bluuebunny/crossref_metadata_2025 huggingface dataset:
Produced Water Chemistry History Matching Using a 1D Reactive Injector Producer Reservoir Model
Authors: Vazquez O. , McCartney R. , Mackay E.
Published: June 2014

Understanding connectivity between injection and production wells is valuable information for reservoir management. Typically, connectivity might be evaluated using downhole pressure information or by injecting tracers into the reservoir. A less established but inexpensive technique is to history-match produced water compositions. For example, previous studies using this method have identified barriers to flow in reservoirs. Information on connectivity is also beneficial to scale management, and particularly where SO4-rich seawater is injected into reservoirs containing formation water rich in divalent cations (i.e. Ba, Sr, Ca) because in these cases the sulphate mineral scaling conditions in production wells are a function of the physical properties of the flow paths connecting the injection and production wells.

In this study, we have considered this latter relationship from a reverse perspective and explored the potential of history-matching produced water compositions to understand the physical properties of flow paths connecting injection and production wells for reservoirs under seawater flood. We have done this using a 1-D reactive transport model connecting an injector and a producer through a number of non-communicating layers characterized by permeability, porosity and height (completion interval). The model simulates the injection of seawater, its mixing with reservoir formation brine and the subsequent deposition of sulphate scales (barium and calcium sulphate among others) in the reservoir under equilibrium and kinetic conditions. The results of interest are the predicted produced water compositions over time from the model.

The model has been used to demonstrate how produced water compositions vary as the physical properties of the layers between the wells are modified and particularly how they vary in the presence of thief zones. Finally, a stochastic method was applied, in particular a Particle Swarm Optimisation algorithm, for the automatic history-matching of actual produced water compositions from individual wells in fields under seawater flooding. The results are promising and show that this technique can provide valuable information about the nature of inter-well connectivity.
Laboratory Characterization of Gel Filter Cake and Development of Non-Oxidizing Gel Breakers for Zirconium Crosslinked Fracturing Fluids
Authors: Reddy B. R.
Published: June 2014

Borate or Group 4 metal-crosslinked biopolymer fluids constitute the bulk of gelled fracturing fluid volumes used in field fracture stimulation operations to date. Oxidizing chemicals remain the primary gel breakers to breakdown the filter cake and establish regained formation or fracture conductivity. These breakers presumably oxidize the polymer backbone, causing chain breakdown, thereby facilitating fluid flowback. Safety hazards associated with using bulk quantities are one of the many potential problems associated with the use of oxidizing agents as gel breakers. Proper timing of gel breakdown is of utmost importance with respect to oxidizing gel breakers. Conversely, premature polymer oxidation can cause premature proppant settling. On the other hand, a long delay between the completion of the fracturing operation and activation of the gel breaker could cause deposition of additional filtercake on fracture faces, which could be difficult to break down. A desirable advancement of designing improved fracturing fluids is to develop non-oxidizing gel breakers that focus on decrosslinking the crosslinked gel structure by reacting with the crosslinking agent, rather than only breaking down the polymer chain. Additionally, by insolubilizing such breakers, they can be embedded in the filter cake and, on activation, they can degrade the filter cake completely without leaving any residues.

This paper begins by examining a study on filter cake characterization using zirconium-crosslinked fracture fluids. The filter cake was formed by flowing, under pressure, crosslinked fluid through synthetic aloxite discs of different porosities. Results from the evaluation of relationships between permeability/porosity of the discs, filter cake thickness, and filter cake polymer concentration are presented. Next, laboratory development and screening of some non-oxidizer type chemical gel breakers that can actively decrosslink zirconium at formation temperatures are discussed. Finally, the paper discusses some insolubilized breakers that become embedded in the filter cake and break it down from within.
Novel High-Efficiency Boron Crosslinkers for Low-Polymer-Loading Fracturing Fluids
Authors: Legemah Magnus U. , Guerin Michael , Sun Hong , Qu Qi
Published: June 2014

Boron based crosslinkers are commonly used to increase viscosity, and improve fluid loss control and proppant transportability of guar and its derivative fluids. Boron crosslinkers are usually preferred because of their ability to reheal after shearing and their favorable environmental properties. More efficient crosslinkers capable of cross-linking fluids with reduced polymer loading have always been of great interest to reduce formation and proppant pack damage from polymer residues, and to reduce overall fluid cost, especially with reduced availability and higher cost of guar.

We recently reported in SPE 140817 the synthesis of poly-aminoboronates, bulky compounds containing multiple boron sites and capable of interacting with multiple polysaccharide strands to form more complex crosslinking networks at lower polymer loadings than conventional guar fluids. However, to improve the marketability and acceptance of the product, a lower-cost combination of raw materials is sought. In addition, a delaying mechanism to improve the control of the fluid viscosity buildup can make the product fit into broader applications.

