bluuebunny/crossref_metadata_2025 huggingface dataset:
Monitoring Waterflood Operations: Hall's Method Revisited
Authors: Silin D. B. , Holtzman R. , Patzek T. W. , Brink J. L.
Published: December 2007

Hall's method is a tool for evaluation of an injecting well performance. It is based on the assumption of radial steady-state flow. Besides time series of historical injection pressures and rates, rigorous implementation of Hall's method requires information about the ambient reservoir pressure. In addition, it is assumed that the influence domain radius is constant during the observation period. Neither of these parameters can be measured directly.

This paper discusses a new method called slope analysis. It is based on analysis of the variations of the slope of the plot of the time integral of pressures versus cumulative injection volume. In particular, it produces an estimate of an apparent average reservoir pressure. This method requires only injection pressures and rates data, which are routinely collected in the course of a waterflood. Thus, slope analysis requires no interruption of regular field operations.

The method has been verified with numerically generated pressure and rate data, and tested with field data. In both cases it proved to be accurate, efficient, and simple. The estimated ambient reservoir pressure can be used to correct the Hall plot analysis or to map the average reservoir pressure over several patterns or an entire waterflood project. Such maps can then be used to develop an efficient waterflood policy, which will help to arrest subsidence and improve oil recovery.
Towards An Adaptive, High-Resolution Simulator for Steam Injection Processes
Authors: Nilsson J. , Gerritsen M. , Younis R.
Published: December 2007

We develop a computationally efficient and accurate adaptive simulation model that is specifically designed for non-isothermal and compositional recovery methods, including steam injection, in-situ combustion and miscible gas injection. The adaptivity is designed to accurately resolve fronts that typically form in the reservoir during such processes. Owing to steep gradients in the solution as well as the strong nonlinearities due to thermal and compositional effects, accurate adaptive modeling is challenging. It is difficult to achieve without appropriate high-order discretization and strong grid refinement. Our framework is based on a Cartesian Cell-based Anisotropic Refinement (CCAR) strategy. CCAR offers aggressive grid adaptation, which allows quick transition to the very fine local grids necessary to resolve solution fronts and the fine local grids desirable to resolve reservoir heterogeneity. We have formulated a higher order pressure solver on the CCAR grids. The discretization uses a compact stencil, which together with an effective storage scheme leads to computational efficiency.

We apply the framework in this paper to a black-oil steam formulation. Although simplified, the simulation demonstrates the main features of our adaptive strategy.
Gas-Water Counter-Current Capillary Imbibition at Different Temperatures
Authors: Babadagli T. , Hatiboglu C. U.
Published: December 2007

Gas water counter-current matrix–fracture interaction due to capillary forces was studied. The focus was on the rate of capillary imbibition and the development of residual gas phase under low (20 °C) and high temperatures (90 °C). Berea sandstone and Indiana limestone samples with different shape factors were obtained by cutting the plugs 1, 2.5, and 5 cm in diameter and 2.5, 5, and 10 cm in length. All sides were coated with epoxy except one end. Static imbibition experiments were conducted on vertically and horizontally situated samples where the matrix-fracture interaction took place upward and lateral directions, respectively. The effects of the matrix shape factor, wettability, surface tension, and core position on the recovery rate and ultimate recovery were investigated.

The experimental scheme followed was useful in identification of the development of residual gas saturation for fully counter-current matrix-fracture interaction. We investigated and clarified to what degrees the rock/fluid properties (wettability and matrix shape factor) and existing conditions (temperature, causing lowered IFT and brine viscosity, and gravity) become effective on the residual gas saturation. It was observed that the residual gas saturation is sensitive to the matrix shape factor. The effect of surface tension on the recovery rate and ultimate recovery was also critical. The vertical cases yielded different recovery rates and ultimate recoveries with increasing temperature. Lower residual gas saturation with increasing temperature was obtained only for large diameters. That was attributed to the reduction in surface tension.

Finally, critical matrix and fluid properties were correlated to the residual gas saturation and different dimensionless groups were tested for scaling.
Improved In-Situ Combustion Performance With Metallic Salt Additives
Authors: He B. , Chen Q. , Castanier L. M. , Kovscek A. R.
Published: December 2007

In-situ combustion is an effective thermal recovery process. A part of the oil is burned in-situ, heat is generated, oil viscosity decreases, and larger oil recovery results. Thus, a key mechanism is effective oxidation of a small fraction of the oil in place to generate heat and pressure. Common, water-soluble metallic salts are known to play an important role as a catalyst for some combinations of crude oil/brine/solid matrix. Metallic additives enhance oxidation and cracking of hydrocarbons and thereby affect the nature and the amount of fuel formed. The mechanism of the catalytic effect is, as of yet, unknown.

