bluuebunny/crossref_metadata_2025 huggingface dataset:
The Role of Open Hole Memory Logging and Wireless Conveyance Systems in the Evaluation of Horizontal Wells
Authors: Elkington Peter A S
Published: December 2007

Open hole formation evaluation logs are not run where the perceived benefits are marginal. In many horizontal wells, the benefits are not fully assessed because cost and/or access difficulties override other considerations. In these cases, sub-seismic lateral variations in reservoir properties can only be inferred - they are rarely measured. Small diameter battery-powered logging tools operating without a wireline have collected high quality data in a broad range of high angle situations. Wireless conveyance techniques are faster and safer than wireline pipe conveyed logging, and have cost, access and data quality benefits over logging while drilling (LWD). Wireless tools have been conveyed in and on drill pipe, on coiled tubing without an electric line, and as part of a modified casing string. The tools can be deployed safely in underbalanced wells.
How Can Horizontal Wells Help in Naturally Fractured Reservoir Characterization?
Authors: Mazouzi A. , Deghmoum A. , Azzouguen A. , Oudjida A.
Published: December 2007

Information obtained from testing horizontal wells is very useful in reservoir characterization, in this paper the experience of horizontal wells in the gas reservoir of TIN FOUYE TABANKORT (TFT), Algeria is illustrated, as well as the contribution in characterizing natural fractures.

The transient response (Build Up) of two horizontal wells were simulated, the two short radii TFT#z329 (400m), and TFTz#333 (200m) were drilled in the same azimuth the numerical match yields to the following permeability tensors: well TFTz#329 (Kx = 2 md, Ky = 90 md, and Kz = 110md), and well TFTz#333 (Kx = 5 md, Ky = 100 md, and Kz = 115 md).

The permeability tensors obtained correspond to a configuration indicating a plan of oriented fractures. The wells have been drilled perpendicular to the fractures. The matrix permeability is K matrix = 5 md and the fractures permeability K fissures = 100 md . these results were confirmed by the imagery (FMI, ARI) run in both wells. Laboratory tests on cores of vertical wells confirmed these results and gave the fractures permeability K fractures = 70 md.
Using Horizontal Gravel-Packing Technology to Optimize Well Productivity and Field Economics: Case History, Uracoa Field, Venezuela
Authors: Benavides Simon P. , McKee John Paul
Published: December 2007

This paper summarizes the evaluation and effects of completion alternatives on the productivity and economics concerning the redevelopment of the Uracoa field in Southern Monagas, Venezuela. It explains how horizontal gravel pack technology restored well productivity and improved longevity. Production from the Uracoa Field consists of heavy crude ranging from 11° to 16° API. The initial redevelopment completion scenario used horizontal wells with slotted liners in open hole. However, subsequent breakthrough of water caused catastrophic sand production that plugged the wells where slotted liners were implemented. In order to produce the Uracoa Field economically, it was necessary to perform a technical evaluation of in-field completion and drilling practices to resolve production issues for sand control, high CO2 production, 13-14% asphaltene content, well productivity, and well longevity.

After evaluating completion and drilling practices, horizontal gravel packing technology was used to restore well productivity and longevity. In order to achieve optimum productivity, it was necessary to do extensive fluids compatibility testing to determine the overall best drilling and completion practices. To date, over 65 horizontal wells have been gravel packed in conjunction with a large number of highly deviated wells. These gravel packs make use of water-packing techniques and maintain higher productivity even after water breakthrough.

The paper reviews completion and well experience with slotted liners, evaluates completion practices, and compares completion technologies implemented in the Uracoa Field to achieve economic productivity. Finally, data presented demonstrates the ability to maintain productivity even after water breakthrough.
Multilateral Pressure-Transient Response
Authors: Yildiz Turhan
Published: December 2007

This study presents a 3D analytical model to analyze the transient flow into multilateral horizontal wells. The model considers arbitrary phasing angle, selective lateral completion, non-uniform formation damage around each lateral, and areal and vertical permeability anisotropy. Using the model, transient pressure, derivative, and rate distribution characteristics of multilateral horizontal wells are investigated. Flow regimes are examined. Asymptotic approximations for each flow regime and pseudoskin equation are provided.

A sensitivity study is carried out to identify the parameters controlling the transient pressure, derivative, and fractional rate responses. The sensitivity study includes the impact of lateral length, orientation, and number, formation anisotropy, and the degree of formation damage around the laterals. If all the laterals are put on production during the test, it is almost impossible to estimate principal permeabilities, their directions, and skin factors around each lateral by examining transient pressure and derivative responses only. When all the branches produce, the transient rate distribution is strongly controlled by the skin due to formation damage. Therefore, if transient rate distribution data, as well as the pressure, is recorded during the test, non-uniqueness in the interpretation of test data may be minimized. Although it is more expensive and time consuming, testing each lateral individually may provide more reliable estimates of formation properties and damage.
Correlating Good Well Design, Drilling and Cleanup Practices with High Well Productivity
Authors: Lacewell Jason L. , Burnett David B.
Published: December 2007

This paper presents three firsts: (1) a complete case study audit for a major oil company of well planning, well construction and well cleanup operations in a Gulf of Mexico (GOM) horizontal well, and ties these practices to well productivity, (2) one of the first horizontal well productivity analyses using early-time wellhead production data and wellbore cleanup data. (3) the direct, scaled correlation of laboratory data to field well productivity.

