bluuebunny/crossref_metadata_2025 huggingface dataset:
Foundation Engineering For Gravity Structures In The North Sea
Authors: Schjetne Knut
Published: December 2007

American Institute of Mining, metallurgical and Petroleum Engineers, Inc.

Discussion of this paper is invited. Three copies of any discussion should be sent to the Netherland Section of the Society of Petroleum Engineers, P.O.Box 228 The Hague, The Netherlands. Such discussion may be considered for publication together with the paper.

The paper outlines the particular problems related to the foundation problems related to the foundation design of offshore gravity structures in comparison with structures on shore. The following aspects are dealt with in more detail:The current NGI method for overall foundation-stability on clay,the effect of cyclic loading on clay,the dynamic analysis of the soil structure system andplatform behaviour during the installation phase.

Introduction

Since 1968, when the Ekofisk oil field was discovered, we have witnessed a hectic activity in the northern part of the North Sea. Many oil and gas fields have been discovered, most of them along the borderline between the British and Norwegian sectors. (Figure 1) Several of the fields are now being developed and the Ekofisk field alone is already producing enough oil to cover Norway's producing enough oil to cover Norway's total petroleum consumption. Most of the fixed platforms installed have been the pile-supported steel jacket type, as developed in Lake Maracaibo and in the Gulf of Mexico. However, new types of structures have been developed, those today commonly known as gravity structures, i.e. structures sitting on the sea bottom by their own weight with no anchors or pile support.

The first gravity structure installed in the North Sea was the Ekofisk Tank in the summer 1973. It was a one million barrel oil storage, concrete tank designed by C.G. Doris (Figure 2).

Two years later, in the summer of 1975, three concrete drilling platforms were installed, Beryl A and Brent B, both the Condeep type designed by A/S Hoyer-Ellefsen and Frigg CDPL, another Doris design. At the moment there are 9 more concrete platforms under construction in the countries surrounding the North Sea (Doris 2, Andoc 1, Sea Tank Co. 3 and Condeep 3).

First of all because of the water depths and the hostile weather conditions in the area, the dimensions are huge compared to on-shore structures.
Multiphase Boosting Technology - The Journey so Far in Shell Nigeria
Authors: Nwadei A.C. , Stam T. , Nwashike O.T.
Published: December 2007

This paper was prepared for presentation at the 23rd Annual SPE International Technical Conference and Exhibition held in Abuja, Nigeria, 4–6 August 1999.
Environmental Aspects of Offshore Disposal of Drilling Fluids and Cuttings
Authors: McAuliffe C.D. , Palmer L.L.
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.

This paper was prepared for the Improved Oil Recovery Symposium of the Society of Petroleum Engineers of AIME, to be held in Tulsa, Okla., March 22–24, 1976. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and with the paper, may be considered for publication in one of the two SPE magazines.

Concern has recently been expressed that the discharge of drilling fluids and cuttings from offshore oil and gas exploration and production wells may cause adverse environmental effects. Laboratory studies using various organisms show these materials to generally be relatively nontoxic. Rapid dispersion and dilution, measured during discharge of drilling fluids and cuttings to seawater, explain the lack of long-term effects in areas with 20 to 40 years of petroleum operations. This indicates that offshore discharge is an environmentally acceptable method for disposal of drilling wastes.

Introduction

During the drilling of offshore exploration and production wells, drilling fluids and cuttings are usually discharged to the surrounding waters. This practice was followed at most of the 19,000 or more wells drilled to date in U.S. coastal and offshore waters.

With the accelerated OCS leasing program, concern has been expressed by program, concern has been expressed by some as to possible adverse effects of such discharges on marine life.

In this paper we review brieflydrilling practices,the composition of drilling fluids,bioassays conducted by Chevron Oil Field Research Company on selecteddrilling fluids,bioassays on drilling fluids and their components as reported in the literature,observations of marine life and measurements for chemicals and turbidity made during cuttings and fluids discharges,observations of marine life in areas where drilling has occurred for long periods of time, anda comparison of fluid and cuttings discharges with sediment inputs from rivers and storm-resuspended near shore and sea bottom sediments.
Acid Stimulation Studies in Simulated Radial Flow Conditions: Laboratory Results Compared With Field Data
Authors: Kotlar Hans Kr. , Hove Arvid O.
Published: December 2007

Most laboratory tests for qualification of acid stimulation treatments are performed in traditional core flow experiments. A single core, with all treatment fluids flowing through the core, in laminar flow pattern is used.

By such set ups the contact time to the matrix and the residence time of the spending acids will not be matched with the actual field conditions. Thus, it will be difficult to reproduce possible secondary and tertiary reactions. Such reactions might prove to be very important, especially in "dirty" sand with high clay content.

