bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of Digital Technology Optimizes Bit Selection to Cut Drilling Costs in Torrente Cigno Field-Italy
Authors: Clark Anthony , Aliko Enis , Scott Dan , Cooley Craig , Vedovato Alberto
Published: December 2007

This paper describes how digital technology was used to make a landmark bit selection decision that significantly reduced drilling costs in Torrente Cigno field of central Italy.

The operator used a new computer program that converted open-hole log data from an offsetting well into a digital format to select an appropriate bit for the expected drilling conditions. This new tool analyzed rock mechanics and helped the operator determine that a particular limestone section in the field traditionally drilled with roller cone bits fell within the limits of new polycrystalline diamond compact (PDC) bit technology. A medium set bit was selected with polished cutters and sufficient face volume and junk slot area to allow efficient drilling through shale. The bit also incorporated a newly developed high impact strength cutter with a highly stabilized layout to resist premature damage while drilling the limestone section. The bit drilled the lime faster than planned and also maintained a good rate of penetration through the shale section under controlled parameters. The bit came out of the hole in excellent condition.

The authors will discuss how the software program unraveled the complex problems associated with calculating rock strengths of the Miocene allochthonous and Pliocene formations. The output of the program, which uses empirical formulas derived from statistical observations and tests, gave the operator the confidence to run a PDC bit for the first time in the lime/shale sequence. This combination of new bit and cutter technology along with the innovative log analysis techniques allowed the 8 ½" section of the well to be drilled with one bit for a savings of $423,000 US compared to the offset well.
Improving Transient Testing Results Using Data Management
Authors: El-Hawary A. M. , Mahgoub I. S. , Sayyouh M. H.
Published: December 2007

The prime objective of data management is the economic optimization of data resources to achieve common goals. Data management is very important to project success, and Data Collection should be carefully planned and carried out. Justification, priority, timelines, Quality, Quantity, and cost-effectiveness should be the guiding factors in data collection and analysis. Each data project should be screened by a cost-benefit analysis.

A clear understanding of the purpose and application of information obtained from well tests is mandatory if this information is to be used properly in managing the reservoir. For instance, skin values calculated from well tests are used to determine the need for workover or stimulation of the wells. Another example is identification of the presence of boundaries. Defining boundaries is particularly important when testing appraisal wells. Occasionally, more work is needed before using the results of the "Well Testing" analysis to identify the reservoir model. Several factors affect the type of information obtained from well tests should be considered.

The input data used in well test interpretations is inevitably subject to measurement or estimation error. Therefore, each of input data type such as net pay, porosity, compressibility, and formation volume factor is subject to its own source of errors. Knowing the effect of these errors on the obtained results helps the engineer to identify the input data that have the most impact on the key reservoir parameters. The challenge for the engineer is to define the level of certainty that should take place, the cost of additional information and the economic benefits of reducing the uncertainty in the data. Reducing the uncertainty for the sake of accuracy should be avoided. The economic benefits of refined well testing results should be justified. On the other hand, Even if the data is perfect, data in isolation from other data may have no value, but when integrated with other data may have significant value. For instance, because transient testing is an inverse problem, more than one model may match the test data. Hence, results should be integrated with those from other methods to select the most likely reservoir model. By crossing the traditional boundaries and integrating the work of geoscientists and engineers, data resources are better utilized. It will be able to correct contradictions, to validate the well test interpretations, and consequently, minimizing costly errors.

In this paper an overview of the practical aspects of data management approaches being used today is provided. It discusses in details the application of the data management in transient testing. The application explores the source of input data errors; their effects on the results of well test interpretation and how these results can be integrated with other methods to obtain reservoir descriptions. Field examples are presented illustrating the effectiveness of this approach.
Integrated Characterization of Complex Khuff-C Carbonate Reservoir in Ghawar Field
Authors: Dasgupta S. N. , Hong M. R. , Al-Nasser M. T.
Published: December 2007

Integration of 3D seismic analyses with petrophysical and other well data has improved the reservoir characterization and reduced the drilling risk for the Permian Khuff-C carbonate reservoir in the Uthmaniyah area of Ghawar Field. The reservoir is heterogeneous, complex and influenced by syndepositional diagenesis. The Khuff-C reservoir rocks were deposited in a peritidal setting where slight changes in sea level created local islands that were sub-areally exposed. This exposure in an extremely arid climate resulted in porosity occlusion by evaporite cements. The occurrences of these tight islands within the Khuff-C reservoir interval are sporadic and randomly distributed.

