bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrodynamics in the Queensland Sector of the Cooper/Eromanga Basins: Identifying Non-Conventional Exploration Plays Using Water Pressure and Chemistry Data
Authors: Webster M. A. , Grimison A. G. , Brew J.
Published: December 2007

Analysis of water chemistry and pressure data from the Queensland sector of the Cooper and Eromanga Basins indicates that two regional fluid flow systems are operating within these basins. In the Eromanga Basin (Jurassic-Cretaceous) a southwestward and descending open flow system is evident, driven by the topographically induced Great Artesian Basin hydrodynamic regime. In the underlying Cooper Basin (Upper Carboniferous-Triassic) a closed system is reflected by overpressuring and ascending flow out of each of the major Permian troughs. Where the two systems interact and equilibrate, mixing of formation waters from Permian and Jurassic reservoirs is apparent in water chemistry data and potentiometric surface minima can be identified in vertical pressure profiles.

The water chemistry and pressure data have been used to identify hydraulic baffles within the Permian and Jurassic sequences. These barriers are likely to provide effective lateral or vertical seals and, once identified, can be targeted in regional mapping projects to identify potential stratigraphic traps. In addition to the potential exploration applications, regional hydrodynamic databases are also valuable in petrophysical evaluations, by providing estimates of water resistivity in areas with poor well control, and for estimating field limits when the only available pressure data are from hydrocarbon columns within crestal wells.
Effective Permeability Estimation for Simulation of Naturally Fractured Reservoirs
Authors: Nakashima T. , Sato K. , Arihara N. , Yazawa N.
Published: December 2007

Appropriate modeling of naturally fractured reservoirs is one of the most important and challenging issues in reservoir characterization. In simulation, a double porosity or dual permeability model is applied when fractures are well developed to form a fracture network. On the other hand, the single-continuum approach, where the fracture system is represented by effective permeability, is commonly used if fractures are discrete or disconnected. Focusing on the latter case, this paper proposes a semi-analytical technique to evaluate effective permeability for periodically or randomly fractured media including infinitely thin, infinite-conductivity fractures.

The complex variable boundary element method is used to compute potential and stream functions in the two-dimensional space for discretely distributed fracture system under the periodic boundary conditions. Effective permeability is evaluated first for discrete fracture systems of regular patterns as well as a single inclined fracture to demonstrate the validity of the method. 500 distributions of stochastic fractures are next generated to establish correlation between effective permeability and the fracture statistics, i.e., total length L, mean length m, and standard deviation of fracture length σ. Sensitivity to the parameters shows that the incremental gain of effective permeability is proportional to L, that the larger m, the larger effective permeability, and that non-zero σ increases effective permeability. The effective permeability tensors are also determined for oriented fractures. Analyses by non-parametric regression show that the diagonal elements, kxx and kyy are highly affected by the angle between the oriented fractures and the pressure gradient, while the off-diagonal elements kxy and kyx are strongly affected by both the total length and the angle.
Case Study of Hydraulic Fracture Completions in Horizontal Wells, South Arne Field Danish North Sea
Authors: Cipolla C. L. , Berntsen B. A. , Moos H. , Ginty W. R. , Jensen L.
Published: December 2007

This paper provides a case history of hydraulic fracture completions in horizontal wells in the South Arne Field, Danish North Sea (9500 ft TVD, chalk formations).1 The first three propped fracture treatments attempted in the South Arne Field "screened-out" very early in the design due to excessive fracture complexity and fluid leakoff. A detailed study of the rock mechanical properties, wellbore stress & fracture initiation characteristics, far-field stress regime & fracture orientation, and fluid leakoff behavior was integrated with fracture modeling studies to evaluate this problem.2 These studies were used to improve the fracture treatment strategy for future wells, resulting in essentially 100% success placing the designed proppant volumes and achieving aggressive tip screen-outs (TSOs) on over 60 fracture treatments.

This paper summarizes the initial fracture treatment problems and provides a detailed discussion of fracture modeling and design issues, mini-frac analysis procedures, and the mitigation and evaluation of fracture complexity.
Case Histories of a Horizontal Well in the Fissured Mudstone Formation of Daqing Oilfield
Authors: Bi Xueliang , Tie Yan , Zhang Shurui , Fan Sen
Published: December 2007

In the mudstone formation with longitudinal cracks in Daqing Oilfield in northeastern China, there were oil and gas shows in vertical exploratory wells with low yield. A horizontal explor- atory well was drilled through sets of cracks to increase flow area and individual-well producing rate, and the distribution of cracks could be clarified, so the exploration domain can be opened up. Mudstone is unstable, which may lead to serious drilling problems such as wall collapse, well control problems and drill stem sticking, and drilling experience of horizontal well in fractured mudstone is scarce all over the world. The well is the first horizontal well drilled in the fractured mudsto- ne in China. The well was successfully finished with depth of 3,192.00m, the horizontal segment of 1,001.50m. Although well path control in fissured mudstone is difficult, the well trajectory is satisfactory with the geosteering technique. The formation is complicated and dangerous, but there was no serious drilling accident. Drilling fluid is one of the key fact- ors in the drilling, so the properties of drilling fluid was caref- ully maintained, and torque and drag problems were aoided. The well was successfully completed with screen pipes.

