bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Flow Conditions and Surfactant Availability on Adsorption
Authors: Grigg Reid B. , Mikhalin Alexander A.
Published: December 2007

Anionic surfactants, good foaming agents, can be used in CO2 foam flooding to improve high-pressure, high-density CO2 reservoir sweep efficiency. In this study, kinetics and equilibrium adsorption were investigated by examining adsorption behavior in a system of solid phase sandstone or limestone and of an aqueous phase of surfactant in 2% brine. Effects on surfactant adsorption density for different solid to liquid ratios as well as surfactant concentration, rock type and state, and flow conditions are presented. Three systems were used: batch tests on crushed rock, circulation tests through core samples, and non-flow, diffusion brine-saturated core tests. The density of an anionic surfactant adsorption on rock is best described as a function of surfactant available in the system (concentration plus volume), rather than by surfactant concentration used by previous investigators. Experiments with solid rock were carried out to determine surfactant capacity of the porous media through flow and non-flow rock samples and crushed rock samples. Adsorption was similar for crushed sandstone and flow tests, while significantly higher in cubed, non-flow rock systems. For limestone the crushed rock and non-flow systems were similar while the flow system was significantly lower. The time to reach equilibrium required less than one hour (generally minutes) for the crushed rock, hours to days for the flow-through tests, and weeks to over a month for the non-flow rock systems. The rate of adsorption dependent on availability (delivery) that is generally much slower than the adsorption kinetics.
Design and Evaluation of an Elastomeric Sealant for Use in Primary Cementing
Authors: Phipps J. S. , Ladva H. K. J. , Craster B. , Caritey J. -P. , Dargaud B.
Published: December 2007

We describe the design and development of an elastomeric sealant for improved zonal isolation. The sealant is intended for use during primary cementing, and has been formulated so that it can be pumped as part of the cement train and placed around the shoe of a casing. In this way reliable isolation at key points in the well can be achieved without incurring excessive costs. The mechanical property specifications of the sealant have been determined using stress analysis; we show how a sufficiently deformable material remains effectively confined by the wellbore and thus cannot be subjected to tensile stresses that could cause its failure, and that it needs to be held in a state of compressive stress in order to prevent gas leakage. By applying pressure to the sealant during curing and allowing it to expand thermally afterwards, a suitable state of compression can in principle be generated. The necessary control over the rheology, density and curing time of the sealant to enable its reliable placement has been achieved. The effect of the initial stress state and the performance of the sealant compared with cement-based materials are demonstrated in a full-scale test.
Internal Breakers for Viscoelastic-Surfactant Fracturing Fluids
Authors: Crews James B. , Huang Tianping
Published: December 2007

Over the past two decades, viscoelastic surfactant (VES) fluids used for gravel packing, frac-packing and conventional hydraulic fracturing have primarily relied on external or reservoir conditions to break the fluid’s viscosity. Unlike polymeric fluids, no internal breakers have been used. Relying on external conditions to break VES fluid has been a point of contention and questionable, especially for dry gas applications.

This paper describes how new internal breaker technology has been developed that allows VES fluids to be broken into easily producible fluids, without the need for contacting reservoir hydrocarbons. The reservoir pressure required to produce VES fluid is no longer compromised: very little pressure or time is required when an internal breaker is present. Mechanisms for internally breaking VES viscosity are discussed. New internal breakers have been found to work over a wide fluid temperature and mix water salinity range, and have compatible with newly developed VES stabilizers and fluid loss control agents. Presented are laboratory results that compare VES fluids with and without an internal breaker. Rheological data is presented that show the performance of internal breakers in degrading VES fluid viscosity, in particular at low fluid shear rates. Core clean-up tests were performed at 150°F, using 3% KCl brine and nitrogen gas as the displacement (clean-up) fluid. The results show that use of an internal breaker significantly improves VES fluid clean-up. This paper also presents VES system compatibility and proppant conductivity results.
A New IMPSAT Formulation for Compositional Simulation
Authors: Haukås J. , Aavatsmark I. , Espedal M. , Reiso E.
Published: December 2007

A new IMPSAT formulation for compositional simulation is presented. The new formulation is based on explicit solution of variables that are isochoric, i.e., complementary to volumes, instead of explicit solution of phase mole fractions, which is the conventional IMPSAT approach. The paper focuses on performance of the nonlinear iteration and numerical stability.

The use of complementary variables in the new IMPSAT formulation makes the nonlinear system better conditioned. Consequently, fewer nonlinear iteration steps are required. The resulting speed-up more than compensates the added costs of introducing and using the isochoric variables.

The stability criterion introduced with the new formulation is in many cases significantly less conservative than the conventional criterion. However, for cases where there is little or no saturation change between the hydrocarbon phases, e.g., for retrograde gas condensate cases or single hydrocarbon phase cases, the difference between the criteria is insignificant.

