bluuebunny/crossref_metadata_2025 huggingface dataset:
Connectivity Prediction in Fractured Reservoirs With Variable Fracture Size: Analysis and Validation
Authors: Masihi M. , King P. R. , Nurafza P.
Published: December 2007

Uncertainty in geometrical properties of fractures affects all aspects of flow in fractured reservoirs. The connectivity of fractures, embedded in low permeable zones, can control fluid movement and influence field performance. This can be analyzed using percolation theory. This approach is used the hypothesis that the permeability can be split into either permeable or impermeable and assumes that the connectivity of permeability contrasts controls the flow. The analysis of the connectivity based on finite size scaling assumes that fractures all have the same sizes. However, natural fracture networks involve a relatively wide range of fracture lengths, modelled by either scale-limited laws (e.g. log normal) or power laws.

In this paper we extend the applicability of the percolation approach to a system with a distribution of size. For scale-limited distributions, we use the hypothesis that the connectivity of fractures of variable size is identical to the connectivity of fractures of the same size whose length is given by an appropriate effective length. It is also necessary to define the percolation probability based on the excluded area arguments. We test this on fracture networks having a uniform, Gaussian, exponential and lognormal length distribution. In the case of the power law length distribution, however, the scaling parameters (e.g. correlation length exponent) have to be modified. We show how the scaling parameters vary as a function of the power law exponent.

To validate the approach we used outcrop data of mineralized fractures (vein sets) exposed on the southern margin of the Bristol Channel Basin. We show that the predictions from the percolation approach are in good agreement with the results calculated from field data with the advantage that they can be obtained very quickly. As a result they may be used for practical engineering purposes and aid decision-making for real field problem.
Reducing Reservoir Prediction Uncertainty Using Seismic History Matching
Authors: Stephen K. D. , MacBeth C.
Published: December 2007

We have developed a method where the spatial and dynamic information offered by Time-Lapse (4D) seismic has been used in history matching of reservoir simulations. Improved predictions of both recovery and areal sweep are then obtained by reducing uncertainty. Flow simulations are converted to predictions of seismic impedance attributes using a petro-elastic transform and suitable re-scaling. The resulting misfit between the model and observed data is combined with an equivalent measure for well data and these are used to constrain simulations by iteratively updating the model. Updated model probabilities can then be used to analyse uncertainty.

The method has been applied to a UKCS reservoir. Previously we described our success in obtaining a good match to both seismic and production data in the field. From the updated probability distribution of the parameters, we now take the best models from the history matching process and make predictions to determine the most likely outcomes.

We have found that the Time-lapse data reduces uncertainty in predictions of the areal sweep and the pressure distribution. The seismic response is strongest at the injector wells but also helps in the inter-well regions. Conventional history matching often struggles to constrain parameters in these regions due to the inherent non-uniqueness of the problem. The uncertainty of permeability and fault transmissibility multipliers was also determined in those areas.
Simulation of Tectonic Deformation and Large-Area Casing Shear Mechanisms—Part A: Operations
Authors: Han H. , Dusseault M. B. , Xu B. , Peng B.
Published: December 2007

We present an analysis of casing deformation mechanisms in one area of extensive casing shear in the Daqing Oilfield, China. Instead of qualitatively stating the cause of large areas of casing shear, as in most previous work, we developed a mathematical model to quantitatively compute the coupled effect between the tectonic stress field and the induced stresses from high-pressure water injection.

Numerical simulation carried out in the area indicated that variation of injection pressure induced a substantial perturbation on the local stress field. Furthermore, the induced stress fields associated with each injection well overlap with each other. Once the maximum compressive stress parallels or nearly parallels the differential pressure, the stability of strata with respect to shear is compromised, and when the thrust stress imposed exceeds the shearing resistance, the strata will slip in a direction coaxial with the vector from high to low-pressure areas. Simulation results of various schemes show that as long as the injection pressure and pressure differential between blocks are controlled to be less than 12.7 MPa and 0.86 MPa respectively, formation shear slip along a horizontal surface will no longer occur.

