the job design must minimize the associated risk to ensure problem free execution. This paper describes the steps required to minimize risks and therefore costs, and illustrates by way of example these steps in action.
Equipment for Mechanized Running of Tubulars on a Fifth-Generation Semi Submersible—Commissioning and Field Experience
Authors: Kinzel Holger , Peyon Albert , Lorenz Joerg
Published: December 2007

Despite the downturn in the industry, a new generation of Semi Submersibles has been developed and put into operation. This so called fifth generation of Semi Submersibles has ambitious goals in regards to operational safety and efficiency. The rig concept includes new ideas on how to make-up and run drillstring components, riser pipe as well as casing and tubing. Doubles, Triples or even Quadruples of pipe are being made-up at special "Mouse-hole stations" including their own mechanized handling and make-up equipment. By this means, many functions such as prefabrication of stands of risers, drill pipe and casing stands can be carried out offline without interrupting or delaying drilling operations. Considerable time- and cost saving is anticipated.

The paper describes the planning, development and implementation of the modular concept of the PowerFrame carrying the fully remote controlled power tongs that were installed on three of those rigs built in Brest/France and in Singapore. Actual field experience from a drilling location was not available when this paper was written (May 2000), as the first rigs are scheduled to arrive on location by June 2000. However, during the commissioning sufficient experience was gained to allow the prediction that the ambitious goals set in regards to time saving will be achieved.
Swiss Cheesing to Bring in a Jack-Up Rig at Anding Location
Authors: Maung U Mya , Ahmad Che Ku Mazuan
Published: December 2007

In April 1999, rapid spud can penetration was experienced while pre-loading a jack up rig at the Anding–A platform. The bow leg punched through a stiff clay layer at 11 meters, which caused the hull to tilt, resulting in all the three legs becoming bent and damaged.

After repairing the rig, it was towed back to the platform, and 26 inch diameter holes drilled in a grid pattern to break up and weaken the stiff clay layer below the aft spud can foot prints. This procedure subsequently allowed the rig to be pre-loaded and jacked up safely.

This "Swiss Cheese" technique of pilot hole drilling has been found successful in allowing an independent leg jack-up rig to be safely positioned on locations where the presence of a thin layer of stiff clay, underlain by soft / weaker soils, indicates the potential for punch-through. It is may also be useful in enabling a jack-up rig to be positioned on a location where there is a compatibility problem between rig spud-can spacing, and existing footprints.
Multi-Phase Flow in Several Layers Limits the Applicability of Conventional Buildup Analysis
Authors: Iakovlev S. V. , Lee W. J.
Published: December 2007

Conventional buildup analysis techniques are based on analytical solutions to the diffusivity equation that are subject to well-known assumptions. Single-fluid flow in a homogeneous reservoir is among them. During actual well tests multi-phase flow is often observed in several layers with different properties.

We investigated the applicability of the conventional pressure buildup analysis technique to the interpretation of complex cases involving flow of oil and gas in two layers communicating through the wellbore only. In this study we estimated the degree of error we should expect when conventional techniques are used. Our research shows that calculated values of average effective oil permeability and skin factor depend on a wide range of parameters, such as contrast in layer properties, production mode, production rate and production time prior to shut-in. We used a commercial black oil simulator with variable bubble-point to generate pressure and production data.

Several production forecasts were made using calculated values of permeability and skin in a single-layer reservoir model. A single-layer analogy produces acceptable results if the contrast in layer properties is not too great. If the contrast is high the forecasts generated by single-layer and two-layer reservoir models can differ significantly.
Oilfield Visualization on the PC Platform
Authors: Buckalew Chris , Mehdizadeh Masoud
Published: December 2007

Oilfield visualization software is still widely viewed as the province of expensive graphics workstations. Applications involving visualization of volumes and very large datasets are usually automatically assumed to require workstations. As PCs gain speed, functionality, sophisticated development tools, and fast graphics cards this assumption is less and less valid. This paper describes an oilfield visualization application developed for the PC platform, the tools implemented (including custom visualization tools for geologists), and the development process. As a result of this PC application, 3D visualization becomes less expensive and available to a wider variety of users.
Complex Hydraulic Fracture Behavior in Horizontal Wells, South Arne Field, Danish North Sea
Authors: Cipolla C. L. , Jensen L. , Ginty W. , de Pater C. J.
Published: December 2007

