bluuebunny/crossref_metadata_2025 huggingface dataset:
Conservation Partnerships as Part of Environmental Management in a Sensitive Coastal Location: Liverpool Bay Oil and Gas Production Operations, UK
Authors: Gilliver R. E.
Published: December 2007

Detailed conservation management agreements form an important part of the environmental management systems of the BHP Petroleum operated Liverpool Bay Asset.

The oil and gas development proceeded following environmental appraisals and detailed impact assessments ensuring that the onshore and offshore facilities could be developed and operated with minimal environmental impact and considerable conservation benefit. Regulatory authorities, statutory and non-statutory consultees had close involvement in the environmental assessment and approval process. This process resulted in a series of agreements and conservation management plans.

In the paper there is a focus on aspect of the environmental management process and conservation work associated with the onshore gas terminal. Monitoring, wardening, auditing and reporting on two areas are described: one a dune site of special scientific importance adjacent tot he gas terminal; the other farmland managed to provide mitigation land for migratory and over-wintering birds. This work is carried out in partnership with scientific and academic bodies, conservation agencies, local conservation groups and wildlife preservation bodies.

The value of these partnerships in achieving the aims of the management plans in a co-ordinated and supportive manner is described.
A Strategy for Co-Existence with the Fishermen in the Gulf of Paria
Authors: Abbott Robert E. , Lopez Glenys , Matamoros Nelson , Wong Teresa
Published: December 2007

Conoco Venezuela B.V. recognized early-on during the seismic program that special efforts would be needed to work in harmony with the local fishermen in the Gulf of Paria. To achieve that goal, Conoco quickly adopted a proactive strategy of co-existence with local fishermen. This strategy is closely tied with Conoco's core values of operating with respect and care for the environment and valuing all people. Specifically for Gulf of Paria, Conoco's intent is to minimize interference to the work program while simultaneously enabling the fishermen to enjoy net gains from our presence in the form of employment and increased awareness of their resources. The key to making this goal a reality is education.

Tactics in this strategy include (1) communicating company plans, evaluating needs and managing expectations through a series of "town-hall" meetings, (2) supporting health and education programs through local charities and NGO's, (3) underwriting a book about the area written by the foremost authority on the fishery of the Gulf of Paria, and (4) sponsoring visits by a medical doctor into the region. Conoco management was assisted in this work by the seismic contractor, Western Atlas.

As a result of these programs, Conoco Venezuela B.V. has started what it believes is a very positive relationship with the local communities. Prior to beginning this communications effort, Conoco experienced numerous costly incidents with tangled fishing nets. However, once the company and community began an interactive dialogue, the seismic operations were completed successfully and many issues and problems were resolved. Conoco Venezuela B.V. plans to continue the strategy of cooperative co-existence into the subsequent operational phases of the program.
The Effects of Porosity and Stress on Dilatancy in Sandstone
Authors: Larsen I. , Fjaer E. , Renlie L. , Zheng Z.
Published: December 2007

Volumetric strains during triaxial tests of 44 sandstone materials were analysed in order to understand the physics of dilation. The samples originate from different North-Sea fields, and the porosities vary from 1 to 39 percent. Different confining stresses were applied to the same material under dry and saturated conditions and the results analysed. The results showed no clear boundary between dilation dominated and compaction dominated behaviours with respect to porosity or confining stress. However, two regimes could be identified: one with low porosities where dilation occur, and one with high porosities where dilation do not occur. The critical porosity separating the two regimes was found to depend on the confining stress. The analysis also showed that the shear stress level at the onset of dilation depends on the ratio between the in situ horizontal stress under which the sample was buried, and the confining stress. A mathematical formula relating the onset of dilation to porosity, confining stress and in situ horizontal stress has been established. The dependency of in situ horizontal stress is likely to be ascribed to core damage. This assumption is supported by previous experimental work on artificial sandstone. Volumetric strain analysis showed that fully saturated samples dilate more than corresponding dry materials. The onset of dilatancy for both saturated and dry materials can be described by the same mathematical formula, however with different coefficients. The results from the use of the model showed that the onset of dilation could be estimated with a fair accuracy if the porosity and the in situ horizontal stress are known.

P. 15
The Integration of Rock Mechanics, Open Hole Logs and Seismic Geophysics for Petroleum Engineering Applications.
Authors: Goodman H.E. , Perrin V.P. , Gregory D.H.
Published: December 2007

The integration of core based rock mechanics with the open hole log and seismic geophysics technologies, has created added value through operational costs savings for Chevron's world-wide drilling and completion holdings. Early development of this integrated technology focused on supplementing core measured rock property data with open hole log measurements to obtain rock mechanical property estimates throughout the horehole. Log derived mechanical property estimates have lead to the development and worldwide use of the following applications:formation drillability assessment for bit optimization and performance prediction,wellbore stability for extended reach and horizontal wells,sanding predictions for completion design, andformation stress profiling and elastic properties modeling for hydraulic stimulation design.