A survey done in the industry reveals that 1/3 of all acid stimulation jobs fail. This is due to various reasons. i.e. incorrect acid formulations as well as pumping schedule procedures, improper placement, specific field related problems with cross flow, etc.

The present paper reports on the first experiments in acid treatments using a multi-core set up simulating radial flow conditions. Furthermore, this is done in combination with two-phase flow.

These experiments are using actual pumping and treatment schedules from the Gullfaks field. The results are compared with the actual field data.

The spent acid flow back, representing the total acid injection volume, is analyzed for dissolved elements and the treated cores are inspected by environmental scanning electron microscope (ESEM).

Tangible evidence gives indications that secondary and tertiary reactions can be detected by this method.
The Near-Well State of Stress and Induced Rock Damage
Authors: Nikolaevskiy Victor N. , Economides Michael J.
Published: December 2007

High-stress concentration and substantial weakness of loosely consolidated to unconsolidated petroleum formations may cause considerable mechanical damage both during the drilling and the subsequent reservoir fluid production. Damage in our context is the appearance of a cloud or swarm of rock defects (microcracks) and the opening or, even, closing of preexisting pores or cracks. A physically and conceptually adequate idea is the mathematical modeling of the phenomena using an elastoplastic approach, which accounts for stress-sensitive matrix failure and solid/mass movements. Volume deformation because of dilatant interaction with shear is also accounted for.

Damage is characterised by the increase of a zone of plasticity augmented by internal-to-the zone phenomena. The emergence of plasticity does not necessarily mean total formation failure or loss of wellbore stability. Such a conclusion can be drawn only with the determination of displacement (i.e., strain) fields. Because problems such as the ones envisioned here are complex and their tracking depends on a number of parameters, computer modeling is necessary along with, at times tedious, laboratory determination of rock parameters. In the absence of measurements, published "typical" data for similar rocks can be used. The parameters include initial porosity and pore pressure, permeability, the elastic moduli, cohesion, and the friction and dilatancy coefficients, which change with changing stress. Problems described in this paper include the near-well damage effects because of high stress anisotropy and pore collapse. In this case local strains are determined. A second problem that is considered is the impact of well curvature and deviation from the vertical and the effects of crossing layers. Finally, sand production and some thoughts on water-shale interaction during drilling are addressed.
Constitutive Law for Permeability Evolution of Sandstones During Depletion
Authors: Boutéca M. J. , Sarda J-P. , Vincké O.
Published: December 2007

Permeability changes have been measured during triaxial tests performed on two sets of Vosgian sandstones. The obtained results led to the definition of a criterion in the p’-q plot (effective mean stress – deviatoric stress) for the evolution of permeability. Inside the domain defined by the criterion, the permeability change is nil or small whatever the loading path is. The results are generalized in a normalized p’*-q* plot. The normalized stresses p’*-q* were previously defined by Wong et al., and depend on the onset of grain crushing under hydrostatic loading. We suggest herein a simpler way to determine the normalizing stress. Furthermore, the experimental results are interpreted to propose an explicit law for the evolution of permeability as a function of the stress path.
Cavity-Like Completions in Weak Sands
Authors: Palmer Ian D. , McLennan John D. , Vaziri Hans H.
Published: December 2007

This study is about when, where, and how to implement an advanced completion technique, based on deliberate sand production, in order to induce "cavities" that increase productivity of a well (a "cavity" can be a void, or an enhanced perm zone of disaggregated sand). The concept spans the spectrum of well life, from a cavity as the initial completion, to managing sand flowback in mature wells. Folds-of-increase (FOI) in the range 3–20 have been found in field applications. This compares with FOI of 2–5 after hydraulic fracturing. In certain field cases, sand does stop coming into the well as the cavity stabilizes. A strong enough caprock (overburden material) is a key to the success of cavity completions in some unconsolidated formations in the field. Two kinds of laboratory tests have been conducted: (1) centrifuge tests in unconsolidated sands with low stresses, (2) large block tests in weakly consolidated sands, with more realistic stresses. In both cases, allowing sand to flow increased the productivity of the well by several fold, and the cavity geometries provided insights into what may happen in the field. The work has also included evaluations of subsidence and casing stability, due to sand production. Also, a model has been created to optimize a cavity completion by calculating the productivity increase (PI), stability of cavity, and sand disposal costs, all as a function of volume of sand removed. The results herein have implications for other business areas: eg, sand management; increasing injectivity for injection wells; and underbalanced drilling, perforating, surging applications.
Viscosification of Oilfield Brines: Guidelines for the Prevention of Unexpected Formation Damage
Authors: Javora P. H. , Ali S. A. , Bowen K. D.
Published: December 2007

Polymer viscosified oilfield brines have been accepted by the industry and routinely used to transport sand in gravel pack applications, to control fluid loss to the formation, and in other oilfield applications. However, recent observations of precipitate formation from heat aged viscosified brines indicated that the thermal stability of viscosified oilfield brines can vary dramatically. Variations were observed not only for the same polymer in different oilfield brines, but also for the same polymer from a different source in the same brine, and even for the same polymer in different concentrations of the same brine.

