bluuebunny/crossref_metadata_2025 huggingface dataset:
The Treatment of Wells, Faults, and Other Singularities in a Black-Oil, Finite-Element Reservoir Simulator
Authors: Shaw D. C.
Published: December 2007

Several previous studies have applied finite-element techniques to reservoir simulation problems. However, these methods prove to be very complicated in the general case, and are not competitive with finite-differences in terms of equivalent speed for a given accuracy. In particular, most previous work has been on, at most, two-dimensional and two-phase problems. The full black-oil and three-dimensional case has been avoided because of its complexity.

By choosing only linear test functions and a first-order approximate integration scheme, the finite-element method simplifies enormously, yielding difference equations no more difficult than finite-differences. At the same time, the scheme has the improved convergence and grid-orientation insensitivity reported earlier in the literature. For equivalent accuracy, computing expense is therefore less than for finite-differences.

The method also allows a more accurate representation of singularities and discontinuities. They both introduce less truncation error with this method and can be located more precisely within a grid. Furthermore, they preserve the banded structure of the matrix problem, without the off-band connections typical of finite-differences.

Numerical results are presented demonstrating improved convergence, accuracy and the effects of locating a well more precisely within an element.
Full-Field Compositional Simulation of Reservoirs With Complex Phase Behavior
Authors: El-Mandouh M. S. , Bette Srinivas , Heinemann R. F. , Ogiamien E. B. , Bhatia S. K.
Published: December 2007

This paper describes the application of compositional reservoir simulation techniques in the management of large reservoirs. The equation-of-state compositional simulator was specifically enhanced to address several technical challenges, such as geologic heterogeneities including crossing faults and widely varying permeability, complex phase behavior of a near-critical fluid, and involved surface facilities operational constraints.

The application of the simulator to the Oso field in Nigeria is presented. The Oso field has two reservoirs. This field study reports on the major reservoir which contains a near-critical fluid and has a highly faulted structure. The fault model, in addition to accurately representing geologic faults and the associated flow across different layers, also reduced computational requirements considerably over the old conventional methods for fault representation. The reservoir fluid and its behavior near the critical region was characterized accurately using an 8-component, equation-of-state model.

The application of the model in the study of reservoir recovery under various production scenarios is discussed. The displacement mechanisms involved in the different depletion strategies are explained through a series of 1-dimensional simulations. This integrated approach in reservoir management enables us to determine an optimal development plan and surface facilities design parameters for the Oso reservoir.
Development of a Mixed Finite-Element-Based Compositional Reservoir Simulator
Authors: Durlofsky L. J. , Chien M. C. H.
Published: December 2007

Geometrically complex geological features, such as faults, cross stratified beds and large scale inclined strata, can have very significant effects on the flow of reservoir fluids. Standard finite difference methodology lacks the geometric flexibility required for modeling flow through or around such structures. Triangle based discretization methods, by contrast, offer an attractive means to discretize and simulate flow through geometrically complex features accurately.

In this paper, a triangle based mixed finite element – finite volume technique for compositional reservoir simulation is developed. The formulation is of IMPES type and is applicable to three phase, multicomponent systems in two dimensions. Most previous mixed finite element formulations were restricted to two phase or fully miscible systems. The compositional approach presented here extends these earlier techniques though it retains the general structure of the more limited formulations. Specifically, the governing equations are cast in terms of a pressure equation and a series of component mass balance equations expressed in terms of the ‘total’ velocity. A triangle based mixed finite element method is applied to the solution of the pressure equation while a finite volume technique is employed for solution of the component mass balance equations. The overall methodology is particularly well suited for the modeling of flow through complex geological strata characterized by heterogeneous, generally anisotropic permeability fields. This is demonstrated explicitly through application of a preliminary implementation of the method to the simulation of flow through a faulted cross section with a complex permeability description. Extension of the formulation to the three dimensional case is also discussed.
The Simulation of Enhanced Oil Recovery Processes Using a Vapor/Liquid Equilibrium Model Based on Critical Scaling Theory
Authors: Sams W. N. , Lynch J. J. , Smith D. H.
Published: December 2007

Vapor-liquid equilibrium (VLB) calculations play an important role in the simulation of enhanced oil recovery (EOR) processes. While reservoir simulators in general must treat the VLE of hydrocarbon mixtures over a wide range of pressures and compositions, the simulation of such EOR processes as vaporizing and condensing gas drives require the VLE algorithm to operate at or near the critical point. Conventional VLE calculations based on cubic equations of state such as the Peng-Robinson or Soave-Redlich-Kwong equation fail to converge or are inaccurate in the critical region. In particular, it is well known that these methods assign the same value.to the critical z-factor for all pure chemical species.

