bluuebunny/crossref_metadata_2025 huggingface dataset:
Dry Gas Reinjection in a Strong Waterdrive Gas-Condensate Field Increases Condensate Recovery—Case Study: The Sleipner Ty Field, South Viking Graben, Norwegian North Sea
Authors: Eikeland Kjersti M. , Hansen Helga
Published: December 2007

The Sleipner Øst Ty Field is a strong waterdrive gas condensate field, with in place volumes of 59×109Sm3 gas and 52×106Sm3 unstabilized condensate. The reservoir consists of deep water turbidite sandstones and associated mudstones, which act as baffles to flow. The reservoir qualities are very good, with high porosity and with permeability in the range of 100 to 1000 mD.

The first production in the area started up from the Sleipner Øst Ty Field in 1993. The initial reservoir pressure of 244 bar was only one bar above the dew-point pressure. Massive dry gas reinjection started in 1996, and the reservoir pressure increased during the next two years causing an increase in the condensate to gas ratio. During the injection period, which lasted until 2005, 29×109Sm3 of dry gas was injected. The main focus during these years was to obtain good vertical and areal sweep of the dry gas in order to vaporize the dropped-out condensate. Chemical gas tracers were injected and analyzed for in the production wells to monitor the movement of the dry gas through the reservoir. This knowledge was used to identify unswept areas, and to change the drainage pattern by doing well interventions and drilling infill wells.

The injection was stopped primarily due to high probability of trapping gas. Compositional reservoir simulation showed that from 10 to 20% of the injected dry gas volume could be trapped in the northern region, which has no producers. The risk of not being able to back-produce the injected dry gas was considered high, since the saddle area separating the producers in the south from the injectors in the north was partly water flooded.

The gas cycling programme has increased the condensate recovery factor substantially; from the originally planned 50; by pressure depletion, to the current estimated ultimate recovery of 81;. At present, the condensate recovery factor is 76;.
Scale Milling and Nipple Profile Recovery with Electrical Wireline—Case Histories from Successful Operations in the North Sea
Authors: Mcinally Gerald , Osaland Espen , Iden Kjetil Systad , Halvorsen Knut Hille
Published: December 2007

During the last decade, wireline tractors have replaced coiled tubing or snubbing for the conveyance of wireline logging and intervention equipment into horizontal or highly deviated wells.

Based on this trend towards lighter and more mobile intervention methods, new techniques and equipment have now been developed to enable PowerTrac Advance (PTA*) wireline tractor technology to deploy rotating equipment such as milling, honing and brushing.

Wells suffering from scale buildup or seal bore damage have been successfully recovered, leading to considerable cost savings compared to conventional methods.

The wireline conveyed rotation technology can be used equally well in vertical pipe sections, as well as in horizontal or highly deviated well bores.

There are operational limitations as to what can be achieved and proper job planning is important to assure success.
Better Reservoir Management through Improved Water-Injection Methods with Data Analysis and Detailed Fracture/Reservoir Modeling
Authors: Jøranson Håvard , Klein Henry H. , Raaen Arne M. , Smith Michael B.
Published: December 2007

The search for practical engineering tools to better manage water injectors has been ongoing for many years. Simple analytical solutions have proven inadequate, and most reservoir simulators do not explicitly model water injectors. This paper proposes a methodology of using detailed and coupled fracture and reservoir modeling to ensure proper injection start-up procedures, and managing injection rates to avoid out-of-zone injection. This is combined with simple rate-pressure data to understand injection behavior, and from that control the process.
Flow through Inhomogeneous Fault Zones
Authors: Soleng Harald H. , Syversveen Anne Randi , Skorstad Arne , Røe Per , Tveranger Jan
Published: December 2007

Faults significantly influence fluid flow in reservoirs. In standard reservoir flow-simulator grids, faults are represented as surfaces or planes. However, outcrop studies show that faults often must be regarded as volumetric elements. Inside such fault zones, the facies characteristics differ significantly from those in the rest of the reservoir. In a fault facies reservoir model faults are represented as volumes populated with facies with properties derived from their origin and faulting history.

In this paper, we compare fluid flow performance of a fault facies model and a conventional fault model. The uncertainties attached to the fault zone properties and architecture included in the fault facies model produce a straightforward effect on the range of simulation outcomes and uncertainty of production parameters. In the conventional model, similar effects can only be reproduced ad hoc using poorly determined random fudge factors. We also look at the effect of upscaling the fault zone. Results show that the flow properties in the fault facies model differ from the conventional model with regard to both water cut and total oil production. As expected, upscaling may introduce a significant bias in the cumulative oil production.
Creating a Great Place To Work: The Result of Clear Strategy and Leadership Development
Authors: MacDonald Sue , Horgan Mike , Gomersall Sam , Brown Margaret
Published: December 2007

In August 2005, Marathon Europe set a clear forward vision and strategy, building upon a rich history and addressing long term direction for the Europe business unit (EBU). To support the implementation of this strategy and to ensure an appropriate focus on our people, five areas of focus, or Pillars, were created: Leadership, People, Values, Delivery & Growth.