The paper describs the main technical challenges, the drilling and cementing processes, and experiences and lessons learned from the construction. A multi-discipline project team was established consisting of geology, exploration, drilling, logging, cementing and completing personnel, which is a key factor leading to the success of the well.
A Parametric Study of Variables Affecting the Coupled of Fluid-Flow/Geomechanical Processes in Stress-Sensitive Oil and Gas Reservoirs
Authors: Guerrero Habib J. , Osorio Jose G. , Teufel Lawrence W.
Published: December 2007

Modeling of coupled fluid-flow/geomechanical processes in stress-sensitive reservoirs has shown that different reservoir conditions yield different degrees of reservoir productivity reduction. Factors affecting the productivity of stress sensitive reservoirs include reservoir permeability, initial loading, aspect ratio, mechanical and physical properties of the reservoir and its surroundings, and fluid compressibility. The effects and interaction among these factors is complex and needs to be investigated if reservoir management is to be optimized.

This study applies the statistical technique factorial design to investigate systematically and efficiently the interactions and effects that the above mentioned factors have on productivity index and cumulative production. To achieve these objectives, this study applies a 3D, finite difference, fully coupled, fluid-flow/rock deformation model.1 The model considers an inner and an outer domain representing the reservoir and its surroundings, respectively. The system is treated as a poro-elastic medium consisting of a deforming solid skeleton and a moving compressible pore fluid. Non-linear elastic deformation is assumed.

Results indicate that the most important variables affecting reservoir productivity and cumulative production are reservoir permeability, aspect ratio, Young's modulus of the inner domain and fluid compressibility (the effect of fluid compressibility and Young's modulus of the inner domain are of the same order). This paper provides a deep discussion on the effect of these factors on both response variables: productivity index and cumulative production
Application of Development Seismic to Infill Technique in Oilfield of Small Size of Sand Body
Authors: Fang Baocai , Wang Qingguo , Xu Hongxia
Published: December 2007

This paper proposes a new approach to infill and adjustment using 3D high-resolution development seismic in blocks which have a complicated structure, smaller sand body and discrete distribution. A detailed description of this structure was interpreted by a full 3D interpretation after effective acquisition of data (bin 10*20m, sampling rate 1ms). Reversion, including wave impedance, laterolog 3 resistivity, spontaneous and natural gamma was done by the application of a thin interbed seismic inversion method. By integrating geological information, logging and production testing, as well as production behavior data, the distribution of the sand bodies was clear and a potentially profitable area of remaining oil was determined. Good results in infill and adjustment were achieved and production in the area was improved.
State-of-the-Art in Hydraulic Fracture Diagnostics
Authors: Cipolla C. L. , Wright C. A.
Published: December 2007

This paper details the state-of-the-art in applying both conventional and advanced technologies to better understand hydraulic fracturing and improve treatment designs. The initial portion of the paper describes the application and limitations of various diagnostic tools and methods, including well testing, net pressure analysis (fracture modeling), techniques that employ open-hole & cased-hole logs, surface & downhole tilt fracture mapping, microseismic fracture mapping, and production data analysis. The bulk of the paper is dedicated to case histories that illustrate the application of these various fracture diagnostic technologies. The case histories include examples of how several fracture diagnostics can be used in concert to provide more reliable estimates of fracture dimensions and allow better economic decisions.
Dynamic Hedging in a Crude Oil Future Market
Authors: Taki Hidesada , Fujita Kazuo
Published: December 2007

The fluctuation of crude oil price is one of the greatest risks that oil-field operators are faced with. Crude oil is a strategie natural resource, and the range of the price fluctuation is quite wide. To avoid the disadvantage caused by the price fluctuation, operators can use oil-linked bonds, such as a crude oil future and a crude oil option on the market. Swap contract is the portfolio of crude oil futures, which is currently utilized in a static manner. Swap contract is preferred, if one wants to minimize the risk. However, this type of contract cannot respond to the boom of oil price and eventually loses the chance of bonus. In this paper, a dynamic hedging strategy is proposed, which can respond to the boom of oil price. The proposed portfolio changes its components in response to the changes of oil market. The performance of the strategy is assessed by using the real trading history on the New York Mercantile Exchange over the period of ten years.
Development Strategy and Reservoir Management of a Multilayered Giant Offshore Carbonate Field
Authors: Tewari R D , Rao Mohan , Raju A V
Published: December 2007

The reservoir performance and management of the Bombay High field with 25 years of production history has been reviewed. Bombay High is one of the most complex fields in terms of reservoir heterogeneity. The major reservoir (L-III) is multi- layered with 10 limestone layers of 5-10m thick which are separated by 2 to 5m shale. More than 600 development wells, both producers and injectors have been drilled. The very nature of this giant field and large and aging facilities have necessitated frequent reviews and changes in the development strategy of the field. The field is in the decline phase and has associated problems like increase in water cut and high GOR, which in-turn is effecting the oil production. Pressure maintenance by water injection is uneven in the reservoir due to heterogeneity. Problems being faced are differential depletion of sub-layers and associated poor primary cementation and mud losses during drilling of infill wells.

