American Petroleum Institute Standards Research Articles

Use of Irradiated Fracture Toughness Values in Nuclear Vessel and Component Design Specifications for Fitness-For-Service Analysis Using the Unified Curve Method

The American Society of Mechanical Engineers (ASME) Section III Rules for Construction of Nuclear Facility Components subsection NB-2331 Material for Vessels requires that the effects of irradiation shall be considered on material toughness properties in the core belt line region of the reactor vessel. The code also states that “the design specifications shall include additional requirements, as necessary, to ensure adequate fracture toughness for the service lifetime of the vessel.” In a design report of nuclear pressure vessel, the design and service loads do not include loads that are affected by fracture toughness of the material. However, in the cases of fitness-for-service assessment for component flaws (prevalent with age of component), irradiated material properties become highly relevant. An example of a fitness-for-service is that of a beyond design basis reactor vessel head drop accident in a pressurized water reactor with a nozzle junction flaw. As a case study, the critical size of a postulated external surface semielliptical circumferential crack in the combustion engineering three-loop pressurized water reactor nozzle–vessel junction is calculated using ansys Workbench (Academic version) with the applied impact load from the vessel head drop accident. Failure assessment diagrams for numerous crack depths and lengths were developed considering the fracture toughness properties of the irradiated reactor vessel steel. The mode I stress intensity results used in the failure assessment diagram were compared with the available finite element and the American Petroleum Institute (API) standard API 579 analytical solutions for validation, showing good agreement. From this case study, it is demonstrated that the effects of irradiation on fracture toughness become prominent at the same postulated crack size in the nozzle–vessel junction dispositioned as “safe” becomes “unsafe” in the fracture assessment diagram. Using the unified curve method, the irradiated fracture toughness data in design specification can be supplied so that it may be used in fitness-for-service analysis to account for component aging.

Integrated FEM and CFD Simulation for Offshore Wind Turbine Structural Response

This paper implements Finite Element Model (FEM)-enabled computational fluid dynamic (CFD) analysis to enable wind and wave time-history analysis with multiple force-induced soil–structure-interaction. The soil–structure interaction of steel monopile supported 5 MW wind turbine has been simulated with two common and applicable soil profiles. Lateral soil springs were used according to the American Petroleum Institute (API) Code for p–y curves, while vertical soil springs were generated according to the t–z and q–z API standards. A modal analysis was performed to verify the joint CFD-FEM exhibited a fundamental frequency in the desired range. A verification of the load applications was completed for maximum force and moment under specific wind and wave loading parameters. Deflection results were generated and compared with reliable results published in past studies. Results reveal that a variation in wind speed has a higher impact on soil structure interaction causing a larger deflection than a variance in the significant wave height. It is also evident that the heterogeneous sand profile has a high enough stiffness to cause fatigue damage during extreme multi-hazard loading. It is anticipated that this proposed modeling technique will provide a basis for more accurate application of multi-wind-wave simulations coupled with soil–monopile-interaction.

Experimental investigation of mixing energy of well cements: The gap between laboratory and field mixing

Previous research on cement mixing energy for oil and gas applications shows dual importance of mixing energy and shear rate. The mixing conditions of the slurry and its mixing energy strongly impact the behavior of slurry. Generally, cement slurries are designed to perfection in the laboratory, however developing similar properties in the field operation is challenging. It is common that the properties of cement slurry obtained from laboratory and field mixing do not correlate very well, which can lead to different cement-job problems. The primary objective in this paper is to show whether matching mixing energy will result in similar properties in cement. In this study, a comparison of cement properties such as cement strength (UCS) and rheology and thickening time are compared with properties of same cement slurries prepared and mixed using yard mixer. Samples prepared in laboratory were mixed according to API (American Petroleum Institute) standards. Our results show that measured properties are different when mixed in the laboratory and yard conditions. Some of the properties such as UCS and rheology demonstrate a strong deviation by changing mixing conditions.