This paper details the systematic study conducted to identify and map the safe operating environments for selected oilfield polymers used to viscosify standard oilfield brines. Polymer viscosified brines were prepared by standard procedures, and statically heat aged at prescribed temperatures. The clarity of aged samples, including precipitation and separation tendencies, retained viscosities, and return permeability measurements were used to determine thermal stability. Systematic polymer-brine composition-temperature relationships were observed, and certain combinations were found to be a significant source of unexpected polymer precipitation and formation damage.

Results from this study provide the basic guidelines for the selection and field application of polymer viscosifiers for oilfield brines presented in this paper. Details concerning the viscosification process, its impact on TCT (True Crystallization Temperature), and the viscosification of zinc based brines are outlined. A two step viscosification process for brines containing low zinc concentrations is presented.
Factors Affecting the Performance of Enzyme Breakers for Removal of Xanthan-Based Filter Cakes
Authors: Luyster Mark R. , Monroe Terry D. , Ali Syed A.
Published: December 2007

The use of enzymes as an external breaker for removal of xanthan based filter cakes has exhibited cost savings and effective clean up in several open-hole horizontal Gulf Coast wells.

Enzymes are specialized proteins produced by cells of living organisms. They act as catalysts to promote specific reactions. Polymer-specific enzymes hydrolyze xanthan resulting in non-damaging fragments. As a catalyst, the structure of an enzyme is unchanged by the reaction it promotes; therefore, the enzyme has the ability to initiate another reaction. The reactivity of the enzyme is essentially infinite with the exception of damage to the enzyme by chemical, thermal, or mechanical means, i.e. denatured. Xanthan-specific enzymes degrade or cleave either the α – 1,2 or β – 1,4 glycosidic linkages of the substituent and the β – 1,4 linkages of the backbone.

Recent laboratory investigations revealed several factors, which can control the effectiveness of an enzyme. These factors include xanthan quality, iron, base brine and hydrocarbons. These factors can function as barriers and prevent the enzyme from cleaving specific linkages of the xanthan structure.

This study presents guidelines for formulating an enzyme compatible xanthan based drill-in fluid for open-hole horizontal completions. These guidelines were recently applied to two recent open-hole horizontal completions in the Gulf of Mexico that yielded optimum results.
Investigation of a Long-Term Cement Deterioration Under a High-Temperature, Sour Gas Downhole Environment
Authors: Krilov Z. , Loncaric B. , Miksa Z.
Published: December 2007

The indications of cement deterioration at one of the greatest gas condensate fields in Pannonian basin (Croatia) was the motivation for research study carried out in order to investigate the possible involved mechanism of impairment. After almost 15 years of hydrocarbon production form naturally fractured carbonates, some wells begun to suffer of plugging across the perforated zone with unidentified debris, which was accompanied with water cut increase.

This paper describes the laboratory evaluation of the actual environmental downhole impact (high reservoir temperature, BHST > 180°C, sour gas: 22% CO2 and 150 ppm H2S) to the cement, as well as debris identification.

The work indicated that oilwell cement under hostile downhole conditions after long-term exposure could be deteriorated loosing of compressive strength and its integrity. The dominant mechanism of cement deterioration is caused by CO2 corrosion process in the form of carbonic acid leaching.

The CBL log data verified the cement disintegration behind 7-in. casing after 15 years of well production period.
Gravel-Pack Evaluation Using a Memory Gamma-Gamma Density Tool
Authors: Fisher Kevin , Kessler Calvin , Rambow Fritz , Tucker Charles , Madigan William
Published: December 2007

Completions in poorly consolidated formations often require gravel packing or frac packing to eliminate the inflow of formation fines. The effectiveness of gravel placement in the screen-casing annulus or openhole annulus or behind casing (such as when prepacking perforation tunnels) may be qualitatively evaluated with treatment-pressure data. Voids in the gravel-packed screen-casing or openhole annulus are evaluated with data from density, neutron, gamma-tracer, or pulsed-neutron logs. When radioactive materials are used for evaluating proppant placement in the formation, however, gamma measurements are affected by the background signal produced by these materials. This signal makes conventional density and pulsed-neutron silicon-activation techniques ineffective. A high-resolution, memory gamma-gamma density logging tool has been developed that measures changes in the bulk density of the annular region of a gravel-pack completion. The source-to-detector spacing and source strength have been optimized to minimize the effects of variations in borehole fluid and of changes in casing-screen size and geometry. Most importantly, this measurement will not be affected by the presence of radioactive tracers used to evaluate proppant placement.