Our analyses include descriptions of the inter-disciplinary team style of well planning, laboratory testing programs using a new drill-in fluid, details of completion operations, and a report on cleanup operations performed on the well before flowback. During early time, the well's productivity was analyzed using two separate analytical methods. Results show that guidelines followed throughout the well construction process resulted in a highly productive well completion. Results of this case study are intended to advance the technology progression of horizontal well drill-in fluid design, filtercake cleanup, and to demonstrate the effect of conscientious planning practices on well productivity.
A Three-Segment Hydraulic Model for Cuttings Transport in Horizontal and Deviated Wells
Authors: Cho Hyun , Shah Subhash N. , Osisanya Samuel O.
Published: December 2007

A new approach of three-segment hydraulic model under two-phase (solid-liquid) fluid in annulus; i.e., horizontal and near horizontal section, vertical and near vertical section, and transit section is proposed to predict and interpret the cuttings transport mechanism. In particular, the model developed in this paper approaches a three-layer hydraulic model (stationary bed of drilled cuttings at the bottom, a moving-bed layer above it, and a heterogeneous suspension layer at the top) for horizontal and near horizontal sections. The existing two-layer model is modified for transit section, and one-layer model is used for the vertical and near vertical sections. This new mathematical model is presented to overcome the limitations in the existing hydraulic models used to predict cuttings transport when drilling a horizontal and deviated wells.

This paper specifically describes model development for each section, solution, and the simulation results of the integrated three-segment model. To ensure a comprehensive understanding the effects of parameters affecting cuttings transport efficiency, the simulation under hole cleaning mode was performed, that involves build-up of cuttings and cleaning out an existing cuttings bed. The results show how to obtain a reasonable pumping velocity and optimize rheology of drilling fluid with the possible lowest pressure gradient that might serve as an operational guideline during drilling. Moreover, the effects of various parameters that affect the efficiency of cuttings transport are discussed. These results are compared with published experimental data. The observed agreement and discrepancies are discussed, and further improvements on the current model are proposed.
Reservoir Management Through Horizontal Well Technology in Algyo Field
Authors: Palasthy G. , Joshi S. D. , Benedek L. , Kristóf P. , Pipicz V.
Published: December 2007

The first horizontal well was drilled in Hungary in 1989 and thereafter 60 horizontal sections were completed. The 76% of these wells are in the Algyo field, which is the largest HC accumulation in the Pannonian basin. After a 25-year production, the inaccessible hydrocarbons, which are deposited in unreachable parts of the reservoirs, have become producible by using horizontal wells. The target of the reservoir management was to maximise the long-term profit of the field by acceleration of reserves, reduction of gas and water coning, and by effective use of depleted gas reservoirs and existing vertical wells. In this paper we have summarised the reservoir management approach to enhance the value of the field.

In a complex turbidite sandstone reservoir the oil production capacity is doubled by infill drilling of horizontal wells. This has added 5.0 Million bbl of incremental reserves. In a multilayered part of reservoir Algyo-2 W-2, approximately 1.2 Million barrel of by-passed reserves have became producible after 25 year water injection.

By reducing gas and water coning in the reservoirs Csongrad-Del-1and 2, the oil production rates and the efficiency of well utilisation have been increased.

The depleted Maros-1 sandstone reservoir is now used for underground gas storage and existing gas wells were re-entered and completed to achieve higher daily peak rates.

A gas cap exists in the most part of the oil reservoirs. Development of the gas production well pattern started in the early 90’s. By decreasing the number of wells, improving the daily gas production capacity, and speeding up the exploitation of gas cap reserves, the NPV value was maximised.

In all cases, to reduce costs, existing vertical wells were re-entered and so the over all value of the assets was improved.
Oil Shale - A Reality in This Decade
Authors: Cha Chang Yul , Fernandes R.J.
Published: December 2007

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

A modified in situ oil shale process developed by Occidental Petroleum Corp. (Oxy), has both economic and environmental advantages compared with aboveground processing. The Occidental process requires processing. The Occidental process requires less capital investment, recovers a higher percentage of the oil in place, eliminates percentage of the oil in place, eliminates the surface disposal of spent shale and requires a minimum amount of "make-up" water for its operations.