These Pillars have provided focus and balance in all aspects of our business and served as a communication vehicle. Appropriate investment has been made in softer areas to develop leadership excellence and to support the development of people. A clear strategy has provided balance between short term delivery and long term growth. The management issues involved are not unique to the upstream oil & gas sector and by participating in surveys across industry sectors, we have identified and addressed areas of weakness and built upon areas of strength.

The results have been an increase in employee engagement and significant progress in achieving the long term vision for the EBU. The externally measurable results have included the achievement of 54th position in the cross sector UK Sunday Times top 100 best companies to work for 2007, the Ireland Top 50 best places to work and a staff turnover rate of only 2.6%.

We challenge others to participate in the Sunday Times top 100 and similar surveys, in order to enhance the reputation of the upstream oil & gas sector and to create more organisations which are great places to work.
Well Integrity Management System (WIMS)—A Systematic Way of Describing the Actual and Historic Integrity Status of Operational Wells
Authors: Corneliussen K. , Sørli F. , Brandanger Haga H. , Tenold E. , Menezes C. , Grimbert B. , Owren K.
Published: December 2007

It is important to be able to have an overview of the well integrity at all times. Statoil, Norsk Hydro and Total E&P UK Ltd. therefore joined forces in a JIP with ExproSoft to develop a software application for data collection, handling and reporting of well integrity. The resulting software is called WIMS, short for Well Integrity Management System. A pilot version was installed and tested by the operators’ spring 2007, prior to the release of the final version.

WIMS enables a uniform and structured approach for describing the status and handling of well integrity issues throughout the production phase of a well. This paper discusses the philosophy behind how WIMS handles well integrity information from when the well completion is installed until the well is permanent abandoned. The well integrity data follows the well from it is new, and is continuously updated when a well leak or other well integrity derogations occur. To assist in leak diagnosis, risk assessment and defining corrective measures; test results, continuous pressure and temperature data, annuli top-up and bleed-off data is presented in WIMS. The paper also describes how information is aggregated from well level and summarized to give an overview of the well integrity status for any defined cluster of wells.

WIMS is developed with the input and needs from three different operators, and the paper also includes a discussion of how WIMS will be used by the three operators.

Apart from the need of systemized and easily communicated well integrity data, the success of WIMS is dependant on the implementation process. Very often the implementation process is neglected, and there are numerous examples of failed attempts at introducing new software in the oil and gas industry. The paper shares the experience from the evaluation and implementation of WIMS.
Novel Service Approach Helps Operator Meet European Environmental Requirements, Reduce Waste Generation and Cut Costs
Authors: Marinescu Pavel , Buchner Alexander , Mertin Mario
Published: December 2007

Planning a well nowadays means not only addressing technical issues like trouble-free drilling and reducing formation damage but also seriously considering the amount and type of waste to be generated, local environmental regulations, possibilities and costs for waste disposal, and lastly, cost effectiveness. To achieve all these targets, a novel concept of integrated services program was initiated back in 2001. Since then more than 70 wells were drilled successfully, amounting to more than 500,000 ft and reducing overall drilling waste volumes by more than 35%.

Aligning all fluid-related services has been tried in the past; however, these efforts were mostly targeted at implementing a joint service project management package. Unfortunately, many of these arrangements proved to perform less than optimally. Main reasons were lack of cooperation and conflicting technological/financial interests.

The paper describes the environmental restrictions, their implications on well planning and waste management concepts and the field results of over 70 wells showing the successful implementation and continuous improvement of an integrated service program on a major drilling campaign in Austria from 2001 until 2006. Key Performance Indicators (KPIs) were defined at the beginning of the project, and incentive scenarios were developed. The Integrated Fluids Engineering (IFE) program was designed to include all aspects of drilling fluid management, from mud mixing, to solids control to controlling waste discharge. The project resulted in substantial and sustainable reductions in drilling waste generation while at the same time improving drilling performance through optimized drilling fluid systems, enhanced wellbore cleaning and consistent gauge-hole performance in soft to medium-hard sediments.

The paper also addresses the development of footage cost during the whole project period, supporting the fact that increased service cost does not necessarily result in increased well cost if the associated drilling performance increase can be realized.
Elastoplastic Fracture Model Improves Predictions in Deviated Wells
Authors: Aadnoy Bernt S. , Kaarstad Eirik , Belayneh Mesfin
Published: December 2007

A 10-years research program at the U. of Stavanger has shown why the commonly used Kirsch equation underpredicts the fracture pressure. The reason is that the plasticly behaving mudcake is not properly accounted for. A new elastoplastic model results from this work, and forms the basis for this paper. This model consists of an anisotropic part (the in-situ stresses) and a hydrostatic part (the plastic mud cake). The paper presents the complete models, which has application to all inclined wells.

