bluuebunny/crossref_metadata_2025 huggingface dataset:
Scaling Issues through Quantitative Analysis between Reservoir Simulation
Authors: Avansi G. D. , de Souza R. M. , Schiozer D. J.
Published: July 2010

Time-lapse seismic has been providing valuable information on identifying fluid movements, to locate bypassed oil and well placement optimization to reduce uncertainties in reservoir development and production management. Nevertheless, most of these are made through a qualitative approach, which limits seismic data integration in reservoir simulation studies due to different scales. In order to overcome this and develop new data integration techniques, many studies involving these processes have the assumption that both frameworks are in the same scale. Nonetheless, the quantification of the lost information in the scaling procedures needs to be evaluated and quantitative seismic data integration into the simulator should improve the mitigation of these problems improving the knowledge about the representativeness of the scaled data.

In this context, it is presented a technique regarding to scale issues relating time-lapse seismic data, geological and simulation models aiming to quantify the information lost due to the scaling problems.

This paper describes a methodology involving seismic attributes and reservoir simulation. Saturation and pressure trends derived from acoustic impedance behavior, which were obtained from seismic data. The lost information due to scaling procedures is evaluated through comparison between flux model properties and seismic attributes, at each respective framework, for estimating the best step to do it. This technique allowed the reliability improvement of the reservoir parameters from seismic attributes regarding to the lost information due to scaling procedures.

It has been shown that it is possible to improve the model and results reliability through a quantitative analysis involving scaling procedures between 4D seismic data and reservoir simulation integrated studies.

As main contributions of this technique are the integration procedures regarding to scaling issues between reservoir simulation models and time-lapse seismic information.
Relative Permeability Estimation from Displacement Experiments Using EnKF Method
Authors: Li Heng , Yang Daoyong , Arhuoma Mohamed
Published: July 2010

The relative permeability is a crucial parameter for accurately evaluating reservoir performance. Two-phase relative permeability curves are normally obtained by either directly or indirectly interpreting the displacement experiment data. As for the direct interpretation, the core samples are assumed to be homogeneous, while the capillary forces are normally neglected. Although the indirect interpreting approach is able to take heterogeneity of the core sample into account, calculating the derivatives of the objective functions through the graphical or numerical methods is prone to considerable errors. In this paper, a new method is developed to calculate the absolute and relative permeability from unsteady-state, two-phase immiscible displacement experiments. The permeability data is determined by history matching the experimentally observed pressure drop, production data and water saturation profiles via the ensemble Kalman filter (EnKF) algorithm. The power-law model is utilized to represent the relative permeability. Both the absolute and relative permeability are calculated simultaneously by assimilating the observed data. The newly developed method is validated using a numerical coreflooding experiment. It has been found that estimations of absolute and relative permeability are improved progressively as more observation data are assimilated. In addition, this method is convenient to be implemented as the derivative of the objective function is not required.
Water/CO2 System at High Pressure and Temperature Conditions: Measurement and Modeling of Density in Equilibrium Liquid and Vapor Phases
Authors: Tabasinejad F. , Barzin Y. , Moore G. R. , Mehta S. A. , Van Fraassen K. C. , Rushing J. A. , Newsham K. E.
Published: July 2010

Accurate density description of saturated liquid and vapor (L-V) phases for the water-CO2 system is important in many fields of engineering and science such as CO2 sequestration, supercritical fluids-based extraction and purification processes, and CO2- related enhanced oil recovery methods. There are only a few studies, mostly dedicated to low pressure and temperature conditions, on densities of equilibrium liquid and vapor phases for this system.

Due to paucity of experimental data at high pressure and high temperature conditions, a series of experiments have been performed to measure the density of both liquid and vapor phases of water/CO2 system from 382 K to 478 K and pressures from 3.48 MPa to 129 MPa. In order to measure the mass of water and volume of gas in the vapor phase, in each experiment the vapor phase of an LV equilibrium system is transferred to an equilibrium flash separator equipped with a desiccant and a gasometer. The gas volume is converted to density based on the ideal behavior of gases at standard conditions. The density of the liquid phase is directly measured by a densitometer.

In addition, a "Two-fluid Model" consisting of the Cubic-Plus-Association equation of state (CPA EOS) and the Henry's law is implemented in phase equilibrium modeling of this system to predict the density of both phases. A comparison between our experimental data, literature data and the results of the model shows the reliability of this model for density prediction of L-V phases of water-CO2 system over a wide range of pressure and temperature conditions.
Role of Gas Markets in Gas Monetization. Case Study: Europe Gas Market Development
Authors: Nikl Harald , Pennington-Bick Debra
Published: July 2010

World gas demand is forecast to increase by more than 40% over the next 20 years. To meet this rising demand, substantial sources of new supplies must be developed. These new supplies are growing in scale and will increasingly come from locations that are further from the major markets of the U.S. and Europe. This increase in scale and distance from consuming markets increases the challenge and complexity of gas monetization. While considerable attention is placed on technology as a driver of gas resource development, from a commercial perspective, the gas markets themselves represent a significant determinant in the ability to monetize gas resources successfully.