One large scale and three pilot size retorts have been successfully processed under actual field conditions. A second large scale retort has been rubblized and is scheduled for ignition about April 1, 1977 and a third large retort is being formed. The processing of the first large retort showed that its performance could be predicted. In light of its past field work and predicted. In light of its past field work and the favorable economics, at current foreign oil prices, Occidental is ready for a commercial demonstration of its in situ technology. Occidental has recently joined with Ashland Oil for the commercialization of the Colorado "B" (C-b) Federal Lease Tract, using the Occidental modified in situ oil shale process. This paper will report on the progress to date of the Occidental field work progress to date of the Occidental field work and outline the development program for the C-b Tract.

Introduction

The potential for recovering oil from oil shale has been recognized since the early 1900's. A general description of the composition of the marlstone which forms the inorganic oil shale matrix and the organic polymer, called kerogen, is described in polymer, called kerogen, is described in reference 2. Therefore, such a description will not be repeated in this paper. One of the major reasons that oil shale yields a liquid fuel similar to petroleum is that the weight ratio of carbon to hydrogen for kerogen (7.8) approximates that of petroleum (6.2 7.5).

The shale oil reserves in the Green River Basin, particularly in Colorado, Utah and Wyoming, are estimated at some 1.8 trillion barrels. If only the oil shale deposits of at least ten feet thick with an average Fischer assay greater than 25 gallons of oil per ton are considered, the oil in place in per ton are considered, the oil in place in the three states has been estimated at 600 billion barrels (1). For more than 50 years, extensive development work has been conducted to find an economic and environmentally acceptable method of recovering oil from oil shale.
Inflow Analysis and Optimization of Slotted Liners
Authors: Kaiser T. M. V. , Wilson S. , Venning L. A.
Published: December 2007

Slotted liners have been used for many years to provide sand control in oil industry applications. They are relatively inexpensive to manufacture and tolerant of installation loads, but historically they have not been able to offer the very small opening sizes of wire-wrap screens for controlling production of fine sands. However, recent advances in slot manufacturing methods provide slot openings that match and surpass the size and tolerance of wire-wrap screens. Furthermore, slotted liners offer an advantage in providing a variable slot density that can be used to optimize inflow or outflow distributions.

In the development of its South Bolney reservoir, Marathon Oil Canada and Noetic Engineering Inc. performed an analytical evaluation of inflow characteristics for a new generation of commercially available slots. Several interesting conclusions were reached, the most significant being that inflow resistance depends much more strongly on slot density than on open area. The inflow characterization was also used to develop an optimized slot density distribution to promote more uniform production over the entire well. The slotting design was incorporated into a new well that was designed to control thermally induced loads, thereby avoiding the sand control characteristics of slotted liner being compromised.
An Innovative Biodegradation Enhancer and Multi-Purpose Bioremediation System for Oil Contaminated Sites
Authors: Kopp-Holtwiesche Bettina , Lauer Ursula , LeDren Isabelle , Groffe Didier
Published: December 2007

Cognis, part of the Henkel group, has developed a liquid product with lipophilic characteristics that can be applied to a number of environmental clean-up problems: oil contaminated soils, contaminated coast lines and off-shore drilling sites; and, in the event of large-scaled accidents, it can be combined with physical and mechanical pre-cleaning methods.

The Cognis product emulsifies hydrocarbons, making them disperse in water and thereby promoting biodegradation. With organic bound phosphorous and nitrogen the product also acts as a nutrient source for microbes. It forms a layer around contaminant molecules, thus reducing leaching of nutrients and fixing microbes to the contamiants. It boosts total cell count of local oil-devouring bacteria rapidly so that the natural self-cleaning capacity rises to a multiple acceleration. The product itself is of outstanding eco-compatibility: it is not washed-out into the groundwater, it does not remobilize contaminants, and it's active ingredients have a food and/or fodder permittance.

A large-scaled pilot test has shown that common agricultural fertilizers are not useful for bioremediation, because mineral nutrients were washed-out, and the biodegradation process was not enhanced.

Beside more cost intensive conventional ex-situ and in-situ bioremediation techniques, a special low cost technology was developed in a joint effort with IABG. This technique is especially suitable for contaminated zones located no more than 2 m below soil surfaces (D.R.O.P.: Decontamination and Revitalisation of Oil Polluted Land). While the product is applied by means of sprinkling systems and subsequently mixed into the soil, this technology is even applicable for water protection areas, wetlands or nature reserves. The overall cost of this measure is only a third of other well-known in-situ methods.
Economic Benefits From Automated Optimization of High Pressure Gas Usage in an Oil Production System
Authors: McKie C. J. N. , Rojas E. A. , Quintero N. M. , Fonseca J. R. Chacón , Perozo N. J.
Published: December 2007

An integrated solution was required to optimise the use of gas in a complex network installed for gas lifting operations, gas export and reservoir re-injection. The solution was required because the compression facilities represent a major element of the cost of operating the field and therefore it is important that the high pressure gas is used as efficiently as possible. It is also important that recommendations from the optimiser are implemented with minimal delay and therefore closed-loop optimisation was selected, which requires that the optimiser is integrated with the field's SCADA system.

