bluuebunny/crossref_metadata_2025 huggingface dataset:
Exact Analytic Solutions for Pipe Buckling in Vertical and Horizontal Wells
Authors: Mitchell R. F.
Published: December 2007

The first buckling solution was developed by Lubinski and Woods. When the differential equation describing buckling was derived, this solution was found to be an exact solution for vertical wells. Since these results were published, no other exact analytic solution has been discovered. Many numerical results have been obtained, however, suggesting that other solutions did exist. Because the buckling differential equation is nonlinear, it is not surprising that no other analytic solutions have been discovered. This paper presents three new analytic solutions for the vertical well problem and two new analytic solutions for the horizontal well problem. These analytic solutions are valuable both for predicting previously unanticipated buckling behavior and for providing guidance in further numerical evaluations of this problem.

In this paper, these five solutions are described, including techniques for evaluating the analytic functions. Buckling length change calculations are determined analytically, and pipe curvature, bending moment, and bending stresses are evaluated. The contact loads between tubing and wellbore are determined, then used to limit the range of validity of the solutions. The critical force for helical buckling is determined for horizontal wells.

Possible applications for these solutions include the analysis of bottomhole assemblies, drillpipe, casing, and tubing. The solutions are simple formulas, but require computer evaluation of the analytic functions.
Experimental and Simulation Analysis of Jet-Perforated Rock Damage
Authors: Mahmoud Asadi , Shirazi Mogdeh K. , Ghalambor Ali , Pratt Dan W.
Published: December 2007

The finite-element method (FEM) is employed to evaluate stress distribution around a perforation tunnel with a sandstone formation. Experimental data are used to confirm the results of theoretical study. In the model, the effect of jet pressure, jet temperature, and the combination of both on formation are studied separately. The results indicated that a 3.5-g RDX charge is capable of disturbing rock formation up to 5 in. longitudinally and 2 in. radially. The extent of this damage zone for a 10.5-g RDX charge is 8 in. longitudinally and 4 in. radially. The linear effect is within the first few inches of the perforation tunnel entrance. In this region, rock grains are under an intensive sudden shock-pressure wave of 2 to 4 million psi for a fraction of a microsecond. As a result, the rock's physical structure will change to metamorphous with a lower bulk density than that of unshocked rock, causing a sudden decrease in formation porosity and, hence, formation permeability.
Well-Test Characterization of Wedge-Shaped, Faulted Reservoirs
Authors: Charles D. D. , Rieke H. H. , Purushothaman R.
Published: December 2007

Two offshore, wedge-shaped reservoirs in south Louisiana were interpreted with pressure-buildup responses by comparing the results from simulated finite-element model studies. The importance of knowing the correct reservoir shape, and how it is used to interpret the generated boundary-pressure responses, is briefly discussed. Two different 3D computer models incorporating different wedge-shaped geometries simulated the test pressure-buildup response patterns.

Variations in the two configurations are topologically expressed as a constant thickness and a nonconstant thickness, with smooth-surface, wedged-shaped reservoir models. The variable-thickness models are pinched-out updip at one end and faulted at the other end. Numerical well-test results demonstrated changes in the relationships between the pressure-derivative profile, the wellbore location, and the extent of partial penetration in the reservoir models. The wells were placed along the perpendicular bisector (top view) at distances starting from the apex at 5, 10, 20, 40, 50, 60, 80, and 90% of the reservoir length. Results demonstrate that boundary distance identification (such as distance, number, and type) based solely on the log-log derivative profile in rectangular and triangular wedge-shaped reservoirs should be strongly discouraged. Partial-penetration effects (PPE's) in wedge-shaped reservoirs are highly dependent on the wellbore location relative to the wedge, and the well-test-data analysis becomes more complex.
Sonic-Magnetic Resonance Method: A Sourceless Porosity Evaluation in Gas-Bearing Reservoirs
Authors: Minh Chanh Cao , Gubelin Greg , Ramamoorthy Raghu , McGeoch Stuart
Published: December 2007

For environmental reasons, there are times when the use of radioactive chemical sources for density and neutron logging is not possible. The inability to use these logging tools seriously affects porosity determination in gas-bearing reservoirs. Several tools, such as the nuclear magnetic resonance (NMR) tool, the sonic tool, or a minitron-based tool, determine porosity without using a radioactive source. These tools, however, are influenced by many effects and, when used alone, cannot deliver an accurate gas-independent porosity.

A new methodology that combines sonic and NMR logs for improved porosity evaluation in gas-bearing reservoirs is proposed. The first variant of the method uses the sonic compressional transit time and the total NMR porosity (ϕt,NMR) to determine the total porosity, corrected for the gas effect, and the flushed-zone gas saturation. In this approach, a linear time-averaged equation corrected for compaction is applied to the sonic compressional log. The simplicity of the solution, much like the previously published DMR1 Density-Magnetic Resonance Interpretation Method, allows fast, easy computation and a complete error analysis to assess the quality of the results.