"Wellbore strengthening" or "wellbore stress cage" are described by the new analytical model. Several cases demonstrate these concepts. Numerous tests in the fracture lab have led to mud design procedures to build a mechanically strong bridge across a fracture. A well was recently drilled using interactive mud design through the lab. The result was a trouble free well giving leak-off value exceeding any other wells in the area.

Several cases will be presented.Calibrating models to measured leak-off data, it is shown that the Kirsch equation severely underpredicts the fracture pressure.
Gas Well Liquid Loading from the Power Perspective
Authors: Dotson B. , Nuñez-Paclibons E.
Published: December 2007

A new perspective is introduced to the problem of liquid loading in gas wells. Gas wells cease producing as reservoir pressure depletes and gas velocity decreases. Below the critical rate, liquids cannot be lifted from the wellbore and instead, settle to the bottom. At this point, we apply artificial lift, which involves either the better use of the remaining reservoir energy, or the addition of external energy.

The objective of this study is to understand the appropriate application of external energy to maximize economic recovery. Our research was conducted in two stages. First, we modeled a simple synthetic gas well and simulated the liquid loading behavior. We observed the natural ability of the reservoir energy to carry the produced fluids to the surface, and then eventually, declining production with increasing liquid accumulation. Second, we performed a sensitivity analysis of the well's energy (i.e. siphon or velocity tubing strings) versus adding energy to the well (i.e. gas lift injection and downhole pumps) for production optimization at each point in the depletion of the well. We used the theoretical power as a proxy for well operating cost to calculate the economic limit.

As expected, ultimate recovery was improved by the addition of external energy. In particular, pumping was found to be favored over gas lift because it provided lower bottomhole pressures and required less power.

This new power perspective provides a systematic way to evaluate deliquification options through the depletion of a well.
In-Situ Density and Viscosity Measured by Wireline Formation Testers
Authors: O'Keefe Michael , Godefroy Sophie , Vasques Ricardo , Agenes Anne , Weinheber Peter , Jackson Richard , Ardila Mario , Wichers Wich , Daungkaew Saifon , De Santo Ilaria
Published: December 2007

A downhole density-viscosity (D-V) sensor is introduced that provides a real time direct measurement of in-situ density and viscosity at reservoir conditions using a wireline formation tester (WFT). The new fluid measurements are obtained during open-hole sampling of reservoir fluids, or alternatively through fluid profiling where downhole fluid analysis (DFA) is performed at a number of depths to characterize the reservoir fluid properties at a vertical resolution much higher than traditional samping methods.

The utilization of these new measurements are outlined, to illustrate the emerging importance of quantifying fluid variations in real time. This leads to more complete reservoir understanding, resulting in better decisions regarding field modelling, facilities planning and production strategy.

An overview of the D-V sensor is presented together with specifications, and extensive laboratory testing is discussed to show validity of the measurements. Five case studies from around the world are examined to show different applications of this measurement in a wide range of environments.

Fluid density and viscosity have long been primary objectives of formation evaluation, as they bear significant impact on field production and economics. The ability to measure true fluid density and viscosity of formation fluids in-situ at reservoir conditions, is a major advancement for reservoir fluid characterization.
Comparison of Numerical Simulations and Laboratory Waterfloods in Fractured Carbonates
Authors: Haugen Åsmund , Fernø Martin A. , Graue Arne
Published: December 2007

Recovery mechanisms in fractured carbonate rocks have been investigated by comparing laboratory experiments with numerical simulations. The experimental data include waterfloods in blocks of carbonate rock with 2D, in-situ fluid saturation of the advancing waterfronts. The waterfloods were initially performed on the whole block, and then repeated on the same block with a fracture network containing both closed and open fractures to isolate the effect from fractures.

The primary objective for the experiments was to investigate how the presence of fractures altered the dynamics of the propagating waterfront. A numerical, grid based model of the block was created and a sensitivity study of the representation of fractures was carried out. Especially the impact of the degree of capillary contact over fractures was studied. Matrix capillary pressure and relative permeability curves were determined by history matching both average oil production and the in-situ fluid saturation profiles from the unfractured block experiment. These were in turn used as input for the matrix properties in the fractured block simulations.