The complexity of the system to be optimised presented a unique challenge. Traditional nodal analysis modelling techniques are generally not robust when applied to complex, non-hierarchical networks. Consequently, the Sequential Linear Programming (SLP) optimisation technique is applied to solve the computer model of the low pressure gas gathering system, multi-stage compression facilities and high pressure gas distribution system. The novel implementation of this technique simultaneously simulates and optimises since it is able to select the best combination of pressures and flowrates from the set of all combinations which will satisfy the problem constraints.

This paper describes the development of the optimisation application, the network and well models and the underlying mathematical techniques. The integration with SCADA and other databases is described, along with a discussion of how the form of the integration reflects the desired workflow for operating and optimising the field. Finally, the paper provides a quantitative assessment of the benefits realised by applying the optimisation application in the field. These benefits are obtained through increased oil production, reduced compressor fuel gas consumption and reduced venting of low pressure gas.
A New Approach to an Old Problem - Lightweight Liquid Concrete
Authors: Rucker Ross , Sauvageau Kent , Randolph Ted
Published: December 2007

Production in the San Juan Basin in Northwest New Mexico is predominantly gas at approximately 5000'-6000' TVD. While cementing, lost circulation makes it extremely difficult to have the top of cement at the required depth, providing zonal isolation and meeting regulatory requirements.

Due to the low fracture gradient of the Fruitland and Mesaverde (0.45 – 0.55 psi/ft) circulation is frequently lost when using conventional lightweight slurries to cement the casing strings, resulting in remedial work and additional time and expense.

The introduction of lightweight (9.5 ppg), high performance (fluid loss control, compressive strength, rheology), liquid concrete has made it possible to maintain full circulation while cementing casing strings. The system, based on optimizing the Packing Volume Fraction (PVF) of the dry blend, uses sized inert particles to provide a cost-effective solution to cementing these low-pressure wells.

The casing program has also been optimized to allow the cementing of both the Fruitland Coal and Mesaverde zones in a single operation with no losses.
Composite Bridge Plug Technique for Multizone Commingled Gas Wells
Authors: Garfield Garry
Published: December 2007

Composite bridge plugs save operator time and money by enabling quick and easy installation and removal. While easily deployed on either standard electric line or coiled tubing equipment, composite bridge plugs (CBPs) can be removed in one-fourth the time required to mill traditional cast iron bridge plugs and with reduced formation damage. CBPs can be installed under pressure in multi-zone, commingled gas wells without expensive formation kill-weight fluids. After remedial operations, CBPs are removed with coiled-tubing-conveyed milling equipment using low viscosity milling fluids that minimize formation damage and easily remove composite cuttings from the wellbore. This is especially important because of the low annular velocities characteristic of coiled tubing operations. The wellbore is left cleaner than those using cast iron bridge plugs in similar operations.

CBPs can withstand high pressures for up to 10 days without compromising their pressure integrity and without the need for a cement barrier on top of the CBP. Initial field runs have demonstrated that CBPs can be milled as quickly as 30 minutes compared to 2 hours for milling conventional cast iron bridge plugs. Multi-zone, commingled gas wells using as many as 7 CBPs have been brought back on production after taking only 12 hours to remove all CBPs, including rig-up and rig-down of the coiled tubing unit. Field runs also indicate CBPs can be milled quickly when set at depths exceeding 19,000 feet.
Experimental Studies Of Low Ift Displacement By CO2 Injection
Authors: Rosman A.
Published: December 2007

An experimental technique is described for isolating the influence of low interfacial tension (IFT) from the influence of other CO2 displacement mechanisms. Also, the capillary number concept was extended to correlate the displacement efficiencies of the CO2-oil systems. Experimental results indicate that low IFT displacement by CO2 is an effective recovery mechanism.

Introduction

The use of CO2 as an enhanced oil recovery agent in petroleum reservoirs has been investigated both in the laboratory and in the field. Several recovery mechanisms were identified among which those most often considered were: swelling, viscosity reduction, and vaporization and extraction of portions of oil. A CO2 displacement may be either immiscible or miscible portions of oil. A CO2 displacement may be either immiscible or miscible depending on injection gas composition, reservoir oil composition, reservoir temperature, and pressure.

The concept of low IFT flooding has been extensively studied for surfactant and micellar enhanced oil recovery processes; however, the literature shows no investigations of the influence of low IFT on CO2 displacement efficiency.