The new memory-based logging system allows the tool to be placed in the washpipe prior to the completion and for the logging pass to be recorded as the washpipe is retrieved from the well. Significant savings in rig costs and in time to production are gained through use of the washpipe-conveyed memory logging technique. This paper reviews the measurement principles of the tool and presents data from tests in calibration pits.
High-Pressure Water Jetting: An Effective Method to Remove Drilling Damage
Authors: Aslam Javed , Alsalat Talib
Published: December 2007

High-Pressure Water Jetting (HPWJ) has been used for decades for various industrial applications. The major uses of this technology have been to clean the various surfaces, as well as demolishing or cutting different materials. The process has been used in oil and gas wells to clean tubulars from deposits of asphaltene, paraffin, and common inorganic scales e.g. calcium and magnesium compounds. These scales are usually very hard and difficult to remove by chemical methods. By utilizing abrasive materials such as sand and beads, the process has been used to cut steel pipes or make perforations.

In recent times, drilling technology has revolutionized the shape of the wells. Most of the new wells are drilled in a horizontal direction across the reservoir thus exposing a relatively large reservoir area for drainage or injection. Majority of the new wells is completed ‘bare-foot’ i.e. without cementing a casing or a liner. As the horizontal wells have usually long open holes, the use of conventional acidization to remove drilling damage requires large volumes of acid. As a result acidization is very expensive. The acid utilization is very inefficient as most of the acid leaks into ‘thief’ zones.

In an effort to reduce the cost of damage removal in long horizontal open holes, Qatar General Petroleum Corporation (QGPC) has utilized HPWJ technology to remove the drilling damage. The treatment has been applied to more than 10 horizontal wells to date and it has been found to be very successful. The process is simple to use because the only consumable is water. Service costs are minimal as the pumping equipment of the rig is utilized for the treatment. This paper covers theoretical aspects of the HPWJ technology, case histories and well performance data.
Through-Tubing Gravel Packs Performed by Electric Wireline–Case History
Authors: Rice R. T. , Navaira G. , Champeaux G.
Published: December 2007

A high success rate has been seen on twelve through-tubing gravel packs performed with a unique electric wireline technique. This paper is a case history and analysis of these jobs.

The method is primarily designed for zones with marginal reserves, which cannot justify costs of more conventional TTGP techniques. The case study shows that this method is profitable for these marginal zones and also higher reserve zones with certain criteria.

The paper discusses the selection criteria, pros & cons of this method, and lessons learned.

Several of the wells have bottom-hole pressure survey data, the results and implications being presented in the paper.
Perforating Requirements for Sand Prevention
Authors: Venkitaraman A. , Behrmann L. A. , Noordermeer A. H.
Published: December 2007

Sand prevention implies an acceptable risk of sand production over the producing life of the well with no sand control mechanisms implemented. This paper reviews available methods to optimize the choice of perforation parameters (phasing, shot density and charge type) for sand prevention. Prior work has shown that sand production is preceded by failure of the perforation tunnels. In order to have successful sand prevention it is necessary to have stable perforation tunnels through rate (drawdown) changes, depletion, and water-cut. Available methods to determine the ability of perforation tunnels to produce sand free can be classified into theoretical models, experimental methods and historical techniques.

Deep penetrating charges are recommended as they produce smaller diameter perforation tunnels that are more stable than larger diameter tunnels produced by big hole charges. Optimum phasing technique relies on the maximization of distance between adjacent perforations in 3-dimensional space for a given wellbore radius and shot density. This is advantageous in avoiding inter-linking of failed zones around adjacent perforations. Data from the Magnus field in the North Sea supports the use of these two techniques in minimizing sand production. Where there are significant stress contrasts in the formation and the directions are known, oriented perforating can be used to increase the stability of perforation tunnels (especially when increasing drawdown and when depleting the reservoir).

It is shown how these three main techniques can be used to perforate for sand prevention. In addition, the paper also provides guidelines on how to avoid sand production at the time of perforation, selective perforating where there is a contrast in formation strength with depth and the use of experimental techniques to determine perforation stability due to rate (drawdown) changes, depletion and water-cut.
Use of Micronized Cellulose Fibers to Protect Producing Formations
Authors: Verret Robin , Robinson Buck , Cowan Jack , Fader Philip , Looney Mark
Published: December 2007

Micronized cellulose fibers have become widely used for seepage loss control on a worldwide basis, in almost every type of drilling fluid system. Cellulose fibers have demonstrated the unique characteristic of quickly forming a seal at the formation face preventing entrance of damaging fluids or solids into producing formations.