Infill drilling through available spare slots and side-tracking/re- drilling of the existing wells, drilling of horizontal wells, drainholes and ERD have been taken up to increase the production and also to augment the water injection. Massive well intervention programs like water shut off and gas shut off are being taken up to reduce the excess water and gas production. The paper also discusses, the utilization of tools like Downhole video and PLT for problem identification, Ball sealer for selective stimulation and Gel treatment for controlling excessive water and gas production, water flood surveillance programs and facilities optimization.

Sectorial approach, adopted for reservoir management has helped, in better well level monitoring, which becomes very essential in mature fields like Bombay High, in the identification of pressure sinks and better voidage compensation, fluid movements and design of well intervention programs and facilities optimization.

A multi-disciplinary team concept has been embraced for better reservoir management. The advantages of multidisciplinary teams, which are working for the re-development plan, with detailed/improved reservoir characterization, incorporating the 3D seismic data and reservoir simulation model, is highlighted.
Sand Management in Bongkot Field, Gulf of Thailand: An Integrated Approach
Authors: McPhee C. A. , Lemanczyk Z. R. , Helderle P. , Thatchaichawalit D. , Gongsakdi N.
Published: December 2007

Sand production in the Bongkot Field, Gulf of Thailand, has led to significant incremental costs and has increased the risk of potential key flowline and control equipment failures. The geological complexity of the field and the many layers that may be perforated in any given well, makes direct identification of sand producing zones problematic.

A multi-disciplinary sand production task force was established to identify the current sand production mechanisms; to evaluate various technical options for implementing sand control; and to recommend appropriate completion and intervention strategies. An integrated core, log and reservoir data acquisition programme allowed the development of a continuous, log-derived and core-calibrated rock strength prediction model, which was coupled to two independent sand prediction models. The models were used to delineate high risk sanding zones and indicated that sand production in Bongkot results from rock failure brought about by rapid and progressive reservoir depletion. The predictive models represent key tools in the development of effective sand management and control strategies for the reservoir life cycle.

Conventional downhole sand control methods are largely inapplicable to Bongkot since they are constrained by the existing well completion types, sand layer heterogeneity, and practical installation problems in both existing and new wells. Cost effective containment of sand production in Bongkot will rest on the application of "best practice" reservoir management policies and the application of emerging sand control technology where conditions allow. Modelling individual well and field network performance will form an important platform for designing and evaluating sand management strategies.
Bokor: Development and Technology Challenges of a Mature Field
Authors: Pauzi N. , Low F. N. , Husin M. T. , Maksari H.
Published: December 2007

Development for further opportunities in a mature field offers a unique set of challenges. The approach to this requires a focused multi-disciplinary team to arrive at a proper understanding of the reservoirs and the right technical solution. These challenges were experienced in the development of the Bokor Field, located 45 km northwest offshore Lutong, Sarawak in the Baram Delta region.

The Bokor Field is featured as a simple domal uplift with a collapsed crest superimposed onto a rollover anticline resulting from growth faulting. The field is deposited in a series of multiple stacked deltaic to shallow marine sandstone reservoirs that contain both oil and gas.

The field was discovered in November 1971 by BO-2 but was put on production only in 1982. The reservoirs were completed commingled to maximize completion strings' utilities and production from the stacked reservoirs. Limited spare well slots and unconsolidated reservoirs which often hinder further development in the past has ignited a flurry of technical creativity in the application of new technology. Due to development strategy of placing wells clustered at the crest of the domal structure in the past, the extent of the structural flank limit of the field is still relatively uncertain providing further future appraisal opportunities. The current field activity is mainly related to maximizing oil recovery and further development opportunity identification.