In the second variant of the method, we show that the rigorous Gassman equation has a very similar response to the Raymer-Hunt-Gardner (RHG) equation for a water/gas mixture. This allows substitution of the complex Gassman equation by the much simpler RHG equation in the combined sonic-NMR (SMR) technique to estimate total porosity and flushed-zone gas saturation in gas-bearing formations.

Both techniques are successfully applied to an offshore gas well in Australia. In this well, the porosity in the well-compacted sands is in the 20 to 25 p.u. range and the compaction factor is approximately 0.77. The sonic-magnetic resonance results compared favorably to the established density-magnetic resonance results and also to core data. In another offshore gas well from the North Sea, the porosity in the highly uncompacted sands is in the 35 to 40 p.u. range, and the compaction factor is around 1.85. Both SMR techniques were able to produce a very good porosity estimate comparable to that estimated from the density-neutron logs.
Analysis of Horizontal-Well Responses: Contemporary vs. Conventional
Authors: Ozkan Erdal
Published: December 2007

Most of the conventional horizontal-well transient-response models were developed during the 1980's. These models visualized horizontal wells as vertical wells rotated 90°. In the beginning of the 1990's, it was realized that horizontal wells deserve genuine models and concepts. Wellbore conductivity, nonuniform skin effect, selective completion, and multiple laterals are a few of the new concepts. Although well-established analysis procedures are yet to be developed, some contemporary horizontal-well models are now available. The contemporary models, however, are generally sophisticated. The basic objective of this paper is to answer two important questions: 1) When should we use the contemporary models? and 2) How much error do we make by using the conventional models? This objective is accomplished by considering examples and comparing the results of the contemporary and conventional approaches.
Reservoir Engineering Aspects of Light-Oil Recovery by Air Injection
Authors: Turta A. T. , Singhal A. K.
Published: December 2007

This paper addresses the reservoir engineering aspects of air injection as an enhanced oil recovery technique for light-oil reservoirs. In its most successful form, the process has been applied in deep, carbonate reservoirs. The development of this process in conjunction with an application of the in-situ combustion (ISC) process to light-oil reservoirs, as well as the main mechanisms pertaining to ISC and to gas miscible flooding, are analyzed. It is seen that various air-injection processes (AlP's) can be classified, depending on their spontaneous ignition potential and gas miscibility at reservoir conditions, into four different processes. Based on an in-depth literature review, the best reservoir conditions for application of each of these four processes are derived. The main differences in operational aspects (pollution, corrosion, safety) for these processes are also discussed. Design considerations for pilot testing of the technique are presented. The crucial point is location of the pilot on the structure, which is also a key element in its proper evaluation, and its subsequent development to a commercial-size operation. Finally, recommendations on laboratory work in support of design and evaluation of a field pilot are also presented.
Characterization of a Carbonate Reservoir With Pressure-Transient Tests and Production Logs: Tengiz Field, Kazakhstan
Authors: Chambers K. T. , Hallager W. S. , Kabir C. S. , Garber R. A.
Published: December 2007

The combination of pressure-transient and production-log (PL) analyses has proved valuable in characterizing reservoir flow behavior in the giant Tengiz field. Among the important findings is the absence of clear dual-porosity flow. This observation contradicts an earlier interpretation that the reservoir contains a well-connected, natural fracture network. Fracturing and other secondary porosity mechanisms play a role in enhancing matrix permeability, but their impact is insufficient to cause dual-porosity flow behavior to develop.

Flow profiles measured with production logs consistently show several thin (10 to 30 ft) zones dominating well deliverability over the thick (up to 1,040 ft) perforation intervals at Tengiz. A comparison of PL results and core descriptions reveals a good correlation between high deliverability zones and probable exposure surfaces in the carbonate reservoir.

Contrary to earlier postulations, results obtained from pressure-transient and PL data at Tengiz do not support rate-sensitive productivity indices (PI's). Inclusion of rate variations in reconciling buildup and drawdown test results addressed this issue.

We developed wellbore hydraulic models and calibrated them with PL data for extending PI results to wells that do not have measured values. A simplified equation-of-state (EOS) fluid description was an important component of the models because the available black-oil fluid correlations do not provide reliable results for the 47°API volatile Tengiz oil. Clear trends in reservoir quality emerge from the PI results.
Recommended Practices for Slim-Hole Steam Injectors
Authors: Castrup Suzanne Griston
Published: December 2007

Single-string and multistring slim-hole completions have become popular in recent years as an inexpensive means of injecting steam into shallow, low-pressure sands. While slim-hole injectors appear to be simpler and cheaper to drill and complete, wellbore heat losses can be excessive at low injection rates. In addition, if a good bond is not achieved during primary cementing, thermal stresses, incurred once steam is injected, increase the likelihood of tubing failure and steam channeling behind pipe. Therefore, an appropriate tubing size and weight must be used to prevent well failures.