The use of cellulose fibers has been restricted in producing formations because of their general lack of acid solubility. However, it has been demonstrated that cellulose fibers are highly soluble in strongly alkaline solutions. These alkaline removal solutions have proven to be as effective in removing cellulose fibers as conventional acid is in removing calcium carbonate. In addition, some of these alkaline solutions have been shown to increase the permeability of certain types of formations, particularly those involving shales and clays.

One major concern with the use of cellulose fibers in gravel pack or screened completions is the question of their flowback through gravel packs and the backside of the screen during completions.

This paper details experimental work that demonstrates: (1) the quick sealing characteristic of low concentrations of cellulose fibers as compared to conventionally used calcium carbonate, (2) the alkaline solubilization of cellulose fibers in a simulated gravel pack or screen completions, (3) the non-damaging aspect of cellulose fibers in gravel pack or screened completions, and (4) a discussion of the factors involved in using alkaline removal solutions versus conventional acids. This paper is an extension of early work on the alkaline solubilization of fibers discussed in SPE 38272.
Discrimination of Natural Fractures from Drilling-Induced Wellbore Failures in Wellbore Image Data—Implications for Reservoir Permeability
Authors: Barton Colleen A.
Published: December 2007

Natural fractures and drilling-induced wellbore failures provide critical constraints on the state of stress in situ and direct applicability to problems of reservoir production, hydrocarbon migration, and wellbore stability. Acoustic, electrical, and optical wellbore images provide the means to detect and characterize natural fracture systems and discriminate these from induced wellbore failures. We present several new techniques to measure and characterize attributes of natural and induced fractures in borehole image data. These techniques are applied to the characterization of fracture permeability in two case studies.
Flow Characterization--Critical for Efficiency of Field Operations and IOR
Authors: Campanella J. D. , Wadleigh E. E. , Gilman J. R.
Published: December 2007

Operational efficiency in highly heterogeneous (channelized or fractured) formations requires unique characterization methods. Reservoir characterization often is performed in sequence: 1) build the static 3D geologic model, 2) generate the saturation governing inputs (capillary pressure, relative permeability curves and PVT data), 3) upscale, and 4) modify the upscaled model to "history match" the dynamic performance data. There has been much recent emphasis on upscaling the static model to preserve appropriate heterogeneity within the simulator; however, during the history match the upscaled model may be substantially altered. This paper describes an alternative approach of incorporating both static and dynamic information at the beginning of the reservoir characterization process. This approach decreases both the modifications to the geologic and saturation inputs and the time required for history matching.

This paper provides an example from the Marathon operated Yates Field showing how flow data compiled by well, area, and total reservoir was used to assess the large scale "plumbing" of the reservoir. Tools developed for 3D geologic modelling have been deployed to distribute the connected secondary-porosity flow features (caves, solution-enhanced fractures, connected vugs, etc.) and barriers. Static geological data from the well scale is honored along with deterministic large-scale flow characteristics. These identified large-scale flow enhancements and barriers were incorporated into field operational planning and simulation construction early in the characterization process. The characterization efforts have lead to improved workover success in the Yates Field. Simulation and Yates Field examples demonstrating the value of simultaneous static and dynamic characterization are provided.
Joint Inversion of MWD and Wireline Resistivity Measurements
Authors: Chunduru R. , Mezzatesta A. , Meyer H. , McWilliams S. , Zhang Z. , Busch R.
Published: December 2007

Traditionally, measurement-while-drilling (MWD) data are used primarily for geosteering purposes and drilling decisions such as monitoring of hole direction, deviation, and delineation of abnormally pressured zones. Wireline resistivity measurements, galvanic and induction, play a fundamental role in identifying and delineating oil- and gas-bearing formations. The availability of both MWD and wireline data at different times not only provides the interpreter with abundant information about subsurface formations but also poses a new challenge to generate a unique model(s) that better explains both data sets. Generally, MWD and wireline data are interpreted independently to estimate formation resistivities that may result in inconsistent earth models. In this study, we performed a joint inversion of MWD Multiple propagation resistivity (MPR), and wireline High Definition Induction log (HDIL) data to come up with an earth model that best explains both the data sets. An inversion strategy using a dual earth model, that describes the appropriate logging conditions of both wireline and MWD was also used in the inversion. Finally, the proposed algorithm was implemented on synthetic and the Gulf of Mexico data examples, and the results were compared with conventional MPR and HDIL processing results.
Transitory Criteria for Design and Requalification of Submarine Pipelines in the Bay of Campeche
Authors: Valdés V. M. , Lara L. , Bea R. G.
Published: December 2007

Hurricane Roxanne is marked in the history of Bay of Campeche as one of the most severe storms that hit the zone during this century, and therefore questioned the validity of the design criteria applied at that time. As a consequence, a newborn own risk based criteria was developed for design and assessment of submarine pipelines and platforms in Bay of Campeche. Petróleos Mexicanos (PEMEX) and Instituto Mexicano del Petróleo (IMP) developed and issued such criteria in 1998, named Offshore Pipeline Transitory Criteria. The Transitory Criteria is based on risk assessment and management approach.

