bluuebunny/crossref_metadata_2025 huggingface dataset:
Wired BHA Applications in Underbalanced Coiled Tubing Drilling
Authors: Tinkham Scott K. , Meek Dale E. , Staal Timo W.
Published: December 2007

Underbalanced directional drilling with coiled tubing is emerging as an instrumental technique for accessing new and bypassed reserves while enhancing overall reservoir recovery since, unlike jointed-pipe operations, circulation does not have to be interrupted every 30 feet to make connections. Coiled tubing drilling (CTD) thus offers the potential to achieve genuine steady state underbalanced conditions resulting in the elimination of formation damage, lost circulation and differential sticking. One of the enabling technologies assisting the growth of underbalanced directional CTD is the wireline-steerable bottom hole assembly (BHA). In contrast to conventional mud pulse telemetry systems, these purpose-built wired BHAs have been designed to accommodate efficient, continuously underbalanced drilling operations while also providing an opportunity for reservoir evaluation while drilling.

The paper details the operational results for several underbalanced and low-head CTD projects involving an integrated wireline-steerable BHA. The most recent wells were completed in the North Sea, Canada and United States in 1999. Topics discussed include equipment performance, nitrified fluids, wellbore stability, well results and learning points. An analysis of time-based underbalanced CTD data is also presented.
Diffusion Osmosis-An Unrecognized Cause of Shale Instability
Authors: Simpson J. P. , Dearing H. L.
Published: December 2007

Problems encountered while drilling shale formations are a major factor in the cost of oil and gas wells. A principal cause of the problems has been shown to be the transfer of water and ions from water-based drilling fluids to shale formations. Prior studies have documented two driving forces involved in such transfer. One is the hydraulic pressure differential between the drilling fluid and shale pore fluid. A second is a chemical osmotic force dependent upon the difference between the water activity (vapor pressure) of the drilling fluid and that of the shale pore fluid under downhole conditions. Generally unrecognized is another driving force, diffusion osmosis, which is determined by the difference in concentrations of the solutes in the drilling fluid and shale pore fluid. Diffusion osmosis results in transfer of solutes and associated water from higher to lower concentration for each species, opposite to the flow of water in chemical osmosis. If the diffusion osmotic force exceeds the chemical osmotic force, invasion of ions and water can increase the pore pressure and water content of the shale near the borehole surface. Additionally, the invading ions can cause cation exchange reactions that alter the clay structure in the shale. All of these effects tend to destabilize the shale.

Destabilizing ionic reactions within a shale can be minimized if a suitable nonionic polyol (such as methyl glucoside) is used to reduce the activity of a fresh-water drilling fluid. In certain situations the addition of salt to such a fresh-water drilling fluid to obtain further reduction of water activity can cause an increase in the diffusion osmotic force that offsets some, or all, of the desired increase in chemical osmotic force. This now is recognized to have probably been a factor when sodium chloride was included in the formulation of a methyl glucoside drilling fluid used with moderate success for drilling in the Gulf of Mexico.

Chemical osmotic effectiveness can be improved by emulsification of a non-aqueous phase in the drilling fluid. A fresh-water drilling fluid containing methyl glucoside for activity control and emulsified pentaerythritol oleate prevented hydration and maintained stability of Pleistocene shale from the Gulf of Mexico. Drill cuttings from such a drilling fluid should be environmentally acceptable for discharge at offshore or land locations.
Drilling More Stable Wells Faster and Cheaper with PDC Bits and Water Based Muds
Authors: van Oort Eric , Bland Ronald , Pessier Rolf
Published: December 2007

ROP enhancer chemistry for water-based muds combined with polished cutter PDC (Polycrystalline Diamond Compact) bit technology is shown to: 1) increase penetration rates and lower costs drilling high pressured shales by reducing bit balling and improving drilling efficiency and 2) improve borehole stability by reducing exposure time and reducing near wellbore fracturing which minimizes pore pressure elevation and loss of borehole integrity. Laboratory drilling simulator and pore pressure transmission results, a case history, caliper logs and summary economics from 16 offshore wells are presented documenting the effectiveness of this technology.
The Directional Difficulty Index - A New Approach to Performance Benchmarking
Authors: Oag Alistair W. , Williams Mike
Published: December 2007

High-level performance measures, used to benchmark drilling performance, have been the subject of several industry-sponsored reports. With the advent of truly three dimensional directional wells, these benchmarks no longer measure true drilling performance due to the uniqueness of each wells' profile. This problem is common to both operators and service companies when both groups are striving to demonstrate their added value to their clients.