This paper provides a case history of complex fracture behavior in Horizontal wells in the South Arne Field, Danish North Sea (9500 ft TVD, chalk formations).1 The first three propped fracture treatments attempted in the South Arne Field "screened-out" very early in the design due to excessive fracture complexity and fluid leakoff. A detailed study of the rock mechanical properties, wellbore stress & fracture initiation characteristics, far-field stress regime & fracture orientation, and fluid leakoff behavior was integrated with fracture modeling studies to evaluate this problem. These studies were used to improve the fracture treatment strategy for future wells, resulting in essentially 100% success placing the designed proppant volumes and achieving aggressive tip screen-outs (TSOs) on over 60 fracture treatments.
Factors That Affect the Success of Mechanical Water Shut-off in Wells
Authors: A/Fotuh Mahmoud , Macary Sameh
Published: December 2007

Today, as the production life of most of the Gulf of Suez Petroleum Company (GUPCO) oil fields enters into maturity, the large offshore quantities of produced water represent severe problems from both technical and cost bases. Over-loading of surface facilities, excess gas required for lifting fluids, corrosion, and damage of the production strings are some of these problems. The handling of produced water becomes even more crucial due to ever-growing ecological and environmental interests and requirements. These constraints nowadays represent tough challenges for the petroleum industry. Therefore, water shut-off (WSO) processes become vital and strategic, especially under offshore production conditions. The present study investigates the history of rigless WSO jobs taken place in various reservoirs of different offshore fields operated by GUPCO. A new database was designed to compile the last 8 years of WSO jobs in GUPCO. The study also represents the most popular reasons for WSO decisions and provides some beneficial conclusions and recommendations based on GUPCO’s wealth of experience in this area. The statistical analysis of the available data has resulted in an optimized mechanical plan for MBPT. The analysis took into consideration all types of technologies, bottom hole conditions and the nature of the problem. The paper also provides a probabilistic analysis of these water shut off jobs to estimate the probability of success under particular circumstances
The Importance of Hydration Heat on Cement Strength Development for Deep Water Wells
Authors: Romero J. , Loizzo M.
Published: December 2007

After placement of cement on conductor and surface casing, the temperature anomalies caused by the hydration of cement can be substantial. From volumetric considerations, it is known that the maximum temperature anomalies depend on the size of the casing-annulus gap and the cement/water ratio as well as on reaction kinetics. For deepwater wells, because of the low temperature and large annular gap, special attention should be paid to the hydration process of the cement to properly design and evaluate the cement treatment. Currently, there is no universally accepted way of defining temperature schedules for testing cement setting. Operators and field locations rely mostly on local experience, and API-proposed temperature schedules are not applicable conditions where setting time is important such as deep-water conditions.

In an effort to better understand the dynamics involved with cement temperature during hydration, a numerical model was developed to predict the temperature evolution in the wellbore, cement and formation during the setting of cement. The model takes into account heat exchange with the formation and casing fluid (heating or cooling effect) as well as the heat generated during the hydration of the cement. The key parameters (formation thermal conductivity, cement thermal properties and annulus size) were assessed with the model.

Based on the model, a study was completed to characterize temperature and cement strength development. And this in turn is essential to properly design conductor and surface casings in deepwater conditions, which represent the most critical sections for ensuring a competent cement hydraulic seal and support the casing. The results of the study allow to define compressive strength schedules that effectively mirror down-hole conditions and thus give reliable estimates of the necessary wait-on-cement time that could lead to substantial savings for deepwater drilling operations.
New Developments in Aerated Mud Hydraulics for Horizontal Well Drilling
Authors: Sunthankar A. A. , Miska S. , Kuru E. , Kamp A.
Published: December 2007

Drilling using aerated muds offers a major advantage in controlling mud effective density, enabling both underbalanced and balanced drilling. However, planning of aerated mud drilling operations is difficult due to complex hydrodynamics of aerated mud flow, resulting in a lack of confidence in predicting and controlling operational variables. It is, therefore, necessary to better understand the hydraulics of aerated mudflows in order to be able to accurately calculate bottomhole pressure and optimal flow rates for drilling.