Recently acquired 3D seismic data in the area, calibrated with borehole information, has permitted the prediction of these local tight Khuff-C porosity areas.

Inverse modeling of amplitude was performed on the 3D seismic data using an initial acoustic impedance (velocity x density) model developed from sonic and density logs from nearby wells. The amplitude inversion technique employed on the 3D seismic volume was target oriented, iterative, and constrained by acoustic impedance computed at the wells. The initial model assigns an impedance log for every trace in the seismic volume by interpolating between the well control points. The inversion process updated the initial model to match the amplitudes for each trace in the seismic volume time window. Six deep wells were drilled based on the 3D seismic inversion results in the Uthmaniyah area of Ghawar Field. As predicted from this inversion model, wells that were located over areas of low impedance penetrated porous Khuff-C gas reservoir. Prior to the seismic modeling some of the deep gas wells drilled in the Uthmaniyah area had encountered poorly developed Khuff-C reservoir.

In this reservoir study the integration of observations from various disciplines has resulted in a synergy that has reduced the ambiguity in the interpretation of results from each individual discipline. Improved characterization of the reservoir resulted in the optimization of each drilling location, reducing the drilling risk of developing the Khuff-C reservoir. A similar approach is being applied to the Khuff-C reservoir in other areas of Ghawar Field.
History Matching of Gas Simulation Models Using Optimal Control Theory
Authors: Dougherty E.L. , Khairkhah D.
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.

This paper was prepared for the 45th Annual California Regional Meeting of the Society of Petroleum Engineers of AIME, held in Ventura, Calif., April 2–4, 1975. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made.

Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Two papers presented at the 1973 Las Vegas meeting showed how to use optimal control theory to history match reservoir simulation models. Distributions of kh and h which minimize mean square pressure error at reservoir control points are thereby determined. In this paper the method is applied to real-gas systems with closed outer boundaries in which pseudogas potential is calculated by pseudogas potential is calculated by the simulation model. Results obtained with three gas models are shown: a nine-cell model, a 36-cell model, and a 51-cell model; the latter is a hypothetical but realistic gas field model. It was concluded that this method satisfactorily generates kh and h distributions for real-gas systems which result in small pressure errors if sufficient control points are provided. The kh and h distributions provided. The kh and h distributions obtained depend upon starting distributions used; however, total pore volume is accurately estimated.

Introduction

Performance (history) matching is the process of varying values of reservoir parameters in a numerical reservoir simulator until acceptable agreement between performance predicted by the simulator and the predicted by the simulator and the observed data is reached. Parameter values must satisfy some criterion of reasonableness. The simplest approach to history matching is the trial-and-error procedure of visually examining simulator procedure of visually examining simulator results and adjusting parameter values by intuition or experience. This procedure is often slow and costly, and is frequently ineffective as well.

In an attempt to overcome these deficiencies of the trial-and-error approach, automatic history matching techniques have been developed. Many authors have investigated the subject of history matching.
Environmental Constraints on Geothermal Development
Authors: Robinson Joel
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.

This paper was prepared for the 45th Annual California Regional Meeting of the Society of Petroleum Engineers of AIME, held in Ventura, Calif., April 2–4, 1975. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made.

Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Introduction

In recent years, questions have been raised regarding the environmental effects of geothermal development. Although geothermal steam is considered by many to be a cleaner alternative source than fossil fuel-generated steam, geothermal development still encounters long delays in receiving approval from governmental regulatory agencies. Delays such as these must be eliminated before geothermal power can expand to its full potential and become a significant contributor to America's energy resources.

Although geothermal power is a relative newcomer to the energy industry, its operating techniques have advanced rapidly. Programs to prevent accidents and pollution Programs to prevent accidents and pollution incidents have been implemented by operators in order to carry out their efforts to remain good neighbors. This effort, coupled with future passage of enlightened and less conflicting government regulations, should result in accelerated geothermal exploration and development.

This paper will explore some of the environmental regulations for geothermal development, describe the chief environmental characteristics of geothermal development and some current environmental studies being performed at geothermal projects, and suggest some possible ways projects, and suggest some possible ways to overcome conflicting laws and jurisdictions in order to avoid delays.