The characterization of rock mechanical properties, in the absence of core, hinges upon the newly created capability of predicting formation shear wave propagation velocities. This breakthrough technique was first developed to estimate formation shear wave velocities for single well (1D) mechanical property predictions using conventional open hole measurements- (compressional wave velocity and bulk density). The technique was then enhanced to utilize surface seismic data sets in a 1D sense to predict formation mechanical properties at undrilled prospect locations. The links to the seismic world have proven particularly valuable for rank wildcat and step out drilling applications where offset well control is absent or extremely limited.

The latest innovation has been to characterize volumetric (3D) formation mechanical properties from 3D seismic data cubes. Volumetric rock properties currently determined include Poisson's ratio, horizontal stress magnitude, borehole breakdown pressure gradient, pore pressure gradient and unconfined compressive strength.

This paper summarizes the shear wave velocity estimation technique and presents several examples. Field examples will also be shown that demonstrate successful applications of log derived mechanical properties for rock strength and minimum horizontal stress profiling applications for fracture stimulation design. A full set of volumetric formation mechanical property cubes will then be presented, demonstrating the feasibility of using 3D seismic data for well planning.

P. 241
Benefits of Assessing the Solids Production Risk in a North Sea Reservoir using Elastoplastic Modelling
Authors: Bradford I.D.R. , Fuller J. , Thompson P.J. , Walsgrove T.R.
Published: December 2007

A reliable, non-conservative assessment of the risk of solids production is essential in order to identify the optimal completion strategy. A technique for such an assessment is developed in this paper through a geomechanical study of the Everest Complex of the North Sea, involving wells 22/10a-T2 and 22/10a-T6.

This process is based on calibrating depth indexed measurements at discrete points using core data. The core samples were selected to be representative of the complete range of porosities and various clay volumes throughout the reservoir. The first step is the construction of the reservoir mechanical model by combining geophyscial well logs, the results of laboratory tests on core samples, and other field data, particularly drilling histories. In the second step, critical calibrated using predictions determined at single points using an elastoplastic theory (Bradford and Cook 1) which incorporates the influences of plastic hardening and delation. Results calculated using a new elastic-perfectly plastic model, which is derived in this paper, are also included. This model is suitable for use with log data. Results have been verified by simulating production through a perforation with thick wall cylinder tests on whole core form 22/10a-T2 (Nicholson et al.10).

The results of the modelling provide formation failure data to build a map of the sanding potential in the Everest reservoirs.

P. 261
Laboratory Studies on the Dependency of Temperature and Fluid Pressure on Fault Zone Strength, Slip Displacement and Sealing Potential
Authors: Odedra Anita , Sammonds Peter , Ohnoka Mitiyasu
Published: December 2007

Temperature and pressure sensitive processes modify rock strength and fault properties with depth. A series of triaxial shear fracture experiments have been conducted on granite under fixed confining pressures (70 to 480MPa), pore fluid pressures (10 to 300MPa) and temperatures (room temperature to 4800C) to investigate relationships between ambient crustal conditions, rock strength and fault displacement. We report here the first investigations of rock fracture experiments under elevated temperatures in the presence of high pore pressures. Our results improve existing models of fault slip displacement and rock strength with depth, based on dry experiments, by incorporating a more realistic water saturated crust, and considering the sealing effect on faults caused by high temperature welding.

The effect of ambient conditions on rock shear fracture parameters may be summarised as follows: rock strength with depth of burial is relatively constant up to temperatures of 3000C, after which strength decreases rapidly. Increasing pore fluid pressure mechanically reduces the strength of rock at all temperatures, and also reduces the amount of fault displacement. Temperature dependent processes at depth may allow a fault to seal (due to welding and mixed deformation processes), but simultaneously leak' nearer the surface (due to brittle fracture induced porosity).

P. 323
A Soil Mechanics Approach To Predict Cement Sheath Behavior
Authors: Thiercelin M. , Baumgarte C. , Guillot D.
Published: December 2007

In this paper, we predict the bulk shrinkage of oil well cements using a soil mechanics model where compaction is a dominant mechanism. In our approach, the bulk shrinkage is the result of the decrease in pore pressure following cement hydration. We perform triaxial tests on set cements to calibrate the model. We perform laboratory experiments to demonstrate the applicability of this approach to shrinkage prediction. We simulate the downhole conditions to predict the consequences of shrinkage on zonal isolation.

P. 329
Analysis of Hydraulic Fracture Closure in Laboratory Experiments
Authors: van Dam D.B. , de Pater C.J. , Romijn R.
Published: December 2007

Conventional models of hydraulic fracture closure make assumptions about the fracture geometry and rock mechanical behaviour, In this paper we present the results of scaled laboratory experiments, We show that deviations from conventional assumptions influence leak-off volumes, mechanical behaviour, and pressure decline significantly. We discuss mechanisms that lead to deviations from assumptions during fracture closure.

