bluuebunny/crossref_metadata_2025 huggingface dataset:
Seismically Derived Variation of Heterogeneity Factor-Application in Estimation of Production Rate and Porosity Variation within the Reservoir
Authors: Mohanty S. N. , Krishna B. R.
Published: December 2007

In heterogeneous reservoirs rate of production of hydrocarbon vary significantly between the wells. Estimation of flow rates prior to drilling is very important in formulating development scheme. Any change in petrophysical properties of a reservoir is reflected in variation of heterogeneity. Quantification of variation of heterogeneity will help in predicting the reservoir performance and production of hydrocarbons. This paper outlines a method for deriving heterogeneity gradient using seismic data and its application in predicting the performance and porosity of unexploited part of the Narimanam field in Cauvery Basin, Southern India.
Legislative Trends in Environmental Regulations Impacting the Petroleum Industry
Authors: Sandosham A. S. , Lim Doris M. F.
Published: December 2007

Emerging changes in environmental regulations in many Asian countries will significantly impact the petroleum industry. These changes include the implementation of more effective ambient air quality monitoring programs in many Asian countries, tightening of point source emission standards, and programs directed at vehicular emissions including changes to fuel specifications. This paper presents the current ambient air quality standards in selected Asian countries and highlights upcoming regulatory trends that will impact the industry. Case studies are presented for Hong Kong and the Philippines to demonstrate how these changes will be implemented in the next five years.

Vehicles are the largest contributor to urban air pollution. Hence, many regulatory programs focus on reducing vehicle emissions to improve air quality. Significant changes to fuel specifications, including the impact of region-wide reductions in fuel sulfur and benzene contents will be discussed. These changes will impact the petroleum industry, particularly in the refining sector. Measures that have been implemented to control vehicular emissions include the conversion of public transport vehicles to Liquified Petroleum Gas (LPG). As LPG and liquefied natural gas (LNG) usage increases, particularly due to environmental considerations, strategic changes will be required in the petroleum industry to profitably manage this transition.
Analysis of a Non-Volumetric Gas-Condensate Reservoir
Authors: Vega L. , Barrufet M. A.
Published: December 2007

Predicting water encroachment can be of critical importance in describing and managing a hydrocarbon reservoir.

This study focuses on the use of the generalized material balance equation (GMBE) proposed by Walsh, et al1,2 along with the analytical solution to the diffusivity equation for a constant inner boundary pressure as presented by van Everdingen and Hurst to determine the size of a water-bearing formation in contact with a gas-condensate reservoir.

When the hydrocarbon reservoir fluid is a gas-condensate, it is essential to use the GMBE. Should the conventional material balance equation (CMBE) be used in lieu of the GMBE, considerable errors could be introduced as will be shown.

The main goal of this paper is to illustrate the ability of the GMBE to determine the size of an aquifer encroaching into a gas-condensate reservoir. Once this size is obtained, it could be used as an input parameter to a reservoir simulator to forecast the future expansion of the aquifer as depletion proceeds.

When the CMBE is used to describe black oil reservoirs, certain simplifying assumptions are normally made. Those include neglecting the effect of the compressibilities of the connate water and the reservoir rock, in addition to the volatilized liquid in the gas phase. The effect of these assumptions in gas-condensate reservoirs will be examined.
Testing of Gas Condensate Reservoirs - Sampling, Test Design and Analysis
Authors: Kool Henk , Azari Mehdi , Soliman M. Y. , Proett Mark A. , Irani Cyrus A. , Dybdahl Bjørn
Published: December 2007

Testing of gas condensate reservoirs requires careful coordination of all parameters in the analytical process. Therefore, the sampling procedure, the laboratory analysis of the collected samples, the design of the testing equipment, and the design and analysis of the test itself are all critical to the accuracy of the analysis. This paper will outline the methodology and procedures used in testing gas condensate reservoirs.

Obtaining a representative formation fluid sample that may be used for compositional and pressure-volume-temperature (PVT) analysis is crucial in testing gas condensate reservoirs. In most cases, this means maintaining a monophasic sample as close as possible to actual reservoir conditions. New sampling technologies have been introduced that improve the quality of the initial sample and can maintain the sample integrity. Additionally, new downhole sensor technologies show promise of improving sample contamination estimates and making in-situ fluid property measurements. The various sampling techniques are discussed, and comparisons of processes that include wireline formation testing and bottomhole sampling, isokinetic sampling used in drillstem and production testing, and surface sampling are made.

Laboratory testing procedures including sample quality validation, error propagation, and sample contamination are also discussed.

The flow of gas condensate in a reservoir is a complicated mathematical problem involving phase changes, condensate loss into the small pores of the rock, multi-phase-flow of the wet gas oil and possibly water, phase redistribution in and around the wellbore, and finally, liquid vaporization back into the condensate gas. A well test can provide identification of the absolute reservoir and relative permeabilities, the source of declining gas permeability, near wellbore damage, and the reservoir pressure. It can also distinguish the extent of the liquid-condensate bank that forms a composite reservoir, as well as the location of the nearby boundaries.