LEGAL REQUIREMENTS ARE NOT UNIFORM AND JURISDICTIONS OVERLAP

A variety of environmental laws, regulations and agencies control geothermal developments.
ESS/EST Marginal Field Development in E-South Area, Offshore Northwest Java
Authors: Silitonga Frans J. P. , Purantoro Ronnie , Simandjuntak Gustaf H.
Published: December 2007

The south area of giant E field, Offshore Northwest Java, contains 5 proven structures: ESW, ESS, EST, ESP and ESR. Only the ESW structure was developed, while the other structures had not been developed by conventional methods due to marginal economics. Development of those marginal fields was accomplished with innovative methods applied by a multidisciplinary team. A three well platform, a cluster, was installed and a multilateral well with two targets in the ES-31 sand in the EST area was drilled through one of the conductors. A second well was drilled with Main/Massive and Talang Akar objectives, and the last well was drilled horizontally to the ES-31A sand in the ESS area. The multilateral well can provide considerable improvement to the total productivity index over the vertical wells and single-horizontal wells. In the presence of permeability barriers such as faults, the multilateral well can also reduce the risk of production uncertainty. The optimum horizontal length and number of branches were determined by balancing incremental production against the drilling and well completion cost. This project was the first application of multi-lateral technology for ARCO Indonesia. The successful application of multilateral techniques has provided an economic means to develop other marginal fields in Offshore North West Java in ARCO Indonesia.
Gel-Cement Combination Squeezes For Gas Shutoff
Authors: Lai Q. J. , Bond A. J. , Cahalane T. W. , Carpenter R. B. , Newhouse D. P. , Singh T. , Styler J. W.
Published: December 2007

Gel-Cement Combination Squeezes have been successfully used for gas shutoff applications. Coupled with coiled tubing selective placement, gels and cements exhibit a synergistic gas shutoff effect. Gels provide an indepth block to gas production by forming a crosslinked polymer network within the porous media. Cements are able to fill voids and cavities to block gas production and provide a strong near wellbore block. Thirteen treatments have been performed to date with an economic success rate of 85%. Implementation of the technology required the use of a well-controlled gel system, consideration of possible contamination issues and modification of current coiled tubing placement strategies.
Analysis of the Success of Cavity Completions in the Fairway Zone of the San Juan Basin
Authors: Ramurthy Muthukumarappan , Rogers Rudy E. , Weida Dana
Published: December 2007

Wells completed by the openhole cavity technique in the Fruitland formation of the fairway zone in the San Juan basin have demonstrated gas production rates nearly ten times greater than production rates from wells completed by fracturing in the same area, but expensive trial and error selection of wells to cavity complete outside the fairway and in other basins must be made. Data from numerous wells were obtained from four companies active in the basin. Five parameters namely in-situ stress, bottom-hole pressure, ash content, volatile matter, and depth to the top of the Fruitland coalseams were statistically ranked by their importance to the success of cavity completion techniques, and these five parameters were contoured using the "Surfer" software. From the resulting contours, boundaries of fairway zones similar to that of the San Juan basin can now be defined in unexplored basins. This study is the first to assimilate enough minimum in-situ stress data in the San Juan basin to statistically correlate with production rates. The statistical analysis shows minimum in-situ stress to be the most important parameter of the five studied for successful cavity completions. A threshold minimum in-situ stress between 2080-2359 psi is required if other parameters of the study are satisfactory. The study is important for coalbed methane development around the world where coalseams as successful as the San Juan fairway are sought for the application of cavity completions.
Pseudo-skin Factors for Partially-Penetrating Directionally-Drilled Wells
Authors: Cinco-Ley Heber , Ramey H.J. , Miller Frank G.
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.

An analytical solution derived recently to study the unsteady-state flow of a slightly compressible fluid toward slanted wells was modified to compute the pseudo-skin effect created by partial penetration and slant of a well. It was partial penetration and slant of a well. It was found, as expected, that the pseudo-skin factor due to the slant of a well has a negative value and it appears to be affected by both the location of the producing interval in the formation and the producing interval length. producing interval length

Introduction

Many authors have studied steady-state and the unsteady-state flow toward a partially-penetrating well. They considered a well partially-penetrating well. They considered a well perpendicular to the producing formation and perpendicular to the producing formation and concluded that this type of well completion causes a decrease in well productivity. However, as pointed out by Cinco, et al., many wells do not penetrate the producing formation perpendicularly. Instead, there is an angle perpendicularly. Instead, there is an angle between the wellbore axis and a normal to the formation horizontal plane. These wells may be termed "directionally-drilled," or "slanted" wells. This situation creates an increase in well productivity with respect to a partially penetrating well which is perpendicular to the penetrating well which is perpendicular to the formation. Cinco, et al., studied the unsteady-state flow of a slightly compressible fluid toward slanted wells in an infinite slab reservoir, and presented a solution which can be applied to presented a solution which can be applied to fully and partially-penetrating wells. It was shown that the unsteady flow toward a slanted line source includes three flow periods:a radial flow period,a transitional flow period, anda pseudo-radial flow period.