The results show how the degree of capillary contact between matrix blocks controlled fluid saturation development and influenced the waterflood oil recovery in fractured limestone. Sensitivity studies on the degree of capillary contact over fractures showed this to be the most significant parameter for the frontal propagation during waterfloods. Numerical simulations together with experimental data gave increased understanding of the waterflood oil recovery mechanisms in fractured carbonate rock.
Value of Information in the Oil and Gas Industry: Past, Present, and Future
Authors: Bratvold Reidar B. , Bickel J. Eric , Lohne Hans Petter
Published: December 2007

An important task that petroleum engineers and geoscientists undertake is to produce decision-relevant information. Some of the most important decisions we make concern what type and what quality of information to produce. When decisions are fraught with geologic and market uncertainties, this information gathering may take the form of seismic surveys, core and well test analyses, reservoir simulations, market analyses, price forecasts, etc., on which the industry spends billions of dollars each year. Yet, considerably less time and resources are expended on assessing the profitability or value of this information. Why is that?

This paper addresses how to make value-of-information (VOI) analysis more accessible and useful, by discussing its past, present, and future. Based on a survey of SPE publications, we provide an overview of the use of VOI in the oil and gas industry, with a focus on how the analysis was carried out and for which types of decisions VOI analysis has been performed. We highlight areas where VOI methods have been used successfully and identify important challenges.

We then identify and discuss the possible causes for the limited use of VOI methods and suggest ways to increase the use of this powerful analysis tool.
Cement Sheath Evaluation in Nonconventional Environment—Case History
Authors: De Paula J. L. , Rodrigues V. F. , Vicente R.
Published: December 2007

Sonic and ultrasonic tools have been widely used for cement sheath evaluation along the last decades. The evaluation main goal is the definition of the presence of cement in the annulus and its ability of promoting hydraulic isolation among different permeable zones, regardless of its density, compressive strength or even quality of the slurry. The challenges interpreting those logs are enormous because the influence of many variables in the acoustic signal. The difficulties increase dramatically if the well configuration is not conventional. In those cases, huge mistakes can occur requiring from the interpreter experience, understanding of the tools and acoustic principles, and detailed information about the well, casing, cement, and so on. The paper describes in detail three well documented cases histories where non-conventional conditions in the wellbore prevailed and required extreme care and experience to obtain the correct log interpretation. The first case reports the evaluation of an annulus with cement between two concentric casings; the disturbances caused by reflections from the second interface in the CBL signal are discussed and recommendations presented to bypass this obstacle. In the second case, the challenges to evaluate the cement sheath in a fiber glass casing are presented; usually in this case, the first signals arriving at the receiver do not come from the casing. Finally, the last case history describes the difficulties to come up with the right evaluation logging a liner cemented with lightweight slurry. For all cases, guidelines and recommendations are suggested to avoid misinterpretations and assure correct decisions about cement sheath evaluation.
Evaluating Crystallization Risks in Liquefied-Natural-Gas (LNG) Production
Authors: Ayala H. Luis F. , Fernández L. Juan Emilio
Published: December 2007

Liquefied Natural Gas (LNG) is anticipated to dominate world energy trade and fill the gap between production and energy demands in few years, especially in the US. LNG is the liquefied version of dry natural gases at ultralow temperatures (about -160 C or -260 F at atmospheric pressure), which aims at minimizing storage volume requirements needed for overseas transportation. Within this context, it is clear that technology must continue to be developed in order to optimize the thermodynamic processes involved in the compression, liquefaction and re-vaporization of LNG and associated operational challenges. One key challenge during the production of LNG is that the presence of trace amounts of heavy components in the gas feed composition is known to induce the precipitation of a solid phase during the cooling process, which presents the risk of equipment plugging and associated hazards. However, there are very few general thermodynamic tools available for the prediction of solid-liquid equilibrium for very low temperature conditions (< -200 F). In this study, available thermodynamic predictive tools are evaluated for the determination of LNG crystallization conditions. Previously presented crystallization prediction models are examined and potential pitfalls identified. The results from this study are expected to provide a better understanding of the thermodynamics of Liquefied Natural Gas (LNG) processes and provide a framework for subsequent work in the analysis of LNG refrigeration and liquefaction processes—which are typically considered the key elements of any LNG project.
A Phenomenological Approach to Analysis of Barite Sag in Drilling Muds
Authors: Paslay P. R. , Sathuvalli U. B. , Payne M. L.
Published: December 2007

Barite sag is the undesirable fluctuation in drilling mud density that occurs due to downhole settling of the weighting agent. Barite sag causes problems such as differential sticking, lost circulation, and can lead to serious well control events.