This paper describes an experimental study combining tube runs that gauge combustion performance and ramped temperature oxidation tests that measure the kinetics of combustion. We propose cation exchange of metallic salts with clay as a mechanism to create activated sites that enhance combustion reactions between oil and oxygen. Sand and clay surfaces are examined with scanning electron microscopy for evidence of cation exchange and alteration of surface properties by metallic salts. The oils studied are heavy and light oil from Cymric (Kern, Co., CA). Effluent gas analysis is conducted and temperature profiles are measured. Additive improved performance in all cases including lower activation energy, greater oxygen consumption, lower temperature threshold, and more complete oxidation. In tube runs, Cymric light oil (34 °API) did not exhibit sustainable combustion, but gave sustained combustion with the addition of iron nitrate. Thus, metallic additives have potential to expand the range of candidate reservoirs for in-situ combustion.
Optimizing Cyclic Steam Oil Production with Genetic Algorithms
Authors: Patel A. , Davis D. , Guthrie C. , Tuk D. , Nguyen Tai , Williams J.
Published: December 2007

This case study describes a project applying a new technology—genetic algorithms—to the problem of scheduling oil production by cyclic steaming at an oil field in the San Joaquin Valley. The paper has seven parts.

In the first part, we discuss the nature of the problem, the importance of solving it well, and the nature of the work process as it occurred before the project began. In the second part, we discuss genetic algorithms and the way that the project adapted them to solve the problem of scheduling cyclical steam injections. In the third section, we describe a pilot project that demonstrated the potential of the approach. In the fourth, we describe the full project that created an optimization tool that has been working daily with oil field personnel to schedule production for the entire field for more than a year. In the fifth, we discuss two types of results of the project—an increase in production and changes to the work process on the part of the oil field personnel owing to their enthusiastic adoption of the optimizer. In the sixth, we discuss some project management factors that led to the success of the project. Finally, we discuss ways in which the success of this project may be relevant to a variety of other types of scheduling and resource allocation problems in the field of oil production.

The paper will center on three themes: the successful solution of a hard production problem with a new technology; the impact of that technology on the oil field personnel; and the potential of that technology to support other types of projects with similar levels of return.
Viscosity Reduction WAG: An Effective EOR Process for North Slope Viscous Oils
Authors: McGuire P. L. , Redman R. S. , Jhaveri B. S. , Yancey K. E. , Ning S. X.
Published: December 2007

A novel EOR method, Viscosity Reducing Water-Alternating-Gas injection (VR-WAG), has been developed to improve oil recovery from viscous oil reservoirs and under-saturated light oil reservoirs. Heavy components are mixed with produced lean gas to manufacture viscosity-reducing injectant (VRI). When VRI is injected into a heavy oil reservoir, oil viscosity can be reduced by up to 90% and the oil recovery can be improved by 15-20%.

VR-WAG may be widely applied in Alaska's heavy oils. The first enriched gas application will be the West Sak 1-J EOR Project (WS-1J) at Kuparuk. Additional projects are likely to utilize VR-WAG, including the Prudhoe Bay satellite fields, Orion and Polaris, and the S-pad EOR Project at Milne Point. Laboratory experimental data, numerical simulation results, and potential project scopes from each of these fields are included.
Understanding Formation Damage in a Stevens Reservoir at Elk Hills California
Authors: Smith S. , Williams W. , Ansari K.
Published: December 2007

As reservoirs mature, understanding the source and reversibility of any formation damage is particularly critical for sustaining production. The 26R Reservoir at Elk Hills contains a substantial oil column. Gravity drainage is the primary recovery process of this remaining oil in place. Recently, two horizontal wells were successfully drilled through the bottom of the oil column to enhance gravity drainage. Subsequent testing revealed drilling fluids leak off will create a wellbore skin; reducing permeability and production potential by over 90%.

This paper will review analytical calculations and assumptions used to determine well production potential and discusses extensive core description and core flow work completed. The core work has validated production potential assumptions. The extensive core description work and core flow tests has generated a better understanding of rock and mineralogical properties, at a pore level. Cores were exposed to various drilling and workover fluids and stimulation procedures. Treatment effects were then measured via return permeability tests and then further evaluated by preparing contaminated core thin sections and using a scanning electron microscope. Workover fluids are now more carefully applied during well remedial operations. In addition, the core work has modified acidizing and perforating procedures. Follow-up well treatments have shown promise by reducing observed skin, and increasing production
The Geochoke Well Test Response in a Catalogue of Systematic Geotype Curves
Authors: Corbett P. W. M. , Ellabad Y. , Egert J. I. K. , Zheng S.
Published: December 2007

A new well test response has been identified. A distinctive restriction – shown as a hump on the derivative curve – is seen in double matrix porosity (dual permeability) reservoirs. High permeability lenses intersecting the well bore give rise to a negative geoskin response at early time. After the middle time period of flow restriction caused by the limits of the lenses connecting to the wellbore and the presence of additional limited extent, discontinuous, high permeability lenses within the reservoir. This phenomenon has been shown in a series of numerical models and is also observed in two field well tests.