Laboratory Foamed-Cement-Curing Evolution Using CT Scanning: Insights From Elevated-Pressure Generation

Summary Computed-tomography (CT) scanning has become a mainstay among scientists (Wildenschild and Sheppard 2013) because it enables nondestructive observation of material processes and formation in real time. Foamed cement is a high-strength, low-density material containing nitrogen gas, and is used to stabilize wellbore casings both onshore and offshore. In-situ foamed cement is subject to pressure changes because the slurry is pumped downhole and cures at depth. To correlate the influence of pressure to the gas-void size and the curing evolution of a foamed cement, two laboratory foamed cements were generated and CT scanned as they cured. One cement was generated following the American Petroleum Institute (API) industry standard API RP 10B-4 (2015) at atmospheric conditions using a blender, and the other cement was created using a foamed-cement generator (FCG) (resembling that of de Rozières and Ferrière 1991) to produce a sample at an elevated pressure. FCG-generated cement qualities (in the range of 20, 25, 30, 35, and 40%) were scanned at their cured state for comparison. From the CT-image time series and the single FCG scans, the volumetric void properties were characterized and compared. The time-series blender voids were an order of magnitude larger than the FCG voids, and void growth was stagnant after a curing period of 100 minutes, whereas the FCG voids gradually increased in volume after 100 minutes. The Hsü-Nadai plots (Brandon 1995) reveal that the FCG and blender voids are weakly prolate, and all FCG voids, regardless of generation quality, relax to a greater final-magnitude strain than the blender voids. These findings confirm that both the void size and the curing process are influenced by the pressure at which a foamed cement is generated.

Microscale Characterization of Field and Laboratory Foamed Cement by Use of X-Ray Microcomputed Tomography

Summary Foamed-cement systems are widely used in deepwater-cementing operations because of their various favorable attributes compared with conventional cement systems. For instance, in the Gulf of Mexico, foamed cement is one of the most commonly used systems for shallow-hazard mitigation. However, because current standard laboratory equipment cannot accurately simulate the foam-cementing process in the field, knowledge of the actual properties of foamed cement produced in field operations is limited. In this study, the microstructure of foamed cement produced by use of field equipment in yard tests is examined in detail. Set foamed-cement samples were analyzed by use of X-ray microcomputed tomography (micro-CT) at different length scales with voxel resolution ranging from 2 to 20 µm. This study establishes the fundamental criteria and procedures necessary to obtain accurate gas-bubble-size distribution of foamed-cement samples by use of micro-CT technology. The test results suggest that foamed cement should be analyzed at multiple length scales to obtain a better characterization of the gas bubbles in the sample. Although a larger region of analysis is useful to obtain a statistically meaningful size distribution of the larger bubbles, small core samples (diameter smaller than 0.5 in.) and fine scan resolutions (5 µm or smaller) are typically required to obtain an accurate measure of the small gas bubbles in foamed cement. By comparing foamed cement produced by use of field equipment with that produced by use of the traditional multiblade laboratory blender—i.e., the standard American Petroleum Institute (API) method—this study identifies the key characteristic differences of foamed cement derived from different methods of generation. Analysis of the CT-scan images reveals that gas bubbles in foamed cement generated by field equipment approximately follows a log-normal distribution with a wide size-distribution range, from less than 20 µm to more than 1000 µm, and the bubble-size distribution appears to show little dependence on foam quality. Conversely, the gas-bubble-size distribution of foamed cement generated by the API method shows a completely different behavior. It approximately follows a Gaussian distribution, with both distribution range and median varying significantly with foam quality. This research serves as a first step toward predicting the influence of gas-bubble-size distribution on the stability and various other properties of foamed cement to better understand the foam-cementing process in the field.

Dynamic Analysis of Jacket Substructure for Offshore Wind Turbine Generators under Extreme Environmental Conditions

In order to develop dynamic analysis technologies regarding the design of offshore wind turbine generators (OWTGs), a special project called Offshore Code Comparison Collaboration Continuation (OC4) was conducted by IEA (International Energy Agency) in 2010. A similar project named INER-OC4 has been performed by the Institute of Nuclear Energy Research (INER) to develop the OWTG technologies of Taiwan. Since the jacket substructure will be applied to Taiwan OWTGs before 2020, the INER-OC4 project has been devoted to the design and analysis of jacket support structure. In this work, the preliminary result of INER-OC4 is presented. A simplified analysis procedure for jacket support structure has been proposed. Both of the NREL (National Renewable Energy Laboratory) 5 MW OWTG FAST model and OC4 jacket substructure model have been built and analyzed under severe design load cases (DLCs) of IEC (International Electrotechnical commission) 61400-3. Simulation results of six severe DLCs are performed in this work and the results are in agreement with the requirements of API (American Petroleum Institute) and NORSOK (Norwegian Petroleum Industry) standards.