Pressure losses are a strong function of gas-liquid flow patterns. The existing methods of predicting flow patterns are based on an extrapolation of results from pipe flow to flow in annuli. Therefore, to verify the applicability of this existing practice, the present study focuses on hydraulics of aerated fluids through a large-scale annulus.

Extensive experiments were performed in a unique field-scale low-pressure flow loop (8" X 4.5", 90’ long) in horizontal position with and without drillpipe rotation. The liquids used were water and aqueous polymer solution (CMC+XCD+water), at flow rates in the range 75–360 gpm and air in the range 10–1000 scfm. Measurements of pressure drop and average liquid holdup over the entire annular section were carried out. To our knowledge, no such data has been published before.

It was observed that intermittent flow was present for most of the cases, which is contradictory to some existing field and simulation practices that assume homogeneous gas-liquid flow. Also, the flow pattern boundaries are shifted as compared to pipe flow, which necessitates the modification of flow transition criteria. To account for these changes, a pipe flow model for prediction of flow pattern boundaries was modified for flow in annuli.

Higher frictional pressure drop was observed in case of flow with drillpipe rotation. Also, a higher frictional pressure drop was found in case of air-non-Newtonian fluid flow as compared to air-water flow. The results of this study show that two-phase pipe flow models, modified for two-phase flow in annuli, considerably under-predict pressure drop occurring during the two-phase flow in annuli.
Advanced Permeability and Anisotropy Measurements while Testing and Sampling in Real-Time Using a Dual Probe Formation Tester
Authors: Proett Mark A. , Chin Wilson C. , Mandal Batakrishna
Published: December 2007

Three new pressure-transient testing methods are employed to determine horizontal and vertical permeability using a dual probe formation tester. Real-time interpretation during acquisition of pressure data, is the focus of all three new pressure-testing techniques. In the first, a new spherical flow model with anisotropy, storage, and skin is developed from first principles for dual probe analysis. Historically, pressure transient solutions are presented as Laplace transforms and approximated in the time domain using numerical techniques. Typically, early, intermediate and late time periods are identified using derivative plots; but very often, the selection of appropriate data results in confusion. Here, the Laplace transform is inverted to yield a single, exact, closed form, analytical, time domain solution valid for all times, making real-time parameter matching possible with high accuracy.

The second technique uses an oscillatory displacement source at the piston face, and the phase delay of the pressure pulse between the probes is used to determine permeability and anisotropic index. This technique is particularly useful when the second monitoring probe signal is weak (as in high permeability zones) or where there is large spacing between the probes. Pulse timing can usually be detected more accurately than its magnitude, thus extending the range of permeability and anisotropic measurements. This methodology, which is based on a derived relationship between wave phase and permeability, was developed by mathematical analogy with resistivity determination methods used in induction logging.

In the above method, it is often possible to encounter "phase wrapping" for excessively tight formations, leaving an indeterminate permeability. To circumvent this problem, in the third method, a short, abrupt "pulse" having a well-defined "center frequency" is produced at the piston face, and its travel time is measured until arrival at the receiver probes. The harmonic, closed form expression is then used to translate this travel time to permeability. This new method is analogous to sonic wave models; although, of course, "waveforms" are often smeared due to the diffusive nature of the problem.

Simulation results using a detailed finite element, dual probe model are compared against the above analytical methods to assess the effects of near wellbore parameters such as mudcake effectiveness, probe, and packer size. Field-test results are shown to demonstrate the successful implementation of these new testing methods. The three methods described above provide a practical level of redundancy in permeability prediction. Also, monitoring permeability and anisotropy changes while sampling are shown to be beneficial in identifying fluid type changes.
Quantifying Uncertainty in Production Forecasts: Another Look at the PUNQ-S3 Problem
Authors: Barker John W. , Cuypers Maarten , Holden Lars
Published: December 2007

A synthetic reservoir model, known as the PUNQ-S3 case, is used to compare various techniques for quantification of uncertainty in future oil production when historical production data is available. Some results for this case have already been presented in an earlier paper1.