The study in this article is somewhat different from previous studies in that a full coupling of the in situ and the induced stress fields was performed quantitatively and based on field experiments, and also in that the results were used to explicitly determine pressure limits on individual wells and differential pressures for the entire region of casing shear. The method and the results can serve as reference for other similar oilfield circumstances.
A Method for Designing A Complex Directional Drilling Program Applied in Cook Inlet, Alaska
Authors: McKayf Thomas Wilson
Published: December 2007

This paper describes a method for designing a complex directional drilling program which was applied offshore in the Cook Inlet of Alaska. Utilizing modern computer and directional drilling technology, Amoco Production Company was able to drill a very complex directional well successfully. Because of this, other wells in the Cook Inlet are also being designed and drilled by Amoco in the same manner.
A Theoretical Model For Determination of Pore Volume Compressibilities of Consolidated Sandstones
Authors: Greenwald Roy F. , Somerton Wilbur H.
Published: December 2007

In another paper (Greenwald and Somerton (1981)) the authors have described experiments which were conducted to determine pore volume compressibilities of Bandera, Berea, and Boise sandstones. The pore volume compressibility is defined as the incremental change in pore volume of a rock with respect to a change in the pore or internal fluid pressure. This work presents a model which allows the pore volume compressibilities of the aforementioned sandstones, and their changes with stress, to be calculated when certain of the samples' physical parameters are specified. The model is semi-empirical in that some of these parameters must be determined experimentally; this is done by actually measuring one or two values of the rock's compressibility. Alternatively, one can make reasonable assumptions for these values when the lithology of the sample is known. Variables required for the implementation of the computational scheme are initial porosity, clay content, a pore shape factor, a length and aspect ratio of representative cracks in the matrix grains, the volumetric density of these cracks, and the mineralogical composition of the sample along with the elastic moduli fo the minerals present. When these data are supplied, the pore volume compressibility can be estimated as a function of any specified stress state of the rock.
A Model of Oil Ganglion Movement in Porous Media
Authors: Egbogah Emmanuel O. , Wright Robert J. , Dawe Richard A.
Published: December 2007

This paper presents a simple theory of the movement of a discontinuous oil droplet (ganglion) through a model porous medium. A quantitative description of the ganglion flow in the system was obtained through a tractable solution to the balance of forces controlling ganglion stability during flow of two immiscible fluids within a well-defined geometry. Calculations were based on a constricted conical (divergent-convergent) pore model. Experimental data from a tetragonally packed sphere model were used interactively with a theoretical static analysis to synthesize the relevant features of the ganglion mechanics into a coherent theory of oil mobilization.
A Method to Determine K-Values From Laboratory Data and Its Applications
Authors: Bashbush Jose L.
Published: December 2007

Retrograde condensate reservoirs and volatile oil reservoirs are not amenable to be studied using traditional material balance methods and simulation techniques. To analize these "variable composition reservoirs", it is necessary to obtain a consistent and reliable set of K-values which might be capable of reproducing the phase behavior of the fluids within the reservoir.

This paper presents a simple and practical material balance method by which liquid compositions, K-values and molecular weights of the heavy fraction in the liquid at different pressures are calculated, based on the data available in a constant volume depletion lab analysis. Results of the analyses of three PVT studies are discussed along with guidelines to evaluate the goodness of reported experimental data and ways to correct inconsistencies commonly found in the reports.

The corrected K-value table generated with the method can be directly used in a compositional study to predict the reservoir behavior. Another use involves the application of the method as a necessary preamble to the adjustment of the parameters of an equation of state. This practice will avoid the great deal of time spent in unsuccessful attempts to match inconsistent information
The Comparative Effectiveness of Propping Agents in the Red Fork Formation of the Anadarko Basin
Authors: Hickey Joe W. , Brown William E. , Crittenden Stephen J.
Published: December 2007

This paper presents the results of an investigation of the comparative effectiveness of various fracture propping agents and their relationship to production performance based on actual field results of twenty-five wells producing from the same formation at approximately the same depth and similar downhole reservoir conditions. All are located in thirteen fields of the Anadarko Basin in Roger Mills and Beckham Counties, Oklahoma (Fig. 1). Every Red Fork well listed in the records of the Oklahoma Corporation Commission for these counties which had been fractured and treated with a propping agent was examined. All wells for which valid production information was available are included. Three of a total of 28 wells were eliminated because of ambiguous data. Fig. 1Location of 25 Red Fork sandstone wells, Beckham & Roger Mills Co., OK

A comparison is made of the actual production of wells measured before and after hydraulic fracture stimulation treatments that employed one or more of the various propping agents; sand, glass beads, resin coated sand, or sintered bauxite. The size and type of treatment varied from well to well.

The relation between actual field results and laboratory tests under simulated field conditions is reviewed for the several types of proppants.
A Useful Technique to Study Particle Invasion in Porous Media by Backscattered Electron Imaging
Authors: Kandarpa Viv , Sparrow John T.
Published: December 2007

The flow mechanism of aqueous fluids containing particles is important for an understanding of the invasion and impairment of petroleum and geothermal formations by particulate matter. This paper describes a relatively new technique that is successfully being used in flow studies of particle suspensions through Berea sandstone cores. The technique is based upon backscattered electron imaging in the scanning electron microscope (SEM). The visual observation by SEM of the particles inside the cores is made possible by using particles made up of elements which are known to have a higher backscattering coefficient than the silicon matrix of the sandstone.