A Low-Temperature Batch Mode Packaging Process for Submillimeter Microsystems in Harsh Environment Applications

This paper presents a low-temperature batch mode packaging process for microsystems that are intended for harsh environments, in particular those with high pressure and high salinity, such as encountered in downhole data logging for oil exploration and production. The package consists of a shell made from a high-strength material, such as stainless steel (SS), and an insert made from a deformable material, such as aluminum (Al). The process includes a batch mode method for chip integration and a batch mode microcrimping method for package assembly. In a process demonstration, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5 \times 5$ </tex-math></inline-formula> array of packages was made from SS 316 and Al alloy 3003, with dummy silicon chips encapsulated inside. Each package had an outer dimension of 0.5 mm along each axis. Two layers of coatings were deposited on the packages, including 50-nm-thick Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> deposited by atomic layer deposition and 5- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> -thick Parylene C made by vapor phase deposition to protect against corrosion. The packages survive at least 72 h in the standard American Petroleum Institute hot brine at 80 °C. The packages also survive pressure >200 MPa.

Technology Focus: Well Integrity

Technology Focus The tragic blowout of Macondo has triggered many technical and managerial developments in the field of well integrity since its occurrence in April 2010. Acting as a catalyzer since then, this event has demanded from all industry players a huge amount of effort to mitigate the risk of well-integrity problems. Originally, these efforts were aimed at deepwater drilling in the Gulf of Mexico, but, with time, they were disseminated throughout the oil industry, where well integrity is a must. Undoubtedly, significant progress has been made in enhancing safety during all phases of the well life cycle, mainly in the areas of well-control equipment and reliability, subsea well control and containment, documentation, training and competency assurance, and well-integrity management systems and processes. Here, I address important headway made in two areas in which I have been deeply involved during my professional career, mainly after Macondo: well-integrity documentation and well-control training and competency assurance. One of the first actions in response to the blowout was the formation of four joint-industry taskforces. Two of them provided recommendations on operating procedures and equipment that resulted in the revision of some American Petroleum Institute standards and the development of new ones. Some other standardization organizations also have been making contributions, elaborating and revising well-integrity-related standards (such as NORSOK D-010 and ISO 16530-2). Many operator companies (including mine) and drilling contractors have been reviewing and updating their well-integrity procedures and practices, especially those related to deepwater operations. Concerning well-control training and competency assurance, following the recommendation of Report 476 of the International Association of Oil and Gas Producers, the certifying bodies executed changes in the contents of the courses to stress important subjects such as barrier management, risk management, well influx detection, and immediate response and to adapt the training to well operation, rig category, and responsibility of the people involved with all types of operations. Thus, the crew members are now trained and assessed better according to their roles on the rigs. More class hours are now dedicated to simulator exercises. Arguably, this move is making the well-control- certification systems more reliable and more standardized among all training institutions. JPT Recommended additional reading at OnePetro: www.onepetro.org. SPE 175523 Searching for Well-Integrity Issues—Automated Generation of Annulus- Pressure Trends by Remco Donders, Total E&amp;P UK, et al. OTC 25256 Enhancing Well Control Through Managed-Pressure Drilling by Oscar Gabaldon, Blade Energy Partners, et al. SPE/IADC 173822 Field Trial of Well- Control Solutions With a Dual-Gradient Drilling System by John H. Cohen, Enhanced Drilling, et al.