A readily available polyamine was used as the base scaffold, and boron incorporated via intermediate borate formed in the condensation reaction between boric acid and ethylene glycol to replace volatile and highly flammable trimethylborate. New chemistry was developed to produce more controlled crosslinking. The resulting compound exhibited desired adjustable delay characteristics.

This paper will show effect of a series of new crosslinkers in terms of delay properties. Testing results of fluids with 20% lower polymer loading, crosslinked with the new crosslinker will be reported and compared to conventional fluids. Analysis and discussion of the chemistry, crosslinker performance, and economics will be presented.
Quantitative and Visual Characterization of Asphaltenic Components of Heavy-Oil and Bitumen Samples after Solvent Interaction at Different Temperatures and Pressures
Authors: Moreno L. , Babadagli T.
Published: June 2014

Due to inefficiency of steam injection caused by technical, economic, and operational reasons, solvent methods have received special attention in heavy oil and bitumen recovery recently. A solvent can be injected in the form of vapor extraction process at reservoir temperature. Hot solvent injection can be applied to improve the recovery rate at lower temperatures than steam injection. These solvent driven recovery processes are quite complex on account of their "asphaltene destabilization" that takes place due to changes in temperature, pressure, and solvent dissolved in oil. As a result of this destabilization, the asphaltene precipitates, flocculates, and eventually plugs the pores in the reservoir.

In this research, the de-asphalting of a heavy oil sample was evaluated in a PVT cell with optical visualization. The experiments were undertaken at different temperature ranges (50°C to 80°C) and pressure (30psig to 500psig), which is the suggested range for hot solvent injection. Three light hydrocarbons (propane, n-hexane, and n-decane) were used as solvents. Applying standard SARA analysis (ASTM D2007 and ASTM D2549), the characteristics of the asphaltene precipitated at the bottom of the PVT cell, were determined quantitatively. Moreover, a methodology for "asphaltene precipitation concentration analysis" was developed in order to determine the effect the temperature, pressure, and solvent type had on asphaltene destabilization. This quantitative analysis was complemented through visual observations of asphaltene characteristics on the PVT cell as well as using optical microscopy. In addition, the refractive index measurements at the onset of precipitation were used to evaluate the changes in the oil after interacting with the solvent at different temperatures and pressures.

Finally, a comparative analysis of the esults was provided. Based on the quantitative and qualitative observations, the characteristics of asphaltene were classified in terms of their shape, size, and amount for different oil/solvent types, pressure, and temperature. This study will eventually lead to the identification of the effects of asphaltene characteristics on pore plugging during heavy-oil/bitumen recovery by gravity drainage from oilsands.
Interrelationship of CO2, Weak Acids, Bases, and pH in Scale Prediction and Control
Authors: Kan Amy T. , Zhang Nan , Shi Wei , Wang Kevin , Wang Lu , Yan Chao , Yan Fei , Tomson Mason B. , Tomson Ross C. , Zhu Huiguang , Razavi Syed M.
Published: June 2014

pH is one of the most important parameters for evaluating the scale and corrosion potential of the water during oil and gas production. The effectiveness of chemical treatment can also be influenced by pH in the production tubing and reservoir. Unfortunately, pH is not a conservative parameter that can be determined independently. pH changes from reservoir to surface facilities due to changes in temperature and pressure of the production system and the corresponding G/O/W phase changes. Measured pH value of a produced water sample is often unreliable and influenced by temperature and ionic strength of the solution, degree of degassing and sample preservation. Measuring pH in line or with downhole probe at real field condition can be expensive and difficult. pH can be predicted theoretically from charge balance equations more economically and reliably by assuming a good knowledge of thermodynamic equilibrium constants, activity coefficients, G/O/W flow rates, temperature, pressure, and reliable produced water composition. The author's research group recently developed a new automatic titration method to simultaneously measure total alkalinity and weak organic acids concentrations of brine. The carbonate thermodynamics were evaluated with calcite solubility studies at ultra-high temperature and pressure. The newly developed thermodynamic data and method enable accurate prediction of produced water pH at temperature and pressure typically encountered in deep water production. In this paper, the influences of water chemistry parameters on pH are reviewed. The newly developed automatic alkalinity titration method is discussed. pH calculated by the recently validated thermodynamic constants and activity coefficients are compared with live water pH measurements.
Enhanced Oil Solubilization Using Microemulsions With Linkers
Authors: Pietrangeli Gianna , Quintero Lirio
Published: June 2014

In recent years, applications of microemulsion technology have increased in the drilling and production industry. Some of these applications include oil-based drilling fluid displacement to water-based fluid, near-wellbore remediation, well stimulation, enhanced oil recovery and flow-back recovery in shale gas wells.