The present paper is part of a major study on Berea sandstone cores in which the effects of fluid flow rate, the particle size, the chemical nature of the particles and the particle concentrations have been studied. The backscattered electron imaging technique has been utilized to determine the distribution and depth of penetration of particles in cores. Other related applications of the technique to determine BaS04 and CaS04 precipitations in cores due to incompatible mixing of waters are also briefly mentioned.
Mechanisms of Formation Damage in Matrix Permeability Geothermal Wells
Authors: Bergosh Gerald L. , Enniss Dan O.
Published: December 2007

A laboratory study was conducted at simulated in-situ geothermal conditions to identify the mechanisms responsible for significant declines in permeability. Testing was conducted on core material retrieved from Well 78-30 in the East Mesa KGRA, Imperial Valley, California. In this paper, apparatus, procedures and results are described. Damage in this formation, which was not originally thought to be water sensitive, is attributed to cation exchange and the removal processes which alter the stability of the clay structures. Fluid shearing dislodges particles, which clog pore throats and irreversibly reduce permeability. The implications of these findings on operating procedures and production of the well can be significant and are discussed.
Petrologic Evaluation of the Silurian Interlake Formation, Vida Field, North-Eastern Montana—The Key to Revitalized Exploration in an Oil Field
Authors: Powell Thomas G. , Stevenson G. M.
Published: December 2007

Potentially productive zones in carbonate reservoirs are often missed because log suites fail to identify the extent and nature of effective porosity. The Silurian Interlake Formation produces at the Vida Field in McCone County, Montana. In 1963, eighty-seven feet of the Silurian Interlake Formation were cored in the Phillips Sievers #1 Well, Sec. 30, T.24N., R.50E., McCone County, Montana. The cored interval was evaluated using core description, thin section petrology, scanning electron microscopy, and log analysis. Data obtained through these methods were integrated to evaluate the nature of the porosity in the Interlake Formation producing from the Sievers #1 Well. As of 1980, its cumulative production was 253,979 barrels of oil and 14,560 barrels of water. Deposition of carbonate mud and bioclastic debris is interpreted to have taken place on a laterally extensive, extremely shallow, slowly subsiding, carbonate shelf. The productive interval is a dolomitized wackestone, packstone, and mudstone. The main porosity types are intercrystalline, moldic, and fracture. This observed porosity is the direct result of diagenetic alterations imposed upon the original sediment. The major diagenetic alteration has been dolomitization. Based on analytical work performed on the Interlake Formation in the Sievers #1 Well, the Staman 2-25 Berreth Well (Sec. 25, T.24N., R.49E.) was drilled and cored in November-December, 1980, to test the possibility that additional reserves remain in the Vida Field. Comparison of the two cored intervals confirms the existence of additional porosity developed in the same lithofacies described in both wells. It is concluded that carbonate log response should be correlated to porosity and lithology to insure maximum exploitation of a reservoir.
The Positive Effects of Side Rake in Oilfield Bits Using Polycrystalline Diamond Compact Cutters
Authors: Huang Hsin I. , Iversen Robert E.
Published: December 2007

What used to be considered a novel drilling technique, the use of synthetic diamond cutters in a drag bit configuration, has now emerged in the drilling industry as a time and cost efficient drilling tool. These bits, utilizing polycrystalline diamond compact cutters for drilling soft or plastic formations have been proven successful through a systematic development. First, the main problem associated with drilling soft or plastic formations was identified as bit cleaning. Second, laboratory tests of a single compact cutting plastic shale under confining pressure with a load dynamometer and high speed photography were studied. The results demonstrated that a compact incorporating side rake angle and ample chip clearance space can provide efficient mechanical cleaning action. Finally, new style drill and core bits, built with side rake orientation along with previous style drill and core bits without side rake features, were field tested and observed in the same drill hole or in the same formation. The drill or core bits with side rake features always drilled or cored faster in the soft or plastic formations than those bits without side rake under the same operating parameters (hydraulic, bit weight and rpm). It was concluded that bits with side rake features can enhance the bit cleaning by mechanical cleaning action and, therefore, improve the bit performance in soft or plastic formations.
The Effect of Temperature on Drainage Capillary Pressure in Rocks Using a Modified Centrifuge
Authors: Samaroo Brian Henry , Guerrero E. T.
Published: December 2007

A commercially available centrifuge was modified to measure drainage capillary pressures of various core samples at temperatures up to 400°F. The modifications provided good control over the following core parameters that needed to be accurately measured: maximum capillary pressure, average wetting phase saturation, and temperature. Measurements were made on twelve core samples of various lithologies, with 5% sodium chloride brine as the wetting phase fluid and either nitrogen or McKittrick crude oil as the non-wetting phase fluid, in the following increasing temperature sequence: 105°F, 200°F, 300°F, and 400°F. The lithologies investigated were as follows: clean sandstones, shaly sandstones, and limestone.