Características de um aço microligado forjado API 5L

RESUMO Nos aços microligados da série API (American Petroleum Institute) utilizados na fabricação de dutos de grande diâmetro, a resistência mecânica deve ser suficiente para suportar as elevadas pressões do fluido transportado na indústria petroquímica. O aumento da resistência mecânica e da tenacidade para permitir a operação da linha em pressões mais elevadas, sem a ocorrência de colapso da estrutura, é o principal requisito para os aços utilizados nestes dutos. No Brasil, as empresas produzem estes aços por meio da laminação de tiras a quente ou chapas grossas, com adição de nióbio, titânio e vanádio, conforme os requisitos da norma API 5L. Considerando a complexidade geométrica dos componentes utilizados na indústria petroquímica, tais como flanges e centralizadores de tubos, é importante desenvolver um processo alternativo para fabricação de acessórios com as exigências desta norma. Dentro deste contexto e com o objetivo de avaliar novas técnicas de processamento, foi elaborado um aço com composição química similar à de um API 5L X70. O metal líquido foi vazado em uma lingoteira e forjado em barras com secção quadrada. As barras foram recozidas e amostras foram cortadas para confecção de corpos de prova que foram submetidos à têmpera e revenimento em diferentes temperaturas. As análises microestruturais e propriedades mecânicas de dureza e tração, após os tratamentos térmicos, foram comparadas às existentes na literatura para tubos de aços laminados. Os resultados mostram que as condições dos tratamentos térmicos são importantes para desenvolver uma rota alternativa de forjamento controlado, para aços com características da norma API 5L.

Development of Polyglycolic- and Polylactic-Acid Fluid-Loss-Control Materials for Fracturing Fluids

Summary Fluid loss is significant for the standard fracturing fluids without adding solid materials. One method to reduce fluid loss is to add silica flour, although it reduces fracture conductivity. Other methods are to use wall-building polymers. However, the fluid loss is still significant, and complete removal of wall-building materials is not possible, even with breakers. We found that powder, granular, and fibrous materials made of polyglycolic acid (PGA) or polylactic acid (PLA) are very suitable for fluid-loss agents because PGA is stronger than steel and PLA is as strong as rock, although they dissolve as liquid acids after applications. Fluid-loss tests are conducted with the standard American Petroleum Institute slot tester and filtrate-loss tester, mixing powders, grains, and fiber, all made of PGA or PLA in fracturing polymer fluids. The ratio of grains, powder, and fiber is optimized to minimize fluid loss for porous media and fractured porous media. Then, the changes of particle size are measured under heated conditions. Fracture-simulation studies are also conducted with a 3D fracture-boundary element model to compare the fluid efficiency of the fracturing fluids with and without the PLA and PGA particles. The results show that the capability of preventing fluid loss and plugging microcracks is maintained for the porous filters and small slots within a reasonable time period. For short-term applications less than 3 hours, both PGA and PLA fluid-loss agents are stable when the temperature is less than 212°F. Mixing these materials often provides more-efficient properties to reduce fluid loss and to bridge microcracks. No residues are left after experiments if the fracturing fluid is kept heated for 24 hours. The amount of the PGA and PLA fluid-loss agents required to reduce the fluid loss is not significant. Hence, their field applications are feasible, judging the cost and the benefit. The advantage in using these materials is that they turn from solid to liquid after applications so that no formation damage and no proppant-conductivity damage occur. The fluid loss is also significantly reduced with the powder particles. In addition, because the PGA and PLA materials are degradable, solids with arbitrary sizes and shapes may be used as long as they control fluid loss and plug fine fractures. Their applications are not only limited to reducing fluid loss, but one may also use them for engineering fracture design to enhance the fracture conductivity.

Fluid filtration and rheological properties of nanoparticle additive and intercalated clay hybrid bentonite drilling fluids

Abstract The fluid filtration and rheological properties of low solid content (LSC) bentonite fluids containing iron-oxide (Fe 2 O 3 ) nanoparticle (NP) additives and two different NP intercalated clay hybrids, iron-oxide clay hybrid (ICH) and aluminosilicate clay hybrid (ASCH), under both low-temperature low-pressure (LTLP: 25 °C, 6.9 bar) and high-temperature high-pressure (HTHP: 200 °C, 70 bar) conditions are investigated. The viscosity of each fluid was measured under LTLP and HTHP conditions using a pressurized and heated rotational viscometer. The LTLP and HTHP fluid filtrate volumes were measured in accordance to American Petroleum Institute standards. The addition of ICH and ASCH into bentonite solutions reduced both LTLP and HTHP fluid loss as much as 37% and 47% as compared to the control, under the respective conditions. The pure addition of 0.5 wt% 3 and 30 nm Fe 2 O 3 NP increased the LTLP fluid filtration as much as 14% as compared to the control. However, this addition of Fe 2 O 3 NP decreased the HTHP fluid filtrate volumes as much as 28% as compared to the control. It was found that the addition of clay hybrids reduced LTLP and HTHP fluid loss due to a restructured mode of clay platelet interaction attributed to a modification in surface charge as demonstrated by zeta potential measurements and scanning electron microscope images.