P. 365
Influences of Heat Convection and Plastic Deformation on Hydraulic Fracture Initiation and Reservoir Compaction
Authors: Shao J.F. , Homand S.
Published: December 2007

In hydraulic fracturing technique, one of the questions is to determine fracture initiation pressure. The resolution of this problem should account for the coupling between material deformation, fluid flow and temperature variation. A finite element solution is proposed in this paper by taking into account non linear coupling due to heat convection and plastic deformation of rocks. A specific numerical algorithm is used to treat long time injection problem. A typical example of cold water injection through a vertical well is then considered. Comparative calculations made with and without heat convection have clearly shown the key role of heat convection in diffusion of stresses, pore pressure and temperature around the well. Two particular issues, reservoir deformation induced by injected cold water (cooling and pore increase) and influence of thermal stress diffusion by convection on hydraulic fracture initiation, are examined. The main finding is that the stress and temperature diffusion is quasi completely controlled by convection. The cold water injection induces relative reservoir compaction, which can become significant (reservoir subsidence) when the injection pressure is low. Concerning fracture initiation pressure, the tangential stress evolution is also strongly controlled by heat convection. The temperature decrease (cooling) induces a significant and time dependent tensile tangential stress zone where the breakdown pressure may be much smaller than that determined without considering heat convection. Moreover, heat convection accelerates the propagation of the tensile stress zone (consequently the fracture propagation) into reservoir. Finally, in the cases studied in this paper, rock plastic deformation plays a secondary role with respect to heat convection.

P. 401
Viscous Rheology and State of Stress in Unconsolidated Sands
Authors: Chang C.T. , Zoback M.D.
Published: December 2007

Observations of triaxial creep and stress relaxation of unconsolidated reservoir sands imply markedly different static and dynamic modulii and may explain observations of very low differential stresses found in the Wilmington Field, CA, the Gulf of Mexico, and elsewhere. Triaxial testing performed on 1 inch plugs of reservoir sands under both stress- and strain-controlled conditions show transient stresses and strains. All tests were performed under dry or drained conditions to eliminate poroelastic effects. We previously observed creep under hydrostatic stress conditions in these unconsolidated sands. The resulting strain vs. time curves could be fit with a standard linear solid viscoelastic model that had a relaxation time of about 10 hours. The data demonstrates the rock's ability to dissipate stress through relaxation and creep. The reservoir material shows viscoelastic rheological behavior in both creep and relaxation tests which appears to be related to the presence of intergranular clay. Measurements of the static Poisson's ratio under large strains yielded values .29 which suggests that the particles in the matrix efficiently coupled the principle strains.

P. 465
Management of Competence in HSE and Application in Training Redesign
Authors: van Kujk E. , van der Velden J.
Published: December 2007

This paper presents the findings and recommendations of a study on the management of competence in the areas of Health, Safety and Environment from an organisational perspective. A conceptual model is developed which describes the management of business processes and the aspect controls for the associated business risks. Within the study, HSE is considered as one of the business risk areas. Progress in competence management in each of the elements of the model was assessed through a survey. The results of this survey support the integrated approach, which is being developed. Skills portfolios have recently been formulated, covering the technical disciplines and business skills for individuals and teams. These skill requirements are supplemented with the required competencies to execute the tasks and maintain the barriers identified in the Hazard and Effect Management Process [1]. Results from a case-study confirm the value of the approach in the development of learning and training programmes as well as provide a tool to assess and demonstrate the extent to which the existing competence assurance programmes match the requirements identified in HSE cases.
Unique PDC Bit Technologies Combine to Consistently Reduce Drilling Time in Interbedded Formations
Authors: Taylor S. , Besson A. , Minto D. , Mampuk I.
Published: December 2007

Interbedded formations cause difficulty when selecting a drill bit for optimum section performance. Hard stringers require bit features that conflict with those required for softer homogeneous formations. Limited by conventional technology, this culminates in the selection of a bit too heavy set to maximise penetration rates through the soft formation or too light set to drill the hard stringers. This paper describes a unique combination of PDC bit technologies that provide a solution to consistently drill interbedded formations without compromising bit selection. The unconventional design consists of features to maintain high penetration rates in soft formations and the stability and life required to pierce through hard stringers.

The technologies are combined on a steel bit body. The nature of this material allows its fundamental engineering properties to be exploited to produce extreme features that cannot be achieved using matrix powder technology. This material is the cornerstone that expands the design and manufacture windows for conventional PDC bit technologies.

Soft formations imply high penetration rates: the technologies developed are a novel hydraulic arrangement, bit face design, cutter size and usable diamond volume. Hard stringers require high stability in order to maintain bit life by preventing premature component failure. Technologies developed are conventional anti-whirl theory, localised cutter placement to extend bit life and an innovative low friction gauge pad that spans two blades and encloses a junkslot.