They also presented results for a fully-penetrating slanted presented results for a fully-penetrating slanted well of infinite conductivity, and concluded that the slant of a well causes an increase in well productivity which can be handled as a negative productivity which can be handled as a negative pseudo-skin effect that is constant for large pseudo-skin effect that is constant for large values of time.

The purpose of this work is to evaluate the pseudo-skin effect for a partially-penetrating pseudo-skin effect for a partially-penetrating slanted well of infinite conductivity (uniform pressure at the wellbore) in an infinite slab pressure at the wellbore) in an infinite slab reservoir, and to show how to correct the skin factor calculated from well test analysis for the deviation from the vertical.
A New Generation of Solid-Free Fracturing Fluids
Authors: McDaniel Robert R. , Houx Mel R. , Barringer David K.
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.

Two new high viscosity water base fluids have been developed for use as spearheads to acidizing treatments and as fracturing fluids used in the placement of proppants. Both fluids are derived from proppants. Both fluids are derived from the same basic chemistry and are completely solid-free. One fluid is designed for high temperature applications (wells with formation temperatures ranging from 220 to 325 deg. F), while the other is for the more prevalent low temperature wells (80 to 220 deg. F). prevalent low temperature wells (80 to 220 deg. F). Using these fluids, proppant concentrations up to and including ten pounds per gallon have been successfully placed into fractures.

The basic advantage to using solid-free fracturing fluids lies in minimizing the permeability damage to both the formation and permeability damage to both the formation and packed fracture. This damage is caused by packed fracture. This damage is caused by solids found in polymers used to impart viscosity to a fracturing fluid, or in the fluid loss additives which help control fluid leakoff. Previous systems that used solid-free polymers were characterized by less than desirable fluid loss control and often required significant amounts of a fluid loss additive. Use of a fluid loss additive meant that these systems were no longer solid-free and, depending upon the amount of additive, could cause significant damage. The two new fluids have achieved a solid-free status without sacrificing fluid loss control and therefore are not used in conjunction with a fluid loss additive. Permeability damage tests, in both cores and sand packs, were run on these new fluids. The results of these tests were cornpared to those obtained when fracturing systems, using other polymers or fluid loss additives, were examined.

This paper describes the underlying chemistry of the two solid-free fluids, their resulting fluid rheology and applications. Field mixing procedures are discussed as are well case histories. Special emphasis is placed on the treatment of high temperature placed on the treatment of high temperature wells in which the fluids were used either as a spearhead to an acid treatment or to carry and place high concentrations of propping agents.
FE-MWD Logging in a Different Environment Induced by Drilling with a Rotary Steerable System
Authors: Berger P. E. , Helgesen T. B. , Kismul J. K.
Published: December 2007

The drilling of horizontal and extended reach wellbores is being revolutionized by rotary steerable systems such as the AutoTrak™ tool. Typically, advanced directional drilling has been performed with steerable mud-motor systems. However, drilling with a steerable mud-motor results in a rough and tortuous wellbore due to the motor's geometry and operational behavior. A rough wellbore may affect the performance of various logging sensors deployed with the system. Different logging sensors are affected differently, and so the ability to compensate for borehole effects varies from sensor to sensor. The result may be a log that suffers in quality.

Rotary steerable systems drill smoother and less tortuous wellbores. As a consequence, typical borehole effects visible on various FE logs may not be apparent when drilling with rotary steerable systems. Knowledge of the logging environment in which the data were obtained is important when analyzing the log.

It is believed that the introduction of rotary steerable systems will improve the economics of long horizontal and extended reach wells. As a consequence, there will be an increase in the drilling of these types of wells. It is desirable to log these wells while drilling, as the deployment of wireline-operated logging tools will be costly and risky. The real-time logging information can be used for navigating in the reservoir and optimizing the wellbore position. Also, FE-MWD logging sensors are continuously being developed and improved, so the desire to perform the logging operations while drilling will tend to increase.

This paper discusses the differences in logging environment as a result of drilling with a rotary steerable system as opposed to a steerable motor system. The paper also discusses the impact of this new logging environment on the results from various FE-MWD logging sensors. Examples of logs recorded in comparable formations with the two drilling systems are included. This may help log analysts in their interpretation of log results, as rotary steerable systems are more commonly used for horizontal and extended reach drilling (ERD).
Simulation of Two-Phase Flow by Finite Element Methods
Authors: Langsrud Oyvind
Published: December 2007

American Institute of Mining, metallurgical, and Petroleum Engineers Inc.