The results of this study showed that for the McKittrick crude oil-brine system, the irreducible brine saturation increased with increase in temperature for all lithologies confirming the results of previous investigators. However, for the nitrogen-brine system, irreducible brine saturation was found to decrease with increase in temperature for all lithologies.

The interplay of the effects of capillary and viscous forces as temperature increases is given as a possible explanation for the observed phenomena. Also the implications of these results as applied to formation evaluation and reservoir engineering are discussed.
Simulation of Relative Permeability Hysteresis to the Nonwetting Phase
Authors: Carlson Francis M.
Published: December 2007

In reservoir fluid flow, the situation described by an increase in nonwetting phase saturation followed by an increase in wetting phase saturation causes a relative permeability hysteresis effect that is well known. The imbibition relative permeability is a function of the historical maximum nonwetting phase saturation, hence there is no single imbibition curve applicable for use in reservoir modeling. This paper presents a method which allows the calculation of imbibition relative permeability starting at any saturation. The data required are the drainage curve, the historical maximum nonwetting phase saturation, and a minimum of one additional point on some corresponding experimental imbibition curve. In this development, all imbibition curves are shown to be parallel. Also significant is the fact that the residual nonwetting phase saturation can be calculated without a complete experimental specification of the imbibition curve.
Review Of Secondary Recovery Operations In The Greater Aneth Area, San Juan County, Utah
Authors: Burchell Paul W. , Coonts Harvey L.
Published: December 2007

Secondary recovery operations presently being conducted in the Greater Aneth Area, San Juan County, Utah, are reviewed. Early in the development of the reservoir it became apparent that initial primary recovery would be a small percentage of the total oil in place. It was concluded by the operators that waterflooding would be the most satisfactory method of secondary recovery. Although it is too early in the life of the flood to substantiate, present estimates indicate that the ultimate recovery of oil will probably be twice the recovery anticipated from the original solution gas drive mechanism. Primary recovery has almost been completed and future production will be the result of waterflooding. In addition to the increase of oil recovery, over-all economics will be enhanced by the 80-acre well spacing now in effect.

Introduction

In April 1956, Texaco, Inc. completed the Navajo "D-1" which was the discovery well in what was to become one of the largest fields in the Rocky Mountain Area, the Aneth Field. During the next four years over 600 wells were drilled which delineated a productive area in excess of 55,000 acres with an estimated reserve around one billion barrels of stock tank oil in place. Primary recovery was calculated to be approximately 14.3 to 18.5 percent, and secondary recovery resulting from waterflooding was estimated to increase the initial recovery an additional 12 to 14 percent. It is the purpose of this report to review both the background considerations relating to secondary recovery and its' progress to date.

GEOLOGY

The Aneth Field, later called the Greater Aneth Area, is located in the Utah portion of the Four Corners Area, see Fig. 1. Geologically the field is located on the Southwestern flank of the Paradox basin. The basin covers parts of Utah, Arizona, Colorado and New MEXICO.

Production is from carbonates at a depth between 5,300 ft. to 6,200 ft. in the Paradox Formation which is middle Pennsylvanian in age, specifically, the Desert Creek and Ismay zones of the Paradox. The Desert Creek zone is better developed and more continuous over the area and contributes around 90 percent of the hydrocarbons. This zone is further divided into three subzones of which only the upper two are significant.

The field can be described as a reef complex with structure playing a minor role in accumulation. Reservoir development and porosity are due to fossiliferous deposition with some mineral solution activity and a highly varying fracture system. The productive area is surrounded by shales and reworked, non-porous, clastic carbonates in a somewhat circular area about 10 miles in diameter.

RESERVOIR CHARACTERISTICS

The primary producing mechanism for the reservoir is solution gas expansion. Original bottom hole pressure was 2200 psi at 900 ft. subsea. General core and fluid analysis are shown in the following tabulations:

Approximate height of oil column.............250 ft. Average permeability......................... 20 ft.
Minimum Gas Flow Rate for Continuous Liquid Removal in Gas Wells
Authors: Ilobi Meshack Ike , Ikoku Chi U.
Published: December 2007

Several publications on the prediction of minimum gas flow rates for continuous liquid removal in gas wells are indicative of the interest the industry has in this subject. Some of the noteworthy studies are those of Duggan (1961) and Turner, et al, (1969). One limitation of Turner's work is the treatment of entrained liquid drops in the gas core independent of the continuous film region, even though it is acknowledged that interactions between the two regions exist and are continuous in the entrainment process. Other treatments of the subject have been mainly empirical, based on observation in particular gas fields, with no claims to general application.

