bluuebunny/crossref_metadata_2025 huggingface dataset:
An Integrated Approach to Basinwide Management Plans
Authors: Engler T. W. , Brister B. , Henke S. , Zent J. , Dembowski R.
Published: December 2007

The San Juan Basin of Northwest New Mexico is a significant contributor to the energy needs of the United States, accounting for 68% of the natural gas produced in the state (approximately 8% of the U.S. production) or 1.135 Tscf in 1999. The reliance on natural gas to meet future energy needs and the desire to manage these resources in a environmentally responsible manner, led to an integrated team of academia, industry and government to evaluate the Reasonable Foreseeable Development (RFD) in support of BLM's Resource Management Plan. The scope of this study encompasses the New Mexico portion of the San Juan Basin, beginning with an effective date of January 1, 2002, with a duration of 20 years.

Two approaches were used to predict the development potential. The first approach was a survey of operating companies in the San Juan Basin, obtaining their perspective of future development based on current reservoir management practices. The second approach applies engineering and geological techniques to optimize infill drilling in naturally fractured, low permeability gas reservoirs of the basin.

The results of this comprehensive study led to an estimate of 10,000 well locations on federally-managed land predicted as reasonably foreseeable over a 20-year duration. Associated with the well development will be the need for additional surface facilities to efficiently recover the gas and transport it to market. As a result of anticipated expansion of the takeaway capacity out of the basin through enhancement of old pipelines and construction of new pipelines, additional gas gathering systems and central compression will be necessary. Furthermore, an important finding of this work was the significant reduction in the number of wells needed to efficiently drain the multiple reservoirs present through opportunities for commingling and dual completions; consequently reducing the surface impact of additional wells.
Stability of an Openhole Completed in a Limestone Reservoir with and Without Acid Treatments
Authors: Morita Nobuo , Doi Tomoki , Kinoshita Takanori
Published: December 2007

Since a borehole in a limestone formation is more stable than expected, an openhole completion without a slotted/perforated liner has become popular recently. However, the following three items are not clear: (1) Why a borehole in a limestone formation is so stable?; (2) A borehole in a limestone formation can be completed without a liner regardless to the formation strength?; and (3) How about the stability after acid treatments? To answer these questions, two types of laboratory experiments are conducted. One of them is a series of borehole stability experiments using 1.5 and 2.36–2.39 inches diameter borehole in a 10.5×10.5×17.5 inches limestone blocks with polyaxial confining pressures simulating a horizontal well with three different principal in-situ stresses. Two types of limestones are used with and without borehole acid treatments and two borehole sizes are used to check the size effect. Another type of experiments are acid squeezing experiments where 15% Hcl acid solution is squeezed from one end of a cylindrical core and the change of porosity, permeability, and hardness are measured throughout the cores. The results showed that (1) boreholes in a limestone induce a shear failure at the borehole surface after a pore collapse is induced. Note that boreholes in other stones normally collapse with a shear failure before a pore collapse is induced within the depth where hydrocarbon reservoirs are discovered. Because of the highly ductile shear failure after a pore collapse, a horizontal well is stable even though the ratio of effective horizontal stress and vertical effective stress is high. (2) The reaction rate between Hcl acid and limestone is so high that most acid reaction occurs within 0.2 inches from the borehole surface. The surface layer of acid treated borehole becomes malleable due to porosity increase, resulting in protecting formation acting as a soft liner. On the other hand, the borehole surface becomes irregular and enlarged. Because the above two factors compensate each other after acid treatment, the boreholes remain reasonably stable although a small strength reduction is observed. (3) Normally, since limestones are relatively strong, openholes are likely stable, however, the strength must be checked if they need to be completed without a linear protection.

To help a reader applying the laboratory results to field problems, a guideline to complete an openhole without a liner protection in limestone reservoirs is provided with calculation results using a non-linear finite element model.
A New Technology for Resistivity Anisotropy Evaluation in Conductive Borehole Environments
Authors: Frenkel Michael A. , Geldmacher Ingo M.
Published: December 2007

The drilling industry is turning from the use of oil-based mud to environmentally sensitive water-based mud systems. However, highly conductive water-based mud tends to limit the effective dynamic range of induction instruments, such as the multi-component induction well logging tool (3DEXSM).

To illustrate the influence of the conductive borehole and invasion on the 3DEX logs, we performed theoretical simulations for a simple 2-D formation model.

To expand the operational range of the 3DEX technology in a water-based mud environment, we propose logging the 3DEX tool in combination with galvanic tools (Dual Laterolog, DLL and Micro Laterolog, MLL, or array lateral log, HDLL, and MLL) and apply the following sequential data interpretation procedure: Determine the formation resistivity structure of the near wellbore environment and the horizontal resistivity of the uncontaminated zone using the galvanic measurements,Determine the vertical resistivity and formation resistivity anisotropy of the uncontaminated zone using the results of the previous step and the deep 3DEX measurements.

