bluuebunny/crossref_metadata_2025_split huggingface dataset:
Production Forecasting of an Unstable Compacting Chalk Field Using Uncertainty Analysis
Authors: Hegdal T. , Dixon R. T. , Martinsen R. 
Published: December 2007

Summary
Past years' forecasting performance has demonstrated that single "most likely" (deterministic) prediction of future production, without quantifying the associated uncertainties, is inadequate for management and planning purposes. Based on this an effort was initiated to improve the forecasting methodology and procedures with special emphasis on quantifying the uncertainty in short-term production forecasting (STPF).
The Valhall field, offshore Norway, presented special problems for production forecasting because many unusual events affect production, even for STPF. The soft compacting reservoir chalk causes well collapses and chalk influxes and makes drilling difficult. Modeling of reservoir fracturing and therefore well performance is also uncertain.
A probabilistic forecasting approach was adopted using a customized spreadsheet and commercially available statistical analysis add ins which allowed deterministic forecasting, partially probabilistic analysis, or fully integrated uncertainty analysis. Uncertainties were characterized by distributions based on historical data where possible.
Communication and integration of knowledge were also key success factors since the process required input from several departments and many individuals to ensure that the "company knowledge" was fully reflected. A "common language" to communicate uncertainty and an auditable process to ensure buy in and consistency were also critical.
A Study of the Chemical Interactions Between Brine Solutions and Dolomite
Authors: Zou B. , McCool C. S. , Green D. W. , Willhite G. P. 
Published: December 2007

SummaryApplication of gelled polymer treatments to change the flow characteristics of a reservoir is a viable improved oil recovery technique. Many gel systems are affected by the solution pH in that gel time is pH dependent. The treatment of carbonate reservoir rock is of particular concern because (1) fluid-rock interaction can alter the pH of the injected solution from the design value and (2) dissolution of carbonate can increase the divalent ion concentration, which can also affect gelation behavior.In this study, the interaction between injected potassium chloride brine and dolomite was investigated through displacement experiments in dolomite cores and mathematical modeling based on equilibrium thermodynamics. Parameters varied were pH of the injected solution, flow rate, and the common ion effect through variation of the calcium and magnesium ion concentrations in the injected solution. Core effluent values of pH and concentrations were measured. Experiments at different flow rates established conditions in which equilibrium was achieved in the core. Equilibrium values of pH were almost constant at a value of 10 when the injected pH was varied between 4 and 10. Results indicate that equilibrium conditions exist for most field conditions.A geochemical model was used to predict equilibrium pH and concentrations, as well as the amount of dolomite dissolved. The model accurately predicted effluent pH of experimental displacement data for the conditions wherein equilibrium was achieved. All model parameters were obtained from literature equilibrium data and were not dependent on curve fitting of the experimental data.
Understanding Wormholing Mechanisms Can Improve Acid Treatments in Carbonate Formations
Authors: Buijse M. A. 
Published: December 2007

SummaryIn this paper, acid wormholing in carbonate formations is studied. The wormhole growth rate and the geometry of the final worm-hole pattern depend on the combined effect of acid spending and fluid flow. Acid spending is studied by modeling the wormhole as a cylindrical pore and numerically solving the convection-diffusion equations. A finite acid-rock reaction rate is assumed, allowing calculation and study of spending profiles in both the diffusion-controlled and the reaction-controlled regime. Flow properties such as fluid loss from wormhole to formation and fluid distribution in a multiple wormhole geometry are studied through numerical simulations. It is shown how wormhole growth properties are affected by the length and distance of neighboring worm-holes. The effect of injection rate and diffusion is studied with a simple model. This model explains several experimentally observed phenomena, such as the existence of an optimum injection rate and a reduced wormhole efficiency at higher rates.
Multipurpose Wells: Downhole Oil/Water Separation in the Future
Authors: Stuebinger L. A. , Elphingstone G. M. 
Published: December 2007

Summary
Promising new technologies are being advanced to reshape development strategies in your fields. It is not always necessary to dedicate wells to production or injection; now, both functions can be performed within one multipurpose wellbore. Technologies exist to reduce water-handling volumes at the surface by keeping the water downhole.
The discovery of downhole oil, water, and gas gravity segregation in the wellbore and the ability to keep fluids separated makes it possible to generate revenue from a wellbore at the same time that it is injecting or disposing water. This paper will discuss:
design and testing at the Rocky Mountain Oilfield Testing Center of the first downhole oil-water separation artificial lift system to utilize downhole gravity segregation; evolving modeling procedures; superior environmental performance; impediments to deploying radically new technologies; and a vision of the future.
Field Results of Separation-Vessel and Multiphase-Flowline Debottlenecking Using an In-line Gas/Liquid Auger Separator
Authors: Weingarten J. S. 
Published: December 2007

