bluuebunny/crossref_metadata_2025 huggingface dataset:
A Review of Design Considerations for Fracture Stimulation of Highly Deviated Wellbores
Authors: McDaniel B. W.
Published: December 2007

It is reasonably well understood that hydraulic fracturing applications can be especially problematic when a fracture will be initiated from a wellbore that is passing through a reservoir at a trajectory that is highly deviated from the in-situ stress field. Numerous papers and texts are available that have addressed laboratory experimentation or example situations. It is generally recommended to avoid this wellbore condition when possible if fracture stimulation will be required. However, this may not always be possible.

Included herein is a summary review of basic problems that may be encountered when it becomes necessary to apply hydraulic fracturing to a zone with a highly deviated wellbore. Guidelines are offered for how to best adapt the well completion parameters to various specific reservoir conditions, including the following:

In regard to rock hardness and competency, the approach and result in soft rock will normally vary greatly from that of harder rock in more ways than simply permeability. Measured depth and true vertical depth of the zone to be completed should be considered variables. Formation thickness can be an important factor. Single pay vs. multiple zone completions. Thinly stratified pay intervals can be quite different Perforating strategy can be the most important variable; it can often prevent effective stimulation, or conversely, can be used to enable fracturing success.

In some fields, the expanding application of horizontal completions may reduce the use of deviated wellbores. However, environmental concerns for reducing surface footprints during land drilling could increase the use of deviated wellbores. This paper will review the factors most critical to successful placement of hydraulic fracturing treatments in deviated wellbores.
Risk Assessment Based on Single Porosity, Alpha Factor, Dual Porosity Simulation of a Naturally Fractured Rich Gas Condensate Reservoir
Authors: Iwere F. O. , Gao H. , Gomez E. , Ma Y. Z. , Gurpinar O. M.
Published: December 2007

Modeling naturally fractured reservoirs is difficult because of the need to characterize the fractures, matrix and the matrix-fracture interaction. It becomes more challenging if the naturally fractured reservoir produces wet gas, condensates and water. Three different three dimensional, compositional models--single-porosity (SP), single-porosity with alpha factor (SPWAF), and dual-porosity single permeability (DPSP) of the study area, were studied.

The models were calibrated against measured pressure, historical oil production, layer contributions and gas-oil ratios. The calibrated models were then used to forecast the performance of wells in the study area. The impacts of the methodology of describing the natural fractures on fluid flow behavior and recovery mechanisms, as well as on the ultimate hydrocarbon recovery were evaluated. The results also were used to ascertain the risks of selecting the optimum methodology for the field development plan.

The forecasted results show little variations in oil recovery, pressure and oil saturation distributions under identical operating strategy for the three models. This is attributed to the absence of some critical properties required to model the oil recovery mechanisms in dual porosity system. For example, imbibition capillary and relative permeability functions were not input in the dual porosity (DPSP) model. However, the DPSP model is considered more efficient than the single porosity (SP and SPWAF) models because it took less time and modifications to obtain reasonable history match of the field performance. It was also more difficult to obtain a reasonable and acceptable history match using the SP and SPWAF models compared to the DPSP model, and the reservoir properties in the single porosity models had to be modified extensively and unrealistically to obtain history match.
Detecting Immiscible Flood Fronts in Heterogeneous Systems from Continuous Monitoring of Rate and Pressure
Authors: Jafroodi Nelia , Ershaghi Iraj
Published: December 2007

In this paper, we examine the monitoring of a moving interface problem in immiscible floods in 1-D heterogeneous systems. The solution is presented for monitoring saturation fronts in an extended case of a classical 1-D Buckley Leverette with various lateral permeability profiles. Flood is assumed to be at a constant injection rate but with the opportunity to continuously monitor injection pressure, fractional composition of produced fluid and production pressures. Lateral changes in effective transmissibilities between the injector and the producers caused by movement of immiscible fluid-fluid interface and detected from the solution of interference pressure equation provide an added dimension for tracking the saturation fronts. The effect of the rock heterogeneities is filtered out by analysis of the incremental changes observed with respect to the base measurements at the early stages of the flood.
Evaluation of the Effect of Complex Reservoir Geometries and Completion Practices on Production Analysis
Authors: Cox S. A. , Sutton R. P. , Stoltz R. P. , Barree R. D. , Conway M. W.
Published: December 2007

Complex reservoir geometries can influence the results obtained from transient production decline analysis. For tight gas reservoirs it is common to observe limited drainage areas and linear flow geometries. In some cases these results are inconsistent with the expected geological structural and depositional character of the reservoir. Complex reservoir geometries and flow conditions such as liquid loading can contribute to this phenomenon. Numerical simulation cases will be used to generate the control data sets to demonstrate these effects. This paper will show the effects of complicated reservoir flow conditions on the results obtained from production analysis.

