bluuebunny/crossref_metadata_2025 huggingface dataset:
Geostatistical Quantification of Geological Information for a Fluvial-type North Sea Reservoir
Authors: Caers Jef K. , Srinivasan S. , Journel Andre G.
Published: December 2007

Accurate prediction of petroleum reservoir performance requires reliable models of the often complex reservoir heterogeneity. Geostatistical simulation techniques generate multiple realizations of the reservoir model, all equally likely to be drawn. Traditional to geostatistics, geological continuity is represented through the variogram. The variogram is limited in describing complex geological structures as it measures correlation between rock properties at two locations only: it is a two- point statistic. Reservoir analogs such as outcrops can serve as training images depicting the interpreted geological structure. Due to scarcity of well data, the variogram models are often borrowed from such training sets. However, the same training images could be utilized to extract more complex information in the form of multiple point statistics measuring the joint dependency between multiple locations.

This paper compares a traditional variogram-based geostatistical model versus a novel geostatistical method utilizing multiple point statistics borrowed from training images. The comparison is made on the basis of flow performance for a typical North Sea reservoir. To obtain such comparison a "true" reference reservoir is generated using object-based simulation that depicts the complex intertwining of fluvial channels. Next, a different but similar reservoir is generated, termed the "training reservoir". The latter is used to extract the necessary structural information, be it variograms or multiple-point statistics, to build multiple geostatistical models of the "true" reservoir conditioned to sparse well data. A water flood flow scenario with inverted 5-spot pattern is simulated using ECLIPSE on the true reference and the various geostatistical models. Water breakthrough characteristics and water saturation distributions are used for comparison.
Application of Intelligent Completion Technology to Optimize the Reservoir Management of a Deepwater Gulf of Mexico Field – A Reservoir Simulation Case Study
Authors: Rester Stephen , Thomas Jacob , Hilten Madeleine Peijs-van , Vidrine William L.
Published: December 2007

The objective of the 'intelligent completion' concept is to provide the operator with a completion method that will allow reconfiguring of well architecture as well as acquisition of real-time data whenever needed — without rig intervention! As with all unique operational strategies that significantly differ from traditional concepts, there are always questions as to whether the new techniques can really achieve the sought- after economic and operational benefits as well as how candidate wells can be chosen.

This paper will discuss a study that was performed to demonstrate 1) that intelligent completion technology could be successful in optimizing the management of a field through controlled commingling of production and 2) that it could increase flexibility of making operational changes.

The project considered a deepwater Gulf-of-Mexico field that consists of several stacked sandstone reservoirs that are separated by shales. A multi-well development plan using dual completions and rig recompletions had been established for this field prior to the commencement of this study. A review was made of the wells in the development plan and the geology of the field to select appropriate candidates for possible replacement of the traditional completions with intelligent completions. Two wells were chosen for the study. Reservoir simulation was used to estimate the production profiles for several cases with conventional completions and for two cases with intelligent completions. In the existing development plan, both of the wells were to be completed in one reservoir initially and recompleted in a different reservoir later.

For each well, the application of intelligent completion technology accelerated production and eliminated the need for a rig recompletion. The simulation results showed that the single well economics would be improved for both wells being studied. Although some of this improvement was offset by well interference effects, overall, the field economics were enhanced. The data obtained from the study will illustrate that there are economic advantages to applying intelligent completion technology in the appropriate well scenarios. Also, methods for estimating the performance of intelligent completions will be evaluated.
A Thermodynamic Modelling Method for Organic Solid Precipitation
Authors: Mei Haiyan , Kong Xiangyan , Zhang Maolin , Sun Lei , Li Shilun , Sun Liangtian
Published: December 2007

A gas and oil system contains a certain amount of heavy organic substances, such as wax, resin and asphaltene which precipitate as a solid phase, causing serious problems to production for oil and gas fields, when thermodynamic conditions are changed.

In this paper, a thermodynamic model of the gas-liquid- solid three-phase equilibrium for an oil and gas hydrocarbon system is presented, based on the regular solution theory, an equation of state and the phase equilibrium principle of fluid thermodynamics. A flash calculation model for the gas, liquid and solid three phases is developed, being combined with a material conservative equation. An equation of state is used to describe both gas and liquid phases, and a regular solution theory is only used to account for the non-ideality of the solid mixture, which can reflect the effects of temperature, pressure and composition of system on solid precipitation. The influence of the heat capacity difference between the liquid and the solid on the solid precipitation is taken into consideration. Some adjustable parameters and a tuning function are introduced in this model because of uncertainty of heavy component properties. It is shown that the model has a good convergency and stability, and the calculated values by this model are in good agreement with the experimental data.
Leveraging off Advances in Internet Technology to Bring Data to the Expert User On-Shore
Authors: McGinley P.J.
Published: December 2007