The modified Leung-Griffiths model is a non-cubic, corresponding states theory that conforms to modern scaling laws, which successfully correlates, evaluates, and predicts VLE boundaries for fluid mixtures. The model performs well from the critical locus down to about half of the critical pressure. It has produced excellent correlations of many sets of binary hydrocarbon VLE data. We discuss the recent extension of the model to mixtures with three or more components and its application in a general purpose conpositional simulator. This paper examines how a flash computation is performed with this model, how the singlephase region is detected, and how the derivatives required in the solution of the non-linear flow equations are obtained from the flash computation. The model is coded in a form that makes it interchangeable with conventional VLE models in a wide variety of general purpose compositional simulators.
Cleaning Up Spilled Gasoline With Steam: Compositional Simulations
Authors: Adenekan A. E. , Patzek T. W.
Published: December 2007

A finite-difference compositional simulator has been developed and tested at U.C. Berkeley to model the flow of mixtures of Nonaqueous Phase Liquids (NAPLs) through the air zone and into aquifers. The simulator has been successfully used to history-match a steam injection pilot at a ‘Clean Site’ near the Lawrence Livermore National Laboratory in California -- a test site for the Gasoline Spill Area (GSA) cleanup pilot plannned for early ’93. Because of its multicomponent capabilities, the simulator has been used to calculate (a) production rates of individual gasoline components in the GSA to size treatment facilities, (b) areal and vertical distribution of gasoline after the first cycle of steam injection, and (c) steam injection rate that limits growth of the steam zone beyond the cleanup area. It has been shown that gasoline present in the penneable sands and gravel layers can be successfully recovered by injecting steam into these layers in a 7-spot pattern. For the conditions assumed in the model, it will take less than 16 days to recover nearly all of the gasoline hi the sands and gravel layers. By that time, the maximum aqueous concentrations of all hydrocarbon components in these layers will have dropped to less than 0.01 mg/1. The results show that vaporization, followed by bulk movement of the vapor to the production well is the dominant recovery mechanism. In tenns of time required for cleanup, model results are most sensitive to penneability of the medium. Other parameters, such as the relative penneabilities and the number of components, also affect the outcome, but to a lesser extent.
Vectorization and Parallel Processing of Local Grid Refinement and Adaptive Implicit Schemes in a General Purpose Reservoir Simulator
Authors: Chien M. C. H. , Northrup E. J.
Published: December 2007

With less computer memory usage and a fewer number of calculations, local grid refinement and adaptive implicit schemes can effectively achieve similar accuracy as fully refined, fully implicit schemes. However, these methods become less appealing on a vector processor because they are not as susceptible to vectorization as the latter. This paper discusses the development of a vectorized, parallel-processed algorithm for the local grid refinement and adaptive implicit schemes in a general purpose reservoir simulator. The adaptive implicit scheme is considered as a subset of the dynamic, multilevel, mixed implicit, local grid refinement models.

The algorithm was tested on an enlarged 12th SPE comparative solution problem. Results indicate a fivefold speed improvement due to vectorization. Compared to a fully implicit, fully refined model, the local grid model requires 63% less computer memory and 42% less computer time without notable loss of accuracy.
Time-Dependent Incorporation of Locally Irregular Grids in Large Reservoir Simulation Models
Authors: Deimbacher F. X. , Heinemann Z. E.
Published: December 2007

In field-scale reservoir simulation the demands to the grid-in-use may change significantly during a simulation run. Introduction of new wells (vertical and horizontal ones) at a later stage of the simulation run, phase breakthrough or coning may require a different grid than initially set up.

While in the past the reservoir simulation grid was considered static, this paper will describe a novel approach of a dynamically used grid. It is only applied locally and just for a specific time period. The geometry within such a local subdomain (window) may be regular or irregular and the grid construction is based upon the principle of perpendicular bisectors (PEBI or VORONOI grid).

Windows may be incorporated into the standard Cartesian simulation grid at any time and at any location. No non-neighborhood connections are used. The windows are linked to the system of equations based on their natural sequence and they are "switched on and off" as required. A multiple timestepping technique is applied that allows the use of different timestep lengths inside and outside the windows.

Examples will demonstrate the potential of this new concept. A local radial grid may be used for well test simulation, or arbitrary direction horizontal wells may be incorporated after history matching. The whole simulation is conducted using the familiar Cartesian grid with the irregular grids included only during a short period.
Validation of an Adaptive, Orthogonal, Curvilinear Gridding Procedure for Reservoir Simulation
Authors: Sharpe H. N.
Published: December 2007

This paper focusses on demonstrating the computational advantages of boundary-conforming, adaptive orthogonal grid systems to practical reservoir simulation problems. We show Improvements In computational efficiency and solution accuracy, with minimum disruption to most existing reservoir simulation codes.
Dynamically Adaptive Godunov Schemes with Renormalization in Reservoir Simulation
Authors: Edwards Michael , Christie M. A.
Published: December 2007