Microemulsion formulations for these applications need to have high oil solubilization and very low interfacial tension, which is achieved with relatively high concentration of surfactants. High-performance microemulsion systems with lower surfactant concentrations are desired to optimize the cost of the technology application.

The reduction of surfactant concentration could be achieved by introducing linker additives in the formulations. The addition of linker molecules enhances the microemulsion solubilization property, which increases the hydrophilicity and/or the lipophilicity behavior of surfactants. Previous studies indicate the addition of a linker substance could double the solubilization of the system by segregating at the interface. The linker molecules create chaos, avoid formation of organized structure and decrease the viscosity, which helps to pack surfactants more efficiently at the interface. Some examples of linker additives include amines, acids, alcohols and phenols.

This paper presents systematic studies that have been carried out to determine the influence of lipophilic and hydrophilic linkers in an anionic/nonionic surfactant mixture when exposed to olefin-based oils that are used in synthetic-based drilling fluids.

The results of the study include phase behavior of a microemulsion system, interfacial properties and kinetic diffusion under several temperatures, as well as evaluation of the system with and without the addition of linker molecules for cleanup of synthetic and oil-based drilling fluids.
Risk Assessment of Concurrent Hydrate and Wax Formation for Deepwater Production Restart Modeling and Experimental Results
Authors: Oschmann H. , Alapati R. , Paso K.
Published: June 2014

This paper presents the successful implementation of a flow assurance strategy for a new deepwater production system offshore Africa derived from results of experimental assessments of associated paraffinic and hydrate formation. The rheological behaviour of production fluids under field conditions at various pressures and temperatures are compared with results from conventional PVT and flow modelling including latest models specifically designed to review pipeline clearance times and pressure wave propagation during restart.

These assessments differentiated between the individual contributions of hydrate formation and paraffin gelling and included analysis of the interaction between hydrate crystals and the wax-gel network.

Additionally, the performances of Low Dosage Hydrate Inhibitor (LDHI) and Pour Point Depressant (PPD) were assessed for various production conditions in the presence of other production chemicals in the temperatures range of 65°C to 4.5°C. The results showed excellent performance of both LDHI and PPD and additionally an incremental performance from the synergy between the two applied chemistries.

The predicted flow behaviour of the multiphase system based on the modelling was aligned significantly with the findings of the experimental assessment creating confidence for planned optimisation of the shutdown/restart procedure.

Simultaneous formation of gas hydrates and paraffinic gels during multiphase transportation poses significant potential risks for interruption of production in deepwater operations. An accurate assessment of these risks is critical in implementing a cost-effective flow assurance strategy which will minimises downtime during shutdown and restart procedures.

This investigation realises the potential development of a best practise solution to gelling problems associated with complex micro-crystalline paraffin wax. Crude oils which contain large fractions of branched and cyclic alkanes typically show poor performance with conventional PPD chemistries, but may show improved effective treatments with new chemistries specifically designed to lower the yield stress. Extension of this new treatment technology on complex waxy crude oils can encourage development of new reserves in regions such as Southeast Asia, west coast Africa, and South America where traditional chemistries are ineffective.
The Evaluation and Optimization of Hydrogen Sulfide Scavenger Applications Using Ion Mobility Spectrometry
Authors: Matherly Ron , Taylor Grahame
Published: June 2014

Field Asymmetric Ion mobility spectrometry (FAIMS) is commercially available equipment has been used to assay certain challenging analytes. This is a field capable method and has recently been applied to optimize the chemical use and flow parameters for conventional and flowing (Ultrafab) type hydrogen sulfide scavenger towers. An analysis method and appropriate calibration for the analytes of interest was developed "in house" followed by the application of this equipment in a field environment. By monitoring the chemical makeup of the partially spent scavenger fluid in these towers it is possible to a) more efficiently use the appropriate scavenger and b) monitor the degree spent to enable more effective monitoring of the consistency of the spent fluids and avoiding troublesome solid deposition.
Enhancement of Heavy Oil Demulsification
Authors: Wiggett A J , Ricza T
Published: June 2014

Demulsification is well known and tested, however with regards to heavy oil treatment, the crudes become more difficult to handle. Demulsification is subject to a number of external factors such as temperature, viscosity and crude oil composition, which affect the rate of water drop and resolution of emulsions. Heavy oil is composed of many components, but especially asphaltenes, which are unstable in produced crudes. As a result of their instability, asphaltenes tend to precipitate and fall out of suspension, eventually blocking production flowlines and separators.

It is widely known that many crude oils contain asphaltenes. They affect the oil/water and emulsion separation in these heavy crudes, causing increased usage of demulsifiers and system upsets. There have been many attempts to improve demulsifiers, but this has met with limited success.

