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Collaborating Authors
China University of Petroleum
A Fractal Model for the Stress-Dependent Permeability and Relative Permeability in Tight Sandstones
Lei, Gang (China University of Petroleum) | Dong, Pingchuan (China University of Petroleum) | Wu, Zishen (China University of Petroleum) | Mo, Shaoyuan (China University of Petroleum) | Gai, Shaohua (China University of Petroleum) | Zhao, Chao (China University of Petroleum) | Liu, Z.K. (China University of Petroleum)
Stress-dependent permeability and relative permeability in porous media are important in petroleum-engineering fields. It has been shown that stress-dependent permeability and relative permeability play important roles in determination of flow characteristics for tight-sandstone porous media. In this work, novel predictive models for stress-dependent permeability and relative permeability in microporous media with lower permeability are developed on the basis of fractal theory. The predictions of irreducible water saturation, normalized porosity, normalized permeability, and the ratio Krw/Krg by the proposed model show a variation trend similar to that of the available experimental data. On the basis of the proposed normalized porosity and normalized permeability model, it is found that the normalized porosity and permeability decrease with effective stress, thus predicted results are in good agreement with former experiments. The proposed normalized porosity and normalized permeability are expressed as a function of the effective stress, rock elastic modulus, microstructural parameters, and initial irreducible water saturation. The theoretical study of relative permeability under stress demonstrates that wetting phase relative permeability is related to the effective stress, microstructural parameters, and initial irreducible water saturation.
- North America > United States (1.00)
- North America > Canada > Alberta (0.46)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.86)
- Information Technology > Modeling & Simulation (0.34)
- Information Technology > Data Science (0.34)
A New Approach To Estimate Invasion Radius of Water-Based-Drilling-Fluid Filtrate To Evaluate Formation Damage Caused by Overbalanced Drilling
Ling, Kegang (University of North Dakota) | Zhang, He (Weatherford) | Shen, Zheng (Weatherford) | Ghalambor, Ali (Oil Center Research International) | Han, Guoqing (China University of Petroleum) | He, Jun (University of North Dakota) | Pei, Peng (University of North Dakota)
Summary Formation damage caused by overbalanced drilling with water-based mud (WBM) is inevitable as a result of mud filtrate invading the near-wellbore formation. The invasion radius is critical to the multiphase flow when the well is put on production. It contributes to the total skin that hinders the hydrocarbon production. Furthermore, the response of the logging tools may be affected as a result of such invasion, rendering many inaccurate calculations in formation evaluation. To evaluate the skin caused by mud-filtrate invasion, it is important to determine the radius of invasion. A thorough literature review indicated that no practical and reliable method with solid theoretical basis to quantify formation damage is available. Former studies assumed that single-phase drilling fluid displaces reservoir fluid during the invasion. The neglecting of residual reservoir fluid in the invaded zone will introduce error to invasion-radius estimation. This work takes the residual reservoir fluid into account; thus, the estimation of invasion radius is more accurate. This work proposes a practical model to determine the depth of mud-filtrate invasion near the wellbore drilled by WBM. The distribution of mud-filtrate saturation in the near-wellbore region is also calculated by using drilling-operation parameters, mud-filtration-test data, relative permeability, and drilling time. With the accurately determined invasion radius and known wellbore radius, reservoir permeability, and damaged-reservoir permeability, one can evaluate skin factor more accurately. With the knowledge of invasion volume and radius, one can design the wellbore-cleanup procedure appropriately. The proposed model allows engineers to predict the well performance and to diagnose wellbore problems by checking any deviation from the predicted production. This study also can assist with the correction of parameters inferred from log measurements, thereby reducing the over- and/or underestimation of log-derived parameters used in various formation-evaluation calculations.