For example, initial slim-hole steam injectors completed with 2⅜-in. and 2⅞-in. tubing are no longer advisable because of insufficient mechanical integrity. Similarly, poor cement bond in triple-string slim-hole injectors has resulted in a high percentage of well failures. Consequently, the costs associated with tubing deformation, poor steam containment, and high wellbore heat losses cannot be ignored when considering slim-hole injectors for a steamflood project.

This paper discusses current drilling and completion practices and addresses the benefits and risks associated with slim-hole steam injectors. The short-term economics of initial low drilling and completion costs are compared to the long-term economics of efficient steam placement to target sands using single-string and multistring slim-hole injectors. Recommended practices and guidelines are presented for proper, cost-effective application of slim-hole injectors to improve steamflood performance.
A New Two-Dimensional Model for Acid-Fracturing Design
Authors: Settari A. , Sullivan R. B. , Hansen Chris
Published: December 2007

The paper describes a 2D model of acid fracturing that is more rigorous than current acid-fracturing simulators. The equations are discretized and solved along fracture length and across the width (in x and y directions), as opposed to a lumped formulation in the conventional model in which the y-solution is replaced by a mass transfer coefficient Kg. In the 2D model, correlations for Kg are not needed, and the model uses directly measurable data only. In addition, the model can represent transient effects (Kg is variable along time and fracture length), combined with dispersion and thermal effects. Two models, one for lab experiments and one for field design, were developed. The lab model was validated, with excellent agreement, against the results of Roberts and Guin1 and compared with the 1D approach on data typical for phosphoria dolomite. The results show large differences in regions of high and low leakoff. Acid spending predicted by the 2D model is also higher, even when the Kg values are comparable. Correspondingly, the field-design model predicts larger spending and fracture conductivity. An example of the field design and post-fracture history match from the Cottonwood Creek Unit, Washakie County, Wyoming, is presented. It shows that the new model is in better agreement with field data. Extensions to 3D modeling are also discussed.
Shale Preservation and Testing Techniques for Borehole-Stability Studies
Authors: Chenevert M. E. , Amanullah M.
Published: December 2007

Shale rocks are known to be the primary troublesome formation that has plagued drillers for many years. Attempts have been made to investigate the characteristics of shales, but results are limited because of the scarcity of test samples. Rapid deterioration of cuttings and cores has made data collection limited at best and a complete failure in many cases. It now appears that the shales become unsaturated as they dry out because of poor storage conditions, which result in false test results owing to the incorporation of capillary pressure artifacts.

This paper discusses results obtained with a specially preserved, highly reactive shale core obtained at a depth of 4,500 ft in the North Sea. A previously developed method was used for the evaluation of shale cores to determine their level of saturation. This study shows that shales must be preserved at their native water content if accurate physical measurements are to be made.

Swelling data show that shales that are altered during handling (hydrated or dehydrated) do not respond properly even when restored to their native hydration conditions. They tend to experience excessive swelling compared to cores kept at their native water content.

Results also showed that the North Sea core used in this study was maintained in a fully saturated condition during coring, retrieval, and storage. The technique used is discussed here.
Applications of Polymer Gel for Establishing Zonal Isolations and Water Shutoff in Carbonate Formations
Authors: Pérez D. , Fragachán F. E. , Barrera A. Ramírez , Féraud J. P.
Published: December 2007

In this paper, we present the results of successful applications of polymer gels to control water production in Mexico. We discuss three case studies that used a systematic methodology to correctly diagnose near-wellbore water channeling behind the casing. The methodology uses diagnostic plots based on the historical behavior of the water/oil ratio (WOR) as a function of time. These include correlation with information from original cement bond logs (CBL's), oxygen-activated logs during production to effectively determine the origin of the water, and saturation logs to determine the water levels independent of the salinity of the water produced.

In addition, we present successful applications of polymer gels to re-establish zonal isolations in the three case studies previously mentioned. We discuss gel placement and present the procedure followed in each case, evaluate a water injectivity test followed by a temperature log taken before gel placement to determine the height propagation of the water, and anticipate potential zone damage of adjacent producing intervals during gel placement. In one case, a new interval completed perforating through the gel with excellent results. Another case involved a zone abandonment with gel, in which positive pressure was tested with 35 and 70 kg/cm2 wellhead pressure at 2500 m. In all cases, the advantages of gel treatments over common cement squeezes are discussed.