We discuss a possible practical chemical technique to help resolve the emulsions in these types of crudes more easily, to maximize separation efficiency.

The use of asphaltene dispersants has been employed to deal with precipitated solids after they have agglomerated, but we investigate examples where the addition of other asphaltene inhibiting products may help improve the demulsification process. The impact of the improved separation would enable the crude oil to better meet its sales specifications. It may also help reduce system upsets and improve the oil production systems, enabling the customer to meet compliance with oil production quotas.
Smart Well With Autonomous Inflow Control Valve Technology
Authors: Aakre Haavard , Halvorsen Britt , Werswick Bjørnar , Mathiesen Vidar
Published: June 2014

A smart well concept with autonomous inflow control valve (AICV) is presented. AICV utilized the best from smart wells (ICV) and inflow control devices (ICD). The technology is presented, discussed and compared against other conventional inflow control technologies, id est (i.e.) passive ICD. The flow characteristics are presented and implemented in reservoir model simulations. Significant increased production and recovery are shown for the application in a thin oil rim with gas cap and heterogeneous reservoir. The AICVs are autonomous, i.e. self-regulating and do not required any external control or force. This makes them simple and robust, and a large number of control valves can be mounted in the well, i.e. one in each screen. When water and/or gas breakthrough occur the valves in the breakthrough zone will autonomously shut-off. This provides the operator with a significantly more efficient production and increased recovery. The AICV technology also enables opportunities to drill longer wells and achieve maximum reservoir contact of each well. In addition, the AICV removes the risk, cost and requirement for separation, transportation and handling of unwanted fluid.
Status of Drill-Stem Testing Techniques and Analysis
Authors: Van Poollen H.K.
Published: June 2014

This paper is a compilation of the latest drill-stem testing techniques. New tools are described, together with present-day interpretation techniques, and their limitations are given. The importance of proper times for shut-in and flow periods are stressed. A number of suggestions for the future are given, and a rather complete list of references in the field of drill-stem testing has been supplied for use by interested readers.

Introduction

A drill-stem test (DST) is a temporary completion. It consists of a combination of a packer arrangement and drill pipe or tubing. Valves are present in this arrangement to open and close the tool, and pressure and temperature recording devices are employed. Upon completion of the test, the entire arrangement is withdrawn from the well.

The purpose of a DST isto determine whether or not to complete the well andto obtain reservoir or aquifer information for exploration applications.

The DST will render a wealth of information - e.g., a sample of the fluid itself, the actual productivity index, the reservoir pressure, the theoretical productivity index and the amount of wellbore damage.

The fluid will show whether the well can be completed as an oil well, a condensate well or a gas well; or, it will show if the formation should be abandoned (for being a water producer or for being dry). Tests can be run on the sample to determine the hydrocarbons present, viscosity of the mixture, API gravity, paraffin content, pour point or gas-oil ratio. The water produced can be analyzed for salinity and electrolytes present to aid in stratigraphic correlation, and the resistivity of the water will aid the logging engineer in his evaluation of the electric logs. The DST further aids in determining gas-oil or oil-water contacts, and the proximity of pinchouts or faults.
Experimental Investigation of Liquid-CO2 and CO2-Emulsion Application for Enhanced Heavy Oil Recovery
Authors: Emadi Alireza , Sohrabi Mehran , Farzaneh Seyed Amir , Ireland Shaun
Published: June 2014

CO2 Injection in heavy oil reservoirs improves oil recovery and at the same time may reduce some of the environmental concerns associated with heavy oil recovery by thermal methods. Depending on the reservoir conditions and oil properties, viscosity reductions of up to two orders of magnitude may be achieved as a result of CO2 dissolution in heavy oil. However, adverse viscosity ratio which results in viscous fingering and early breakthrough of CO2 is a challenge for application of CO2 in heavy oil reservoirs. Therefore, CO2 injection needs to be combined or augmented by other displacement mechanisms (e.g. waterflood, foam injection) to efficiently displace the heavy oil diluted with CO2. In our previous papers, the micro-scale displacement efficiency and mechanisms involved in CO2 and CO2-foam injection in heavy oil systems were investigated and presented through vivid micromodel images. This paper presents the results of a series of coreflood experiments performed to evaluate the potential of liquid-CO2 and CO2-emulsion injection in a heavy oil reservoir.