The timestep sizes for which instabilities occur with the new and the conventional formulation are practically the same, and no oscillations have been observed unless both the new and the conventional criterion are violated. Consequently, the stability properties are similar, and the new criterion seems to apply to both the new and the conventional formulation.

Our conclusions are supported by numerical results.
Hydraulic Fracture Model Sensitivity Analyses of a Massively Stacked, Lenticular, Tight Gas Reservoir
Authors: Green Christopher A. , Barree Robert D. , Miskimins Jennifer L.
Published: December 2007

This paper critically assesses the importance of various inputs that are used for a common methodology to develop a simulator model of hydraulic fractures in geologically complex, fluvial, tight gas reservoirs. A planar 3-D fracture simulator is used with a fully coupled fluid/solid transport simulator. The geo-mechanical rock properties from logs (Young's modulus, Poisson's ratio and Biot's constant) and diagnostic mini-frac injection tests of individual sandstone reservoirs were investigated to assess their importance in developing a valid stress model.

The work describes the investigations using a model previously matched using both net surface pressure and micro-seismic/tiltmeter data. From these results it is possible to get a better understanding of how fracs grow and interact with complex fluvial reservoirs, allowing operators to better optimize field well performance and completion methods in these geologic settings. Additionally, the minimum critical data recommendations necessary to develop such a model have been identified and will aid operators in developing their data acquisition programs. Although developed in the Rocky Mountain region, the presented technique can be extrapolated to other similar geologically complex reservoirs world-wide.
Use of Nitrate or Nitrite for the Management of the Sulfur Cycle in Oil and Gas Fields
Authors: Voordouw G. , Buziak B. , Lin S. , Grigoriyan A. , Kaster Krista M. , Jenneman G. E. , Arensdorf J. J.
Published: December 2007

The production of sulfide by sulfate-reducing bacteria (SRB) in oil and gas fields causes problems including enhanced corrosion risk, reservoir plugging and deterioration of product quality. Injection of nitrate or nitrite stimulates heterotrophic nitrate-reducing bacteria (hNRB), which compete with SRB for oil organics, such as volatile fatty acids (VFA). Nitrate also stimulates nitrate-reducing, sulfide-oxidizing bacteria (NR-SOB), which lower sulfide levels. Nitrite is a strong and specific inhibitor of the SRB enzyme responsible for sulfide production, whereas nitrate does not inhibit SRB.

Hence, injection of nitrate or nitrite can prevent or remediate problems in the oil and gas industry caused by SRB activity, provided hNRB and NR-SOB are present.

A survey of 8 oil fields, 2 gas storage reservoirs and an oil storage tank indicated that SRB and hNRB were widely distributed, whereas the distribution of NR-SOB appeared more limited. The SRB and hNRB were able to use lactate, as well as VFA as electron donor for sulfate or nitrate reduction. However, the order of use of VFA components appeared to differ with acetate being used preferentially by hNRB and propionate and butyrate being used preferentially by SRB. The production of nitrite by hNRB and NR-SOB varied greatly with quantitative conversion of nitrate to nitrite (up to 30 mM) being observed in one case; the nitrite formed was then reduced further. Samples from a high temperature North Sea oil field had thermophilic SRB, but no hNRB or NR-SOB activity, causing sulfide production to be inhibited by nitrite only. Although nitrite appeared to react chemically with sulfide under these conditions, causing all nitrite to disappear within 100 h, the observed inhibition was long-lasting (>500-1500 h). Hence, nitrite can be used successfully to control SRB activity in fields where hNRB and NR-SOB are absent.

In summary, it appears that many oil and gas fields contain hNRB and NR-SOB populations, which are activated upon injection of nitrate or nitrite, allowing sulfide remediation in situ. Characterization of these populations as described in this paper may allow prediction whether these injections will be successful and whether use of nitrate or of nitrite is preferred.
Fracturing Fluid for Low-Permeability Gas Reservoirs: Emulsion of Carbon Dioxide With Aqueous Methanol Base Fluid: Chemistry and Applications
Authors: Gupta D. V. S. , Hlidek B. T. , Hill E. S. W. , Dinsa Harpreet S.
Published: December 2007

High-quality emulsion of carbon dioxide (CO2) in aqueous alcohol-based gel (CO2 emulsion) was introduced into the Western Canadian Sedimentary Basin (WCSB) as a fracturing fluid in 1981. Since that time, the use of the fluid has been very successful, particularly in low-pressure, tight gas applications. The fluid has all the advantages of conventional high-quality CO2 foams/emulsions, with the added advantage of minimizing the amount of water introduced into the well.