A large bank of available experimental data by several investigators for upward annular dispersed flow was used to develop correlations for the prediction of entrainment, film thickness and pressure drops by Hughmark (1973). These correlations have been applied, with some modifications to the gas well situation. Duns and Ros pressure drop correlation has been incorporated in this model because of its better accuracy in the annular-mist flow region.

Comparison of results from this model with field results show marked improvement in minimum gas flow rate prediction accuracy that should be beneficial to the industry.
Pressure Behavior in Vertically Fractured Wells Subject to Limited Entry and Bottom Water Drive
Authors: Ichara Mark J.
Published: December 2007

This paper presents an analytical study of the wellbore pressure behavior for a vertically fractured well subject to limited entry and bottom water drive. The well is producing at a constant rate from (1) an infinitely large reservoir and (2) the center of a rectangular drainage region. The upper boundary of the formation is impermeable but the lower boundary is maintained at constant pressure equal to the initial pressure of the reservoir. Two fracture locations (top and center) within the producing interval are considered. Both infinite-conductivity and uniform-flux fractures are examined. Analysis of drawdown and buildup pressure data by conventional semi-logarithmic techniques are conducted to determine the combined effect of limited entry and bottom water drive on well test analysis.

The study indicates that the use of conventional Horner and Miller-Dyes-Hutchinson semilog methods would give inaccurate results. Consequently, the type curves presented in this paper may be used to estimate reservoir and fracture characteristics in oil, gas and geothermal reservoirs.
A Comparison of Laboratory Linear and Pattern Flow Chemical Floods Using a Volumetric Linear Scaling Concept for Oil Saturation Distributions
Authors: Haskin Helen Kay , Davis Lome Arthur
Published: December 2007

A laboratory quarter five-spot pattern chemical flood was conducted in a consolidated, homogeneous porous matrix for comparison with standard linear core floods. In addition to the routine material balance information, quantitative areal oil saturation isometric and contour plots were obtained from microwave attenuation measurements made during the flood. The microwave instrument provides the actual observation of oil banking and movement in a laboratory pattern chemical flood. Pattern flood oil banking characteristics are compared with those observed in linear floods.

A volumetric linear scaling approach was used to predict the behavior of the pattern chemical flood from linear flood data. First, a stream tube model was assumed for the quarter five-spot flow pattern. The oil saturation distribution in each tube was computed from scaled linear core flood oil saturation distributions obtained by microwave attenuation. Details of this procedure are given. The comparison between predicted and observed pattern flood behavior is most encouraging. The average tertiary residual oil saturation and the tertiary oil breakthrough time were very accurately predicted. The observed tertiary Sor contours in the pattern flood did show slightly more cusping toward the producer than predicted by the simple model. An interpretation of the pattern flood response is proposed in terms of the scaling theory, its assumptions and its limitations.
Log Evaluation in Wells Drilled With Inverted Oil Emulsion Mud
Authors: Edwards David P. , Lacour-Gayet Phillipe J. , Suau Jean
Published: December 2007

As greater use is made of inverted oil emulsion muds in the development of North Sea oil fields, the need for more precise log evaluation in this environment becomes apparent.

Since the presence of non-conductive mud prevents the utilisation of the Dual Laterolog-Micro Spherically focused Log, the true formation resistivity has to be determined by Induction logging techniques. This paper demonstrates an approach using the Dual Induction Log, taking into account invasion and boundary effects.

Lithology and porosity are derived from the Formation Density or Litho-Density* Log, Compensated Neutron Log, Sonic Log and the Natural Gamma Ray Spectrometry Log. The effect of invasion by the oil component of the mud filtrate is treated in the evaluation, and a measurement of Moved Water is made.

Computations of petrophysical properties are implemented by means of the GLOBAL interpretation program, taking advantage of its capability of adaption to any combination of logging sensors.
Well Performance Analysis: A Synergetic Approach to Dynamic Reservoir Description
Authors: Stewart George , Wittmann Manfred J. , Lefevre Didier
Published: December 2007

In the paper the quantitative interpretation of production logs, i.e. simultaneous recordings of bottom-hole flow profile and pressure, using a vertically distributed single well model (VDSWM) is described. In this approach a production log is run in the steady flow period preceding a well shut-in and then again, where necessary, during the closed-in period in order to detect any layer crossflow through the well-bore. The local reservoir description i.e. individual layer permeabilities and damage/perforation skin factors are then systematically altered from initial estimates until the predictions of: the flow profile and drawdown during the flow period,the transient pressure response and layer crossflow during shut-in,

from the single well simulation match the corresponding measurements. The initial estimate of permeability distribution is obtained from the open-hole logs using a zonation algorithm and a permeability transform calibrated with core data from key wells.