This paper puts forward a simple methodology called the Directional Difficulty Index, (DDI), which provides a first-pass evaluation of the relative difficulty to be encountered in drilling a directional well. This index was developed through use of a straightforward questionnaire distributed so as to reach consensus on identifying key performance measures. The index can be used to group wells of similar characteristics and complexity. Data from these similar groups can then be examined for learning-curve improvements and thus provide a measure of performance. This was not possible with previous benchmarks for random well designs.

The key value drivers of quality, service and time can then be examined on a like-for-like basis. The key principles of performance measurement can then be addressed with a much more balanced approach focused on value drivers, adding value, demonstrating organizational learning, linking planning, strategy and service company performance.

Actual well data demonstrate the validity of the Directional Difficulty Index as a methodology for the performance benchmarking process, allowing the user to evaluate the same process on wells of similar complexity and measure improvements in that process. Goals and targets set for future wells can also be used to truly measure real performance to the benefit of both the service provider (remunerative) and the service user (cost as opposed to price).
Deepwater Subsalt Development: Directional Drilling Challenges and Solutions
Authors: Cromb J. R. , Pratten C. G. , Long M. , Walters R. A.
Published: December 2007

Gulf of Mexico deepwater drilling activity has increasingly discovered economic hydrocarbon deposits lying below salt formations. Subsalt reservoir development is becoming one of the major challenges for operators, with the salt providing challenges in both seismic interpretation and drilling.1 This paper looks at how one operator successfully undertook a subsalt development in Mississippi Canyon. The project covered the completion of an exploratory well and the directional drilling of two development wells which produced from a state-of-the-art subsea system of wells, manifold and flowlines. The Gemini development was one of the first deepwater subsalt projects in the Gulf of Mexico and provided unique challenges for the directional drilling operations. These challenges included kicking off the well riserless in large-diameter hole, controlling wellbore trajectory through more than 3000 ft of salt and executing sidetracks to revised bottomhole targets after initial geological evaluation

Success was achieved through detailed planning from a directional drilling aspect that considered the geological, engineering and economic requirements and novel application of technology. In this paper we describe how these challenges were met from the standpoint of wellbore trajectory, bottomhole assembly design and operational procedures, and we review the performance of the directional drilling operations.
The Economic Viability of Multilateral Wells
Authors: Oberkircher James P.
Published: December 2007

Multilateral wells are receiving much attention in the oil industry. Despite the increasing amount of publicity, multilateral wells in practice account for only a small fraction of the total number of wells drilled in the world today. One reason for this limited application may be that the economic benefit of drilling these wells may be in question, even though the higher construction costs associated with drilling a multilateral well can usually be justified on paper by the resulting, projected rise in well producibility.

Several factors can contribute to the economic success of a multilateral project:

Reservoir Charecteristics Production and Facilities Capabilities Operator and Service Company experience with multilateral installations. Technological advances and refinements in the multilateral drilling and completion system Complexity of the drilling program Effective contingency planning prior to the commencement of the drilling operations.

This paper examines multilateral wells that have been drillled in the North Sea and reviews their true economic impact. The paper proposes a balanced score card for tracking and benchmarking the economic performance of these wells. The paper also discusses suggestions for enhancing the probablility of both the economic and technical succes of multilateral wells.
Improving Drilling Performance in Troublesome Clay Formations in the Heidrun Field
Authors: Stjern G. , Horsrud P. , Agle A.
Published: December 2007

Despite the use of inhibitive water-based mud (KCl), high pump rates to obtain good hole cleaning and relatively high mudweight, problems with cavings, pack-offs and lost circulation persisted when drilling Tertiary clay formations in the Heidrun field offshore Mid-Norway. A study was therefore initiated, including extensive data collection (logging and coring of the shale) and subsequent core testing, data analysis and evaluation of field experience.

The study showed that the major problem zone was not the low-density zone as anticipated. However, the core revealed a fractured and crushed zone, which was eventually found to be the main source of the problem. The study has resulted in a new strategy. An improved borehole stability model has been established, and the mud and operational strategy has been revised. The mudweight has been reduced, the salt content of the mud has been reduced, and good hole cleaning is obtained through a low-viscosity mud which is kept close to turbulent flow. Furthermore, wells are now planned without steering in these formations, if possible.

An economic evaluation of the study was also performed, showing a substantial benefit/cost ratio. So far, the cost reduction for an average well is close to 20 MNOK (ca. 2.5 million USD). With more than 50 wells left to drill in the field, the potential for cost-saving is large. Additionally, there is a huge and non-quantified effect from accelerated production.
Problems in Drilling through Abnormal / Subnormal Pore Pressures of Post Eocene Formations in the Potwar Basin of Pakistan with Special Reference to Adhi Field
Authors: Afzal M. , Rasool S. Anisur
Published: December 2007

The drilling conditions in the Potwar basin, the traditional oil producing region of Pakistan, are extremely tough, hazardous and challenging due to sudden reversal of pressure regimes from near geostatic to near hydrostatic. Pressures close to geostatic have been encountered at shallow depths because of the uplifting of the Himalayan foreland, resultant of collision between the Eurasian plate and the Indian plate. The orogenic movements in the presence of huge salt thickness created these ‘pop up’ structures which brought associated pressures to shallower depth. These sudden pressure reversals have resulted in the inflow of high pressure formation water and severe losses of circulation simultaneously, causing internal and surface blowouts. The other related problems which have resulted in the premature abandonment of wells are casing collapse, bridging and tightness of hole, caving and heaving of shale and stuck pipe due to differential pressure.