This paper addresses the role of gas markets in monetizing gas resources, using the development of the European gas market as a case study. Specifically, the paper describes the evolution of the European gas markets from their traditional country-focused structures, based on long-term oil-indexed contracts, through the emergence of liquid markets in individual countries, to the current development of a pan-European liquid market. The paper considers the key milestones marking each stage of development and the changing role of both market players and regulators in driving that development over time.

Finally, a perspective is provided of the challenges ahead in achieving continued progress in the development of the European gas market. This includes the implications these challenges have for market players and regulators as they seek to create competitive markets that provide reliable gas supply, investment and resource monetization.
Hydrate Formation: Considering the effects of Pressure, Temperature, Composition and Water
Authors: Rajnauth J. , Barrufet M. , Falcone G.
Published: July 2010

The main components in producing natural gas hydrate (whether for gas storage or for transportation), are water and natural gas, at low temperatures and high pressures. Each variable has a significant effect on the formation of gas hydrate. It is therefore critical to analyze the effect of each variable on hydrate formation to ascertain the best conditions required for a successful gas hydrate formation process.

This research evaluates the effect of these critical elements: temperature, pressure, gas composition, and water upon gas hydrate formation. This paper summarizes the findings of a sensitivity analysis using varying natural gas compositions. Results show that the composition of the natural gas can affect the temperature and pressure required for formation of the hydrate. Even more significant is the effect of impurities in the natural gas on the pressure temperature (PT) curves of the hydrate. Carbon dioxide, hydrogen sulfide and nitrogen are the main impurities in natural gas affecting the hydrate formation. At a particular temperature, nitrogen increases the required hydrate formation pressure while both carbon dioxide and hydrogen sulfide lower the required hydrate formation pressure.

The quantity of water required for hydrate formation is an important variable in the process. The water to gas ratio vary depending on the composition of the natural gas and the pressure. Generally the mole ratio of water to natural gas is about 6:1; however, to achieve maximum hydrate formation an incremental increase in water or pressure may be required. This is an interesting trade off between additional water and additional pressure in obtaining maximum volume of hydrate and is shown in this analysis.
Pressure Transient Behavior for Stress-Dependent Fracture Permeability in Naturally Fractured Reservoirs
Authors: Tao Qingfeng , Ghassemi Ahmad , Ehlig-Economides Christine A.
Published: July 2010

Fractures are the main channels of production/injection in naturally fractured reservoirs; therefore the fracture permeability is a key parameter to production optimization and reservoir management. Pressure depletion in naturally fractured reservoirs can result in effective stress change that, in turn, can change fracture permeability. Recent work described a new model employing a fully coupled poroelastic displacement discontinuity method with a nonlinear fracture deformation model and showed that fracture permeability can decrease or increase with decreasing pore pressure depending on in situ stress conditions. The model application featured in this paper is a radial composite reservoir with a dual porosity inner region surrounded by a homogeneous matrix of infinite extent. Similar models in the literature have not included stress dependent fracture permeability. In this model, fracture permeability values vary spatially and with time. The resulting pressure transient behavior is shown for several cases of potential practical interest including both fracture permeability loss and enhancement. The model behavior offers new explanations for commonly observed pressure transient responses and underscores a need for additional rock mechanical properties to ensure conclusive analysis of these systems. Field data experiences indicate that without such data, interpretations may be seriously flawed.
Approximate Simulation of Complex Reservoirs by Using Commercial Simulator
Authors: Peng Xiaolong , Liang Baosheng , Du Zhimin
Published: July 2010

Complex heterogeneous reservoir exhibits special characteristics, such as multiple storage types, wide range of storage sizes, complicated storage combinations, and various flow behaviors. Most fracture-matrix dual-porosity models in current simulators have difficulties to capture the complicated fluid flow in those complex reservoirs and are not well suitable to be used directly. Some numerical and experimental studies are in process but they have not been available in field practice yet.

This paper considers various impact complex reservoir characteristics and proposes an approximate numerical simulation method on the basis of dual-porosity theory and current simulators. The simulators are extended to more accurately model flow behaviors in the complex reservoirs. Several steps developed in this paper are as follows: First, reservoir storage is categorized into continuous and non-continuous media according to storage scale characteristics, distribution and intensity. In general, small cavities, small fractures, and pores in the rock are continuous while large-scale fractures, big cavities or caves are non-continuous. Second, an M-medium model is determined and applied to the continuous region which has N storage types. M is less than or equal to N. The determination of N is illustrated through a dual-porosity model: a continuous medium with two different storage types (such as vug and fracture) or different scales should be treated by a dual-porosity model only if the direction of the flux is ignorable. A new calculation for the flux transfer is then derived for such fracture-vug dual-porosity system. On the other hand, if the flux is directional, a single-medium model is sufficient to the reservoir simulation. Third, flow in a filled non-continuous medium is described by Darcy's law. Free flow in large unfilled cavities or caves follows Navier-Stokes equation and an approximate approach to using Darcy flow simulation is provided. The determination of the critical value for the cavity permeability is illustrated through a cross-sectional model. Lastly, the complex fracture-vug reservoir is simplified into four types of dual-medium models.