Thus conventional well test analysis, which typically deals with overall average permeability and skin factor, is extended to give estimates of these quantities on a layer-by-layer basis by matching the flow distribution as well as the pressure response. The main objective is to identify, firstly, layers whose effective permeability is greater than the value indicated from core/log studies i.e. potential thief zones with anomalous characteristics and, secondly, completion problems associated with groups of perforations which do not flow. The VDSWM allows the synergetic interpretation of data from several sources viz open-hole logs and cores, production logging, transient well testing and RFT* pressure surveys to obtain a layered reservoir description which is as realistic as possible.

Given this model it is shown how the steady-state inflow performance of the well, in the situation where the layers have depleted to different potentials, can be represented by partial productivity index matrices which when multiplied by the vector of layer drawdowns yield either the layer flows at the sand-face or at the external face of the radial flow region surrounding the well; these are different due to near well-bore flow convergence. These matrix formulations can be used as the lumped parameter single well models in layered reservoir simulators on the basis of the concept of the equivalent block radius of Peaceman (15) generalized to a layered system.
Development and Production Forecasting for Government Planning in Norway
Authors: Heiberg Sigurd , Knudsen Kjell Reidar , Lund Tor B. , Njå Steinar , Ervik Leif Kolbjon
Published: December 2007

Government planning requires information on the course of established development and production activity and on the consequences of initiating new developments. A review of the basis for forcasts show that they will contain considerable uncertainty throughout the time period of greatest importance in planning. Much of the discrepancy between early forecasts and actual production is so far found to be caused by development time overruns. Special procedures are developed to adjust the results of lengthy rigorous procedures to late incoming information on development and operation. Further improvement in development forecasting is sought through the use of empirical data and assessment of the quality of development plans.

Although there is room for improving the accuracy of forecasts, it is essential to recognize their elements of uncertainty. A procedure is therefore proposed to compile the effects on production of quantified uncertainties in start of production, production build-up, peak rate and production decline performance.
An Analytical Study of Transient Flow in Stratified Systems with Fluid Banks
Authors: Satman Abdurrahman
Published: December 2007

A study was made of the behavior of reservoirs composed of horizontal layers with fluid banks, unconnected except at the well and filled with a slightly compressible fluid. The new solution described in this paper is an analytical solution for a circular well with a skin effect and wellbore storage. Each layer has a composite system with a circular inner region whose diffusivity is different from the one in the outer region. There may be either a constant pressure, closed, or infinitely-distant outer boundary. The solution method is Laplace transformation followed by a numerical inversion scheme.

A recent study of transient flow in one layer systems with radial discontinuities, paper SPE No, 93997, indicated that it was possible to measure the volume of the gas filled displaced region with accuracy and the method did not depend upon regular geometry for the displaced region. There appeared to be very important potential application for enhanced oil recovery and geothermal reservoirs with phase boundaries. This paper is an extension of that study to the reservoirs composed of horizontal layers and investigates the effects of various reservoir and fluid parameters including the shape of the fluid front.

Theoretical injectivity and falloff curves from such reservoirs are presented, and the influence of a skin effect and wellbore storage are also evaluated. The results of injectivity and falloff tests are given.

The study of injectivity tests indicate a short duration wellbore storage effect, followed by a semilog straight line whose slope is related to the average permeability-thickness of the swept volume. The semilog straight line is then followed by a pseudosteady Cartesian straight line characteristic of the swept volume. Finally, a second semilog straight line appears, characteristic of the average permeability-thickness of the unswept region. It is possible to find the nearest distance to the front and also the average distance to the front by evaluating the first a few hours of the injectivity test data.

The analysis of the falloff tests also shows a short duration wellbore storage effect, followed by a semilog straight line. It is then followed by a transition region. To detect the nearest distance to the front may be possible but the falloff tests do not show any pseudosteady state behavior. Detecting the nearest distance to the front is not always possible due to the fact that the producing time makes the analysis of a falloff test for such a system more complex as indicated in the literature. When the producing time is not long enough a flattening region following the first semilog straight line masks the portion of the data whose characteristic is used to detect the nearest distance.
The Phase Behavior of CO2 - Appalachian Oil Systems
Authors: Monger T. G. , Khakoo A.
Published: December 2007

The phase behavior of carbon dioxide with two Appalachian crude oils was examined at temperatures below and above the CO2 critical temperature. Swelling indices were determined throughout the CO2-crude oil compositional range. Equimolar CO2-crude oil mixtures were used to probe the effects of brine and additions of contaminant gases (5-10 mole % N2, CH4 H2S or SO2)·