In this paper, we present some additional results for this problem, and also argue an interpretation of the results that is somewhat different from that presented in the earlier paper. The additional results are obtained with the following methods: (i) rejection sampling, (ii) history matching of multiple models using a pilot-point approach, and (iii) Markov Chain Monte Carlo (MCMC).
A Novel Approach for Reservoir Forecasting under Uncertainty
Authors: Mishra S. , Choudhary M. K. , Datta-Gupta A.
Published: December 2007

This paper presents a novel approach for developing statistical estimates of uncertainty in reservoir performance from only a limited number of multiphase flow simulations while using information from a full suite of geostatistical realizations. The proposed methodology involves ranking and weighting geostatistical models on the basis of a surrogate performance measure, and estimating the mean/variance of the desired performance measure via a weighted average of simulation results from a few selected realizations. The streamline time-of-flight based volumetric sweep efficiency is used as the surrogate performance measure to rank geostatistical models, and their weights are determined from a moment-matching algorithm which enables the approximation of a continuous distribution by a discrete distribution. A field example is used to demonstrate the applicability and computational efficiency of the proposed methodology.
Gas Cap Monitoring in high flow rate, low porosity clastic reservoirs in Colombia gives big economic returns
Authors: Bullion David , Gonzalez Fabio , Markley Marvin E
Published: December 2007

Cased hole neutron logging has been around for a long time and is often used to monitor gas movement in reservoirs behind pipe. This often works well in high porosity reservoirs but is rarely successful in low porosity reservoirs. In Colombia, there are high flow rate reservoirs with significant permeability, that have low porosity (5-6 PU).

The challenge was to monitor gas cap expansion, fluid movement due to re-injection, and voidage. At the same time the objective was to identify low GOR intervals behind pipe for possible recompletion.

A number of different examples are shown to illustrate both the technique and the economic benefit of the monitoring program. Many of these wells contributed significant additional oil from bypassed zones that were initially thought to be dry gas. In some wells, the instantaneous incremental production was over 10,000 BOPD from a single recompletion.

Gas cap monitoring in very low porosity reservoirs in Colombia proved to be not only feasible, but extremely profitable by differentiating dry gas zones from low GOR zones.
Using Fibre-Optic Distributed Temperature Measurements to Provide Real-Time Reservoir Surveillance Data on Wytch Farm Field Horizontal Extended-Reach Wells
Authors: Brown G. A. , Kennedy B. , Meling T.
Published: December 2007

BP-Amoco operated Wytch Farm has installed fibre optic distributed temperature systems on 2 of their recent ERD (extended reach drilling) wells in order to provide real time reservoir surveillance. This novel new approach to reservoir monitoring has provided important information about the well and reservoir performance. This type of zonal contribution and fluid data would normally be acquired by running production logs on the end of coiled tubing at infrequent intervals, however the dual completion on Wytch Farm’s M-12 well made conventional production logging impossible.

Distributed temperature data has been recorded over 2 years throughout well tests and shut-ins, as well as during normal periods of production. Data analysis is performed both visually, by correlating time related thermal events observed in the well with known reservoir and production anomalies, and theoretically by comparing recorded temperature data with that predicted by thermal profiles generated using nodal analysis fluid flow and heat transfer software*. Use of this software* allows estimates of production by zone to be compared to actual recorded temperature data, enabling a variety of production scenarios to be investigated and the most likely identified.