The coreflood results show a very good performance for CO2 injection. An ultimate recovery of around 70 %OOIP as a result of secondary and tertiary CO2 injection was achieved which was twice the recovery obtained by waterflood in this heavy crude oil. This substantial recovery improvement was a consequence of a massive viscosity reduction (up to 97.5% of the original oil viscosity) at reservoir conditions. Co-injection of liquid CO2 and a selected surfactant also resulted in in-situ formation of a very stable CO2-emulsion which reduced mobility of injected CO2 by three orders of magnitude in presence of oil. In-situ generation of CO2-emulsion as evident from an increased in the pressure drop across the core was observed even at high oil saturation of up to 50%. The results of this work show significant potentials for immiscible CO2 and CO2-emulsion injection as an effective enhanced heavy oil recovery technique.
Investigating Residual Trapping Mechanism in CO2 Storage in the Brine through Analytical and Numerical Simulation Methods
Authors: Soroush Mansour , Wessel-Berg Dag , Kleppe Jon
Published: June 2014

Injecting CO2 in subsurface formations bearing brine creates different storage mechanisms. Firstly, CO2 will have an upward movement due to the buoyancy and it will be trapped below a geological barrier. During this stage of flow brine starts to imbibe into the pore spaces already occupied by CO2. Because of the wetting behavior of the system and CO2-brine capillary pressure, fractions of CO2 remain as residual saturation in the pore spaces. This is an important phenomenon that affects the storage capability and security. Later, and in a long term process, CO2 starts to dissolute into the brine and its density will be increased; and as a result convection mixing phenomena will starts.

To clarify the trapping mechanism, two different issues are discussed. One is the one dimensional, two phase behavior during CO2 injection and the second is the water imbibition process that includes the trapping mechanism. By arranging the flow equations and normalizing them by dimensionless parameters, main scaling parameters that define the physics in each problem are obtained. These parameters are CO2-brine mobility ratio and special gravity and capillary dimensionless numbers for each problem. In the water imbibition problem, hysteresis in relative permeability results in modifications to the dimensionless scaling parameters. These parameters are key factors in design and scaling of the experimental measurements to the simulation and analytical results.

To verify the analytical analysis, a numerical simulation model is constructed for the problems. Reservoir parameters of the Sleipner CO2 storage reservoir and the Viking formation (Bennion et. al. 2008) are used in this study in order to construct the model. This time, dimensionless parameters are defined according to the reservoir parameters. Analytical models are established based on simplifying assumptions, while simulation results are dependent on key scaling parameters obtained from analytical clarification. This means that they are good representatives of phenomena at reservoir conditions and can be used as a conceptual model before performing a fine scale, time consuming reservoir simulation study.
Impact of Completion on Wellbore Skin Effect
Authors: Alshawaf Mohammed H. , Gringarten Alain
Published: June 2014

Wellbore completions are a key well component and could have a positive or a negative impact on productivity, thus designing a suitable completion and implementing it properly must be a priority for production engineers. Consequently, well productivity indices related to specific completion designs have received much attention in the literature, with analytical and numerical models used for simulating various completion properties. The completion impact on wellbore skin effect, however, is seldom documented.

This paper looks at the effect of completion and reservoir characteristics on skin factors, and focuses on perforated, gravel-packed and frac-packed wells. For this study, a commercial black oil simulator was used to simulate different reservoir conditions and completion strategies, and the resulting skin effects were estimated by well test analysis of the corresponding synthetic pressure and rate data.

Results show that decreasing perforation density and tunnel length leads to high skin values due to wellbore flow restrictions. Moreover, it shows how a damaged gravel-pack completion coupled with a highly permeable formation results in high skin values that range between 1 and 100. Finally, in frac-pack completions, it is important to find the right balance between formation permeability and proppant permeability in the fracture as well as the permeability contrast between the proppant and the gravel as this dictates how a frac-pack will perform. Thus, depending on permeability of proppant and gravel-pack, skin values for frac-pack completions range between -2.5 to 15
Use of Oil Reservoir Simulation to Estimate Value of Flexibility
Authors: Marques Mateus D. , Gaspar Ana T. , Schiozer Denis J.
Published: June 2014

The selection of production strategy under uncertainties is a complicated task due to the high number of variables and uncertainties. While new information aims to reduce the uncertainty of one or more variables, consequently reducing the risk, flexibility may be used to change field operation in the future. The objective of this work is to estimate the value of flexibility through a risk-return analysis in which a company profile is taken into account represented by the iso-utility curve.

The methodology is an extension from Value of Information (VoI) assessment under uncertainties. It comprises a complete uncertainty analysis, use of representative models, generation of risk curves, optimization steps to define the strategy without flexibility which is then simulated in several scenarios verifying the bottlenecks of the strategy that may be assessed through flexibility. Finally, the benefit of each selected flexibility is estimated through risk-return analysis. The work includes a Latin Hypercube technique to combine uncertain scenarios and the use of an assisted optimization procedure to select the production strategy. It is then applied to a 28° API, low viscosity offshore oil field including production history.