The analysis procedure and techniques will be illustrated through presentation of two field cases. In the first case, the flowing pressure is above the dewpoint pressure. Thus, the fluid inside the reservoir is a single-phase gas, and liquid dropout causes phase segregation in the wellbore. In the second case, the well is producing below the dewpoint pressure while the original reservoir pressure is above the dewpoint pressure. This caused the well test to resemble that of a composite reservoir with earlier phase-segregation effects.
Managing Change in a Changing Environment: Creating an Improved Logistics Organization for Offshore East Kalimantan
Authors: Kovacevich S. T. , Hinrichs L. J. , Hasan U.
Published: December 2007

This report documents an original case study summarizing the success of an East Kalimantan oil & gas operator in creating an improved logistics organization. The Logistics and Supply-Chain Management (L&SCM) Project was designed and implemented in an eighteen (18) month period beginning in October 1998. It focuses on the operational aspects of aviation, marine services and the supply base function. The paper describes key project management aspects from preliminary planning, sponsorship and team selection through the management of change (MOC) during transition to implementation. A chronological review addresses the original charter, the discovery phase, analyses, recommendations, implementation and provisions for continuity and continuous improvement.

Performance to deliverables, keys to success and lessons learned are detailed including the implementation of new standards/policies/procedures, innovative technology and empowered personnel. Dealing with challenges both internal and external to the organization will be discussed, in particular resistance to change, legacy thinking and the supply market.

The paper also reveals new information generated from field data and computer modeling of marine logistics activities. These applications and resulting information were paramount in leading us to a successful business solution to improving the logistics operation.

Final conclusions revolve around an implemented logistics program that created quantifiable value to all stakeholders and generated client/market acceptability. Major results include creating a new, accountable logistics organization that operates 20% less expensively. Internal clients enjoy a transparent operation providing safer and more reliable service. Management has a more cost-effective, disciplined organization that is measurable. Suppliers and contractors better understand business needs and have provided quality resources.
Peninsular Malaysia Gas Utilisation Project – Challenges in Gas Supply Planning
Authors: Samsudin Abdul Rahim , bin Mohamed Mohd Sabri
Published: December 2007

The history of natural gas utilisation in Peninsular Malaysia started with the commencement of the Peninsular Malaysia Gas Utilisation (PGU) project in 1984. The project was developed in three phases over a period of less than two decades covering almost the entire area of Peninsular Malaysia.

While the power sector will continue to drive the future growth of PGU gas demand, the demand from the gas based industries is also expected to increase rapidly in tandem with the growth of the national economy. In recent years, the role of natural gas is becoming more important as the existing and upcoming petrochemical industries rely heavily on the natural gas for the feed stocks to generate high value added products. Indeed, the PGU project acts as a catalyst to the power generation sector and other gas based industries providing significant contribution to the national economy.

Malaysia is endowed with abundant natural gas resources to support the long term development of the PGU project. In addition to the commitment to develop the discovered gas resources, PETRONAS through its Production Sharing Contractors (PSCs) is also committed to intensify exploration efforts to discover new gas resources. Prudent planning is therefore vital for ensuring a sustainable natural gas supply to the gas projects.

This paper will review the historical and future outlook of the gas industry in Peninsular Malaysia. Among others, the paper will cover topics on an overview of the PGU project and challenges in gas supply planning to meet demand. Prudent gas supply planning will result in an optimum gas supply and demand matching, sufficient excess capacity margin and optimisation in gas development and evacuation which in turn will improve companies' bottom line as well as other benefits to all parties.
Conductor Sharing Wellheads - More for Less
Authors: Anchaboh L. , de Lange F. P. A. , van Beelen C. J. , Tan R. K. W.
Published: December 2007

All brown field operators face the challenge to further develop mature fields from existing facilities, whilst ensuring that infill wells continue to add value to their business. Implementation of innovative drilling and completion technology is an important ingredient to achieve this objective. Conductor Sharing Wellhead (CSW™) technology was identified by Brunei Shell Petroleum Company Sdn. Bhd. (BSP) as one of several key enablers for the cost effective development of mature fields offshore Brunei. This technology maximizes the utilization of the remaining existing surface facilities by accommodating two (or more) new wells in one single conductor slot. Additionally, it has been demonstrated that the application of CSW™ technology markedly reduces overall development costs.

The application of CSW™ technology is therefore not restricted to brown field developments only, but it will also allow new field developments to become more attractive. It is demonstrated that CSW™ allow the installation of smaller platforms that can realize the full potential of their big brothers at reduced capital investment, engineering and installation costs.