Production analysis is commonly performed in tight gas reservoirs as the analytical technique can be used to quantify reservoir flow capacity, gas in-place, and reservoir geometry (both area and aspect ratio). The results have been used to estimate the effective drainage area, infer completion efficiency and evaluate potential infill drilling spacing for tight gas reservoirs. Complex reservoir cases considered in the paper include stress dependent permeability in both single and dual porosity reservoirs, radial composite systems, and multi-layered reservoirs. From a completion point of view the paper presents the effects of fracture clean-up, fracture damage over time, and the effects of liquid loading on transient production behavior.
Modeling of Equalizer Production System and Smart Well Applications in Full-Field Studies
Authors: Su HoJeen , Dogru Ali H.
Published: December 2007

Equalizer production systems and inflow control devices are used to mitigate water or gas coning problems for mature fields. We have developed new modeling methods to simulate equalizer and interval control valve (ICV) performance in full-field multimillion-cell reservoir models under a parallel computational environment.

We present single-well performance predictions with and without an equalizer, and the results are significantly different in some cases. Full-field modeling with equalizers and ICV controls for several examples has been conducted. In such cases, many individual wells would have significantly improved performance. At full-field level, however, using equalizers or smart well applications without total field optimization would not improve performance much, for reasons we will discuss.

The frictional pressure loss across an equalizer can be considered as a skin, and we have developed an analytical well equation to include it. With this theoretical development, it is now possible to confirm or monitor equalizer performance in terms of pressure drop from pressure transient analysis.
Property Modelling Small Scale Heterogeneity of Carbonate Facies
Authors: Creusen Anouk , Maamari Khalid , Tull Simon , Vahrenkamp Volker , Mookerjee Abhijit , Van Rijen Michiel
Published: December 2007

A heterogeneously complex carbonate reservoir has been characterized texturally and petrophysically at the plug- and core-scale. This rock typing has been used as input to a series of dynamic "mini-models" aimed at correctly deriving static and dynamic rock properties for input into a full field model. Simulation of these mini-models clearly demonstrates the importance of small-scale heterogeneities on hydrocarbon displacement. These small-scale heterogeneities are commonly omitted from standard reservoir modeling workflows.
Sand Clean Out and Acidization of Predrilled Liner Horizontal Hole Sections: A Field Experience
Authors: Ayeni O. L. , Blackall D. , Emeka C. O. , Obadare A. , Uchendu C.
Published: December 2007

This paper describes sand cleanout / acidizing operations of four horizontal pre-drilled liner completions in the UU field, offshore Nigeria. These wells were drilled and completed concurrently with similar completions in 1996. Production from the wells declined after four years. The wells were studied using production history curve analysis and nodal analysis techniques. Analysis indicated that the most probable cause of the decline in productivity was plugging of the completion with solids/deposits.

Detailed analysis and flow testing were carried out on the available core samples from an analogue well to determine the mineralogy of the possible plugging solids and the most effective treatment recipe to be used to remove the plugging materials. Based on the results of the core analysis, sand cleanout /acid stimulation operations were executed on the subject wells, using coil tubing and specialized coil tubing tools.

The operation resulted in a 300% increase in productivity, and was both a technical and economic success.
Equitable Gas Pricing Model
Authors: Ogwo O. U. J. , Mbeledogu I. U. , Nwokedi M.
Published: December 2007

A multi-parameter functional model is generated that would ensure fair gas pricing and minimize subjectivity in the determination of gas prices. Equitable gas pricing would prevent undue price imbalance while ensuring that all stakeholders maximize the benefits of their resources. In the development of this model, various factors are considered ranging from cost of supply and cost of processing (including return on investment) through market availability, gas quality, available fiscal incentives, to market maturity factors. The model (an original analysis on gas pricing) is suitable for determining both short-term and long-term contractual gas prices. A template is presented for evaluating the cost of gas at various supply points. A simulation of gas prices is made using the model, with a given developing gas economy as a test case. The data used for the sensitivity analysis are real data though presented in unclassified form. It is observed that at present the upstream gas of some developing gas economies is not appropriately priced when compared with the cost of production or when reference is taken from the price at the international market.
Optimization of Information/Data Quality Amongst Dispersed Project Teams and Management Groups in the Nigerian Oil and Gas Industry
Authors: Edehe Kufre
Published: December 2007

Recently, Oil and Gas upstream Industries have made tremendous gains in efficiency, productivity and operational performance through the utilization of portal solutions to access their petrotechnical data. This paper provides an insight on the implementation of a complete Data Management Solution aimed at optimizing the quality of data/Information flow amongst project teams and Management groups in the Nigerian Oil and Gas upstream Industries. Data Management anchored on the use of Web portal solutions does not only provide access to various data repositories for modeling, interpretation, simulation, analysis; etc purposes, it helps to improve the operations based on data browsing and access in real time, accelerating the transformation of data to timely decisions thereby increasing productivity and promoting collaboration amongst project teams.