Evaluation of this technology on a series of synthetic models allows us to outline the expanded 3DEX operational environment. The presented field example validates the technology.

The conclusion is that the combination of galvanic and induction measurements along with an inversion-based data interpretation method can effectively extend the dynamic range of the 3DEX technology, allowing the use of this technology in wells drilled with conductive water-based mud systems.
Well-site Resistivity Anisotropy Interpretation: A 2-D Method and a Case Study from the Gulf of Mexico
Authors: Frenkel Michael A.
Published: December 2007

A novel rapid inversion method has proved to be one of the fastest methods designed for accurate, multi-dimensional interpretation of array resistivity logs. In this paper, we discuss the development of this method as a basis for future well-site anisotropy interpretation, using data recorded with the 3D ExplorerSM multi-component induction instrument (3DEXSM).

The new method demonstrates the feasibility for a substantial reduction of computing time by partitioning the two-dimensional (2-D) inverse problem into a sequence of smaller one-dimensional (1-D) problems (radial inversion). It rapidly converges to a true earth model. In the case of a vertical well (2-D), the method requires multiple 1-D, yet only a few 2-D forward model calculations. To achieve this substantial extra increase in computing speed, 1-D forward responses are pre-calculated and stored as look-up tables to be consulted at inversion time. The computations required for a full 2-D interpretation process is thus reduced to a set of four to five 2-D forward response calculations at a limited number of observation points. As a result, the proposed method allows the entire spectrum of measurements to be combined as a part of an interpretation scheme suitable for well-site processing. The method is capable of providing a consistent and accurate picture of formation resistivity anisotropy.

The potential for the technique is presented and illustrated by anisotropy interpretation results from 3DEX data acquired in a vertical well in the Gulf of Mexico. These results are shown to be in excellent agreement with what is inferable directly from the raw 3DEX logs. They are also in good agreement with results from an independently performed anisotropy interpretation based on a rigorous 2-D inversion technique.

A field example confirms the capability of the proposed technique to deliver comparable quality results now achievable with standard log analysis center processing in run times comparable to run times for other familiar well-site deliverables.
Achieving 100 Percent Success in Acid Stimulation of Sandstone Reservoirs
Authors: Rae Phil , Di Lullo Gino
Published: December 2007

Acid stimulation of sandstone reservoirs is viewed by many as a risky enterprise and one that should be undertaken only as a last resort. Much of this reluctance stems from the complex, heterogeneous nature of sandstones(1) and the unpredictability of their response to conventional oilfield acid formulations. Indeed, with an inappropriate acid design, or poor job procedures, even the best candidate well can be damaged, sometimes irreversibly. With the loss of experience and expertise due to industry downsizing, there is some concern that the risk of such failures has increased.

This paper discusses the implementation of an acidising methodology with the goal of attaining 100 percent success in acid stimulation treatments. A cornerstone of the strategy involved the development of a personal acidising mentor for every engineer to help them avoid the pitfalls of inappropriate design. The only practical way to achieve this was by the use of computers, programmed with the many rules used by human experts in the design of acid treatments. These rules take into account such variables as mineralogy, temperature, formation fluids, permeability, porosity and tubular metallurgy, amongst others. Integration of these rules, based on an array of algorithms coupled with heuristic principles, outputs a preferred acid design along with recommended acid volumes, pre- and post-flushes, nitrogen ratios for flowback and a customized message board with hints, tips or warnings about the potential treatment. The design advisor also incorporates recommended loadings of corrosion inhibitors, iron control agents, clay control additives, surfactants, solvents, anti-sludges and diverting agents, etc. as and when required.

Application of this approach has helped fill the gap caused by the widespread loss of experienced industry personnel and has accelerated the learning process among younger engineers. It has also helped ensure that only appropriate acid treatments are recommended and pumped in any location, worldwide. The paper reviews the results of over 100 acid jobs designed using this methodology.
The Economics of CO2 Capture and Geological Storage
Authors: Nguyen D. N. , Allinson W. G.
Published: December 2007

Capturing CO2 from stationary sources such as power stations and petroleum processing plants and storing the CO2 into deep geological formations can potentially reduce greenhouse gas emissions in Australia. The cost of capturing CO2 could vary from below US$30 to above US$70 per tonne of CO2 avoided for coal-fired power stations typical of the stations used in Australia. In addition, storage costs can vary from below US$5 to above US$20 per tonne of CO2 avoided. These figures are based on capturing and storing pure CO2. Capturing other greenhouse gases in addition to CO2 might lower the unit costs of capture significantly. However, this needs to be balanced against the consequent increase in storage costs.