Finally, we present the treatment results, including the analysis of pressures recorded during gel placement and the oil and water production before and after treatment.
A Note on the Skin Effect
Authors: Hawkins Murray F.
Published: December 2007

Horner and van Everdingen have shown that the pressure drop within the wellbore, as a result of having produced the well at a constant rate q for time t, where t is sufficiently large, is:

(Equation 1)

van Everdingen observed that better agreement between theory and well performance can be obtained if, instead of assuming the permeability is ke everywhere about the well, it is assumed the permeability near the wellbore is substantially reduced as a result of drilling, completion and/or production practices. In order to account for the additional pressure drop he introduced the dimensionless quantity S, the skin effect factor, so that Eq. 1 becomes:

(Equation 2)

Eq. 2 might have also been obtained as follows. Assume a zone of altered permeability ka exists about the well out to a radius ra, and beyond that the unaltered, external permeability ke. The additional pressure drop required to overcome this skin of reduced permeability may be calculated with sufficient accuracy using the incompressible flow equation; for Brownscombe and Collins have shown almost no difference between compressible and incompressible steady-state flow, in the vicinity of the wellbore, and the small volume of fluid in the vicinity of the wellbore makes unsteady-state mechanics unnecessary. Then,

(Equation 3)

The sign of this skin pressure drop will be positive or negative depending upon whether the altered permeability ka is smaller or larger, respectively, than the external permeability ke.
Three-Phase Relative Permeability
Authors: Corey A.T. , Rathjens C.H. , Henderson J.H. , Wyllie M.R.J.
Published: December 2007

The results of three-phase relative permeability tests on nine water-wet consolidated Berea sandstone samples are presented as composite ternary diagrams showing isoperms of oil, water and gas. Capillary pressure control was exercised over the flow of gas and oil in the presence of water. The water saturations ranged from 17 to 71 per cent pore volume.

A method of calculating both the oil and water permeabilities of a three-phase system from the easily measured gas relative permeability is presented.

Experimental Procedure and Results

A renewed interest has been shown in three-phase relative permeability as a result of recent developments involving underground combustion processes, steam injection, and other multiphase displacement processes. The experiments and results described here involved simultaneous flow of oil and gas in consolidated Berea sand with brine present as the wetting phase.

Gas and oil relative permeabilities were measured on nine cores with CaCl2 brine present as the wetting phase in saturations ranging from 17 to 71 per cent.
Orifice Metering of Two-Phase Flow
Authors: Mattar Louis , Nicholson Murray , Aziz Khalid , Gregory G.A.
Published: December 2007

Several correlations for two-phase flow through orifice meters are reviewed and verified experimentally, using air and oil mixtures in a 2-in. (5.08-cm) orifice meter. A simple, empirically determined relationship is shown to be valid for a limited range of oil/gas ratios when separator tests are possible. For predictive purposes, however, a more complex relationship is recommended.

Introduction

The flow of two-phase mixtures in a single pipeline is becoming more common. To determine the rates of flow in such systems, the phases are separated first, and the flow rate of each phase is measured individually.In many instances, we need to know the flow rates without having to separate the phases. A typical example would be when continuously (automatically) monitoring sour gas fields, where retrograde condensation occurs before measurement by an orifice meter. Sometimes existing installations, which were once producing dry gas, now are producing in two-phase flow, and satisfactory interpretation of these orifice meter readings is desired. Another application of interest is the determination of steam quality during the flow of wet steam when the total mass flow rate (boiler feed rate) is known.This study tries to obtain a relationship between the orifice-meter differential reading and the flow rates of the individual phases, using air and oil as the flowing fluids.

Review of the Literature

Most investigations into two-phase flow-rate measurement with orifices have been concerned with the flow of wet steam. Occasionally, air/water systems were studied. There are few papers relating to natural gas/oil flow.

All correlations presented in the literature are based on the single-phase, orifice-meter equation, which may be written as

(1)

James, working with geothermal steam wells, used Eq. 1, but replaced the density with an effective two-phase mixture density. He obtained this density by raising the mass dryness fraction to the empirically determined power of 1.5.In another approach, Smith and Leang used a "blockage factor" to modify the coefficient of discharge, Kd, and expressed it as a function-of-dryness fraction.Smith and Leang and Smith et al., reviewed and evaluated several published correlations.Murdock, Bizon, and Chisholm and his coworkers took a different approach from those mentioned before. They related the two-phase pressure drop to that obtained by flowing the gas and liquid pressure drop to that obtained by flowing the gas and liquid separately. Murdock and Bizon assumed there was no interfacial shear between the gas and liquid phases (no slip model) and derived the relationship,

(2)

We show in the Appendix that / is proportional to the liquid-to-gas ratio. When there is no proportional to the liquid-to-gas ratio. When there is no liquid flowing, the liquid-to-gas ratio is zero, and must equal one. Eq. 2 then becomes equivalent to that reported by Wichert,

(3)

JPT

P. 955
Modeling the Propagation of Waterflood-Induced Hydraulic Fractures
Authors: Hagoort Jacques , Weatherill Brian D. , Settari Antonin
Published: December 2007

A mathematical reservoir model is presented to simulate the propagation of waterflood-induced hydraulic fractures in a symmetry element of a waterflood pattern. The model consists of a conventional single-phase reservoir simulator coupled with an analytical fracture model.