The first CSW™ system was installed offshore Brunei in December 1998 in Block 14 in the Champion field. This development utilized two of the existing spare 30" conductors to drill and complete three new horizontal wells with one shared well slot remaining for future use. This initial success led to the identification of additional similar applications and an alternative application such as drilling two wells (per slot) from abandoned conductor slots, recovering their conductors and drilling four new wells from the salvaged conductor slots.

The experience gained with CSW™ technology indicates that drilling two wells from one conductor can save USD 1.0 million compared to two conventional wells, whilst better planning and design improvements have reduced the installation times of the CSW™ by some 50 percent.

This paper describes the details of the planning and execution phases during the CSW™ project. We will also discuss lessons learnt during the course of the project, which resulted in significant cost savings, specific design changes and the delivery of a wellhead system that has now been established as a new drilling standard for the development of brown fields and new field developments alike. Close cooperation between field staff and office staff of both the operator and the wellhead supplier were key in realizing a step change in technological and economic opportunities.
Estimation of Rock Dynamic Elastic Property Profiles through a Combination of Soft Computing, Acoustic Velocity Modeling, and Laboratory Dynamic Test on Core Samples
Authors: Widarsono B. , Wong P. M. , Saptono F.
Published: December 2007

This paper presents a new approach for estimating rock elastic properties in wells, especially for wells with limited log suites. The approach is basically a combination of efforts that are put is a series of steps. Firstly, is to model a synthetic S-wave velocity profile for a key well, with support from laboratory acoustic measurement on core samples, enabling the establishment of profiles of elastic properties through the theory of elasticity. Secondly, the modeling and validating of relationship between P-wave velocity, Poisson ratio (as an example in this paper), porosity, water saturation, shale contents, and matrix density based on the log data available for the key well. Thirdly, prediction of all missing log suites (if any) for other wells using soft computing (artificial intelligence/neural network) that has been ‘trained’ using data from the key well and other wells that have more or less complete log data. Fourthly, estimation of rock elastic properties for all wells (except the key well) using soft computing. Finally, evaluation of results using comparison with the model validated in the key well. The method has been applied on 14 wells of an active oil reservoir in Java, Indonesia. Comparisons of porosity and water saturation values between results from standard log interpretation and results from the validated model serve as indicators for the success of the method. The reasonably good comparisons achieved have proved that the new approach is applicable, and the use of the model relationship avoids ‘blind’ estimation often practiced in reservoir characterization.
Introduction Experiences of a New High Accuracy Through-Tubing Pulsed Neutron Reservoir Management Solution in Asia-Pacific
Authors: Simpson G. A. , Fox P. , Chafai N. , Truax J. A.
Published: December 2007

Evaluation of three-phase reservoirs in gas injection fields has been a major challenge in the Asia-Pacific region. Low-to-mid porosity and complex wellbore completion environments create a difficult, pulsed neutron logging environment for analyses of remaining oil saturation, fluid contacts, and identification of flood breakthrough.

A new, through-tubing, pulsed neutron measurement system has recently been introduced to the industry in the Asia-Pacific region. Refinements have achieved the highest available spectral resolution and accuracy of any slim tool, extending multi-phase reservoir evaluation to lower porosity formations and to more complex wellbore environments. Features of the tool include single-pass simultaneous carbon/oxygen (C/O) and capture cross section (S) logs, quantified water flow analysis, porosity logs, and elemental analysis, all acquired at higher speeds than previously available. Modern tool characterization and adherence to well-established best practices have enabled reliable decision making based on application of the higher quality pulsed neutron measurements to these difficult situations, which were previously considered infeasible.

This paper discusses potential for economic gains that can be realized from enhanced reservoir characterization with the new pulsed neutron system. Additional hydrocarbon reserves can be delivered from application of the modern technology within these more challenging environments. Log examples included in this paper will show that the new tool is capable of determining gas, oil, and water volumes in formations with less than 10 percent porosity. It includes details of an interpretation method tailored to a specific reservoir yet applicable to many multiphase situations. With advanced pulsed neutron devices as part of a well designed investigative package, more robust support of reservoir management can be realized.
Monetising Small Oil Fields-In Pursuit of Innovative Solutions
Authors: Hashim Kamarudin , Shabudin Aidil
Published: December 2007

One of the challenge for the petroleum industry sector in Malaysia is to monetise oil resources at earliest possible timing. After production since early 1970's, there are about 3.43 billion barrels of remaining oil reserves located offshore Malaysia. About 550 million barrels of the oil reserves are contained in some 62 fields with estimated ultimate recovery (EUR) of less than 30 million stock tank barrels (MMstb) per field. For these small oil fields, efforts undertaken by the petroleum producers in Malaysia, for examples; PETRONAS Carigali Sendirian Berhad (PCSB), Esso Production Malaysia Incorporated (EPMI) and Sarawak Shell Berhad / Sabah Shell Petroleum Company (SSB/SSPC), have yielded achievements which have begun to pave paths for prospective successes in developing the small oil fields.