A number of wells have been drilled in Potwar basin by different oil companies including Pakistan Petroleum Limited (PPL). In this paper we first discuss the origin of these high pressures and the pressure reversals. Then we will discuss the experiences gained during the drilling of 12 wells in the Adhi field and how it has led to the development of a methodology by PPL for predicting and handling these abnormal/subnormal pore pressures. Out of the 12 wells, 6 wells were prematurely abandoned because of these high pressure problems. Normal Drilling Exponent (Dxc) pore and fracture pressure gradient prediction/detection technique has limited effectiveness in this area. The water inflows were controlled by raising mud weight and placing barite plugs. The losses of circulation were cured with LCM pills and cement plugs. The loss and gain situation was very well negotiated with LCM pill or cement plug against the thief zones and the barite plug against the inflow zones. The casing design was changed and the trouble string was introduced to isolate high and low pressure zones. The cement design was also changed and new methodology was introduced to control the water flow through the annulus after casing cementation.
Drilling Optimization Using Drill-bit Seismic in the Deepwater Gulf of Mexico
Authors: Armstrong Philip , Nutt Leslie , Minton Reginald
Published: December 2007

Drill Bit Seismic has been used successfully on land and in shallow marine environments for many years. The technique utilizes the acoustic energy radiated during the drilling process to provide vital information about the drilling operation. It provides time-depth and formation velocity information at the well site, allowing the position of the bit to be plotted on the surface seismic section as drilling progresses. By generating look ahead VSP images, the approach to critical horizons such as casing points or overpressure zones, can also be monitored, leading to significant cost savings and enhanced safety.

The technique has recently been extended to water depths of almost 4000ft in the Gulf of Mexico, where time-depth data was obtained down to a depth of 12500ft, drilling in soft formations with a rollercone bit. This information can be used to calibrate pre-drill velocity models and helps to prevent unexpected occurrences during drilling.
The Use of Resistivity-at-the-Bit Images and Annular Pressure While Drilling in Preventing Drilling Problems
Authors: Rezmer-Cooper Iain , Bratton Tom , Krabbe Helle
Published: December 2007

The cost of well construction can dramatically exceed budget if the drilling operations are plagued by wellbore instability problems, and excessive time and resources are needed to free stuck pipe, regain circulation, or clean the hole efficiently.

Annular pressure while drilling has recently been recognized as one of the key downhole measurements for aiding real-time diagnosis of the condition of the wellbore and the drilling fluids. In addition to conventional drilling mechanics measurements, time-lapse logging-while-drilling (LWD) documents the dynamic change in the measured properties during well construction. This can be essential in diagnosing wellbore failure, and the mechanism of failure, in addition to dynamic processes such as cuttings build-up.

An example from a horizontal well in the North Sea is used to illustrate how LWD resistivity images can be used in conjunction with annular pressure while drilling measurements to detect the onset of drilling-induced fractures. Although the majority of azimuthal images have been acquired to understand the geology and petrophysics of reservoirs, the images usually contain features resulting from geomechanical processes.

Analysis of these features reveals important information for optimizing drilling and understanding the geomechanics of the well. Coupling the resistivity images to the pressure measurement enables problem identification, and the correct remedial actions to be taken to optimize the drilling operation, for example, ensuring that swab and surge pressures are kept to a minimum, and correct hole cleaning procedures are utilized to prevent irreversible formation breakdown.
Field Test Results for a Real-Time Intelligent Drilling Monitor
Authors: Corser G. P. , Harmse J. E. , Corser B. A. , Weiss M. W. , Whitlow G. L.
Published: December 2007

Under funding from both Sandia Labs and GRI, Marconi has developed a real-time system, called the Intelligent Drilling Monitor (IDM), to detect circulation problems at the rig site. IDM monitors standard surface measurements, measured flow out, and, if available, measured flow in. Using these measurements, IDM performs real-time modeling, problem detection, and problem diagnoses using Kalman filters, advanced statistical processing, and artificial intelligence. The problems that can be detected by IDM include loss of circulation, kicks, pump efficiency losses, pump stroke counter errors, inflow meter errors, outflow meter errors, bit plugs, and washouts. This paper will present the results of processing field data from two different wells through IDM.
Lateral Drillstring Vibrations in Extended-Reach Wells
Authors: Heisig G. , Neubert M.
Published: December 2007

Drillstring dynamics and hole cleaning problems are some of the most important limiting factors in extended reach applications. Here, long sections of the drillstring lie on the low side of the wellbore while rotating. When the rotary speed exceeds a critical threshold the drillstring starts to "snake", sliding up and down the borehole wall. If rotated well beyond the threshold speed, the drillstring will eventually start to "whirl" which can cause severe damage to string components after only a short period of time.