This paper was prepared for presentation at the 1999 SPE Annual Technical Conference and Exhibition held in Houston, Texas, 3–6 October 1999.
Stochastic Boolean Simulation of Fluvial Deposits : A New Approach Combining Accuracy with Efficiency.
Authors: Viseur Sophie
Published: December 2007

Object-based approaches seem particularly suitable for sim-ulating large-scale heterogeneities, as they directly incorporate information such as dimensions, sinuosity and amplitude. How-ever, these approaches are often based on a simulated annealing process, that may converge slowly when numerous constraints should be honored. For this reason, we propose in this paper a direct approach, enabling well markers to be honored by a set of simulated large-scale heterogeneities, such as the channel- belt bodies, within an overbank deposit underground. Our approach enables to combine results from the realm of CAD with stochastic procedures and sedimentological results. Therefore, we propose here a method driven by the simulation of avulsion events, which results in a geologically coherent fluvial archti- tecture. Another interesting aspect of our method is that it is very easy to extend by adding the capability to account for deterministic data.
Tracking Miscible Processes in the Subsurface Utilizing Time Lapse Shear Wave Seismic Data
Authors: Bard Karen C. , Pranter Matthew J.
Published: December 2007

The Reservoir Characterization Project (RCP) is an industry- sponsored consortium. Its mission is to develop and apply 3-D and 4-D (time-lapse), multi-component seismology and associated technologies to improve reservoir performance and hydrocarbon recovery while reducing environmental impact. Current research is focused on utilizing 4-D multi-component seismic to track a CO2 injection project at the Central Vacuum Unit, Lea County, New Mexico. This field produces from the San Andres reservoir, a shallow shelf carbonate reservoir located on the Northwestern Shelf of the Permian Basin, Southeastern New Mexico (See Figure 1). Figure 2 is a detailed schematic of the seismic and geologic/reservoir simulation areas. Also included within this diagram is the type, quantity, and location of the available data. This portion of the Central Vacuum Unit is in the area where the Lovington siltstone is present. The Lovington effectively separates the San Andres into two producing intervals.

A CO2 Huff-n-Puff pilot project was performed in well CVU-97 at the Central Vacuum Field and the repeated 3-D, 3-C seismic surveys were performed from October 1995 to December 1995. The initial survey was acquired prior to CO2 injection. The second survey was acquired during the "soak" period of the Huff-n-Puff process after fifty (50) million SCF of CO2 had been injected into the well during a four (4) week period.

Interpretation of this time lapse seismic data showed an anomalie due south of the CVU-97 well in the vicinity of the observation well, CVU-200. The simulation results showed an increase in CO2 concentration going in the same direction. Caution needs to be applied in the emphasis placed on these results due to the relatively small volume of CO2 injected during the pilot program. However, the results demonstrate the potential of using shear seismic data in tracking miscible processes. It is also interesting that the simulation results indicate that the shear waves seem to be more sensitive to the change in fluid properties rather than pressure.

The staged implementation of the CO2 injection program started in the spring of 1997. Injection started in the 4-D seismic area in April 1998. In November of 1997 a new base line of multicomponent seimsmic data was acquired. The time-lapse seismic acquisition was performed in November of 1998. Interpretation of these results is still ongoing.
Analysis of Overpressured Reservoirs with a New Material Balance Method
Authors: Wang S. W. , Stevenson V. M. , Ohaeri C. U. , Wotring D. H.
Published: December 2007

This work presents application of a new material balance method to detect aquifer influence and calculate water influx and original gas in place for four over-pressured reservoirs. Calculation of water influx needs to satisfy a set of three equations as opposed to the existing method of one equation of unit slope. In each application, the presence of aquifer influence was identified first, and then material balance was used to determine original gas in place and water influx. The overpressure effect was handled by integrating rock compressibility over operating reservoir pressure. Compositional effects were modeled with Rv (volatile oil/gas ratio) by matching PVT data using Walsh-Towler algorithm or an Equation-of-State. This new method is internally consistent, which avoids potential pitfalls of existing methods. Comparison with other methods in analyzing overpressure reservoirs shows this new method is more robust and comprehensive.
Chemical Defoamer Reduction with New Internals in the Mars TLP Separators
Authors: Chin R. W. , Inlow H. L. , Keja T. , Hebert P. B. , Bennett J. R. , Yin T. C.
Published: December 2007

