bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface BOP: Testing and Completing Deepwater Wells Drilled With a Surface-BOP Rig
Authors: Mason D. L. , Tharp W. , Wilie C. L.
Published: April 2006

Many deepwater-development projects in operators' portfolios require lower costs to meet internal economic thresholds. Because of this, Shell has looked at extending surface-blowout-preventer (BOP) activities to include well testing and completion techniques for deepwater wells in conjunction with surface-BOP drilling.

The cost advantages of surface-BOP-drilled wells have been demonstrated (notably in the Far East), but the recent surface-BOP-drilled well in Brazil is a milestone in terms of extending the applicability to deeper water and harsher environments. The enabling technology has been the subsea isolation device (SID). Testing and completion techniques have been developed to be compatible with surface-BOP wells drilled with an SID.

This paper focuses on the following aspects:

Well testing using surface-BOPs from a moored rig and Well completions using surface-BOPs from a moored rig.

Shell has developed a testing configuration to carry out a DST, essentially using standard equipment. The well-testing equipment configuration is currently ready for use and has been run in a subsea-BOP well.

In completion operations, the availability of a high-pressure (HP) riser does not add significant complexity and even actually simplifies some of the completion activities. Conceptual studies and early hazard/risk assessments have shown there are no obvious "showstoppers," and the duration of a surface-BOP-rig completion is expected to be very similar to a subsea-BOP-rigcompletion.

This paper describes the results of the conceptual studies, early hazard assessment exercises used to define the basic design parameters, and more detailed hazop studies.
Bounds on In-Situ Stress Magnitudes Improve Wellbore Stability Analyses
Authors: Aadnøy Bernt S. , Hansen Ann K.
Published: April 2006

Wellbore stability analysis is becoming a necessary tool to improve operational economy and to avoid wellbore problems. Essential elements of this process include estimation of critical fracturing and collapse pressures to obtain an optimal mud-weight window.

The input data for this analysis is mainly pore pressure predictions from many sources such as logs and drilling exponents, overburden stresses from logs or drilled cuttings, leakoff tests at casing shoes, and breakout analysis from caliper logs. From these and other data, estimates for in-situ stresses and directions are obtained, which again serve as input for wellbore stability modeling. It is evident that the input data come from many different sources and can therefore not be considered consistent.

During wellbore stability modeling, it has often been observed that unrealistic results appear. Sometimes one observes a critical collapse pressure that exceeds the fracturing pressure, clearly a faulty result. There is often an inherent error in some of the input data. This paper addresses this problem and concludes that the relative magnitudes of the in-situ stresses are its main cause. Equations are given that define the bounds on the in-situ stresses for different stress regimes.

By using the bounds on the horizontal in-situ stresses on field cases, realistic fracturing and collapse prognosis are always obtained. Because the models also define the minimum permissible anisotropic stress state, these can be used as default parameters when field data are missing.

A field case from the North Sea demonstrates the application of the stress bounds and shows that prognoses are obtained that better correspond to observed behavior of the wells.
A Model for Changes in Coalbed Permeability During Primary and Enhanced Methane Recovery
Authors: Shi Ji-Quan , Durucan Sevket
Published: April 2006

The natural fracture network of a dual-porosity coalbed reservoir is made up of two sets of orthogonal, and usually subvertically oriented, cleats. Coalbed permeability has been shown to vary exponentially with changes in the effective horizontal stress acting across the cleats through the cleat-volume compressibility, which is analogous to pore compressibility in porous rocks. A formulation for changes in the effective horizontal stress of coalbeds during primary methane recovery, which includes a Langmuir type curve shrinkage term, has been proposed previously. This paper presents a new version of the stress formulation by making a direct link between the volumetric matrix strain and the amount of gas desorbed. The resulting permeability model can be extended readily to account for adsorption-induced matrix swelling as well as matrix shrinkage during enhanced methane recovery involving the injection of an inert gas or gas mixture into the seams. The permeability model is validated against a recently published pressure-dependent permeability multiplier curve representative of the San Juan basin coalbeds at post-dewatering production stages. The extended permeability model is then applied successfully to history matching a micropilot test involving the injection of flue gas (consisting mainly of CO2 and N2) at the Fenn Big Valley, Alberta, Canada.
Predicting Carbonate Scale in Oil Producers From High-Temperature Reservoirs
Authors: Ramstad Kari , Tydal Trine , Askvik Kjell Magne , Fotland Per
Published: April 2006

Calcium carbonate (CaCO3) scale is a common problem in the oil industry, leading to reduced well performance and obstruction of safety valves. Recent field experiences indicate that scaling may be a problem at lower saturation ratio (SR) than earlier anticipated. In a high-pressure, high-temperature scale cell, crystal growth in synthetic formation water has been studied. Induction times and growth rates have been determined by use of a microscope cell. The results have been interpreted by use of nucleation theory. The findings indicate that wells may be safely operated at SR below 2.5 at 85°C. At higher temperature, crystal growth is less dependent on SR and the temperature dominates the system. Care should therefore be taken when operating wells at temperatures greater than 100°C.
Multiresolution Wavelet Analysis for Improved Reservoir Description
Authors: Sahni Isha , Horne Roland N.
Published: April 2006