Current geosciences and engineering workflows; ranging from defining data acquisition programs, to building subsurface models, to working up development plans, to actual drilling and productions operations: are relatively disjointed and unstructured. The incoming data required by each of these project teams need to be identified, verified and made available on timely bases. Consequently, web portals tailored to meet E & P needs helps in bringing these data and information to the user's petrotechnical desktop; thus connecting people to data and information.

The scope involved in the implementation of a complete Data Management Solution in one of the Major Oil and Gas Company in Nigeria would be referenced in detail with a view to illustrating how web portal data access solutions has helped in the optimization of the quality of data amongst project teams and Management groups in the Oil and Gas Industry. The importance of this implementation which include and are not limited to the following;

Enhance reservoir recovery production optimization Better Decision made with upfront access to high-quality data Increased efficiency in connecting the field to the office Time wasted in data search is reduced More effort is rather geared into search for Hydrocarbon rather than data Data can be retrieved easily Data update can only be altered through the Web by Database administrator would also be discussed.
Applications of Through Tubing Water Shutoff – SPDC West Experience
Authors: Tope Tunde , Enoto Oton , Kayode Ayeni
Published: December 2007

Water production poses a great challenge in realising maximum value from an oil and gas producing asset. The problems associated with water production include but not limited to early well quitting, resulting in poor oil recovery, restriction of ullage in the surface facilities and huge spend on water handling.

In an attempt to arrest water production downhole, a number of techniques have been successfully deployed. These can be broadly classified as chemical and mechanical water shutoff techniques.

The focus of this paper is on case histories ranging from the conventional mechanical methods to novel chemical water shutoff solutions. The techniques have been applied in completion with diverse complexities ranging from Single String, Short String in a dual completion, Internal Gravel pack, External Gravel Pack to Horizontal well.

The success recorded in most case histories ranges from 100% to about 50% reduction in the original water production while in some cases no success was achieved. Application of these techniques resulted in over US$10 million savings as compared with cost of water shutoff by workover.
Crude Oil Metering Experience in the Niger-Delta
Authors: Iwegbu Michael , Appah Dulu , Ogwo Emma Agu
Published: December 2007

There are increased concerns for improved fluid flow rate measurement by oil & gas producing, processing and distribution companies in order to search for increased flow measurement accuracy and precision.

This work looks at the existing metering procedures and practices of fiscal equipment from custody transfer points of various producing onshore and offshore assets in the Niger Delta region of Nigeria. The work also highlights the sources, magnitudes of these errors and the economic implications of the accruing losses from crude oil metering practices in the Niger Delta.

Results were obtained from field trips, discussions, observations and results of the study showed that usually unity meter factor is applied to meter throughput, meter linearity curves and tables are not established for each meter, optimum or mean K-Factors are used In calculating meter factors. These metering practices ranged from not having appropriate fiscal equipment to not proving meters when required. Significant measurement errors can be further reduced via correction of equipment, procedural and metering problems which would improve metering practices in the Niger Delta region of Nigeria.

Introduction

The Science and Philosophy of Measurement

Measurement is a reference standard used for the quantitative comparison of properties. It is the quantitative and numerical assessment of the dynamic and static properties of naturally occurring phenomena and substances. In the hydrocarbon industry, this is translated to the measurement of fluid flow and static tank gauging. Examples of fluid properties are:Cold (absence of heat) Temperature (T) °F or °C.Mass Volume (V) Cubic Length (cu. ft.- cu. m.).Energy Velocity (S) Length/Time (ft/s. - m/s.).Rate Flow (Q=V/t) Cubic Length/Time (cu. ft./s.-cu m/s.).

Other parameters are pressure, viscosity, density and so on.

Petroleum Measurement

The measurement of the quantity and quality of petroleum and its products, in a liquid or gas phase, has always been important to producers, royalty owners, shippers, transporters, refiners, government agencies and the general public. Measurements are made in connection with custody transfer, inventory control, hydrocarbons movement, and quality determination. Measurements are complicated, so specialized technologies and equipment are developed.
Akpo, Nigeria: From Seismic Interpretation to Geomodel
Authors: Itiola Timothy Oluyemi , Michel Bruno , Bez Martine
Published: December 2007

Akpo is a very light oil to condensate gas field located offshore Niger Delta, discovered end 1999 by Akpo-1 well at a water depth of 1350m, by SAPETRO (operator) - Total TUPNI (technical advisor) and PETROBAS in OPL246.