The proposed method is applied to a naturally fractured carbonate reservoir with cavities in the Tarim Basin in China. The simulation results match production data and meet the accuracy required in engineering.
Case History of Horizontal Well Fracturing Performance in the Daqing Oilfield, China
Authors: Wenjun Wang , Liu Xinghui , Pengfei Tang , Yu Liu , Changming Zhao , Zhongsheng Wu
Published: July 2010

The Daqing Oilfield, a huge complex consisting of many individual oil fields, is located in the Songliao basin in northeastern China. As reservoir development continues, the target zones become thinner and tighter. Horizontal well completion and fracture stimulation have thus become applicable. To understand fracture growth behavior and well performance, fracture diagnostic techniques, such as temperature logging and microseismic monitoring, as well as fracture modeling have been performed. The case history in this paper involves fracture treatments in several horizontal wells to target tight oil reservoirs in the Daqing Oilfield. Fracture diagnostic results for one horizontal well indicated that longitudinal fractures were obtained as planned. However, fracture diagnostic results in other horizontal wells in different reservoirs showed that the fracture orientation was off significantly from the designed longitudinal fractures. Several fracture models were calibrated using the fracture diagnostic results. The fracture diagnostic and modeling results were used to optimize fracture design for subsequent well stimulation. This case history demonstrated that integrated studies can help engineers optimize well performance.
The Permeability Factor in Coalbed Methane Well Completions and Production
Authors: Palmer Ian
Published: July 2010

After 30 years of CBM production in the USA, and internationally more recently, general principles and decision trees have emerged to guide an operator in choosing a well completion based on permeability. If enough permeability measurements are made, well completions can be prioritized, and hybrid well completions evaluated. The benefits of horizontal and multilateral wells are made clear. Low permeability is a serious challenge for CBM ventures, and further success will entail finding regions of enhanced permeability, utilizing horizontal wells, and "creating" permeability by new-paradigm methods. Perm-based guidelines for CBM well completions are given, which include permeability bands and benchmarks. Industry success has led to two benchmarks for evaluating ahead of full-field development (1) commercial success from reservoir parameters, and (2) effectiveness of well completions. The perm-based guidelines are simple and practical, and should benefit any CBM completions strategy. We also re-examine the striking observations of permeability increases with depletion (10-100 times) in the San Juan basin. The latest attempts to model and match the strong permeability increases with depletion in the San Juan basin are evaluated. Although there remain differences, a consensus has been obtained for some reservoir parameters.
Modeling Shear Dominated Hydraulic Fracturing as a Coupled Fluid-solid Interaction
Authors: Nassir M. , Settari A. , Wan R.
Published: July 2010

Microseismic monitoring in Barnett Shale indicates elliptical zones of failure propagating away from the wellbore and confirms the development of shear fracturing as the main failure mechanism arising from hydraulic fracturing operation. This paper presents a new technique for numerical modeling of both the creation and propagation of shear fractures in fluid induced fracturing. The method employs a coupled geomechanical/single phase flow code. The main role of the geomechanical module is to predict shear failure and provide fracture information to the flow module so that the permeability tensor can be updated accordingly during any coupling loop. In this paper, the technique, constitutive models and formulation implemented to develop the code are briefly presented. Brick type finite elements are used to model the geomechanical as well as the flow parts of the coupled problem. At any time step, the change in the effective stress tensor induced by the block pressure alteration is calculated in the geomechanical module. If the block is not initially fractured, it will be transformed into a fractured block when the shear failure criterion is attained. A pseudo continuum technique is developed and implemented to describe the mechanical behaviour of the fractured rock in which both normal and shear deformation of the fracture are taken into consideration. An example problem is shown to illustrate the application of this work to hydraulic fracturing modeling. This fundamental integrated study is an important advancement in fracture modeling as previous published techniques do not model the shear mechanism rigorously. The work can be extended and applied in other types of fluid injection operations which involve fracturing, such as coalbed methane and CO2 storage.
Reduced-Variables Method for General-Purpose Compositional Reservoir Simulation
Authors: Pan Huanquan , Tchelepi Hamdi A.
Published: July 2010