The two field examples come from testing in a braided fluvial oil reservoir. Other interpretational possibilities (e.g., sub- seismic faulting, fluid changes), which might also be considered given the non-uniqueness of pressure data, are eliminated by careful consideration of the geophysical interpretation, the depositional environment and the fluid properies. Sub-seismic faults are often interpreted in well tests from braided fluvial reservoirs. However, we consider that the response in these cases, and possibly in a wider range of cases, is due to geological effects of sedimentary heterogeneity due to secondary channels within the braided system. Braided fluvial sedimentary processes result in heterogeneous reservoirs with double matrix porosity. The heterogeneity and the double matrix porosity nature of these reservoirs are evident from the Lorenz Plot. Such sandstones can produce a variety of well test responses as the two matrices interact at various length scales.

The geochoke model in double matrix porosity reservoirs is an end-member response for reservoirs with short lateral and vertical correlation length. A family of geotype curves can be generated to consider a range of correlation lengths to systematically explore the limits of early, middle and late time responses for specific reservoir cases.
Downhole Harmonic Vibration Oil-Displacement System: A New IOR Tool
Authors: Zhu T. , Xutao H. , Vajjha P.
Published: December 2007

Excessively large amplitude excitations resulting from earthquakes, explosions, or mechanically vibrated systems are found to generate macroscopic and microscopic mechanisms that have beneficial effects on the production of wellbores. A downhole harmonic vibration oil-displacement system (DHVOS) that generates a sudden large amplitude excitation to the liquid in the wellbore was developed by researchers at CNPC (China National Petroleum Company). Compared with other downhole artificial vibration systems, the DHVOS system is a heavy-duty unit that can provide long period operations and large amplitude excitations. This system has been implemented in CNPC's oil fields such as Liaohe, Huabei, Shengli and Zhongyuan. The DHVOS system provides a harmonic vibration frequency of 88 shocks per minute with each shock having 5-ton strength. More than 100 oil-producing wells have been stimulated with the downhole vibration system since 1997. The field results demonstrated that periodic application of large amplitude excitation to oil reservoirs led to increased oil production rates and decreased produced fluid water content. The observed oil production-rate increments ranged from 27.5% to over 400% with an average increment of 47.6% compared to the pre-vibration production rates. The reduction in water oil ratio (WOR) varied 10% to 75% with an average of 48.4% in WOR reduction.
New economic indicator to evaluate SAGD performance
Authors: Shin H. , Polikar M.
Published: December 2007

The steam-assisted gravity drainage (SAGD) process simulations described in this study have been optimized to have the lowest cumulative steam-oil ratio (CSOR), highest RF and highest CDOR in order to obtain optimal operation conditions. In addition, net present value (NPV) calculations were performed for each simulation case to take the time factor into account.

A simple thermal efficiency parameter (STEP), based on CSOR, CDOR and RF for the time corresponding to SOR = 4, was developed to evaluate the performance of a SAGD project under optimized conditions. A linear relationship was found to exist between STEP and NPV, with a correlation coefficient in excess of 0.96 for most of the cases studied. For each simulation case, highest values of NPV and STEP indicated optimum SAGD operating conditions.
Chemical Treatments for Removal of Drill-in-Fluid Damage in Horizontal-Multilateral Gas Wells: Lab Studies and Case Histories
Authors: Al-Otaibi M. B. , Nasr-El-Din H. A.
Published: December 2007

Water-based fluids have been used to drill various wells in Saudi Aramco fields. A typical water-based mud consists of xanthan, starch or cellulose polymers, plus bridging agents like sized calcium carbonate or salt particles. The polymers in the drill-in fluids are needed to build the required viscosity to transport cuttings and form a filter cake around the wellbore to reduce the fluid loss. Some of these polymers invade the critical near wellbore area and may cause formation damage.

One of the treated wells was the first multi-lateral ever drilled in a deep sandstone gas reservoir in Saudi Arabia. The dual-lateral well was completed with a pre-drilled liner completion. Mineral and organic acids can be used to remove the filer cake, but they cannot be applied in horizontal and multilateral wells without using an effective diversion technique. In addition, the sandstone formation in this case is acid-sensitive. As a result, a filter cake cleanup process was performed separately in each lateral, using a completion brine wash followed by a specific enzyme treatment.

Several lab studies were conducted using field mud samples to determine the cleaning efficiency of enzymes used to remove damage which occurred while drilling the target zone. For the first time, an enzyme solution was spotted in one lateral and left in the hole for more than four months, until the second lateral was drilled and the well was ready for testing.

Various tests were conducted on well flowback samples after the enzyme treatments. These tests included: chemical analysis of the aqueous phase and full analysis of the produced solids using acid solubility, sieve analysis, XRD, XRF, and SEM. In addition, the carbohydrates content in the aqueous phase was measured using the anthrone method.