High injection rates of chemical defoamers had been required to operate the production and test separators on the Mars TLP. In an effort to reduce the chemical consumption, different means of mechanically breaking the foam were investigated in the test separator: gas outlet axial flow demisting cyclones and inlet cyclones. For two different wells, the chemical rate was reduced by 20% and 80% respectively when the existing vane packs were replaced by axial flow demisting cyclones using liquid carryover in the gas outlet as a performance measure. Additionally, the chemical rate was further decreased for several wells by about 30% by replacing the existing 6-tube cyclone inlet with a different design single tube cyclone inlet. On the basis of the successful test separator results, the four main production separators were retrofitted with new internals. Chemical reduction has been on the order of 50%. Description of the old and new internals, test separator results, and the main vessel retrofits are discussed in this paper.
A Comparison of Wireline and Drillstem Test Fluid Samples From a Deepwater Gas-Condensate Exploration Well
Authors: Witt C. J. , Crombie A. , Vaziri S.
Published: December 2007

Successful sampling of gas-condensates is not straightforward with wireline fluid sampling tools, and ambiguous results are often obtained. As a result well testing has often been regarded as the only method of ensuring representative samples. However, testing is expensive and environmentally unfriendly so to be able to rely on wireline fluid samples would be of great value in exploration and appraisal. Few examples exist where both test and wireline samples have been obtained and compared.

In a recent deepwater exploration well offshore Mid-Norway (6305/7-1 Barden) which confirmed the presence of hydrocarbons in the southern extension of the Ormen Lange Dome structure, BP took both wireline and DST samples. This study compares the two sample types and discusses the sampling operations.

The drillstem test was justified by the requirement for high quality PVT samples which were needed to give an accurate assessment of the liquid content of the gas. This is critical to determining the processing requirements in a future development of the discovery. The well was drilled in 860m of water and the cold wellbore conditions were considered a key risk to wireline fluid sample quality. The well was drilled with water-based mud and a relatively dry gas (5–30 bbls/mmscf) was expected; the dew point was unknown. The MDT tool was used to take wireline samples using a ‘low shock’ sampling technique (controlled drawdown). The test samples were taken isokinetically from the separator and just upstream of the choke.

The two sets of samples show a remarkable similarity in fluid properties, encouraging us to believe we may be able to rely on wireline samples in future wells. The reasons for the success are discussed.

This experience demonstrates that, where water based-mud is used, representative fluid samples can be obtained from undersaturated gas-condensate wells using the MDT wireline fluid sampling tool, even in a cold deepwater environment. This experience could enable operators in future to minimise or avoid the need for well testing.
Deliverability Enhancement via Advanced Fracturing Technology in Gas Storage Wells
Authors: Reeves S. R. , Pekot L. J. , Koperna G. J. , Ammer James R.
Published: December 2007

As a result of formation damage, individual US gas storage wells are prone to deliverability loss at a reported average rate of 5% per annum. To bypass this damage and sustain/enhance well deliverability, several new and novel fracture-stimulation technologies have been tested in gas storage fields across the U.S. as part of a joint U.S. Department of Energy and Gas Research Institute R&D program that began in 1994. These new technologies include tip-screenout fracturing, hydraulic fracturing with liquid CO2 and proppant, extreme overbalance fracturing, and high-energy gas fracturing. This paper presents, in summary form, the final results obtained from this multi-year R&D project, which concludes in 1999.

A total of nine field test sites have been involved in the project; fracturing operations at all sites is completed, and limited post-stimulation deliverability and pressure-transient testing remains for each. In total, over 30 new and novel fracture treatments have been performed, close to 100 deliverability and pressure transient tests performed, and about 45 pre and post-fracture diagnostic tests performed.

Significant accomplishments have been numerous. First, the potential application of the various new and novel fracture stimulation technologies to gas storage wells has been demonstrated. Secondly, a lack of analytical design tools has been identified for some of the fracture stimulation technologies investigated. In response, a dynamic fracture and wellbore simulator has been modified to model the extreme overbalance fracturing process, and for the first time EOB downhole pressure records have been collected for analysis. Similarly, for the first time, downhole pressure/temperature records have been collected for a liquid CO2 with proppant fracture treatment. Finally, a comprehensive data set of multipoint deliverability and pressure transient tests has been assembled. This has provided a unique insight into the impact of fracture stimulation on gas storage wells, particularly with respect to the reduction of important non-Darcy flow effects, deliverability profiles, post-frac cleanup effects and how these factors change over time.

Based on the results derived from the project, conclusions have been drawn concerning the applicability and utility of these technologies, storage well damage conditions and remediation candidate selection, and future technology needs.
4D Seismic Modelling of the Statfjord Field: Initial Results
Authors: Al-Najjar N. F. , Brevik I. , Psaila D. E. , Doyen P. M.
Published: December 2007