A finite element approximation to the differential equations for flow of two compressible fluids (oil and gas) through a porous medium is presented. Following a Galerkin approach, the algebraic equations are derived using matrix notation. Time integration is done by a simple finite difference scheme, and the resulting non-linear equations are solved by a chord slope technique. Some simple means for stabilizing the solution are pointed out and incorporated in the method.

Numerical results are presented for a displacement and a gas percolation problem, and the finite element results are shown to be slightly superior to those of a conventional model.

Introduction

The finite element method (FEM) has come to be recognized as an effective analysis tool for a wide range of problems. In particular, it has become the dominating numerical particular, it has become the dominating numerical method within static and dynamic structural analysis, for which it was originally developed some twenty years ago. The FEM gained immediate popularity because of its systematic formulation, ability to handle irregularly shaped boundaries and general appeal to engineers. It was soon recognized as an extension of the variational methods. The basic idea of variational calculus is that the solution is found as the function which results in an extremum value of some integral, the functional, often related to the energy of the system. The problem is to identify a functional which problem is to identify a functional which will yield the same result as direct solution of the differential equation. If a functional exists, an approximate solution can be found by finding the extremum value when the solution is restricted to linear combinations of a finite number of basis functions.
Orthomin, an Iterative Method for Solving Sparse Sets of Simultaneous Linear Equations
Authors: Vinsome P.K.W.
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.

An iterative method is proposed for the inversion of sparse band-structured matrices of the type that are common in numerical reservoir simulators. The method utilizes orthogonalizations and minimizations to achieve a fast convergence rate. Tests have shown that the method is highly competitive compared with other iterative techniques. The rate of convergence is insensitive to the use of iteration parameters, non-symmetry of the matrix, and ratios of off-diagonal bands in symmetrical matrices.

1.

Introduction

A time-consuming part of the calculation in numerical reservoir simulators is the inversion of a large set of simultaneous linear equations.

(1)

For example when effecting a solution by the Implicit Potential - Explicit Saturation method x would represent the pressure or potential field, whilst A would be a matrix of transmissibility coefficients describing the interflow of fluids between grid blocks. In the common finite difference approaches, A is a sparse banded matrix, as depicted in figure 1 for a five-point finite difference representation of a two dimensional system. Often, the diagonal element of A is approximately equal to the negative sum of the off-diagonal elements in a given row.

Because of the sparseness of A, iterative methods appear at first sight attractive compared with direct methods. However, specialized direct routines with increased efficiency have become available in recent years. Of the iterative methods SIP (strongly implicit procedure) is possibly the most widely used. SIP has the possibly the most widely used. SIP has the disadvantage that its convergence rate depends strongly on a set of iteration parameters whose optimal values can be difficult to find.

A new highly competitive iterative method for symmetric matrices, a minimization process conceptually based on the conjugate-gradient technique, has lately been developed. The numerical examples and proofs quoted in reference 4 indicate that minimization processes can be expected to offer the following advantages:

Convergence more readily guaranteed. No need for iteration parameters. Insensitivity to number of equations. Insensitivity to transmissibility ratios (the ratios of the off-diagonal bands in figure 1).
Deep Dredging for Off Shore Purposes A Method to Clear Stones and Boulders From the Seafloor
Authors: van Oostrum ir Wil H.A. , Lubbers A.
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.

This paper was prepared for the SPE-European Spring Meeting 1976 of the Society of Petroleum Engineers of AIME, held in Amsterdam, The Netherlands, April 8–9, 1976. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal, provided agreement to give proper credit is made.

Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Nowadays offshore engineering requires constructions and working methods suitable for water depths up to several hundred meters. Especially for the North Sea operations adverse weather and sea conditions have an important influence on workability of applied equipment.

With respect to dredging, even advanced techniques are generally not applicable for depths over 30–40 m in exposed areas.

In the case of-the production platforms of the gravity type platforms of the gravity type Condeep 2, problems arose, when inspection of the sea bottom showed the presence of many stones and large boulders. Before the platform could be placed, these platform could be placed, these obstructions had to be cleared from the sea bottom. For this purpose, methods such as blasting, purpose, methods such as blasting, airlifting and grab dredging had to be rejected being impractical. Based on experience elsewhere, a method of dredging with steelnets together with acoustic positioning was also considered. As this method appeared to be a promising proposition, it was tried out and proved proposition, it was tried out and proved to be successful.