The model is capable of simulating fracture propagation as a function of (1) injection and production rates or pressures, (2) reservoir and fluid properties, and (3) formation-fracturing pressures.

Examples are given that clearly illustrate the characteristics of hydraulic-fracture growth. The key variables are injection rate and voidage/replacement ratio. Fractures can be contained by restricting the injection rate and by imposing a voidage/ replacement ratio equal to or less than 1.

The modeling technique presented here also may be applied to other fracturing problems, particularly in cases where leakoff is significant and, thus, should be taken into account rigorously.
A Finite-Element Method for Reservoir Simulation
Authors: Young Larry C.
Published: December 2007

Several previous studies have applied finite-element methods to reservoir simulation problems. Accurate solutions have been demonstrated with these methods; however, competitiveness with finite difference has not been established for most nonlinear reservoir simulation problems.

In this study a more efficient finite-element procedures is presented and tested. The method is Galerkin-based, and improved efficiency is obtained by combining Lagrange trial functions with Lobatto quadrature in a particular way. The simulation of tracer performance, ion exchange preflush performance, and adverse mobility ratio miscible displacements is considered. For the problems considered, the method is shown to yield accurate solutions with less computing expense than finite differences or previously proposed finite-element techniques.

For the special case of linear trial functions, the method reduces to a five-point central difference approximation. In contrast to previously reported results, this approximation is found to simulate adverse mobility ratio displacements without grid orientation sensitivity, provided a sufficiently fine grid is used.
A Streamline Approach for Integrating Transient Pressure Data Into High-Resolution Reservoir Models
Authors: Kulkarni Kari Nordaas , Datta-Gupta Akhil , Vasco D.W.
Published: December 2007

We generalize the streamline approach to transient pressure applications by introducing a "diffusive" time of flight along streamlines. This allows us to define drainage areas or volumes associated with primary recovery and compressible flow under the most general conditions. We then employ developments in seismic tomography and waveform imaging to formulate an efficient approach for integrating transient pressure data into high-resolution reservoir models. The proposed approach exploits an analogy between a propagating wave and a propagating "pressure front" via high-frequency asymptotic solutions to the transient pressure equation. A key advantage of the asymptotic approach is that parameter sensitivities required for solving inverse problems related to production data integration can be obtained analytically using a single streamline simulation. Thus, the approach can be orders of magnitude faster than current techniques that require multiple flow simulations. We demonstrate the power and utility of the approach by applications to both synthetic and field examples. In the field example, the predominant fracture patterns emerging from the inversion are shown to be consistent with outcrop mapping and crosswell seismic imaging.
Experimental Study of Fracture Conductivity for Water-Fracturing and Conventional Fracturing Applications
Authors: Fredd C. N. , McConnell S. B. , Boney C. L. , England K. W.
Published: December 2007

Hydraulic fracturing treatments that use treated water and very low proppant concentrations (commonly referred to as water-fracturing treatments or "waterfracs") have been successful in stimulating low-permeability reservoirs. However, the mechanism by which these treatments provide sufficient conductivity is not well understood. To understand the effects of fracture properties on conductivity, a series of laboratory conductivity experiments was performed with fractured cores from the east Texas Cotton Valley sandstone formation.

The results of this study demonstrate that fracture displacement is required for surface asperities to provide residual fracture width and sufficient conductivity in the absence of proppants. However, the conductivity may vary by at least two orders of magnitude, depending on formation properties such as the degree of fracture displacement, the size and distribution of asperities, and rock mechanical properties. In the presence of proppants, the conductivity can be proppant- or asperity-dominated, depending on the proppant concentration, proppant strength, and formation properties. Under asperity-dominated conditions, the conductivity varies significantly and is difficult to predict. Low concentrations of high-strength proppant overcome the uncertainty associated with formation properties and provide proppant-dominated conductivity. The implication of these results is that the success of a water-fracturing treatment is difficult to predict because it will depend significantly on formation properties. This dependence can be overcome by using high-strength proppants or proppants at conventional field concentrations.
Identifying and Estimating Significant Geologic Parameters With Experimental Design
Authors: White Christopher D. , Willis Brian J. , Narayanan Keshav , Dutton Shirley P.
Published: December 2007