As part of a major drive to improve recovery in the Statfjord Field, a large-scale 4-D seismic monitoring program was recently undertaken by the operator. One of the objectives of the 4-D program is to identify unswept oil pockets and zones experiencing early water influx in the producing sandstones of the Middle Jurassic Brent Group. A base 3-D seismic survey, acquired in 1979 at the beginning of production, plus two repeat surveys acquired in 1992 and 1997 have been processed and cross-equalized for 4-D analysis. To assist the interpretation of reservoir fluid movements from the time-lapse seismic data, a detailed 3-D earth model has been constructed by integrating log data from 180 wells with flow simulation results. The model framework consists of a series of 3-D stratigraphic grids spanning the Upper and Lower Brent reservoirs plus the encasing formations. Grid-cell reservoir properties include static parameters such as porosity and volume of clay as well as pore pressure and water saturation predictions downscaled from the flow simulation grids for each seismic survey time. Time-dependent elastic parameters such as P-wave and S-wave velocity, density and acoustic impedance have been computed at the three survey times and stored as extra grid-cell attributes. This computation uses a rock physics model linking the elastic properties in each cell to porosity, volume of clay, and saturation and pressure values extracted from the flow simulator. Synthetic amplitude volumes have been generated via forward modelling of the 3-D elastic models for the three survey times. Difference volumes derived from the synthetic datasets are thus representative of the seismic signature of the fluid movements predicted by the flow simulator.
Using 3D seismic-derived information in lithofacies simulations. A case study
Authors: Beucher H. , Fournier F. , Doligez B. , Rozanski J.
Published: December 2007

This paper details a methodology for taking into account seismic information into 3D high resolution stochastic simulations of lithofacies. The simulation is based on a non stationary truncated gaussian approach. Within this frame, a 3D matrix of facies proportion is built. It is estimated from both well and seismic-derived proportions. Thus the seismic attributes are previously turned into soft estimates of proportions with different possible statistical calibration techniques. An application of this methodology to the simulation of lithotypes for a carbonate reservoir is described.
Borehole Stability of Multilateral Junctions
Authors: Aadnøy Bernt S. , Edland Cecilie
Published: December 2007

The number of multi-lateral wells are increasing in the North Sea area. Potential for improved accessibility and recovery has led to a significant interest both from oil companies and the service industry. With improved technology, these multi-lateral branches will be key elements in the development of the so called "smart" wells.

Several multi-lateral wells recently drilled in the North Sea have experienced problems. One well had severe problems as the casing inside the branch deformed into the main wellbore, making both branches unavailable for reentry. Clearly, the formation at the junction had collapsed, forcing the casing to deform.

A rock mechanics study was undertaken. The hole geometry above the junction was a circular hole, which became oval at the junction, and then split into two adjacent boreholes below the junction. Since the solution to this problem was not found in the literature, a new mathematical model had to be developed to model these geometries. This model was coupled to a stress model and a failure model for the rock. The paper will present the complete models. It was found that both the critical fracturing pressure and the collapse pressure changed as the hole geometry changed from a circular hole.

The paper present a field case using the new models. The study showed that the stress concentration increased as the hole became oval at the junction. It was found that the oval geometry created more severe conditions both for mechanical hole collapse and fracturing. It was also found that at certain borehole pressures, this geometric effect diminished.

One main conclusion of the study is that the allowable mud weight window is smaller at the junction itself compared to the holes above and below. The fracturing pressure is lower, and, the critical collapse pressure is higher in the junction than outside the junction. Therefore, the optimal mud weight is the most important condition for trouble-free drilling of a junction. The optimal stress conditions for the geometries will be defined in the paper, and based on these, the paper will present optimal mud weight selection criteria to drill multi-lateral junctions.
Petrophysical Implications of Laboratory NMR and Petrographical Investigation on a Shaly Sand Core
Authors: Chitale D. V. (Vivek) , Day Peter I. , Coates George R.
Published: December 2007

Nuclear magnetic resonance (NMR) measurements on rocks directly respond to the hydrogen content of the fluids in the pore space. Thus, besides the routine application of NMR in measuring the producible water- and hydrocarbon-filled porosity in the rocks, NMR technology has the potential to characterize the surficial clay-bound water. The exact nature of NMR transverse-relaxation T2 spectra obtainable from the clay-bound water has been discussed in recent studies conducted on both pure clays and reservoir rocks. The paper presents the results of a laboratory investigation on systematically sampled shaly sand rocks. We explore the relationship between the T2 distribution as a function of the rock texture, pore size distribution, clay mineralogy, and clay morphology.

A 10-ft conventional core, cut in water-bearing, clay-rich sandstone, was sampled for this study. Mineralogy, texture, pore size distributions, and clay morphology were analyzed by X-ray diffraction (XRD), thin section petrography, scanning-electron microscopy (SEM), and petrographic image analysis (PIA). In addition, fully polarized NMR signals were acquired from brine-saturated and desaturated samples with inter-echo spacings (Te) of 0.3 and 0.6 millisecond.