This paper discusses how it is possible to turn around a "brown" field by identifying the occurrences of the bypassed oil and at the same time replenishes reserves from the appraisal targets. It will also highlighted on the effectiveness of the new technology that has been implemented in the Bokor Field; from multi-lateral to "Triple wellhead" technology. This technology has allowed more reserves to be developed with fewer wells.
Identifying, Evaluating and Modelling Key Dynamic Parameters: Sunrise Troubadour Gas Condensate Fields
Authors: Stephenson P. M. , Ainsworth R. B. , Johnson D. A. , Koninx J.M. P. , Seggie R. J.
Published: December 2007

The Sunrise and Troubadour Fields form a massive offshore gas-condensate resource located in the Timor Sea, 450 kilometres northwest of Darwin. The commercialisation, marketing and contract negotiations for such a world scale gas development requires confidence in reservoir performance and product composition, plus a clear appreciation of their uncertainties. This paper discusses how the key dynamic uncertainties have been identified, evaluated and modelled to determine their impact on development decisions.

Early cross section models identified connected gas- initially-in-place and reservoir quality as key uncertainties, impacting field performance. Simultaneously, preliminary marketing efforts and facility design recognised fluid properties as a key parameter. This directed data acquisition through appraisal wells, which were fully cored and production tested.

Iso-kinetic sampling and careful well test design has resulted in representative compositional data and identified compositional variations across the field. High rate dependent skins measured in appraisal wells have been evaluated and re- quantified for development wells. Detailed single well models have evaluated the effects of condensate banking.

As marketing efforts progressed, full field simulation became warranted to capture remaining uncertainty on reservoir quality and distribution, and fault transmissibility. A suite of full field dynamic models built around the key dynamic uncertainties has provided confidence that uncertainties are manageable and that the development and customer commitments are robust. The case for further data acquisition, aimed at optimising the final development, can readily be made using the suite of dynamic models which integrate the input from all sub-surface disciplines.

Focused appraisal has reduced and quantified the key uncertainties. The leading edge evaluation methods have removed the need for several additional appraisal wells that might otherwise have been required.

Effective communication and teamwork between sub- surface, facility engineering, commercial and marketing has proved crucial to ensure that the appropriate uncertainties were addressed in a timely manner as each discipline matured their part of the project.
Application of HDR Stimulation Technology to Develop Tight Gas Reservoirs
Authors: Hossain M. M. , Rahman M. K. , Rahman S. S.
Published: December 2007

Conventional, cross-linked gel, hydraulic fracture treatments face several challenges in naturally fractured, tight gas, hard rock environments. These challenges include the potential for fracture complexity, pre-mature screen-out caused by pressure dependent leak-off and the likelihood of severe gel induced formation damage. To alleviate these potential problems and to economically develop these challenging environments, a new stimulation technology, which has been proven to be successful for Hot Dry Rock (HDR) reservoirs, has been investigated in this paper in the context of tight gas reservoir stimulation. The paper first presents a 3D model in which naturally fractured, tight gas reservoirs can be simulated by integrating available log and core data. Simulated natural fractures are then treated considering a novel fracture propagation and shear dilation concept. The model presented also predicts the resultant hydraulic conductivity and the reservoir growth pattern.

Finally, the paper reviews the productivity performance of the ‘shear dilation’ fracture treatment and compares this with a conventional style fracture treatment. Results are useful to indicate reservoir conditions under which the economic viability of ‘shear dilation’ fracture treatments may exceed conventional fracture treatments.
Quick Look Methodology for Gas Detection Using NMR and Density Porosity
Authors: Breda Eduardo , Silveira Anibal , Homovc Juan , Minetto Carlos
Published: December 2007

The constant compromise between oil production and reserves requires differentiating gas from oil. For the detection of gas we have used the density porosity vs. neutron porosity plots, including all the environmental correction processes and the influence of the clay content in the evaluated layers. Nevertheless, it is not always an accurate method because of the nature of the stratigraphic column of the San Jorge basin which is composed of fine sand and shale layers of lenticular geometry, with different types of clay, mostly generated in a continental environment with marked volcanic participation that make forecasts unreliable.

With the introduction of NMR technology we have obtained, among other parameters, a total porosity curve. From this data, a successful quicklook technique has been developed using the cross over density porosity vs. total porosity, which allows the identification of gas levels and to figure out the clay content for its use in the log analysis.

This paper presents the method for gas detection at well site and its economic impact in logging costs. In some oilfields of the San Jorge Basin, Argentina, logging costs were reduced by 12 %.
A Non-Destructive Method of Cake Thickness Measurement
Authors: Amanullah Md. , Tan C. P.
Published: December 2007

A novel non-destructive laboratory technique and apparatus have been developed to eliminate inaccuracies associated with the conventional direct contact methods of mudcake thickness measurement. The system consists of a laser head containing a transmitter and a position sensitive receiver, a signal conditioner, a digital read-out system and a DC power source. The position of the laser beam spot incident on the measuring surface is recorded by the receiver, transferred to the control box where it is amplified and then displayed as a standard current signal on a digital read-out system. As the method is non-destructive, the mechanical characteristic of the cake such as softness has no influence on the accuracy of the measurement.