In this paper an analytical solution for the threshold rotary speed is derived and presented. It is shown to be in the range of the rotary speeds used in modern extended reach applications. The analytical results are verified using a versatile finite element formulation to model the drillstring in greater detail. Animated time domain simulations with this model provide deeper insight into the dynamic behavior of the drillstring.

Conclusions on improved drilling practices in extended reach applications - especially with respect to hole cleaning problems - are drawn from the theoretical results.
Drilling Dynamics in the Presence of Mud Flow
Authors: Schmalhorst Bernd , Brommundt Eberhard , Baumgart Andreas , Richter Uwe
Published: December 2007

A new drillstring dynamics model takes into account the interaction between the drill string and the instationary mud flow circulation. Most papers in the past neglected the influences of fluid-structure coupling forces and fluid flow excitation forces on drillstring dynamics. The drill string under consideration includes a Bottom Hole Assembly that consists of a PDC bit, a mud driven positive displacement motor, and optionally a Measurement While Drilling pulser. Besides mud flow vibrations, the assembly is excited by axial bit vibrations caused by a profiled bottomhole, motor imbalance and friction effects between the borehole wall and the string. Coupled axial, torsional, lateral and pressure vibrations are calculated. Simulation results include damaging bit bouncing, self excited stick-slip and whirl effects of the assembly. Vibration response of a positive pressure MWD pulser is also treated. The application helps to avoid critical operating conditions and to select the corresponding system parameters. Therefore a significant reduction in project cost can be achieved.
Automatic Inclination Controller: A New Inclination Controlling Tool for Rotary Drilling
Authors: Yinghui Liu , Yinao Su
Published: December 2007

The working principles, structural features and application of Automatic Inclination Controller(short in AIC) designed by Professor Su Yinao are introduced in this paper. It includes the analyses of controlling principles of the tool and the mechanical properties of the BHA with AIC. As a new type of adjustable stabilizer, AIC provides one downhole closed-loop system which relies solely on hydraulic feedback. The BHA with AIC reduces the number of round trip and saves drilling costs. It especially meets the requirements of China's oil fields.
Improvement on the Procedure in Exploration Well By Unbalanced Drilling: A Case History in BS7 Well in People's Republic of China
Authors: Yongfeng Guo
Published: December 2007

The paper has discussed some questions in unbalanced drilling, and state that the most important question is determining the information pressure gradient before drilling in the design. The paper put out some principles and formulae for determining the information pressure gradient, which are different from that were put forward by some scholars in past to some extent. The author introduced a case history about unbalance drilling – BS7 well, which was drilled in Dagang oil field, Tianjin city, People's Republic of China, and explain the application of the principles and formula in the well. There are two points in this paper. First, in term of new principle and formula of design formation pressure gradient, the time that is from starting show of some omen to having blow out in well, is longer than predicting in other method in past, and this predicting had been testified by the practise in the well. So the operator has more time to deal with well kick and protect the blow out of well, in other words, designer can take a risk to determine the formation pressure gradient more than in past. Second, when determining the formation pressure gradient, the designer would not consider abnormal layers, which are much smaller in thick than the length of naked section in the hole. Because not only the operator have enough time to deal with well blow out if the blow out really happen, but also some situations have not happened, in speciality to the block faulted oil field, for example, Dagang oil field. The mainly reason is the level of forecast the formation pressure gradient is not very accurate, and it is not worthy of raising the value of it in the whole section in well only according to a predicting value of the formation pressure gradient in shorter section, which predicting value of it mainly depend on the data from neighbor wells. Since beginning of 1999, the most of oil fields in main land of China have accepted these principle in the drilling of explored well so that decease the mud density, and get obvious effect, which have found several huge oil fields so far.
A method to realize the surface-to-downhole communication while drilling
Authors: Zhou Jing , Fu Xingsheng , Shang Haiyan , Li Changxing
Published: December 2007