It is well documented that history matching is a problem with possibly nonunique solutions. In the past few years, several automated or semiautomated history-matching algorithms have been proposed. Depending on the algorithm used, it is possible that the final estimated reservoir-property distribution that allows for a good history match may not be geologically realistic. Therefore, there is a need to include other constraints to generate multiple, geologically realistic history-matched realizations. These constraints might, for example, include the variogram, a training image, the distribution of net-to-gross, pore volume, or other geostatistical information about the reservoir. This inclusion is particularly useful because it introduces uncertainty information in the reservoir description when we have limited history from existing wells in the field and intend to drill infill wells or implement a secondary-recovery process.

The algorithm proposed in this paper uses multiresolution wavelet analysis to integrate history data with the geostatistical information contained in the variogram proposed for the reservoir. Wavelets allow the representation and manipulation of property distributions at various resolutions at the same time. Using wavelets, information from different sources such as production history and seismic surveys (that would be at different resolutions) can be incorporated directly at the appropriate resolution level. In the first step, we fix the wavelet coefficients sensitive to the history-match data. This has the effect of fixing the field history without fixing individual gridblock properties. In the second step, the remaining free wavelet coefficients are modified to integrate variogram information into the reservoir description. Generating multiple realizations of only the second set of wavelets coefficients results in multiple history-matched, variogram-constrained descriptions of the reservoir. The computational investment is very modest because the history match is done only once.

In a number of example cases, different areal Gaussian fields with varying amounts of available production-history data were studied to test the algorithm. It was found that the wavelet coefficients constraining the history can be decoupled from those constraining the variogram. The implication of this observation is that the history data and variogram can be integrated sequentially into the reservoir model—that is, after the initial history match, new information can be added to the model without disturbing the original match to yield multiple history-matched and geostatistically constrained realizations.
The Cement-to-Formation Interface in Zonal Isolation
Authors: Ladva H. K. J. , Craster B. , Jones T. G. J. , Goldsmith G. , Scott D.
Published: April 2006

Maintaining zonal isolation for the lifetime of oil and gas wells is critical. Leakage behind casing can reduce the cost effectiveness of the well and cause health and safety risks from pressure buildup and contaminated aquifers. During the completion and production phases of the well, temperature and pressure variations can cause stresses at the cement-to-formation interface. The ability of the casing-cement system to maintain a seal at the cement-to-formation interface depends on the condition of the formation surface before slurry placement. The condition of shale will depend upon the nature of the drilling fluid used, whereas the condition of a permeable rock will depend upon the presence and nature of the filter-cake deposited during drilling and circulation.

In this paper, we present an improved understanding of chemical interactions at the cement-to-formation interface and the factors that determine bond strength and the position of the plane of failure. For permeable formations, the role of the mud filter cake for different mud types is explored. For nonpermeable formations, the presence and effect of a mud treatment are also examined. The extent and depth to which chemical alteration of the mudcake occurs when in contact with cement is determined together with measurements of the yield stress and water-content profile of the altered mudcake. The effecton bond strength of exposing swelling and nonswelling shales to inhibitive drilling fluids is presented. Laboratory-scale test equipment and a small-scale wellbore simulator, developed for tests under realistic field conditions, are described. A flexible (i.e., lower Young's modulus) cement plays a role in bonding and is demonstrated by the simulator tests. This improved understanding enables us to confirm the key issues at the cement-to-formation interface and propose some solutions for effective zonal isolation.
Innovative Remedial Cementing Solution Provides Annular Isolation in Duyong B-4
Authors: Morris Thomas C. , Bidi M. Zuki , Elmarsafawi Y. , Nair Devan , Said Rifat , Tugcu Reha , Ong Jane
Published: April 2006

Whether a cement-squeeze operation results in an annular seal depends heavily on how far the cement can penetrate and disperse in the fine channels of a partially cemented annulus. In many cases, a conventional- or microfine-cement slurry will dehydrate and bridge off before it can achieve its objectives (Nelson et al. 1990). This paper describes the use of an engineered, optimized slurry for a squeeze operation in the Duyong B-4 well, which had a perforated zone that demonstrated a low rate of seawater injectivity. This paper also presents the slurry design and properties, execution procedure, and prejob and post-job log evaluations.