Variability in production predictions caused by geologic heterogeneity and uncertainty was examined with a new method. The experimental design maximized the information derived from the flow simulation of various geologic models. Empirical response surface models were fit to simulation results to assess the consequences of varying several geologic factors. Posterior distributions of geologic parameters were estimated from flow responses. Improvements in the accuracy of the reservoir model were quantified by computing changes in factor uncertainties resulting from response measurements. Monte Carlo simulations with prior and posterior factor distributions illustrate uncertainty reduction. This approach can be used for model comparison, sensitivity analysis, and estimation of probability distributions of geologic model parameters.
Unified Model for Steady-State Foam Behavior at High and Low Foam Qualities
Authors: Alvarez J. M. , Rivas H. J. , Rossen W. R.
Published: December 2007

Foams are routinely used worldwide to divert acid in well-stimulation treatments, and to divert gas flow in improved oil recovery (IOR) projects on a pilot basis. The complexity of foam behavior and the apparent contradictions among foam studies have bedeviled attempts to understand foams and to design effective field treatments.

In 1992, Osterloh and Jante1 identified two distinct foam-flow regimes: a high-quality (dry) regime, in which the steady-state pressure gradient is independent of the gas flow rate, and a low-quality (wet) regime, in which the pressure gradient is independent of the liquid flow rate. New data for strong foams in a variety of porous media, with various surfactant formulations, and over a range of flow rates, show this behavior to be general. In each regime, foam behavior is dominated by a single mechanism: at high qualities by capillary pressure and coalescence, and at low qualities by bubble trapping and mobilization. Based on these insights, a new, unified model unites foam behavior in acid-well stimulation and gasdiversion IOR and reconciles apparently contradictory data. This model correlates the effects of parameters, such as rock permeability and surfactant formulation, on foam behavior in the two flow regimes and on the transition between the two regimes. A variety of laboratory data supports the model's assumptions.

The implications of these results for designing foam processes for IOR and acid diversion are discussed. These insights can guide the selection of foam formulation and injection quality for foam applications.
A Newton-Raphson Iterative Scheme for Integrating Multiphase Production Data Into Reservoir Models
Authors: Wu Zhan
Published: December 2007

This paper presents a new linearized iterative algorithm for building reservoir models conditioned to multiphase production data and geostatistical data. The significant feature of the proposed algorithm is that the computation of the sensitivity coefficients of production data, with respect to model parameters, can be avoided. This leads to dramatic reduction of computational cost. Instead of generating the sensitivity matrix as required for the least-squares algorithms, the proposed approach relies on solving the inversion equations, which are derived from the necessary conditions for a functional extremum.

It is proved that the proposed method requires considerably less computational effort than the traditional algorithms such as the Gauss-Newton method, the Levenberg-Marquardt method, and the generalized pulse-spectrum technique (GPST). This is because the computation of the sensitivity coefficients makes the traditional algorithms computationally intensive. However, for the proposed linearized iterative scheme, the computational requirement only depends on the timesteps used in the reservoir simulator rather than the number of parameters or the number of observed data.

The linearized iteration scheme converges quickly because the inversion equations can be solved through the Newton-Raphson method. At each iteration, the new approach requires solving the finite difference equations and the linear adjoint equations only once, respectively. Since the solver for the flow equations can be used to solve both the adjoint equations and the inversion equations, the proposed algorithm can be easily applied to commercial reservoir simulators. In this paper, two numerical examples for incorporating water oil rate data into geostatistical models are given to prove the efficiency of the proposed algorithm.
A Semianalytical Model for Calculating Pressure Drop Along Horizontal Wells With Stinger Completions
Authors: Jansen J. -D.
Published: December 2007

Pressure drop along horizontal wells causes unequal drawdown along the well, thus reducing the effectiveness of the toe of the well, and increasing the tendency for water and gas coning at the heel. Completions have been proposed to combat this effect using a stinger that extends from the heel into the horizontal section. This reduces the magnitude of the pressure drop over the wellbore, because the well is effectively split into two segments of reduced length. If the stinger also has an intermediate inflow opening, possibly equipped with a remotely controlled inflow control valve, a further reduction in the wellbore pressure drop can be obtained. We present a semianalytical model to compute the flow in stinger completions in a reservoir that may have varying inflow characteristics along the wellbore. The model is capable of handling flow in a looped configuration, which occurs when the stinger has an intermediate inflow point. It combines either numerical integration or analytical integration in terms of Jacobian elliptic functions, with an iterative "shooting" method to solve the two-point boundary value problem for pressure and flow rate along the well. It can be used to rapidly determine the optimal configuration of a stinger completion with intermediate inflow.
Laboratory and Theoretical Evaluation of Corrosion-Inhibiting Emulsions
Authors: Civan Faruk , Weers Jerry J.
Published: December 2007