Summary
Field results of Auger separator installations are presented which demonstrate the following new applications of in-line gas/liquid partial separation: (1) increasing separation vessel capacity (or reducing required vessel size for a given flow rate) and (2) reducing pressure drop in multiphase lines that transport produced hydrocarbons. The Auger separator is a device which partially separates liquid and gas, has no moving parts, and requires no power or level controls. The diameter of the separator is typically a few inches, generally about the same diameter as the line, and is installed as a spool piece in the line. In one application, a field test was conducted where the Auger separator was placed just upstream of a conventional test separator. By removing a portion of the gas upstream, the liquid capacity of the vessel was approximately doubled. In a different application, Auger separators were installed to remove gas from multiphase-flowlines and provide raw gas lift on the drillsite. By doing this, the amount of gas in the production line was reduced, decreasing the backpressure and increasing the capacity for produced fluids. The operating conditions before and after the installations, equipment descriptions and photographs, piping layouts, and operational considerations are included. The design of the Auger separators and performance comparisons to predictions from design equations are also discussed.
Efficient Finite-Difference Model for Flow in a Reservoir With Multiple Length-Scale Fractures
Authors: Lee S. H. , Jensen C. L. , Lough M. F. 
Published: December 2007

Summary
In this paper we describe a hierarchical approach for modeling fluid flow in a naturally fractured reservoir with multiple length-scale fractures. Based on fracture length relative to the finite-difference grid size, fractures are classified as short disconnected fractures, medium-length fractures, and long fractures. Effective grid-block permeabilities, associated with the short-and medium-length fractures, are used as input to a finite-difference simulator. We also present a separate transport equation for flow through long fractures to capture effects of large-scale high permeability pathways. Simulation results from the new hierarchical approach are compared with those from the conventional dual porosity/permeability model.
Helical Buckling of Pipe With Connectors in Vertical Wells
Authors: Mitchell R. F. 
Published: December 2007

Summary
The effect of connectors on pipe buckling is acknowledged, but has received little attention. Lubinski analyzed the effect of connectors on pipe in tension in a curved borehole, while Paslay and Cernocky extended this analysis to pipe in compression. These papers indicate that bending stresses are greater due to connector standoff. However, these papers do not consider a buckled pipe.
This paper presents an analytic solution of the beam-column equations in three dimensions for a helically buckled pipe with connectors in a vertical well. For low axial compression, the solution approximates helically buckled pipe without connectors, however, at higher axial forces, the effects of connectors on contact forces and bending stress becomes significant. Sag between connectors is calculated so that pipe body contact between connectors can be determined.
Applications include the analysis of bottomhole assemblies, drillpipe, casing, and tubing. The solutions are simple formulas that are suitable for hand calculations.
Geomechanical Modeling of Reservoir Compaction, Surface Subsidence, and Casing Damage at the Belridge Diatomite Field
Authors: Fredrich J. T. , Arguello J. G. , Deitrick G. L. , de Rouffignac E. P. 
Published: December 2007

Summary
Geologic, and historical well failure, production, and injection data were analyzed to guide development of three-dimensional geomechanical models of the Belridge diatomite field, California. The central premise of the numerical simulations is that spatial gradients in pore pressure induced by production and injection in a low permeability reservoir may perturb the local stresses and cause subsurface deformation sufficient to result in well failure. Time-dependent reservoir pressure fields that were calculated from three-dimensional black oil reservoir simulations were coupled unidirectionally to three-dimensional nonlinear finite element geomechanical simulations. The reservoir models included nearly 100,000 gridblocks (100 to 200 wells), and covered nearly 20 years of production and injection. The geomechanical models were meshed from structure maps and contained more than 300,000 nodal points. Shear strain localization along weak bedding planes that causes casing doglegs in the field was accommodated in the model by contact surfaces located immediately above the reservoir and at two locations in the overburden. The geomechanical simulations are validated by comparison of the predicted surface subsidence with field measurements, and by comparison of predicted deformation with observed casing damage. Additionally, simulations performed for two independently developed areas at South Belridge, Secs. 33 and 29, corroborate their different well failure histories. The simulations suggest the three types of casing damage observed, and show that, although water injection has mitigated surface subsidence, it can, under some circumstances, increase the lateral gradients in effective stress that in turn can accelerate subsurface horizontal motions. Geomechanical simulation is an important reservoir management tool that can be used to identify optimal operating policies to mitigate casing damage for existing field developments, and applied to incorporate the effect of well failure potential in economic analyses of alternative infilling and development options.
Novel Application of Emulsified Acids to Matrix Stimulation of Heterogeneous Formations
Authors: Buijse M. A. , van Domelen M. S. 
Published: December 2007