Results indicate that this methodology is able to identify flexibility, in this case, the expansion of production capacity, which is then added to the production strategy with two objectives: to mitigate risk and to increase value. The tested flexibility changes the project risk and return in both objectives and allows the company to produce more efficiently in different scenarios, by producing with a higher use of installed capacity. The main conclusions are that the flexibility of production capacity expansion can be used not only to mitigate risk, but also for value creation, allowing the company to adapt its production strategy as new information is revealed.

The main contribution of this work is a new perspective in risk assessment from a probabilistic point of view, combining production strategy selection and optimization, numeric reservoir simulation and risk-return analysis. The flexibility is an alternative to information for risk mitigation, with the advantage of not holding the project back to collect new data. Furthermore, flexibilities can also be used to exploit the upside of the uncertainty if, during the production phase, such scenarios occur.
A New General Flow Model for Well Test Analysis for Fluids Used in Enhanced Oil Recovery Projects
Authors: Valdes-Perez Alex R. , Cinco-Ley Heber , Pulido-Bello Héctor , Hveding Frode , Samaniego Fernando
Published: June 2014

Fluids used in Enhanced Oil Recovery (EOR) projects, such as polymers, micellars solutions and surfactants are classified as non-Newtonian fluids, due to their viscosity behavior. The measuring and analysis of pressure data during injection of non-Newtonian fluids and during fall-off periods has become popular. However, the lack of appropriate tools for its interpretation might yield incorrect results when characterizing parameters are computed, such as flowing geometry around wellbore, formation permeability, skin factor at wellbore, injected fluid consistency index, etc.

This paper presents a new general flow model for non-Newtonian fluids governed by a partial differential equation. Analytical solutions for such model are also presented. The model and its solutions are suitable to identify three of the most common flow geometries (linear, radial and spherical flow), when a displacement agent is flowing within the porous media in EOR projects. Due to its behavior, this model is appropriate when extra heavy oil is flowing in the reservoir. A better understanding and representation of the fluid flowing into the reservoir can improve the monitoring and execution of EOR projects and reservoir exploitation schemes.

Linear, Radial and Spherical diffusivity equations for Newtonian fluids are particular cases of the new model. For different flow geometries, graphs of the pressure and its derivative behavior against time are presented. A method for determining fluid consistency index and flow geometry is presented. A synthetic example that describes the application of the new model is also shown.
Uncertainty Based Approach for Predicting the Operating Window in UBO Well Design
Authors: Udegbunam John Emeka , Arild Øystein , Fjelde Kjell Kåre , Ford Eric , Lohne Hans Petter
Published: June 2014

Underbalanced operations are carried out to bypass drilling challenges that could be difficult to resolve using conventional drilling techniques. Steady state multiphase flow models are used to construct underbalanced drilling operational windows. These advanced software models are deterministically formulated. It is known that some of the model input parameters such as the multiphase flow parameters, friction factors, and reservoir productivity, are subject to uncertainties. Failures to capture these variabilities may introduce some error in the model prediction, resulting in poor well planning and implementation.

The purpose of this work is to implement probabilistic modeling of underbalanced drilling using a simple steady state two-phase model. Both predefined uncertain and fixed factors serve as inputs to a pre-existing deterministic model. By applying Monte Carlo simulations, the model predicts outputs which follow a statistical distribution. A sensitivity analysis is conducted to determine the input factor mostly responsible for the uncertainty in the predicted bottomhole pressure.

The results demonstrate that uncertainty modeling can improve underbalanced drilling design and operations. A more realistic operational window is obtained, ensuring that underbalanced condition is maintained throughout the target section.

With a better understanding of uncertainties and the corresponding impacts, well planners can make better decisions regarding well design criteria and safe operational conditions, and avoid huge economic consequences.
Effect of Non-uniform Fracture Spacing and Fracture Half-length on Well Spacing for Unconventional Gas Reservoirs
Authors: Sahai Vivek , Jackson Greg , Rai Rakesh
Published: June 2014

Early in the development of a shale gas resource, optimal well spacing remains unknown as wells are sparsely drilled to hold leases by production. Developing the acreage requires operators to select locations, specify drilling plans, and design completions for multi-stage horizontal wells to maximize the operating metrics as defined by the company.

This paper builds on our earlier work which presented sensitivity analysis for optimal well spacing with respect to permeability, fracture spacing and half-length under the assumption of uniform and symmetric completion configurations. The well spacing sensitivity to heterogeneity in completion configurations (i.e., non-uniform fracture half-length and asymmetric fracture spacing) are presented in this paper using forward and stochastic modeling approaches.

Forward modeling results show a strong bias towards the longest repeated fracture half-length in determining the optimal well spacing. Higher reservoir permeability abates the impact of fracture heterogeneity. Fracture modeling, constrained by production logs, temperature logs, and/or microseismic, can be used to aid in the identification of the longest repeated half-length.