Compositional flow simulation is necessary for planning EOR (Enhanced Oil Recovery) and CO2 sequestration projects. We refer to the standard approach for performing the Phase Equilibrium (PE) computations as the Conventional-Variables (CV) method. In compositional simulation, the cost of PE calculations increases dramatically as the number of components increases, and the PE computations can become the most time consuming part of a simulation run. To reduce the number of components, lumping procedures are used, but that often entails the loss of possibly important phase-behavior information. The Reduced-Variables (RV) method is a robust and efficient scheme for PE calculations. However, there is limited information regarding the performance of RV in practical compositional flow simulation (i.e., coupled flow, transport, and thermodynamics). For example, there is only one published work with small 2D IMPEC (IMplicit Pressure, Explicit Compositions) simulations. Here, we integrated the RV method with a General Purpose Research Simulator (GPRS). This modular, object-oriented, computational framework allows us to make direct performance comparisons of RV- and CV-based compositional simulations. We use five different fluids, ranging from 6 to 26 components, and we focus on challenging multi-contact miscible displacements. We use two reservoir models: the first is the top layer of the SPE10 problem, and the second is a Discrete Fracture Model (DFM) with unstructured grids. The RV-based simulations are significantly more efficient than state-of-the-art CV-based computations. For the problems we describe here, the RV-based PE calculations can be up to seven times more efficient than the standard (CV-based) approach, and the total simulation time using RV can be a quarter of that used by the standard method. We show that the cost of the RV method for PE calculations is a linear function of the number of reduced variables, and we show that the total simulation time using RV is a weak function of the number of components used to describe the fluid. These properties of the RV approach enable us to study complex EOR processes in large-scale reservoir models, where large numbers of components and grid blocks are required. We propose that generalpurpose simulators use the RV approach for the PE computations associated with large-scale compositional simulations.
Impact of Rock Microstructures on the Supercritical CO2 Enhanced Gas Recovery
Authors: Wang J. G. , Liu Jianxin , Liu Jishan , Chen Zhongwei
Published: July 2010

Supercritical CO2 can be used as a driving gas to displace the native gas CH4 for methane production enhancement. A preferential flow path may result in an earlier CO2 breakthrough. This early breakthrough will in turn reduce the overall sweeping efficiency. In this study, numerical simulations for the supercritical CO2 enhanced gas recovery were conducted on a virtual rock core which contains an inclined fracture for potential preferential flow paths. This paper contains four parts. First, a 3D virtual core is expressed by local porosity. X-ray CT scanning captures a series of 2D digital images of the rock sample. Each 2D CT image is then processed to ascribe a map of pixel values. This map is related with local porosity through threshold techniques. These 2D CT images are then used to build a 3D virtual rock core within which the porosity is defined at each voxel. Second, other physical properties such as diffusivity and permeability within the core are introduced through their empirical relationships with the porosity. Third, a convection and diffusion equation is formulated based on the CO2 injection-driven flow. In this equation, the heterogeneity of the rock core is introduced via the distribution of initial porosity. Further, its convection velocity is proportional to the concentration gradient of the injected CO2 and the diffusive coefficient is contributed by both molecular and hydrodynamic diffusions. Therefore, a porosity-based finite element CO2-CH4 displacement model is completely formulated. Finally, the effects of fracture-induced heterogeneity on mass transfer and local diffusion mechanisms are numerically studied. The dramatic impact of the preferential pathway on the earlier CO2 breakthrough as well as the overall gas recovery is observed in the numerical simulations.
Challenges of Using Electrical Submersible Pump (ESP) in High Free Gas Applications
Authors: Bagci A. Suat , Kece Murat , Nava Jocsiris
Published: July 2010

One of the limitations of achieving full potential in pumped wells is the presence of excessive free gas at pump intake. Presence of free gas at pump intake affects the pump performance negatively, reducing the liquid rates and the pressure added by the pump. This performance reduction may sometimes be quite severe, resulting in unstable pump operation, significant production losses, lower reliability and increased operating costs due to premature equipment failure. Currently some operators need to produce wells under challenging operational conditions with very high free gas ratios. ESP in wells with a high free gas liquid ratio that requires the use of special gas handling technologies is becoming more and more common. Recent advances in ESP gas handling technologies expand the use of ESPs to more gassy applications in the industry.

This paper presents the methods used, the results and learnings from the application of ESPs with various gas handling technologies based on real field data. Present natural flow conditions were simulated to determine the operating envelope for each well. ESPs were evaluated for the selected design ranges governed by the drawdown (bubble point) constraints. The operating envelopes for each selected well were established over its life cycle with various free gas volumes and water cuts.