During CO2 flooding, low IFT occurs simultaneously with vaporization, swelling, and viscosity reduction, making its influence difficult to isolate. In this paper we discuss an experimental technique designed to isolate low IFT effects.

EXPERIMENTAL TECHNIQUE

The following procedure was used to isolate the effect of IFT on CO2 displacement efficiency from other CO2 displacement mechanisms:CO2 and reservoir oil were mixed at the desired temperature, pressure, and CO2-to-oil mole ratio.The mixture was brought to equilibrium.Compositions, densities, and viscosities of the equilibrated oil and gas, as well as the IFT between phases were measured. IFT measurements used the pendant drop method.The core was saturated with the equilibrated oil as described below.The equilibrated oil was displaced from the core with equilibrated gas.

As the displacing gas and reservoir oil were preequilibrated, their compositions and physical properties, including IFT, remained constant during displacement. Injection rate was also constant. The pressure drop across the core was kept at a minimum to preserve the equilibrium between the displacing gas and the displaced liquid.

Each experiment consisted of three stages:Bringing the core to the experimental stage. This included the following operations:saturating the core with brine,measuring permeability to brine, anddisplacing the brine with several volumes of equilibrated oil to a specified irreducible water saturation, Swi.Performing the displacement. The equilibrated gas was injected at a constant rate, and the pressure drop across the core was continuously recorded.
Improved Prediction of Waterflood Sweep Efficiency Using Multi-Exponent Matrix-to-Fracture Transfer Functions
Authors: Civan Faruk , Rasmussen Maurice L.
Published: December 2007

A generalized methodology is presented that obtains analytical solutions for imbibition waterfloods in naturally fractured oil reservoirs undergoing multi-step matrix-to-fracture transfer processes. The phenomenological representation of the oil transfer from matrix to fracture is based on a three-exponential matrix-to-fracture transfer function, the necessity for which is seen by examination of experimental data. The resulting in-tego-differential equation is converted to a fourth-order partial differential equation, linearized by invoking the unit end-point mobility ratio approximation, and then solved analytically by asymptotic means. It is shown that the asymptotic-approximation approach significantly reduces the complexity of the solution process and yields adequate solutions for longtime evaluation of waterfloods in naturally fractured reservoirs. The solution is not only computationally advantageous, but it also provides a physically meaningful interpretation of the propagation speed and diffusive spreading of the progressing wave front, which could not be readily obtained from the usual type of solution methods, such as the direct application and inversion of the Laplace transformation.
Water Sensitivity and Swelling Characteristics of Petroleum-Bearing Formations: Kinetics and Correlation
Authors: Civan Faruk
Published: December 2007

Frequently, the composition of petroleum-bearing formations includes certain minerals and clays, the swelling of which in contact with water-based drilling and completion fluids, may cause formation damage and adversely affect the wellbore stability. This paper presents a kinetic model for correlation and prediction of the water sensitivity and swelling characteristics of petroleum-bearing formations and its verification by experimental data.

The swelling of petroleum-bearing formations is perceived to occur via the absorption of water by a water-exposed surface hindered diffusion mechanism. Hence, a theory of swelling and alteration of petroleum-bearing clayey formations is developed and applied for correlation of various properties of practical importance, including water content, permeability, volume expansion or porosity, and basal spacing of clay. An analytical solution is derived and reformulated for convenient straight-line plotting of experimental data. It is demonstrated that this model accurately represents the swelling characteristics of petroleum-bearing formations, successfully correlates various experimental data, and allows for accurate determination of the swelling rate parameters.

The theoretical treatment provides insights into the mechanism of the swelling of petroleum-bearing formations and leads to the development of a practical and theoretically rigorous method for accurate straight-line correlation of experimental data and determination of the swelling rate parameters. This model can be used for accurate description of the swelling characteristics of petroleum-bearing formations, prediction of conditions causing wellbore stability problems, and development of optimal strategies for effective mitigation of the undesirable consequences of swelling in petroleum reservoirs.
Accurate Measurement of Gas Diffusivity in Oil and Brine Under Reservoir Conditions
Authors: Civan Faruk , Rasmussen Maurice L.
Published: December 2007

This paper presents a physically and mathematically rigorous transient-state non-equilibrium diffusion model for accurate determination of the gas diffusion coefficient from experimental measurements of the gas pressure decline in a closed tank by dissolution of gas in a liquid (oil and brine). The short- and long-time solutions of this model for equilibrium and nonequilibrium transfer processes are derived analytically. These solutions are reformulated to enable direct determination of the best estimate of the diffusion coefficient by regression of the resultant analytical expressions to experimental data. These analytic expressions are also facilitated to develop a set of charts, similar to the type-curves used in well testing for routine applications in the laboratory. The experimental data given by previous researchers are analyzed by means of the present improved methods and the diffusion coefficients obtained are compared with the previous studies. The accuracy of the present results are confirmed by comparing their values to those measured and reported at the gas saturation conditions of the liquid phase, which are accurately known, because the saturation is a well defined state, at which state the amount of dissolved gas attains a maximum. This model can be used for determining gas diffusivity in oil, brine, as well as drilling mud and completion fluids.
Underbalanced Drilling: Real Time Data Interpretation and Decision Support
Authors: Lorentzen Rolf J. , Fjelde Kjell Kåre , Frøyen Johnny , Lage Antonio C. V. M. , Nævdal Geir , Vefring Erlend H.
Published: December 2007