One of the developments, at present, on drilling technology is to realize closed-loop control of wellbore path geologic pilot drilling. It is also a new high technical engineering that integrates drilling, machinery, electronic, microelectronic, sensors and control technology into a whole. This article is involved in the research of realization on communication channel necessary to closed-loop control of the project. It is well known that there are commercial products used in up-channel from the well to ground, and no one from ground to downhole. The research is by signaling "1" or "0" indicated as the clear difference of the vibration of drill pipe at operation and stopping, based upon that, and then to code the signal for downward transfer. It has been proved that method for signal transfer could be realized in normal well condition at indoor and oil field.
Detection of Asphaltene Deposition by Capillary Flow Measurements
Authors: Broseta D. , Robin M. , Savvidis T. , Féjean C. , Durandeau M. , Zhou H.
Published: December 2007

This paper presents an experimental methodology that allows a sensitive determination of the onset and rate of deposition in asphaltene-containing fluids when the pressure, temperature, or fluid composition are varied. This determination is inferred from pressure drop measurements across a capillary tube in which the fluid is injected at a constant flow rate and at specified conditions of temperature, pressure and composition. When the conditions for deposition are met the pressure drop across the capillary tube is no longer stationary but increases with time as a result of the buildup of a deposition layer on the tube walls.

In the experimental set-up that has been constructed, the fluid composition is controlled by co-injecting the various fluid components into the capillary by means of different pumps. This setup has been utilized to determine, at some given temperature and pressure, the deposition envelope of systems made of crude oil, solvent (xylene) and precipitant (heptane). The measured deposition points coincided with bulk flocculation thresholds determined by a conventional light transmission method. The light transmission method was, however, difficult to for fluids with a very low asphaltene content, whereas the proposed method was efficient for fluids containing as low as 0.04 wt.% asphaltenes.

The rate of deposition was observed to increase with the distance from the deposition onset. Reversibility of deposition was significant only when the asphaltene-containing fluid was returned to conditions remote from those of the deposition onset.
Controlling Gelation Time and Microgel Size for Water Shutoff
Authors: Chauveteau G. , Omari A. , Tabary R. , Renard M. , Rose J.
Published: December 2007

Injecting stable preformed microgels as relative permeability modifiers to reduce water production is an attractive new procedure to minimize the risk of formation plugging and consequently of inefficiency of in-depth treatments. This paper describes the mains results of theoretical and experimental investigations carried out to know how to control both size and conformation of microgels formed under constant shear flow. Since gelation kinetics strongly depends on crosslinker chemistry, Zr K-edge XANES and EXAFS studies of zirconium speciation were performed under the complex conditions of polymer gelling for water shutoff. The results show that crosslinking species may be dimers, tetramers and associations of tetramers depending on pH and Zr concentration in presence of lactate. In polymer gels, Zr monomers were observed. The generalisation of our crosslinking-under-shear theory described in this paper provides simple power laws. The microgels formed in diffusion regime are isotropic and their size decreases significantly as shear rate increases, while when formed in correction regime, they are anisotropic and their size decreases negligibly with shear rate. All experimental data are in agreement with this theory so that conclusions can be derived to optimize microgel preparation as a function of their role in the aimed application, either relative permeability modifiers for water shutoff or viscosity enhancers for polymer flooding.
An Investigation into Enhanced Recovery under Solution Gas Drive in Heavy Oil Reservoirs
Authors: Kumar R. , Pooladi-Darvish M. , Okazawa T.
Published: December 2007

Some of the heavy oil reservoirs in Western Canada and Venezuela show anomalously high primary recovery under solution gas drive process. Pressure decline rate in these reservoirs is low compared to that expected under solution gas drive in conventional oil reservoirs. Several theories have been proposed for these anomalous behaviors.

The objective of this study is to examine one of the proposed theories, which suggests that gas mobility in heavy oil is low. In this study, gas mobility under solution gas drive is measured by performing depletion experiments. The depletion was carried out at four different rates. The Eclipse-100 Black oil simulator was used to match the experimental data.

The direct results from the experiments show that the critical gas saturation is not very high. Thus, critical gas saturation cannot explain high recovery. However, it was found that the gas mobility in heavy oil is quite low, when compared to that expected in conventional oil.

Experimental results indicated that higher rates of pressure drop resulted in higher super-saturation, higher critical gas saturation and lower relative permeability to gas. Physical explanation of the observed behavior is offered in light of the anomalous behavior of heavy oil reservoirs. An empirical model was developed to predict gas mobility, critical gas saturation and supersaturation as a function of depletion rate for the system studied.
Wall-Effect/Gel-Droplet Model of Disproportionate Permeability Reduction
Authors: Liang J. , Seright R. S.
Published: December 2007

Many polymers and gels can reduce the permeability to water more than that to oil or gas. However, the mechanism of this disproportionate permeability reduction is not clear. This paper considers a promising potential explanation that is based on a combined "wall-effect" and "gel-droplet" model. Disproportionate permeability reduction can be explained by a wall-effect model if the gelant is prepared from or matches the wetting phase, and by a gel-droplet model if the gelant is prepared from or matches the non-wetting phase. The combined model predicts that disproportionate permeability reduction should increase with increasing residual nonwetting-phase saturation. New experimental results support this prediction. Maintaining high residual oil saturations in the treated region of an oil zone could significantly reduce damage to oil productivity after a gel treatment.