NMR porosity, computed by summing the signal in the T2 spectra, match favorably with the helium porosity, indicating that the full spectrum of pore sizes is included in the NMR porosity. The NMR T2 spectra obtained from brine-saturated samples show three distinct T2 classes: 1 to 3, 5 to 20, and 30 to 200 milliseconds. These appear from core properties to be controlled by pore-size changes, which are primarily influenced by the changes in clay type and morphology. The <5-millisecond components likely correspond with <5-μm sized pores typically trapped within the flakes of detrital illite. Features in the 5- to 20-millisecond range are also likely associated with the authigenic aggregates of kaolinite and chlorite that enclose 5- to 30-μm sized pores. T2 spectra obtained from desaturated rocks support the match of the specific features in the T2 spectra to the clays present in the rocks. Finally, the water in the relatively larger pores (30 to 150 μm) is associated with the signals at about 30 milliseconds and greater.
Enhancing Mineral Scale Dissolution in the Near-Wellbore Region
Authors: Williams G. D. , Collins I. R. , Wade S. R.
Published: December 2007

Mineral scaling in the near-wellbore region of oil wells can cause significant formation damage and have a major impact on well productivity. Removal of scale from the reservoir is usually limited to chemical means, or, if the completion is a cased hole, to re-perforating through the damage. Chemical removal of scale from the reservoir is limited by the contact that can be achieved between the scale deposits and the scale dissolver chemical, and by the volume of chemical which can be injected. In addition, scale deposits can become coated in hydrocarbons, preventing contact between the deposit and the chemical dissolver. Furthermore, owing to the nature of the dissolvers (comprised of chelants and acids), there is the potential for the dissolver to cause formation damage by (i) dissolving cementing minerals thereby generating fines; (ii) swelling authigenic clays; and (iii) forming water blocks. We have developed a proprietary mixture of non-ionic materials which has been shown to enhance the dissolution of both calcium carbonate and barium sulfate scales in porous media (using commercial scale dissolvers in the tests). This chemical, when used as a pre-flush, removes hydrocarbon deposits on the scale surface thus increasing the surface area accessible to the dissolver. In addition, the pre-flush chemical might remediate some aspects of dissolver induced formation damage. In this paper we describe laboratory experiments validating the chemical package.
On-Site, Near-Real-Time Monitoring of Scale Deposition
Authors: Emmons D. H. , Graham G. C. , Holt S. P. , Jordan M. M. , Locardel L. P. , Locardel B.
Published: December 2007

Inorganic scale deposition is a problem associated with petroleum production. Scale deposition is often managed or mitigated by the use of scale inhibitors. The current industry standard for managing scale programs relies on the determination of scale inhibitor concentration in the scaling brine and then relates this concentration to program performance. Scale inhibitor residual tests are not ideal because the tests themselves are often time consuming to run, subject to interference from components in the produced water, and specific to the inhibitor used. There are delays associated if samples are sent off for analysis. Most important, the results offer no direct information about actual scaling potential. This paper presents a novel technique for scale management which involves direct, near-real-time monitoring of the stability of produced water towards scale deposition. Our method couples together a unique piezoelectric sensor for on-site, near-real-time detection of scale deposition with a method of applying low-level stress (addition of scaling cations or anions) to produced water in order to detect incipient scale. The tests can be run on-site, are independent of scale inhibitor, and results are obtained within hours. Lab studies and field studies are presented for barium sulfate scale deposition. The potential for real time on-line monitoring is discussed.
Reconstructing Petrophysical Borehole Images: Their Potential for Evaluating Permeability Distribution in Heterogeneous Formations
Authors: Anxionnaz H. A. , Delhomme J. P. , De Haan S.
Published: December 2007

Borehole electrical images have very high vertical and azimuthal resolution, and thus have proved to be of paramount importance over the past 10 years in assessing formation layering and internal organization. Standard openhole log measurements (e.g., density or photoelectric factor) have also experienced improvements in accuracy and vertical resolution. These improvements are the result of more compact integrated tools and the systematic use of accelerometer-based speed corrections and inclinometry devices to measure the orientation of sensors within the borehole. Recent advances in nuclear magnetic resonance (NMR) logging have also cast a new light on petrophysical evaluation, especially on continuous permeability logs.

The technique proposed in this paper combines information from borehole images and advanced petrophysical logs in a two-step approach. In the first step, a transform or relation is established between two oriented borehole measurements. For example, the transform is computed between azimuthal resistivity from an imaging tool and a high-resolution density measurement, conditioned on the readings of nondirectional volumetric measurements such as neutron porosity, gamma ray and image-derived textural indicators. This transform, which is in most cases inherently nonlinear, is not explicitly determined. Rather, it is approximated by an artificial neural network, which is trained over key representative facies zones. As a quality control step, the procedure uses the resistivity and other measurements to compute a synthetic density curve. This is compared to the actual density log, and error bars are attached to the reconstruction process.