SummaryHistorically, emulsified acids have primarily been used in fracture acidizing. By combining information from theoretical studies, experimental studies, and field testing, a better understanding has recently been gained of the application of emulsified acids in matrix acidizing. This paper discusses the use of emulsified acid as a stimulation fluid for matrix treatments in heterogeneous carbonate formations.Emulsified acid is diffusion retarded which makes it an effective wormholing fluid at low injection rates that occur, for example, in low permeabiliy or damaged formations. At these low rates, plain HCl acid will mostly spend on the formation face and is unable to create wormholes that penetrate deep into the formation.In this paper, results of flow tests are presented that compare the efficiency of emulsified acid with that of plain HCl acid. Several emulsified acid systems were tested. The effects of the injection rate, viscosity, and acid/oil volume ratio were analyzed on core samples. Rheological properties and temperature stability (up to 250°F) of the emulsion systems were analyzed by means of Fann-50 tests.Acid-in-oil emulsions are effective stimulation fluids in large intervals where streaks of high permeability can act as thief zones. This is shown by means of example calculations of the fluid flow and distribution in a well.
Reaction Rate and Fluid Loss: The Keys to Wormhole Initiation and Propagation in Carbonate Acidizing
Authors: Huang Tianping , Hill A. D. , Schechter R. S. 
Published: December 2007

SummaryThe efficiency of the matrix acidizing process in carbonates depends strongly on the wormholing phenomenon—if wormholes are formed, the effects of near-wellbore damage can be overcome with relatively small volumes of acid. Numerous previous studies have shown that wormhole patterns can be placed in these general categories: compact dissolution in which most of the acid is spent near the rock face; the wormholing pattern; and uniform dissolution in which many pores are enlarged, as typically occurs in sandstone acidizing. We have developed a theory of the wormholing process, which predicts when the wormholing pattern is most efficiently created as a function of the acid flux and other treatment variables.By testing this theory with several independent sets of laboratory data, we can now demonstrate the important roles that surface reaction rate and fluid loss play in the wormholing process. This theory accurately predicts the optimal flux (that which leads to dominant wormholes with a minimum of branching, and hence, a minimum acid volume) for experiments with HCl in limestone and dolomite at several temperatures and with acetic acid in limestone. The surface reaction rate differs by several orders of magnitude in these experiments and is the only process variable that differs greatly among them. Paradoxically, though wormholes are formed because the overall reaction rate is controlled by mass transfer in the wormholes, diffusion rates play only a minor role in the wormholing process.Fluid loss through the walls of the wormholes ultimately limits the distance to which wormholes can propagate. Because of this effect, laboratory linear corefloods will give optimistic predictions of wormhole penetration distances. We developed a cylindrical flow model to represent the flow field around a wormhole propagating from a wellbore which illustrates how to translate laboratory results to field conditions.We have used these theories to predict optimal acid formulations and injection rates for field conditions. In general, the lower the reaction rate (such as at low temperatures in dolomites or with weak acids in limestone), the lower the injection rate required, making it easier to propagate dominant wormholes under matrix treating conditions in the field.
Effect of Brine Salinity and Crude-Oil Properties on Oil Recovery and Residual Saturations
Authors: Sharma M. M. , Filoco P. R. 
Published: December 2007

SummaryCentrifuge experiments were conducted on Berea cores to measure the drainage and imbibition relative permeabilities in two-and three-phase systems. Three crude oils, Prudhoe Bay and Shell Mars A-1 and A-20 crude were used in our tests. No effect on oil recovery was obtained in the drainage experiments when the crude oil was displaced by air at connate water. However, in the imbibition experiments the oil recovery increased significantly with the salinity of the connate brine. The salinity of the displacing brine had no significant influence on the oil recovery. The relative permeability curves obtained during drainage were also found to be insensitive to the salinity of the brine. However, the imbibition relative permeability curves show strong salinity dependence. A comparison of the two crude oils and a nonpolar mineral oil indicates that the more water-wetting Mars crude oil shows a higher oil relative permeability at the same bond number compared to the mixed-wetting Prudhoe Bay crude oil. The salinity dependence of the residual saturations and the relative permeabilities clearly indicate that the change in wetting properties of the rocks surfaces from water-wet to mixed-wet during the drainage process is an important factor controlling the imbibition relative permeability curves. This suggests that the performance of waterfloods will be strongly affected by the composition of the crude oil and its ability to wet the rock surfaces, the salinity of the connate brine in the reservoir, and the height above the oil/water contact.
Litho-Facies and Permeability Prediction From Electrical Logs Using Fuzzy Logic
Authors: Cuddy S. J. 
Published: December 2007