The case history demonstrates the significant performance improvement that can be achieved through interbedded formations by combining innovative PDC bit technologies. The study examines the development of the 12 1/4, section in the Tunu Field, Indonesia.

The continual development of the project is discussed including a lighter set variant to complete the same application and the successful translation of the design philosophy into a slimhole program.

P. 75
Barite Sag: Measurement, Modelling and Management
Authors: Bern P. A. , van Oort E. , Neusstadt B. , Ebeltoft H. , Zurdo C. , Zamora M. , Slater K.
Published: December 2007

A joint industry project was established to study barite sag mechanisms and to develop field guidelines to manage the consequences. A simple empirical model was developed to compare sag potential for a wide range of fluid types. In the study, physical properties of the mud, wellbore conditions, and characteristics of the weighting material were shown to have a large influence on sag behaviour. The study also included direct measurements of the properties of settled weight-material beds. These results provide new insight into the mechanisms of barite sag and how best to manage problems in the field.

Data from the tests clearly demonstrate that the parameters affecting sag are interrelated and seldom act in isolation. For all muds tested, the highest sag occurred at low annular velocities over angles from 60–75°. Drill-pipe rotation was particularly beneficial in minimising barite settlement. Rotation also assisted in re-distributing barite deposits formed on the low side of the hole.

The improved understanding of the mechanisms of barite sag enabled development of practical field guidelines. Case history studies presented in the paper demonstrate how the results of the work together with better field monitoring have been successfully applied to manage the effects of barite sag in HP/HT and extended-reach drilling operations.
Fatigue Life Evaluation: A Key to Avoid Drillpipe Failure Due to Die-marks
Authors: Hossain M.M. , Rahman M.K. , Rahman S.S. , Akgun F. , Kinzel Holger
Published: December 2007

Slips and tongs produce permanent marks on pipe body and tool joints. Such marks develop high stress concentration that reduces strength of pipes. The remaining strength of pipes often falls below the pipe stresses which can lead to tubular failure. Slim pipes are most susceptables to failure due to die- marks. In many instances, slim pipes are handled using double elevator system to reduce pipe failure. In this paper, results of a recent study of various die-mark related failures of drill pipes under different loading conditions, with particular emphasis on fatigue damage are presented. Stress concentration due to die-marks is characterised by finite element analyses as a function of mark sizes to cover various gripping systems available in the market. Then a methodology is presented for the prediction of failure due to cumulative fatigue damage. Effect of stress concentration arising from die-marks is taken into account in the analysis. Results of this study suggest that the effect of stress concentration on the cumulative fatigue damage may be significant depending on particular gripping system in use. In most cases, the fatigue life evaluation based on conventional assumption of smooth pipe surface is found to be very unsafe. Thus, a new approach is proposed in this paper for prediction of true safe life of marked drillpipes against fatigue failure. Fatigue damage results are presented in graphical forms. Calculation of cumulative fatigue damage of drillpipes used in a number of drilling events is then presented systematically in tabular form to assist drilling engineers in the evaluation of actual remaining fatigue life of drillpipes for the target drilling event using a particular gripping system.

P. 125
Addressing the Problem of PDC Bit Performance in Deep Shales
Authors: Smith John Rogers
Published: December 2007

Oil and gas wells that are drilled into deep, overpressured sediments frequently encounter slow penetration rates that result in high drilling costs. A cooperative effort between industry and university researchers has begun to study this problem and seek potential solutions. The current work has identified characteristics of the problem, its economic significance, its possible causes, and the best historical field practices for addressing it.

P. 261
Solving Casing Subsidence Problems with Downhole Activated Casing Slip Joints
Authors: Eriksen Eric Peter V. , Schwall Gene , Mahmoud Salah
Published: December 2007

Subsidence in chalk fields loads casing and liners with axial compression loads and results in uneven radial loading of the pipe wall. Eventually the casing or liner will fail from plastic collapse under the stress generated by the uneven radial loading combined with axial compressive load.

Casing Slip Joints placed in the compacting zones can reduce the combined stress in the cross sections thus increasing the stress level from uneven loading that can be tolerated.

Current designs require an activation load of 150,000 lbf. to initiate closing. The effect of a slip joint will be greatly improved if the Slip Joint is able to close when subjected to a small compressive load instead of the 150,000 lbf. currently required.

A system has successfully been developed that allows the Slip Joint to be run-in and cemented in its open position and yet be able to stroke freely after a preset time.

The system uses metallic shear screws that transmit a force equal to their full cross sectional shear strength when running- in. After a pre-set time their strength will be reduced to nearly zero through controlled stress corrosion cracking.

A number of materials were evaluated and one material was tested. The internal tensile stress required for the Stress Corrosion Cracking (SCUC) process can be adjusted to achieve a predetermined and predictable time to failure.