A significant improvement in gas production from this well has been realized through the application of the enzyme treatment for the removal of starch and XC polymers used in drilling operations. This paper will discuss in detail laboratory work that was conducted to assess this field treatment.
Injection Fracturing in a Densely Spaced Line Drive Waterflood - The Halfdan Example
Authors: Rod M. H. , Jørgensen O.
Published: December 2007

Induced fractures are actively steered along horizontal water injection wells in a densely spaced line drive water flood, thus ensuring efficient sweep and minimising random connections between parallel producer and injector wells. Due consideration of flow-induced changes to the stress field reduces the risk of premature water breakthrough during injection at fracturing conditions. The paper differs from other works concerning flow-induced stresses by focussing on the application of this phenomenon and the practical experiences from a field-wide implementation.

A technique, named "Fracture Aligned Sweep Technology" (FAST), has been implemented on the Halfdan chalk field in the Danish North Sea with horizontal wells drilled at 600 ft lateral spacing in a parallel pattern of alternating producers and water injectors with 10,000 to 15,000 ft long reservoir sections. Fracturing of the injector wells is the key to the process of voidage replacement, due to the low mobility of water compared to oil and gas.

FAST uses the fact that fluid flow in rock of low permeability affects reservoir stresses. Before propagating a fracture, the prevailing pressure field is manipulated through a period of injection below fracture propagation pressure and simultaneous production from the neighbouring wells. Numerical simulation of fracture propagation shows that seepage forces strongly influence the propagation direction when an injection fracture propagates in a laterally varying pressure field. At slow propagation rates the pressure diffusion from the fracture itself causes alignment of the fracture with the injection well, i.e. the technique works because the injection rates are actively controlled.

Confinement of injection fractures along horizontal injector wells is verified by production data from areas where FAST has been implemented. After 2-3 years of injection, water breakthrough to the neighbouring producers has not occurred. A positive production response to the high rate injection is demonstrated by increasing oil rate and decreasing gas-oil ratio.
Visual Investigation of Oil Depressuristion in Pores with Different Wettability Characteristics and Saturation Histories
Authors: Nejad K. S. , Danesh A.
Published: December 2007

When the water-cut is too high for economical production, the field is usually abandoned with significant quantity of oil and gas still remaining in the reservoir. It is likely that in some cases a significant amount of gas and residual oil can be produced by the process of depressurisation. The underlying physics of the above complex three-phase flow is not well understood to allow reliable predictions to be made for economic evaluation of the process.

We have conducted flow visualization at the pore level using high-pressure glass micromodels to identify the key features of the process. Depressurisation tests were conducted on model fluids simulating black and volatile oil samples at several depletion rates. Micromodels with realistic pore patterns and different wettability characteristics, including water-wet, oil-wet and mixed-wet, were used in the tests. A series of experiments were performed to investigate the effect of fluid properties, depletion rate, saturation conditions, and wettability and saturation history on the nucleation process, gas evolution and hydrocarbon movement. Tests were conducted on water-flooded oil as well as virgin oil.

Our observation highlighted that gas nucleation was dependant on fluid properties, particularly the gas/oil interfacial tension (IFT). In high IFT systems, the nucleation behaviour and the degree of supersaturation were affected by the saturation history and system wettability. In volatile oil systems with low interfacial tension between gas and oil, nuclei could form homogeneously and independently of wettability conditions and saturation history. Critical gas saturation and subsequent gas/oil production are strongly affected by the critical value of supersaturation and the number of bubbles that are formed during the depressurisation process. Two generalized correlations were developed to predict the critical supersaturation and the number of bubbles. The correlations reliably predicted independent experimental data reported in the literature. The data generated by the study provides information on gas nucleation sites, the gas nucleation rate and build up of the gas phase, which are essential in field development planning and estimation of oil and gas recovery.
Development of a Hydraulically Expanded Metal Internal Casing Patch
Authors: Louden F. , Mathiassen E. , Hazel P. , Skjerping F. , Gorrara A. , Bøe K.
Published: December 2007

This paper details the technical development & implementation of a Coiled Tubing (CT) deployed, expandable internal metal casing patch. The driver for the development of the technology was to introduce an internal casing patch system for deployment in 7" tubing, designed to extend the completion life and delay a full workover operation. The compliant patch would provide a substantive localised tubing repair (e.g. water shut-off, leak repair, patch corroded pipe) with minimal internal diameter restriction to optimise access for future well interventions, and hence minimise the restriction to oil production (or water injection).
Physical and Rheological Behaviour of High Pressure-High Temperature Fluids in Presence of Water
Authors: Gozalpour F. , Danesh A. , Fonseca M. , Todd A. C. , Tohidi B. , Al-Syabi Z.
Published: December 2007

An equation of state-based phase behaviour model has been developed to describe the behaviour of high pressure-high temperature (HPHT) fluids in presence of water. The interaction between water (polar) and hydrocarbon (non-polar) has been simulated by addition of an asymmetric (non-random) term to the attractive term of a conventional (random) mixing rule. Vapour-liquid and liquid-liquid hydrocarbon-water solubility data of a wide range of hydrocarbons have been used to determine the binary interaction parameters of the conventional and non-random terms. The developed phase behaviour model was evaluated against two-phase and three-phase equilibrium data of hydrocarbon and water binary and ternary mixtures, not used in developing the model, over a wide range of temperature.