The present paper will discuss a fluid that is an emulsion of liquid carbon dioxide in a base fluid of aqueous methanol. The discussion will include chemistry, rheological evaluations, and successful field utilization of these fluids in the Western Canadian Sedimentary Basin over the last decade.
Integrated Fracture Analysis– Three Brief Case Studies
Authors: Ozkaya S. I.
Published: December 2007

Three short case studies are presented to demonstrate the power of data integration in fracture evaluation and to sample the wide spectrum of challenges each field may present. The three short case studies reveal the kind of problems that may arise specific to each field and reservoir. In the first case, an unexpected observation that the mega-fractures are associated with a sharp Gamma ray anomaly allowed field scale mapping of the mega-fractures using gamma ray logs from horizontal wells. In the second case, identification and correlation of highly fractured layers and water invaded zones made it possible to determine whether fractured layers acted as thief zones. In the third case, the challenge was to find a means of separating fluid conductive and sealing fractures and faults in a clastic reservoir and generate a water breakthrough risk map. In each of the three cases, a solution or partial solution to the fracture problems was possible only by integrating all the available seismic and dynamic data with borehole image and openhole logs.
Wellbore instability of Shale Formation; Zuluf field, Saudi Arabia
Authors: Abass H. , Shebatalhamd A. , Khan M. , Al-Shobaili Y. , Ansari A. , Ali S. , Mehta S.
Published: December 2007

Significant wellbore instability problems are being experienced during the drilling of horizontal wells in a shaly sand member of the Khafji reservoir in Zuluf field. This paper presents the results from a case study that integrates detailed rock mechanics and swelling tests with information from petrophysical logs and core properties acquired to evaluate, define and predict the instability mechanism in this portion of the Khafji reservoir.

The study has tackled the effect of drilling fluid on shale strength and swelling. Additionally the effects of water activity, osmosis and hydraulic diffusion on shale stability were investigated. The mechanical properties and stress field in the khafji shale was determined. The results provided recommendations to minimize instability problems encountered during drilling. All drilling fluids that have water phase including the oil-based drilling fluid were found to cause instability problems. However all-oil drilling fluid was found to maintain shale strength. Drilling mud salinity to encourage resverse osmosis was determined based on measurement of shale-pore-water salinity. The critical mud weight window was calculated considering the Chemoporoelastic properties of the Khafji shale.
Analytical Calculation Of Minimum Miscibility Pressure By Using Stability Analysis In Reduced Variable Space
Authors: Shahri Mohammad R. Rahmanian , Edalat Mohsen
Published: December 2007

Miscible gas injection is one of the most efficient methods in enhanced oil recovery and Minimum Miscible Pressure (MMP) is a vital parameter in miscible injection projects. In this paper a new method of MMP calculation is presented which is based on stability analysis in reduced space variables and consists of a fast and robust algorithm which guarantees that increasing the number of components of oil and injection gas has no effect on the volume of calculations; nevertheless the accuracy of calculation does not change. It is illustrated that using stability analysis in reduced space for miscibility development and consequently in MMP calculation causes that the number of equations for "C" components to reduced marvelously to "m" equations (m is less than or equal to 6). Thus in addition of accuracy and fastness this method offers that there is no need for splitting, lumping or pseudo component definition. Comparisons in examined cases demonstrate that this claim is correct. By this method of MMP calculation, the hardships in phase calculation due to existence of the ragged shape of Gibbs free energy function and consequently the existence of several minimum points and difficulty in finding a proper solution for nonlinear Ratchford-Rice equations especially near the critical point and also complication in analytical tie line intersection approach for MMP calculation are obviated. The analytical algorithms for calculating MMP for general multi component systems are tested against slim tube test data for real crude oil systems. It is shown that for all the crude oil systems considered, the displacement is a condensing/vaporizing gas drive. The MMP calculation results indicate that the analytical stability analysis approach can be used to calculate MMP accurately for systems with an arbitrary number of components, provided that an appropriate equation-of-state based on phase behavior characterization is available. This approach is significantly faster than the conventional compositional simulation approach. It is applicable to all systems with any type of displacement mechanism, and hence it can be used in areas that call for rapid calculation of MMP.
Eliminating Disposal of Effluent Water to Pits and Utilizing the Water To Recharge an Ever-Falling Reservoir Pressure
Authors: Quttainah Riyad , Al-Khamees Waleed , Al-Qabandi Salman Ahmad
Published: December 2007

Since the discoveries of West Kuwait (WK) oil fields, and for 40 years before commissioning the Minagish water injection plant (MNWIP), all effluent water from WK fields was disposed off into huge evaporation pits. And, as a result of a thin layer of oil forming on the top, the rate of evaporation was reduced and in some cases completely eliminated which left large amounts of effluent water in those pits. This practice subjected all animal life to be affected and threatened. Moreover, the seepage of water into the ground and mixing with spring water caused multiple concerns. Polluting the water and hence making it hazardous for usage and consumption. Therefore, it was considered to be a health and an environmental hazard to continue with this practice.