It is intended in this paper to show the result obtained so far of that development. Safety and serviceability categories for pipelines are defined. Safety factors for design and reassessment of wall thickness by internal pressure are determined based on risk approach. Practice recommendations for the design and requalification for hydrodynamic stability of submarine pipelines and risers are established. Safety factors for hydrodynamic stability are obtained following this criteria, and oceanographic characterization of the Bay of Campeche are presented in easy-reading charts for design and requalification.
Drill-In Fluid Selection for High-Temperature, Sour Gas, Naturally Fractured Reservoirs
Authors: Krilov Z. , Domitrovic D. , Soric T. , Gracanin M.
Published: December 2007

The paper is based on laboratory research and field evaluation data incorporated in a study carried out to select a suitable drill-in fluid for use in naturally fractured HTHP sour gas reservoirs. Laboratory results were verified by monitoring drilling process and initial production of a particular well located at the gas condensate field in SW Pannonian Basin, Croatia.

Production zone, naturally microfractured limestone (21% porosity, 2 md matrix permeability) at 2500–2600 m (BHSTI150°C) was left openhole. Reservoir fluid contains 53% CO2 and 800 ppm H2S.

Two aspects of a drill-in fluid evaluation were considered: optimal drilling process performance, complicated by harsh reservoir conditions; and minimizing formation damage of plugging susceptible microfracture system.

Drilling data, using the selected drill-in fluid, showed a good ROP and borehole stability. Production tests after well completion indicated no damage.

Even under extreme downhole conditions, the balance between optimal drilling performance and minimal formation damage could be achieved using described laboratory testing procedure.
Numerical Modeling of a Large, Naturally Fractured Oil Complex
Authors: Gurpinar O. , List D. F. , Kalbus J.
Published: December 2007

The large, naturally fractured reservoir under investigation is unique with its highly heterogeneous carbonate characteristics. The largest hydrocarbon bearing formations are not only naturally fractured, but also have matrix and vuggy porosity. Special relative permeability, capillary pressure, and compressibility relationships were developed to simulated multi-phase flow in this triple porosity system. Well and interference tests were re-analyzed at several stages in the project to provide input to geology on fracture properties and later to condition the fracture properties coming from the geologic model. The calibrated model acceptably matched the historical pressure and the production of oil, water, and gas for the reservoir complex.
Evaluation of Horizontal Well Production
Authors: Leon-Ventura R. , Gonzalez-G. G. , Leyva-G. H.
Published: December 2007

When drained volumes want to be increased or to reduce investments with additional drilling wells, we can use horizontal wells as a good alternative for optimum exploitation of the oilfields. This is supported because the horizontal wells productivity becomes higher than in a vertical, due to that they communicate a large area of the producing formation, cross natural fractures, reduce pressure drops and advances of water-oil or gas-oil contacts are delayed.

In Mexico, several horizontal wells have been drilled in different kinds of formations, which initially have responded with production expectantions. However, after a short production time, productivity conditions have been reduced significatively, which have practically condemned the use of this technology in the development of hydrocarbons exploitation.

Therefore, in this work a comparative evaluation of the initial productivity of horizontal wells with respect to vertical wells is made to know their behavior and to identify design parameters that govern the feasibility of obtaining successful horizontal wells.

Analysis of horizontal wells on Agua Fria, Cantarell and Abkatun fields (North, Northeast Marine and Southwest Marine Regions, respectively) are included in this study.
Abkatún-Pol-Chuc Integrated Study: The Value of Information
Authors: Rosales A. C. , Sánchez A.
Published: December 2007

This paper shows the methodology and results from the Integrated Study performed to the Abkatun, Pol and Chuc Reservoir Complex. These three fields, account for the largest light oil reserve in the Gulf of Campeche. Proven communication through the associated acquifer established the need of grouping the three fields in one simulation model.

The main producing formation is a fractured, vuggy carbonate breccia. The complex nature of porosity in the Breccia, received a special treatment. Vug percentage and vug connectivity maps were created to properly distribute vug porosity into matrix and fracture systems. Based on special core analysis and core flooding simulation, relative permeability and capillary pressure pseudo curves were developed to mimic the flow in the composite matrix + vug system.