After several years of production, gas bubbles appeared in various locations throughout the Duyong field. Shallow seismic readings showed gas charging in several shallow gas layers throughout the Duyong field. Several wells were investigated as possible contributors to the charging of the shallow sandstone layers, and Duyong B-4 was selected as a probable contributor. Duyong B-4 is a gas well that was completed in November 1983 with four producing zones. In September 2003, this well was selected as a test well to evaluate the cement quality behind the casing. Both cement-bond logs and ultrasonic-imaging logs showed gas and fluid channels behind the casing. An optimized cement slurry (OCS) was engineered and tested in the laboratory under well conditions. Results showed excellent penetration in narrow gaps, optimum fluid-loss control, and low rheology, both at surface and downhole conditions.

The slurry was used in the squeeze operation; post-job logs demonstrated the success of the treatment. The slurry penetrated the narrow gaps without dehydrating, and good mechanical properties were achieved in short setting times (Moulin et al. 1997). These properties are especially important in gas-producing wells, and they met all the objectives set forth by the client.
Optimization of Coalbed-Methane-Reservoir Exploration and Development Strategies Through Integration of Simulation and Economics
Authors: Clarkson C.R. , McGovern J.M.
Published: April 2006

The unique properties and complex characteristics of coalbed methane (CBM) reservoirs, and their consequent operating strategies, call for an integrated approach to be used to explore for and develop coal plays and prospects economically. An integrated approach involves the use of sophisticated reservoir, wellbore, and facilities modeling combined with economics and decision-making criteria.

A new CBM prospecting tool (CPT) was generated by combining single-well (multilayered) reservoir simulators with a gridded reservoir model, Monte Carlo (MC) simulation, and economic modules. The multilayered reservoir model is divided into pods, representing relatively uniform reservoir properties, and a "type well" is created for each pod. At every MC iteration, type-well forecasts are generated for the pods and are coupled with economic modules. A set of decision criteria contingent upon economic outcomes and reservoir characteristics is used to advance prospect exploration from the initial exploration well to the pilot and development stages. A novel approach has been used to determine the optimal well spacing should prospect development be contemplated. CPT model outcomes include a distribution of after-tax net present value (ATNPV), mean ATNPV (expected value), chance of economic success (Pe), distribution of type-well and pod gas and water production, reserves, peak gas volume, and capital. An example application of CPT to a hypothetical prospect is provided.

An integrated approach also has been used to assist with production optimization of developed reservoirs. For example, an infill-well locating tool (ILT) has been constructed to provide a quick-look evaluation of infill locations in a developed reservoir. ILT, like CPT, is used for multiwell applications, combining the single-well simulator with a multilayered reservoir model and economics. An application of ILT to a CBM reservoir is provided, and the results are compared with the predictions of an Eclipse* reservoir simulation.
Controls of Coal Fabric on Coalbed Gas Production and Compositional Shift in Both Field Production and Canister Desorption Test
Authors: Cui Xiaojun , Bustin R. Marc
Published: April 2006

The production rates of coalbed gas wells commonly vary significantly, even in the same field with similar reservoir permeability and gas content. The compositional variation in produced gas is also not everywhere predictable, although in most fields produced gas becomes progressively enriched in CO2 through the production life of a reservoir, such as parts of the San Juan basin. In contrast, it is generally observed that the ratio of CO2:CH4 declines with time during field and laboratory desorption testing of coal cores. In this study, we investigate numerically the importance of coal fabric, namely cleat spacing and aperture width, on the performance of coalbed gas wells and gas compositional shifts during production. Because of the cubic relationship between fracture permeability and fracture aperture width (and thus fracture porosity) for a given cleat permeability, the production profile of coal seams varies depending on whether the permeability is distributed among closely spaced fractures (cleat) with narrower apertures or more widely spaced fractures (cleat) with wider apertures. There is a lower fracture porosity for coal with widely spaced fractures than for coal with closely spaced fractures. Therefore, the relative permeability to gas increases more rapidly for coals with more widely spaced cleats as less dewatering from fractures is required, assuming that the fractures are initially water saturated. Increase in cleat spacing from 0.01 to 10 cm significantly enhances the peak gas production and shortens the period to reach peak production.

The main stage of gas production is controlled by equilibrium desorption of gas from coals due to the relatively slow changes in reservoir pressure. The enrichment of CO2 in the production gas with time occurs because of the stronger adsorption of coals for CO2 than CH4. However, during desorption of coal cores, CO2 desorbs more rapidly than methane because desorption rate is governed more by diffusion than by sorption affinity, and CO2 has much higher effective diffusivity in microporous coals than CH4. Therefore, during canister desorption, there is a rapid increase in CO2 concentration in the desorbed gas followed by a steady decline in CO2 concentration, in contrast to the progressive enrichment of CO2 in produced gas from wells.
Thermoporoelastic Effect on Wellbore Stability
Authors: Chen Guizhong , Ewy Russell T.
Published: April 2006