This paper describes a fundamental theoretical effort to describe dynamic sag in drilling muds by considering the behavior of a system of particles in a non-Newtonian Bingham fluid. A continuum mechanics based model of dynamic sag in an inclined annulus is presented in terms of the fluid and particle properties. The results of the model are used to understand the influence of typical oilfield variables in precipitating sag. The analysis presented in this paper represents one of the first modeling/computational efforts to predict sag using phenomenological models (rather than empirical correlations or observational rules of thumb).
Success of SAG Foam Processes in Heterogeneous Reservoirs
Authors: Renkema W. J. , Rossen W. R.
Published: December 2007

In principle, miscible gas injection can displace nearly all of the oil from the portions of a reservoir swept by gas. However, reservoir heterogeneity, low gas density and high gas mobility reduce sweep efficiency and drastically decrease recovery. Fortunately, the use of foam can reduce gas mobility and the effect of heterogeneity and therefore increase sweep efficiency. Based on the work of Shan and Rossen, an optimal design strategy is proposed here for surfactant-alternating-gas (SAG) foam processes and tested in a homogeneous reservoir and in two layered rectangular reservoirs. Fractional-flow theory, Stone's and Jenkins' model for gravity segregation, and an idealized model developed by Shan and Rossen are used design the process and interpret the results.

In the homogeneous reservoir, fixed-pressure SAG processes result in better sweep efficiency than fixed-rate SAG processes. A one-cycle SAG process, where one big slug of surfactant is followed by one big slug of gas, gives better sweep than multiple-cycle SAG processes; sweep efficiency is higher and the process proceeds faster. Adsorption can be dealt with by adjusting the size of the first surfactant slug. The optimal SAG process gives much better sweep efficiency than a WAG process without foam. Simulations reveal factors not accounted for in Shan and Rossen's idealized model for a single-cycle SAG process; nonetheless the model accurately predicts the rate of advance of the foam front at the top of the reservoir and qualitatively predicts the shape of the foam front. A ten-cycle SAG process performs somewhat better than predicted by Stone's model for continuous injection.

In heterogeneous reservoirs, a maximum-fixed-pressure SAG process also gives best results. The surfactant slug sized for a homogeneous reservoir is much too large in this case, however, and much of the surfactant wasted. Again, a one-cycle process SAG performs better than multiple, smaller cycles, but sweep is not as good as in a homogeneous reservoir. A high-permeability layer at the top of the reservoir leads to better sweep efficiency at gas breakthrough than when the reservoir has a low-permeability layer at the top. A low-permeability layer at the top allows early gas breakthrough once gas in high-permeability layers below it reaches the edge of the surfactant bank above. Compared to WAG processes, the optimal SAG process shows much better sweep efficiency.
Straining of Fine Particles in Gaps in Porous Media
Authors: Rodriguez Elena , Bryant Steven L.
Published: December 2007

This paper presents an extension of the theory of retention of fine particles in formations. The mechanism of interest is straining, which depends only on the shape and distribution of constrictions in pore space. To quantify the geometry of constrictions, we used computer-generated dense random packs of spheres as model porous media. A characteristic feature of dense packings is a pair of neighboring grains that do not quite touch. We refer to the void space between pairs of such spheres as gaps. Gaps are smaller than pore throats, which are the void space between three spheres. Geometric analysis of throats and gaps was combined with a new methodology to compute flow rates in gaps. The results were input to an existent straining theory to study the dependence of straining rate on fines size. Only the flow of a single fluid phase is considered.

Numerous experiments show evidence of straining of particles smaller than the smallest pore throat in the column, under conditions that exclude the possibility of filtration. The simplest test of a theory is whether it can account for these anomalous observations. Existing theories that consider pore throats as the constrictions cannot explain these observations, whereas including gaps in the set of pore space constrictions correctly predicts the observations.

A more stringent test of straining theory is to predict the dependence of particle straining rate in a column flow experiment upon the size of the particles. Classical pore-throat-based theories make the physically reasonable assumption that once a particle enters a small constriction, it is guaranteed to be trapped there. Thus the probability of trapping is proportional to the flow rate through the constriction. These theories significantly overestimate the influence of particle size for small particles. We argue that the probability of particle retention in a gap need not be 100% even if the particle enters the gap. The particle may rebound from the grain(s) rather than become wedged in the gap. If this happens, the particle may eventually be swept around the gap.

We therefore extend the theory by postulating retention probability to be proportional to flow rate through the gap and inversely proportional to the momentum or to the kinetic energy of the carrier fluid. The extensions bracket the scaling behavior reported in experiments.

Our analysis of particle straining in gaps explained a longstanding set of observations for which previous theories could not account. These results suggest that a more detailed study of particle/grain collisions is needed to explain fully the straining rates observed in experiments.
Learning Curve Benefits Resulting from the Use of a Unique BHA Directional Behaviour Drilling Performances Post-Analysis
Authors: Studer Regis , Simon Christophe , Genevois Jean-Michel , Menand Stéphane
Published: December 2007

With the current market's high prices for drilling units and sophisticated directional and formation assessment services, low systems reliability or poor directional performance in the execution of complex wells (ERD, HPHT, Deep Water applications) can spell costly Non Productive Time (NPT) for operators. Over the past two decades, many Bottom Hole Assembly (BHA) models have been developed to address the directional performance issue, but their application in an operational environment has generally failed for lack of strong associated BHA analysis methodologies.