The disproportionate permeability reduction increased with increased pressure drawdown between 45 psi/ft to 180 psi/ft. Therefore, to a certain extent, an increase in pressure drawdown after a gel treatment might reduce damage to oil productivity without increasing water production.
Application of Partitioning Tracers for Remaining Oil Saturation Estimation: An Experimental and Numerical Study
Authors: Chatzichristos C. , Dugstad Ø. , Haugan A. , Sagen J. , Muller J.
Published: December 2007

This paper presents the first results of an ongoing experimental work at IFE for developing new tracers to be used for estimation of remaining oil saturation. The methodology is based on the chromatographic theory, which states that various components flowing through porous media will be delayed according to their partition coefficient to the immobile phase. Two experiments, one with gas tracers and the other with water tracers, are presented here, demonstrating the applicability of the methodology in the laboratory scale. Moreover, a numerical model (ITRC-SIM module) developed at IFE especially for simulating the tracer flow in hydrocarbon reservoirs is validated against the experimental data and used to demonstrate the use of tracers in small and field scale generic cases.
A Streamline Approach for History-Matching Production Data
Authors: Wang Yuandong , Kovscek Anthony R.
Published: December 2007

This study proposes and develops a streamline approach for inferring field-scale effective permeability distributions based on dynamic production data including producer water-cut curve, well pressures, and rates. The approach simplifies the history-matching process significantly.

The basic idea is to relate the fractional-flow curve at a producer to the water breakthrough of individual streamlines. By adjusting the effective permeability along streamlines, the breakthrough time of each streamline is found that reproduces the reference producer fractional-flow curve. Then the permeability modification along each streamline is mapped onto cells of the simulation grid. Modifying effective permeability at the streamline level greatly reduces the size of the inverse problem compared to modifications at the grid-block level. The approach outlined here is relatively direct and greatly reduces the computational work by eliminating the repeated inversion of a system of equations. It works well for reservoirs where heterogeneity determines flow patterns. Example cases illustrate computational efficiency, generality, and robustness of the proposed procedure. Advantages and limitations of this work, and the scope of future study, are also discussed.
Support-Operators Method in the Identification of Permeability Tensor Orientation
Authors: Silin Dmitriy B. , Patzek Tad W.
Published: December 2007

The dependence of rock permeability on direction, or permeability anisotropy, is confirmed by numerous field examples. Ability to measure permeability anisotropy is very important for correct placement of wells. There exist several methods of identifying the maximum and minimum permeability coefficients by interpreting specially designed well tests. Here we develop a new method of estimating the angle of orientation of permeability tensor away from the well. We assume that the principal permeabilities near a cored or otherwise logged well are already known. To accomplish this task we need pressure measurements in monitoring wells.

The orientation of permeability tensor is identified by minimizing the square of the differences between measured and computed data. The underlying boundary-value problem is discretized by the support-operators method, which imposes few restrictions on the grid structure; produces a conservative finite-difference scheme and can be applied to very heterogeneous systems. The gradient and second differential of the minimization criterion are obtained through two systems of adjoint equations, called the first and second adjoint systems. The gradient of the criterion is obtained both in continuous and discrete versions. As an illustration, we analyze a steady-state isothermal, single-phase pressure equation in an anisotropic porous medium. A few applications of the technique developed in this paper for rectangular and curvilinear grids confirm good performance of the algorithm.
Automatic Simulation Algorithm for Appraisal of Future Infill Development Potential of Prudhoe Bay
Authors: Farnstrom K. L. , Litvak M. L.
Published: December 2007

The Prudhoe Bay field is a large, mature, Alaskan reservoir. During its 22 year production life, over 40 percent of original oil in place has been recovered. Since beginning decline a decade ago, ambitious fieldwide, infill development has been performed. As the light oil column thins, advanced sidetrack drilling has been employed using coil tubing units and horizontal wells to reach infill targets. The strategy is to accelerate production, to access new reserves, and to replace aging wellbores producing at elevated water cuts and / or GOR's. From 60 up to 100 new completions have been drilled annually in recent years.

This paper reviews the design and application of an automated simulation algorithm constructed to appraise the remaining infill reserves potential of Prudhoe Bay. The algorithm operates in conjunction with a state of the art, full field simulation model (FFM). The FFM is comprised of a reservoir model operating in parallel with elaborate surface pipeline and facilities models. The algorithm is comprised of two modules: an automated drilling routine which drills new infill wells from surface and an automated recompletion routine which sidetracks existing well bores when their productive lifetimes have been reached.