As regards capturing CO2 from petroleum extraction activities, the corporate income tax and Petroleum Resource Rent Tax ("PRRT") regime in Australia could potentially have large effects on the economics of CO2 capture and storage depending on the situation. If capture and storage attracted full income tax and PRRT relief, the after tax cost of CO2 capture and sequestration could be less than 50% of the before tax cost. However, such tax savings would be offset by benefits that might arise from any future carbon tax or carbon credit trading.
Environmental Responsibility: A Panacea for Operational Disturbances in Offshore West Africa
Authors: Ifebajo Adebayo J. , Ibizugbe Osaze
Published: December 2007

Reports from onshore E & P activities in Nigeria have shown that operating in the Niger Delta region poses some of the toughest challenges in the world. This region has witnessed a spate of attacks on oil and gas facilities, staff and contractors. Consequently, major oil and gas players have to contend with complex operational uncertainties due to increase pressure from the local communities for improved environmental control measures.

To effectively de-risk this region of this category of operational uncertainties, the industry must begin to see environmental performance as not only a measure of how well she can comply with existing environmental regulations, but also as a measure of how well she can pre-empt environmental pressures as well as maintain constant harmony with all concerned stakeholders and seeing herself as responsible to the environment with a view to improve performance.

In this project, we have been able to develop SMART* models based on continuous consultation, integrated management approach and continuous improvement attitude (CIA). With a good FOCUS* approach, this will help in safe and effective operations, pre-empt pressures, maintain harmony with local communities and effectively manage operational disturbances within complex environmental settings like the Nigerian Niger Delta area. Finally, we are of the opinion that every industry that seeks to remain efficient and relevant in this millennium should constantly be looking for ways of becoming more environmentally responsible -because no business can call itself efficient if it threatens the environment within which it operates.

• SMART is an acronym for Specific, Measurable, Achievable, Realistic and Time Bond.

• FOCUS is an acronym for Fair, Objective, Consistent, Unbiased and Succinct.
Eliminating Environmental Risks in Well Construction and Workover
Authors: Rae Phil , Di Lullo Gino , bte Ahmad Atikah
Published: December 2007

We are fortunate to live in a world where awareness of the detrimental effects of pollution is on the increase. Such awareness will help ensure protection of the biosphere and safeguard future generations. The oil and petrochemical industries, which have been responsible, to a large extent, for the development of the modern world and vast improvements in living standards in many places, are often targeted mercilessly by environmental activists. This is done without due regard to the criticality of oil both as a fuel and as the fundamental raw material for countless pharmaceuticals, dyes, plastics and consumer products.

In general, despite press reports to the contrary, our industry has a fairly good pollution record, when compared to other major businesses. However, there is no room for complacency and it is important that we continue to be proactive in the implementation of strict environmental controls. Oil itself is usually perceived to be the biggest acute environmental threat, but, in addition, there are many well construction and workover operations that involve the use of chemical additives. Some of these materials are toxic and some may not biodegrade at acceptable rates. With an increasing awareness of the potential environmental impact of chemical additives, particularly in the marine environment, there is a continuing need to develop more efficient, less toxic alternatives.

Thanks to intense efforts, many potentially harmful chemicals have already been removed from active service and replaced with new, field-proven and eco-friendly systems that have been tested in accordance with OSPARCOM guidelines, or their equivalents. Use of such materials offers benefits in terms of health and safety and, ultimately, potential cost reductions when disposal and waste handling charges are factored in.

This paper reviews the development and field application of several novel materials for well completion and stimulation and suggests ways to improve or accelerate the implementation of environmental strategies.
Emulsion Treatment Utilizing Hot Produced Water
Authors: Razalli Ir. Razmahwata Mohd. , Sahat Marwan
Published: December 2007

Emulsion treatment has always been a constant challenge in offshore crude production, even more so when the success of chemical treatments are critically dependant on process temperature. In the Guntong Complex operation, production from satellite platforms were cooled by sub-sea transit and made the emulsion processing of crude at the central processing platform(CPP) difficult. Emulsion is broken at the CPP using demulsifier chemical and the effectiveness is temperature dependant. Ineffectiveness of the demulsifier chemical coupled with constraints on BS&W (Basic Sediment & Water) and produced water discharge quality eventually created a production bottleneck as the satellite production water cut increased. Recognizing emulsion chemical treatment is still applicable but ineffective due to insufficient temperature, various heat addition options were evaluated while taking into account the set-up and limitations of existing facilities. The ‘hotwash’ concept, where the ‘hot’ central processing platform fluid is mixed with the incoming ‘cold’ satellite streams to raise processing temperature was implemented as it is also the most cost effective solution. As Guntong Complex is a matured field, the project has greatly increased the ability of CPP's facilities to sustain satellite production by implementing the ‘hotwash’ concept.
Integrated Reservoir Management in an Intelligent Well Environment
Authors: Martinez J. K. , Konopczynski M. R.
Published: December 2007

This paper describes the work process, data management, analysis tools, architecture and capabilities of integrated reservoir management in an intelligent well environment. An example of a "real-time," web-enabled intelligent-well reservoir management system is provided. The challenges associated with implementing the system are described, and benefits realized from its use are documented.