As for some other turbiditic fields, modelling of the 5 to 20m thick individual channels was the main challenge as they act as the elementary flow units of the reservoir. Although such flow units are under the current available seismic resolution, the developed methodology with object modelling constrained by sedimentological interpretation and seismic derived Vclay cube, allowed to provide reservoir engineers with geologically representative model to be able to simulate properly the flow behaviour and further estimate the reserves.
Reconciling Subsurface Uncertainty with the Appropriate Well Design Using the Mechanical Earth Model (MEM) Approach
Authors: Goodman H. E. , Connolly P.
Published: December 2007

The involvement of the well engineer (WE) competency from the earliest phases of exploration is reaping economic benefit for major capital projects (single wells costing at least $25,000,000 US). As the geological and geophysical modeling work of the Explorationists matures and the subsurface picture becomes clearer, the appropriate well design flexibility is being achieved using Mechanical Earth Model (MEM) technology. This approach to well planning is particularly beneficial for deepwater exploration.

For deepwater subsalt plays, the capital outlays are immense, with single wells costing up to $100,000,000 US. For these projects, MEM technology has been found to be extremely valuable, particularly in characterizing drilling risks associated with well exit points below salt where in-situ stress perturbations can occur. These stress perturbations are being reliably mapped using MEM techniques and the consequences to borehole stability addressed. An example of principal stress rotation gleaned from a deepwater MEM and the consequences to borehole stability is summarized in this paper.
Constructing Inflow Performance Relationship from Surface Measurements: Retreating to the Fundamentals
Authors: Lawal Kazeem A.
Published: December 2007

The Inflow Performance Relationship (IPR) is a key input for integrated studies and optimisation of well/reservoir performance. Constructing the IPR requires reliable flowing bottomhole pressure (FBHP) data. The relatively cheap and evolving option of using flowing tubing head pressure (FTHP) and other surface production data to estimate FBHP depends heavily on a reliable multiphase flow model, as flow in the wellbore is typically multiphasic.

Most of the common multiphase flow correlations relating FBHP and FTHP are empirical, and in spite of their relative complexities, have limited applications. With the conventional modelling approach of assuming an equivalent ‘liquid’ and gas system, these correlations are inherently limited to two-phase flow conditions. In order to honour field data, they often require some form of tuning algorithms, undermining their reliability under situations where such field data are not available.

In this paper, a strictly analytic (mechanistic) four-phase model is presented. The model, hinged on the

basic principles of mass, momentum and energy conservation, accounts for slip between phases, and estimates FBHP from surface measurements, fluid properties, wellbore geometry and completion string data. Its use for IPR construction is also illustrated.

A field example, comparing its performance against an intrinsic two-phase (Beggs and Brill) and an intrinsic four-phase model (Guo), demonstrates its applicability and reliability. Considering its simplicity and robustness, its use can easily be extended to the analysis of drilling hydraulics and other multiphase flow systems that are not explicitly amenable to the so-called generic two-phase approach.
Improved Characterization of Heptanes-Plus Fractions of Light Crudes
Authors: Isehunwa O. S , Falade G. K.
Published: December 2007

Heptanes plus fractions have strong effects on the physical properties and phase behaviour of petroleum fluids. It is therefore very important to properly characterize plus fractions. A step to achieving improved characterization is to obtain more realistic molecular weights. Most of the current methods of heptanes plus characterization assume their molecular weights are accurate. However, what is commonly measured in the laboratory is the molecular weight of the complete fluid; the molecular weight of the heptane-plus fraction is then estimated using Kay's mixing rule. Unfortunately, physical properties like molecular weight obtained using ‘equivalent fluid’ principles by mixing pure components, do not give the same values with actual measurements. Therefore, while a very accurate estimate of the molecular weight of a reservoir oil could be available, that of the heavy fractions, which is ‘inferred’ could be unreliable, because of the mixing rule.

A simple technique has been formulated to achieve improved characterization of petroleum fluids and the heavy fractions. We suggest ‘fine tuning ’ Kay's mixing rule in order to achieve a match between actual measured molecular weight and the ‘equivalent fluid’. Experimental data from over 400 PVT reports from over 100 fields in the Niger Delta were collected and studied. A correlation was established between oil gravity and molecular weight and. compared with other commonly used correlations. Statistical error analysis was undertaken. Heptanes plus molecular weights which were generally estimated using Kay's mixing rule were found to be generally high and hence fine tuned using a simple technique.

The results of this study show that the well-known Cragoe's and Standing correlations gave absolute average deviation of 126.8 and 53.3 respectively for light crudes, compared to 2.5 obtained in this study. Furthermore, better description of heavy fractions was achieved with more accurate molecular weight.

It is concluded that the proposed technique perhaps provides a theoretical basis for the usual ‘tuning’ of heptane-plus properties during fluid modelling. It is also concluded that a more accurate correlation for estimating the molecular weight of light crudes has been developed.
Development and Successful Application of Unique Steerable PDC Bits
Authors: Norris J.A. , Dykstra M.W. , Beuershausen C.C. , Fincher R.W. , Ohanian M.P.
Published: December 2007

This paper describes the development and successful application of unique polycrystalline diamond compact (PDC) bits for use on steerable motor assemblies. The development phase comprised an extensive series of laboratory and field experiments. These showed that proper design of face and gauge aggressiveness were the keys to improved steerability. Notably, the common perception that a short, aggressive gauge is required for steerability was found to be misguided. Field applications from around the world have demonstrated that the new designs minimize tool face fluctuations despite erratic weight on bit (WOB), allow the theoretical build up rate (BUR) to be attained, create superior quality well bores, and provide improved net rates of penetration (ROP) over conventional designs.