Simulation of unstable flow pr.cesses requires the use of both accurate and efficient techniques. Accurate results have been obtained efficiently for flow in a uniform permeability field, by using a higher order Godunov scheme combined with dynamic grid adaptivity. Application of the adaptiye higher order scheme to unstable flows resuiting from a randomly varying permeability field is described here. Use of dynamic grids with varying levels of refinement demands an adaptive definition of the permeability field. Effective permeabilities of coarsened grid blocks are defined by local cell renormalization. High resolution results are obtained together with large savings in computer time.
A Finite-Element Black Oil Simulation System for Heterogeneous Reservoirs with Horizontal Wells Having Vertical Hydraulic Fractures
Authors: Kocberber Sait
Published: December 2007

In this study, a newly developed threedimensional, fully implicit, finite element black oil simulation system for heterogeneous reservoirs with horizontal wells and vertical fractures is presented. This simulation system utilizes an efficient and almost fully automatic three-dimensional finite element grid generation technique with natural grid refinement capabdities around wells and fractures. The region between the well/fracture system and the outer boundary is gridded by an automatic tettahedronization scheme such that selective refinement and accurate representation of heterogeneities are achieved. The result is a fine and well graded grid based on expected flow patters around the well/fiacture system.

In this simulation system the wellbore is tteated as a hollow tube. The multi-phase black oil flow within fractures is accurately modeled including variable fracture conductivity. Furthermore fracture and reservoir flow equations are analyticaly coupled utilizing continuity of fluxes at the domain interfaces. This allows easy application of established black oil simulation techniques to reservoirs with horizontal wells and vertical fractures.

The use of the model is demonstrated in simulating waterflooding in a square reservoir using one horizontal injection well and two vertical production wells. The model seems to produce accurate numerical results almost free of grid orientation effects.
The Fractal Nature of Viscous Fingering: Saturation Profiles and Fractional Flows From Modeling of Miscible, Two-Component Flows in Two-Dimensional Pore Level Models
Authors: Ferer M. V. , Sams W. N. , Geisbrecht R. A , Smith D. H.
Published: December 2007

Use of saturation-dependent relative mobilities leads to linear flow in wliich the saturations scale as x/t (i.e., position/time). However, experiment and theory liave shown ttiat, in the limit of very large viscosity-ratio, the flow is not linear but fractal. Thus, two questions naturally arise: i) If the actual viscous fingering were fractal, what would be the effect on traditional reservoir simulation? and ii) Is the viscous fingering fratfal for viscosity-ratios of real reservoirs?

To study the first question, we used general arguments to show that fractal flow produces saturations which scale not as x/t but rather as x/t1+ε and fractional flow curves which are functions not solely of saturation S but rather t ε S Thus, when the flow is fractal, fractional flows and the relative mobilities depend on time t and saturation s not solely on saturation. Earlier studies have determined the values of ε : in three dimensions, ε ≈ 1 : in two dimensions, ε ≈ 0.4. Using a standard pore-level model of twodimensional, miscible floods, we have shown that the flow for this model is fractal for a large viscosity-ratio (M=10,000) and that the functional dependencies of the saturation and fractional flow agree with the results of our general arguments but not with the results from the traditional models, such as Buckley-leverett or Koval.

We addressed the second question using our model, witfi viscosity-ratios, M = 3 → 300. Our modeling of, the finite viscosity-ratio showed that, initially, the flows are fractal; but that they become compact or stable on a time scale, τ, which increases with viscosity-ratio.as τ =τOM0.17. Once stable, the saturation front advances as x = VOM0.068 t.

Furthermore, using our functional dependency of fractional flow, we showed that the factor M0.068 plays the role of a two-dimensional Koval factor.
Adaptive Implicit Volume Balance Techniques
Authors: Farkas Èva
Published: December 2007

Implicit improvement possibilities of the VB modeling technique are studied in this paper. Short overviews deal with the different variable sets of reservoir simulators, and the IMPEM(E) VB solution. Then, the felly implicit approxhnation is discussed. The IMPEM and implicit parts of this technique are separated and analyzed. Two adaptive implicit VB methods, are examined. Some comparisons of the calculations are demonstrated using a ID radial model.
Development of Dynamic Local Grid Refinement in Reservoir Simulation
Authors: Ding Yu , Lemonnier P. A.
Published: December 2007

In reservoir simulation, the grid size is usually too large, to give accurate results, especially in active regions near wells and displacement fronts. A grid refinement of the whole domain is very memory and CPU time consuming for field-scale simulations. Dynamic local grid refinement can be used to overcome this problem.

In this paper, an adaptive local grid refinement method is presented for two-phase threedimensional immiscible flow. Data structure and grid management are proposed which are very efficient for dynamic grid monitoring. Several levels of refinement are allowed, space discretization is based on the finite-volume method. The linear system is solved by an ILU-ORTHOMIN method well-suited for irregular gridding. The criteria for refinement and unrefinement are based both on the saturation threshold and the flux tolerance.