The conventional methods of cake thickness measurement provide an estimate only due to damage to the cake during measurement. The accuracy varies depending on the cake consistency. The variation is low for hard mudcakes but high for soft cakes. The newly developed apparatus and measurement technique eliminate the direct contact-related errors and thus can provide reliable input values for modelling mudcake thickness dependent parameters such as formation and cake permeabilities, sticking force, friction coefficient etc. Statistical analyses of the measured values show a standard deviation of less than 0.025 mm and a coefficient of variation of less than 1%.

The apparatus is portable, easy to operate and suitable for quick measurement of mudcake thickness at the rig site. The performance of the system was reviewed by analysing the results of a range of muds and also by comparing with the measured values obtained using other methods.
5-axis CNC Whirlwind Milling Method of PDM's Rotors
Authors: Yi Xianzhong
Published: December 2007

The positive displacement motor (PDM) is a very important downhole motor in petroleum exploration and production. The key element in positive displacement motors is the rotor/stator coupling which convert hydraulic potential of fluid medium into mechanical energy. Normally both the rotor and the stator are cylindrical helix surfaces. The special properties of PDM directly rely on the machining quality of a rotor and a stator.

3-axis and 4-axis NC milling machines are usually used to machine the rotor helix surface or helix surface of stator mandrel, which is an injecting moulding part utilized to shape the inside cavity of rubber stator. The current CNC milling technology for manufacturing large and complex spiral curved surfaces still retains the drawbacks such as consuming time of long duration, over-tolerance and gouging scores. In this paper, a new 5-axis CNC machining scheme with the whirlwind milling method is proposed based on 5-axis CNC rotary-table horizontal milling machine specialized. The important strategy of the whirlwind milling technique is to optimize the directions of principal curvatures of the surface being machined with those of the rotational surface of milling cutter to generate a perfect fit. So, it can avoid the above-mentioned shortcomings and enhance the productivity. This paper focuses on the analytical characteristics of helix surfaces, the fundamental mathematical equations of whirlwind milling technique and its implementation.
The Application of Thin Bed Information Resolution of Well-Logs to Enhance the Vertical Resolution of NMR Logs
Authors: Wang Ning , Qian Yongxian
Published: December 2007

The concept of thin bed information resolution (TBIR) of well logs was first published by Yongxian Qian (1995; Acta Geophysica Sinica, v. 38, Supp. 1). The resolution of thin bed information is carried out by the Walsh Transforms (WT) inversion. NMR logging, among other logging tools, faces the issue of vertical resolution because the aperture of the tool is relatively large (about 24 in.); and the raw echoes acquired have to be stacked to some degree. Until now, WT inversion was not applied to NMR data, but its application to NMR data follows naturally as part of an effort to enhance its vertical resolution.

As long as an application's response functions are of an averaging nature and its final products are results of a linear signal processing, WT inversion can be applied. The T2 distribution from NMR logging falls into this category of final products. Therefore, it is not necessary to start with the raw echoes and the complexity of the algorithms to achieve a higher vertical resolution can be reduced.

After the brief review of Walsh functions, Walsh expansion and TBIR, this paper focuses on their application to NMR data. In order to demonstrate that WT inversion does improve NMR vertical resolution, controlled data were used. The best way to provide these data was through simulation; and the paper provides information about a simulation procedure for a layered formation and the NMR data derived from it. The results of WT inversion on the simulated NMR data clearly shows that vertical resolution is enhanced to a third of the simulated tool's aperture for the assumed logging conditions.

WT inversion was also applied to the NMR data from a well in the southeastern part of the United States. These results show an improvement of NMR vertical resolution as illustrated by comparison of density porosity with NMR effective porosity before and after WT inversion.
Lithology, Gas Detection, and Rock Properties From Acoustic Logging Systems
Authors: Kithas Bill A.
Published: December 2007

Lithology and physical rock properties of formations can be derived by utilizing acoustic logging systems. Compressive travel time from acoustic logs and shear travel time from full wave train logs are the two systems that are considered here. The ratio of shear travel time to compressive travel time is the relationship from which lithology is identified. Established techniques and existing commercial services we used to derive physical rock properties.

In order to establish the practicability lithology derivation, it was decided to incorporate this calculation into a computer program from which the physical rock properties program from which the physical rock properties are calculated from Acoustic, MICRO-SEISMOGRAM, and Density logs. The results of actual field tests in West Texas and Southeastern New Mexico were interesting and also uncovered a technique of gas identification from well logs.