Water management in WK was designed to integrate all effluent water from gathering centers in WK through the Effluent Water Transfer System (EWTS) and the MNWIP. All effluent water is transferred from the gathering centers through the EWTS to the MNWIP for re-injection into the Minagish Oolite (MO) reservoir in the Minagish field (MN) for pressure maintenance. The reinjection of all effluent water produced from WK fields into the MO reservoir has significantly increased reservoir pressure. This operation increases the well potential (oil production) and helps insure that oil production is available to fill the gathering centers to meet oil export demands. Also, disposal wells were drilled to inject off spec or surplus water into the Shuaiba reservoir as a back-up plan in case of any planned or unplanned shutdown of the MNWIP.

Since mid-2003, all effluent water in WK has been routinely disposed of in an environmentally friendly manner with no discharges to pits and in return, increased reservoir pressure which will have huge economical benefits.

Technical Contributions: The environmental impact from disposing off into large disposal and evaporation pitsThe total production from all WK fields and the unique and complex network of transfer lines between all centers to gather effluent water and disposal design.The economic impact from injecting effluent water to re-pressurize a constantly depleting reservoir.
Oilfield Surfactants Improve Recovery by Imbibition
Authors: Weiss W. W. , Xie X.
Published: December 2007

Most carbonate reservoirs are naturally fractured and typically produce less than 10% OOIP during primary recovery. Spontaneous imbibition is an important oil recovery mechanism from these types of reservoirs. In some situations, imbibition of water can be promoted by chemical stimulation with surfactants to alter the reservoir wettability toward water-wetness such that oil is expelled at an economic rate from the rock matrix into fractures. Here, we investigated the use of chemicals to modify the wettability of reservoir rock to a more water-wet state in order to produce additional oil via imbibition. Five chemicals that effectively improved water-wetness were used in the imbibition tests: two nonionic surfactants Tomadol T91-8 and Pluronic L-64, two anionic surfactants Rhodacal A-246L and Rhodapex CD 128, and an amphoteric surfactant Mirataine CB.

The San Andres formation in the Permian Basin of Texas and New Mexico is a great oil-producing formation in the United States. An estimated 50,000 wells produce oil from this oil-wet carbonate reservoir. Laboratory imbibition tests were conducted on core plugs and fluids from the Fuhrman Masho and Eagle Creek fields. Thin section analysis indicated that both fields contain dolomite, calcite, and anhydrite. The core plugs were soaked in imbibition cells containing formation water at a reservoir temperature of 40°C (104°F). For Fuhrman Masho cores, maximum oil recovery via water alone was less than 4% of the original oil in place (OOIP). After the oil production stopped, the water was replaced with a surfactant solution at a concentration of 1500 to 3500 ppm. The imbibition process then continued until no oil was produced. The incremental oil recovered varied from 0 to 48% OOIP; higher permeability and bulk volume of oil in the cores resulted in higher oil recovery by surfactant imbibition. No oil was produced by brine imbibition for some Eagle Creek cores; however, others produced up to 34% of the OOIP. Surfactant treatment did not improve oil recovery every core. The laboratory tests indicated that the improved oil recovery by surfactant treatment depended on rock mineralogy, porosity, permeability, and pore heterogeneity. Each field must be individually evaluated.
Recent HP/HT Coiled-Tubing Intervention and Perforating Operations on the Jade Field
Authors: Turner Alan , Gordon William , Nicol Iain , Cromar Steve
Published: December 2007

This paper describes the results obtained, as well as the equipment and techniques used on the Jade Field in the UK Central North Sea to provide the perforation and completion operations of two new high-pressure/high-temperature (HP/HT) production wells.

This paper begins by discussing the types of equipment that are required for HP/HT coiled-tubing (CT) intervention. The completion design and methodology of these two wells will be discussed. The CT interventions and different perforating operations will then be presented for these wells. The paper outlines the specific types of downhole equipment that were needed for these operations. This includes, for example perforating gun hangers and detachable perforating connectors. This paper includes the application of new equipment designs and novel solutions to both surface and downhole constraints.

Lessons learned from each case history will be presented and conclusions will be drawn.
The Possibility of Replacing Oil-Based Mud With the Environmentally Acceptable Water-Based Glycol Drilling Mud for the Iranian Fields
Authors: Samaei Seyed Mohsen , Tahmasbi Koorosh
Published: December 2007

Oil-based mud has been used in the last few decades in the drilling operation in the world. Due to high initial cost and environmental problems associated with oil-based mud, the application of this type of drilling fluids has been gradually reducing. This has therefore dictated the companies and institutions dealing with drilling fluids technology to work on finding a suitable substitution to replace oil based mud.

A proper alternative has been known to be Water-based glycol mud. Water-based glycol mud is becoming increasingly popular due to its exceptional shale inhibition properties, environmental effectiveness, and ease of handling and high lubricity.