Measurement and correlation of the typical properties of the corrosion-inhibiting emulsions that affect their placement and gradual decomposition in oil wells are presented. The mechanisms of the emulsion breakup and inhibitor release by shearing and heating are determined, formulated, and verified by experimental data. The viscosity, drying and stability processes, surface tension, repetitive film coating on tubing and casing walls, and inhibitor resolution of typical water-external and oil-external emulsions are correlated by relevant theories.
Laboratory and Field Evaluation of an Inelastic Neutron Scattering and Capture Gamma Ray Spectrometry Tool
Authors: Hertzog R. C.
Published: December 2007

An experimental system for gamma ray spectroscopy logging has been developed which uses prompt and capture gamma radiation induced in formations by 14-MeV neutrons from a pulsed-neutron generator to determine relative concentrations of various elements in the formation. The logging system uses computer-processing techniques based on spectral modeling that has been developed to analyze the inelastic and capture gamma ray data obtained with a borehole spectrometer.

The physics of the production of gamma rays from fast-neutron interactions with elemental nuclei in formations is discussed, leading to a simple but realistic interpretation model for the tool's response. This model is confirmed by laboratory and field tests.

The relative spectroscopic contributions from carbon, oxygen, silicon, calcium, iron, chlorine, and hydrogen are used for various cased-hole and openhole logging applications. Particular emphasis is placed on the carbon/oxygen ratio used to obtain oil saturation independent of formation-water salinity. Carbon/oxygen ratio determinations made in the laboratory are compared with values predicted on the basis of known lithologies, porosities, and oil-saturation changes.

In addition, the spectral contributions from iron, silicon, and calcium are used to interpret lithology; hydrogen, silicon, and calcium contributions are used to determine the effects of porosity; and chlorine and hydrogen contributions are used to investigate salinity changes.

Field-test log examples of these elemental determinations are shown.
A Generalized Friction-Factor Correlation To Compute Pressure Drop in Horizontal Wells
Authors: Yalniz M. U. , Ozkan E.
Published: December 2007

This work investigates the effect of fluid ingress on flow through perforations in a horizontal wellbore and correlates this effect in the form of an apparent friction factor. The investigation uses theoretical and experimental models. It is shown that when there is no influx, the perforations, or slots, on the well surface cause a reduction in the pressure gradients proportional to their area. The well-bore pressure gradients increase with influx from perforations, but unless the ratio of the influx rate to the wellbore flow rate is sufficiently large, pressure gradients are lower than those of an unperforated well. The results of this study are combined to develop a generalized friction-factor correlation that is a function of the Reynolds number and the ratios of the influx to wellbore flow rate and perforation to wellbore diameters.
Foam Property Requirements for Proper Hole Cleaning While Drilling Horizontal Wells in Underbalanced Conditions
Authors: Martins A. L. , Lourenço A. M. F. , de Sá C. H. M.
Published: December 2007

This paper summarizes an extensive experimental program to determine effective foam drilling conditions in horizontal wells. The program included foaming-agent selection (considering optimum concentration and salt/oil contaminants), rheological characterization of foams, development of a flow loop to test the foam-carrying capacity in high-angle wells, definition of the test procedure and matrix, and analysis of the results. After 60 bed tests were performed at a cuttings-transport flow loop, correlations were proposed to predict the cuttings-bed erosion capacity in horizontal wells as functions of the foam quality and the mixture's Reynolds number.
Wettability Effects on Oil-Recovery Mechanisms in Fractured Reservoirs
Authors: Graue A. , Bognø T. , Baldwin B. A. , Spinler E. A.
Published: December 2007

Iterative comparison between experimental work and numerical simulations has been used to predict oil-recovery mechanisms in fractured chalk as a function of wettability. Selective and reproducible alteration of wettability by aging in crude oil at an elevated temperature produced chalk blocks that were strongly water-wet and moderately water-wet, but with identical mineralogy and pore geometry. Large scale, nuclear-tracer, 2D-imaging experiments monitored the waterflooding of these blocks of chalk, first whole, then fractured. This data provided in-situ fluid saturations for validating numerical simulations and evaluating capillary pressure-and relative permeability-input data used in the simulations. Capillary pressure and relative permeabilities at each wettability condition were measured experimentally and used as input for the simulations. Optimization of either Pc-data or kr-curves gave indications of the validity of these input data. History matching both the production profile and the in-situ saturation distribution development gave higher confidence in the simulations than matching production profiles only.
Development of an Integrated Reservoir Model for a Naturally Fractured Volcanic Reservoir in China
Authors: Abbaszadeh Maghsood , Corbett Chip , Broetz Rolf , Wang James , Xue Fangjian , Nitka Tom , Zhang Yong , Liu Zhen Yu
Published: December 2007