This paper demonstrates the challenges associated with stochastic modeling of well performance. Examples from synthetic and field case studies are presented to illustrate uncertainty in reservoir and completion parameter determination. The spacing optimization workflow used captures this uncertain range to effectively determine the impact on recovery factor and Net Present Value (NPV). The importance of the quantity of production history needed to determine optimal well spacing is also presented. Results reveal that with increasing heterogeneity longer production history is required for reliable determination of optimal well spacing. Finally, a field case study applying a production log and fracture modeling is examined to identify the impact of non-uniform fracture spacing and fracture half-length heterogeneity.

These conclusions, via the application of deterministic and stochastic modeling on production from field cases and synthetic wells, will aid operators in answering the multi-billion dollar question: how many wells should be placed in a given area? The workflow described in this paper not only can answer this question but also help us to understand how to maximize economic return and the ultimate gas recovery.
Strategy and Planing EOR for Caracara Sur Field, Colombia
Authors: Cubillos H. , Stofferis M. , Vanegas G. , Lager A. , Rolf A.
Published: June 2014

The Caracara Sur Field (Llanos Basin, Colombia) consists of multilayered compartmentalized fluviodeltaic reservoirs. Sands have Darcy-level permeability, contain a medium-quality oil (21° API), and are subject to very strong aquifer support. The reservoirs are produced with artificial lift, either selectively or commingled. After six years of development, oil production is expected to decline. Ongoing efforts to maintain the production plateau include infill and horizontal attic oil drilling and selective completions. However, there is a limit to what can be achieved considering the strong aquifer drive and unfavourable mobility ratio. This encouraged the investigation of enhanced/increased oil recovery (EOR/IOR) methods which has resulted in screening a number of EOR processes and the planning of a pilot project in the field.

EOR/IOR screening evaluation identified chemical EOR processes as the most suitable techniques for the field. Polymer, alkaline-polymer (AP), Alkaline-Surfactant-Polymer (ASP) and surfactant-polymer (SP) are the technologies under consideration.

A careful and complete project plan has been developed, customized for the field’s most challenging characteristics: fresh formation water, in-situ oil viscosity of 12 cP, relatively high reservoir temperature (above 175 °F), the need to inject and produce commingled, (up to six stacked reservoirs) and most importantly the strong and drifting aquifer, which is expected to influence sweep efficiency.

The plan includes laboratory studies, multi-scale high-resolution reservoir simulation, single-layer single-well tests of injectivity and residual oil saturation, and a multi-layer inter-well pilot prior to full-field deployment. Tracer technology has been developed in-house to support the project. Back flow tracer tests and single-well tracer tests will be conducted in the field to evaluate aquifer drift and to determine the remaining oil saturation. Comprehensive evaluation will permit the design of an efficient vertical injection profile, appropriate injectivity and chemicals displacement in a multi-reservoir field.

The planning stage of the Caracara Sur EOR strategy, including the screening evaluation and the first project results, provides guidelines and solutions that can be used on other EOR projects in similar fields and facing similar challenges, not only within the Caracara Block itself, but within the Llanos Basin and elsewhere:

A ‘fast-track’ program, whereby screening and field studies are done partly in parallel targetting shortened elapsed time for the pilot evaluation. If results are technically successful this will allow profitable full-field EOR implementation. Use of an in-house project team supported by integrated laboratory expertise (leveraging CEPSA’s petrochemicals experience) is proving to be efficient and successful in delivering a high quality technical solution.
A New Interpretation of CO2 Diffusion Experiments
Authors: Potsch K. , Toplack P. , Gumpenberger T.
Published: June 2014

The injection of CO2 underground has been investigated by many scientists, be it for sequestration or enhanced oil recovery. When CO2 enters the reservoir, the main questions, into which phase the CO2 concentrates first (oil or water) and in which amounts it is going into solution, will be answered. Both, numerical and experimental studies in the literature report two different diffusion parameters, differing by more than one order of magnitude. These findings are confirmed in our experiments. In the literature, rapid dissolution is attributed to the appearance of natural convection due to density differences of the CO2-enriched liquid, entrailing a faster mixing, sometimes being called super-diffusion. This paper reviews the physical effects appearing during CO2 injection and investigates the mathematical basis for the determination of solubility and diffusivity together with the assumptions made in this case. We come to the conclusion that a parabolic diffusion law cannot explain the two different diffusion constants, but a hyperbolic law can. In a detailed dimensional analysis of the Navier-Stokes equation dimensionless groups are formed, the magnitude of which determines the importance of the different terms, in our case the importance of convection. Using the parameters of our physical setup we find that the convection is only prevalent in a thin layer close to the interface of gas and liquid. This is in contrast to present belief. Stability considerations for the onset of convection complete the scope of this work.
Offshore Environmental Management: Monitoring Guidelines in Oil&Gas Activities
Authors: Buffagni Melania , Cova Carlo Alberto , Pedroni Luisa Valentina , Zappacosta Ilaria , Aiello Gennaro
Published: June 2014

Offshore Environmental Monitoring can be defined as technical and institutional activity aimed at measuring, evaluating and tracking potential physical, chemical and biological environmental changes which could be induced by operative activities or by external causes.