Highlights of the recompletion module include the identification of candidate wells to be sidetracked based upon marginal performance and the location of productive, recompletion targets for each candidate. Well hydraulics for each new recompletion are then defined, and each is connected to the surface pipeline network and to fluid processing facilities. An optimization routine next tests recompletion targets and selects the best performers to be drilled based on the number of sidetracks scheduled for the field. The automated drilling module has commonalties with the recompletion module, and its design and function are also presented in this paper.

The use of the algorithm for the evaluation of various infill development parameters is reviewed. Procedures for analysis of simulation results are presented. Simulation results provide estimates of improved oil recovery from different areas of the reservoir. Rate streams from simulation provide input to economics programs for analysis of program benefits.
Impact of Natural Fractures in Hydraulic Fracturing of Tight Gas Sands
Authors: L. Rodgerson James
Published: December 2007

The presence of natural fractures in hydraulic fracturing candidates can present an array of well completion problems. Natural fractures can be very difficult if not impossible to model without adequate pre-job diagnostic testing to calibrate simulation.

Left undetected natural fractures can cause premature screen-out as well as formation damage. In tight gas sand formations, natural fractures can be the predominate production mechanism in the reservoir. If polymer residue is left in the natural fractures after drilling, stimulation or work-over, a substantial amount of potential production may be left behind. Often this type of damage may be documented by the sheer fact that production may decrease after these types of operations.

Techniques have been perfected to determine the impact on leakoff due to natural fractures. In many cases production may exceed the predictive capability of production simulators without the introduction of permeability numbers that might be considered high for that area. This could lead one to believe that some portion of the production is dominated by natural fractures. A better understanding this type of leakoff could help in the development of methods to predict production results or economics of a well based on pre-job testing.

It is the intention of this paper to discuss methodology to predict the presence of natural fractures and show key considerations when trying to simulate their behavior. This paper will also investigate stimulation problems and damage mechanisms, describing methods that may be used to help minimize their impact.

An earlier version of this paper was presented by this author at the Forty-Sixth Annual Southwest Petroleum Short Course April 21-22, 1999.
New, Lower-Cost Acid Gas Removal and Sulfur Recovery Technology for Permian Basin Natural Gas Production Operations
Authors: Leppin Dennis
Published: December 2007

Technology developments for lowering gas treating and sulfur recovery costs for Permian basin gas have been underway for several years by GRI (formerly Gas Research Institute) and other technology development organizations. Several of these technologies are now nearing the point where commercial applications should be evaluated since significant cost savings and operational simplifications could be achieved by early adopters. After a cursory review of current technology in gas treating and sulfur recovery, this paper summarizes applicable new technology in this area developed by the author's company and others including advances in H2S scavenging, small-scale sulfur recovery up to 15-20 TPD and large-scale gas treating for high acid gas concentration applications.
Seismic Models Enhanced with Well Logs Have Located Sand Rich Areas from South Texas to the Rockies
Authors: Allen Rob L.
Published: December 2007

Seismic models enhanced with well logs help to locate sand concentrations. Many well log curves contain patterns with very high frequencies compared to seismic responses. Quantitative analysis of log patterns can create large numbers of sand vectors for plots that resemble and complement 3D seismic attribute maps. Complex log patterns and improved predictions about changes in log responses over distances have been integrated with broad geophysical coverage. Detailed and extensive reservoir models were created.
Effect of the Wellbore Conditions on the Performance of Underground Gas-Storage Reservoirs
Authors: Tureyen Omer Inanc , Karaalioglu Hulya , Satman Abdurrahman
Published: December 2007

This paper presents results of an underground gas storage modeling study using the reservoir and fluid properties of the Northern Marmara gas field, a recently developed field in the Thrace region of Turkey. It has an area of 3.6 km2 with nearly 3 billion sm3 of GIIP. The reservoir model used in this study is based on the theoretical as well as the empirical deliverability equations. The deliverability equations reflect the production and injection performances of the wells with given completion characteristics.

Our approach is based on maximizing working gas volume for a particular configuration of reservoir, well and surface facilities. The importance of the type of well completion was emphasized in this paper because this is the most likely place for operating problems to occur. The deliverability performance strongly affects the design factors such as the working gas volume and the number of wells operated. Results indicate the performance dependence on wellbore damage and hence the importance of cleanup of wells.

The effects of the mechanical skin factor on the working gas capacity with different number of horizontal wells as well as vertical ones were studied. Results show that the working gas capacity decreases while the mechanical skin factor increases. This behavior becomes especially more dramatic as the horizontal well length decreases. The increasing number of wells increases the working gas capacity as expected. These results are discussed in detail through application to N. Marmara gas reservoir data.