The installation of real time fibre optic distributed temperature monitoring on Wytch Farm field has enabled the asset to recognise flow behind casing and cross flow during shut-in in the M-12 well and water finger encroachment to be identified in the M-17 well. This data has provided important information about both the reservoir and well performance in real time, which would not usually have become available until later in the wells life.
Fluids for Drilling and Cementing Shallow Water Flows
Authors: Whitfill Donald L. , Heathman James , Faul R. R. , Vargo Richard F.
Published: December 2007

Industry experience has emphasized the necessity for quick detection and quick control of shallow water flows. Pressure While Drilling (PWD) instruments showing an increase in annular pressure when drilling riserless with seawater will indicate produced sand. Shallow, well-developed, clean, geo-pressured formations will produce very large quantities of brine during an uncontrolled drilling operation. Because of high fluid velocities and the unconsolidated nature of shallow formations, large volumes of produced sand — and subsequent borehole enlargement — should be expected.

There are options for successfully drilling shallow water flow zones. A common scenario is to drill riserless with sea-water using high viscosity sweeps while also having kill fluid ready. If a saltwater flow occurs, evaluate the risk and cost scenarios of continuing to drill under-balanced versus containing the flow with large volumes of weighted fluids. This paper reviews a number of approaches using specialty fluids for drilling, along with their case histories.

Hundreds of case histories have proven that foam cement is the preferred approach to cementing casing across shallow water flow zones. Benefits include but are not limited to (1) vastly-improved displacement efficiency; (2) flow-control owing to the fact that an expansive fluid is in place during the phase transition from a liquid slurry to a gel with strength sufficient to suppress water flows; (3) ease of on-location job modifications. However, specialized blends are often required so that the cement (foamed or non-foamed) will function as intended at the low temperatures encountered across these zones. Use of these blends can complicate material handling logistics, especially on rigs with limited bulk volume capacity. The paper discusses the benefits of an all-liquid additive approach that allows the use of any Class A or Class H neat cement that may be on a rig. The chemistry of the additive package produces a slurry with the same capacity to control shallow water flows as the specialty blends. Case histories of these systems will be discussed.

The paper also discusses a decision flow chart designed to help the engineer better plan for controlling water flows related to drilling through shallow water flow environments.
Extending the Option Pricing Theory for the Valuation of E&P Projects
Authors: Zettl M.
Published: December 2007

Many attempts have been made to use option pricing theory (OPT) for the valuation of investment projects and especially for E&P projects. In this paper the various approaches are compared to each other. The discrete method using two kinds of binomial trees to describe the pre-drilling and the production phase, respectively is considered the most promising way to model complex nested options that exist in E&P projects. This model, however, has two major disadvantages. First, the oil price can reach unrealistic values due to using a multiplicative binomial process to model the price process. Second the uncertainty of other input values, besides the oil price, is not considered. To overcome the problem of extreme oil prices a price band that confines the oil price process is used. The uncertainty of the input parameters is incorporated by combining OPT with Monte Carlo simulation. Furthermore, it is proposed in this paper which evaluation technique should be used in a certain phase of an E&P project.
Identifying Controls on Reservoir Behavior Using Designed Simulations
Authors: White Christopher D. , Willis Brian J. , Narayanan Keshav , Dutton Shirley P.
Published: December 2007

Reservoir simulation is widely used to investigate the effects of geologic heterogeneity and engineering parameter variability on reservoir production behavior. Because many geologic and engineering factors interact to affect recovery behavior, an exhaustive examination of variations due to all possible parameter combinations is prohibitively expensive. The factors that most strongly influence production behavior must be identified to focus analyses and measurements. Experimental design varies multiple factors simultaneously and minimizes the number of simulations required to construct accurate response models. Response models can statistically test the relative importance of the factors examined in designed simulations.

In this paper, a method based on response surfaces, Monte Carlo simulation, and Bayes’ theorem (RSMCB) was used examine the effects of several types of geologic variability and different modeling methods. The method is demonstrated in an analysis of outcrop data from a heterolithic tide-influenced deltaic sandstone. The data set includes thousands of probe permeameter measurements, detailed bedding maps, shale diagrams, cement maps, facies maps, facies-specific rock properties, and variograms.

Because of the importance of geostatistical methods for reservoir model construction, designed simulations examined the effects of varying geostatistical parameters and compared geostatistical and quasideterministic models of geologic variability. Intrafacies variations have statistically significant effects at the bed scale, although shale resistance dominates these effects.