Introduction

With the advent of large-volume frac treatments, interest has increased in obtaining in-situ rock properties for use in well treatment design. Also, studies have been made relating acoustic properties of formations to lithology. In the process of applying techniques for these purposes using well logs, it was observed that the presence of gas distorted the usual relation between compressive and shear velocity for the particular lithology. particular lithology. In the application of these techniques, compressive travel time is measured with conventional Compensated Acoustic Velocity Logs. Shear travel time can be calculated from full wave train logs. The relationship between compressive and shear travel time as a function of lithology is shown below.

delta ts = 1.9 = LIMESTONE delta tc 1.8 = DOLOMITE

1.6 - 1.7 = SANDSTONE

where delta ts = shear travel timedelta tc = compressive travel time

Physical rock properties such as Poisson's ratio are determined from the ratio of compressive to shear travel time.
Employing both Damage Control and Stimulation: A Way to Successful Development for Tight Gas Sandstone Reservoirs
Authors: Kang Yili , Luo Pingya , Jin Xu , Xinghua Xu
Published: December 2007

Tight gas sands exhibit extremely low porosity and permeability, so most people think that it is impossible to produce gas economically without stimulation. During past several decades, great efforts have been paid to improve hydraulic fracturing, but the results are mixed. Formation damages induced by drilling and completion fluids to natural fractures and tight matrix retard artificial fractures to give full conductivity.

Tight gas sands in Western Sichuan Basin are characterized with natural fractures developed in heterogeneity, complexity in micro-macro multi-scale structures, and very sensitive to environmental changes. Drilling fluids invasion into tight formation mostly occurred through natural fractures, which leads to solid plugging, water trapping, clay mineral impairments, chemical adsorption and retention. The paper presents application cases of temporary plugging fluids for naturally fractured sands in two tight gas fields. As the invasion depth localized to within 3cm of the well-bore, perforation can bypass the cake easily and efficiently. Wells with damage control give relatively higher initial production and the production rates after hydraulic fracturing treatments are highest owing to the fact that artificial fractures can connect natural fracture systems and matrix without damages. These wells also show stable and high productivity with longer periods and output satisfactorily economical results.
A Study of the Phase Behavior in Gas-Cap Reservoirs
Authors: Guo Ping , Li Shilun , Liu Shunsheng , Budurexiti A.
Published: December 2007

A conventional viewpoint is that almost all of the gas-cap reservoirs are saturated oil reservoirs. However, based on the studies and research, there exist some other special gas-cap reservoirs. What types are the gas cap reservoirs? Because of the effect of sample collection and the representation of producing data, to judge the type of a gas cap reservoir is a difficult problem. This paper analyzes and summaries different kinds of gas cap reservoirs that can be classified as saturated and equilibrilium reservoirs and special unsaturated reservoirs. The special unsaturated reservoirs can be classified as following three categories: 1) either the gas cap or the oil rim is saturated, the other phase is under-saturated (SGCR1), 2) both the gas cap and the oil rim are not saturated (SGCR2), and 3) the saturated pressures and properties of fluids vary with formation depth (SGCR3). This paper takes gas-cap reservoir RES1 (saturated and equilibrilium) and RES2 (special unsaturated) as examples to show how to determine the types of gas-cap reservoirs. And this paper analyzes the phase behaviors of all kinds of gas-cap reservoirs. In the examples, we use phase state regaining theory and phase equilibrium principles, and use a software Desktop-PVT, Landmark, USA to analyze and calculate.
The Engineering and Technical Aspects of Polymer Flooding in Daqing Oil Field
Authors: Wang Demin , Li Qun , Gong Xiaohong , Wang Yan
Published: December 2007

Petroleum is a non-renewable resource, it is crucial to a country’s economic development. However, during the development of reservoirs, especially at a high water cut stage, its economic and technical indexes will all turn worse. The water cut will increase, production rate decrease, capital construction and production costs increase. How to produce the 60~70% oil remaining underground is a task that reservoir engineers all over the world are striving to solve.

In the 60~70’s, petroleum professionals in many countries conducted extensive studies on polymer flooding technology. Screening and evaluation methods were set up; field tests were started. But from statistical data, the incremental recovery of polymer over water flooding was on the average only 2~5% OOIP (original oil in place), the economic results were not satisfactory. This directly influenced the industrial application of polymer flooding.

Since Daqing Oil Field is not suitable to use thermal and miscible methods to enhance oil recovery, one of the main targets was to have breakthroughs in polymer flooding technology. After a long period of research, a more thorough knowledge of the entire polymer technology was obtained. A breakthrough was obtained on the common belief that polymer flooding cannot increase the micro-scale displacement efficiency, the visco-elastic properties of polymer fluid is the crucial factor of increasing the displacement efficiency was proposed, deepening the knowledge on polymer flooding mechanism. A normalized method to more accurately evaluate the incremental recovery of polymer flooding was developed. An optimization method to determine the molecular weight and slug size of polymer drive fluid was developed. Numerical simulation methods were advanced. A highly automated, technically advanced method of "centralized preparation, localized injection" of polymer fluid and produced polymer fluid treatment and utilization technology was developed. Polymer injection well completion and multi-zone injection technology was developed.