The impact of water on the viscosity of pure and binary mixtures of hydrocarbons at HPHT conditions has also been investigated. A HPHT facility equipped with a capillary tube viscometer was used to make the measurements at 150 and 200°C and up to 20000 psia. The generated data have been used to evaluate residual viscosity models.
Micro-PIV: A New Technology for Pore Scale Flow Characterization in Micromodels
Authors: Perrin C. L. , Sorbie K. S. , Tardy P. M. J. , Crawshaw J. P.
Published: December 2007

Etched micromodels have often been used to visualize complex fluid flow and displacement mechanisms at the pore scale. Studies have been reported of two and three phase processes such as waterflooding and water-alternating-gas (WAG) injection. Many of these models have been etched in glass although the use of etched silicon in their manufacture allows for the much more precise replication of two-dimensional (2D) network structures. A feature of previous micromodel studies is that they have almost exclusively been confined to making qualitative observations; e.g. descriptions of pore-scale displacement events, the effects of wettability, the formation and collapse of films etc. However, quantitative information relating for example to the network velocity field at the pore scale has never been reported and this issue is addressed in this paper for the first time.

Particle Imaging Velocimetry (PIV) is a well-known technique used in large-scale fluid mechanics experiments. It has recently been adapted to study microfluidics problems. As a result, the velocity field can now be measured at any location in pore-scale micromodels where the channels have widths of typical rock pores (10s – 100s μm). For the first time, this new technology, known as micro-PIV (μ-PIV), has been used to study the flow of Newtonian and non-Newtonian fluids in model pore channels with sizes typical of natural sandstone.

In this study, we apply μ-PIV to the flow of water, and non-Newtonian fluids in straight micro-capillaries. The μ-PIV experimental velocity profiles match the analytical solution for water, and the finite element calculations for non-Newtonian fluids, thus validating the technique. μ-PIV was then applied to the flow in a Berea sandstone replica micromodel. The potential of this technique is highlighted for use in several other applications of complex flows in porous media.
Reservoir Management for Fields Sharing Common Aquifer: A Case Study from North African Sandstone Reservoirs El-Sharara Fields A, H and M NC-115, Libya
Authors: Mohammed K. , Elbekshi A. , Ghnia S. , Al_lottai O. , Naas A. , Izaguirre G. L. E. , Fanjul J. P. , Grinberg M. , Mustieles F. J. , Montes G.
Published: December 2007

The El Sharara A, H and M fields lie in the centre and eastern part of Block NC-115, some 50 km west of the town of Ubari in SW Libya (Figure 1). The producing reservoirs are Ordovician Mamuniyat and Hawaz formations. Those fields form a 3-way dip structure with a fault closure to the east against the Tanezzuft shale.

The Mamuniyat sequences are the main reservoir in the A, M, West-H and North H-Fields. This reservoir is characterised by coarsening up-ward parasequences consisting of fine, medium to coarse-grained sandstones. The East-H field is producing from Hawaz reservoir. This reservoir comprises fine to medium grained, locally argillaceous sandstones.

The main drive mechanism is weak water drive. Initially, the oil is highly undersaturated. Moreover, the oil has high API and low GOR.

The fields have been on production since late 1996, and are produced through facilities shared with other fields in the area. The four producing reservoirs are the Mamuniyat A-Field, Mamuniyat M-Field, Mamuniyat H-West, and the Hawaz H- East. A total of 71 wells have been drilled in the producing area (Figure 2).

Before the H and M field came on stream a decline in pressure was observed while producing only from A-Field.

The main objectives of this study is a broad understanding of the nature of the intercommunication of those fields through an integrated regional reservoir engineering study and consequently optimize the field development and depletion plans.

This paper sets a framework for an integrated reservoir study and also demonstrates the benefits of a regional study to optimize the reservoir performance by considering the global approach instead of treating each field individually.

The El-Sharara fields are under a pressure maintenance project using water injection to support the weak natural drive. This study has set the guidelines for optimizing the water injection rates and areal distribution through understanding the strength of the aquifer and estimating the energy needed to arrest the decline in pressure of these reservoirs.
An Assessment of Seabed Impacts of Synthetic-Based Drilling-Mud Cuttings in the Gulf of Mexico
Authors: Neff J. M. , Hart A. D. , Ray J. P. , Limia J. M. , Purcell T. W.
Published: December 2007