In This study, the possibility of replacing oil-based mud with the environmentally acceptable water-based glycol drilling mud for the Iranian fields is investigated. Rheology test is done on both OBM and glycol mud. In addition, the inhibitive property of the glycol mud is assessed using Shale particle disintegration test by hot rolling. This test is done on the cuttings from Maroon oil field and outcrop shale from Goorpi formation in Iran and shale recovery percentage is measured to evaluate the inhibition performance of glycol mud. The laboratory results confirm that the glycol mud system significantly reduces clay dispersion and hydration of cuttings and can be considered as a good alternative to oil-based fluid and other water-based mud systems.
The Integration of HSE&C—Communities, Contractors, Operators, and Regulators
Authors: Doyle Rex , LeBlanc Tad
Published: December 2007

Continuous improvement in safety and environmental performance is a goal for most all companies in the energy industry. But substantially improving performance, that is creating a step change in the metrics used to measure performance in the field, requires an expanded view of Health, Safety, Environment, and Compliance (HSE&C) programs. These programs must be viewed as both an integral part of each company's organization and more importantly as programs that are continually integrated into an expanded network of organizations – operators, contractors, suppliers, communities, and regulators. Companies must proactively move from successful stand alone programs to programs that easily and effectively interact with all participants and participating organizations.

Two factors that are highly correlated with improved performance in this network environment are workforce competency assessment and communication. Competency assessment is critical in that employees must be placed in the right job and have the knowledge required to successfully and safely execute the skills required of the job. Effective two-way communication between all organizations in the network is vital in creating an environment where information and expectations are shared among participants. It is especially important to engage the regulatory authorities, both internal departments and governmental agencies, in the process.

Integrating HSE&C into a network of organizations does not necessarily require a complete redesign of existing programs, rather it requires a new approach that actively looks for ways to work with each of the other participants to improve the performance of the group.
Field Development Optimization Technology
Authors: Litvak Michael , Gane Brian , Williams Glyn , Mansfield Mark , Angert Patrick , Macdonald Chris , McMurray Lesley , Skinner Roger , Walker Greg J.
Published: December 2007

This paper describes the development and application of a new field development technology to optimize the locations of new and sidetracked wells within an oil or gas field, the drilling schedule, water and gas injection strategies, production/injection rates, and surface facilities. The field development plan optimization is informed using BP’s Top-Down Reservoir Modeling (TDRM) methodology. An economic indicator (e.g. net present value, incremental rate of return, capital efficiency, discounted payback, etc.) or oil/gas recovery is maximized subject to field development constraints. Only drilling targets in geologically defined areas are considered. Sidetrack wells are additionally limited by distance from their parent well. Drilling rig constraints (rig availability, drilling time, drilling costs, etc.) are incorporated. Economic constraints on project costs are also taken into account.

Multiple integrated reservoir models, representing different combinations of sub-surface description and surface facilities, can be handled within this new field development optimization system. The system generates the optimum field development option by maximizing a percentile of either the selected economic indicator or the oil/gas recovery. Associated risks can be considered as constraints. Probability distribution functions of the maximized objective function and associated constraints are determined with a powerful optimization procedure developed using a combination of public and proprietary techniques. A large range of field development issues from well locations, drilling schedule, injection strategy and facilities modifications can be addressed.

Applications of the developed technology for field development optimization in a giant new offshore oil field, and a mature oil field are presented. These applications clearly demonstrate that the new development optimization technology is a sufficiently general tool for analysis to inform field development planning. Significant improvements in oil recovery, sweep efficiency, and net present value are demonstrated in the comparison with the reference field development cases.
A New Finite-Volume Approach to Efficient Discretization on Challenging Grids
Authors: Aavatsmark I. , Eigestad G. T. , Heimsund B.–O. , Mallison B. T. , Nordbotten J. M. , Øian E.
Published: December 2007

MPFA methods were introduced to solve control-volume formulations on general simulation grids for porous media flow. While these methods are general in the sense that they may be applied to any grid, their convergence properties vary.

An important property for multiphase flow is the monotonicity of the numerical elliptic operator. In a recent paper [1], conditions for monotonicity on quadrilateral grids have been developed. These conditions indicate that MPFA formulations which lead to smaller flux stencils are desirable for grids with high aspect ratio or severe skewness and for media with strong anisotropy or strong heterogeneity. The ideas were recently pursued in [2] where the L-method was introduced for general media in 2D. For homogeneous media and uniform grid, this method has four-point flux stencils and seven-point cell stencils in two dimensions. The reduced stencils appear as a consequence of adapting the method to the closest neighboring cells

Here, we extend the ideas for discretization on 3D grids, and ideas and results are shown for both conforming and nonconforming grids. The ideas are particularly desirable for simulation grids which contain faults and local grid refinement.