In the second step, the same transform is then applied to each available azimuthal resistivity channel (column in the electrical image) to reconstruct a quantitative density image on the borehole wall from these reconstructed density channels. The same approach provides a method to interpret a permeability curve from NMR data. The recorded orientation of the CMR* Combinable Magnetic Resonance tool skid enables a transform to be established between NMR-derived permeability and azimuthal resistivity, azimuthal density and nondirectional volumetric measurements (neutron porosity, gamma ray and textural indicators). Reconstructed permeability images can then be obtained by applying the transform to the full suite of image channel data.

The proposed technique is illustrated with examples from clastic and carbonate formations. It provides a powerful means to better understand permeability variations in heterogeneous formations.
A Dipole Array Sonic Tool for Vertical and Deviated Wells
Authors: Tello Lucio N. , Blankinship Thomas J. , Roberts Edwin K. , Kuzmiski Rick D.
Published: December 2007

Dipole array sonic tools are particularly suited for estimating acoustic shear wave velocities in soft, unconsolidated, slow formations. Dipole sources induce flexural waves which are sustained in such formations. By contrast, monopole sources create pseudo-Rayleigh waves, related to shear wave velocity, which, in slow formations, refract away from the borehole and vanish before reaching the receivers.

One of the main challenges of dipole sonic logging has been to descend into deviated wells. Operating in deviated wells requires a tool body competent enough to withstand compressive forces. But for a dipole tool, a rigid tool body is impractical because it conveys a strong direct arrival that interferes with the flexural mode. Therefore, in most traditional dipole tools, the sonde body is replaced by an acoustic isolator made of steel cables, which suspends the receiver array from the transmitter array. While such designs eliminate nearly all body arrivals, they restrict the range of application to wells with little or no deviation.

A new tool design overcomes these problems, allowing comfortable logging of both dipole and monopole in deviated wells. The main feature of the design is a semi-rigid tool body, which consists of a series of interlocking steel rings configured in a special pattern and individually isolated by an elastomer. The dipole acoustic source has a broad frequency bandwidth extending down to the 600 Hz range, low enough to excite large boreholes and very slow formations. A comparison log in a vertical well between a cable-type isolator and the new semi-rigid isolator yields nearly identical data. Furthermore, a series of example logs run in deviated wells with the semi-rigid acoustic isolator validates this new approach for both the dipole and the monopole arrays. Random road noise, which is observed in deviated wells, is filtered using frequency and depth domain processing. Logging in free and bonded cased wells is also possible with this device. Comparison of travel time and porosity calculations in previously run open-hole logs with cased-hole dipole and monopole logs provided accurate results in both bonded and free casings.
Novel Approach to Optimization of Infill Drilling Using Conformance Mapping Technique
Authors: Beecroft W. J. , Shtern V. N.
Published: December 2007

Predicting, monitoring, and optimizing oil production from fields, having complex shape, require powerful and user-friendly software. This paper develops such software using conformal mapping and analytical functions. The approach includes (a) geometrical and (b) fluid mechanics parts. Part (a) approximates the horizontal projection of an oil field by a polygon and then transforms the polygon onto the upper half-plane. Part (b) models production and injection wells by point sinks and sources. The advantages of the approach are (i) separation of the geometrical and flow problems and (ii) analytical solution for the velocity field. These two features significantly accelerate modeling and allow optimization of well positions in a few minutes on a laptop computer as shown here for a real oil field. The software currently addresses two-dimensional (2D) domains and will be generalized for 3D domains.
Empirical Risk Assessment of Infill Drilling Locations, Barrow Island, Australia
Authors: Allard D. N. , Hillyer M. G. , Gerbacia W. E. , Rychener L. M.
Published: December 2007

The Barrow Island Field has been producing oil since 1967. Full development of the field with 40 acre inverted 9-spot injection patterns was completed by 1970. In order to increase production, infill drilling started in 1979. Infill drilling was carried out in a campaign manner, with a total of 182 infill wells drilled to date. The most recent infill drilling campaigns were Phases 1, 2 and 3 in 1995, 1996 and 1997 respectively. There are now approximately 450 active producing wells and 250 water injectors in the field.

Infill well location selection-methods were primarily empirical. These methods were modified as more information was learned from subsequent campaigns. The last three campaigns utilised an empirical algorithm based on the offset producer liquid-rate and water-cut. The algorithm was adjusted based on the results of Phases 1 and 2 such that by Phase 3 its statistical accuracy was within a few percent. Indicative economics based on forecast decline curves showed positive results.

There are still many viable infill locations in the field. A Phase 4 campaign has been evaluated with the same algorithm that was used in the successful Phase 1, 2, and 3 campaigns. In order to continually improve the accuracy of economic performance prediction, a probabilistic approach was used for this campaign. The results of the previous campaigns were used to define the uncertainties in each of the parameters. These uncertainties were then used in a decision analysis model to estimate an expected value and the financial uncertainty of the project. After incorporating risk, the planned Phase 4 program showed good economics.