Summary
Several areas of the geosciences have benefitted from the application of the new mathematics of "fuzzy logic."1,2 The oil industry now routinely uses new interpretation techniques, based on fuzzy logic, to predict permeability and litho-facies in uncored wells. Litho-facies and permeability prediction have presented a challenge to formation evaluation due to the lack of tools that measure them directly. The method described can be used as a simple tool for confirming known correlations or as a powerful predictor in uncored wells.
Fuzzy logic is simply an application of recognized statistical techniques. Whereas conventional techniques deal with absolutes, the new methods carry the inherent error term through the calculation rather than ignoring or minimizing it. This retains the information associated with the error and gives surprisingly better results.
One clear application is to litho-facies determination. Litho-facies typing is used in well correlation and is important for building a three-dimensional model of an oil or gas field. The technique makes no assumptions and retains the possibility that a particular litho-facies type can give any well log reading although some are more likely than others. This error or fuzziness has been measured and used to improve the litho-facies prediction in several North Sea fields. In one study, descriptions from 10 cored wells were used to derive litho-facies descriptions in 30 uncored wells. This technique gave near-perfect differentiation between aeolian, fluvial, and sabkha rock types. In addition, it went some way towards differentiating between sandy, mixed, and muddy sabkhas. Using the fuzzy logic technique gives much better predictions than more complicated methods such as neural networks or cluster analysis.
A second application is permeability calculation. Knowledge of permeability is important in determining the well completion strategy and the resulting productivity. The problem with permeability prediction is derived from the fact that permeability is related more to the aperture of pore throats rather than pore size, which logging tools find difficult to measure. Determining permeability from well logs is further complicated by the problem of scale, well logs having a vertical resolution of, typically, 2 ft compared to the 2 in. of core plugs. The new techniques quantify these errors and use them, together with the measurement, to improve the prediction. This new approach has been used in several fields to obtain better estimates of permeability compared to conventional techniques. In addition, the method uses basic log data sets such as gamma ray and porosity rather than depending on new logging technology.
Unified Mechanistic Model for Steady-State Two-Phase Flow: Horizontal to Vertical Upward Flow
Authors: Gomez L. E. , Shoham Ovadia , Schmidt Zelimir , Chokshi R. N. , Northug Tor 
Published: December 2007

Summary
A unified steady-state two-phase flow mechanistic model for the prediction of flow pattern, liquid holdup and pressure drop is presented that is applicable to the range of inclination angles from horizontal (0°) to upward vertical flow (90°). The model is based on two-phase flow physical phenomena, incorporating recent developments in this area. It consists of a unified flow pattern prediction model and unified individual models for stratified, slug, bubble, annular and dispersed bubble flow. The model can be applied to vertical, directional and horizontal wells, and horizontal-near horizontal pipelines. The proposed model implements new criteria for eliminating discontinuity problems, providing smooth transitions between the different flow patterns.
The new model has been initially validated against existing, various, elaborated, laboratory and field databases. Following the validation, the model is tested against a new set of field data, from the North Sea and Prudhoe Bay, Alaska, which includes 86 cases. The proposed model is also compared with six commonly used models and correlations. The model showed outstanding performance for the pressure drop prediction, with a −1.3% average error, a 5.5% absolute average error and 6.2 standard deviation. The proposed model provides an accurate two-phase flow mechanistic model for research and design for the industry.
Horizontal-Wellbore Stability and Sand Production in Weakly Consolidated Sandstones
Authors: van den Hoek P. J. , Kooijman A. P. , de Bree P. , Kenter C. J. , Zheng Z. , Khodaverdian M. 
Published: December 2007

SummaryLong-term stability of horizontal wellbore completions with uncemented liners in weakly consolidated to unconsolidated sandstone formations (e.g., the Gulf of Mexico and Nigeria) remains an area of concern. In this paper we present the results of dedicated polyaxial cell laboratory experiments that address this issue. In addition, the influence of rock failure in the near-wellbore region on well productivity was studied.Large blocks of a weak artificial sandstone were prepared. A hole was drilled in these blocks, and production conditions at various values of in-situ stress, drawdown and water cut, both in the absence and presence of a liner, were simulated. During testing, the hole was kept at a horizontal position in order to realistically simulate the influence of gravity forces on the movement of sand debris. The process of hole failure and re-stabilization was continuously monitored by an endoscope coupled to a video camera.The experimental results show that in the presence of a slotted liner, and in the absence of a water cut, rock failure leads to gradual annulus fillup with loose sand, eventually resulting in a stable configuration in which only a small fraction of the far-field stresses is transferred to the liner. These results are further supported by elasto-plastic calculations. Rock failure around the liner is shown to have only a minor effect on productivity. This result implies that rock failure around uncemented liner completions will generally not be noticed at the wellhead.The introduction of a small (&lt;5%) water cut resulted in massive sand production and subsequent liner collapse. This can be explained by the fact that a water cut destroys capillary cohesion, thereby destabilizing sand arches over the slots.