We present numerical results herein which include convergence results for single phase flow on challenging grids in 2D and 3D, and some simple two-phase results. Also, we compare the L-method with the O-method.
A Study of Acid Cement Reactions Using the Rotating Disk Apparatus
Authors: Nasr-El-Din H. A. , Al-Yami A. , Al-Aamri A. , El-Marsafawi Y.
Published: December 2007

Cement is extensively used for zonal isolation. This cement comes in contact with corrosive fluids during matrix treatments to the formation. Acids can react with various components present in cement and cause severe damage to cement. The damage depends on cement type, acid type and concentration, temperature, pressure, surface area, and exposure time. Previous studies on cement acid reaction are sparse and typically use a 2"x2"x2" cubes soaked in acid under static conditions. The objective of the present work is to examine the acid cement reactions under dynamic conditions.

The reaction between regular cement (118 pcf) and HCl was examined using the rotating disk apparatus. Cement disk 1.5 inches in diameter and 0.6 inch in thickness were used. The effect of disk rotational speed (0 to 1,000 rpm), on the dissolution rate of regular cement was determined. The system pressure was maintained at 1,000 psi and the reaction was allowed to proceed for 120 minutes. Samples from the reaction vessel were collected at various times and were analyzed for various key cations using inductively coupled plasma emission spectroscopy (ICP).

The results obtained indicated that HCl acid leached calcium, iron and aluminum from the cement disks. The concentrations of these ions increased with time. Calcium concentration was significantly higher than other cations. The reaction rate was controlled by diffusion of H+ to the surface of cement. This paper will discuss the results obtained and address their implication on field applications.
Chemical Diversion Techniques Used for Carbonate Matrix Acidizing: An Overview and Case Histories
Authors: Chang Frank F. , Qiu Xiangdong , Nasr-El-Din Hisham A.
Published: December 2007

The purpose of matrix treatments in carbonate reservoirs is to increase connectivity of a formation with the wellbore in the entire zone of interest. Successful matrix treatments depend on the uniform distribution of the treating fluid over the entire interval. When fluids are pumped into a well, they naturally tend to flow into the zone with the highest permeability or least damage. Field experiences showed that there is no assurance of complete zone coverage without proper diversion. Therefore, diversion is recommended in all treatments, especially in extended reach and multi-lateral wells.

Diversion techniques can be classified as mechanical or chemical. Mechanical control of treating fluid placement can be accomplished by coiled tubing with an inflatable packer, or with conventional straddle packers or ball sealers. Although mechanical techniques are very effective, they are more expensive and time consuming than chemical techniques and they are often not applicable or not effective in wells with open-hole completion. More importantly, mechanical means diverts treatment fluids from the wellbore; however, there is no control once the fluid enters the formation. Chemical diversion can be achieved through placing a viscous fluid, foam or gel to lower the penetration of treatment fluid in the created wormholes and their surrounding matrix, or a particulate carrying fluid, which creates a filter cake on the surface of the wormholes. This filter cake results in temporary skin effect which alters the injection profile. Gelled and foamed acids are also being used as a means of improving acid placement by combining stimulation and diversion in one step.

Diversion is a critical step to ensure the success of matrix acid treatments. Understanding how chemical diverters interact with the formation rock and fluid is the key to selecting the proper product for a specific treatment. It is the intent of this paper to provide a technical overview of mechanical and chemical diverters used in the oil industry. The various mechanisms by which these chemicals to achieve acid diversion, their application histories, and their limitations are presented. This paper provides guidelines for production engineers to optimize the fluid placement.
Advances in Microbial Ecology Relevant to the Application of Nitrate to Control Reservoir Souring
Authors: Maxwell S.
Published: December 2007

During the 1980’s, studies initiated to resolve problems due to the activity of sulfate-reducing bacteria in oilfield systems were instrumental in the early recognition of the importance of biofilms in natural environments, the use of radiotracers to measure bacterial activity, the application of molecular techniques to study non-culturable bacteria and the detection of previously unknown Archaea in subsurface aquifers.

Over the past 15 years, however, oilfield microbiology practices have not kept pace with other fields of environmental microbiology research and now the ideas and practices applied in the oilfield lag significantly behind the most recent scientific advances. This is despite the fact that the oil industry is currently attempting to control very diverse and extensive sulfide producing microbial populations by the application of nitrate to bring about a shift in the population dynamics in a process of biological competitive exclusion.

Environmental microbiology is now in the midst of a revolution in the understanding of the marine and subsurface microbial world, much of which is resulting in completely new concepts of the interaction between microbes and the environment and vice versa. These advances must be recognized and wherever possible incorporated into oilfield microbiology technology.