P. 153
Automation of BOP Bonnet Access: A No Bolts Approach
Authors: Levett B.A. , Brugman J.D.
Published: December 2007

The increased use of drill floor automation has greatly reduced the frequency of accidents involving rig personnel. One area that has yet to benefit from automation safety is the BOP stack. A new BOP bonnet attachment system has enabled automatic opening and closing of BOP bonnets, representing a major step toward automation of BOP servicing. Several operational benefits could be derived from this system both in surface and subsea applications.

P. 465
The Implementation of a Computerised Maintenance Management System
Authors: Godot A. , Villard P. , Savournin A.
Published: December 2007

In 1993, after years of using a manual maintenance system based on individual historical cards (T-CARD board), Forasol-Foramer decided to update the system by installing a Computerised Maintenance Management System (CMMS) on all drilling units, the objective being to eliminate the non-productive time.

In accordance with the criteria that the Company highlighted, the Technical Department selected a CMMS software. This program, made up of interconnected modules, can handle all aspects of maintenance, including work order management, preventive maintenance scheduling, history of maintenance done on the equipment, equipment costs, stock control, purchasing and reporting.

In order to adapt the standard product to the Company's specific Preventive Maintenance System, the Technical Department modified the screen presentation and the dialog boxes and created new reports before its implementation on the drilling units. In addition to interface modification, more important was the incorporation of nearly forty years of experience in all the job plan that had to be defined.

The responsabilities and the procedures the users are required to follow have been defined and a user's manual has been created.

A CMMS training course has also been introduced in order to familiarise senior staff to the customised software and to facilitate manoeuvring in the Windows environment for those personnel who are not computer literate.

After 4 years of operational experience, the Company claims that the use of a CMMS leads to an improved system of maintenance, together with an enhanced work reporting indicating precisely which maintenance work has been completed and providing a diminution of non-productive time.
Improving Multilateral Drilling and Completion Efficiency with a Hollow Whipstock
Authors: Foster Jeffrey L. , Olds Kelly T. , Stebbings R. Paul K. , Giangiacomo Leo A. , Durst Doug , Carter Thurman
Published: December 2007

A multilateral completion allows one or more laterals to be connected to a parent wellbore so that production from each can be isolated or commingled, and all laterals can be accessed. One of the challenges in multilateral drilling has been in regaining access to the main wellbore after the window has been milled and the lateral drilled. Typically, a solid whipstock has been used to mill the window and drill the lateral; it was then retrieved, and a hollow whipstock run to provide access to the lower main wellbore and allow for the passage of produced fluids. Difficulties were sometimes experienced, however, when retrieving the solid whipstock and realigning the hollow whipstock.

This paper will discuss a new single-trip hollow whipstock that can be used for milling a window as well as for production. This innovative design eliminates the risk posed by retrieving the solid whipstock and realigning the hollow whipstock with the window. Since the hollow whipstock is set only once, it remains aligned with the window throughout the life of the well. This assures reentry into the lateral and eliminates any restrictions due to misalignment across the window from a reset whipstock. The discussion in this paper will include information on the design, application, and testing of the new whipstock and will verify its capability to reduce the risks, number of trips, and cost of multilateral installations as well as enhance downhole performance under the challenging conditions inherent with multilateral configurations.

P. 629
Rotary Liner Drilling for Depleted Reservoirs
Authors: Sinor L.A. , Tybero P. , Eide O. , Wenande B.C.
Published: December 2007

This report summarizes the testing and field application of a rotary liner drilling system. Liner drilling was first attempted by Amoco Norway Oil Company (ANOC) in 1993 and there have since been eight additional wells drilled using rotary, motor, and a combination rotary/motor liner drilling system. This paper will focus on six of those wells drilled with a rotary liner drilling system. Key learnings from these well applications in the Norwegian sector of the North Sea are reviewed.

P. 879
Mathematical Modeling of Secondary Precipitation from Sandstone Acidizing
Authors: Ying-Hsiao Li , Fambrough John D. , Montgomery Carl T.
Published: December 2007

Field and laboratory experience clearly demonstrate that besides primary dissolution, precipitation from both secondary and tertiary reactions with alumino-silicates adversely affect matrix acid treatment success. In the secondary reaction, fluosilicic acid from the primary dissolution will further react with aluminosilicates to form hydrated silica on the matrix surface. In the tertiary reaction, aluminum fluoride also extracts aluminum from alumino-silicates to form silica gel by lowering the F/Al ratio in the solution. In the presence of a high concentration of metal ions, metal fluorides and fluosilicates are also likely to precipitate.