- North America > United States (1.00)
- Europe (1.00)
- Asia (1.00)
- Europe > United Kingdom > Irish Sea > East Irish Sea > Morecambe Bay > East Irish Sea Basin > Morecambe Bay > Block 110/8a > Morecambe Field > South Morecambe Field (0.99)
- Europe > United Kingdom > Irish Sea > East Irish Sea > Morecambe Bay > East Irish Sea Basin > Morecambe Bay > Block 110/7a > Morecambe Field > South Morecambe Field (0.99)
- Europe > United Kingdom > Irish Sea > East Irish Sea > Morecambe Bay > East Irish Sea Basin > Morecambe Bay > Block 110/3a > Morecambe Field > South Morecambe Field (0.99)
- Europe > United Kingdom > Irish Sea > East Irish Sea > Morecambe Bay > East Irish Sea Basin > Morecambe Bay > Block 110/2a > Morecambe Field > South Morecambe Field (0.99)
- Well Drilling > Formation Damage (1.00)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid selection and formulation (chemistry, properties) (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)
Acoustic and elastic modeling by optimal time-space-domain staggered-grid finite-difference schemes
Ren, Zhiming (China University of Petroleum) | Liu, Yang (China University of Petroleum)
ABSTRACT Staggered-grid finite-difference (SFD) methods are widely used in modeling seismic-wave propagation, and the coefficients of finite-difference (FD) operators can be estimated by minimizing dispersion errors using Taylor-series expansion (TE) or optimization. We developed novel optimal time-space-domain SFD schemes for acoustic- and elastic-wave-equation modeling. In our schemes, a fourth-order multiextreme value objective function with respect to FD coefficients was involved. To yield the globally optimal solution with low computational cost, we first used variable substitution to turn our optimization problem into a quadratic convex one and then used least-squares (LS) to derive the optimal SFD coefficients by minimizing the relative error of time-space-domain dispersion relations over a given frequency range. To ensure the robustness of our schemes, a constraint condition was imposed that the dispersion error at each frequency point did not exceed a given threshold. Moreover, the hybrid absorbing boundary condition was applied to remove artificial boundary reflections. We compared our optimal SFD with the conventional, TE-based time-space-domain, and LS-based SFD schemes. Dispersion analysis and numerical simulation results suggested that the new SFD schemes had a smaller numerical dispersion than the other three schemes when the same operator lengths were adopted. In addition, our LS-based time-space-domain SFD can obtain the same modeling accuracy with shorter spatial operator lengths. We also derived the stability condition of our schemes. The experiment results revealed that our new LS-based SFD schemes needed a slightly stricter stability condition.
- Geophysics > Seismic Surveying > Seismic Modeling (1.00)
- Geophysics > Seismic Surveying > Seismic Processing (0.93)
Pore-scale modeling of elastic wave propagation in carbonate rocks
Wang, Zizhen (China University of Petroleum) | Wang, Ruihe (China University of Petroleum) | Weger, Ralf J. (University of Miami) | Li, Tianyang (China University of Petroleum) | Wang, Feifei (China University of Petroleum)
ABSTRACT The relationship between P-wave velocity and porosity in carbonate rocks shows a high degree of variability due to the complexity of the pore structure. This variability introduces high uncertainties to seismic inversion, amplitude variation with offset analysis, porosity estimation, and pore-pressure prediction based on velocity data. Elastic wave propagation in porous media is numerically modeled on the pore scale to investigate the effects of pore structure on P-wave velocities in carbonate rocks. We built 2D models of porous media using pore structure information and the similarity principle. Then, we simulated normal incidence wave propagation using finite element analysis. Finally, the velocity was determined from received modeled signals by means of crosscorrelation. The repeatability and accuracy of this modeling process was verified carefully. Based on the modeling results, a simple formulation of Sunโs frame flexibility factor (), aspect ratio (AR, the ratio of the major axis to the minor axis), and pore density was developed. The numerical simulation results indicated that the P-wave velocity increases as a power function as the AR increases. Pores with small AR () or large created softening effects that decrease P-wave velocity significantly. The P-wave velocity of carbonate rocks was dispersive; it depends on the ratio of the wavelength to pore size (). Such scale-dependent dispersion was more evident for carbonate rocks with higher porosity, lower AR, and/or lower P-wave impedance of pore fluids. The P-wave velocity of carbonate rocks with complicated pore geometries (low AR, high , small ) was much lower than that of rocks with simple pore geometries (high AR, small , large ) at low and high . The pore-scale modeling of elastic wave properties of porous rocks may explain the poor velocity-porosity correlation in carbonate rocks.