The accurate prediction of the downhole pressures and the returning flow rates in low-head drilling (LHD) and underbalanced drilling operations (UBD) is a major concern in the oil industry. The present work shows an original formulation of a dynamic two-phase flow model based on the classic drift-flux set of conservation equations. However, different from the traditional approach, the closure of the system is obtained by using measured data acquired during the execution of the operation. The innovative concept consists of formulating simple closure relations that are dependent on unknown parameters, which are calculated and updated from time to time to minimize the differences between model predictions and measured data.

The potential of this new approach is discussed by presenting some transient examples of application. The current study represents a first step on the development of a methodology for the introduction of a learning while drilling process in the hydraulic design and follow-up of LHD and UBD operations.
Conductorless Concept for Offshore ‘Disposable’ Exploration Wells
Authors: Hoving P. G.
Published: December 2007

The first offshore ‘disposable’ exploration well in NAM (G14-1) proved the technical viability of the conductorless concept. The concept can be applied to any offshore exploration well in an area with a stable seabed. Cost savings can be achieved (20" conductor or 10¾" casing)

From a study aimed at reducing offshore exploration well costs it was concluded that Mudline Suspension (MLS) systems could in future be omitted from all wells. As a consequence these wells will always be abandoned. This design approach further allows for conductor elimination. The first casing string would then be subjected to the environmental load imposed by the sea.

Two wells were identified to trial this concept, both initially designed with a 95/8" surface casing.

The conductorless concept was technically proven on the first well. Learning's could not be transferred to the next well due to significant problems encountered in top-hole drilling. The conductorless trial for this well was cancelled. Concept application to all future wells will depend largely on finding an effective method for drilling the near seabed formations.
Downhole Flow Control Optimization in the Worlds 1st Extended Reach Multilateral Well at Wytch Farm
Authors: Gai H.
Published: December 2007

This paper introduces an optimization method for multi-zone or multi-lateral flow control completions. This is developed around a real application, in the world first Extended Reach Multilateral well at Wytch Farm.

The flow control completion is described before the theoretical framework is set out against the background of the specific Wytch Farm well. Then the optimization plan is sketched, with detailed graphical explanation of how the optimization is performed and the assumptions and analytical relationships described. Some Wytch Farm data is presented and analyzed, showing that more work is still needed to complete this important work which is attempting to fill up a gap left by the fast development in flow control hardware over the past 5 years.

The key issues in optimization are discussed along with the lessons learnt. In the closing remarks the authors state that the main objective of this paper is more to push the industry to put some much needed effort in this area than to develop a reliable tool first time round.
Rheological Properties of Drilling Muds in Deep Offshore Conditions
Authors: Herzhaft Benjamin , Peysson Yannick , Isambourg Patrick , Delepoulle Amaury , Toure Abdoulaye
Published: December 2007

The development of deep and ultra-deep offshore operations brings new and more complex technical challenges due to the harsh conditions encountered at these water depths. In particular, temperature around 2°C and pressure up to 400 Bars are not uncommon at the mud line. The drilling fluid, while flowing through the well, will experience temperatures from 0°C to 150°C and must keep its properties for this whole range of temperatures. The mud rheological properties will strongly depend on the temperature and pressure variations, and also on mud formulations.

This work is an experimental study of the influence of temperature and pressure variations on various muds rheology. Rheological characterizations were performed with laboratory rheometers down to temperatures as low as 0 °C. Various oil based muds were investigated. Rheological properties of the base oil were measured and correlated with the mud properties. This was used to determine the influence of the nature of the based oil and of the type of additives present in the formulation. Gelation phenomena occurrence was evidenced for some formulations, and the kinetic of gelation was quantified by using specific experimental setup. Mathematical laws were established to characterize and predict the temperature and pressure dependency of oil based mud rheology. The influence of the mud rheology temperature and pressure dependency on down-hole pressures prediction was demonstrated by comparing simulations to field data.
Brent In-Fill Drilling Programme: Lost Circulation Associated With Drilling Depleted Reservoirs
Authors: Addis M. A. , Cauley M. B. , Kuyken C.
Published: December 2007

Drilling in the Brent field began to experience severe lost circulation problems after the start of depressurisation in 1998. The losses occur in the reservoir sections which are penetrated by extended reach and near-horizontal wells. In contrast, wells drilled before the onset of depressurisation experienced few losses.