The simple empirical methodology proved very effective in selecting infill locations, and the probabilistic approach effectively reduced the risk uncertainty. The evolution of this methodology is discussed and analyzed in this paper.
Conditioning of Lévy-Stable Fractal Reservoir Models to Seismic Data
Authors: Gunning J. , Paterson L.
Published: December 2007

We have developed methods of conditioning non-stationary Levy-stable geostatistical models1,2 to 3D seismic data. The technique involves adapting the sequential Levy simulation method such that the convolutional response of the realisations acceptably ‘matches’ the seismic amplitude map. A rejection scheme is used, which requires fast repetitive simulation of gridblock columns and generation of convolutional responses. The non-stationarity of the model means that this cannot be achieved using the conventional large kriging system. We use a different, but comparably rapid method, based on storing the relevant parts of a sequential simulation calculation for the column. Working directly with the amplitude traces also has the advantage of avoiding the ambiguities and non-uniqueness involved in inverting the traces to acoustic impedance.

The most difficult part of the problem is estimation of the seismic wavelet, and this is often done non-optimally. We describe a sophisticated method of estimating the wavelet, and show that this can yield better than expected results. Suitable rejection criteria are proposed, based on reasonable probabilistic models. The application of the technique is demonstrated with a field example.
Creation of the Fractional Flow Curve from Purely Production Data
Authors: Macary Sameh , Al Hamid Walid A.
Published: December 2007

The paper uses the X-plot technique for recovery prediction and for obtaining permeability ratio and the fractional-flow curves, which have great importance in the displacement efficiency calculations. This technique being applied only to reservoirs producing with water cuts higher than 50%, requires the linearization of the relationship between recovery and water cut. The straight line allows extrapolating to any desired water cuts to obtain the corresponding recovery. Before running linear regression production data have been treated by some filteration and considerations that comply the logic evolution of oil field exploitation. The slope and the intercept of this straight line are used to generate a plot of field relative permeability ratio, which forms the basis for creating the fractional flow curve. This approach was applied to two actual field cases: El-Morgan South Kareem and South Belayeem reservoirs. Both reservoirs are producing with water cuts higher than 50% since 1987. In addition to recovery prediction, the created permeability ratio and fractional-flow curves, unlike the laboratory derived ones, are composite curves that include not only the displacement characteristics of the fluids but also the reservoir geometry, heterogeneity and operational conditions of the field. Therefore, the created Frac-Flow curve could serve as a quality-check tool for lab measurements. Another important privilege is that the method is cost-free and completely relies on production data.
Application of Diamond-Enhanced Insert Bits in Underbalanced Drilling
Authors: Tetley N. P. , Hazzard V. , Neciri T.
Published: December 2007

Drilling underbalanced with foam fluids affects bit selection. Compound the use of foam drilling with a known abrasive, hard sandstone and proper bit selection becomes critical. This paper details the application of fully diamond-enhanced insert bits using foam fluid systems to the drilling of a depleted reservoir. It discusses the field trials, which have been carried out at the Rhourde el Baguel field of Algeria and the conclusions that have been reached. The paper also presents the outcome of investigations to further improve rate of penetration by offering a more aggressive point-loading to the rock through the application of shaped inserts instead of the semi-round, top inserts currently used.
Integrated Modelling of the Southern North Sea Carboniferous Barren Red Measures Using Production Data, Geochemistry, and Pedofacies Cyclicity
Authors: Stone Greg , Moscariello Andrea
Published: December 2007

Effective development of the Carboniferous Barren Red Measures in the Silverpit Basin of the U.K. Southern North Sea, is reliant on a robust correlation framework. This complex, low net:gross, fluvial reservoir is interpreted as being deposited as discrete, low sinuosity, braidplain channel bodies within a floodplain shale. Production history over the last 2 years indicates significant vertical and lateral variability of reservoir architecture, and drives the requirement for improved reservoir performance prediction. Biostratigraphic markers are sparse in the Barren Red Measures and previous attempts at defining reliable stratigraphic subdivisions were based on the identification of potential ‘flooding surfaces’ derived from the correlation of Gamma Ray (GR) peaks between wells.

Geochemical analysis has enabled the generation of a robust, 5-zone chemostratigraphic correlation framework. Each zone defined broadly equivalent packages of strata, recording changes in the basin wide hydrology of the depositional system, and as a result provided a reliable, stratigraphic subdivision. Through analysis of reservoir parameters, and production data, the regional palaeogeographic model was refined, and an improved understanding of the reservoir architecture controls on hydrocarbon flow were achieved.