This paper presents the consistency of thermal effects (i.e., the thermal-induced pore pressure and rock stresses) between two available models for inclined boreholes. Thermal effects for both a permeable and an impermeable boundary are studied. The solutions of pore pressure and stresses are provided, and the singularity is solved in the solutions for the condition of hydraulic diffusivity being equal to thermal diffusivity. The analytical solutions in the Laplace domain and in the real-time domain are verified using the finite-difference solutions. The collapse failure index and critical mud weights, as well as thermally induced pore pressure, are presented and analyzed under the circumstances of heating and cooling the wellbore. Results show that heating the wellbore can destabilize the near-wellbore region by raising both the collapse and the fracturing mud weight. The model presented in this paper can be applicable to deepwater drilling, where a narrow mud-weight window often occurs.
Subsurface Uncertainty Management and Development Optimization in the Harweel Cluster, South Oman
Authors: O'Dell Mike , Lamers Edwin
Published: April 2006

In the past 5 years, there has been a string of exploration successes in discovering some 350 million m3 (2 billion bbl) of oil in the Harweel Cluster in south Oman. This oil is deep, under high pressure, and comes with a high gas/oil ratio (GOR), and the fluids contain 15% CO2 and 5% H2S. Of the nine Precambrian carbonate reservoirs, six are lithostatically pressured, and three are hydrostatic. The Harweel Cluster is more than 70 km from existing infrastructure. If gas can be reinjected, miscible displacement is expected in many of the reservoirs. The Harweel Cluster is one of Oman's major opportunities for "green field" oil development.

There is a large degree of subsurface uncertainty in gross rock volume and oil/water contact (OWC), reservoir architecture, faults and fractures and reservoir compartmentalization, degree of dolomitization, permeability level and heterogeneity, fluid properties, and so on. However, little is known about the scale and relative importance of each of these uncertainties. Some uncertainties, such as compositional grading, might turn out to be more important than anticipated when evaluating development options because of non-linearities and dependencies.

Analyzing the effects of all uncertainty combinations in all reservoirs is not a realistic option. Therefore, a structured scenario-based approach has been developed to analyze and assess all potential factors influencing recovery schemes, reserves, and productivity. After evaluating the range of possible values and calculating the impact of each uncertainty, realizations were created to represent the range of possible values in each new reservoir. Field-scale equation-of-state models were used to simulate both primary depletion and gas reinjection. Development scenarios were optimized for each discrete realization. The resulting reservoir models serve as a basis for the development-concept selection and the subsequent field-development plans.
Improved Oil Recovery From Carbonate Reservoirs by Chemical Stimulation
Authors: Xie X. , Weiss W. W. , Tong Z. , Morrow N. R.
Published: April 2006

Oil reserves from shallow-shelf carbonate reservoirs account for 22% of the original oil in place (OOIP) of the entire U.S. oil resource. Many of these reservoirs are naturally fractured. A pressure-pulsing technique has been used in fractured fields to improve oil recovery. In some situations, imbibition of water can be promoted by chemical stimulation to alter the reservoir wettability toward water-wetness such that oil is expelled at an economic rate from the rock matrix into fractures. Shallow-shelf (i.e., Class II) carbonate reservoirs typically produce less than 10% OOIP during primary recovery and respond poorly to water injection.

In this work, promotion of imbibition was determined for a cationic surfactant, cocoalkyltrimethyl ammonium chloride (CAC), and a nonionic surfactant, an ethoxylated alcohol (POA). Cores from three dolomitic Class II reservoirs, Cottonwood Creek, Dagger Draw, and Lustre, were used in the laboratory tests. After preparing core samples using the corresponding reservoir crude oil and brine, spontaneous expulsion of oil was measured in glass imbibition cells at elevated temperature for more than 50 core samples. When reservoir brine was used as the imbibition fluid, oil recovery was in the range of 0 to 35% OOIP. After imbibition of reservoir brine had ceased, the cores were transferred into surfactant solutions at or somewhat above the critical micelle concentration (CMC) to test for enhanced recovery by further imbibition. Typically, immersion in the surfactant solution resulted in an additional recovery of 5 to 10% OOIP. The increased recovery is mainly ascribed to increased water–wetness. The effect of acidization before surfactant treatment was also tested and found to be detrimental to oil recovery.
Development and Application of a New Technique for Upscaling Miscible Processes
Authors: Hui Mun-Hong , Zhou Dengen , Wen Xian-Huan , Durlofsky Louis J.
Published: April 2006

To better design and manage miscible gas injection, a fast and accurate coarse-scale miscible simulation capability is required. In this paper, we present a new technique for the upscaling of first-contact miscible displacements. The method comprises two components: effective flux boundary conditions (EFBCs) and the extended Todd-Longstaff1 with upscaled relative permeabilities (ETLU) formulation. The former accounts approximately for the effects of the global flow field on the local upscaling problems, while the latter modifies the way that effective fluid properties and upscaled relative permeabilities are computed so that effectively residual oil is properly represented.