Frequency trend attribute analysis for stratigraphic division and correlation
Xu, Jingling (China University of Geosciences, China University of Geosciences, China University of Geosciences) | Liu, Luofu (China University of Petroleum) | Qin, Yuxing (Wireline Logging Company) | Zhang, Jianbo (Wireline Logging Company)
ABSTRACT Stratigraphic sequence interpretation and correlation are part of basic geologic research, but present frequent problems such as subjective and accurate division and correlation of sequence cycles, and a multiplicity of solutions to high-frequency sequences. We developed a novel method, termed frequency trend attribute analysis (FTAA), to solve these problems and improve the accuracy of division. The method was based on maximum entropy spectrum analysis data, built on theoretical foundations, and tested on geologic models as well as empirical data. We developed examples of how FTAA can improve stratigraphic division and correlation. We extracted frequency trend lines from well logging data (using all or a selected part of a facies-sensitive log such as the natural gamma-ray log) whereby the FTAA outcome reflected the overlay series and cycle structures. The resulting frequency trend lines also indirectly reflected changes to the sedimentary environment and base level, and the precise stratigraphic division and isochronous comparisons were automatically deduced from the frequency trend lines. According to the practical comparison with wells in the field, the frequency trend lines were found to be more accurate than using outcrop data, and the method proved to be effective and convenient in use. The FTAA significantly improved the precision and accuracy of automatic division and correlation of sequence cycles.
- Asia > China (0.96)
- North America > United States > Mississippi > Marion County (0.24)
- Geology > Geological Subdiscipline > Stratigraphy > Sequence Stratigraphy (0.72)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.47)
- Europe > United Kingdom > Anglo-Dutch Basin (0.99)
- Europe > Netherlands > Anglo-Dutch Basin (0.99)
- Europe > Germany > Anglo-Dutch Basin (0.99)
- (6 more...)
- Reservoir Description and Dynamics > Reservoir Characterization > Geologic modeling (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)
Assessment of Oil Reservoirs Suitable for CO2 Flooding in Mature Oil Reservoirs, Changqing Oilfield, China
Zhao, Dongfeng (China University of Petroleum, Beijing) | Liao, Xinwei (China University of Petroleum, Beijing) | Yin, Dandan (China University of Petroleum, Beijing) | Li, Zhen (China University of Petroleum) | Gai, Jian (China University of Petroleum, Beijing) | Wang, Huan (China University of Petroleum, Beijing)
Abstract Most oil reservoirs in Changqing Oilfield area are low permeability. After several ten years of production, the effect of water flooding becomes worse and worse as the reservoir enters middle development stages. CO2 flooding is an important method for oil fields in the future to enhance recovery factor. In this paper, based on the data of 253 mature oil reservoirs, a set of potential evaluation method for CO2 flooding were builded to assess the potential of CO2 EOR in Changqing Oilfield. A numerical model was established to study the effect of the related factors to CO2 miscible flooding and immiscible flooding. These factors are reservoir properties (thickness, Angle, temperature, pressure, depth), rock physical property (porosity, permeability, saturation, permeability differential, fracture development degree and permeability) and fluid properties (viscosity, density). Technical and economic benefits is assessed, to determine screening criteria and index for CO2 miscible flooding, their relative importance, and the index weights. Using comprehensive fuzzy evaluation method, this paper sets up a comprehensive evaluation method of CO2 miscible flooding and immiscible flooding, Which suit for the different blocks of Changqing Oilfield. Comprehensive evaluation value of reservoir was calculated, according to the evaluation method. With evaluation value of 0.53 as a boundary, CO2 flooding potential assessment of Changqing Oilfield has been done. Among 253 reserviors, 213 reservoirs are suitable for CO2 flooding EOR, which accouts for 84% of the total number of reservoirs within the block. The geological reserves which is suitable for CO2 flooding could be 25.05ร10 t, equaling to 80% of the total reserves of Changqing Oilfield. Therefore, CO2 flooding has a good application prospect in Changqing Oilfield, and it would bring huge economic benefits to Changqing Oilfield.