This paper presents a unique automated methodology for Post Analysis of BHA directional behaviour. It is based on modern 3D analytical models, combining BHA, BIT and formation effects with highly flexible data management. Implemented in user-friendly BHA management software, it can be used to define a BHA run segmentation and to determine the influence of the BHA settings in particular geological formation blocks. The Post Analysis clearly displays the final results of the BHA (objectives and performances versus prediction window), highlighting any problematic intervals drilled.

Already, the methodology has solved challenging directional performances issues, generating significant savings and optimising the learning curve process. The field applications referred to in the paper have demonstrated that, without a proper methodology, a model offers little added value.

The examples discussed here from Total E&P affiliates deal respectively with Rotary, Rotary Steerable System (RSS) and Steerable Motor (SM) directional BHAs. Case studies have led to BHA and bit design modifications. The results were well beyond expectations, ensuring good well positioning through the reservoir by improving BHA stability and manoeuvrability. Efficient drilling (reduced sliding, improved hole quality) was also achieved with a single SM BHA in 17 1/2" applications during kick-off, and successive build-up and slant drilling intervals.

The methodology and its associated BHA Management® software have proved an undeniably valuable tool for the drilling community. The model is also run at the well Pre Engineering stage to check BHA design proposals by making multiple sensitivity analyses and by fine-tuning solutions to the operational context. Finally, in an industry with high personnel turnover, the software's global data management system ensures good capitalization of know-how and ongoing learning curve benefits.
Simulation Study Investigating Gas Cap Contamination Caused by Miscible CO2-WAG
Authors: Janssen P. H. , Lackner A. S. , Stensen J. Å. , Haugse V.
Published: December 2007

The gas cap contamination level and mechanisms caused by CO2-EOR operations in an oil field have been investigated by compositional reservoir simulations on a sector model of the Upper Tilje reservoir. The impact of different EOR and gas cap drawdown operational parameters on the contaminated gas volumes has been determined.

The results show that the contaminated part of the produced gas from the gas cap, with more than 2.5% CO2, can be correlated to the final position of the CO2 front during the EOR-period. Massive CO2-breakthrough on the other hand, which is responsible for the contaminated part of the produced gas with more than 7.5% CO2, is a nearly linear function of the stored CO2 mass. This implies that EOR-operations which both increase oil recovery and CO2 storage, such as SWAG-injection, short-cycle WAG or oil producer gas shut-off will significantly increase gas cap contamination.

Gas cap contamination however can be reduced by well-positioned horizontal gas producers and large gas blowdown flow rates.
Physics-Driven Interface Modeling for Drainage and Imbibition in Fractures
Authors: Prodanovic Maša , Bryant Steven L.
Published: December 2007

The geometric distribution of immiscible fluid phases in fractures is not readily accessible experimentally, so aperture-scale simulations of drainage and imbibition in realistic fractures can provide valuable insight. We implement a level set method for computing the location within a fracture of the interface between two fluids controlled by capillary forces. The movement of the interface in response to changes in capillary pressure is approximated as quasi-static displacement. Fluid interfaces are thus constant mean curvature surfaces, satisfying the Young Laplace equation. We apply a progressive-quasistatic (PQS) algorithm to determine when spontaneous pore-level events occur during fluid displacement. The algorithm captures reversible and irreversible behavior. We illustrate the approach in two types of rough-walled fractures. One type is a 3D crack between irregular, impermeable surfaces; the other type is a gap between irregular 2D and 3D grain packs. We focus on the disconnected (defending) fluid volumes and (advancing) fluid main pathway as the geometric properties of the fracture are varied, notably aperture and the number of contact points between the upper and lower fracture surfaces. The curvature of the fluid-fluid interface in the plane of the fracture is often ignored by invasion percolation simulation techniques, yet it is known to influence strongly the fluid cluster properties. Our simulations establish the exact position and shape of the interface in realistic fracture geometries, from which fluid volumes, contact areas and interface curvatures can be obtained. This establishes a new, mechanistic basis for predicting relative permeabilities in fractures and for evaluating transfer functions in dual-porosity flow models.
Openhole Gravel Packing With Zonal Isolation
Authors: Barry M. D. , Hecker M. T. , Haeberle D. C. , Blacklock J. , Yeh C. S.
Published: December 2007

Many current deepwater and high rate wells are being completed in an openhole environment as openhole completions provide the greatest opportunity to maximize reservoir flow potential. Current technology, however, lacks the subsurface control necessary to effectively manage the reservoir in situations where sand control is required. ExxonMobil is pioneering technologies to model well performance more accurately and to provide subsurface control during completion and production operations. The first hardware developments within this initiative build on the success of Alternate Path® and NAFPacSM gravel packing technologies and address water or gas breakthrough in openhole, multi-zone gravel pack completions. ExxonMobil affiliates collaborated with third party suppliers to design and qualify new hardware to facilitate zonal isolation, extend gravel pack reach, and simplify rig site operations. This process included engineering design, component testing, and full-scale prototype evaluation. First application of this technology is targeted for early 2008.