For a sequence of partially layered, synthetic 2D permeability fields, the technique is shown to be successful in reproducing reference fine-scale solutions. The method is also shown to outperform other upscaling techniques over a wide range of coarsening factors. The upscaling procedure is then applied to a 3D simulation of a miscible gas-injection field study. A near-well upscaling technique is also incorporated into the methodology. We show that the new approach provides coarse-scale simulation results that match the reference solutions closely. In addition, the technique is shown to be very efficient computationally.
Monte Carlo Simulation of Vertical-Separators Handling in a Network of Intermittent Gas Lift Wells
Authors: Caicedo Sergio , Trujillo Militza , Florez Horacio
Published: April 2006

To date, most of the research concerning the separation process has had a deterministic approach because of its orientation to steady-state-flow regimes. However, this assumption is far from true when many artificial intermittent gas lifted (IGL) wells are connected to the same separator. IGL wells have flow/no-flow periodic conditions associated with long accumulation stages and short production stages lasting approximately 20 minutes and 1 minute, respectively. A stochastic algorithm was developed to simulate the separation process and the proper periodicity of each IGL well, along with the unpredictable delay or synchronization between those wells. The simulation couples the dynamic mass-balance equations in the separator and the Monte Carlo method for predicting the gas and liquid rates associated with the superposition of the IGL wells. The input parameters for this simulation include daily gas/oil production and cycle time of each well, the oil properties, separator pressure and temperature, and the control scheme. The simulator output matched with less than 10% of the field data. The results obtained with the approach suggested in this work could be used for new criteria in design, simulation, and evaluation of separation facilities under fluctuating conditions.
Exploring Reservoir Engineering Aspects of Completion in Gas/Condensate Reservoirs: West African Examples
Authors: Kabir C. S. , Chang M. -M. , Taghizadeh O.
Published: April 2006

This paper explores multiple completion options in gas/condensate reservoirs with compositional simulations. Besides intelligent-well completion (IWC), options included commingling two reservoirs of contrasting conductivity (permeability-thickness product) and selectively perforating zones or reservoirs to offset the permeability contrast. At the outset, a value-of-information exercise suggested probing downhole sensing and completion issues in a stacked-reservoir situation. The ultimate objective of this study was to ascertain economic completion strategy so that depletion of reservoirs occurs evenly at the project's termination.

Single-well compositional simulations formed the backbone for our evaluation of three completion options. Each reservoir was characterized by history matching drillstem tests (DSTs). Experimental design (ED) reduced the large number of simulation runs to a manageable few for probabilistic forecasting. Comparison of three options suggested that all of them nearly produced the desired results of maximum liquid recovery despite a 10-fold difference in permeability between the two horizons.

Results further showed that condensate banking was a nonissue in this high-kh system of reservoirs as far as the gas deliverability is concerned. In other words, although 40 to 60% degradation in the gas productivity index (PI) occurred, gas deliverability remained intact. In contrast, both the liquid PI and rate declined with time owing to phase-behavior and relative permeability issues. Finally, we learned that the net income generated by IWC is no better than the specific-perforation completion (SPC).
Proppant Distribution and Flowback in Off-Balance Hydraulic Fractures
Authors: Daneshy Ali
Published: April 2006

The vast majority of industrial hydraulic fractures propagate in off-balance mode (in which the fracture is not in a single plane), including many shear fractures and branches, and are shorter and narrower than computed by existing models. Proppant transport, deposition, and flowback in these fractures are also substantially different from what occurs in single fractures. Presence of shear fractures leads to the formation of many randomly distributed tight proppant packs. Many of these are inherently unstable and serve as sources for proppant flowback, but they are also the source for fracture conductivity. Gravity causes the formation of proppant beds. These are usually formed at the lower extremities of the fracture. Branches generally trap the proppant and are unlikely sources for flowback. They also add little to the productive capacity of the fracture. Some of the proppant in the fracture is loosely scattered inside and is free to move when sufficient drag is exerted by fluid flow.

This paper places special emphasis on proppant flowback and shows that the three requirements for its occurrence are motion initiation, motion maintenance, and infinite conductivity along the return path. Gravity plays a very important role in this process, as does well completion. Tendency for equilibrium between reservoir-fluid velocity and deposited proppant results in a gradual decrease and, eventually, stoppage of proppant return at any given flow rate. This equilibrium can be disrupted by sudden increases in flow rate, which then trigger instability and proppant flowback.

Case histories from actual treatments illustrate and reinforce the findings of this paper.
Streamline-Based Production Data Integration in Naturally Fractured Reservoirs
Authors: Al-Harbi Mishal , Cheng Hao , He Zhong , Datta-Gupta Akhil
Published: April 2006

Streamline-based models have shown great potential in reconciling high-resolution geologic models to production data. In this paper, we extend the streamline-based production data integration technique to naturally fractured reservoirs. Describing fluid transport in fractured reservoirs poses additional challenges arising from the matrix/fracture interactions. We use a dual-porosity streamline model for fracture-flow simulation by treating the fracture and matrix as separate continua that are connected through a transfer function. Next, we analytically compute the sensitivities that define the relationship between the reservoir properties and the production response in fractured reservoirs. The sensitivities are an integral part of our approach and can be evaluated very efficiently as 1D integrals along streamlines. Finally, the production data integration is carried out by a generalized travel-time inversion that has been shown to be robust because of its quasilinear properties and that uses established techniques from geophysical inverse theory.