By carrying out this activity, the oil company can take the appropriate corrective measures for creating a Monitoring Plan related to the offshore e&p projects and operations.

According to this approach, the baseline information on pristine conditions is compared against exploration drilling, development and post-development impacts. Efficiency of mitigation and restoration measures can be assessed through the monitoring activity.

Since early ‘90s, eni has carried out several environmental monitoring campaigns around its offshore installations worldwide aiming at evaluating changes in the current state of the interested area and in order to assessing evolutionary trends of environment. These surveys were able to provide early warning of any potentially serious impact and to provide data for strategic decisions. Besides they have been supporting to determine whether any detected change in physical, chemical and biological components was caused either by e&p activities or by natural occurrences.

Based on the above considerations, this paper introduces guidelines on strategy approach carried out by eni in offshore environmental monitoring, during the project life-cycle.
Changing in the Dark with Your Fingers Crossed: Safety Interventions Without Diagnosis and Evaluation
Authors: Bowen Mathew , Maneotis Sarina
Published: June 2014

Safety culture refers to the implicit assumptions, values, and beliefs that employees hold about workplace safety. Essentially, it is "the way things are done around here when it comes to safety." This is a simple definition for a complex concept that has been the focus of decades of research within Occupational Health Psychology. This presentation focusses on the sound research methods and measurement strategies that can be used to more effectively design and evaluate safety culture interventions.

Organisations spend significant resources implementing initiatives with the goal of improving the safety culture. Too often, critical steps of the intervention, namely diagnosis and evaluation, are not thoroughly considered or completed with the necessary rigour. For instance, an organisation may design an intervention based on the assumed cause of a debilitating safety culture, rather than going through the proper due diligence to diagnose the cause. Furthermore, organisations often scramble after the intervention to identify what safety metrics, most notably global lag indicators, are available to demonstrate that the intervention had an impact.

This presentation offers solutions to these challenges by providing attendees with the knowledge and skills to engage in more thorough diagnostic and evaluation practices when trying to improve an organisation’s safety culture.

The following specific topics will be addressed in this presentation:

Defining and modelling safety culture Qualitatively and quantitatively diagnosing safety culture challenges Developing an efficacy framework to evaluate the effectiveness of safety culture interventions

To illustrate these topics, the presenters will use findings from applied safety culture research projects focussed on diagnosing the areas for improvement within organisations’ safety culture and evaluating safety culture interventions.

Although safety culture is often seen as a "soft" concept, there is a significant opportunity to use more structured processes and sophisticated measurement techniques when designing, implementing, and evaluating safety culture interventions.
A Recommended Fitness Standard for the Oil and Gas Industry
Authors: Milligan G.. , House J. R. , Tipton M. J. , Hildenbrand B.. , Maeso M..
Published: June 2014

Fitness standards are becoming common practice in industry and the emergency services. Such standards are used by the Fire and Rescue services, the Royal National Lifeboat Institution and the Military amongst others. These standards include measures of strength, endurance, anthropometrics, flexibility, motor skills and cardiac and metabolic fitness.

The main benefit to introducing a fitness standard into the workplace is to ensure that an employee is physically capable of completing the essential tasks of the job to at least the minimum acceptable standard, thus the risk of employing physically unfit individuals in physically demanding jobs is minimised, and the associated human and economic effects (e.g. through injury) are reduced. Furthermore, standards ensure selection is based solely on ability to complete the essential tasks and is therefore fair and unbiased. The Energy Institute (EI) is the professional body for the energy industry, delivering good practice and professionalism across the sector. On behalf of the EI’s Health Technical Committee (HTC) work was undertaken by the University of Portsmouth (Department of Sport and Exercise Science) to provide an introduction to fitness standards and to make recommendations for a minimum fitness standard for the Oil and Gas Industry (OGI).

The findings of this work are presented in the EI’s 2010 publication ‘A recommended fitness standard for the oil and gas industry’. Minimum standards have been evaluated based on the essential tasks with a significant physical fitness component e.g. manual handling, casualty handling and ladder/stair climbing. The evidence-base for the standards is contained within the report, as is guidance on administering the tests. The report does not provide guidance on policy issues or implementation strategies as this is considered to be a matter for individual companies.