Some examples are given to show the ability of the adaptive method to track the displacement fronts in heterogeneous reservoir simulations. The quality and accuracy of the solution are similar to those obtained with a fine discretization over the whole domain while great savings of grid blocks and computer time are obtained.
Pollution and Pollution Control
Authors: Shakely Sam F.
Published: December 2007

Pollution - the very word brings to mind in each of us a variety of abuses that man has perpetrated on his fellow man. lie has fouled the air, polluted streams and lakes and made vast dumping grounds out of once scenic areas. Water is impossible to destroy. Eventually, all water evaporates and later returns to the earth as rain or snow in a relatively pure state. Through this never-ending cycle there is just as much water now as there ever was, but the amount of water does not increase. Industry and population have expanded, thus increasing man's water needs. By withdrawing water from streams in greater quantities and by depositing too much untreated or improperly treated waste, we can upset The balance of nature's built-in renovation processes for conserving water quality. processes for conserving water quality. Wet deserts are the possible result in some of our streams and lakes, for even though they are still full of water—the water can become so polluted that it supports almost no life at all. America's future is dependent upon tile quality of water we use and re-use. Today, we use almost 400,000,000,000 (400 billion) gallons of water per day in the United States, and it is estimated that only 650 billion gallons of water per day is available for development. By the year 2000, we will need more than 1,000 billion gallons of water per day—which is over twice the amount being used at present. In order to meet these rising needs, it is necessary to preserve the quality of every gallon of preserve the quality of every gallon of water so that it can be safely used several times over. Water pollution control is the answer to the problem. To keep our water of high quality—methods of prevention, abatement and control of water pollution must be studied and understood. Citizens must be willing to support programs and objectives in water quality control and management, and everyone must take an interest in keeping our water pure. Prevention would have been much more desirable than the corrective action that must be taken - not only to hold our own but to roll back the vast pollution that has accumulated in the past due to mans greed and unconcern for the future generations. Pollution and Pollution Control is the popular topic for general discussion and it popular topic for general discussion and it is regrettable that the tremendous amount of publicity has resulted in a feeling of an approaching "doom's day".As has been widely publicized, we all know that during the last 40 years Lake Erie has been polluted to such an extent that the ecology has been permanently changed and the once prosperous commercial fishing industry is lost.
Reservoir Engineering Aspects of Horizontal Drilling in an "Ultra-Thin" Oil Column: A Case Study
Authors: Curnutt R. C. , Benesch J. M. , Prikel K. M. , Indrarto Dradjat , Sumolang F. G. H.
Published: December 2007

This paper focuses on P.T. Stanvac Indonesia's (PTSI) efforts to evaluate, justify and drill a horizontal well at the current edge of Industry technology. This pilot well, Gunung Kembang 7 (GK-7), located in a remote area of South Sumatra, Indonesia, was drilled successfully within an "ultra-thin" 33-foot oil column encompassed by both a gas cap and aquifer (see simplified cross section, Figure 1). Vertical wells in this field produce at low oil rates and yield marginal to non-commercial economic results.

The paper details efforts to numerically model the optimum case for vertical and horizontal wells to allow a fair economic comparison. Each alternative's optimum was derived by determining the respective spacing and rate for maximum profitability. Other associated studies are also discussed in addition to well performance and the actual horizontal drilling and completion results.
Reservoir Limit Testing in Water-Drive Systems
Authors: Kaczorowski N. J.
Published: December 2007

Reservoir limit testing is a powerful tool to determine the reservoir volume of a bounded system. This procedure was first recognized by Jones1 Its use, however, has been restricted to depletion drive systems due to the boundary conditions assumed to solve the radial pseudo steady state flow diffusivity equation.

There are many instances when determining the remaining hydrocarbon volume is desired after production has commenced. In a bounded system, Jones' method is applicable. But in water drive systems, water influx affects test results and Jones' method is not applicable.

An empirical method has been developed to accurately determine the moveable hydrocarbon volume in water drive systems. This new technique provides a means to determine not only the moveable hydrocarbon volume but also aids in the determination of accurate values of permeability and skin. It has been verified with numerical reservoir simulations and applied to actual field data.

This method is particularly applicable to determine remaining moveable hydrocarbon volumes in water driven gas reservoirs of small to moderate size and oil reservoirs above the bubble point. Because this method requires reaching pss flow at two different rates, it may prove impractical in large, low pressure gas reservoirs or those with many wells.
Simulation of Rapid Depressurization and Blowdown of an Offshore Oil Pipeline
Authors: Zagalai B. M. , Montgomery D. W. , Redus C. L. , Tan T. K.
Published: December 2007

A practical investigation is reported of rapid depressurization and blowdown in case of riser rupture of an offshore pipeline exporting live oil at high pressure. This work was performed to assess the environmental and safety consequences of not installing sub-sea isolation valves on the Heather-Ninian pipeline. The Heather Field is close to its economic limit, consequently, the overriding objective was to evaluate changes in operating procedure which would provide an equivalent level of safety to that of installing a sub-sea isolation valve.