This paper describes how the application of even a few of the recent advances in environmental microbiology offers a huge potential to improve our understanding of control and remediation of sour reservoirs using nitrate treatments.
Assessment of Barite Scaling Potentials, Sulfate Removal Options, and Chemical Treating Strategies for the Tombua-Landana Development
Authors: Chen Huey J. , Hinrichsen Charles J. , Burnside Christopher A. , Widener Mark
Published: December 2007

This paper discusses the development of a holistic water and scale management plan for a green-field development, which faces a new order of scale management challenges. Specifically, this paper documents a scale risk assessment and the development of a scale management plan during the front-end engineering design of the Tombua–Landana development in West Africa. The complexity of scale management is compounded by the presence of multiple reservoirs with very different scaling potentials and by the plans for produced water reinjection. The objective of the study was to define a complete scale management plan, which incorporates flexibility for future unknowns and minimizes the total cost of scale management, without over-capitalization.

The Tombua-Landana field will produce from multiple reservoirs that incorporate several distinct formation waters with barium content as high as 800 mg/l and will require seawater injection for reservoir pressure maintenance from day one. Scaling tendency predictions were made for the major groups of formation water, both with and without seawater injection. In addition, a variety of produced water reinjection scenarios were investigated.

Due to the predicted severity of barite scaling, it was determined that scale would not be effectively controlled solely by scale inhibitor chemicals. It was therefore necessary to investigate alternative mitigation strategies, primarily sulfate removal. The impact of sulfate ion removal from seawater on barite scaling was investigated in order to determine the level of sulfate ion removal that would be necessary for each water type to limit the extent of scale deposition to a level that most residual scaling could be controlled by downhole chemical injection.

Because of the considerable cost associated with processing low sulfate injection water, it was necessary to optimize the size of the sulfate removal membranes (SRM) primarily by using produced water reinjection.

This field study typifies several industry trends in inorganic scale management: (i) Deepwater West Africa is emerging as a new focus area for sulfate scaling; (ii) Deepwater economics require co-production of multiple reservoirs in order to reach threshold reserves and will necessitate the installation of major infrastructures; (iii) Economic and environmental drivers support the use of produced water reinjection, even though this exacerbates water compatibility problems and creates new challenges for reservoir monitoring.
Unstructured Upgridding and Transmissibility Upscaling for Preferential Flow Paths in 3D Fractured Reservoirs
Authors: Vitel S. , Souche L.
Published: December 2007

Most existing upscaling methods attempt to evaluate effective permeabilities of coarse-scale gridblocks, so that the upscaled model locally reproduces the behavior of the fine-scale grid, under a set of boundary conditions. When applied to fractured reservoirs, this approach shows several drawbacks. First, it assumes the existence of a representative elementary volume (REV), which size is constrained by the practical needs for an efficient simulation. Yet, no REV exists for fractured systems which are characterized by a wide variety of fracture sizes. Second, the dynamic behavior of the model is unknown far from the applied boundary conditions. Third, this approach tends to underestimate the impact of steep pressure gradients that may occur between fracture and matrix media.

The presented method overcomes all three limitations by upscaling transmissibilities, so that the coarse-scale model preserves the same pressure response as the detailed geological model at a set of arbitrarily chosen observation points. A discrete fracture network and a corner-point grid are first jointly discretized using a dual approach (pipe network). Nodes of the pipe network represent either discrete fractures or matrix blocks. Pipes stand for matrix-to-matrix, fracture-to-fracture and matrix-to-fracture connections. Then, upgridding and upscaling are simultaneously performed, without imposing any boundary conditions: nodes are iteratively removed by applying electric simplifications (series, parallel, star-mesh transformations) until only the selected observation points remain. This process introduces new connections that may link nodes that were initially not connected, thus better modeling features such as super-K or large-scale fractures. This tends to convert a large sparse system into a smaller but fuller one; therefore parts of the network need to be lopped off before informing a flow simulator. Pipes holding the lowest transmissibilities are decimated and the remaining transmissibilities are updated accordingly in an optimization procedure. Flow simulation results obtained for several data sets on upscaled models are in good accordance with those obtained before upscaling, and show appreciable improvements compared to conventional structured local approaches.
Semistiff Carbon-Fiber Rod Pushed into Live Wells for Reservoir Performance Monitoring and Leakage Detection
Authors: Hansen H. , Wilberg T. , Naldrett G. , Meldrum N.
Published: December 2007

This paper describes how a patented intervention based DTS logging system can be used to address the many and varied reservoir management challenges faced in declining fields, complex well profiles and complex completion methodologies. A description of the prototype system is provided along with the test results from the test well, and full suite of a Data Management System for Data Acquisition, processing and capabilities for Reservoir Flow Analysis. The paper closes with a draft overview of where this technology may be in the near future.
Real-Time Monitoring: A Critical Review of a Multidisciplinary Collaboration Environment for Timely Business and Technical Decision Making
Authors: Tan EeVern , Kok Keng H. , Noor Harun M. , Noordin Khairul Annuar
Published: December 2007

Real time solutions: an innovative approach to making business-time critical driven decisions. It is designed to monitor, support, and optimize operations in real time and remotely to mitigate cost and risk at work sites. The workflows allowed real time monitoring and intervention of the drilling operating parameters from the office which resulted in greater operating efficiency and thus greater financial saving. This technology was instrumental to the Angsi development team's success in drilling Malaysia's longest development well to-date, Angsi-A028ST1 at a total depth of 6,339 meters.