The Gulf of Mexico Comprehensive Synthetic Based Muds Monitoring Program used a combination of physical, chemical, and biological measurements to survey fourteen drill sites on the continental shelf and continental slope of the Gulf of Mexico where cuttings generated during drilling with synthetic based drilling muds (SBM) had been discharged. The three continental shelf and three continental slope sites selected for more intensive investigation are the focus of this paper. The objective of the program was to document the distribution of cuttings in drill site sediments and to characterize the areal and temporal extent of chemical and biological changes due to cuttings discharges. None of the drill sites had large cuttings piles such as have been observed in the North Sea. Chemical and physical measurements in sediments collected during two surveys one year apart at a subset of eight of the drill sites showed that deposition of discharged SBM cuttings solids was limited to a radius of less than about 250 m from the discharge location. Mean synthetic based fluid chemical (SBF) concentrations in near-field sediments decreased during the year between sampling surveys. Benthic ecology parameters were measured at the three continental shelf discharge sites and sediment toxicity to amphipods was measured at the three continental shelf and three continental slope discharge sites. The benthic community within 250 m of the site with the highest SBF concentrations in sediments had reduced benthic faunal abundance and diversity. Benthic communities were only slightly disturbed at the other two sites. Amphipod survival exceeded 75% in sediments collected within 250 m of most of the drill sites on the continental shelf and slope, indicating that most SBM cuttings-contaminated sediments, even those close to the drill sites, were not toxic. A sediment quality triad (SQT) analysis, used to characterize the impacts of drilling discharges on sediment quality at the three continental shelf sites, identified a gradient of decreasing disturbance with distance in sediments collected within 250 m of the drill sites compared to sediments > 3000 m away. There was strong evidence that chemical and ecological recovery of sediments near SBM cuttings discharges was progressing during the year between the sampling surveys.
An Effective Hydrajet-Fracturing Implementation Using Coiled Tubing and Annular Stimulation Fluid Delivery
Authors: Surjaatmadja J. B. , East L. E. , Luna J. B. , Hernandez J. O. E.
Published: December 2007

The use of coiled tubing (CT) in fracturing was uncommon until a few years ago. Its applications have usually been limited to small jobs, and in reality, CT stimulation treatments have often been limited to acid placement treatments. With the inception of hydrajet fracturing technology, the use of CT has become more popular. Historically, CT fracturing methods were limited to placement of small fractures in the formation, and in some acidizing situations, near-wellbore damage-bypass methods.

CT technology has progressed until now it is used to place large fractures, some reaching over 600-ft half-lengths. Obviously, in most formations, such fracture sizes would not be possible with fluid delivery originating from the CT alone, so the use of the annulus to deliver the primary fracturing fluid becomes vital. This paper discusses the knowledge gained from recent field applications that have used this new annular path hydrajet-fracturing technology. Unique features of this technology are presented. Added benefits, such as the ability to deliver large proppant volumes, will be a focal point of this paper.

Case studies involving placement of multi-fracture treatments in three wells treated with this procedure will be discussed. Production improvements experienced in these wells will also be presented.
A Framework for Uncertainty Quantification and Technical-to-Business Integration for Improved Investment Decision-Making
Authors: Bos C. F. M.
Published: December 2007

To support the E&P investment decision-making process we use computer models extensively. This paper discusses in a conceptual way the potential merits of moving much more than what is currently being practised into the direction of "fully probabilistic" and "fully holistic" modeling, initially at the cost of model precision. In our opinion, the currently prevailing paradigm of maximum model precision (i.e. more physics, more grid blocks, more detail) may severely limit the optimization of the E&P decision-making process. Evidence for this statement is obtained when analyzing why the average of production and cashflow forecasts generally fails to coincide with the truth, as revealed in time: high-precision models on average result in biased forecasts and, hence, often lead to sub-optimal decisions or missed opportunities.

To explain our approach, we introduce two postulates, discuss three modeling dimensions and link this to the business process of decision-making. The first postulate, when modeling the E&P value chain for investment decision-making, is that all uncertainties having a potential material effect on the model outcomes must be quantified within a comprehensive, internally consistent framework, and be taken into account when making E&P investment decisions. The second postulate is that, when trading-off the degree of "model precision" vs. the degree of uncertainty modeling and/or the degree of holistic value chain modeling, the latter two are more important than the former, especially when uncertainties are large. Initially therefore, reduced-physics or "approximate" models may be used, enabling a more comprehensive decision analysis. After having thus optimized the decisions, the sensivity (or "robustness") of the optimal decision to model precision should be tested. Multi-tiered decision-making, real options and an extended definition of "value" are also discussed within the framework's context.
Probabilistic Discharge Forecasting For Improved Asset Investment Decision Support
Authors: Jannink J. W. , Bos C. F. M.
Published: December 2007

In this paper we present a new way of integrating discharge forecast uncertainties in asset investment decision-making. The approach can be useful in the face of uncertainties with respect to future government regulations and in the face of uncertainties in the environmental implications of a given development. We present a hypothetical case study on how an oil company could optimize its investment decision-making by comprehensively risking the various regulatory scenarios and combining these with capex and opex items of mitigating measures on the one hand, and financial penalties for exceeding certain tolerance limits on the other hand. Decision trees are used as decision-making framework. The proposed methodology is fully probabilistic in the sense that it models both discrete uncertainties (scenarios, or possible events beyond one's control) and continuous uncertainties (i.e. probability density functions of uncertain input parameters). The Monte-Carlo sampling process generates a statistical population for the production, discharge and cash flow time-series curves, and ascertains that the full information is propagated to each investment alternative at the decision nodes of the tree. For each alternative decision, the risk of exceeding discharge tolerance limits is directly calculated and translated into the financial risk of having to pay a levy.