An optimum acidizing design package can be derived for a specific formation mineralogy and damage mechanism if this complex reactive system can be modeled properly. A geochemical model for acidizing has been developed for this purpose. The numerical simulator is a reactive flow model that solves the reactive system with both reaction kinetics and chemical equilibrium calculations. All possible reactions among all species in the system are solved simultaneously. As acid spends the computer simulation shows the progress of aluminosilicate dissolution and the formation of different precipitates as the change of dissolved species along the reaction path occurs. The evolution of the damage skin can be evaluated as simulation continues. Based on the simulation, different pumping schedules with different types of acids can be quickly evaluated in order to optimize treatment volume and minimize precipitation of hydrated silica and other precipitates.

To validate the model a series of laboratory coreflood tests has been fully analyzed. The results indicate that the formation of silica gel is significant based on the HF effluent analysis. The same set of kinetic data derived from the laboratory coreflood data adequately predicts and explains a sandstone acidizing field case.

P. 27
Formation Damage Prevention by Using an Oil-Based Fracturing Fluid in Partially Depleted Oil Reservoirs of Western Siberia
Authors: Cikes Marin , Cubric Srecko , Moylashov Mekhraly R.
Published: December 2007

Comparing with water-based fluids, oil-based fracturing fluid is not in wide use. The main reasons are lower cost effectiveness and more dangerous handling of oil-based fluid. However, as non damaging fracturing fluid, the oil-based fluid has numerous advantages over water-based. In fact, in many cases, where water-based fluid failed, switching to oil-based fluid resulted with successful stimulation of well productivity. One of such cases is fracturing of partially depleted oil reservoirs of Bakhilov and North Khokhryakov fields in Western Siberia, Russian Federation.

The oil fields were discovered in 1983. Production started in 1987 and water injection began in 1988. The peak oil production was reached in 1991/92, followed by drop of 50%. An attempt was made to increase wells productivity by performing small hydraulic fracturing treatment using water- based fluid. Although it resulted in some increase in wells productivity, the analysis of that treatments suggested necessity for longer fractures and careful tailoring of fracturing fluid.

Recently the twenty-three fracture treatments have been performed using an oil-based fracturing fluid and pumping significantly higher quantity of proppant. The result is excellent: nearly all wells started to flow at the average initial oil rate of 70 m3/day [440 bopd] what is more than ten-folds production increase in comparison with pre-fracture production. Comparison of median values of early and late post-fracture production indicates sustained productivity improvement.

P. 121
New Single Trip Perforating and Gravel Pack Procedure with Advanced Stimulation Design Reduces Formation Damage in High Permeability Sandstone Reservoirs: Case Histories
Authors: Jones Ralph H. , Bolin Tommy D.
Published: December 2007

Fluid loss that can occur when performing sand control operations in high-permeability sandstone formations has traditionally caused operators much concern because of the formation damage that can result, reducing production potentials and increasing operational costs. In the Gulf Coast area, wells are usually perforated with tubing conveyed perforating (TCP) guns in an underbalanced condition. After the perforating and well flow processes have been performed, the wells are killed. Unfortunately, at any time after the well has been perforated until it is completed, fluid loss can occur.

This paper will discuss a new process in which the perforating gun assembly is incorporated with the gravel pack assembly to allow perforating and gravel packing to be accomplished in a single trip. By eliminating the time and additional trips required to perforate and clean up the well before gravel packing the zone of interest, the chance of fluid loss is significantly reduced. Other innovative methods have also been introduced to minimize formation fluid losses and eliminate the use of formation-damaging lost circulation material (LCM) during performance of the sand control procedures. Several operators have recently completed wells in the Gulf Coast area using the new single-trip perforate-and-gravel-pack procedure (STPP) and advanced stimulation design, and low skin factors have been experienced.

The operating procedures as well as the increased efficiency and cost savings for which the new procedures have been responsible will be discussed, and the post-operational data provided will verify that reduction in formation damage is experienced when the new methods are used.
Development of a New Crosslinked-HEC Fluid Loss Control Pill for Highly-Overbalanced, High-Permeability and/or High Temperature Formations
Authors: Chang F.F. , Ali S.A. , Cromb J. , Bowman M. , Parlar M.
Published: December 2007

The loss of brine to the hydrocarbon formations has been one of the major concerns during well completion operations. Fluid-loss control pill scontaining sized particulates, such as CaCO3 or sized salt, have often been used. However, damage to the formations and gravel packs by the solids due to solids invasion often causes reduced production and an expensive workover. The cleanup of the carbonate pill is often ineffective, especially in long intervals, since the reaction between acid and carbonate is too fast for the acid to cover the entire zone. Therefore, a reliable viscous fluid system without solids is more desirable than a particulate system. In high-permeability reservoirs, a highly crosslinked gel is needed to achieve good fluid-loss control hydroxyethylcellulose (HEC) is known for its low residue content and difficulty to be crosslinked. A highly elastic zirconium crosslinked HEC gel is achieved by using an activator and a chelant. A delaying agent is used to adjust the timing of the crosslink process. The gel is capable of stopping fluid loss in formations of 2 darcies and above at temperatures upto 290 F. Internal and/or external breakers can be used to reduce the gelviscosity to near water consistency.