From 1995, Daqing Oilfield started to industrialize polymer flooding. By the end of 1999, the annual production was more than 8 million tons of crude, the cumulative production more than 20 million tons with sales revenue of more than 20 billion yuan (RMB). Practice has shown that the polymer flooding can increase the recovery be more than 12% OOIP, its production cost is comparable to that of water flooding.
Mordovo-Karmalskoye Field: The Bitumen Composition in Productive Strata after Passing of the Combustion Front in Well
Authors: Kayukova G. P. , Romanova U. G. , Sharipova N. S. , Smelkov V. I. , Uspenskiy B. V. , Romanov G. V.
Published: December 2007

The specific features of the composition of both natural bitumens of the Mordovo-Karmalskoye field and products of the bitumen thermal transformation in strata after passing of the combustion front in a well are studied.

The composition of organic matter and its bitumen components left in reservoir after passing of the combustion front and the parameters of bitumen which underwent no artificial impact are compared. The combustion is found to cause the deep transformations in the bitumen composition and the differentiation of bitumen properties through a cross section. The rather light bitumen (density is equal to 0,94 g/cm3) is in the low concentration in the roof part of stratum. A content of paraffin-naphtene hydrocarbons, particularly n-alkanes, increases in the hydrocarbon part of bitumen. Accordingly to the group and hydrocarbon compositions, the elemental composition is altered, the hydrogen content increases and the sulphur content decreases. Contrarily, the bitumen in the combustion interval is heavier (1,013 g/cm3). A quality of the bitumen is minimal there. The interlayers having an enhanced content of the insoluble organic compounds are found. The high content of asphaltenes causes the low hydrogen content and the high carbon content in the bitumen composition. All these parameters are abnormal if to compare with the ordinary, non-transformed bitumens of the Mordovo-Karmalskoye field. In the lower part of cross section underwent no combustion, the content and composition of bitumen become ordinary for the productive thickness. At the same time, the lower oil content and the higher content of asphaltenes and sulphur in bitumens are an evidence to the displacement of light to the productive wells hydrocarbons simultaneously to passing of the combustion front. That confirms the earlier observed fact that the oil is produced at the part of reservoir which underwent no in situ combustion. In addition to the alterations in the organic matter composition and content, the bitumen-bearing rocks are also transformed, particularly a ratio between iron(II), iron(III) compounds and pyrite is changed. The revealed factors which effect the quality of recovered bitumens and the alterations in the mineralogy make possible to control the temperature regime and passing of the combustion front.
2D and 3D Multi-Domain Iteration Statics in Complex Areas
Authors: Mao Jingen , Liang Xiuwen , Zhang Nianchun
Published: December 2007

In view of large residual static correction values after field static correction in complex areas, the field near-surface data and field static correction data are used as the initial condition of the method. The first break time is used for the basic constrain of the method. The residual time shifts can be determined in common-shot, common-receiver and common-offset domains. Thus, the global optimized residual static correction values are estimated by doing statistics of a great deal of data and by making orthogonal iteration and step-by-step approximation. After being repeatedly revised, this result plus datum correction values forms the final static correction values. This paper takes actual data as example to show the good application results of this method.
A Comprehensive Model of Multilateral Well Deliverability
Authors: Chen W. , Zhu D. , Hill A. D.
Published: December 2007

We developed a deliverability model to predict the performance of multilateral wells. We first constructed a horizontal lateral model, which couples a reservoir inflow model with a wellbore flow model to calculate the production rate from each lateral. Pressure drop along the lateral was considered in the model. Then we implemented the lateral model into a well system with more than one lateral commingled to a main wellbore. The production from each lateral, the overall production rate, and the pressure in the well system are predicted by the multilateral deliverability model. For reservoir inflow, we have developed a new model using an imaging well method to calculate a single-phase inflow performance relationship (IPR) for a segmented horizontal lateral. The results from the new model are compared with existing analytical models. For flow in the laterals, we adopted single phase and two phase wellbore flow models. The single-phase lateral flow model incorporates frictional and accelerational pressure drop, and also the pressure drop caused by inflow turbulence. The two-phase lateral flow model uses the Beggs-Brill correlation or Ouyang’s homogeneous model which accounts for the effects of wall inflow, acceleration and flow patterns.The pressure drop in the tubing from the upper most lateral to the surface was calculated using a two-phase flow correlation.

We present example calculations for a well with three laterals draining separate reservoirs. The examples illustrate the effect of interference between laterals on lateral and overall well performance.
Improved Experimental Characterisation of Cement/Rubber Zonal Isolation Materials
Authors: Bosma M. G. R. , Cornelissen E. K. , Schwing A.
Published: December 2007

Recently, various companies published sophisticated design methodologies to engineer the ‘cement’ sheath in a oil/gas well completion such that the zonal isolation would remain intact (i.e. pressure tight) during its projected lifetime. Loading within a prescribed design envelope (e.g. pressure and/or thermal cycling or mechanical compaction processes) are the main considerations.