The paper confirms that ESP can operate successfully with the pump intake gas fraction up to 75% through use of appropriate gas handling technologies and challenging the norms.
A Study and Application of Multi-section Acidizing Technology with Original Production String in Horizontal Well
Authors: He Liu , Fangjun Biao
Published: July 2010

The formation damageability of drilling and completion fluids on horizontal wells is more critical than on vertical wells, due to longer horizontal section of horizontal wells and the larger reservoir exposure area during operations, resulting in rapid productivity decrease. As such, acidizing techniques for horizontal well is an important solution to increase the reservoir productivity. However, the long horizontal section passes through various lithology layers due to geological heterogeneity. This cause the mud invasion time and formation damage degrees are different in various layers. All factors will bring in potential negative impacts derived from common acidizing and coiled tubing acidizing and lead to non-uniform acid distribution and poor acidizing effect. Therefore, it is necessary to make use the mechanical multi-section acidizing technology. For that, the wellbore should be divided into several sections according to the reservoir lithology, physical characteristics, and damage degree to realize the purposes of acid uniform distribution and productivity increase. Conventional process is hard to acidize the multi-sections in horizontal wells, because the deflected section exist in horizontal well and the target layer is located at horizontal section, which make downhole string operations more complicated, and stresses in horizontal well is quite different from that of vertical well. The ball-shooting sliding sleeve mechanical multi-section acidizing string is available to resolve these problems successfully. This string is made up with safety joint, connected vessel, hydraulic anchor, centralizer, spring sand blasting devise, K344-110 packer, low density ball, etc, with 40 MPa tolerance pressure and 90°C tolerance temperature. It can perform enforced sectionalizing. Four times shooting, five sections treatments, and residual liquid's reverse circulation cleanup and backflow after acidizing process can be carried out through the original production string in this technique. In addition, only 110 mm diameter of the packer outer, additional installation of centralizer at two ends and the application of connected vessel can reduce not only upward loads of the string, but also potential hazards of pipe stuck, and provide the feasibility for releasing pipes and fishing operations. Up to now, 12 wells and 36 layers have been conducted the multi-section acidizing technique in Daqing Oilfield, the greatest treatment is up to 4 sections with one trip string, the success rate is 100%. Considerable yield increase effect is available. It is statistic 5.9 m3/d average fluid increase, 4.8 t/d average oil increase, and 182% the average productivity increase rate of single well in the early stage after the operation. The horizontal well acidizing technique provides an efficient way to develop oil field in the peripheral areas of Daqing Oilfield and has a wide application in prospect with lower costs, higher efficiency and simpler operation.
Fracture Geometry Inversion Technique in Low Permeability Reservoir for Horizontal Well
Authors: Wenjun Wang , He Liu , ying Yu , Bing Wang
Published: July 2010

The validity and pertinence of hydraulic fracture performance of horizontal well is important issues. How to combine multi disciplines such as reservoir engineering and logging and so on to implement the research project is a critical concern. Also, how to optimize the orientation and magnitude of parameters in analyzing fracture treatments is one of key steps to produce low permeability reservoirs in fields. Based on practical examples, fracture shape inversion technique of horizontal well fracturing was carried out by analyzing logging data, monitoring fracture data, and running 3-D fracture numerical simulation computer tools. Fracture spreading characteristics were analyzed and fracturing effect was verified. This fracture inversion technique is able to optimize fracturing design, evaluate and establish feasible development program for the region.
Drilling Technology of HTHP Ultradeep Well and the Crucial Technique Application
Authors: Zhankui Liu
Published: July 2010

There are many difficulties in HTHP ultradeep well drilling, drilling technology of HTHP ultradeep well is still the focal point of drilling researching and developing at present. This paper introduce drilling technology of HTHP ultradeep well moshen-1 well. Specially, this paper give information of the crucial technique application in Xinjiang Karamay Oilfield. Moshen-1 well is an important exploration well of CNPC, the designed well depth was 7380m, the actually completed well depth 7500m. Drilling engineering encountered huge challenges for instance high bottom hole temperature and high formation pressure coefficient, no reference data below depth 5300m. By optimizing drilling design, the construction of every drilling section was successfully finished. By optimizing BHA and using Power-V vertical drilling system, combine a large-sized PDM with PDC bit, using turbodrilling, all helped controlling wellbore quality effectively. By optimizing bit design and PDC bit selection increased drilling bit footage. Specially, 35MPa high pressure jet drilling technique had effectively increased bit hydraulic horsepower and improved the drilling ROP, reduced drilling cycle, achieved success contrast with neighboring well. The success of Moshen-1 well drilling and the application of high pressure jet drilling technique provide valuable experience for other ultradeep wells drilling and for other wells ROP enhancement.
Mesoscopic Simulation of Rheology of Polymer Solution
Authors: Li Xiaobo , Song Jie , Yuan Jiangru , Dai Yang
Published: July 2010