P. 215
Asphaltene Near-wellbore Formation Damage Modeling
Authors: Leontaritis Kosta J.
Published: December 2007

When during oil production the thermodynamic conditions within the near-wellbore formation lie inside the asphaltene deposition envelope of the reservoir fluid, the flocculated asphaltenes cause formation damage. Mathematically, formation damage is a reduction in the hydrocarbon effective mobility. Three possible mechanisms of asphaltene-induced formation damage have been discussed in the literature. Asphaltenes can reduce the hydrocarbon effective mobility by a) blocking pore throats thus reducing the rock permeability, k, b) adsorbing onto the rock and altering the formation wettability from water-wet to oil-wet thus diminishing the effective permeability to oil, kO, and c) increasing the reservoir fluid viscosity, by nucleating water- in-oil emulsions. In the most frequently encountered case of asphaltene-induced formation damage where an under- saturated oil is being produced without water, the most dominant damage mechanism is blockage of pore throats by asphaltene particles causing a reduction in rock permeability k. This paper presents a rather simple, yet realistic way of modeling asphaltene-induced near-well formation damage caused by blockage of pore throats by asphaltene particles. The model utilizes both macroscopic and microscopic concepts to represent the pore throat blockages. It also utilizes the Thermodynamic-Colloidal Model of Asphaltene, TC Model SM, an existing AsphWax asphaltene phase behavior model capable of simulating the asphaltene particle size distribution as a function of the thermodynamics of the system. The new asphaltene near-well formation damage model is applied in one case where it is used to track the degree of formation damage as a function of time and the effect it has on near-wellbore and wellbore hydraulics. Similarily the model can be used to study a propr: the economics of developing a reservoir knon to contain an under-saturated aspaltenic oil.

P. 277
Use of Downhole Diagnostics Enhances Determination of Damage Mechanisms
Authors: Yeager V. J.
Published: December 2007

This paper presents a systematic approach used in an intensive, 2-year study that was funded by the Gas Research Institute (GRI) and Department of Energy (DOE) and undertaken to determine the damage mechanisms that affect the over 15,000 U.S. gas storage wells.1 Multiple diagnostic tools were used to determine the damage mechanisms in 32 wells in 12 different reservoirs.

The approach used included (1) transient pressure analysis and well testing to quantitatively determine if damage existed, (2) downhole video to observe the wellbore and formation areas, (3) physical sampling of downhole liquids and solids, and (4) rotary sidewall coring of the wellbore face to provide a "biopsy" of the formation of interest.

This paper also includes (1) special sampling/handling considerations and laboratory procedures that were developed and (2) illustrations of some of the various damage mechanisms that were identified.
Post-Frac Analyses Indicating Multiple Fractures Created in a Volcanic Formation
Authors: Sato Kozo , Wright Chris , Ichikawa Makoto
Published: December 2007

The technology of hydraulic fracturing is faced with a conceptual transition from a classical single-planar fracture to a tortuous fracture network and simultaneously propagated multiple hydraulic fractures. This new concept is applied to analyses of two propped fracture treatments conducted in a volcanic formation. In both cases, the productivity was doubled, but the treatments themselves were unsuccessful, experiencing extremely high net fracturing pressures and very premature screen-outs.

The classical concept of a single-planar fracture could not explain either the fracturing-pressure behavior or the post-frac production rate/pressure. Adopting a multiple-fracture geometry resolves this problem. The fracturing pressures are successfully simulated, and the resultant fracture geometries are consistent with both the premature screen-outs and the post-frac production performances. Combined analyses of fracturing pressure and subsequent production performances firmly confirm the creation of multiple fractures in a volcanic formation.

P. 145
A New Semi-Analytical Pressure Transient Model for Layered Gas Reservoirs Under
Authors: Gomes E. , Reza Z.A.
Published: December 2007

Reservoir deposition occurs over geologic period of time and thus, most of the reservoirs are layered in nature. These layers may or may not communicate with each other. This study develops a new semi-analytical model for pressure transient analysis of layered gas reservoirs. Apart from layering, in a gas reservoir the flow problem is further complicated by high velocity effect, pressure dependent gas properties, and wellbore storage and skin. Discretizing only the vertical direction term to account for the cross flow, and using pseudopressure and pseudotime approach, the diffusivity equation has been solved as a generalized eigenvalue problem. The model takes into account inter-layer crossflow, high velocity effects, wellbore storage and skin (both as thin skin and finite damaged zone), and different possible inner and outer boundary conditions.