The results of the simulated decision process with two types of financial government instruments indicate that probabilistic discharge forecasting can support both governments and asset managers. Governments can quantify prior to roll-out the chance that a certain policy will have the desired impact. Asset managers can use probabilistic emissions forecasting to optimize the asset's value by improving their decisions on mitigation facilities and operational policy. The hypothetical case study, assuming realistic developments in regulatory measures, indicates that an asset manager with an assignment to optimize net present value, will choose not to make any upfront investments in discharge mitigation facilities, resulting in less potential for future environmental protection. As a result of discounting, the long-term benefits do not sufficiently compensate the early investment.
K12-B A Test Site for Co2 Storage and Enhanced Gas Recovery
Authors: van der Meer L. G. H. , Kreft E. , Geel C. , Hartman J.
Published: December 2007

As part of the Dutch Climate Policy on the implementation of the Kyoto protocol, the Netherlands government is currently investigating to what extent CO2 sequestration in the deep subsurface could help reduce CO2 emissions. On 7 February 2002 the Dutch Minister of Economic Affairs introduced a new policy to promote feasibility studies into CO2 storage in the subsurface (The CRUST program).

Gaz de France Production Netherlands B.V. (GPN) is currently producing natural gas from the Dutch North Sea continental shelf. As one of the players in the Dutch gas supply market, GPN supports the idea of injecting CO2 into depleted gas fields in order to reduce CO2 emissions into the atmosphere.

The gas produced at one of GPN's platforms, the K12-B platform, contains a relatively high proportion of CO2. This CO2 is at present separated from the produced natural gas and released into the atmosphere. Preliminary assessment shows that it may be relatively easy to re-inject this CO2 into the Rotliegend gas reservoir. The reservoir is located at a depth of some 3800 meters; with a hydrostatic pressure regime and a formation temperature of 132 °C. Hence GPN's K12-B platform offers a good opportunity to study the technical conditions of CO2 injection at greater depths including the behavior of the gas reservoir itself. Developing the CO2- injection demonstration facility at the K12-B platform will increase our understanding of the benefits and drawbacks of this technique.

This paper reports on the results of the phase 1 and 2 studies of the ORC project - Offshore Re-injection of CO2. Phase 1 included a desk feasibility study into the possibility of underground CO2 injection at the K12-B platform. Phase 2 comprises of actual demonstration of the concept of underground storage. Some results of the early CO2 injection tests ar1 reported.
Quantifying Bypassed Oil in the Vicinity of Discontinuous Shales during Gravity Dominated Flow
Authors: Muggeridge A. H. , Jackson M. D. , Agbehi O. , Al-Shuraiqi H. , Grattoni C. A.
Published: December 2007

Gravity-stable, miscible gas injection is a common oil recovery technique throughout the world. In homogeneous environments recovery efficiencies may be more than 90%. However the influence of heterogeneity on the sweep efficiency in these recovery schemes is not well understood. For example most clastic reservoirs contain ‘discontinuous’ shales that cannot be correlated between wells. Several numerical studies have suggested that these may cause significant bypassing of oil during waterflooding or gas injection. However flow experiments and detailed simulation of viscous dominated displacements, without gravity, indicate that very little oil is bypassed1.

In this paper, we investigate flow patterns around discontinuous shales during vertical, gravity-influenced miscible gas injection in well-characterised bead-pack experiments at three flow-rates corresponding to unstable, partly stable and completely stable flow regimes. We examine the volume of oil bypassed and whether viscous fingering is reduced by gravity or altered by the presence of a discontinuous shale. The results are compared to the predictions of detailed simulation. We find that, during miscible displacements, an isolated shale causes negligible bypassing. However, during adverse mobility ratio displacements, the simulation program erroneously predicts significant bypassing of oil both upstream and downstream of the shale at high and intermediate flow-rates.
The Effect of Cross-Bedding Laminations on the Efficiency of Gas/Oil Multi-Contact Miscible Displacements
Authors: Al-Wahaibi Y. M. , Muggeridge A. H. , Grattoni C. A.
Published: December 2007

Many oil fields produce from fluvial sands where cross bedding lamination is one of the most common type of small-scale heterogeneity. To our knowledge, there are no published studies on the effects of cross-bedding laminations on multi-contact miscible (MCM) displacement processes and how they might alter the development of miscibility during oil recovery by gas displacement. This work aims to remedy this deficiency. A particular objective was to quantify the accuracy of compositional simulation when modelling sub-miscible displacements in these systems.