Emphasis is made to show that this study is the result of a sustained effort to acquire data throughout the life of the reservoirs, its analysis and interpretation by geoscientists, reservoir, production and facilities engineers.
New PDC Bit Technology and Improved Operational Practices Saves $1M in Central North Sea Drilling Program
Authors: Mensa-Wilmot Graham , Booth Martin , Mottram Andrew
Published: December 2007

The improved performances of Polycrystalline Diamond Compact (PDC) bits have increased their acceptance in the industry as efficient drilling tools. In addition to drilling faster and longer, tremendous gains have also been made in performance consistency and predictability, especially in medium hard and homogeneous formations.

However, the performance of PDC bits in hard, abrasive, heterogeneous or multiple formation intervals leaves much to be desired. Although industry efforts have focused on the development of technologies and products to improve performance in these challenging environments, the results have lacked consistency, especially when bigger hole sizes are drilled.

This paper will describe the work done to identify the causes of PDC bit inefficiency in these demanding applications. It will describe the developmental concept and optimization cycle of a specialized PDC bit that was developed to address the challenges of hard, abrasive and heterogeneous formation drilling. Finally the paper will show how operational efficiency was improved, and the associated cost savings that were accrued as a result of the improved technology and processes.
The Blowout at CHK-140W
Authors: Grace Robert D. , Cudd Bob , Chen Jui-Shiang
Published: December 2007

The CHK Gas Field, located approximately 2 hours south of Taipei, is one of the largest and oldest gas fields on the island of Taiwan. Beautiful, steep mountains covered with dense jungle like growth characterize Taiwan. Average annual rainfall is high. Landslides are common. As a result, drilling locations are small, confined to the valley floor, have limited access and are in very close proximity to the general population.

The CHK-140W was dually completed in 1993 with a combined open flow potential of approximately 22 mmscfpd. During routine production in July 1996, the CHK-140W blew out at the surface. The primary broach was approximately 25 meters from the wellhead. By December of 1996, surface recovery operations by the original well control contractor included several failed kill attempts. A new prime contractor was selected. Surface recovery operations were resumed in early March 1997. A new recovery plan was adopted involving challenging snubbing objectives and innovative fluid dynamics.

Several airplane loads of equipment and materials were air lifted to Taiwan. The CHK-140W was successfully controlled on 21 May 1997 according to plan and procedure. The success of the project is a tribute to the cooperation between the employees of the Chinese Petroleum Corporation and her international service providers.
Simultaneous Drill and Case Technology-Case Histories, Status and Options for Further Development
Authors: Hahn Detlef , Van Gestel Wilhelmus , Fröhlich Norbert , Stewart Glenn
Published: December 2007

Drilling liner technology has become a standard for entering depleted reservoirs in areas of the North Sea and Southeast Asia and interest continues to increase for use of drilling liners to overcome other drilling problems. Marketing analyses have shown that further development of drilling liner technology and application has been rated with high priority.

Based on experience gathered during the last five years, this paper covers possible further Drilling Liner applications, new challenges, and requirements for new systems. "Drill and Case" systems will be introduced and benefits shown by means of case histories of jobs carried out in Norway and Indonesia.
High-Power Slim-Hole Drilling System
Authors: Cohen J. H. , Leitko C. E. , Long R. C.
Published: December 2007

Recent field tests showed that a reliable high-power slim-hole motor developed for the U.S. Department of Energy (DOE) drills twice as fast as conventional systems. This slim-hole drilling motor has the potential to significantly reduce drilling costs by reducing drilling time, mud, cementing and casing costs and minimizing environmental impact. The DOE slim-hole drilling system consists of a double-length, high-power PDM motor that delivers twice the torque and power of conventional motors, and hybrid PDC/TSP bits that can operate at these high power levels. Laboratory dynamometer and drilling tests confirmed the high-power output of the motor while field tests conducted at the GRI Catoosa test facility in Oklahoma showed that these motors drill twice as fast as conventional motors. These motors should stimulate increased use of slim-hole drilling while taking advantage of the resulting 30 to 50 percent cost savings associated with these smaller diameter wells.
Central Graben Extreme Offshore High-Pressure/High-Temperature Cementing Case Study
Authors: North John , Brangetto Martial P. , Gray Elizabeth
Published: December 2007

This paper presents the cementing case histories of six wells in two offshore high-pressure, high-temperature (HPHT) fields in the Central Graben area of the North Sea. Well depths averaged 6000 m true vertical depth (TVD), temperatures were greater than 200°C, the fracture/pore-pressure margin was small, and the bottomhole pressure exceeded 1,100 bar. The well deviation varied from near vertical to a maximum of 35°. These downhole conditions are the most extreme yet experienced in a field development in the North Sea.