A current hurdle to realizing the economic potential of intelligent wells is the lack of integrated tools and work processes to manage the wealth of production data. The systems described in this paper are designed to overcome this hurdle. The systems are applicable not only to assets employing intelligent wells, but also to conventional assets or those with a mix of intelligent and conventional wells.

Technically, an Internet connection transmits "real-time" data from the wellsite to a central host. The latest in industry standards including communication, security, data warehousing, streaming protocols are utilized. Statistical, nodal analysis and predictive modeling techniques are provided and are continually enhanced in the webenvironment. These allow the petroleum professional to examine what-if scenarios to quantify the effect of changes in reservoir conditions or well geometry and to recommend optimum settings for enhanced recovery.
Prevention and Control of Gas Hydrates for Foam Combination Flooding
Authors: Zhang Jicheng , Song Kaoping , Dong Bo , Chen Donghui
Published: December 2007

Foam combination flooding is one of the most capable tertiary oil recovery techniques. For the pilot test of foam combination flooding performed in Sa-Nan, Daqing, gas hydrates affect the normal gas injection badly. The designed gas injection is 182 days, however, due to the influence of gas hydrates, only 59 days of gas injection is conducted. The injected gas is just about 36 days' work in the design. Based on the pilot test in Sa-Nan, this paper elucidates the structure, phase state and forming condition of gas hydrates and proposes a number of effective measures to prevent and remove the formation of gas hydrates in the process of foam combination flooding. Two models for predicting the forming condition of gas hydrates for foam combination flooding are presented in this paper. Phase-equilibrium-constant method is proved to be more accurate and reliable than empirical graphic method and is recommended for use in research work and field practice to determine the forming condition of gas hydrates in foam combination flooding. With this method, the forming condition of gas hydrates in Sa-Nan pilot is calculated. The result shows that gas hydrates will generate at temperature lower than 73.4°F. Three ways are proved effective to prevent the formation of gas hydrates for foam combination flooding, which are reducing the water content of natural gas, improving the injection technology to avoid the contact of water with gas and adding certain suitable inhibiting agent. Heating, lowering pressure and adding deicing agent are suggested as the three good measures to get rid of the plugging in injection pipelines caused by gas hydrates for foam combination flooding.
Abductive Networks: A New Modeling Tool for the Oil and Gas Industry
Authors: Osman E. A. , Abdel-Aal R. E.
Published: December 2007

Artificial neural networks have been proposed for solving many problems in the oil and gas industry, including seismic pattern recognition, permeability and porosity prediction, identification of lithofacies types, prediction of PVT properties, estimating pressure drop in pipes and wells, and optimization of well production. However, the technique suffers from a number of limitations. This paper introduces Abductive Networks as an alternative modeling tool that avoids many of the neural networks limitations. While the processing elements in neural networks are restricted by the neuron analogy, abductive networks use various types of more powerful polynomial functional elements based on prediction performance. Based on the self-organizing group method of data handling (GMDH), this technique uses well-proven optimization criteria for automatically determining the network size and connectivity, and element types and coefficients for the optimum model, thus reducing the modeling effort and the need for user intervention. The abductive network model automatically selects influential input parameters and the input-output relationship can be expressed in polynomial form. This enhances explanation capabilities and allows comparison of the resulting data-based machine learning models with existing first principles or empirical models.

The main objectives of this paper are to introduce abductive networks and outline their advantages over neural networks. Also, to put abductive networks into perspective from petroleum engineering point of view and encourage petroleum engineers and researchers to consider them as a valuable alternative modeling tool. The technique was successfully used in areas such as weather prediction, energy forecasting, spectrum analysis, and medical informatics, but has not been much utilized in the oil industry. To demonstrate the usefulness of the technique in this area, we describe the use of abductive networks for predicting the Pressure-Volume-Temperature (PVT) properties. Results indicate that abductive network models outperform other models and empirical correlations. Finally, some other potential applications in the oil and gas industry are briefly discussed.
Permeability Characterisation: A Novel Technique for Estimating Gas Recovery Factors
Authors: Kabir Mohammad I
Published: December 2007

A novel method is developed that allows estimation of gas recovery factor without permeability averaging. In this method recovery factor as a function of permeability is generated for each depth-interval (in a wireline log) utilising a one-dimensional (1-D) radial model. The 1-D recovery data over producing intervals is then volumetrically added to obtain recovery factor for the well. The reservoir average recovery factor is then calculated on the basis of permeability-thickness weighting of individual wells to account for lateral variations.