In addressing the challenge to monetise oil reserves expeditiously, the petroleum producers in Malaysia have harnessed their efforts to achieve cost effective development for the reserves. Cost effective developments lead to improved project profit margin. Optimization efforts on small oil field development concepts have been aggressively pursued since the middle 1990's. Depending on development concept adopted, the development costs estimated for small fields offshore Malaysia have since improved from over RM 400 million (USD 160 milion) to less than RM 100 million (USD 26 million) per platform excluding the development drilling costs. The difference in cost is the result of continuous efforts in development concepts optimisation.
Geothermal Hot-Water Flood-Balam South Telisa Sand, Sumatra, Indonesia
Authors: Pederson John M. , Sitorus Jayadi H.
Published: December 2007

Hot water flooding is a mature technology that dates back to the 1960's. Although a technical success, heating injected water by burning a fuel proved to be uneconomic in those days. However, using hot water from geothermal sources eliminates the need to burn oil and results in a true increase in ultimate recovery with attractive development costs.

This technique is particularly useful in fields with shallow, high viscosity waxy oil formations and deeper water bearing formations with relatively low salt concentrations. Many oil fields in the Sumatra basin fit this category. Costs to drill geothermal source wells in Sumatra are economic because of the high geothermal gradient observed in the central Sumatra basin (0.03 to 0.04 °F/ft).

This paper shows a novel approach of combining typical waterflood operations with geothermal hotwater sources is not only cost effective for new enhanced oil recovery projects but is also an effective optimization technique for existing waterfloods. A case study of the Balam South Telisa reservoir is presented. Results from two other fields in Sumatra are also shown to illustrate the application of this concept to other fields.
Studying the Mechanism of Magnetic Field Influence on Paraffin Crude Oil Viscosity and Wax Deposition Reductions
Authors: Tung Nguyen Phuong , Van Vuong Nguyen , Long Bui Quang Khanh , Vinh Ngo Quang , Hung Pham Viet , Hue Vu Tam , Hoe Le Dinh
Published: December 2007

Dragon and White Tiger crude oils are two different kinds of paraffin crude oils of Vietnam. The screening studies on their fluidity changes under the influence of magnetic forces have been completed. The relationships between their viscosity changes and magnetic force strength, temperature, and duration of treatment were obtained, the optimal conditions for the viscosity reducing were found. The changes in paraffin crystallization under magnetic fields were studied using scanning electronic microscopy (SEM). The possibilities to defense and remove wax clogging and deposition obtained by magnetic treatment was also studied and proved. Base on these data, the mechanism of the influence of magnetic fields on paraffin deposition control was proposed. The data can also serve as a basic in designing and construction high effective magnetic tools to improve liquidity of high waxy crude oils in this area.
Investigation of a Problematic Well to Restore Production
Authors: Gai H.
Published: December 2007

This paper describes a series of investigations carried out in an ESP lifted well (below bubble point production) that experienced a cluster of unexpected problems resulting in loss of production, and how the investigations restored production. The problems among others included apparent severe productivity drop coupled with downhole temperature rise, and the investigations eventually led to the discovery of asphaltene that has not been found in the field before. Analysis of all the problems and investigations including lessons learnt are shared in detail.
Determination of Volumetric Sweep Efficiency in Barrancas Unit, Barrancas Field
Authors: Vicente M. , Crosta D. , Eliseche L. , Scolari J. , Castelo R.
Published: December 2007

This paper describes the analysis of the evaluation and surveillance of the waterflooding in the South of the Barrancas Field, after more than 30 years of water injection. The volumetric sweep efficiency is a parameter of complex evaluation in a mature field, and it has importance in the determination of the amount and spatial distribution of the additional oil recovery.

The volumetric sweep efficiency can be calculated and predicted by means of two complementary methods that use basic principles of material balance, oil displacement by water and conformance plots. This procedure may help to evaluate the water injection efficiency with the current operation. Therefore the displacement efficiency and the remaining average oil saturation can be predicted.

The evaluation techniques of volumetric sweep efficiency and water injection efficiency are tools that can be used with conventional decline curve analysis, to estimate and predict the unswept fraction of the reservoir by water injection and the additional oil recovery potential. This method needs production and injection data, and can be applied to any configuration of patterns. Finally, this lead to take the correct actions in the management of the waterflood and estimate whether the success of the performance of the waterflooding depends on volumetric efficiency or displacement efficiency.
Simulation Based Dimensionless Type Curves for Predicting Waterflood Recovery
Authors: Dunn M. D. , Chukwu G. A.
Published: December 2007

Predicting waterflood recovery with simulation based dimensionless performance curves has advantages over the more traditional approaches in certain applications. This paper discusses the advantages of the type curve approach, how the curves are created, and how they can be applied to predict pattern and full-field performance. This technique is suitable for screening/ranking projects, and is particularly helpful when sensitivity and uncertainty analyses are necessary to improve reservoir management decisions.