Three methods – simple analytical, approximate and rigorous numerical simulation were used to predict leak rates in case of riser rupture. To build confidence in the predictions, a blowdown test to the separators on the exporting platform was performed. The test results are in good agreement with the model predictions.

The oil was found to have a bubble point pressure near the threshold pressure at which riser rupture could cause sustained hydrocarbon release due to solution gas drive in the sub-sea pipeline. As a result, the process facility on the exporting platform was modified to lower the bubble point pressure. The effects are compared to the installation of a sub-sea isolation valve. A blowdown system on Heather platform was shown to be effective when the leak is from a hole with a diameter of less than 2 inch (50 mm).
Monel Cladding as Splash Zone Coating for Pipeline Risers
Authors: Vastenholt H. , Fukuda T.
Published: December 2007

It has been identified that neoprene coated risers of large gas pipelines, expose continually manned platforms to high safety risks. The neoprene is susceptible to impact damage and due to peeling, corrosion may occur along the edges of the coating. Available alternatives to reduce those risks are for instance: to terminate those gas pipelines at a separate riser platform, or to install riser fenders in combination with improvements to the riser splash zone coating. Monel has been used in some instances in the oil industry as an alternative to neoprene as riser coating. In these cases the Monel was applied as sheeting; however inspection of the riser by ultra-sonic means was not possible because of the gap between the Monel sheets and riser pipe.

This paper addresses the possibility of continually bonding the Monel onto the riser pipe by means of hot rolling, thereby maintaining the ability to inspect the risers with ultra-sonic means. However this production process has some areas of concern: in particular, iron contamination of the Monel reduces its corrosion resistance in sea water. This paper reports on the trials that were conducted to quantify the above problem associated with iron contamination and a solution is provided.
Gas-Lift Optimisation on Barrow Island, Western Australia
Authors: Mantecon J. C.
Published: December 2007

Improving the design and Operation of gas lift Systems to obtain Optimum production (within the limits of existing facilities) is very attractive with low Investment and a corresponding acceleration/increase in reserve recovery to maximise profit.

This paper discusses the studies conducted and methods used to increase oil production and optimise the gas injected/fluid produced ratio in the Barrow Island Field by utilising the existing compression capacity and field staff.

This multi-stage optimisation program used on Barrow Island (BWI) can be readily adapted to other producing areas, even those with limited remaining field life. During the first stage, emphasis was placed on: (1) individual well optimisation; (2) improving gas lift design techniques; (3) Converting to intermittent gas lift (IGL), gas assisted plunger lift (PL) or sucker rod pumping when continuous gas lift (CGL) was no longer efficient; (4) improving System diagnostics; (5) field personnel training, and; (6) enhancing Operations / Engineering communication. After the first stage is completely implemented and results evaluated, fieldwide optimisation is planned and will be actively pursued.

Performance results indicate a very attractive retum from a low risk Investment. Significant improvements have been obtained in: (1) individual well profitability; (2) optimising injection gas usage; (3) well monitoring, and; (4) the amount and quality of collected well data.

Additional intangible benefits have come from the much closer well surveillance, such as faster detection and diagnosis of problems, and quicker response to failures.

The results demonstrate the potential that exists in producing areas similar to BWI for maximising economic retum through the application of sound engineering and operating principles. A united effort from Operating and Engineering personnel that is strongly supported by Management, along with an effective communication and training program can improve gas lift System efficiency quicker and more consistently to minimise costly errors and/or delays.
Emulsion Treatment Program
Authors: Soffian Roslan M. , Niven T. L.
Published: December 2007

Increasing emphasis has been placed by Esso Production Malaysia Inc. (EPMI) to address the potential emulsion concems in its existing operations in light of projected increases in water production offshore and in anticipation of potential impact on its export crude quality. The proper approach to demulsification is offen a point of contention, as a generic solution to oil treatment is relatively difficult to find. Although oil treating approaches can be grouped into four main categories, i.e., heat, Chemical, settling time, and agitation, each producing System is unique and must be reviewed individually to arrive at its respective solution.

This paper will discuss EPMI efforts to identify methods of resolving its emulsion concems, with focus on one of its offshore locations, Guntong Complex. This paper will discuss the initial provisions included in the original platform design basis, tests performed to identify resolution requirements and studies to determine the Optimum practical facility requirements.