This is a simple technique based on a simple depletion model which allows a quick estimate of recovery from multizone, multi-well gas fields with variable permeability making recovery from different zones and different wells vary widely. This paper presents the basis of the technique and illustrates its application using several field examples.
The Multiphase Flowmeter, A Tool for Well Performance Diagnostics and Production Optimization
Authors: Kettle R. J. , Ross D. , Deznan D.
Published: December 2007

The Dual-Energy Venturi Multiphase Flowmeter (MPFM), has gained acceptance within the Oil and Gas Industry as an accurate and cost-effective solution to multiphase metering. has now been implemented by the Australian Petroleum industry on the Apache Energy Simpson Alpha, Bravo and Gibson remote mini-wellhead platforms.

Eliminating the conventional test separator has led to wide-ranging improvements in engineering, financial and Operations areas. In addition, the field data are being used in a wide range of new and beneficial applications, including new field development, rapid deployment, artificial lift optimization and well-clean up optimization operations.

Integration of the MPFM packages into Customer supervisory control and data acquisition system (SCADA) and the connectivity achievable through these compact metering packages, has shown the benefits the customer may obtain by providing real-time data to operations and reservoir critical management functions. Connectivity for remote fault diagnosis and maintenance actions significantly reduces Field Service Operational Expenditure (OPEX) costs, and nonproductive time for field service personnel, which is particularly beneficial for installations in areas that lack infrastructure.

The applications, and commissioning of the MPFM packages and other low-cost technologies are illustrated in the paper. The straightforward nature of the Vx* multiphase well testing technology installation process brings distinct advantages to these applications, provided that methodical preparation is performed beforehand.

The key to the success of the multiphase flowmeter, as a tool for well performance diagnostics and production optimization, is its high availability and long-term performance stability, underpinned by the local and regional support network available to customers.

In the future, challenges remain in the interpretation of the new information being gathered, which document previously unrecorded inflow and outflow behaviors, with unmatched resolution and dynamics.
Applications of Permanent Downhole Pressure, Temperature, and Flow Rate Measurements for Reservoir Description and Production Optimization: a Taxonomy, Processes, and Benefits
Authors: Queipo Nestor V. , Verde Alexander , Goicochea Javier , Romero David , Zambrano Alexander , Bracho Annette
Published: December 2007

The resolution and accuracy provided by the existing technology for downhole (pressure and temperature) and rate measurements are unprecedented. However, while the potential benefits have been outlined, the models and processes required to reap these benefits (in particular the quantifiable ones) have not been sufficiently documented. In addition, considering the increasing number of reported work in this area, it is necessary to provided a framework for the analysis and discussion of existing and upcoming applications.

This paper presents a: i) summary and classification of downhole and flow rate measurements applications, ii) a discussion of their benefits for reservoir description and production optimization, and iii) the models and processes required to obtain those benefits.

The above-referenced applications are classified in three main areas: reservoir characterization, reservoir/well flow modeling, and process monitoring. The discussion of each application includes: benefits, previously reported work, required measurements and other relevant data, and a general description of the necessary models and processes.

The paper is expected to be useful assessing the possible impact of investments (business cases) in permanent downhole and flow rate measurements, designing plans for the development or acquisition of applications, and establishing the knowledge requirements in the context of training programs.
An Analytical Model for Production Estimation from Hydraulically Fractured Tight-Gas Reservoirs
Authors: Rahman M. M. , Rahman M. K. , Rahman S. S.
Published: December 2007

In relatively high-permeability reservoirs, the pseudo-steady state (PSS) flow condition dominates the production life of a well, and therefore modeling of production profile considering this flow condition only is found adequate. In tight-gas reservoirs, however, the early production period is dominated by the transient flow condition whereas the later period by the PSS condition. Neither of these conditions alone can be used to adequately model the production profile during the entire production life of a tight-gas reservoir. The creation of hydraulic fracture also influences the flow conditions and thus the production profile. This paper presents an analytical method, which combines both the flow conditions and account for the effect of hydraulic fracture and non-Darcy components for computationally efficient estimation of production from tight-gas reservoirs. An algorithm is then presented to couple these two different models by a production rate matching technique, which has resulted in a hybridized transient-pseudo-steady-state (TPSS) model to predict the production profile during the whole production life. The production profiles and resulting pressure profiles for both TPSS and PSS models are verified by a reservoir simulator for a range of reservoir permeability. The TPSS model is found to be closer to the results from simulation for low-permeability reservoirs.
Completion, Perforating and Hydraulic Fracturing Design Changes Yield Success in an Area of Problematic Frac Placement— the Cooper Basin, Australia
Authors: Johnson Raymond L. , Aw Keong P. , Ball David , Willis Mike
Published: December 2007

High stress, high near-wellbore pressure losses (NWBPL) and pressure-dependent leakoff (PDL) contribute to premature screen outs during some fracturing treatments in the Cooper Basin of South Australia and Queensland. In one case, an unsuccessful attempt to hydraulically fracture a well occurred because of limitations raised by completion design, insufficient stress data forewarning high-stress observations, and inadequate ability to counter high NWBPL and PDL effects.