The need for high performance polymers used in chemical EOR is increasing in some oil fields, especially in China. It is a challenging issue to simulation the flow of polymer solution through pores. What make the complexity of this problem are the multiple physical phenomenons that the transformations of macromolecule interact with the macroscopic flow. Both molecular and hydrodynamic effects are of important at this scale, but not all of which can be resolved by the traditional continuum-based approaches that involves solution of the Navier-Stokes equations with a phenomenological constitutive equation. Microscopic molecular dynamics, on the other hand, requires excessive calculation time before macroscopic effects become visible, and therefore dissipative particle dynamics (DPD) is used to simulate the rheological properties of polymer solution in our work. As a particle-based mesoscopic method, the DPD method is appropriate to study complex fluids including polymer or surfactant [1]. In this study, the polymer molecule was represented with a chain of beads connected with finite extensible nonlinear elastic (FENE) springs that led to viscoelastic flow, and the periodic Poiseuille flow method proposed by Backer et al [2] was applied to measure the viscosity of simulation system. The rheological properties of linear, branch- and star- polymers solution were simulated, and some factors including molecular weight, molecular topology and concentration were evaluated quantitatively. Besides that, the radius of gyration of polymers was recorded in simulations. In our opinion, the numerical instabilities of many conventional methods can be avoided in this approach, and the simulation results gave a clear physical insight into the flow of polymer solution.
New Cementing Technologies Successfully Solved the Problems in Shallow Gas, Low Temperature and Easy Leakage Formations
Authors: zhen Nie , Dong benjing , Xia boru , Zheng xiu shan , Xie chengbin
Published: July 2010

The buried depths of reservoirs in North Buzachi oilfield range between 400~500m, but Its geologic structure is very complex due to the existence of shallow gas and aqueous layer within 20~160m and a HP gas layer at 300m(1.30–1.50 g/cm3). In addition, the reservoir is easy to leak for its high permeability and low fracture gradient (1.6g/cm3), and the ground temperature is −40□ in winter. All these factors bring great challenges for the cementing jobs here and often result in poor cementing quality such as shallow water & gas channeling from wellheads and serious leakage in reservoirs. 72 out of the 97 wells cemented during 1974~2000 were abandoned due to poor cementing jobs. Gas and water channeling were found from 15 wellheads that were cemented from 2003 to 2004. This paper focuses on how we develop a new cementing technology to improve the cementing quality in this oilfield. Based on the High Packing Theory, we developed the High Performance Low Temperature No-waiting & Low Density Cementing ™ technology(NLDC) whose slurry density can as low as 1.20g/cm3, which includes high performance cementing additives, superfine active mineral materials, Super-low temperature accelerator, and Anti-migration additive, etc. This technology are characterized by good anti-channeling & Anti-leakage & early strength development ability under the temperature 20~30□. Up to now, more than 300 wells have been cemented successfully with this technology, 97% of which are with excellent bonding quality. Those problems which have puzzled the North Buzachi for long have been radically solved, such as bad isolation, annular migration, shallow gas and water blowing off from wellheads and leakage during cementing. This NLDC cementing technology has been widely applied in North Buzachi oilfield for 5 years and also a good solution to shallow gas & water cementing and low pressure-easy-leakage formation cementing.
The Study of Fracture in Volcanic Reservoir
Authors: Fang Jie , Jia Chengzao , Ran Qiquan , Hui Gang , Zhou Xinmao
Published: July 2010

The 1'st members of Yingcheng formation, lower Cretaceous in Xingcheng development area, Songliao Basin mainly have rhyolite gas reservoirs. The 1'st member of Yingcheng is belong to the low-porosity and low-permeable reservoir, the reservoir space are mainly fracture-pore. By the means of field out crops observation, core description, thin section analysis, well logging identification and the seismic forecasting, the fractures of 1'st member of Yingcheng volcanic reservoir was analyzed in three aspects: the genetic, the attitude and the width. The dominate fracture type of 1'st member of Yingcheng are the tectonic related fractures(78.5%), then the diagenetic related fractures(17.0%), corroded fractures(4.2%) are the last. The high angle fractures and the vertical fractures are most common in tectonic related fractures; the oblique fractures are the following. The dominate type of diagenetic related fractures are level fractures, followed by high angle and oblique fractures. The fractures in the reservoir were mainly wide fractures (width>1mm) and narrow fractures (0.1mm<width<1mm), the fractures of middle width are the minority. The distributions of the fractures were mainly controlled both by the regional stress field and the activity of the faults, the fractures are displayed by belts in coincident with the strike of the main faults.
Scour and Deposit Analysis of Artificial Island in Nearshore Oilfield Development
Authors: Wang Shipeng , Qin Yanlong , Yao Zhiguang
Published: July 2010

In nearshore oilfield development, artificial island is the better method because of the economic and technical convenience. But compared with the traditional way of reclaiming land from beaches, the construction of artificial island should be given with more attention to the ocean hydrological and dynamic changes, the mutual implication between engineering zone and marine environment. It will spend more time and money to deal with the sedimentation scour and deposition around the island. So the island construction should consider the sedimentation transportation and environmental safety.