This paper will focus on EPMI's efforts to remove water from emulsified crudes (forward emulsion treatment) only. Produced water treatment disposal is not addressed in this paper.
Vertical-to-Horizontal Permeability Relationship: Arun Reservoir
Authors: Atmadibrata R. R. M. , Joenoes Syafri
Published: December 2007

The purpose of this study was to investigate the relationship between horizontal and vertical permeability of the Arun Limestone reservoir in the Arun field. The study utilized core data from wells in which both horizontal and vertical permeability measurements had been made.

The Arun natural gas field, one of the world's largest gas fields, is located onshore in the North Sumatra Basin, Indonesia. This field has been producing gas and condensate since 1977. Gas production has increased since start up to the current average level of 3,300 million Standard cubic feet per day (MMSCFD). Of this total daily volume 2,230 MMSCFD is transported to the LNG plant for liquefaction and export, and after NGL recovery 145 MMSCFD is supplied for the domestic market, 55 MMSCFD is used for fuel and 870 MMSCFD is reinjected into the reservoir to maximize condensate recovery.

The current geological model, which incorporates a 7-layer zonation based on porosity trends, is the basis for input to reservoir Simulation studies. A good understanding of permeability distribution within the reservoir is critical to accurate forecasting of reservoir deliverability and injectivity performance.

The benefits from the results of the horizontal and vertical permeability relationship study are as follows: –An improved knowledge of vertical flow in the reservoir.–Improved reservoir modeling and compositional flow Simulation.–Enhanced ability to select zones for well Stimulation.

The study shows that there is a log-log linear relationship between the horizontal and vertical permeabilities in each zone.
High-Strength Coiled Tubing Assists High-Pressure Well Servicing in the Gulf of Mexico
Authors: Coats E. A. , Tatarski A. M.
Published: December 2007

Until recently, the removal of scale from high-pressure wells in the Gulf of Mexico required the use of a conventional or hydraulic workover (snubbing) rig. The conventional methods, which mechanically removed the scale, were costly and time consuming. Although removal of scale with coiled tubing provided a cost-effective alternative, coiled tubing was only considered for applications with well pressures of 5,000 psi or less. Now, however, with the advent of high-strength coiled tubing, scale-removal operations in more hostile well conditions can be performed.

The case histories presented in this paper will provide an overview of the significant benefits that the operator was able to obtain from the use of high-strength coiled tubing in scale-removal operations in high-pressure wells.
Overview of Acid Stimulation Practices in Malaysian Oil Fields
Authors: Hashim A. M. , Yasin Z. A. M.
Published: December 2007

Significant decline in production performance has been observed during the first few years of production in some completions in Malaysian oil fields. Near wellbore damage is thought to be the cause of this decline. Acid stimulation is the method of choice in removal of near wellbore damage and has proven to be successful in removing about 50% of this impairment.

Stringent screening criteria for acid stimulation candidates have contributed to the success of the acid jobs. Two methods viz bullheading and coiled tubing are currently being practiced. Coiled tubing has been widely used since the start of the acid campaign in 1986 while bullheading was tried only recently. Both methods give comparable results with bullheading costing about half that of coiled tubing. Standard acid formulation common to the industry together with additives has given good results at certain optimum volume of acid pumped. Nitrogen or available gas lift gas has been used to kick-off the wells.

Post acid production performance has shown improvements as substantiated by PI increases up to 200%, better gaslift efficiency, lower skin factors and average gains up to 350 STB/D. However, 20% of the candidates (with gains less than 60 STB/D) were unsuccessful due to low remaining reserves and/or high pre-stimulation water cut during the first campaign. More stringent screening criteria such as low water cut and sufficient remaining reserves have helped to reduce the rate of failures in later campaigns to 15%.
Field Evaluation of Acid Simulation Diverter Materials and Placement Methods in Arab-D Injection Wells With Openhole Completions
Authors: Ginest N. H. , Phillips J. E. , Al-Gamber A. W. A. , Wright D. W.
Published: December 2007

Hydrochloric acid (HC1) stimulation is a common method of removing shallow damage in carbonate formation completions resulting from drilling and workover operations. Current practice in the Ghawar Field is to bullhead large volumes of acid into the power water injection (PWI) wells to stimulate the long, open hole completions in the Arab-D formation. Small stages of particulate materials in a viscous carrying fluid are normally included in the treatment for diversion. This report describes the field testing and evaluation of three different acid treatment designs; (1) the conventional, bullhead treatment, (2) a coiled tubing placed, nitrogen foam diverted treatment and (3) a coiled tubing placed treatment without diverting materials. The treatment designs utilizing coiled tubing were developed in an effort to improve upon the conventional method by providing better formation damage removal throughout the entire porous interval and to reduce costs. A review of the conventional bullheading technique is presented along with case histories of wells that were stimulated with the two treatment techniques utilizing coiled tubing placement. The data presented indicates that the treatments combining coiled tubing placement and nitrogen foam diversion were more effective in stimulating the Arab-D formation and in improving injectivity than the conventional bullhead jobs.
Importance of Compression Ratio Calculations in Designing Sucker-Rod Pump Installations
Authors: McCafferty J. F.
Published: December 2007

Current sucker rod pump design procedures ignore calculating and comparing the pump's maximum available compression ratio with the required compression ratio of the installation. As a result, subsurface pumps are often installed with too small of a compression ratio for the production requirement. These pumps then experience chronic gas locking problems resulting in lost production and/or premature equipment failure.