We reviewed the current completion, hydraulic fracturing design and treatment execution practices and concluded that changes should be made in these areas: stress modeling/layering, completion design, perforating practices, hydraulic fracture design strategy, management of PDL and on-site treatment execution strategy. The largest departure from current practices was the use of 0- and 180-degree oriented perforating; thus, we describe the methodology chosen for this case, discuss current means to orient perforations and review alternative methods available.

The specific changes in hydraulic fracturing design and execution included: developing and calibrating log-derived rock-mechanical properties; incorporating PDL characteristics in the hydraulic fracturing treatment design; and applying specific job steps to reduce PDL and NWBPL. Our evaluation presents our frac implementation strategy and describes field fracturing treatments applying all these changes. Wherever possible, we will discuss the considerations that lead to our choice of actions and must be made when evaluating the potential applications of these technologies.
Marine Transportation of Compressed Natural Gas a Viable Alternative to Pipeline or LNG
Authors: Wagner Jan V. , van Wagensveld Steven
Published: December 2007

The invention of the "Coselle" pressure vessel by Cran & Stenning of Calgary, Alberta, Canada and the development of the Coselle Compressed Natural Gas (CNG) Carrier promises to improve the economics of shipping natural gas over short sea routes, and from modest reserves. This invention also ignited renewed interest in CNG marine transportation and a few other concepts entered the scene: Enerseas' VOTRANS and TransCanada's GTM.

The general promise from all these CNG concepts is to economically explore modest reserves in moderate daily volumes over shorter transportation distances, thus unlocking reserves which would remain stranded where either pipeline or LNG are considered.

This paper provides an overview of current CNG technologies, compares those to pipeline and LNG and provides general insight regarding the commercialization of this concept.
Asphaltenes Characterization: A Key to Deepwater Developments
Authors: Jamaluddin A. K. M. , Nighswander J. , Joshi N. , Calder D. , Ross B.
Published: December 2007

The continuous pursuit to discover new hydrocarbon reserves is driving oil and gas exploration companies to explore in more challenging environments, such as in deep water. One of the major challenges in these environments is to understand the characteristics of hydrocarbon solids deposition and its potential for production disruption. Asphaltenes are one of the hydrocarbon solid materials that have the potential to form, flocculate, and deposit in the production circuits. This process can come about as a result of changes in pressure, temperature, and/or composition.

In this paper, we present a systematic approach to characterize asphaltene materials using state-of-the-art technologies. In summary, a fixed-wavelength near-infrared light-scattering technique (NIR) is used to prescreen the thermodynamic onset of asphaltene flocculation. Subsequently, a variable-wavelength spectral analysis system (SAS) is used to estimate the asphaltene particle size and the growth kinetics. Finally, a high-pressure microscopy (HPM) technique is used to better understand the morphological behavior of the asphaltene materials.

These laboratory techniques can greatly enhance the understanding of asphaltene flocculation and the risk of potential deposition at the beginning of field development. As a result, operators may have the option to proactively prevent deposition or design remediation methods during the planning phase of the deepwater development that will reduce the risk of flow disruption.
Stress Induced Changes in Two-Phase Permeability
Authors: Jones C. , Smart B. G. D.
Published: December 2007

An accurate knowledge of porosity and permeability is crucial to accurate simulation of reservoir performance and enhanced reservoir management. Porosity and single-phase permeability of reservoir rocks is dependent on the stress experienced by the rock mass, which in the simplest case is given by the overburden stress minus the pore pressure. Hydrocarbon production decreases the pore pressure causing an increase in stress. This causes coupled changes in permeability and porosity, which have a significant effect on production rates. The stress and permeability changes are particularly large in the near wellbore region.

The experimental programme was performed to examine the changes in two-phase permeability during deformation. This consisted of experiments where, starting from a given hydrostatic stress level, σ1 was increased until the rock failed and a shear fault was formed. In all experiments core flooding took place during the stress changes, either single-phase core flooding, oilflooding at Swi or waterflooding at Sor. The experiments were performed on a water-wet sandstone.