In this paper, a preliminary analysis on marine dynamic variation was presented based on the analysis of available data. Numerical model of tidal currents with wave effects was established in order to analyze the influence of nearshore oilfield artificial island on the environment. Sedimentation transportation under the coactions of wave and tide was investigated in order to analysis the stability of artificial island and marine dynamic geomorphology.

By taking a practical example of a typical artificial island, the effects of the construction of artificial island on environment and sand transportation were investigated. The artificial island should build with appropriate plane layout and make full advantages of the existing topographic and hydrodynamic condition. The construction of artificial island must minimize impact on environmental condition to reduce sedimentation scour and deposition and enhance the safety of oilfield.
A Downhole Blowout Preventer with the Equipment of Pressure Measurement
Authors: Gao Benwen , Chen Ruoming , Song Zhaohui , Li Xiaojun , Mu Zongjie
Published: July 2010

With the rapid development of Under-balanced Drilling (UBD) technologies, more and more people come to realize that the UBD is one of the most effective drilling technologies in reservoir exploration. However, the conventional Underbalanced Drilling Technology has its own faultiness. Take tripping pipe and liner for instance, we have to operate the well killed for well-control safety. The kill weight mud (KWM) will increase Bottom Hole Pressure (BHP) and make the down hole overbalanced. This will decline the effectiveness of reservoir protection in UBD technology.

The present paper aims to provide a new type drilling tool, named Downhole Blowout Preventer (DBOP), developed by Xinjiang Drilling Technology Research Institute of Western Drilling Engineering Corporation of CNPC, which could achieve a wellbore full-procedure underbalanced effectively. There’re some advantages in DBOP, such as hydraulic control, reliable gas/ liquid sealing property, pressure real-time transmission of valve, etc. Moreover, the DBOP can save drilling cost enormously and guarantee the behavior of barren bore safely.

The DBOP tripping in wellbore as one of intermediate casing, is in open condition during the running casing procedure. When tripping occurs, the DBOP, which has a valve, will isolate the wellbore into two sections (upside section and underside section) by closing its valve. For the sake of well isolation, the DBOP has perfect sealing property to isolation fluids which may include drilling mud and formation fluids. During the procedure of coming out of the hole, when the bit arrives at the upside section, the DBOP will close its valve timely; while, during the procedure of going in the hole, the DBOP's valve will be unclosed when the bit closes to the DBOP.

Because of DBOP's coordinating with Rotating Blowout Preventer (RBOP), the full-procedure underbalanced drilling achieves efficiently.

The Downhole Blowout Preventer (DBOP) has been used in some oilfields successfully, such as Xinjiang Oilfield, Huabei Oilfield, Sichuan Oilfield, etc. The effectiveness of DBOP has been proven to be efficient and successful.
Genesis and Prediction for Overpressure Carbonate Reservoir-Case study of Kenkiyak Sub-salt carbonate reservoir in Kazakhstan
Authors: Yefei Chen , Lun Zhao , Zifei Fan , Yunjuan Li
Published: July 2010

The genesis of the overpressure carbonate reservoir is not controlled only by lithofacies, karstification and tectonic movement, but also by overpressure. The hydraulic fractures formed under overpressure and its connection and expansion to early solution vugs and structural fractures are the key factors to the high productive zones.

Kenkiyak Pre-salt Oilfield is the carbonate reservoir with a burial depth of more than 4300 meters. The matrix permeability is only 0.98md. It was considered as a very low permeability porous-type reservoir and was defined as the oilfield without economic benefit. According to this study, under the overpressure condition, that the pressure of the porous liquid is up to 80Mpa, the carbonate reservoir cracks to form natural hydraulic fractures. Reticulate hydraulic fractures combined with structural fractures and solution vugs make very good spatial configuration, and then form the pore-fractural dual- media reservoir. The high productive reservoirs form under the condition of the favorable sedimentary facies, karstification cells and structural locations.

Because of the overlying salt-dome with 120–3800 meters in thickness, the imaging of the seismic data is very poor and it is very difficult to predict reservoirs. The seismic processing techniques such as kirehhoff prestack time migration, diving wave tomo and CIP grid tomography are applied to improve the migration image and signal-noise ratio. Based on analysis of the control factors to the carbonate reservoir, using the data of the drilling, logging and dynamic test data, the lithofacies, palaeokarst and the fracture system are predicted and the distribution of the high productive zone is successfully predicted by applying the techniques of the seismic muti-attribute clustering analysis and seismic inversion. The average productivity of the new drilling wells in the predicted high productive zones is up to 300t/d, and the oil rate per day of the 2 wells is over 1000t.
New Development and Application of Underbalanced Drilling Technology in China: A Critical Review
Authors: Cheng R. C. , Wang H. G. , Ge Y. H. , Cui M. , Ma G. Z. , Fei H. M.
Published: July 2010

Most of mature oil fields in China have been developed for decades of years, the majority of hydrocarbons being exploited today are found in pressure depleted formations or complex and lower quality reservoirs. Underbalanced drilling (UBD) is identified as an effective way to address problems associated with conventional overbalanced drilling, but its development and application in China is still on the preliminary stage. To cost-effectively serve for the complex exploratory situation, CNPC (China National Petroleum Corp.) initiated a large-scale UBD campaign from 2007 as a major change of its economic growth pattern.