Because of the extreme HPHT conditions, all aspects of cementing operations had to be carefully evaluated. In addition, new and enhanced equipment, processes, and materials had to be developed. Even though the potential for gas influx of the cement was high, the cement slurry formulation and placement techniques for resisting gas migration were successfully designed through the use of materials with a low environmental impact. Because the formations were weak and unconsolidated, a special cement blend was used at the top of the well. The mixing equipment was modified to withstand the high-density fluids required for the liner section.

For job success, both a well-defined top-of-cement (TOC) and good casing support had to be obtained without exceeding the allowable equivalent circulating density (ECD) limit. Therefore, effective mud displacement, correct slurry placement, and precise rheology measurement were required.

No remedial HPHT cementing operations were necessary during these operations, which was an important objective. Remedial operations could have posed extreme risks and high associated costs.

This paper describes how the cementing process was optimized for HPHT field development, thereby minimizing risk and costs. Considerable emphasis is placed on the production liner cement job, because it was the most critical string on the well.

Improvements to equipment, slurry testing, placement, and bond logging procedures are also described.
Anglia In-Fill Drilling Campaign: Drill-In Fluid Design and Application
Authors: Marshall David S. , Haywood David
Published: December 2007

The Anglia gas field was originally developed in the late 1980s with the first wells being drilled with mineral oil-based mud in the reservoir sections. In most cases, production from the original wells was below expectation and only five years later, plans were being made to re-develop the field in order to maintain its economic viability as a gas producer, and meet gas delivery commitments. Well-bore placement and drilling fluid selection were determined to be critical factors in ensuring the success of planned in-fill wells. This paper reports on the planning and testing which was conducted during the selection of the drilling fluid for the reservoir phase of the new wells, changes in drilling practice and the subsequent production obtained from utilising this new approach, in comparison to the production from the original wells. Reasons for the poor production from the first phase of the development are discussed. Due to the more complex trajectories and longer well-paths required by the well design team, additional difficulties were created for the drilling fluid, notably that of lubricity. Further testing is described in the paper, where the best combination of good lubricity and minimal formation damage was sought. Final production data on three wells drilled during 1997-9 are reported. The overall experience confirms that a detailed drilling fluid selection process which takes into account key reservoir-specific factors, combined with a holistic approach to the drilling and completion of the reservoir section of a well can significantly enhance its resultant productivity.
A New Selective Lateral Re-Entry System
Authors: Rivenbark W. Mark , Al-Sowayigh Mohammed I. , Al-Furaidan Yousef A.
Published: December 2007

Since the mid-1990's, a major Middle Eastern operator has been exploiting short-radius horizontal technology to maximize oil recovery from existing wells. Although the use of this technology has resulted in significant production increases, the operators recovery efforts were somewhat hampered by not having through-tubing access to the short-radius lateral. This problem has been solved with the introduction of a new selective lateral re-entry system.

Short-radius recompletion involves reentering an existing well, opening a window through the casing, and recompleting the well as a horizontal well within 100 ft (lateral displacement) of the re-entry point. This technology is typically used in wells that still contain zones with thin oil columns in place but are no longer able to flow because of high water cut. In wells in which this technology has been applied, production rates have generally been higher, water cut has been reduced, and recovery has improved.

The new system allows for re-entry into the lateral via wireline or coiled tubing. Utilizing isolation and commingling sleeves, the operator can control production from both the main bore and the lateral. Re-entry whipstocks (deployed by wireline or coiled tubing) allow logging, acidizing, and any other coil tubing intervention to be accomplished in the lateral with relative ease.

This paper describes the deployment and operation of the new system and presents field examples of its use. The paper also discusses applications under development that will require entry into multiple laterals within the same main bore.
Feedback Is Not Enough - An Innovative Safety Culture Improvement Case Study
Authors: Richardson Ross , Watkiss Richard , Brown Megan
Published: December 2007

Having a positive Safety Culture is central to good health and safety management. It is an indication of an organisation's determination and competence to control hazards at work. This paper describes an innovative project undertaken both to measure and to improve Safety Culture within a platform drilling contractor operating in the North Sea.

In this context, safety culture is defined as ‘the product of individual and group values, attitudes, perceptions, competencies and patterns of behaviour that determine the commitment to, and the style and proficiency of, an organisation's health and safety management’.

The project in itself was innovative, not in that the company recognised the problem and sought to assess it through the use of a Safety Culture survey, but that they also committed to using their entire workforce to help solve or improve upon issues highlighted by the survey. The process used in this project is one that other drilling contractors and operators within the Oil and Gas Industry should consider as a method for developing solutions to break the safety cycle and achieve continuous safety improvement.

This paper describes the process of assessment and the results obtained. The successes and pitfalls of the approach and project are discussed in an attempt to guide others through the process.