Iron Oxide Nanoparticles Grafted with Sulfonated Copolymers are Stable in Concentrated Brine at Elevated Temperatures and Weakly Adsorb on Silica

Magnetic nanoparticles that can be transported in subsurface reservoirs at high salinities and temperatures are expected to have a major impact on enhanced oil recovery, carbon dioxide sequestration, and electromagnetic imaging. Herein we report a rare example of steric stabilization of iron oxide (IO) nanoparticles (NPs) grafted with poly(2-acrylamido-2-methylpropanesulfonate-co-acrylic acid) (poly(AMPS-co-AA)) that not only display colloidal stability in standard American Petroleum Institute (API) brine (8% NaCl + 2% CaCl2 by weight) at 90 °C for 1 month but also resist undesirable adsorption on silica surfaces (0.4% monolayer NPs). Because the AMPS groups interacted weakly with Ca(2+), they were sufficiently well solvated to provide steric stabilization. The PAA groups, in contrast, enabled covalent grafting of the poly(AMPS-co-AA) chains to amine-functionalized IO NPs via formation of amide bonds and prevented polymer desorption even after a 40,000-fold dilution. The aforementioned methodology may be readily adapted to stabilize a variety of other functional inorganic and organic NPs at high salinities and temperatures.

On transferring new constant pressure heat capacity computation methods to engineering practice

Pressure-volume-temperature relationships (equations of state) and energy models are two pillars underlying calculations in the chemical process industries. While, equations of state tend to be the focus of research, development and customization, energy models appear to be underdeveloped even though accurate and generalized energy models are needed for sizing individual pieces of heat transfer equipment (i.e.: heaters/furnaces, heat exchangers, chillers/coolers), and for process integration tasks. Thus energy models also impose implicit and explicit capital and operating cost consequences for processes designed using them. These uncertainties and their consequences are frequently invisible to users of simulation software and even more so as processes designed around ill-defined fluids, or fluids where practitioners have limited experience (e.g.: heavy oils, bio-fuels) become more important, or where the proposed operating conditions are outside common practice. There are two general approaches for computing constant pressure heat capacities for fluids. One is based on generalized correlations for ideal gases plus departure functions based on equations of state to address non-ideal gases and liquids. The other is to compute liquid phase heat capacities directly from generalized correlations for liquids, which can be used independently, or in combination with departure functions to back calculate non-ideal gas or ideal gas heat capacities, or to validate liquid heat capacities computed from ideal gas + departure function based calculations. Generalized ideal gas and liquid correlations, based on the concept that compounds or mixtures possessing the same number of atoms per unit mass possess the same specific heat capacity were recently developed [1, 2]. The concept is illustrated in Figure 1 for liquids where molecular structure, molar mass, and the nature of the elements present have only secondary impacts on heat capacity if the numbers of atoms per unit mass are the same. The ideal gas correlation is shown to be preferred over four Lee-Kesler correlations and the Harrison-Seaton correlation on the basis of accuracy and range of application for general-purpose calculations. For large molecules, the correlation approaches the accuracy of the benchmark Benson method, even though no compound specific information other than elemental composition is required. The correlation for liquids also provides accurate heat capacity values for a broad range of fluids at saturation and is, for example, preferred over the widely used LeeKesler correlation for liquids based both on accuracy and range of application. Both the liquid and ideal gas correlations are simple and predictive, and well suited for inclusion in process simulators. Implementation was expected to be straightforward. For compounds, or mixtures comprising constituents defined on a molecular basis, elemental compositions of streams are readily calculated. For mixtures defined on other bases, American Petroleum Institute standards can be applied to obtain elemental composition, or elemental analysis can be measured exogenously and included in the input data set. In practice, significant sources for dissonance have arisen: between computed and measured elemental analysis, and between computed differences between liquid and ideal gas heat capacities based on correlations and departure functions. While these correlations have been made available as options in a process simulator [3], these sources of dissonance have complicated the implementation of the heat capacity correlations and underscore the underdeveloped nature of energy modeling in process calculations more broadly. Web of Conferences DOI: 10.1051/