This paper points out the need to consider compression ratio in addition to properly designed down hole gas separation as a critical part of a subsurface pump's design and installation.
Conceptual Sucker-Rod Design: An Unsolved Problem
Authors: Laine R. E.
Published: December 2007

The available set of engineering design tools for sucker-rod pumping units is incomplete. There is no sucker-rod design tool that has the combination of speed and accuracy needed for traditional conceptual design. The existing design tools lack either speed or accuracy. The solution is to develop a simulator specifically for the conceptual design phase. A conceptual design simulator must be fast enough to evaluate hundreds of system alternatives in a short time. A conceptual simulator must be accurate enough to provide meaningful data. The new simulator achieves speed by modeling a tapered sucker-rod string as a dimensionless equivalent-uniform-diameter rod. The new simulator uses simple boundary conditions.
Optimizing High-Volume Sucker Rod Lift
Authors: Pope C. D.
Published: December 2007

An optimum pumping unit installation can be made for high volume sucker rod lift wells. Using three phase inflow performance relationships, vertical flowing gradients and predictive sucker rod design programs the ideal setting depth of the pump and the size of the equipment can be selected.
Hydraulic Gas Pump and Gas Well De-Watering System: Two New Artificial-Lift Systems for Oil and Gas Wells
Authors: Amani Mahmood
Published: December 2007

This paper presents the concepts for two new artificial lift systems. The systems utilize the same operating principles. One system is for oil wells, the other unloads gas wells. The first system uses gas pressure to produce liquids through the tubing. This is called a Hydraulic Gas Pump. The other system uses gas pressure to unload gas wells and is called Gas Well De-watering System. In this system gas is produced through the tubing and liquid is produced through the casing tubing annulus.

The Hydraulic Gas Pump is suitable to pump oil wells with high gas liquid ratio and viscous crude production. The De-watering System can be used to maintain a gas well in an unloaded condition for maximizing its production rate and recoverable reserves.

Additional advantages of these systems are:

❖ They can be installed in shallow, deep, directional or offshore wells. ❖ They are wireline retrievable systems. ❖ Gas Lock and cavitation are not problems. ❖ They preform well in corrosive environments.
Vertical Permeability Determination drom Single-Well Test: Phase I—Constant Flow Rate Test
Authors: Luo Fang , Miska Stefan
Published: December 2007

This paper presents a new method of pressure transient analysis for determining the vertical and horizontal permeabilities from a single-well test conducted on partially penetrated or perforated wells. Generally, well testing data from wells with a restricted flow entry potentially carry the information about directional permeability. It has been recognized that the test data can be characterized by two parameters: the ratio of the flow entry to the total thickness of the producing zone, and the ratio of the vertical permeability to the horizontal permeability. Fully-featured pressure drawdown data display two straight-line segments connected by a transition curve when plotted versus the logarithm of time. This paper defines a characteristic time that corresponds to the intersection point of the extrapolations of the two straight lines, and shows that the characteristic time is a function of the penetration ratio and the permeability ratio. By using the slopes of the two straight lines and the characteristic time, one can determine the vertical and horizontal permeabilities, and the net thickness of the producing zone. This paper demonstrates that the slope of the second straight line can be obtained from pressure buildup data. Hence, a full development of the pressure drawdown process is not necessary and the total testing time can be reduced. Also, by applying the real gas pseudo pressure concept, the proposed method can be extended to single-phase, highly compressible fluid flow in reservoir under Darcy's flow conditions. Examples show the test data interpretation procedure for liquid and gas flow problems.
Characterization and Prediction of Formation Damage in Two-Phase Flow Systems (Formation Damage and Filter Cake in Laboratory Core Tests - Part II: Model Assisted Analaysis)
Authors: Liu Xinqhui , Civan Faruk
Published: December 2007

A predictive model for formation damage resulting from particulate processes involving two-phase flow of oil and water in sandstone formations is presented. The invasion and retention of externally introduced particles, the release and capture of formation in-situ fines and the resulting formation damage in terms of permeability reduction are modeled mathematically. The release of in-situ fines, retention of external particles and in-situ fines, and interphase transfer of particles are represented by empirical rate expressions. Permeability reduction is evaluated by taking into account the effects of pore plugging and porosity variation. The effects of relative permeabilities, capillary pressure and wettability of fine particles and pore surfaces on two-phase flow formation damage are considered.