Incorporation of detailed core analysis resulted in the interpretation of pedofacies in each stratigraphic unit. Sediment maturity was described in terms of the degree of bio/pedoturbation of the original sediment fabric and a link to aggradation rates and reservoir architecture proposed. The cyclic nature of the reservoir was analysed and direct links to the geochemical subdivisions identified. This supported the theory of basin wide hydrological changes fuelling the architectural variations in the reservoir. The integration of production data into the geological model provided support for the formulated theories on reservoir architecture.

Through this integration of geochemical correlation techniques, analysis of pedofacies, cyclicity and production data, it was possible to redefine the geological model and derive a robust framework on which to base both static and dynamic reservoir modeling. This in turn enables improved reservoir performance prediction.
Erskine Field: Early Operating Experience
Authors: Allen R. F. , Walters M.
Published: December 2007

Erskine is the first High Pressure, High Temperature (HPHT) field in production on the UK continental shelf. Modest reserves of rich gas condensate demanded innovative development concepts to achieve an economic project for field operator Texaco and co-venturer BPAmoco. A normally unattended wellhead platform is linked to a third party processing host platform by a multiphase pipeline. Since first production in December 1997 the three reservoirs have behaved broadly in line with expectations while the design concepts, technologies and operational practices have been thoroughly tested and proved to be conspicuously successful. The experience gained through design, commissioning and operation on this landmark development is recounted.
An Analysis of OSD's Well Incident Database; Results can Improve Well Design and Target Well Control Training.
Authors: Hinton Andy
Published: December 2007

This paper is an analysis of the well kicks recorded on the Wells IT database of the Offshore Safety Division (OSD) of the Health and Safety Executive (HSE). The purpose of the paper is to warn of failings that have led to kicks and suggest ways of avoiding these failings.

Kick frequencies have been calculated using the numbers of wells drilled and the numbers of kicks reported. The analysis indicates that kicks are taken in 11% of all wells drilled on the United Kingdom Continental Shelf (UKCS). This frequency has not decreased over the last eleven years. The frequencies are higher in wells drilling the Zechstein (13%) and for High Pressure High Temperature (HPHT) wells (22%). About 11% of the total kicks can be considered serious (That is out of 100 wells drilled in the UKCS 11 will have kicks of which 1 will be serious). Half the kicks take place during drilling operations with the others spread amongst cased hole, tripping and casing operations.

The appendix describes case histories of kicks which illustrate important lessons to be learnt. For well designers:-

♦ anticipation of raised pressures in the reservoir from water injection; ♦ assuming the worst when drilling the Zechstein; ♦ make every effort to ensure the integrity of casing shoes and liner laps before displacing to a lower mud weight.

For well control training:-

▪ emphasising the importance of monitoring pit volume during non-standard operations; ▪ ensuring the driller has authority and confidence to shut the well in if there is any doubt; ▪ the importance of a clear chain of command for kick control operations; ▪ the Offshore Installation Manager (OIM) should not be too closely involved in technical aspects of killing the kick but should concentrate on the overall safety of the installation.

Kick simulators can be useful both in training personnel and planning wells.
Kick Simulation for Well Design and Kick Management on the U.K. Continental Shelf: Current Industry Practice and Challenges for the Future
Authors: Spencer R. , Tatsis A. , Glass A. W.
Published: December 2007

HSE research spanning a period of nearly 10 years has resulted in approximately one hundred projects in the ‘Well engineering and operations’ topic area. About half of these projects have addressed kick development and control. A computer-based model developed for practitioners, has been thoroughly tested and applied to numerous incidents.

Having reached the position where a tool is now commercially available and is used extensively by practitioners, an evaluation of current Industry practice in the area of kick simulation for well design and kick management on the UKCS has been undertaken. The study also addresses the future direction of work in this area.

An Industry wide sample including operating companies, drilling contractors, training providers and relevant associations has been surveyed, augmented with a substantial sample of well engineering professionals.

Broadly, the results of the study suggest that the HSE's work on kick control has made a significant contribution to well design and kick management. The industry indicates that they feel more confident in their ability to predict kick pressures and manage kick incidents as a result of the use of kick simulator software.

Industry views on the needs for future work in the area of kick pressure prediction; kick detection and kick control have been received and form the basis for recommendations arising from the study.
Enhancing Activity Levels in the UK Continental Shelf in a Low Price Environment
Authors: Kemp Alexander G , Stephen Linda
Published: December 2007

This paper examines the longer-term prospects for activity levels in the UKCS under low oil prices with the employment of a financial model incorporating the use of the Monte Carlo technique. On current trends, from the early years of next century production could fall at a substantial pace even when discoveries from exploration are included in the analysis. Compared to recent years new investment would fall to much lower levels under the $14 price case and collapse under the $10 one. If major reductions in unit costs, such as those in the CRINE Network targets were achieved, the decline rates of production could be greatly modified. The CRINE targets are extremely ambitious and their achievement requires the widespread use of new technologies. This requires funding and contracts which encourage innovation and risk-taking.