This paper is a critical summarization of the ongoing campaign, with its purpose to explain where we are and what to do next. It highlights the new developments in techniques and auxiliary equipments in: 1) the whole process UBD, in which self-made equipments like the liquefied gelling valve and casing valve were particularly introduced; 2) underbalanced horizontal drilling, which plays a more important role in developing fractured reservoirs; 3) gas drilling, which gains further enhancement in air hammer, circulated medium diversion, water production prediction and reduction, and significantly improves drilling speed in deep formations; 4) managed pressure drilling (MPD) based on UBD equipments, which more precisely controls the annular pressure profile and effectively eliminates lost circulation in highly fractured zones; 5) bottom hole pressure measurement while drilling, which provides necessary information for the design of equivalent circulating density (ECD) as well as the control of bottom hole negative pressure in UBD. Case histories show that the UBD campaign not only improves drilling speed, reduces non-productive time (NPT), protects reservoir, but also enables comprehensive characterization of the reservoir while drilling, making smaller-reserves targets viable and previous low quality formations producible. In addition, the development trend of UBD in CNPC was discussed, and recommendations were proposed.
Detailed Hydraulic Simulation of MPD Operation in Narrow Pressure Windows
Authors: Cui Longlian , Wang Haige , Ge Yuhua
Published: July 2010

Hydraulic simulation is an integral part of any Managed Pressure Drilling (MPD) operation. Engineers rely on hydraulic calculation throughout an MPD project. A very detailed wellbore hydraulic analysis will not only foretell the success of various MPD methods but may also guide the drill engineer in real-time while contenting with difficult hydrodynamcis scenarios. Most MPD operations are conducted in narrow pressure windows formation, which require the pressure in "precise control". However, there are many parameters that play a part in the managing of wellbore pressure during circulation. Bottom hole pressure are impacted by fluid density and rheologic properties, injection rates, temperatures in annular and pipe, casing and drilling string configuration. The effects of these parameters on the bottomhole pressure are different, but interact with one another. A good understanding of the effects of these parameters on bottomhole pressure is essential in the hydraulic simulation.

In the paper, detailed hydraulic analyses of MPD operation in narrow pressure windows are presented. The detailed inform collecting is the first step for hydraulic simulation. According the drilling fluid used in the MPD operation, the rheology models of drilling fluid were compared and determined. The Roberston-Stiff model was employed in this paper. Based on experiments and theoretical analysis, the effects of temperature and pressure on ESD and shear stress of drilling fluid were considered. Some often overlooked parameters such as tool joint parameters, pump feed efficiency etc., were also considered Integrated into account the above factors and other conventional factors such as hole geometry, drilling string configuration, etc., the hydraulic simulations of MPD were conducted. The simulation results were compared with on-site real time PWD data. The hydraulic simulation results are in good agreement with on-site real time PWD data.
New Development on Expandable Casing Hole Liner and Expandable Open Hole Liner
Authors: Gao Xiangqian , Li Yiliang , Zhang Lixin , Han Weiye
Published: July 2010

High-temperature Expandable casing hole liner (ECL) was unsuccessful. The rubber element can not sustain the temperature higher than 160 °C, and steel bevel elements can not meet the requirements for sealing and hanging. In our research copper bands were inlayed on the steel pipe; an optimal manufacture process made the welding of copper had little effect on the mechanical behaviors for both steel and copper, which insured the lower expansion pressure and better sealing. These were tested by the expansion experiments and the following cycled temperature loading and hydrostatic test, the sealing elements can sustain the external pressure 20MPa. We designed an ECL for casing remediation in horizontal well, in which the expansion cone moves downwards. This design avoided the gravity and fraction of oil tube, which leads to the lower expansion pressure. Expandable open-hole liner (EOL) was a well completion plan for sidetracking well for its bigger inner diameter (I.D.), but decentralized EOL led to the cementing failure. In our plan the reamer was not used after the sidetracking, the expansion cone expanded the tubular up to the open hole together with swelling rubber elements for zonal isolation. The most important aspect that affects the intensity of Expandable Tubular was the thread. We modified the structure of thread: increasing the wall thickness at both ends before threads are done, upsetting or welding thicker pipe at the ends are both applicable.