This paper discusses newly developed sand control screen hardware that is enabling technology to perform openhole gravel packs with true zonal isolation. The equipment provides the ability to seal off bottom water, selectively complete or gravel pack targeted intervals, perform a stacked openhole completion, or isolate a gas/water-bearing sand following production. Application of the technology is expected to extend well life and ultimately increase volumes and reserves capture.
Integrated Wellbore/Reservoir Model Predicts Flow Transients in Liquid-Loaded Gas Wells
Authors: Chupin Gaël , Hu Bin , Haugset Tor , Sagen Jan , Claudel Magali
Published: December 2007

An integrated transient wellbore/reservoir model is described and applied to investigate the liquid loading in a gas well. The well produces from a storage reservoir with water coning from its aquifer.

The integrated model shows that the water cone causes the gas flow rate from each gas layer to decrease and the liquid holdup in the wellbore to increase. Depending on reservoir conditions, the well may enter into a mode of unsteady production during which the gas flow rate cycles over a period of several days. The reason for this unsteady flow is uncovered by the simulation.

Simulation results are compared with operational experience and full field reservoir simulations. The integrated model provides more realistic results compared to methods where the reservoir and the wellbore are modeled separately.
Field Validation of Drillpipe Rotation Effects on Equivalent Circulating Density
Authors: Hemphill Terry , Bern Peter , Rojas Juan Carlos , Ravi Krishna
Published: December 2007

It is important to predict the Equivalent Circulating Density (ECD) of fluids as closely as possible for safe drilling and completion of wells. This is especially true for those challenging wells where the margin between hole collapse and formation fracturing is very narrow. These characteristics of narrow safe drilling windows are commonly seen in extended-reach drilling (ERD) and deepwater wells, and pose significant drilling and cementing challenges.

Over recent years, the changes in ECD caused by fluid compressibility, downhole fluid rheology, drillpipe eccentricity, and rate of penetration have been widely studied. In contrast, work on the modeling of drillpipe rotation effects on pressure drop and ECD have received relatively little attention. Early studies have looked at the relationship between circulating pressure drop, especially in slimhole drilling configurations, and at very high drillpipe rotational speeds. More recently the predicted effects of rotation on ECD in concentric and eccentric wellbore geometries have been studied and model improvements have been made. These technical approaches are summarized in this paper.

The effect of drillpipe rotational speed on the predicted ECD for different drillstring combinations are presented and discussed. The calculated effects of drillpipe rotation on pressure drop and ECD are compared to actual field measurements using downhole annular pressure gauges.

From the results discussed in this paper, the reader can gauge the accuracy of the current calculation methods. The changes in ECD with drillpipe rotation can now be better predicted, something especially important for those wells whose safe drilling window is narrow. Ultimately this reduces drilling and completions risk and helps assure safe and efficient well construction.
Permeability Predictions Based on Two-Dimensional Pore Space Images
Authors: Jurgawczynski Mathieu , Lock Peter A. , Jing X. D. , Zimmerman Robert W.
Published: December 2007

A model is developed that allows accurate prediction of the permeability of a core sample of sedimentary rock, based solely on two-dimensional image analysis of its pore structure. The only required input data are the areas and perimeters of the pores observed in, for example, an SEM image. The hydraulic radius approximation is used to estimate the individual pore conductances. Prior to this, stereological corrections are used to convert apparent pore geometries, and various hydraulic corrections are applied to account for converging–diverging flow paths. These various corrections are the principal and crucial differences between our approach and previous methods based on two-dimensional images. Finally, Kirkpatrick's effective medium approximation is used to find the effective value of the hydraulic conductances of the individual pores.

The method has been applied to several data sets, including consolidated North Sea reservoir sandstones, outcrop sandstones, outcrop carbonates, and carbonates from Middle East oil and gas fields. The permeabilities of this entire data set range from 0.5-1377 mD, which covers a significant portion of the range of permeabilities that are relevant in reservoir engineering. In 80% of the cases, the permeabilities predicted by our method are within a factor of two of the measured values, and the predictions are within a factor of three in over 90% of the cases. The method requires minimal data manipulation and computation when compared to approaches that require three-dimensional imaging and/or full solution of the Navier-Stokes equations, and is much more accurate than primitive empirical methods such as the Kozeny-Carman equation.