Within five working days of the 1975 season, 470 stones with largest dimensions ranging from 0.30 to 2.0 m have been removed from the seafloor at the Condeep 2 location Brent field at a water depth of approximately 150 m.Other applications of these techniques have been prepared since and are expected to be executed during the 1976 season.

Introduction

Dredging in exposed areas has been rapidly developed in the past decade. Self propelled trailing hopper dredgers are able to work now in exposed areas up to wind-force 8–9 Beaufort.
A New Technique to Evaluate Matrix Acid Treatments in Carbonate Reservoirs
Authors: Al-Dahlan M. N. , Nasr-El-Din H. A.
Published: December 2007

This paper discusses a new technique that was used to evaluate matrix acid treatment conducted on a cased water disposal well in a carbonate reservoir. The technique relies on calculation amount of corrosion products and minerals dissolved by the acid. It was used to calculate the amount of iron dissolved by the acid and the live acid present in the flowback following the pickle treatment. Chloride ion concentration was used to determine the degree of mixing between the spent acid and formation brine. The degree of mixing was then used to calculate the volume of the produced spent acid and the amount of minerals (calcite and dolomite) that were dissolved by the acid. The chemical efficiency of the acid, defined as the actual amount of calcite dissolved by the acid/the theoretical amount of calcite that the should dissolve, was finally determined.
Removing Mechanical Skin in Heavy Oil Wells
Authors: Dusseault Maurice B. , Davidson Brett C. , Spanos Tim J.
Published: December 2007

High-amplitude, low-frequency pressure pulsing was developed as a new oil well workover technique, and has been used in > 40 heavy oil wells in Alberta and Saskatchewan during the period October 1998 to October 1999, with a good success ratio. The method is particularly effective in initiation sand production and in cases where mechanical skin arising from blocked perforations, immobilized fines and asphaltenes are responsible for a high skin factor.

Perforation blockage, restriction of near-wellbore flow paths through fines accumulation, pore throat precipitation of asphaltenes, and sand re-compaction around the well are all thought to be responsible for rapid production rate declines in many wells. In heavy oil wells, chemical treatments alone are rarely useful, but large physical perturbations of the material around the wellbore have been found to be effective in reestablishing production.

A downhole device was developed to apply large periodic pressure pulses to the perforation face. This device also permits injection of fluid at measured rates into the nearwellbore region while executing prolonged (9–12 hour) high-amplitude perturbation. The action loosens mechanical skin, allowing the source of flow blockage to be physically removed through remolding and liquefaction of the sand around the wellbore. This liquefied zone is produced when the well is placed back on production, and in most cases the well is rejuvenated. In some cases, wells that never produced economic rates of oil because sand influx could not be initiated were turned into reasonable producers after a pressure pulse treatment. The method can also be used to deliberately introduce treatment chemicals while reducing the negative effects of channeling and fingering, as the front of treatment fluid ingress is well dispersed by the pressure pulsing.
Development of a Downhole Scale Management Philosophy for Water Sensitive Reservoirs
Authors: Scott Graham C. , Littlewood Michael J.
Published: December 2007

Scale deposition in the near well bore and the production tubing of an oil production well can have a major impact on the productivity of the well. Normally, this problem can be avoided by pumping a concentrated solution of an aqueous scale inhibitor followed by displacement of the inhibitor into the reservoir with sea water. The scale inhibitor is allowed to absorb or precipitate in the reservoir so that when the well is returned to normal flow the scale inhibitor is able to desorb and inhibit scale formation over several months. However, there are many reservoirs that are water sensitive such that if an aqueous scale inhibitor treatment is deployed then severe productivity impairment can occur.

This phenomena occurs in Amerada Hess’s Scott & Telford fields where core studies have shown that severe productivity impairment would result if a well with a water cut of less than 30% was treated with an aqueous scale inhibitor treatment.