The lost circulation problems result from a narrowing of the drilling operating window as reservoir depletion gradually reduces the fracture gradient. Numerous interbedded reservoir shales, which are sub-seismic in thickness, require a minimum mud weight to maintain stability especially in the sub-horizontal sections. Problems become acute when the fracture gradient is reduced to a level below the equivalent circulating density required to successfully drill the shales.

The rate of decline in the fracture gradient has been much lower than would have been predicted from a conventional geomechanics estimation, and this has extended the duration of the Brent drilling programme during depressurisation.

The Brent in-fill drilling programme continues very successfully, through accurately estimating the fracture gradient decline which accompanies depletion using the field validated depletion constant model, and through a team wide Equivalent Circulating Density (ECD) management approach to drilling. The key objectives of this paper are, a) to explain several of the Brent mud loss incidents which accompany depletion, and b) to outline the approach used to develop a reliable depletion constant model in support of continuing drilling operations and the enhanced ECD management strategy.
Computing the Danger of Hydrate Formation Using a Modified Dynamic Kick Simulator
Authors: Petersen Johnny , Bjørkevoll Knut S. , Lekvam Knut
Published: December 2007

Planning offshore wells in deep water depths needs special tools to optimize operation and safety procedures. One of the many technical problems in deep-water operations is the possible formation of hydrates in the BOP or Kill/Choke line. Hydrates are ice type substances consisting of frozen mixtures of water and hydrocarbons which may plug the BOP stack and well circulation path and will be very difficult and time consuming to remove.

An advanced dynamic kick simulator, developed at Rogaland Research, has recently been expanded to include the determination of the potential for hydrate formation. Using dynamic temperature simulation, detailed PVT computations of the hydrocarbon influx on the component level, and an advanced hydrate formation program it is possible to obtain the ‘distance’ in temperature from hydrate formation throughout the well at any time during a simulated operation.

The simulator includes code that takes into consideration the effect of hydrate inhibitor chemicals such as salts and alcohols. Thus it is possible to make several trial runs with differently inhibited muds to compare the danger of running into hydrates.

The paper briefly discusses the physical and chemical models used, and points out how to circulate in a way to minimize the chance of hydrate formation.

Simulating kick with hydrate formation is a novel and significant contribution. This will enable the industry to perform planning and engineering of complicated well control situations. In particular it will allow the planning engineer to evaluate the risk of hydrate formation versus the cost of mud inhibition – this will be very useful for low mud weight situations where providing hydrate inhibition is very expensive.
Real-Time Well Construction Monitoring – A Case History of Sincor's Heavy Oil Project
Authors: Branch A. J. , Andersen K. , Lavillonniere J. L. , Larsen T. , Kremer Y. , Capacho G. A.
Published: December 2007

Sincor, an operating company owned by TotalFinaElf/ PDVSA/Statoil is utilizing real-time well construction monitoring technology for its field development program in the Zuata area of Eastern Venezuela. From each rig site, real-time Logging-While-Drilling (LWD) and surface drilling parameter data are transmitted via satellite, 300 km to Sincor’s headquarters in Caracas.

The survey information (inclination and azimuth), along with the gamma ray and resistivity LWD data are for the first time directly and automatically loaded into a Landmark Graphics Openworks™ database. The well trajectory (with LWD curves) can then be viewed on the seismic profile. The seismic profile is automatically posted to the Sincor intranet allowing viewing either by the rig site team members or by Caracas team members from their offices or homes, thus ensuring 24-hour coverage. Multiple wells are monitored simultaneously. With this information, the geo-science and drilling engineering teams both in Caracas and at the rig sites can immediately make better-informed decisions, such as redefining the well trajectory.

This paper will discuss the processes involved from the initial well design on the seismic section through to the real-time acquisition of data while drilling and its subsequent transfer to Caracas. There, the actual well trajectories and the LWD curves can be viewed in real time against the seismic sections and proposed well paths.
Shallow Casing Shoe Integrity Interpretation Technique
Authors: Wojtanowicz A. K. , Zhou D.
Published: December 2007

In contrast to leak-off testing in deep wells, leak-of plots from the shallow well sections subsea, exemplified in the paper, are inconclusive because there is no obvious point of deflection from the initial linear section of the plot. In the paper, simultaneous effects of geo-mechanical factors and fluid loss mechanism have been combined to explain and analyze the tests in shallow marine sediments SMS.

Based on theoretical analysis, three main stages of leak-off plot from SMS, pressure buldup, stabilization and fall-off are identified and explained. Non-linearity of the pressure buildup and mechanisms controlling pressure stabilization are explained and used to develop a method to analyze LOT.