Aside from giving insight into the influence of pore structure on permeability, our method offers the potential of permitting permeability predictions to be made using drill cuttings, in situations where it is not possible to recover intact core. Another possible future application is to use downhole borehole imaging technology to provide an image with the appropriate resolution, thereby allowing in situ permeability estimation, without the need for core samples.
Enabling Technologies for Drill-In Sand Screen Liners
Authors: Coronado Martin P. , Pickle Brad R. , O'Malley Edward J.
Published: December 2007

Following successful field applications of solid-liner drill-in systems, efforts now focus on drill-in sand screen liners. This paper will discuss enabling technologies to meet the unique challenges of drill-in sand screen liners.

Rotating the screen liner to drive the bit may damage screens, so a drilling motor at the bottom of the liner must be utilized. Also, conveying fluid to drive the motor and remove debris is required. Using a conventional inner circulating string inside the screen liner may be prohibitive due to the addition of sufficient weight which may significantly limit horizontal and highly deviated well angles and length. The screen liners therefore must be able to contain pressure when drilling to allow circulation through the bit, and subsequent wellbore inflow during production. Additionally, the screen's filtration media must also be protected from possible plugging with solids during drilling.

This paper addresses a new technology that temporarily blocks flow through the screens during drilling/reaming to provide a pressure-tight circulation path through the liner to the motor, eliminating the need for an inner circulation string. Once drilling is completed and the liner is in place, the screen joints are simultaneously opened using hydraulic pressure applied within the liner, and the well is ready to be put on production. Temporarily closing off the screen joints also has application for simultaneously setting hydraulically set open-hole packers remotely without an inner circulating string.

The paper also discusses a time- and temperature-sensitive protective film applied to the screens during fabrication to prevent fluid egress into the filtration media until the film dissolves. Sufficient time for dissolution is designed into the film to allow the liner to be drilled into place while protecting the screen's filtration media from possible plugging during drilling/reaming.

Qualification testing of these technologies are discussed, along with additional applications for this technology where utilizing a temporarily closed screen system has advantages.
Microseismic Monitoring Quality-Control (QC) Reports as an Interpretative Tool for Nonspecialists
Authors: Zimmer U. , Maxwell S. , Waltman C. , Warpinski N.
Published: December 2007

In the oilfield industry microseismic monitoring is widely applied to determine induced fracture network geometry and stress changes in reservoirs. The basic result is usually a map of the distribution of the microseismic events describing the area influenced by injection/production of reservoir fluids, e.g hydraulic fracturing. As every microearthquake event, i.e. ‘dot’ on the map, is processed individually, it has its own level of location accuracy. To prevent any misinterpretations based on events with low accuracy, Quality-Control (QC-) reports can provide important information regarding location accuracy and other attributes which help in the overall interpretation of the maps, in addition to the standard event location. However, much of the information that is needed to assess the quality of the data is very specialized and technical, so that the figures presented in the QC- reports often appear complicated and are not easy to read for the non-specialist. By introducing easy-to-read figures that summarize the essential information, these reports have become more useful to the occasional user.
Fire Protection In The Petroleum Industry
Authors: Dawoud Sam
Published: December 2007

The risk of fire is present during all stages and operations of the petroleum industry, whether during exploration and production (E&P) both in onshore and offshore installations or during refining/processing or transportation, storage or during dispensing to the end user. All petroleum products from crude to final products produce vapor that is being mixed with air creating the potential for ignitable mixture. While petroleum products have different rates of releasing vapors to the environment, they all share the risk of starting a fire when an ignition source is introduced to the mixture. Fires involving hydrocarbons can take several shapes from pool fires to fire balls and jet fires. Due to the severity and Heat Release Rate (HRR) of Hydrocarbon fires (which may result in catastrophic consequences), fire prevention, protection and mitigation measures are considered to be of utmost importance/most advanced in relation to same measures in other industries.
Completion Design, Installation, and Performance—Cannonball Field, Offshore Trinidad
Authors: Healy J. C. , Powers J. T. , Maharaj M. , Ramlogan M.
Published: December 2007

The Cannonball field is a one Tcf gas condensate development offshore Trinidad producing at an initial rate in excess of 800 MMcf/D from three wells. The completion design selected was 7⅝ inch production tubing with an open-hole gravel pack (OHGP). The initial well (CAN01) has produced at an initial rate of 320 MMcf/D. The calculated deliverability of this well is 415 MMcf/D. This paper discusses the completion basis of design, detailed engineering assurance of the design, qualification of critical engineered equipment, and actual results.