This paper describes the development of an effective downhole scale management strategy that allows scale control to be achieved without incurring major loss of productivity. The strategy was achieved by the sequential use of oil soluble scale inhibitors, aqueous inhibitors in conjunction with relative permeability modifying chemicals and micro-encapsulated scale inhibitors. This type of strategy would also be applicable to other fields where a water sensitive reservoir makes downhole scale control problematic.
Iron Release Following Mineral Dissolution Following Scale Inhibitor Application In a North Alaskan Reservoir
Authors: Hill P. I. , Graham G. M. , Dyer S. J. , Coleman J.
Published: December 2007

High levels of dissolved iron present in produced waters have caused concern in a number of wells in North Alaskan Reservoirs. In this paper, two dynamic "reservoir condition" scale inhibitor core flooding experiments have been conducted to simulate scale inhibitor treatments using a pre-selected commercial phosphonate based scale inhibitor. In these floods very high levels of iron were released during the chemical injection and shut-in stages (> 450ppm in solution). Evidence from pre and post treatment SEM analysis revealed that the major cause for the excessive iron release was extensive dissolution of siderite, inducing considerable mechanical weakness of the core, which was particularly evident for core 1, and much less so in core 2. However, although both cores have similar percentages of siderite, it is the textural arrangement, which is of prime importance in relation to formation damage. In core systems where siderite supports many grain contacts any fluid/mineral dissolution reactions will significantly impair mechanical strength (core 1), potentially leading to sand production. Where siderite is enclosed within finer carbonate mud lenses, or is not grain supporting, the mechanical damage is much less severe (core 2). Reactions of siderite with the core are quite complex. In this paper we demonstrate the formation of an oxidised rim of hematite which surrounds remnant siderite, with voids present between it and the hematite rim.

The high levels of iron release recorded in such systems have considerable implications with regard to the effectiveness of the pre-selected scale inhibitor. Inhibitor performance tests for a range of generically different inhibitor clearly indicate that the performance of certain types of scale inhibitor products is significantly reduced in the presence of dissolved iron. These results concur with field experience where phosphonate based inhibitors (initially selected based upon performance in the absence of iron) have proven less successful in the field.

In summary it is evident that potential dissolution of iron bearing minerals, and the subsequent influence of dissolved iron on performance, has a significant bearing on scale inhibitor selection.
High Angle OHGP’s In Sand/Shale Sequences: A Case History Using a Formate Drill-In Fluid
Authors: McKay G. , Bennett C. L. , Gilchrist J. M.
Published: December 2007

Historically, application of open hole gravel packs have mainly been limited to completion of deviated and vertical wells. Other limiting factors affecting selection of this type of completion are reservoir quality and heterogeneity, or the need for selective completion. However, with an increasing number of high angle and horizontal wells being drilled, the industry is focusing more attention on how to use gravel packs to greater effect in long heterogeneous sections. Keys to success are productivity, management of formation damage through optimal filter cake design, and attainment of long term sand control by ensuring complete gravel placement over the entire producing interval.

This case history discusses a high angle open hole gravel pack application for a sand shale sequence. Inhibition of these highly reactive intra reservoir clays was achieved using a low solids formate based mud system. Full gravel placement along the high angle (75°) reservoir section was accomplished using an alternative path gravel pack technique. Filter cake removal, unlike other industry approaches using acids, relied on application of enzymes to enhance the cleanup/back production of filter cake through the oversized gravel and so maximise productivity.

The discussion will focus on the system design approach to drill-in fluid design / clean-up, and the actual gravel pack placement. Finally, the productivity performance, as deduced from pressure transient analysis, will be presented to demonstrate the success of the unique clean-up approach adopted for this operation.
Development of a Novel Fluid-Loss Control Pill for Placement Inside Gravel-Pack Screens
Authors: Luyster M. R. , Foxenberg W. E. , Ali S. A.
Published: December 2007

Controlling fluid losses to the formation, both before and after sand control completions, is critical to optimizing production. While mechanical devices, such as flapper valves, remain the preferred choices for preventing fluid loss when the service tools are removed from the production packer, they sometimes fail or otherwise cannot be used. In those instances, chemical fluid loss control pills are frequently used as supplements or contingencies. Unfortunately, this option normally requires remedial treatment that adds cost and can cause a host of additional problems, not the least of which is the risk of formation damage.

This paper describes the development of a uniquely engineered fluid-loss control pill, designed for placement inside the gravel pack screen and that has been shown to effectively control fluid loss without the subsequent need of remedial treatment. The authors demonstrate that optimizing the particle size distribution of the bridging particles within the fluid loss pill for specific screen types deposits a surface filter cake against the inside surface of the gravel-pack screen assembly. Complementing the development of the fluid loss control pill, which can be pumped at comparatively small volumes, is a proprietary additive specifically designed to reduce the adhesive forces to metal or rock surfaces and which allows complete cake removal, using only production as the flow medium.