The deformation experiments were performed over a range of confining stress. Single phase, oilfloods and waterfloods, were performed at each stress. The stress strain behaviour, peak stress, residual sliding stress were independent of flooding type, but the variation of permeability was different depending on whether it was single or two phase flow. At low confining stress the single-phase experiments showed a smooth drop in permeability with strain, the oilflood showed first a decrease then a recovery then a steep drop at failure. The waterflood gave an intermediate behaviour between the other two. The results can be explained as an interplay between two mechanisms, compaction induced increase in tortuosity decreasing permeability and a dilatant increase in pore volume increasing permeability. At high confining stress the results showed the same effects except that the higher pressure inhibited dilatant cracking.

This work has applications in determining the effect of the stress path on the permeability of the reservoir. The differences between the single and two-phase permeability are of great importance when the reservoir stress changes are likely to cause failure. The single-phase data greatly underestimates the actual permeability change.
Continuous Scratch Testing on Core Allows Effective Calibration of Log-Derived Mechanical Properties for Use in Sanding Prediction Evaluation
Authors: Suárez-Rivera Roberto , Stenebråten Jørn , Dagrain Fabrice
Published: December 2007

This paper discusses the use of continuous scratch testing for evaluation of rock heterogeneity and effective correction and calibration of mechanical properties predictions using wire line logging. Understanding the vertical variability of rock properties (strength and moduli) along the reservoir thickness is of primordial importance for sanding prediction analysis. Logging measurements (GR, Sonic, Density and Porosity) are traditionally used to identify troublesome intervals, to select sections for laboratory testing and for extrapolating laboratory data to untested reservoir sections. However, depending on the scale of the reservoir heterogeneity, the log measurements, by providing integrated values over their window of vertical resolution, can considerably underestimate the strong reservoir sections and overestimate the weak reservoir sections. This leads to misrepresentation of critical weak layers with high potential for sanding and potentially to large errors in the completion strategy with costly long-term consequences. Corrections are thus necessary and are traditionally based on simple unconfined compression (UCS) tests conducted sparsely or at high density, varying from operator to operator. This paper presents a method for log-correction based on continuous core scratching in the laboratory and shows that the methodology is effective in evaluating changes in properties with high accuracy and a resolution of at least 1 cm.
Shale-Fluid Interactions Measured Under Simulated Downhole Conditions
Authors: Ewy R. T. , Stankovich R. J.
Published: December 2007

Preserved shale samples, from four different shale cores, were exposed to various fluids while under simulated downhole stress conditions. Prior to fluid exposure, the samples were not contacted by any aqueous fluid, including simulated pore fluid. Time-dependent measurements of pore pressure, swelling and acoustic velocities were made. Pore pressures both less than and greater than the applied fluid pressure were observed, and apparent osmotic membrane efficiencies are calculated. Swelling was found to depend not only on the shale type and the fluid, but also on the level of confining stress. Swelling anisotropy was observed. Acoustic velocities were found to change as a result of fluid exposure, and the amount of change is dependent on the fluid type and on the existence of swelling.
Investigation of the Undrained Loading Effect and Chemical Effect on Shale Stability
Authors: Chen G. , Ewy R. T.
Published: December 2007

An investigation was performed to determine and compare pore pressure, stresses, and critical mud weights using poroelastic analyses with and without including the undrained loading effect. The undrained loading effect, which enables a fully-coupled poroelasticity analysis for wellbore stability, can be crucial to the stabilization of near-wellbore formations within the critical time even though it will diminish at long time. The critical time, or the duration, of the undrained loading effect is found to be inversely proportional to formation permeability and will vary considerably for formations with different permeabilities. It is also demonstrated in this paper that it is the dimensionless time, not the dimensional time, that controls the duration of the undrained loading effect.

Chemical effects, caused by the imbalance between the water activity in the drilling mud and the shale water activity, are also found to affect shale stability by changing pore pressure and shale strength with exposure time. Including all effects (hydraulic diffusion, undrained loading, and chemical effects), one finds that the required mud weight can increase with time, decrease with time, or first decrease and then increase. Furthermore, the change in required mud weight with time is different at different radial positions. The chemical effect does not alter the undrained loading effect, but it may counterbalance the common destabilization of the undrained loading mode.
New Model for Predicting the Rate of Sand Production
Authors: Willson S. M. , Moschovidis Z. A. , Cameron J. R. , Palmer I. D.
Published: December 2007