P. 277
Applications of Acid Fracturing Technique to improve Gas Production in Naturally Fractured Carbonate Formations, Veracruz Field, Mexico
Authors: Perex Daniel , Huidobro Efrain , Avendano Jose
Published: December 2007

This paper presents the results of successful applications of Acid Fracturing to increase gas production in mature carbonate fields in Mexico. Production comparisons show a substantial improvement in well performance following acid fracturing treatments. Six case studies are provided where a systematic methodology was employed to correctly determine candidates, and treatments. The methodology discusses the use of a novel technique that consist in alternating stages of acid and a non reactive fluid.

The fracture acidizing treatment technique, is designed to stop wormhole growth once growth has begun. The technique consists of initiating a fracture with a nonreactive pad of gel led fluid followed by alternating stages of alcoholic acid and nonreactive pad.

This system has been chosen to overcome two main problems, those are fracture extension and well cleanup.

This technique improves live acid penetration in a naturally fractured reservoir, thus sustaining greater and longer production increases than prior stimulation treatments.

The benefit obtained from the used of alcoholic acid as a reactive fluid in gas wells is observed during the initial production stages, when the well cleanup is rapidly achieved and gas production established.

Results of the treatments performed are discussed in details, including acid and gel volume, designs and analysis of the pressures recorded during placement, also data on load recovery times following the job are shown as wells as Prior and post fracture well analysis interpretations showing effective skin reduction and fracture length. Finally gas and condense production are presented including stability with time.

P. 285
Area-Specific Analysis Reflects Impact of New Generation Fluid Systems on Deepwater Exploration
Authors: Friedheim James E.
Published: December 2007

The worldwide acceleration in deepwater exploration and the accompanying technical and environmental complications have been well documented in the literature. From a drilling fluids perspective, the demands intrinsic to deepwater drilling and completions are especially acute as operators must reconcile performance and economic objectives with unique technical and environmental obstacles. Beyond standard fluid criteria, mud systems designed for deepwater projects must also address such unique problems as shallow gas hazards/water flows; gas hydrate formations; loss circulation/lower fracture gradients and hole cleaning in the riser section.

This paper reviews the latest developments in synthetic and water-based mud systems geared specifically for deepwater drilling and completions. The inherent advantages and disadvantages of the various systems will be reviewed. Moreover, to illustrate the technical and economic impact of latest generation fluid systems in deepwater projects, the author will present case studies from deepwater theaters worldwide.
A New Approach to Designing High-performance Lightweight Cement Slurries for Improved Zonal Isolation in Challenging Situations
Authors: Revil Philippe , Jain Bipin
Published: December 2007

A new approach to cementing allows the design of high- performance slurries at low as well as high densities. The technology decouples slurry and set cement performance from the slurry density. Using this technique new lightweight cement slurries as low as 10 PPG can be designed with high compressive strength, low permeability, and low porosity for applications such as completion in reservoirs with low fracture gradients, matched density kickoff plugs, geothermal wells, single slurry for both lead and tail, grouting jobs and many more.

The technology is based on the correct selection of components for the dry blend with compounds of proper specific gravity and in an optimum ratio. The subsequent reduction in usage of liquid for slurry preparation leads to beneficial effects on set cement properties.

The advantageous properties provided by the proposed system are:

– Very high compressive strengths of 2000 psi at 10.0 PPG and 4000 psi at 12.0 PPG, at low densities – Very low permeability and porosity of set cement – Improved stability, fluid-loss control and in most cases no free water compared to conventional systems – Excellent perforability for the set cement – Improved robustness to possible density fluctuations

In this paper the technology is presented and illustrated through a comprehensive set of laboratory data. Also, results are presented from various field applications where the technology has been used. Significant savings have resulted for the operator, especially when replacing conventional multistage operations with single-stage ones.

P. 339
Determination of Casing and Tubing Burst and Collapse Design Factors to Achieve Target Levels of Risk, Including Influence of Mill Source
Authors: Burres C. V. , Tallin A. G. , Cernocky E. P.
Published: December 2007

This paper provides examples of the opportunity for significant change away from historical burst and collapse design factors through the use of risk-based design. The roles of D/T ratio, grade, and mill source are accounted for in the determination of the design factor to use for a chosen target level of risk. The paper provides examples of what the burst and collapse design factors should be set to, in order to meet corresponding target levels of risk. The paper shows that the influence of grade and mill source can sometimes have significant impact on the pressure capacity of the pipe for a fixed risk of failure. The figures summarize the role that pipe parameters and service pressures play in setting the risk of failure.
Select Topics and Applications of Probabilistic OCTG Design
Authors: Payne M.L. , Sathuvalli U.B. , Crabtree S.R.
Published: December 2007