P. 223
Effect of Friction and Leak-Off on Fracture Parameters Calculated form Hydraulic
Authors: Soliman M.Y. , Azari M.
Published: December 2007

Hydraulic impedance may be used to determine fracture geometry, length and height. However, the models for analysis of impedance tests presented in literature usually ignore the effect of friction and fluid leak-off. This paper presents and solves an impedance testing model that considers the effects of friction and fracturing fluid leak-off. A test that has been presented in literature has been analyzed, and this paper will show from this analysis that ignoring these two factors may cause a significant error in estimating fracture parameters.

P. 245
Formation Evaluation in Lower Eocene Reservoirs in Upper Assam Basim: An
Authors: Borah N.M. , Mallick R.K. , Choudhuri B. , Raju S.V. , Mathur N.
Published: December 2007

Evaluation of thin, highly permeable, stratified reservoirs in the Lower-Eocene Formation in Upper Assam, India poses a formidable challenge. The problems include identification of thin beds, ascertaining the type of fluid based on wireline log response. establishing vertical and lateral continuity of the reservoirs and stratified nature of these thin reservoirs. An integrated multidisciplinary approach has been adopted for solving these complex formation evaluation problems.

P. 315
Artificial Intelligence Approach for Well-to-Well Log Correlation
Authors: Lim Jong-Se , Kang Joe M. , Kim Jungwhan
Published: December 2007

This paper describes a new approach to automated well-to-well log correlation using artificial intelligence and principal component analysis. The approach to correlate wireline logging data is on the basis of a large set of subjective rules that are intended to represent human logical processes. The reliable correlation can be established from the first principal component logs derived from both the important informations around wellbore and the largest common part of variances of all available well log data. The data processed are mainly the qualitative informations such as the characteristics of the shapes extracted along log traces. The apparent geologic zones are identified by pattern recognition for the specific characteristics of the computed principal component log trace. The characteristics are collected as a set of objects by object oriented programming. The correlation of zones between wells is made by rule-based inference program.

Correlation with field log data shows that this approach can make well-to-well correlation more reliable and accurate. This method can be used for well-to-well log correlation with efficiency and accuracy.

P. 333
Array Induction Modeling Results From Indian Formations
Authors: Suryanarayana K. , Singer J.M.
Published: December 2007

The Array Induction Tool (AIT) has significant advantages over standard induction tools in terms of vertical resolution, depth of investigation and the ability to detect moved oil. India is generally considered Laterolog country. However in many areas the conditions are such that either Induction or Laterolog is appropriate; the Laterolog has often been chosen because of its higher vertical resolution compared to the standard Induction.

The AIT offers vertical resolution down to 0.3 Mts. and depths of investigation up to 90 inches in many conditions. This is significantly better than the Laterolog. In order to understand the response of the AIT, the resistivity characteristics of five Indian reservoirs have been examined. This study includes cases of resistive and conductive invasion, invasion profiling in shaly sandstones, invasion seen by standard induction, thin beds and response in a layered reservoir. In each case the response of the standard logs (Laterolog or Induction) have been modeled and compared with the response of the modeled AIT

The results show that in the most situations the AIT provides a better estimate of true formation resistivity, Rt. The improvement is towards reading resistivity values close to the Laterolog resistivity in the oil zone, and also reading a correct resistivity value in the water zone as expected by the Induction tool. The combined improvement enhances confidence in the computation of hydrocarbon saturation significantly. The AIT, therefore, detects moved oil more reliably, and hence facilitates decision on further investment.

The theoretical modeling work has been validated by two field cases in a sandstone environment. Comparison with the available Laterolog data clearly brings out the advantage of the AIT in terms of vertical resolution as well as in describing the invasion profile. Using the field data, the AIT logs were reconstructed through modeling. The reconstructed values match the field data, except in cases where highly irregular profiles are seen on the field data.

P. 353
Dealing with Uncertainty: Geostatistics and the New Era in Reservoir Studies
Authors: Simlote V.N. , Nikolayenko S.A.
Published: December 2007

Predominantly, reservoir characterization techniques involved the traditional layer-cake models, which are known to be simplistic for complex sedimentologic environments. One of the Oxy operated fields presented a problem in accounting for the heterogeneity of its reservoir. Limitations posed by the conventional models prompted the search for newer methods in order to describe this reservoir more accurately. With the help of the leading integrated geostatistical package that offered stochastic modeling Options, the new full-fledged reservoir model was successfully built. Unlike its deterministic predecessor, it demonstrated an increased flexibility in accounting for the heterogeneities in the field. The strength of the geostatistical software is in its ways of dealing with uncertainty. The software is based upon the Boolean technique that allows for building a reservoir model created from objects that have some genetic significance rather than the model being built up one elementary node at a time.

P. 383