A number of robust predictive methods for establishing sanding thresholds have been developed over the past decade. Having identified when the onset of sanding occurs, recent research efforts have focused on determining the rate at which sand will be produced once these thresholds are exceeded. In this paper a new analytic model for predicting the rate of continuous (steady-state) sand production is described. This sanding rate model is consistent with the threshold prediction model, and utilizes as its basis the non-dimensionalized concepts of loading factor (near-wellbore formation stress normalized by strength) and Reynold's number (a function of permeability, viscosity, density and flow velocity). Interpreted this way, the results of laboratory sand production experiments are used to derive an empirical relationship between loading factor, Reynold's number and the rate of sand production. A second empirical sand production ‘boost factor’ incorporates the effects of water production. The derived model is compared with field data from a total of six wells from two fields, for a wide range of flowing conditions. The predictions are a good match to the field data, typically overestimating the field-measured data by a factor of less than four. However, as the model is for continuous sanding only, this degree of overprediction is considered acceptable for field application, as it provides some compensation for short-lived transient sand production at rates higher than steady-state values.
Borehole Design: Stability Considerations
Authors: Gil Ivan , Roegiers Jean-Claude
Published: December 2007

In recent years drilling for hydrocarbons have become a much more challenging task as nice, blanket-type reservoirs are now part of history and appear mostly in textbooks and old reports. The current economic and political world environment demands fewer, more "difficult" wells to be drilled and produced. Wellbore stability problems account for huge over-costs worldwide.

Tectonically active areas, thin interlayered horizons, unconsolidated rocks; deep and hot formations are part of the geological environments where hydrocarbons are currently produced from. The degree of planning and problem anticipation at both drilling and production stages will determine the difference between a productive reservoir and a technical/economical failure.

In the literature, some specific cases have been analyzed but the lack of a more general methodology for wellbore design is a problem that needs to be addressed. The vast majority of models utilize two-dimensional (2D) descriptions of the problem in order to determine the best well trajectory from a geomechanical point of view. In this paper, several situations are presented, where different stress field patterns were assumed for different rock types. The generality of this study provides a tool for well design under different stress environments. The maximum principal stress was allowed to follow different directions in different planes (horizontal, vertical and inclined) depending upon the case being analyzed.

The model represents wellbores drilled in shallow, medium-deep, and deep basins. The effect of both differential stress and loads magnitude were evaluated throughout this work.

The model developed here was based on the finite element method, for both linear-elastic and elasto-plastic materials. The description of the problem is a fully three-dimensional (3D) representation of the wellbore and the applied stresses. This paper has two parts: a theoretical approach, which provides the basis for the solution setup, and a set of numerical experiments with their correspondent results. Since several real-life situations were evaluated, the potential applicability of the results obtained here is apparent; and the results of these simulations could be used as a cross check for calculations made for more particular situations in the field. The aim of this work is to provide a more global vision of the effects of stress variations upon the optimum design of oil and gas wells.
Experimental Study of Hydraulic Fracture Initiation in Colton Sandstone
Authors: Lhomme T. P. , de Pater C. J. , Helfferich P. H.
Published: December 2007

We performed laboratory scale experiments for the study of horizontal fluid driven fracture initiation from an open-hole section. In order to clarify the role of material microstructure and fluid infiltration, we used viscous Newtonian fluids to initiate penny shaped fractures from radial notches in blocks of natural sandstone. We varied the fluid viscosity and injection rate over ranges allowing for significant fluid losses toward the dry porous rock. For low efficiency fluids, the fracture propagation was characterized by non-monotonic pressure variations. We propose a formulation of the problem of hydraulic fracture initiation in an elastic homogeneous permeable material. Our model accounts for fluid losses toward the rock and a cohesive zone at the fracture tip. We performed dimensional analysis in order to lump the physical parameters into meaningful dimensionless groups. Scale effects concerning the fluid efficiency, decompression effects and material failure could be predicted from dimensional analysis and corroborated with experimental observations. We also propose a numerical solution for this model. The numerical results compare well with experimental results. This work provides a proper scaling for hydraulic fracture initiation. This scaling is necessary for comparing laboratory scale results to field observations.
New Iterative Coupling between a Reservoir Simulator and a Geomechanics Module
Authors: Tran David , Settari Antonin , Nghiem Long
Published: December 2007

Interactions of solid mechanics and fluid flow have been studied by numerous researchers for the past several years. Different methods of coupling such as full coupling, iterative coupling, etc., have been used. Nevertheless, the accuracy and the large run time of the coupled solid-mechanics fluid-flow model are outstanding issues that prevent the application of the coupled model in full-field studies. In this work, a novel relationship of porosity as a function of pressure, temperature and mean total stress is developed for iterative coupling of stress and flow. The new formula not only improves the accuracy of the coupling, but also reduces substantially the number of coupling iterations. The latter feature decreases significantly the CPU time. The new approach was implemented in a modular, iteratively coupled system. The rapid convergence provides the equivalent of a fully coupled method that is necessary to investigate complex coupled problems. The main advantage of this type of coupling is that a geomechanics module can be easily coupled with different reservoir simulators. The paper gives some comparisons of results obtained by the new porosity formula with another formulation.