A series of well-characterized laboratory experiments in a two-dimensional, cross-bedded beadpack were carried out. A two-phase three-component (IPA/water/cyclohexene) liquid system, that exhibits an upper critical point at ambient conditions, was used as the fluid model. First contact miscible (FCM), immiscible and MCM displacement experiments were performed in the model laminated media. They were then simulated using a commercial compositional simulator with a single set of EOS parameters and without using history matching (the relative permeabilities as a function of IFT were obtained independently from displacement experiments in homogeneous packs).

The produced oil and gas in the experiments were found not to be in compositional equilibrium. This was observed both in homogeneous and heterogeneous packs. As a result the oil recoveries and gas cut predicted by compositional simulation for MCM displacements in laminated media differed significantly from the experimental results, although an excellent match was obtained for the FCM and immiscible displacements. The use of alpha factors, derived from MCM experiments in a homogeneous pack gave a much-improved prediction of experimental results for both condensing and vaporizing gas drives in both homogeneous and cross-bedded porous media.
Successful Peripheral Miscible Gas Injection in RKF Field, Berkine Basin, Algeria – Field Case History
Authors: Cubillos H. , Stright D. , Navarro J. M.
Published: December 2007

The paper discusses the discovery, development, and operation of a miscible gas cycling project in a highly undersaturated, volatile oil TAGI reservoir in center of the Berkine Basin, Algeria. Miscible gas injection was initially considered to be high risk and marginally economic; however, with a flexible development plan and careful reservoir management carried out by an integrated team of surface and subsurface disciplines, a successful project was implemented.

In RKF field, a significant portion of the oil-in-place is in the oil-water transition zone, permeability is low, clay content is high, the oil contains asphaltenes, the formation water is salt-saturated, and the fluvial stratigraphy is complex. Design of a successful gas injection project was particularly challenging under these conditions.

The RKF project demonstrates the importance of acquiring dynamic data early in the appraisal phase tracers and extensive data acquisition was critical to project optimisation and for solving operational `problems such as salt and asphaltene precipitation, minimisation of downtime, maximising liquid recoveries, and balancing of reservoir pressure throughout the field. Integrating all surface and subsurface engineering data, on a continuous basis, with the evolving geological and geophysical interpretations was critical to project success.
A Semi-Analytical Model for Productivity Testing of Multiple Wells
Authors: Fokker P. A. , Brouwer G. K. , Verga F. , Ferrero D.
Published: December 2007

This paper presents a new, semi-analytical method for calculation of the productivity of vertical, horizontal or multilateral wells draining either gas or oil reservoirs. Well interference effects and the presence of natural or induced fractures are accounted for.

The method is based on an earlier derived productivity prediction tool in which now moving pressure boundaries have been implemented to account for time dependence. The semi-steady-state pressure equations are solved using combinations of exact solutions around the well in an infinite reservoir and additional solutions to the Laplace equation are introduced to approximate the boundary conditions. The pressures and rates for all the flowing wells are solved in a single step for each required value of the time. Both numerical and analytical approaches have been used to validate the new method. The validity of the moving-boundary approach for the transient well behaviour has been checked against analytical results, whereas a numerical method has been employed to analyse the multi-well response in homogeneous, isotropic reservoirs.

Finally, the new method has been applied to real production test data. Both single-well and multi-well production tests performed in different types of reservoirs have been analysed with satisfactory results.
Drilling With Success: BHA Optimization for Coiled-Tubing Drilling in Harsh Environment
Authors: Maehs J. , Law A. , Pruitt R. , Weihe A. , Kiesl C.
Published: December 2007

Today's drilling environments require a CTD bottom hole assembly (BHA) be designed to perform in harsh environment. These include drilling in Underbalanced conditions (UB), challenging formations and high temperatures. This paper details findings from Coiled Tubing Drilling (CTD) operations in Alaska, Algeria and Sharjah.

These challenging operations required a complex CTD BHA that should be capable of withstanding temperatures in excess of 150°C (300° F), severe vibrations, over-speeding of motors, high-performance positive displacement motors (PDM's), nitrogen intrusion in BHA and PDM elastomer as well as many other challenges.

As a result, the CTD BHA was engineered to meet these various challenges. For example, in order to reduce (or better manage) BHA dynamics under extreme vibration levels, a multi-axis vibration sensor was used to optimize the BHA with weight and flexible bars. This permitted the driller to monitor vibration levels in real-time and adjust drilling procedures and parameters (WOB, mud flow, use of circulating sub, etc.) to reduce excessive vibrations. The BHA also had to address telemetry issues and, on the Sharjah nitrogen-drilled wells, an E-line CTD BHA was employed as it was the only way to transmit MWD/LWD data in the multiphase mud flow.

The paper will also describe some of the special BHA features like multi-cycle circulating sub use, ECD/pressure management, high-speed motor use and more. And the results of these efforts will be documented with performance and vibration graph comparison.

In the previous two years, drilling processes on the Sharjah and Alaska wells were significantly improved for increased footage per day and lower overall well costs. As a result, these projects have been recognized as economic successes and the findings from these wells can be applied to optimize the drill string and drilling parameters for enhanced performance in other challenging environments.