The dimensionless type curve methodology can be applied to many types of fields. A case study of a large, waterflooded field is presented to show how the curves are created and how they can be applied. In this field, a study of the geology and stratigraphy indicated that reservoir continuity, permeability variance, and effects of faulting were the most important drivers of recovery efficiency. Simulations were performed on 45 datasets to describe waterflood performance over the range of variation. A spreadsheet program was created to predict recovery of any description, based on interpolations of the simulation results.

The dimensionless curves can be used to compare actual well performance to predicted performance, to predict full-field performance by summing well curves, and/or as the basis of an integrated evaluation tool. Using correlations to predict recoveries allows for ease of sensitivity analyses, and ease of application by casual users in an organization. This paper should benefit anyone who struggles with the task of applying simulation-based knowledge to everyday decisions when optimizing waterflood recovery.
Funding For Abandonment of Cook Inlet Alaska Oil and Gas Facilities: A Landowner's Perspective
Authors: Van Dyke William , Zobrist Daniel H.
Published: December 2007

Offshore oil and gas production platforms must undergo (possibly) expensive abandonment operations at the end of field life. In Cook Inlet Alaska, lessees are required, at abandonment, to dismantle and remove materials, machinery, equipment, etc. and return the leased lands in good order and condition as required under the oil and gas leases. Failure to complete abandonment responsibilities allows a claim for damages, as well as causing a default of the lease. In the worst-case scenario, default forces the landowner to step in and assume the responsibility of abandonment operations. To mitigate this risk, the landowner requires of the lessee financial guarantees such as bonds or independent escrow accounts funded to cover the cost of abandonment. At the Middle Ground Shoal Field in Alaska the landowner (State of Alaska) considers the value of the oil and gas reserves as collateral. This reduces other mitigation mechanisms that may be required of smaller independent producers when taking an assignment of the leases and facilities from giant, multinational, integrated oil firms. Accepting underlying proven reserves as collateral lowers the overhead costs to lessees, and frees investment dollars for incremental field development and exploration.
Field Test of a Novel Low Viscosity Fracturing Fluid in the Lost Hills Field, California
Authors: Vasudevan S. , Willberg D. M. , Wise J. A. , Gorham T. L. , Dacar R. C. , Sullivan P. F. , Boney C. L. , Mueller F.
Published: December 2007

The Monterey formation, Belridge Diatomite is a high porosity (45%) low permeability (0.5 – 7 md), low Young's modulus (~100,000 psi) oil reservoir with few stress barriers for fracture containment. Due to the low permeability it is desirable to optimize the fracture length per pound of proppant placed. Conventional cross-linked fluids are not well suited for this purpose as they create excessive width – reducing the effective fracture length generated for a given amount of proppant. Post-treatment production tests often show only 30 – 100 ft of effective fracture length even for relatively large treatments designed for longer length. Not only is production limited by these shorter-than-designed half-lengths; excessive fracture width combined with low closure stress often leads to serious sand production problems. Pseudo-3D simulations indicated that longer fractures could be realized by significantly reducing fluid viscosity.

A novel low viscosity fracturing fluid, designed to address the serious problems unique to low-modulus formations, was field-tested in the Lost Hills field, California. The low-viscosity fluid developed for this application was composed of a linear gel and a fibrous material. Laboratory studies established that the fiber greatly hinders proppant settling, while maintaining a low slurry viscosity required for fracture length creation. Proppant concentrations up to 12 PPA were pumped with this fluid.

Seven new wells were treated with the novel fluid. All wells were fractured in multiple stages; 1,250,000 to lbm of proppant was used in each well. Real-time pressure data was collected on all stages, and treatments on the first two wells were observed with downhole tiltmeters. Both pressure and tiltmeter data indicated that for similar sized treatments, longer fracture half-lengths were achieved with the new fluid – 200–400 ft – versus 30–100 ft for conventional crosslinked gels. Production from the test wells compares favorably to offsets, while using 30% less proppant than conventional treatments. Furthermore, it appears that proppant flowback and sanding problems are significantly reduced.
Assessment of the Stability of Inclined Wells
Authors: Garrouch Ali A. , Ebrahim Abdullah S.
Published: December 2007

The need for wellbore stability analysis during the planning stage of drilling is rising due to the economic considerations, and because of the increasing use of highly-deviated, extended-reach, and horizontal wells. Wellbore instability can cause lost circulation when tensile failure occurs, and can cause caving and hole closure when collapse failure occurs.