- Asia > China > Shanxi Province (1.00)
- Asia > China > Shaanxi Province (1.00)
- Asia > China > Ningxia Hui Autonomous Region (1.00)
- (2 more...)
- North America > United States > Wyoming > Grieve Field (0.99)
- North America > United States > California > Sacramento Basin > 2 Formation (0.99)
- Asia > China > Shanxi > Ordos Basin > Changqing Field (0.99)
- (4 more...)
Experimental Study on Sand-Carrying Mechanism and Capacity Evaluation in Water-Producing Gas Wells and its Application in Artificial Lift Optimization
Dong, Changyin (China University of Petroleum) | Li, Yanlong (China University of Petroleum) | Zhang, Qinghua (China University of Petroleum) | Feng, Shengli (Research Institute of Drilling and Production Engineering, Qinghai Oilfield, PetroChina) | Zhang, Lihui (Research Institute of Drilling and Production Engineering, Qinghai Oilfield, PetroChina)
Abstract For the unconsolidated gas reservoir with sand production, when the gas well produces water, the flow in wellbore is essentially gas-liquid-solid three-phase flow. The flow mechanism and sand-carrying capacity tend to obviously affect the artificial lift system operational situation and optimization. In this paper, the gas-liquid-solid multi-phase flow with different water-gas ratio (WGR) and sand concentration were experimentally simulated to investigate the flow mechanism and sand-carrying capacity of gas-liquid flow. The results indicate that once the well starts to produce water, it's more difficult for the gas to carry produced sand than there is no water produced. Gas flow rate and WGR are the dominant factors affecting the flow mechanism. As WGR increasing from zero, the flow pattern tend to be mud-gas flow with no sand carried, annular flow with sand, plug flow with sand and further patters similar to these of normal gas-liquid two phase flow with the same WGR. The prerequisite of sand-carrying can be described as that the gas be able to carry liquid flow to a certain velocity, at which the liquid has enough velocity to carry the sand flowing contained. According to the systematic experimental results, the critical sand-carrying gas rate and the quantitative relationship of sand rate and gas flow rate were obtained. Based on the experimental data, a sand-carrying evaluation model for gas well with and without water production are developed. The model is used to predict the critical sand-carrying gas flow rate with certain sand diameters and the maximum sand rate carried by a given gas flow rate. Finally, considering the characteristics of sand-carrying in wellbore, a new integrated coordination chart for gas well with water and sand production is put forward to evaluate the real well operational situation and help to make decision of well measurement such as adjusting gas nozzle, sand control and others. The method has been applied in Sebei gas filed, a typical gas filed with serve sand and water production, and the effect is good.
- Asia > China > Qinghai Province (0.28)
- North America > Canada > Alberta (0.28)
- Research Report > New Finding (0.64)
- Research Report > Experimental Study (0.64)
- Asia > China > Shandong > North China Basin > Shengli Field (0.99)
- Asia > China > Qinghai > Qaidam Basin > Sebei Field (0.99)
- Asia > China > Qinghai > Qaidam Basin > Qinghai Field (0.99)
Long Stroke Pumping Unit Driven By Low-Speed Permanent Magnet Synchronous Motor
Cui, Junguo (China University of Petroleum) | Xiao, Wensheng (China University of Petroleum) | Feng, Hao (China University of Petroleum) | Dong, Weibin (Petroleum Machinery Co., LTD) | Zhang, Yanjing (Petroleum Machinery Co., LTD) | Wang, Zhigang (Petroleum Machinery Co., LTD) | Jianghan, Wuhan (Petroleum Machinery Co., LTD)
Abstract At present, CNPC is using more than 120,000 conventional beam pumping units for oil production. The average efficiency of this conventional pumping system is only about 24%, so the energy consumption is very high. For energy-efficient, two types of long stroke pumping unit based on permanent magnet synchronous motor (PMSM) were developed: direct-drive pumping unit (DDPU) and chain transmission pumping unit (CTPU). For DDPU, the driving wheel is directly connected to a low-speed high-torque PMSM and drives the belt by friction to achieve oil pumping. The maximum polished rod load of DDPU is below 200kN. The CTPU is another version of DDPU: a chain transmission was added between the PMSM and driving wheel. CTPU is mainly larger type pumping unit, the maximum polished rod load of which is above 200kN. A DDPU is tested on X9-4 well in Jianghan oilfield and a CTPU is tested on Dugu-4 well in Liaohe oilfield. Test results show that both pumping units run smoothly and have low noise, and the stroke is stepless adjustable. Compared with the replaced conventional beam pumping units, the energy consumption for DDPU is 21 percent lower and for CTPU is 28 percent lower. Fewer pumping cycles result in decreased sucker rod vibration and higher pump filling factor. The dynamic indicator diagrams are much closer to the static indicator diagram. Now the two types of pumping unit have been deployed on more than 40 wells - mainly in Tarim oilfield for deep or viscous oil wells, and will be a new energy-saving and cost-reducing means of oil production.