We also apply the streamline-derived sensitivities in conjunction with a dual-porosity finite-difference simulator to combine the efficiency of the streamline approach with the versatility of the finite-difference approach. This significantly broadens the applicability of the streamline-based approach in terms of incorporating compressibility effects and complex physics. We demonstrate the power and utility of our approach using 2D and 3D synthetic examples designed after actual field conditions. The reference fracture patterns are generated using a discrete fracture network (DFN) model that allows us to include statistical properties of fracture swarms, fracture densities, and network geometries. The DFN is then converted to a continuum model with equivalent gridblock permeabilities. Starting with prior models with varying degrees of fracture information, we match the water-cut history from the reference model. Both dual-porosity streamline and finite-difference simulators are used to model fluid flow in the fractured media. Our results indicate the effectiveness of our approach and the role of prior information and production data in reproducing fracture connectivities and preferential flow paths.
Analysis of Oil/Water-Flow Tests in Horizontal, Hilly Terrain, and Vertical Pipes
Authors: Abduvayt P. , Manabe R. , Watanabe T. , Arihara N.
Published: April 2006

Flow pattern, pressure drop, and water holdup were measured for oil/water flow in horizontal, hilly terrain (±0.5 and ±3°), and vertical pipelines at a temperature of approximately 35 (±5) °C and a pressure of approximately 245 kPa using the large-scale multiphase-flow test facility of Japan Oil, Gas and Metals Natl. Corp. (JOGMEC). Test lines of 4.19-in. (106.4-mm) inner diameter (ID) and 120-m total length were used, which included a 40-m horizontal or hilly terrain (near-horizontal) and a 10-m vertical test section sequentially connected. The flow pattern was determined by visual observation with video recordings, and a flow-pattern map was made for each condition.

New flow patterns were identified for horizontal and hilly terrain flow such as oil flow in a snake-like shape at top of pipe at high rate of water flow and water flow at bottom of pipe at high rate of oil flow.

New holdup and pressure-drop data are presented for each flow condition. Flow rate and inclination angle influence holdup and pressure-drop behaviors. In vertical flow, when the oil superficial velocity exceeds a certain value, the pressure drop decreases exponentially as the superficial oil velocity, vSO, increases.

Slippage between the phases was analyzed using the measured water holdup plotted against the input water cut with inlet-oil flow rate as a parameter and slip velocity vs. measured water holdup. It was found that the slippage changed significantly with slight changes in inclination angle.

This paper provides new experimental data of flow pattern, water holdup, and pressure drop measured particularly at horizontal, hilly terrain, and vertical conditions, with large-diameter pipes. This is indispensable information for developing reliable prediction models for oil/water two-phase and gas/oil/water three-phase flow in pipelines.
Compositional Modeling by the Combined Discontinuous Galerkin and Mixed Methods
Authors: Hoteit H. , Firoozabadi A.
Published: April 2006

In this work, we present a numerical procedure that combines the mixed finite-element (MFE) and the discontinuous Galerkin (DG) methods. This numerical scheme is used to solve the highly nonlinear coupled equations that describe the flow processes in homogeneous and heterogeneous media with mass transfer between the phases. The MFE method is used to approximate the phase velocity based on the pressure (more precisely average pressure) at the interface between the nodes. This approach conserves the mass locally at the element level and guarantees the continuity of the total flux across the interfaces. The DG method is used to solve the mass-balance equations, which are generally convection-dominated. The DG method associated with suitable slope limiters can capture sharp gradients in the solution without creating spurious oscillations. We present several numerical examples in homogeneous and heterogeneous media that demonstrate the superiority of our method to the finite-difference (FD) approach. Our proposed MFE-DG method becomes orders of magnitude faster than the FD method for a desired accuracy in 2D.
Unified Model of Heat Transfer in Gas/Liquid Pipe Flow
Authors: Zhang H.-Q. , Wang Q. , Sarica C. , Brill J. P.
Published: April 2006

A unified model of multiphase heat transfer is developed for different flow patterns of gas/liquid pipe flow at all inclinations −90° to +90° from horizontal. The required local flow parameters are predicted by use of the unified hydrodynamic model for gas/liquid pipe flow recently developed by Zhang et al. (2003a, 2003b). The model prediction of the pipe inside convective-heat-transfer coefficients are compared with experimental measurements for a crude-oil/natural-gas system in horizontal and upward-vertical flows, and good agreement is observed.
Including Nonequilibrium Relaxation in Models for Rapid Multiphase Flow in Wells
Authors: Civan Faruk
Published: April 2006