Improvements in reservoir model accuracy were quantified by computing the expected changes in factor uncertainties resulting from response measurements. Posterior distributions of geologic and geostatistical parameters were estimated from flow responses. Monte Carlo simulations with prior and posterior factor distributions quantify the uncertainty reduction caused by measurements. Uncertainty reduction can be compared to measurement cost, enabling better informed measurement decisions.
Model Errors Inherent in Conditioning a Stochastic Channel to Pressure Data
Authors: Zhang Fengjun , Reynolds A. C. , Oliver D. S.
Published: December 2007

This work discusses an automatic history matching procedure to efficiently condition a stochastic channel to well-test pressure data, plus well observations of the channel thickness and depth of the channel top. Our emphasis is on computational difficulties that are related to the nonlinearity of the objective function or arise from the definition of effective permeability on a reservoir simulation gridblock that is intersected by one or more channel boundaries. We show that upscaling gridblock permeabilities for gridblocks intersected by channel boundaries introduces modeling errors. This errors cause spurious local minima in the objective function that must be optimized to obtain a realization of the model. We suggest a procedure to reduce the occurrence of spurious local minimum. We show that an automatic history matching procedure can be used to define upscaled permeabilities. We show, however, that when permeability contrasts across fades boundaries are extreme, this upscaling process may be dominated by the difference in local trucation errors between the fine and coarse grid systems.

One important objective of this work is to provide computational insight for the general problem of conditioning a reservoir fades model to production data by automatic history matching.
A Relationship Between the Fractal Dimension and Scaling Groups of Unstable Miscible Displacements
Authors: Gharbi R. B. , Qasem F. , Peters E. J.
Published: December 2007

A detailed two-dimensional flow visualization study was performed to examine the dynamics of viscous fingering in miscible displacements. Detailed quantitative miscible displacement experiments using a microcomputer-based imaging workstation on a variety of oil recovery fluid systems were performed. The effect of two dimensionless scaling groups, namely gravity number and viscosity ratio, on the displacement behavior was investigated. Based on image analysis, the irregular fingering patterns of the flow visualization experiments were analyzed for fractal characteristics.

Results indicate that the areal sweep efficiency of unstable miscible displacement follows a fractal scaling law with a fractal dimension and proportionality constant related to the gravity number and the viscosity ratio. The study shows that the fractal dimension decreases with decreasing gravity number and increasing viscosity ratio. This relationship was mapped by an artificial neural network model, which can be used to estimate the fractal dimension and the proportionality constant of miscible displacements as functions of the two scaling groups. These results have potential application in the mathematical modeling of unstable EOR displacements and in the scaling of laboratory displacements to field conditions.
The Evolution of a High Near-Wellbore Pressure Loss Treatment Strategy for the Australian Cooper Basin
Authors: Roberts Geoffrey A , Chipperfield Simon T , Miller William K
Published: December 2007

An extensive hydraulic fracturing program has been ongoing in the Australian Cooper Basin since 1994. Close to 100 "vertical" wells have been treated during this period in a high temperature/pressure hard rock sandstone environment, with a placement success rate of around 90%. The remaining 10% have almost all experienced some degree of high Near-Wellbore Pressure Loss (NWBPL), ie. 600–1500 psi, with this near-well fracture complexity preventing the placement of treatments. Despite the focus and publicity on this subject in recent years, severe and consistent NWBPL problems in vertical wells are "rare". Exceptions to this are highly naturally fractured formations (coal seams) and/or poor perforation practices. While it is often difficult to determine the exact cause of NWBPL, an understanding of its’ potential causes, coupled with field trials and accumulated experience in the Cooper Basin, has been distilled to obtain a set of tools and procedures to minimise its’ impact on all but the most severe cases.

Summaries of the Cooper Basin field trials conducted over the past five years are presented. This paper also introduces a cost effective, NWBPL management strategy based on the results from these trials that has been successful in over half of the problem wells. This strategy is based on a three-phase approach. It requires the use of NWBPL mitigation, remediation and tolerance initiatives.

Finally this paper presents three case studies in which the NWBPL management strategy has been successfully employed.