- Asia > China > Hubei Province (0.48)
- Asia > China > Liaoning Province (0.34)
- North America > United States > California (0.29)
- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > Asia Government > China Government (0.34)
- South America > Colombia > Cundinamarca Department > Guaduas Field (0.99)
- Asia > China > Liaoning > Bohai Basin > Liaohe Basin > Liaohe Field (0.99)
- Asia > China > Hubei > Jianghan Basin > Jianghan Field (0.99)
Application of unsplit convolutional perfectly matched layer for scalar arbitrarily wide-angle wave equation
Chen, Hanming (China University of Petroleum) | Zhou, Hui (China University of Petroleum) | Li, Yanqi (China University of Petroleum)
ABSTRACT A classical split perfectly matched layer (PML) method has recently been applied to the scalar arbitrarily wide-angle wave equation (AWWE) in terms of displacement. However, the classical split PML obviously increases computational cost and cannot efficiently absorb waves propagating into the absorbing layer at grazing incidence. Our goal was to improve the computational efficiency of AWWE and to enhance the suppression of edge reflections by applying a convolutional PML (CPML). We reformulated the original AWWE as a first-order formulation and incorporated the CPML with a general complex frequency shifted stretching operator into the renewed formulation. A staggered-grid finite-difference (FD) method was adopted to discretize the first-order equation system. For wavefield depth continuation, the first-order AWWE with the CPML saved memory compared with the original second-order AWWE with the conventional split PML. With the help of numerical examples, we verified the correctness of the staggered-grid FD method and concluded that the CPML can efficiently absorb evanescent and propagating waves.
- Geophysics > Seismic Surveying > Seismic Modeling (0.94)
- Geophysics > Seismic Surveying > Seismic Processing (0.93)
Abstract Temperature measured from a permanent downhole gauge in a well after the well shut-in provides a unique perspective for surveillance and production management purposes. For example, in deepwater environment, production engineers need to know the temperature status of a shut-in well before it is being restarted since different temperature profiles along the wellbore may need very different restarting strategies for flowing assurance purposes. A number of "rule-of-thumb" or complicated numerical simulations are either not reliable or impractical. This paper presents a semi-analytical model to estimate the temperature transient behavior after the well shut-in. The model is solved numerically through inverse Laplace transform and integration. This solution gives temperature distribution profile and history in any location along the radial direction for a given production time and shut-in duration. To make it more general for other wells, an empirical correlation is provided through regression on the calculated type curves. The difference between this semi-analytical solution with other previous efforts will be discussed. The applications of the solution to this model are multiple folders. For example, we can use the solution to predict the temperature behavior after the well shut-in, which can be used for flow assurance purposes. Furthermore, matching the calculated temperature with the measured temperature at the same location will yield the well local heat transmissibility coefficient. Some field examples are provided to demonstrate these applications.
- North America > United States > Texas (0.46)
- North America > United States > Colorado (0.29)
- North America > United States > California (0.28)