The modeling of rapid flow of multiphase reservoir fluids in wells involving nonequilibrium partial separation of dissolved gases from the metastable oil and water phases is reviewed and formulated. The multiphase-fluid flow is described by means of the differential mass, momentum, and energy-balance equations along the well. The rate of gas transfer from the metastable liquid phases to the gas phase is expressed in terms of the relaxation time determined by the prevailing gas-phase volume fraction and the pressure and temperature conditions. The differential equations are solved numerically under a typical scenario involving the constant gas-, oil-, and water-production rates at the wellhead. It is demonstrated that the nonequilibrium saturation and pressure distributions in wells deviate from the equilibrium results, depending on the variation of the local relaxation time along the well. It is concluded that inclusion of nonequilibrium relaxation effects in models for rapid multiphase flow in wells is required.
Practical Considerations for Pressure-Rate Deconvolution of Well-Test Data
Authors: Levitan Michael M. , Crawford Gary E. , Hardwick Andrew
Published: April 2006

Pressure-rate deconvolution provides equivalent representation of variable-rate well-test data in the form of characteristic constant rate drawdown system response. Deconvolution allows one to develop additional insights into pressure transient behavior and extract more information from well-test data than is possible by using conventional analysis methods. In some cases, it is possible to interpret the same test data in terms of larger radius of investigation.

There are a number of specific issues of which one has to be aware when using pressure-rate deconvolution. In this paper, we identify and discuss these issues and provide practical considerations and recommendations on how to produce correct deconvolution results. We also demonstrate reliable use of deconvolution on a number of real test examples.
Lessons From Integrated Analysis of GOM Drilling Performance
Authors: Iyoho A. W. , Meize R. A. , Millheim K. K. , Crumrine M. J.
Published: April 2006

Offshore drilling continues to be extremely cost intensive, with U.S. $50 million wells not uncommon. This paper discusses one company's experience and the lessons it learned from a comprehensive analysis of Gulf of Mexico (GOM) historical data for drilling-performance benchmarking and continuous cost reduction. Drilling operations were broken down into discrete activities, and the best times from all the wells—including trouble time—were aggregated to form the "best composite time" (BCT). The BCT, introduced in recent papers,1–3 was applied, along with learning-curve analysis and other investigative tools, to examine drilling problems and the lessons learned to capture the best practices and, there by, challenge well-planning and construction practices.

The "best composite cost" (BCC), or the monetary equivalent of the BCT, was also calculated and used for well-cost benchmarking. Correlative analyses of the wells (i.e., crossplots of drilling events along side mud-log data, wireline logs, and geologic data) were used to elucidate major well problems and abnormal flat times that caused deviations from the BCT. Correlative analysis also helped explain why some wells were drilled relatively trouble-free, even in difficult environments.

From a more detailed trouble-time analysis of company-operated wells, tool/equipment failure was seen as a significant trouble-time component. Major drilling problems were also found to be mostly well-pressure related (e.g.,well control, lost circulation, and stuck pipe), supporting increased emphasison improved planning and quantification of equivalent circulating density(ECD), deepwater geopressures, and narrow drilling margins, especially in ultradeepwater environments. Overall, the company's 2003 trouble time was 26% of the total drilling time from spud to rig release.

The BCT/BCC methodology is actually one element of "The Ten-Step Process" discussed exhaustively in Refs. 1 and 2. Applications to two onshore areas, so far, have shown encouraging results in drilling-costreduction. Applications to more-complicated offshore GOM wellbores, cost components, and narrow geopressure margins are the focus of this paper. The fields investigated are located in different parts of the GOM (Table 1). For brevity, results are shown only for the subsalt area of South Timbalier, the deepwater Green Canyon (GC) area, and the ultradeepwater eastern Gulf of Mexico(EGOM).
Well-Control Analyses on Extended-Reach and Multilateral Trajectories
Authors: Choe Jonggeun , Schubert Jerome J. , Juvkam-Wold Hans C.
Published: April 2006

For economic and technical reasons, the industry has used directional, extended-reach, horizontal, and multilateral wells. Although technologies are well developed for these wells, and there are numerous successes in the last decade, these wells still have high level of risk in drilling and completion. Well control is one of the relatively unanswered, but important, operations because improper well control, followed by a blowout is one of the most expensive and feared operational hazards.

To maintain a specified bottomhole pressure (BHP), surface choke pressures highly depend on kick vertical height in the well and well trajectory. As the final hold angle of the well increases from vertical, shut-in casing pressure (SICP) reduces to shut-in drillpipe pressure (SIDPP) and remains the same as long as the kick stays in the horizontal section. For equal vertical depths, the maximum choke pressure is insensitive to hold angles or hold lengths, aslong as the initial pit-volume gain is the same. However, for directional andextended-reach wells, choke pressure can increase, even without kick expansion, because of the gain of kick vertical height in the build section. This may maskchoke-pressure reduction because of larger annular capacity when the kick passes the casing shoe, especially if the kickoff point (KOP) and casing-shoe depth are close.