This paper presents the method and results of wellbore stability analysis for three common reservoir lithologies consisting of a consolidated sandstone, a shaly sandstone, and a limestone formation. The effect of stress anisotropy on the mechanical stability of wellbores is evaluated while varying the inclination angle from 0 to 90°, for both the Mohr-Coulomb and the Drucker-Prager failure criteria.

The selected failure criterion, and the in-situ rock stress regime are found to have significant effects on the safe drilling fluid density required to maintain wellbore integrity. According to some field examples, the Drucker-Prager failure criterion appears to systematically mimic rock conditions more realistically than the Mohr-Coulomb failure criterion. The simulated consolidated sandstone formation is found more stable with lesser drilling fluid density, at any inclination angle, than the simulated shaly sandstone formation. The simulated limestone formation is even more stable than the consolidated sandstone at all inclination angles since it requires lighter fluid density to prevent wellbore collapse. For all these rock types, the higher the deviation angle (from vertical), the higher the drilling fluid density needed for maintaining wellbore integrity. For the depth and rock conditions simulated, both consolidated and shaly sands are unstable in a strike-slip stress regime, but stable in an extensional stress regime. The simulated limestone formation was found stable in both stress regimes. However, in an extensional stress regime, the limestone formation required lighter fluid density to maintain wellbore integrity than in a strike-slip stress regime.

This study provides a valuable insight into the influence of inherent factors such as the in-situ stress regime, pore pressure, and formation properties, and conditionally variable factors such as wellbore directions and inclination angle on wellbore stability. Results of this investigation can be used to improve the management of wellbore integrity, thereby increasing drilling efficiency and reducing drilling costs.
Application of a Concentrated Oxidizing Breaker Preflush in High-Permeability Frac-Pac Treatments
Authors: Park E. I. , Bennett Scott , Powell Ron , Procyk A. D. , Griffin D. E.
Published: December 2007

A major operator has used a novel approach to improve the performance of stimulation fluids in high-permeability, deepwater completions. A concentrated breaker solution is pumped into the formation before the introduction of crosslinked gel. This breaker solution improves cleanup of fractured and non-fractured perforations during high-permeability fracturing operations. This technique was developed because laboratory testing indicated that conventional breakers can be consumed by sediments, resulting in less than optimal gel breaks. This observation, when combined with the knowledge that whole crosslinked gel leakoff occurs in high-permeability formations, makes it necessary to pre-treat the near-wellbore region with a sacrificial concentrated breaker.

This paper includes studies on core materials with specific mineral compositions to determine the effectiveness of the concentrated breaker technique. Interaction between fracturing-fluid breakers and formation materials has been investigated at temperatures between 120° and 225°F. Core-flow experiments measuring the amount of active breaker present in the fluid exiting the core have also been performed with both enzyme and oxidizing breakers, and retained breaker activity of enzyme and conventional oxidizing breakers was compared.

Enzyme stability is affected by the presence of minerals as well as the formulation of the stimulation fluid. A comparative study performed at 175°F showed that breaker activity decreases as temperature increases for both a conventional oxidizing breaker as well as a stable, high-temperature oxidizing breaker. However, at 225°F the stable, high-temperature oxidizing breaker maintained some activity upon exiting the core.

This paper highlights three successful applications of the concentrated breaker solution in the Gulf of Mexico (GOM). These successes are compared to performance from offset wells, providing a benchmark for identifying the benefits of this new process.
Acidizing Carbonate Reservoirs: Numerical Modelling of Wormhole Propagation and Comparison to Experiments
Authors: Golfier F. , Bazin B. , Zarcone C. , Lernormand R. , Lasseux D. , Quintard M.
Published: December 2007

Many acidizing treatments in carbonate reservoirs do not produce expected increase of productivity, especially in the case of open-hole horizontal wells. This is due to the poor modelling of near well-bore mechanisms. This paper describes a new 2D numerical simulator which features a better description of the physics and which is validated on experimental data.

The numerical simulator presents the coupled mechanisms of flow and dissolution at the origin of the wormhole instability. The macroscopic dissolution equation is derived from a volume averaging of the advection/diffusion and reaction equations written at the pore scale. The flow description is based on Darcy-Brinkman equation which accounts for Darcy's flow in the matrix and Stokes flow in the wormhole.

Two series of experimental results are used for the validation: acidizing experiments with carbonate cores previously published by IFP and other investigators and new model experiments. These experiments consist in injecting under-saturated salt water into a porous medium made of salt. The dissolution instability, channel development and wormhole propagation are recorded by a video camera.

The results predicted by the numerical model reproduce most of the observations in salt and carbonate: 1) the effect of the flow rate on the dissolution regime, i.e. compact, wormholing or uniform behaviour; 2) transitions from wormholing to ramified which slow down the wormhole propagation rate; 3) the effect of the injection conditions on the wormhole propagation rate, the optimum flow rate and the maximum distance of wormhole penetration. Optimum conditions for wormhole propagation are deduced.