The laboratory developmental program and a large-scale screen-flow model designed to simulate pill deposition on various gravel-pack screen types are described. Further, through field experiences, the authors will document the ability of these fluid-loss control pills to produce near zero skin and maximize production without the need for costly and risky remedial removal treatments.
Experimental Approach to Characterize Drilling Mud Invasion, Formation Damage and Cleanup Efficiency in Horizontal Wells with Openhole Completions
Authors: Longeron D. G. , Alfenore J. , Salehi N. , Saintpère S.
Published: December 2007

The increasing number of horizontal wells being drilled, together with the continuing development and use of open hole completions has resulted in increasing reliance on formation damage testing to select the appropriate drilling fluid and/or cleanup technique. A two-year laboratory study was conducted to evaluate i) near wellbore invasion and related damage due to two typical Drill-In fluids (D.I.F.) and ii) performance of various cleanup procedures using specific "breakers".

In the first part of the paper, values of Flow Initiation Pressure (F.I.P.) and return permeability measured on rock samples damaged with an Oil-Based Mud (OBM) and with a Water-Based Mud (WBM) are compared to evaluate the self cleaning properties of sandstone core samples having a large permeability contrast. In the second part, the performance of various "breakers" (mutual solvent, emulsified acid, surfactants for OBM, oxidizers and enzymes for WBM) is presented. Results show that the OBM present better filtration properties and is less damaging than the WBM. The general trend is that near wellbore return permeability (0–10 cm) and self cleaning properties are strongly related to the Jamming Ratio (Mean pore throat diameter/mean mud solids diameter). The use of OBM breakers may induce additional damage if the soaking time is not carefully controlled. On the other hand, WBM breakers may be efficient if they are used under optimum conditions.

Finally, some recommendations are given for designing a low-damaging D.I.F. and to define, if necessary, the best cleanup procedure.
Minimising Clay Sensitivity to Fresh Water Following Brine Influx
Authors: Conway Michael W. , Himes Ron E. , Gray Russell
Published: December 2007

Well productivity or injectivity can be significantly affected by damage to the reservoir section of a well due to reaction between the formation and the introduced fluids. Most reservoirs in the mid-continent region of the United States have varying amounts of illite (and mixed layer illite/smectitie) and kaolinite clays. These non-swelling clays are susceptible to migration thus causing permeability loss due to plugging of pore throats. When abundant amounts of these clays are identified by petrographic techniques, water sensitivity is usually proposed as a potential problem in the reservoir.

Surprisingly, we have found that many reservoir rocks with greater than 10% clay can be perfectly stable to the introduction of fresh water. The cation content of the reservoir brine present at the time of clay diagenesis or the resident formation brine dictates whether or not the clays will be sensitive to fresh water. Many of these reservoirs have low salinity connate fluids of less than 30,000 total dissolved solids. We have identified that previously stable clays can become sensitised to freshwater due to introduction of an intermediate brine such potassium chloride as commonly used in completion operations. Laboratory studies will be presented that identify the factors responsible for permeability stability in rocks containing illite and kaolinite clays.
Interaction Between Growing Channels in Proppant Packs: Length and Number of Channels
Authors: James Simon G. , Lee Chengho , Howard Paul R. , Cundall Peter A.
Published: December 2007

The formation of channels in propped fractures, in the presence of fibers, has been demonstrated experimentally under a wide variety of conditions. The presence of channels can have a significant impact on the effective fracture conductivity and consequently the productivity of a given well. While single channels are observed in experiments, a question is how many channels may be present in real proppant packs and how long do they grow? The length is especially important when proppant flowback control additives are used as "tail-ins" with the last part of the proppant pack. To complement the experimental study, the understanding of channel propagation and the interaction between multiple growing channels was modeled using finite difference codes.

Modeling was performed using a 2-dimensional explicit finite difference program. The formation of channels was predicted by using two parameters – a critical flow rate and a curvature limit. Results demonstrated that the curvature limit is a critical parameter in determining the stability of channels. Calibration of the model with laboratory experiments with proppant and fibers provided clear explanation as to why channel formation provides proppant pack stability at high flow rates.

For a given flow rate, channels grew until a stable length was attained; increasing the flow rate would cause the channel to grow further until a subsequent stable length was attained. Multiple channels were generated but a dominant channel grew once the length of the channel was greater than the spacing between channels. The presence of one, or several widely spaced, long channels will have a much larger impact on productivity than many short channels. Bilinear flow conditions resulted in channel growth to a stable equilibrium length. This is expected to occur in real fractures. A consequence of this behavior is that fractures should be flowed back at high rates to grow channels that will then be stable at subsequent production rates.