This paper presents the development of an integrated, multidiscipline reservoir model for dynamic flow simulation and performance prediction of a geologically complex, naturally fractured volcanic reservoir in the Shang 741 Block of the Shengli field in China. A static geological model integrates lithological information, petrophysics, fracture analysis, and stochastic fracture network modeling with Formation MicroImage (FMI) log data and advanced 3D seismic interpretations. Effective fracture permeability, fracture-matrix interaction, reservoir compartmentalization, and flow transmissibility of conductive faults are obtained by matching various dynamic data. As a result of synergy and multiple iterations among various disciplines, a history-matched dynamic reservoirsimulation model capable of future performance prediction for optimum asset management is constructed.
Slim Hole Logging and Analysis for Uranium Exploration
Authors: Howell Eddie P. , Gant Orland J. , Crebs Terry J.
Published: December 2007

Significant improvements have been made in uranium logging equipment and analysis techniques. Logging systems now provide geological, geophysical, and geochemical data from routine measurements. Through computer analysis, these systems also can determine porosity, density, permeability, lithology, formation-water resistivity, and thermal and mechanical properties.

Introduction

Deeper targets for uranium exploration warrant more complete logging systems than those used previously. Such systems can produce adequate data for a geologic understanding of the ore deposition processes with fewer drill holes. As the formation depth increases, data extrapolated from surface outcrops become less reliable and make log-derived data more important. An alternative to a complete logging package is extensive coring of ore-bearing and related formations, but this is expensive and time consuming. We are using reasonably sophisticated logging systems that provide data for geologic models, which are used to understand the sedimentary environment, groundwater, and other physical and chemical properties of uranium deposition. These models, based largely on log-derived data, are important when designing infill drilling for exploration, evaluation, or production.

Uranium log interpretation is simplified somewhat by short drilling times that restrict invasion and by lack of hydrocarbons that complicate fluid properties. However, less-sophisticated small-diameter downhole tools can have the opposite effect.

Logging System

The digital logging systems that we use have been designed for relatively simple operation. Analog records are produced during logging to verify equipment operation and allow operator adjustments if necessary.

For most logging tools, digital data are generated uphole from a depth encoder, two count-rate meters, and four 4.5-digit volt meters. Signals are recorded from all of these devices at operator-selectable digitization intervals. Recordings are made with cassette tape decks using a 1,200-baud transfer rate. With this recording rate, logging speed is limited by the downhole instruments themselves. Up to 2,000 ft (600 m) of multiplexed logs can be recorded on one side of a cassette.

Each truck is designed to run at least 12 separate downhole tools with minimal operator intervention. At present, three sondes are used routinely and several others are used on an experimental basis. These include a gamma-ray log that uses a 0.75×1.25 in. (1.91×3.18 cm) Nal crystal with downhole scaling in areas where count rates are high. This tool also generates 16- and 64-in. (41- and 163-cm) normal calibrated resistivity curves. A single-point resistivity curve can be recorded for correlation with older uranium logs. Also, a spontaneous potential (SP) curve is measured but is difficult to interpret in mineral logging since this potential is the sum of several variable potentials including chemical, membrane, and filtration.
Characterization of Spontaneous Water Imbibition Into Gas-Saturated Rocks
Authors: Li Kewen , Horne Roland N.
Published: December 2007

A method has been developed to characterize the process of spontaneous water imbibition into gas-saturated rocks. Water relative permeability and capillary pressure can be calculated simultaneously from water imbibition data using this method. A linear relationship between imbibition rate and the reciprocal of the gas recovery by spontaneous water imbibition was found and confirmed both theoretically and experimentally, even at different initial water saturations. There was almost no effect of initial water saturation on residual gas saturation by spontaneous water imbibition. The higher the initial water saturation, the lower the imbibition rate and the ultimate gas recovery. It was found that the capillary pressure did not vary with initial water saturation in a certain range. The capillary pressure and the water relative permeability calculated using the new method was consistent with the experimental results measured using other techniques. The method developed in this paper is also of importance for scaling up experimental data.
Quantifying Uncertainty in Production Forecasts: Another Look at the PUNQ-S3 Problem
Authors: Barker John W. , Cuypers Maarten , Holden Lars
Published: December 2007

A synthetic reservoir model, known as the PUNQ-S3 case, is used to compare various techniques for quantification of uncertainty in future oil production when historical production data is available. Some results for this case have already been presented in an earlier paper.1

In this paper, we present some additional results for this problem, and also argue an interpretation of the results that is somewhat different from that presented in the earlier paper. The additional results are obtained with the following methods: importance sampling, history matching of multiple models using a pilot-point approach, and Markov Chain Monte Carlo (MCMC).