The model is built to provide relations on wormhole propagation rate depending on the reservoir properties and the injection conditions. These relations will then be integrated in a near well-bore simulator coupled to a reservoir simulator for a better design of the acidizing treatments in carbonates.

Corresponding Author: Mrs Brigitte Bazin, IFP.
Hydroxyaminocarboxylic Acids Produce Superior Formulations for Matrix Stimulation of Carbonates
Authors: Frenier W. W. , Fredd C. N. , Chang F.
Published: December 2007

In this paper, we will describe the development and testing of hydroxyaminocarboxylic acid chelating agents (HACA) as components of matrix acidizing formulations for stimulating carbonate formations. The pioneering work of Fredd and Fogler1 demonstrated that organic acids and chelating agents have unique attributes that lend themselves to efficient production of wormholes in many acidizing situations. We have applied the techniques for determining transport and reaction kinetics to stimulation fluids containing the hydroxy amino chelating agents. Linear core flood tests were used to study wormhole formation. Rotating disk tests with marble samples were employed to elucidate the kinetics and mechanisms of the dissolution processes over a temperature range of 20 °C to > 100 °C (65 to >200 °F).

Both HACA chemicals studied, that is, hydroxyethylethylenediaminetriacetic acid (HEDTA) and hydroxyethyliminodiacetic acid (HEIDA) produced wormholes in limestone cores when tested at 150 °F. However the efficiency and capacities differ. Because these chemicals have high solubility in the acidic pH range, it was possible to test acidic (< pH 3.5) formulations. These solutions have properties of both mineral acids and complexing agents. The rotating disk tests allowed us to measure the diffusion coefficients as well as the surface reaction rate coefficients, at different temperatures. These parameters were used to determine the efficiency of wormhole formation as a function of temperature, by an overall reaction rate vs. pump rate relationship; i.e., the Damköhler number.
Screenless Completions: The Development, Application and Field Validation of a Simplified Model for Improved Reliability of Fracturing for Sand Control Treatments
Authors: Guinot Frédéric , Zhao Jun , James Simon , Emmanuel d'Huteau
Published: December 2007

The successful application of fracturing for sand control has been reported from many different areas. Several explanations have been advocated for these successes such as "re-stressing" the wellbore, creation of a "halo effect" around the wellbore and maintaining the bottom hole pressure above a critical level to prevent perforation collapse. The latter approach has led to complex models predicting the conditions of perforation failure.

However, once the perforations have collapsed, the production of formation sand is governed by the transport of the sand from the perforation tunnels. Frequently, decreasing the production rate stops sand production, indicating that there is a critical flow rate below which sand cannot be transported into the wellbore. In this study, we present the development, application and field validation of a spreadsheet tool to improve the reliability of fracturing for sand control treatments.

A universal curve was generated from numerical simulations, showing that the percentage of the total flow through the perforations not connected to the fracture was a function of the formation and fracture properties and was independent of the reservoir fluid properties. The generation of a universal curve eliminates the need to use a reservoir simulator and allowed the development of a tool to aid the design of fracturing for sand control treatments. The spreadsheet tool has been validated with data from successful fracturing for sand control treatments.
Achieving High Rate Completions with Innovative Thru-Tubing Sand Control
Authors: Bell Thomas A. , Martch William E. , Morrison Dan W.
Published: December 2007

An improved through-tubing sand control technique was utilized recently to enhance reservoir recovery and improve life-cycle economics. This coiled tubing-conveyed method uses several technical innovations that improve the reliability of the vent screen sand control completion. The innovations can be shown to: (1) improve the rate at which reserves can be recovered; (2) improve completion efficiency; (3) reduce mechanical risk; (4) reduce completion costs; (5) extend the economic life of the well; and (6) control fines migration.
Thermogelf Project: An Efficient In-Situ Insulation Method to Enhance Production
Authors: Kuperus Eddy , Beauquin Jean-Louis , Jansen Bernard
Published: December 2007

Besides curing wax, hydrate or viscous flow problems, thermal insulation should also improve lift performance and producing time of wells and risers, since it helps to reduce by various ways the liquid content in a gaseous column of production. "Thermogelf" project objectives were to prove benefits of thermal insulation on well performance and to test one specific method to set a super insulation (an aerogel) in a producing well, avoiding a work-over. Thus, a silica aerogel has been processed into a self-killing gas well in the Netherlands, in autumn 1999. Although the process was not completed, because not so fast as expected, this field trial enhanced significantly the well production, and produced a decisive experience to improve the implementation method. Therefore, this project demonstrated that "Thermolift" methods could be lucrative on numerous mature and new fields, and aerogel processing in the annulus of wells should be next developed as a relevant technology.
Measurement of the Mechanical Properties of Filtercakes
Authors: Cerasi P. , Ladva H. K. , Bradbury A. J. , Soga K.
Published: December 2007