This paper was prepared for presentation at the SPE Applied Technology Workshop on Risk Based Design of Well Casing and Tubing held in The Woodlands, Texas, U.S.A., 7–8 May 1998.
Will Risk Based Casing Design Mean Safer Wells?
Authors: Hinton Andy
Published: December 2007

Although Working Stress Design is well understood, and has been used successfully, it does have drawbacks for industry. QRA / Risk Based Design are valid methods of designing casing. Full understanding of a new system is required by users and there is some concern about the validity of load data compared to resistance. Risk Based Design alone will not mean safer wells and it must be justified by being part of a total system which includes improved Quality Control and more accurate failure equations.
Probabilistic Well Design in Oman High Pressure Exploration Wells
Authors: Dahlin A. , Snaas J. , Norton S.
Published: December 2007

Historically, deep HPHT exploration wells in South Oman have been designed in a deterministic manner. In the design phase certain assumptions are made somewhat risk-averse, resulting in well designs catering for "worst-case" conditions. With hindsight this method, although proven to be sound, has resulted in over-designed wells.

The cost conscious Well Engineer, by better accounting for uncertainty, needs to minimise the over-design without risking the loss of pressure control and its possible effects on Health, Safety and Environment. It is evident that a careful balance needs to be found between risk and the level of over-design.

A novel approach to reducing the over-design is through applying a "Probabilistic Well Design" method. This method differs from the conventional design methods by defining a model in which the geological variables are defined in a probabilistic rather than a deterministic manner.

Once the model is described outcomes are simulated with statistical "Monte Carlo" software to calculate the distribution in the range of maximum design loads. Based on this distribution curve the Well Engineer can define the maximum safe operating limits of the well. The method results in a "fit for purpose" well design, with the clear understanding that if the worst case conditions (which have a low probability of occurring) are approached, some of the well objectives may not be achieved. If this should turn out to be the case the downside is that a subsequent well that does cater for these conditions is then required.

The technique has been successfully applied to two deep onshore HPHT wells during 1997 and is planned for two further wells in 1998. In the first application the technique resulted in a well, that if designed in the deterministic manner would have been drilled as a 15000psi well. After applying the probabilistic analysis it was determined that there was a 93% chance that the objectives could be met without the maximum surface pressure exceeding 10,000 psi. The well was drilled and all the objectives were met within the 10,000 psi design rating.

The probabilistic design technique is now applied to all the HPHT exploration wells and it is anticipated that it will result in considerable reductions in drilling costs in the future.
Africa's First Dual Horizontal / Dual Completion Multilateral Well
Authors: Aloko J. A. ‘Ayo’ , Fischer Stephen P. , Osselburn Jeff , Lee Dean
Published: December 2007

In April 1997, TOPCON, a joint venture of Texaco, Chevron and the Nigerian National Petroleum Corporation (NNPC), spudded the well Funiwa-43ML, offshore Nigeria. This multilateral well, with a level 5 junction, was drilled as a dual horizontal oil producer targeting an 11-foot thick oil column between gas and active water layers in an unconsolidated sandstone reservoir. The opposing laterals were 3052′ and 2242′ long horizontal sections respectively, within a ± 2-foot target window and were completed with 7″ slotted liner completions. Since the wellbore trajectories penetrated the reservoir's gas-cap prior to landing the well in the target oil column, the casing in the build sections was cemented to provide hydraulic isolation.

The junction in the main bore, from which the 2nd lateral was drilled, was created by milling a window in the casing with a drilling whipstock. This drilling whipstock was then replaced with a guidestock prior to running and cementing the 7″ liner in the 2nd lateral. The portion of the 7″ liner that extended back into the main bore was then washed over and retrieved along with the guidestock. This resulted in a full bore, full access junction providing mechanical support at the junction.

Completion equipment was then installed to hydraulically isolate the junction. This was achieved by running single string production packers below the junction in each lateral. Separate tubing strings were then tied-back, through the junction, to a dual string production packer above the junction. This resulted in the level 5 junction, ie.; a junction with mechanical and pressure integrity. The well was then completed as a dual string completion to surface.

This paper will describe the drilling and completion aspects of this project highlighting the construction of the junction thus allowing the well to be completed as a dual horizontal, dual completion multilateral well.
Extended-Reach Drilling -- What is the Limit?
Authors: Mason C.J. , Judzis A.
Published: December 2007

British Petroleum has continuously been at the forefront of ERD (Extended-Reach Drilling) achievements, with its operations at Wytch Farm in Southern England, Pompano in the Gulf of Mexico, numerous fields in the North Sea and the Niakuk and Milne Point developments off the North Slope in Alaska. In order to access reserves and extend the life of mature fields, a strong demand for cost effective ERD has now materialised. As the ERD envelope has rapidly evolved during the 1990s, many operators are now reassessing field opportunities previously considered uneconomic, when an onerous capital investment in new equipment was necessary.