The model is first tested with laboratory data of single phase flow of water through water-sensitive sandstone cores with and without presence of residual oil, and then with two-phase flow data involving the displacement of an oil-saturated, water-sensitive sandstone core by water. It is shown that there is a reasonable agreement between model predictions and experimental data. Typical simulation results illustrating the effects of wettability of externally introduced particles on permeability impairment in two-phase flow are also presented. However, the later results could not be verified due to the lack of experimental data. The model presented in this study can be used to estimate formation damage, identify governing damage mechanisms, and provide a guide for controlling formation damage for a given rock-fluid system.
Deformation Effects on Formation Damage During Drilling and Completion Operations
Authors: Thallak S. G. , Holder Jon , Gray K. E.
Published: December 2007

This paper deals with mechanical damage linked to stress and deformation changes associated with drilling and well completion operations and associated permeability changes. Irreversible or plastic deformations caused by pore collapse and particle rearrangement result in permanent fabric alterations due to induced anisotropy. Permeability changes are linked to damage state, anisotropic damage, dilation and stress state changes. Molecular dynamics simulations using disc assemblages and laboratory triaxial test experiments on weakly cemented sandstones clearly indicates that the induced anisotropy and deformation due to shearing significantly alters the permeability; and also its value depends on the direction in which it is measured. Severe anisotropy in permeability is the result of local heterogeneity due to damage. The molecular dynamics simulation is shown to be a powerful tool to generate insights into the physical processes of particulate behavior. The paper illustrates the implications of induced anisotropy effects on formation damage.
Numerical Evaluation of Gravel-Pack Damage
Authors: Morita Nobuo
Published: December 2007

Oil industry statistics show that gravel-packed wells, in hydrocarbon production for more than a year from formations with permeability greater than 500 md, exhibit an average skin excess of 20. This paper utilizes laboratory and field data to investigate causes of high skin value. A finite element transient nondarcy model, simulating gravel-packed wells, was used to investigate the damage.
The Rheology of Foam
Authors: David Amiel , Marsden Sullivan S.
Published: December 2007

Both experimental and theoretical analyses were carried out on the rheological behavior of foam. This foam was generated by simultaneously injecting compressed air and an aqueous solution of a commercial foaming agent into a short porous medium. It then flowed into a capillary tube viscometer having four interchangeable glass tubes of different radii. A mathematical analysis was developed whereby both the very pronounced effects of fluid slippage at the tube wall and the foam compressibility were taken into consideration. The apparent viscosity was independent of foam quality but not of tube radius.

Bubble size and bubble size distribution were measured under a microscope and the change of bubble size with-time studied through photomicrographs. Both the mean bubble diameter photomicrographs. Both the mean bubble diameter and bubble size distribution were functions of foam quality. The cumulative size distribution as a function of a quality is represented by a modified Weibull function.

Although the flowing foam behaved like a pseudoplastic fluid, the static foam had a pseudoplastic fluid, the static foam had a measureable gel strength which increased with foam quality.

Introduction

Foam is a gas-liquid dispersion in which the liquid is the continuous phase and the gas is the discontinuous phase. It occurs widely and is used in many industrial applications. In the petroleum industry, foams are often encountered in gas-oil separators. In recent times, aqueous foams have been used in several oil field applications such as removal of brine from low pressure gas wells and as a drilling and completion fluid in low pressure, water sensitive reservoir rocks. Their use has also been proposed to plug thief formations and to seal caprock leaks in underground/natural gas storage reservoirs, and as a displacing agent in conjunction with water floods. Some of these applications are involved with foam flowing through tubes or pipes whereas others are concerned with the flow or retention of foam in porous media. porous media. The many physical properties of foam have been described by scientists and engineers in numerous papers and these are reviewed elsewhere. The many papers concerned with the flow properties of foam are particularly pertinent properties of foam are particularly pertinent to its use in petroleum production. In these, foam is usually considered as a fluid, which is probably a valid assumption if the bubble size is small compared to the instrument's dimensions or the size of the fluid conduit.
Characterization of Surfactant-Enhanced Cement Fluid-Loss Additives
Authors: Mueller D. T. , Bray W. S.
Published: December 2007

Modified surfactants, in the form of ethoxylate-coated resins (ECR), serve as the foundation for fluid loss additive systems that are functional in a wide range of applications and environments. ECR's, when combined with polyvinyl alcohol, produce fluid loss additives that: (1) are minimally retardive, (2) can be placed in turbulent flow, and (3) possess anti-gas properties. Blending ECR with hydroxyethylcellulose yields a multi-purpose fluid loss agent with higher efficiency, greater salt tolerance, and improved thermal stability as compared to conventional fluid loss additive systems.

Presented are the laboratory data substantiating the use of surfactant enhanced fluid loss additives, as well as supportive case histories demonstrating the utility of these systems in field cementing operations.