The underground gas storage modelling approach followed in this study is shown to be an effective way to forecast the production / injection performance and to estimate the important design parameters when converting a depleted gas reservoir to a gas storage reservoir. Our approach yields the better understanding of the effect of the wellbore conditions on the performance of the underground gas storage reservoirs as well.
Selection Of Materials For Optimum Performance Of Wellhead Assemblies In Petroleum Production Operations
Authors: Fowler E.D. , Rhodes A.F.
Published: December 2007

The influence of well fluids and external environments, including offshore and cold weather, on metallic and non-metallic materials is discussed. Methods of selection based on field data, assisted by accelerated laboratory testing, is dealt with in detail Tabulations or material in everyday use are shown, including carbon steels, low alloy steels, stainless steel and elastomers, with suggestions for specific uses.

The selection of materials for petroleum production operations is based primarily on environmental compatibility. cost is an important but secondary consideration. Through the years, users and manufacturers have come to realize that a rather large group of economical materials will serve adequately in a large percentage of fields. Cold weather operations, hydrogen sulfide, carbon dioxide, all influence the need for special materials or routine materials in a different condition.

Chosen materials must be compatible with oil and gas environments as encountered in the production cycle. Well streams contain oils, condensates, methane, carbon dioxide, nitrogen, hydrogen sulfide, ethane, and many heavier fractions plus salt water in varying concentrations and quantities. plus salt water in varying concentrations and quantities. Methane is the least harmful as to its effect on metallic materials.

Table No. I illustrates the effect of individual fractions on metallic materials.

Two basic failure modes are encountered in petroleum production:stress corrosion cracking due to hydrogen production:stress corrosion cracking due to hydrogen sulfide and/or chlorides, andmetal loss in the form of pitting or general corrosion.

pitting or general corrosion. Both failure modes are very important but pitting may be more misleading in that if a corrosion monitoring system is based on well stream iron count, the observer may be content, this while his tubing is being perforated in a zone not of his choosing!

Sufficient data has been accumulated through field experience to permit users and manufacturers to evaluate the problem and make reasonably accurate predictions as to the performance of a material in specific environments. When new performance of a material in specific environments. When new alloys or new applications for established alloys are considered, accelerated laboratory testing can be helpful for screening purposes prior to field testing. purposes prior to field testing. Internal and external accessory items are made from the various materials shown in the tables on the next page.

Table No. 2 and 3 offer several materials in common use for parts wetted by the well stream. parts wetted by the well stream.
Insight into "Agarwal Equivalent Draw-down Time"
Authors: Foster Gary A.
Published: December 2007

A common method in industry to correct pressure build-up data for producing time effects is use of Agarwal equivalent drawdown time (SPE 9289). But how does this correction affect the presentation of data and interpretation when performing well test analysis? It can be argued that a reasonable pressure match to a particular reservoir model can be achieved regardless of how the data is presented. An appropriate match can be quantified by goodness of fit criteria and the best match (model) selected on that basis. Because of the presence of non-unique solutions, it is difficult to know which flow geometry is most appropriate from the match alone. Future flow predictions will be effected by the selection an appropriate model with late time boundary conditions having the largest effect on forecasted volumes. The method presented in this paper will try to reduce the uncertainty when selecting a model to match the pressure behavior plus demonstrate that the Agarwal corrected and Horner corrected derivative are identical.
Modeling Plunger Lift for Water Removal from Tight Gas Wells
Authors: Maggard J. B. , Wattenbarger R. A. , Scott S. L.
Published: December 2007

Many tight gas wells produce at rates below their potential, due to water loading. Plunger lift is often applied to remove produced (or condensed) water, reduce bottomhole flowing pressure, and increase both gas production rate and ultimate recovery. Previous authors have discussed dynamic models of the plunger lift process. However, these previous models considered only stabilized reservoir production. Because of the assumption that reservoir production is stabilized, these older models have only limited applicability to tight gas wells. This paper presents a study of the application of plunger lift to the problem of water removal from tight gas wells. A numerical simulation model was developed which includes gas flow in the reservoir, wellbore/annulus effects, and dynamic plunger lift cycles. Transient reservoir performance is an important feature of the new model. Transient reservoir performance is a significant factor for tight gas reservoirs, especially as average reservoir pressure decreases during the life of the reservoir.

Field data from tight gas wells with plunger lift for water removal can be more thoroughly analyzed using the new simulation model. Calibration of model parameters with field cases allows the plunger lift design to be optimized for a particular well. Improved understanding of the plunger lift process for tight gas wells with water loading problems may lead to more efficient water removal, increased gas production rates and recovery, and longer well life.