A now common question is "Using ERD, how far can we drill using an existing rig and what is the impact of upgrading various rig components?" This paper attempts to address this question by exploring a number of recent case studies where offset field data and advanced analysis techniques are utilised. Increased emphasis is being placed on data collection and analysis, both of which are necessary in understanding critical ERD operations. With this improved learning, predicting future performance in higher step-out wells is more manageable.

For future ERD campaigns it has been determined that drilling hole is not necessarily the most limiting operation in significantly extending reach. The "drilling" constraint that is now emerging is more often associated with excessive drag levels when running long casing strings or sliding drilling in high angle, high step-out wells. Most of this recent experience relates to shallow reservoirs where the highest step-out wells have been drilled. This however is where the most productive engineering advances have been made.

The paper will also provide a vision of the future and highlight areas where technological breakthroughs will be required in order to drill and complete ultra-reach ERD wells of the future.

P. 87
Extended Reach Drilling at the Uttermost Part of the Earth
Authors: Naegel M. , Pradie E. , Beffa K. , Ricaud J. , Delahaye T.
Published: December 2007

The paper presents the recent development of marginal oil and gas accumulations in the vicinity of the offshore Hidra field, by Total Austral operator and partners Deminex and Pan American Energy.

Lying 12 km off the Coast of Tierra del Fuego in 35 m of water, the Hidra field was originally developed in 1989-1990 with conventional deviated wells drilled from two wellhead platforms, Hidra Centro and Hidra Norte. In 1996, three ER wells were drilled with a jack-up from these platforms to tap the Ara Sur and Hidra Sur accumulations. Although technical difficulties had to be overcome, the project was successfully completed. The first well (HNP-7) reached a horizontal departure of 6.2 km at 1700 m TVD representing more than twice the reach of previous conventional wells. This experience established the feasibility and cost effectiveness of ER wells, as a means of developing marginal oil deposits.

Total and its partners decided to launch a second, more ambitious campaign in 1997, in which 9 ER wells were planned to be drilled, this time from the coastline. By May 1998, after a year of operations, 5 wells had been completed including the new American Continent record ER well, AS-3. Drilled late 1997 to a maximum departure of 7973m at a vertical depth of 1615 m, giving a HD/TVD ratio of 4.9, AS-3 was drilled and completed in 90 days. This technical achievement was the reward of intense engineering preparation, proactive attitude on the part of the project team and multidisciplinary teamwork and efficient risk management.

The engineering preparatory studies are described, together with the rig mobilization, modifications and drilling operations highlights. A primary consideration of this project is protection of the unspoiled environment at the drilling site. The utter remoteness of the location has added a significant degree of difficulty to an already challenging task.

An effort has been made with the mud logging company to improve the monitoring of hole condition, especially during the critical 12 1/4" phase, which reached 6700 m in length, at 80-85 inclination, using a device which measures in real time the total amount of cuttings flowing at the shale shakers. This data is combined with Pressure While Drilling data to further estimate hole cleaning efficiency and ECD. To overcome friction, the 9 5/8" casing of well AS-3 was run to 7720 m MD in flotation, requiring careful engineering and unconventional procedures and equipment.

Landing into and drilling through the Springhill reservoir which is only 10 to 20 m thick and can exist locally in lenses, requires delicate geosteering techniques. This paper lists the main challenges that had to be overcome and the techniques employed. An economic comparison with other more conventional development schemes is outlined.

The results achieved so far open the way to more ambitious targets which are presently under evaluation.

P. 99
Design, Implementation and Simulation Analysis of a Single-Well Chemical Tracer Test To Measure the Residual Oil Saturation to a Hydrocarbon Miscible Gas at Prudhoe Bay
Authors: Cockin A.P. , Malcolm L.T. , McGuire P.L. , Giordano R.M. , Sitz C.D.
Published: December 2007

In 1990 a single well chemical tracer (SWCT) test was performed in Prudhoe Bay to measure the effective water flood and miscible gas flood residuals over a 12 ft reservoir interval. This is believed to be the first such use of this technology for a hydrocarbon miscible gas. This paper describes how the usual SWCT design was modified to accommodate the miscible gas, the results of the SWCT, which for the miscible gas part were significantly higher than miscible gas coreflood residuals, and the subsequent simulation of the test which has provided good agreement with the observed results. The paper explains, with simulation support, what caused the measured residuals to be higher than expected, and draws on the experiences of this test to make recommendations for the design of future SWCT tests measuring residuals to gas flooding.

P. 61
Net Pay Determination for Primary and Waterflood Depletion Mechanisms
Authors: Cobb W. M. , Marek F. J.
Published: December 2007

Net pay, as represented by thickness (h), is one of the most important parameters used in volumetric estimates of in-place hydrocarbons, well test interpretations, fluid injection analysis (water, gas, or enhanced recovery methods), reservoir engineering studies, or unitization procedures. Unfortunately, the petroleum engineering and geological literature provides very limited insight into how net pay should be computed. For a porous interval to be counted as net pay, the interval must contain hydrocarbons, be reasonably permeable, and for waterfloods, be laterally continuous from injector to producer. The issue is what portion of this interval can be produced to yield meaningful quantities of hydrocarbons under the particular drive mechanism.