Overall the observed phase equilibria emulate that reported for Western crude oil systems at low reservoir temperatures, but several contrasts in phase behavior are also apparent. Phase behavior differences are in-terpreted in light of carbon-13 nuclear magnetic resonance spectroscopy measurements which show that the Appalachian crudes have significantly higher paraffinic and lower aromatic contents than those typically observed for Western crudes. Data analyses suggest that CO2 preferentially condenses into a high paraffin oil, whereas hydrocarbon extraction by a CO2-rich phase is the predominant mechanism for crude oils with significant aromatic content.
A Wellbore Model for Two-Phase Flow in Geothermal Reservoirs
Authors: Chierici Gian Luigi , Giannone Gino , Schlocchi Gustavo , Terzi Luigi
Published: December 2007

The capability to accurately predict flowing pressure and temperature profiles in geothermal wells under various operating conditions is of paramount importance in order to exploit geothermal resources in a rational way. This prediction capability is the more important because of the difficulties encountered in running flowing pressure and temperature surveys in geothermal wells.

The calculation of pressure and temperature profiles along wells producing mixtures of steam and water (either fresh or salty) calls for the following effects to be evaluated: (1) phase change and mass transfer between phases; (2) flow regime change; (3) two-phase pressure drop; and (4) heat loss to the surrounding formations. All these effects, which are interrelated, are accounted for in this work.

The system considered is composed of two parts, namely: –the flow string, through which the geothermal fluid flows from the reservoir to the surface, and–the formation surrounding the wellbore, where heat is transferred farther away into the earth.

The momentum equation, the total energy equation and the continuity equations for the water and salt species which are present in the flowing stream are solved simultaneously using an iterative implicit procedure. The effect of water salinity, and of its change along the flow string, on phase behavior mass transfer between phases and liquid phase properties are accounted for.

Comparisons are presented of measured and calculated pressure and temperature profiles in geothermal wells producing under various operating conditions.
Steamflood Pilot Design for a Massive, Steeply Dipping Reservoir
Authors: Williams Richard Llewellyn
Published: December 2007

A three-dimensional simulation model was developed to determine the production response to steam stimulation and steam displacement in a massive (285′), steeply dipping (40–60°) reservoir that contained an undersaturated zone. Because recoveries from this reservoir were expected to be good under steam stimulation due to gravity drainage effects, an investigation was made to determine the relative advantage of steam displacement over conventional steam stimulation, A numerical model was developed to analyze the production response to various pattern configurations, injector locations, and injection rates. The model was also used to examine changes in fluid saturations, temperature and pressure profiles and sweep efficiencies as a result of changes in operations during the life of the project.
Numerical Study of Transport of Injected and Reservoir Water in Fractured Reservoirs During Steam Stimulation
Authors: Geshelin Boris Michail , Grabowski Janusz Wocieck , Pease Eric Clive
Published: December 2007

Reservoir water concentration profiles obtained during the production periods of steam stimulation processes are presented and correlated with the geometric, hydrodynamic and thermodynamic characteristics of the reservoir fracture zones. A modified version of the general thermal simulator ISCOM, with parameters adjusted to allow for the incorporation of two miscible water components (injected and reservoir water), has been employed. A source distributed fracture model has been developed to make possible the simulation of fractured reservoirs. Injected steam is distributed along the arbitrarily assumed fracture path in accordance with the well bore boundary conditions. Profiles of concentration versus time and the amount of reservoir water produced during steam stimulation processes can be estimated by measuring the concentration of salts in the produced water. This information, in turn, can be used to determine the shape, size and other thermo- and hydrodynamic characteristics of the reservoir fracture zone.

Results of this work show that the effective size of the heated zone for a horizontal, penny-shaped fracture is approximately half of its radius. It is also shown that the production characteristics of reservoir water are strongly affected by the geometric parameters of the fracture zone. Time profiles of reservoir water concentration depend on whether the fracture is horizontal or vertical. In the case of a short fracture, the cumulative oil-water ratio is larger at the end of the first cycle than at the end of the second cycle, and for a long fracture the situation is reversed.
Dynamic Analysis of Marine Risers
Authors: Egeland O , Wiik T , Natvig B J
Published: December 2007

Drilling and production in deeper water set new requirements to the design of marine risers. In this paper the most common methods of dynamic analysis of such risers are reviewed and discussed with reference to a set of full scale data.

The measurements were taken by CONOCO in 1975 on a drilling riser operated from a semisubmersible. A spectral approach is applied in evaluating these data and the results include standard deviations, response, spectra and transfer functions. The quality of the data is found to be generally good. Some doubt is expressed as to the exact conditions at the top support, but it is still considered that important trends are revealed.