In order to improve drilling mud design to cater for specific well situations, a more comprehensive knowledge and understanding of filter cake failure is needed. This paper describes experimental techniques aimed at directly probing the mechanical properties of filter cakes, without having to take into account artefacts due to fluid flow in the substrate. The use of rheometers allows us to determine shear yield stress and dynamic shear modulii of cakes grown on filter paper. A new scraping technique measures the strength and moisture profiles of typical filter cakes with a 0.1 mm resolution. This technique also allows us to probe the adhesion between the filter cake and its rock substrate. In addition, μdometer drained consolidation and unloading of a filter cake give us compression parameters useful for Cam Clay modelling. These independent measurements give similar results as to the elastic modulus of different filter cakes, showing an order of magnitude difference between water based and oil based cakes. We find that these standard cakes behave predominantly as purely elastic materials, with a sharp transition into plastic flow, allowing for the determination of a well-defined yield stress. The effect of solids loading on a given type of mud is also studied.
The Relative Importance of Solids and Filtrate Invasion on the Flow Initiation Pressure
Authors: Roy Rana S. , Sharma Mukul M.
Published: December 2007

Studies conducted earlier indicate the importance of solids invasion on determining the magnitude of Flow Initiation Pressure (FIP). Other studies have shown that relative permeability effects can play an important role in determining the FIP. In this paper we clearly identify the conditions under which solids invasion and relative permeability effects can play important roles.

Experiments are conducted with brine saturated cores and cores containing a residual brine saturation. FIP measured by flowing back with brine and with oil are reported. For low permeability rocks and small mobility ratios, relative permeability effects appear to play a dominant role. For higher permeability rocks (>100 md) and large mobility ratios, solids invasion becomes increasingly significant. A key difference between these two components of FIP is that while relative permeability effects will dissipate with time, internal filter cakes may not.

A model to calculate the FIP is presented which allows us to evaluate the relative magnitude of the pressure drop caused by relative permeability effects versus that caused by solids invasion. The results of this study clearly show that both solids invasion and filtrate invasion can play an important role in determining the FIP. In addition factors such as the relative mobility of water and oil and the depth of invasion of solids are important parameters. A method is presented that allows us to estimate FIP values in the field based on static filtration tests conducted on cores.
Modelling of Near-Wellbore Damage Removal by Natural Cleanup in Horizontal Open Hole Completed Wells
Authors: Ding Y. , Longeron D. , Renard G. , Audibert A.
Published: December 2007

Formation damage in horizontal wells, often open hole completed, is a critical point for oil fields developed in deep offshore where acceptable development costs are based upon a limited number of highly productive wells. This paper describes a simplified numerical approach to model filter cakes removal by natural cleanup when the well is put under a drawdown pressure difference. A flow simulator taking into account the near well permeability variation has been developed using cylindrical grid with very small gridblocks around the well. Laboratory data obtained on sandstones damaged with an oil-based mud have been used as input data to model filter cakes removal by natural cleanup. The purpose of this modelling is to optimize the applied drawdown pressure to study the variation of well productivities as a function of the pressure drawdown to get the best possible well performance preventing sand production problems in poorly consolidated formations.
Effects of Non-uniform Skin Distribution on Horizontal Well Inflow Performance
Authors: Permadi P. , Wibowo W.
Published: December 2007

Formation damage around a horizontal wellbore has been a long-standing problem. The damage zone is expected to be a cone-like shape, extending from the heel end to the toe. This situation leads to a difficulty in studying the inflow performance. In fact, previous studies assumed clean and homogeneous formations and ignored any skin factor in predicting pressure drops along a horizontal wellbore, critical rate, and water breakthrough time.

The present study is focused on investigating influx and flowing pressure distribution along a horizontal wellbore in the presence of non-uniform formation damage. The relevance with the inflow performance is also discussed. Modified wellbore hydraulics correlations coupled with a reservoir inflow equation are used to accommodate this effort. Calculations are performed for different skin distribution, damage severity quality, and wellbore diameters.

Results obtained show that non-uniform skin causes reduced influx rate toward the heel end. The undamaged well reveals an opposite trend as expected. For a given total production rate, the influx rate at some portions of the wellbore increases as the formation damage gets heavier, as well as for smaller wellbore diameter, resulting in greater pressure drops. Thus, the presence of non-uniform skin promotes an increase in pressure gradients within the wellbore. The changes in pressure losses are more sensitive to the level of damage severity in smaller wellbore diameter. Such a study has not been previously reported in the literature.

Overall, this investigation improves our knowledge to better understand flow behavior in a horizontal wellbore. The paper presents information to be considered in predicting the inflow performance and also provides a guide for deciding or optimizing a horizontal well completion strategy.