Frequently, a permeability cutoff is selected and net pay is defined as being that part of the reservoir interval possessing permeability greater than the cutoff value. Due to the lack of core permeability measurements throughout all wells, the permeability cutoff cannot be directly used everywhere to differentiate between pay and nonpay rock. Consequently, net pay determination procedures usually relate the permeability cutoff to a log porosity cutoff. The resulting porosity cutoff, often coupled with a gamma-ray or other log cutoffs, is applied to available well log data to determine net pay on a well by well basis. It should be recognized that unless certain guidelines are followed, the porosity cutoff can result in very misleading net pay values because there is often not a strong direct relationship between permeability and porosity.

This paper provides insight into the selection of the appropriate permeability cutoff to compute accurate porosity and other log cutoff values. Results indicate that the permeability cutoff for a particular reservoir is dependent on a number of variables including (1) fluid viscosity, (2) permeability distribution, (3) reservoir pressure differentials, and (4) reservoir drive mechanism (primary or waterflood).

This paper provides guidelines for computing permeability cutoffs in primary and secondary recovery projects and defining those intervals which can be anticipated to be productive under various development scenarios. Also, improved techniques for converting permeability cutoffs to porosity cutoffs are discussed. Example calculations of permeability cutoffs for net pay determination in two waterflood projects are presented.
A General Linear Material Balance Method for Normally and Abnormally Pressured Petroleum Reservoirs
Authors: Wang Shie-Way
Published: December 2007

This work presents a generalized straight line, material balance method to determine the initial fluid in place of a petroleum reservoir without restrictions on fluid composition, pressure gradient, water influx, or constant pore volume assumption. All preexisting methods are applicable to either restricted ranges of reservoir fluids or reservoirs of normal pressure gradient. This work extends the method presented by Walsh in handling compositional effects of fluid composition for constant pore volume reservoirs to include the effects of abnormal pressure gradients and expansion of formation water. This method can be shown to degenerate to preexisting methods under appropriate reservoir conditions. New examples are given to illustrate how to apply this method to over-pressured gas condensate reservoirs, and detection of water influx. The significance of this work is that it provides a unified formulation of material balance calculation, which can be applied to determine the initial fluid in place for oil and gas reservoirs with (1) compositional or non-compositional effects, (2) volumetric or non-volumetric conditions, (3) normal or abnormal pressure gradients, or (4) a combination of all of these. All previously published works become subsets of the present method.

P. 101
Drilling Fluids Filtration and Permeability Impairment: Performance Evaluation of Various Mud Formulations
Authors: Longeron D.G. , Alfenore J. , Poux-Guillaume G.
Published: December 2007

This paper describes the results of a three-year programme achieved in a Joint Industry Project aiming at evaluating formation damage arising from overbalanced drilling and completion operations.

Eight typical drilling fluid formulations, including water-based and invert synthetic oil-based muds have been used to perform static and dynamic filtration tests on outcrop sandstone core samples. The performance of each mud formulation has been quantified from continuous monitoring of fluid losses during mud invasion and from return permeability measurements after mud exposure. The impact of various parameters on permeability impairment, such as initial core permeability, fluid saturations (oil or gas), temperature and shear rate has been evaluated.

Results show that fluid losses and permeability impairments obtained with water-based muds are significantly greater than those observed with invert oil- based muds. Return permeabilities measured on six sections of long core samples. at increasing distances from the inlet face, showed a dramatic near-wellbore permeability reduction due to the invasion of filtrate generated from water-based muds. On the contrary, a stimulating effect, i.e. oil return permeability greater than initial oil permeability, was observed after invasion of filtrate from invert synthetic oil-based muds. This was attributed to a favorable relative permeability effect due to a reduction of connate water saturation during mud filtrate invasion.

The use of a heavy brine as completion fluid has generated a significant additional permeability impairment due to the trapping of the wetting phase. inducing an adverse relative permeability effect.

P. 237
Uncertainty Analysis in Predictive Reservoir Simulation Using Gradient Information
Authors: Lepine O.J. , Bissell R.C. , Aanonsen S.I. , Pallister I. , Barker J.W.
Published: December 2007

We demonstrate how gradient-based techniques can be used to estimate uncertainty in predictive reservoir simulations made following history-matching. We discuss how the gradient calculations can help in finding the parameters that make the largest contributions to the uncertainty, estimating the uncertainty on these parameters, and estimating the uncertainty in predicted quantities by use of a linear analysis. The methodology is illustrated on two field examples, and compared with other methods of uncertainty quantification.

P. 141