In the theoretical analysis four different computer programs are investigated, covering six different methods. The programs employ either linearized frequency domain solution or time integration techneques with varying degrees of non-linearities included and for either regular waves or irregular sea. Most of comparisons with measurements are carried out in terms of linearized transfer functions. The validity of this approach is discussed as part of the evaluation of the results.
Southeast Asia Looks to 1990
Authors: Gaffney P. D. , Moyes C. P. , Archer J. D.
Published: December 2007

Following a long quiet spell since the peaks of 1974 the Asia Pacific region has again come back into the news, with an overall increase in activity throughout the region, rather than concentrated in any one country. The authors suggest that the improved scenario is the result of appreciation that there are still excellent opportunities and that legislation is competitive in the region. There continues to be a wide selection of opportunities in every geological sphere, of every size, providing incentive for both the largest and smallest companies. Costs, while increasing, have not risen as staggeringly as they have in other areas of the world, as in the North Sea, and entry expenditures such as bonuses and work obligations, are modest relative to the large areas and typical block sizes. With a stable or softening oil price, the authors foresee a growth in Asia Pacific activity and achievement of an all time high in the 1982–83 period.
Financing the World Petroleum Industry
Authors: Emerson John D.
Published: December 2007

As bankers to the world petroleum industry. Chase naturally has an interest in the outlook for oil and natural gas. What will be the demand for oil? How will it be met, and at what price? And, of course, what will be the future financing needs of the industry?

The report that I am presenting to you today is by no means the last word on this subject. It represents just one view of the future, but one that is built around clearly defined assumptions. As we make further progress in modelling the financial side of the industry, we will be able to test other views of the future, which we will present in future reports.

Any attempt to assess the future financing needs of the petroleum industry must be set in a specific framework reflecting future economic growth, future energy needs and the outlook for oil supply and demand in particular. These factors are all linked, although the linkage is flexible, not fixed. For example, it changes with changes in relative prices, among other things.
Geology and Hydrocarbon Prospects of East Coast Basins of India and their Relationship to Evolution of the Bay of Bengal
Authors: Talukdar Shri S. N.
Published: December 2007

Four sedimentary basins, extending onto the Continental Shelf, occur along the east coast of India — the Mahanadi, Godavari-Krishna, Palar and Cauvery basins. All except Palar Basin have two structural stages; 1) pull-apart basins developed during the Gondwana episode and 2) filled up by Lower Cretaceous time with locally derived elastics, unconformably overlain by Upper Cretaceous-Palaeocene carbonate-elastics (in Cauvery Basin) succeeded by Eocene to Recent, mainly deltaic, sediments thickening seawards. Sedimentary sequences, up to 7 km in thickness, were deposited in the east coast basins and contain source as well as reservoir rocks, adequately matured at depths in excess of 1-5 kms. Traps are formed by basement drape, tilting and faulting, by growth-faults and diapirism in deltaic sequences, by updip seals of porous elastics and carbonates, and by onlapping by major shale sequences over the sloping basement. Two wells have been drilled in the Mahanadi basin with some hydrocarbon shows in the Eocene; four wells have been drilled in Godavari-Krishna basin, three offshore and one onshore, and flows of oil and gas have been obtained from them in the Lower Cretaceous and lower Pliocene; 25 wells have beeri drilled in Cauvery Basin, 7 offshore and the remainder onshore, and shows of oil or gas have been obtained from the Eocene in three of them onshore, and from the basement in two offshore wells. No commercial discoveries have yet been made, but the prospects of finding them are considered good. Palaeocurrent data indicates ESE or SE palaeo-slopes, and marine tongues of Upper Permian (in Palar Basin) and Jurassic and Lower Cretaceous ages suggest that Bay of Bengal developed by rifting, perhaps earlier in the south, extending north and north-eastward during the Mesozoic. Parallelism between the eastern edge of Indian shield along the east coast and the island-arc system of Arakan Yomas - Andaman-Nicobar Islands — Indonesia suggests that the Bay of Bengal is a part of the Indian Plate rotated counterclockwise and subducted under S.E. Asia.
Stage 1 Development of the Kamojang Geothermal Power Station and Steamfield – West Java, Indonesia
Authors: Wilson Raymond H.
Published: December 2007

The paper describes the history of the work at Kamojang from the start of the original investigations in 1971, through the exploratory drilling phase, preparation of the feasibility study, the production drilling programme from 1976 to 1979, and development of the steamfield and power station from 1979 to 1982.

Details of both the exploration and production drilling programmes are given along with a brief description of the reservoir model. The major aspects of the design and construction of both the station and steamfield and associated works are sununarized. Problems and progress to date are covered briefly. Environmental studies carried out are described. Finally, the nature of the operation and management of the station, training being carried out and prospect of possible future development at Kamojang and elsewhere are given.