In multilateral wells with more than one kicking wellbore, SIDPP is affected by both formation over pressure and kick size in each wellbore. The maximum value among them will appear at the surface. Therefore, we should be careful in the interpretation of the shut-in pressures. For safe kick circulation, we must consider additional pressure to compensate for hydrostatic-pressure reduction resulting from kick migration and expansion in branch wellbores.
The Multi PDZ Domain Protein MUPP1 as a Putative Scaffolding Protein for Organizing Signaling Complexes in the Acrosome of Mammalian Spermatozoa
Authors: Heydecke Diana , Meyer Dorke , Ackermann Frauke , Wilhelm Beate , Gudermann Thomas , Boekhoff Ingrid
Published: April 2006

ABSTRACT: Spermatozoa undergo complex sequences of precisely timed events during the process of fertilization. These priming events, which comprise capacitation, egg recognition, acrosome reaction, and sperm‐oocyte fusion, are regulated by the activation of different intracellular signaling pathways. The efficacy and accuracy of signal transduction pathways often depend on the assembly of multiprotein signaling complexes, thereby coordinating and guiding the flow of regulatory information. To address the question whether PDZ‐domain proteins, the most abundant protein interaction modules involved in the assembly of supramolecular signaling complexes, are present in rodent sperm, homologue of the RT‐PCR approaches were performed with specific primer pairs for the vertebrate INAD‐like PDZ domain protein MUPP1. The results revealed that this scaffolding protein, which comprises 13 different PDZ domains, is expressed in mouse testis. To obtain further support for the expression of the multi‐PDZ domain protein MUPP1 in testicular tissue, immunohistochemical as well as immunocytochemical experiments were performed using a MUPP1‐specific antibody. Detailed analyses of the spatial MUPP1‐expression profile revealed that immunoreactivity is concentrated within the acrosomal region of round as well as elongated mouse spermatozoa. These results were confirmed in experimental approaches demonstrating that MUPP1 immunofluorescence was shed off from the acrosome region after acrosome reaction. To examine whether MUPP1 is also present in other mammalian sperm, immunocytochemical approaches were performed with isolated bovine as well as human sperm. The results revealed prominent MUPP1 expression which was restricted to the apical acrosomal region and, most notably, to the equatorial segment of the acrosome. The predominant expression profile of MUPP1 in sperm of different mammalian species suggests that this PDZ‐domain protein may be involved in organizing signaling molecules mediating primary reactions of fertilization.
Irradiated Mouse Testes Efficiently Support Spermatogenesis Derived From Donor Germ Cells of Mice and Rats
Authors: Zhang Zhen , Shao Shan , Meistrich Marvin L.
Published: April 2006

ABSTRACT: Testicular cell transplantation has been widely used to investigate the biology of spermatogonial stem cells, production of transgenic animals, and restoration of fertility in rodent models. One critical step in successful transplantation is the preparation of the recipient testes. Busulfan has been widely used, but irradiation has been often suggested as an alternative. There have only been limited reports of the use of irradiated animals as transplant recipients for studying differentiation of transplanted cells, and there has been no direct comparison of irradiation and busulfan as preparation methods. Mouse testes treated with local fractionated irradiation (1.5 + 12 Gy) were compared with busulfan‐treated testes as recipients using mouse‐to‐mouse and rat‐to‐mouse germ cell transplantation. The fractionated irradiation schedule resulted in depletion of endogenous spermatogenesis similar to that produced by busulfan doses of 50–55 mg/kg. When immature mouse or rat testicular germ cells were transplanted into the irradiated testes, donor cells derived from either rat or mouse spermatogonial stem cells were able to form colonies of differentiated spermatogenic cells 10–13 weeks after transplantation with similar efficiencies as in busulfan‐treated testes. Locally irradiated testes could be considered as an alternative to busulfan treatment for animal recipients of germ cell transplants that cannot endure the systemic toxicity of busulfan.
Understanding rural Zambia today: the relevance of the Rhodes-Livingstone Institute
Authors: van Donge Jan Kees
Published: April 2006

Opening Paragraph

In the colonial period Zambia, then Northern Rhodesia, was a field for brilliant social research. The social scientists who worked at the Rhodes-Livingstone Institute (hereafter abbreviated to RLI) in Lusaka produced studies which can be found in libraries throughout the world. Yet the relevance of this literature for understanding present-day Zambia may not be immediately obvious. Our knowledge of society turns into historical knowledge, especially when great social changes such as decolonization take place. Social scientists inevitably capture one particular historical moment. The work of those connected with the RLI can therefore be treated as part of history; Kuper (1973) has characterised its role in the development of British anthropological thought as a part of the history of ideas, and Brown (1973, 1979) has written evocative accounts of the involvement of its members in the country as an example of the white man's presence in Africa.