The presented interpretation procedure considers separately the pressure stabilization and the pressure builup and fall-off sections of the LOT plot. The procedure combines well data with pressure testing record. Well data includes overburden pressure – calculated from correlations specific for SMS, and the maximum cementing pressure at the time of slurry placement.

The stabilized LOT pressure analysis identifies the maximum strength of the casing shoe controlled by the rock stress (overburden pressure) and the failure by rock fracturing. Also presented is a graphical procedure for comparing the plots of actual and equivalent pressure fall-off. The graphical procedure provides a pattern-recognition method to distinguish the mechanism of cement-rock parting from the fluid loss mechanism.
A Practical Method for Evaluating Effects of Fracture Charging and/or Ballooning When Drilling High Pressure, High Temperature (HPHT) Wells
Authors: Helstrup Ole A. , Rahman M. K. , Hossain M. M. , Rahman Sheik S.
Published: December 2007

Fluctuations in the returned mud volume have often been observed when drilling HPHT wells. There are several contributing factors for this, out of which increased wellbore volume due to elastic deformation and mud taken by natural fractures are considered in this paper. These effects are significant in HPHT wells as a result of the high mud pressure required to control the well. This, however, can give the driller the misimpression that the extra mud volume is lost to the formation due to wellbore breakout and/or fractures. When the mud weight is reduced to prevent such a suspected mud loss, the formation quickly regains its original volume and the "lost" mud is returned. This might again be misunderstood as a kick and the mud weight is increased immediately to prevent the suspected kick. The repetition of this process a few times might eventually lead to an actual wellbore failure.

This paper presents a method to estimate the volumetric expansion of wellbores as a function of wellbore pressure. The wellbore near-breakout/fracture pressure, which is of interest for this analysis, is established by considering different failure modes including helical shear, elongated shear and tensile fracture. The increases in wellbore volume are estimated at this pressure as a limit below which the driller should not be fooled by the suspected breakout/kick situation and thus avoid it leading to wellbore failure.

The method to estimate the volumetric expansion is based on analytical and numerical approaches. Analyses show that the diametric expansion of the wellbore may be in the range of centimetres at a critical pressure, and thus a deep well may consume a significant number of extra mud barrels before actual breakout occurs. This might be alarming enough to lead the driller to suspect breakout/fracturing in the absence of any analytical guidance. Thus, the paper has presented a novel approach to analyse such a suspected situation during well drilling at HPHT conditions, and the information presented will assist engineers to avoid confusion and manage the well efficiently in such a situation.
Tortuosity versus Micro-Tortuosity - Why Little Things Mean a Lot
Authors: Gaynor Tom M. , Chen David C-K. , Stuart Darren , Comeaux Blaine
Published: December 2007

Tortuosity is commonly defined as the amount by which the actual well bore deviates from the planned trajectory. Elimination of excessive tortuosity has been regarded as a critical success factor in extended reach drilling operations. In this paper the authors will refer to "micro-tortuosity", not measurable by survey data, in which the hole axis is a helix instead of a straight line. It is argued that this is Lubinski's "crooked hole" described in the early 1950's. The paper presents a study of micro-tortuosity using field data from hundreds of wells. The paper details how and why microtortuosity occurs and the negative impact micro-tortuosity can have on the entire drilling operation. The paper also presents a solution that eliminates or drastically reduces micro-tortuosity.

Field results will be presented to demonstrate that microtortuosity is in fact the dominant component of the total tortuosity.
Two-Phase Steady-State and Unsteady-State Relative Permeability Prediction Models
Authors: Ibrahim M. N. Mohamad , Koederitz L. F.
Published: December 2007

Laboratory measurement of relative permeability using either steady-state or unsteady-state methods can be expensive and time consuming. Each method has certain advantages, resulting in preferences of one particular method over the other. The primary advantage of the unsteady-state method is that it is faster than the steady-state method. This paper presents a Linear Regression Model approach for developing prediction equations for water-oil and gas-oil relative permeability from steady-state and unsteady-state experimental data. These equations offer an alternative technique in determining relative permeability values and provide a better statistical representation of relative permeability values for a reservoir as a whole since ample amounts of data were used in developing them. The data for this study were obtained from published literature of the Society of Petroleum Engineers and various industry sources. Equations were developed for water-oil and gas-oil systems based on formation type and wettability in addition to the methods of measurement. Only equations for sandstone formations are presented in this paper due to the lack of data available for other formations. The adjusted coefficient of multiple determination, R2adj is used as a criterion of a good prediction model in this study in addition to a residual plot. The equations developed in this study are easy to use: nine out of twelve developed equations require only one independent variable in order to generate a relative permeability curve, and consist of no more than seven terms in each equation. The prediction equations are compared with previously published correlations where possible and the plot of the prediction equations indicates that the unsteady-state method results in lower oil relative permeability values and higher water relative permeability values at a given saturation than the steady-state one.