Improved performance of a candidate zonal isolation material is achieved by adjusting its material properties, especially the Young’s modulus and the compressibility.

These earlier studies indicated that apart from a proper mechanical characterisation of the ‘cement sheath’ (preferably described by non-linear material models), the in-situ stresses in the ‘cement’ play a prominent role as well. The latter are influenced by the volumetric behaviour of the slurry during setting and the thermal expansion coefficient of the set ‘cement’.

However, often these parameters are not known for ‘real life’ well construction materials.

Therefore, Shell International E & P B.V., the Netherlands, decided to design and construct dedicated laboratory equipment to determine those parameters for commercial ‘cement’ formulations at conditions encountered in typical well completions.

A first feature of this unique system (which can operate at pressures up to 1500 Bar and temperatures up to 300°C) is to monitor i) the progress of the ‘setting’ reaction of Oil Well Cements and or thermosetting resins, ii) their reaction behaviour (from the onset of gelling to the ‘final set’) and iii) the softening or swelling phenomena encountered in thermoplastic and thermoset materials.

The apparatus has inter alia the same functionality as conventional API Cement Consistometers or Ultrasonic Cement Analysers. However, it can also be used in combination with self-vulcanising rubbers, that cannot be used in the conventional API devices.

A second aspect of the apparatus is the determination of the volume changes (at constant pressure) or alternatively the pressure changes (at constant volume), during setting of the cement (or resin) system.

All measurements can be performed at either isothermal conditions or for prescribed temperature sweeps over time. Either volumetric properties (shrinkage or expansion) or compressibilities of cements / resin systems can be measured in a time frame ranging from the onset of gelling to far beyond ‘final set’.

In yet another operational mode, the volume change of set materials as a function of temperature (i.e. their volumetric thermal expansion coefficient) can be quantified.

In addition to a review of the principles of this novel apparatus, this paper also presents a typical application of the data in a Plug and Abandonment design (i.e. the Finite Element Engineering design of a thermally pre-stressed ‘rubber’ abandonment plug).
CNOOC and Industry Working Together – Huizhou 26-1 North Development Project
Authors: Sheng Lin Yao , Pratico Antonio , Hassing James R.
Published: December 2007

The Huizhou 26–1 North development project began with the discovery in September 1997 of an extension of the Huizhou 26–1 oil field, located north of the Huizhou 26–1 platform. Based on the information available after the discovery, the accumulation appeared to be justifiable for a project. However, reserves on the undrilled side of a fault were recognized as unproven. With the low oil prices that existed in late 1998 and early 1999, it was difficult to justify a decision to proceed with development. The offshore installation window and marginal economics of the project could not support an up-front expendable delineation well. Evaluation indicated that development as a subsea tieback to Huizhou 26–1 platform was potentially viable, but a wrong decision to commit to use either one or two wells would be very damaging to the economics of the project. Faced with those challenges, CNOOC, Agip, Chevron and Texaco agreed to initiate development of the accumulation without a final decision as to the number of wells. This allowed the operator, CACT Operators Group, to quickly begin the development of the accumulation and provided sufficient flexibility to customize the project as new information became available. The project was completed on June 10, 2000 with satisfactory economic results as a one-well field.
Coupled Reservoir Simulation Applied to the Management of Production Induced Stress-Sensitivity
Authors: Jin M. , Somerville J. , Smart B. G. D.
Published: December 2007

Reliable data input into the reservoir simulator of production-induced changes in matrix and fault permeabilities is essential for the successful planning and management of oil and gas reservoirs. Withdrawing and injecting fluid from/to the reservoir causes a change in pore pressure, which in turn, changes the three dimensional effective stress state. The stress path followed by the reservoir controls the evolution of the effective stress state, and with it the changes in deviatoric stresses which cause reservoir rock deformation and permeability changes. In order to allow for these effects, a new type of reservoir simulator – the stress-sensitive simulator – is required. This paper presents the results of a stress-sensitive simulation using a nonlinear finite element geomechanics model coupled to a finite difference fluid flow simulator, applied to a typical North Sea reservoir. This reveals the effects of dynamic changes in permeability and the reactivation of faults on the reservoir performance.

In the 3D coupled field-sized reservoir model, the permeability of intact rock is stress sensitive; faults are represented by joint elements with a permeability which is strain sensitive. The stress path is recorded and the hysteresis effect is considered in an interface program to modify the permeability according to the current and previous stress states. The results show that the evolution of the stress state, captured as a stress path, significantly affects the oil production profile. The pressure recovery caused by injection may also be diminished by hysteresis. The results also show the spatial and temporal changes in stress state, which are useful data for the analysis and exploitation of production induced anisotropy in permeability, with particular reference to the location of by-passed oil.