Graphene Oxide as a High-Performance Fluid-Loss-Control Additive in Water-Based Drilling Fluids

Graphene oxide (GO) performs well as a filtration additive in water-based drilling fluids at concentrations as low as 0.2 % (w/w) by carbon content. Standard American Petroleum Institute (API) filtration tests were conducted on pH-adjusted, aqueous dispersions of GO and xanthan gum. It was found that a combination of large-flake GO and powdered GO in a 3:1 ratio performed best in the API tests, allowing an average fluid loss of 6.1 mL over 30 min and leaving a filter cake ~20 μm thick. In comparison, a standard suspension (~12 g/L) of clays and polymers used in the oil industry gave an average fluid loss of 7.2 mL and a filter cake ~280 μm thick. Scanning electron microscopy imaging revealed the extreme pliability of well-exfoliated GO, as the pressure due to filtration crumpled single GO sheets, forcing them to slide through pores with diameters much smaller than the flake's flattened size. GO solutions also exhibited greater shear thinning and higher temperature stability compared to clay-based fluid-loss additives, demonstrating potential for high-temperature well applications.

AN ENHANCED API 546

The standard American Petroleum Institute (API) 546 third edition was written by and for users, consultants, and manufacturers to provide a common performance standard for large synchronous machines. The standard is designed as a stand-alone document listing the requirements of all aspects of a synchronous machine. When compared with earlier editions, this edition has various enhancements designed to make it easier to purchase or specify a more durable machine. It has new requirements in some areas such as excitation systems, frame vibration, and insulation tests, as well as improved sections concerning dynamic analysis and thermally induced vibration changes. To reduce the risk of confusion, it should be used with the supplied data sheets.

A Comparison Between Two Biopolymers Used in Drillings Muds

The study of biopolymers is increasing considerably in the oil industry because they possess desirable properties such as environmental friendliness. Xanthan gum and scleroglucan are biopolymers used to reduce mud toxicity. These biopolymers are exopolysaccharides added to aid in control of fluid loss to the formation and to increase the viscosity of the drilling mud. In this article, we suggest evaluating the properties of biopolymers used in drilling mud. We constituted a fluid model compliant with the American Petroleum Institute's standards, where the composition differs by the nature of biopolymer. Biopolymer properties were investigated by using two main analytical methods: X-ray diffraction (XRD) and rheology. The substances used in this study are considered to cause little or no risk to the environment. This article describes the characterization of these polymers and the effect of additives such as clay and weighting material on drilling muds.

American Petroleum Institute welding neck flange design for subsea pipelines

Flange design has been a subject of intensive research and discussion over many decades as engineers strive to maximize the capacity of flanges in application while reducing costs and providing effective seals. Calculation frameworks such as those contained within American Society of Mechanical Engineers (ASME) VIII have been used for a considerable number of years to provide reasonably accurate models for analysing the various factors contributing to flange selection. However, they do not cover all situations and this is especially significant within the oil and gas industry where American Petroleum Institute standards can ‘confuse’ the design and selection process for flanges. Therefore, in this article the authors present a revised approach to the design of welding neck flanges used in subsea applications that is based on the existing design approaches contained within ASME VIII, Kellogg, Kuppan and PD8010. This revised approach to welding neck flange design also examines the key influences of gasket geometry and loading, as well as the matching of a particular flange to its pipe capacity. Finally, results of the authors’ calculations are compared against existing finite element-derived data contained within API 6AF.