Real time well construction workflows begin when real time data on the rig site are gathered and transmitted to PETRONAS Carigali Sdn.Bhd, PCSB office via VSAT link. Data can be accessed via a web-based interface for 24 hours coverage anytime anywhere. The real time data are integrated into a geological and geophysical project database and fed into a 3D visualization tool which amalgamates the planned and current well trajectories within the geological earth model incorporating neighbouring wells with operations data. The simultaneous display of "knowledge-management-cubes" from daily drilling operational reporting software enables the team to review contingency plans and be pre-emptive by the captured lesson learnt.

This technology creates multidisciplinary collaborations through the ether space, reducing communication gaps and greatly improving the decision making process. Examples: reducing the number of check trips, shortening the planned TD by comparing the real time data against correlated model, and helping in handling operational problems. The team has greatly benefited from RTO - technologies, people and processes - with a total cost saving of more than USD 1 million.

This paper presents the real time system setup, architecture and scope of work in enabling 2D and 3D well visualization and integration. The value-added and the relative cost savings, observations and feedback are also presented
Scaling of Thermodynamic and Transport Processes for Predicting Methane Hydrate Saturation in Marine Sediments Worldwide
Authors: Bhatnagar G. , Chapman W. G. , Dickens G. R. , Dugan B. , Hirasaki G. J.
Published: December 2007

Modeling the accumulation of marine gas hydrates has previously been attempted for specific sites with separate sources of methane, i.e. biogenic or upward flux from deeper sources. We have developed a numerical model in one spatial dimension that simulates the formation and accumulation of hydrates due to either or a combination of the two sources. The results are scaled using combinations of the dimensionless variables, such that the dependence of average hydrate saturation on the numerous parameters can be summarized using two contour maps, one each for in-situ and deeper methane sources. We also show points corresponding to well studied hydrate locations on these saturation maps. As compared to the earlier site-specific parameter studies, our model presents a unifying picture of hydrate accumulations, that can be used to predict hydrate saturations and distribution at sites for which seismic or core data is not available.
The Influence of Ultrasonic Energy on Capillary Fluid Displacement
Authors: Hamida T.
Published: December 2007

In recent years, field tests and laboratory investigations have demonstrated that high intensity acoustic stimulation may enhance oil recovery in rocks. This technology is not only technologically feasible, but also serves as an economical, environmentally friendly alternative to currently accepted EOR methods. It requires low capital expenditure, and yields almost immediate improvement without any additional EOR agents. Despite a vast body of empirical and theoretical support, this technology lacks sufficient understanding to make meaningful, consistent engineering predictions. This is in part due to the complex nature of the physical processes involved, as well as due to a shortage of fundamental/experimental research. Much of what we believe is happening within ultrasonically stimulated porous media is speculative and theoretical.

This paper aims at identifying and analyzing the influence of high-frequency, high-intensity ultrasonic radiation on the miscible and immiscible displacement of oil in capillary media. We first investigate the effect of ultrasound on flow through a capillary via the pendant drop method. Water was injected into a capillary which is submersed into various processed mineral oils and kerosene. The average drop rate per minute was measured at several ultrasonic intensities, and we determined that there exists a peak drop rate at a characteristic intensity, which strongly depends on oil viscosity and the interfacial tension between water and the oil. The second set of experiments comprises of Hele-Shaw type experiments designed to study instabilities at liquid-liquid interface when ultrasound is applied. Fractal analysis techniques were used to quantify the degree of fingering and branching, allowing a rough assessment of the degree of perturbation generated at the interface. Miscible Hele-Shaw experiments are also presented to illustrate the effect of viscous forces alone. We found that ultrasound acts to stabilize the interfacial front, and that such effect is most pronounced at low viscosity ratios. The third series of experiments focuses on the effect of ultrasound on spontaneous (capillary) imbibition of an aqueous phase into oil-saturated Berea sandstone and Indiana limestone plugs. Both counter-current and co-current geometries were tested. Due to the intrinsically unforced, gentle nature of the process, and their strong dependence on wettability, interfacial tension, viscosity and density, such experiments provide valuable insight into some of the governing mechanisms behind ultrasonic stimulation.
Stereoscopic Endoscopic Optical System for 3D Measurement of Pipeline Welded Unions’ Internal Geometry
Authors: Hofmann A. C. Henri
Published: December 2007

During fabrication of Steel Catenary Risers, the welding process is considered critical to its lifetime. Control the girth weld misalignment during fabrication would improve fatigue performance.

The present work develops an optical system capable of quantifying the misalignment between the welded risers sections and to detect common geometrical welding defects like lack of fusion and excess of penetration utilizing a stereoscopic assembly.