A Small-Scale Fracture-Conductivity Study

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 106272, "Small- Scale Fracture Conductivity Created by Modern Acid-Fracture Fluids," by M. Pournik, SPE, C. Zou, SPE, C.M. Nieto, M.G. Melendez, D. Zhu, and A.D. Hill, SPE, Texas A&amp;M University, and X. Weng, Schlumberger, prepared for the 2007 SPE Hydraulic Fracturing Technology Conference, College Station, Texas, 29-31 January. A series of acid-fracture-conductivity tests was conducted that simulated flow in a hydraulic fracture, both in the main flow direction along the fracture and in the fluid-loss direction. Three commonly used acid-fracturing fluids were tested at 200 and 275°F. The acid-fracture-conductivity apparatus is similar to a standard American Petroleum Institute (API) fracture-conductivity cell, but with the ability to hold core samples that are 3 in. thick in the leakoff direction. Introduction Acid fracturing, a well-stimulation process in which acid dissolves reservoir rock along the face of the hydraulically induced fracture, is expected to create lasting conductivity after fracture closure. However, conductivity after fracture closure requires that the fracture face be nonuniformly etched by the acid while the strength of the rock is maintained at high levels to withstand closure stress. At low closure stress, the etched pattern of the fracture face should have a dominant influence on the resulting fracture conductivity as long as the rock strength can with-stand the load. As the closure stress is increased, surface features along the fracture faces may be crushed, which makes fracture conductivity more dependent on the rock strength than on the initial etching pattern. Success of the acid-fracturing process depends on the resulting fracture conductivity, which is difficult to predict because it depends on a stochastic process and is affected by a wide range of parameters. Most predictions of conductivity are made with the empirical correlation developed by Nierode and Kruk. This correlation was based on experiments with 1-in.-diameter, 2- to 3-in.-long fractured cores with no fluid loss through the rock samples. To ensure that laboratory experiments represent field conditions, the phenomena that occur in the acid-fracturing process must be scaled properly. In this study, experimental conditions were scaled to give the same magnitude of acid transport along the fracture, acid leakoff, and acid reaction at the fracture face as occurs in field treatments. Acids Three acid systems were used in the conductivity tests: a gelled-acid system with an acid-soluble polymer as a gelling agent, an acid-in-oil emulsion, and an acid/viscoelastic-surfactant acid solution. The polymer-gelled-acid system contained 15% HCl, 2.5% gelling agent, and a corrosion inhibitor. The emulsified acid was a mixture of 28% HCl and diesel with an emulsifier and a corrosion inhibitor. The diesel forms the external phase of the emulsion. The viscoelastic-surfactant acid has unique "self-diverting" characteristics. The fluid viscosity increases significantly as the acid spends, which creates effective diversion of the acid in matrix acidizing. The same characteristics have been found to reduce the acid-leakoff rate and increase stimulation effectiveness in acid fracturing. The viscoelastic diverting acid system used in this study consists of 15% HCl, 7.5% viscoelastic surfactant, and a corrosion inhibitor.

Empirical Correlations for Estimating Filtrate Volume of Water Based Drilling Fluids

Standard American Petroleum Institute (API) filter press is generally used for identifying the filtrate volume of drilling fluids and works only at very low pressures. In fact, during a drilling operation, at downhole conditions, the pressures encountered are significantly higher than what is used during standard API filter press tests. A relationship between the well-known fluid properties and the filtrate volume test is developed. In this study, experiments have been conducted for different water-clay mixtures with varying concentrations at different pressure values by using standard API filter press and HP&HT (high-pressure high-temperature) filter press. The relationship between physical and chemical properties of water-clay mixtures and filtrate volume is analyzed. An empirical correlation has been developed for estimating filtrate volume using basic information of the mud (i.e., rotational viscometer readings, density, pressure, cation exchange capacity, and chemical composition). The developed correlation can estimate filtrate volume with an error less than 20% for a wide range of pressure values.

Assessment of a new selective chromogenic Bacillus cereus group plating medium and use of enterobacterial autoinducer of growth for cultural identification of Bacillus species.

A new chromogenic Bacillus cereus group plating medium permits differentiation of pathogenic Bacillus species by colony morphology and color. Probiotic B. cereus mutants were distinguished from wild-type strains by their susceptibilities to penicillin G or cefazolin. The enterobacterial autoinducer increased the sensitivity and the speed of enrichment of B. cereus and B. anthracis spores in serum-supplemented minimal salts medium (based on the standard American Petroleum Institute medium) and buffered peptone water.