Research on reservoir bed heterogeneity, interlayers and seal layers and controlling factors of 2＋3 sands of upper second member, Shahejie Formation, in the west of the Pucheng Oilfield

Terminal fans have formed the sedimentary system of the 2＋3 sands of the upper second member, Shahejie formation in the west of the Pucheng Oilfield, Bohai Bay Basin, East China. Based on well logging data and physical properties of the reservoir beds, the 2＋3 sands were divided into 16 sublayers. The heterogeneity of reservoir beds and distribution of interlayers and seal layers in the 2＋3 sands were investigated. The intra-layer heterogeneity and inter-layer heterogeneity primarily belong to the severely heterogeneous classification. The spatial differentiation of sedimentary microfacies resulted in a change of reservoir bed heterogeneity, strong in the middle and southern parts, weak in the northern part. Spatial distribution of interlayers and seal layers is dominated by sedimentary microfacies, and they are thick in north-eastern and middle parts, thin in the south-western part.     

Fractured reservoir modeling by discrete fracture network and seismic modeling in the Tarim Basin, China

Fractured reservoirs are an important target for oil and gas exploration in the Tarim Basin and the prediction of this type of reservoir is challenging.Due to the complicated fracture system in the Tarim Basin,the conventional AVO inversion method based on HTI theory to predict fracture development will result in some errors.Thus,an integrated research concept for fractured reservoir prediction is put forward in this paper.Seismic modeling plays a bridging role in this concept,and the establishment of an anisotropic fracture model by Discrete Fracture Network (DFN) is the key part.Because the fracture system in the Tarim Basin shows complex anisotropic characteristics,it is vital to build an effective anisotropic model.Based on geological,well logging and seismic data,an effective anisotropic model of complex fracture systems can be set up with the DFN method.The effective elastic coefficients,and the input data for seismic modeling can be calculated.Then seismic modeling based on this model is performed,and the seismic response characteristics are analyzed.The modeling results can be used in the following AVO inversion for fracture detection.     

Biodegradation and origin of oil sands in the Western Canada Sedimentary Basin

The oil sands deposits in the Western Canada Sedimentary Basin （WCSB） comprise of at least 85% of the total immobile bitumen in place in the world and are so concentrated as to be virtually the only such deposits that are economically recoverable for conversion to oil. The major deposits are in three geographic and geologic regions of Alberta： Athabasca, Cold Lake and Peace River. The bitumen reserves have oil gravities ranging from 8 to 12° API, and are hosted in the reservoirs of varying age, ranging from Devonian （Grosmont Formation） to Early Cretaceous （Mannville Group）. They were derived from light oils in the southern Alberta and migrated to the north and east for over 100 km during the Laramide Orogeny, which was responsible for the uplift of the Rocky Mountains. Biodegradation is the only process that transforms light oil into bitumen in such a dramatic way that overshadowed other alterations with minor contributions. The levels of biodegradation in the basin increasing from west （non-biodegraded） to east （extremely biodegraded） can be attributed to decreasing reservoir temperature, which played the primary role in controlling the biodegradation regime. Once the reservoir was heated to approximately 80℃, it was pasteurized and no biodegradation would further occur. However, reservoir temperature could not alone predict the variations of the oil composition and physical properties. Compositional gradients and a wide range ofbiodegradation degree at single reservoir column indicate that the water-leg size or the volume ratio of oil to water is one of the critical local controls for the vertical variations ofbiodegradation degree and oil physical properties. Late charging and mixing of the fresh and degraded oils ultimately dictate the final distribution of compositions and physical properties found in the heavy oil and oil sand fields. Oil geochemistry can reveal precisely the processes and levels that control these variations in a given field, which opens the possibility of model-d     

Hybrid connectionist model determines CO_2–oil swelling factor

In-depth understanding of interactions between crude oil and CO_2 provides insight into the CO_2-based enhanced oil recovery(EOR) process design and simulation. When CO_2 contacts crude oil, the dissolution process takes place. This phenomenon results in the oil swelling, which depends on the temperature, pressure, and composition of the oil. The residual oil saturation in a CO_2-based EOR process is inversely proportional to the oil swelling factor. Hence, it is important to estimate this influential parameter with high precision. The current study suggests the predictive model based on the least-squares support vector machine(LS-SVM) to calculate the CO_2–oil swelling factor. A genetic algorithm is used to optimize hyperparameters(у and б~2) of the LS-SVM model. This model showed a high coefficient of determination(R~2= 0.9953) and a low value for the mean-squared error(MSE = 0.0003) based on the available experimental data while estimating the CO_2–oil swelling factor. It was found that LS-SVM is a straightforward and accurate method to determine the CO_2–oil swelling factor with negligible uncertainty. This method can be incorporated in commercial reservoir simulators to include the effect of the CO_2–oil swelling factor when adequate experimental data are not available.     

Genetic algorithm application for matching ordinary black oil PVT data

In the study of reservoirs, it is vital that we have a realistic physical model of the reservoir fluid that accurately describes the hydrocarbon system and its properties. The available equations of state (EOS) to model the fluid phase behavior have some inherent deficiencies that may cause erroneous predictions for real reservoir fluids, so these models should be tuned against experimental data by adjusting some parameters. Since there are many matching parameters, tuning the EOS against experimental data is a tedious and difficult work. In this study, a genetic algorithm as an optimization technique is used to solve this regression problem. This study presents a new method that uses a specially designed genetic algorithm to search for suitable regression parameters to match the EOS against measured data. The proposed method has been tested on three real black oil samples. The results show the surprising performance of the developed genetic algorithm to match the experimental data of the selected fluid samples. The main advantage of the used method is its high speed in finding a solution. Also, finding more than one solution, working automatically, confining the role of experts to the last stage, reducing costs and having the possibility of evaluating the different situations are the other advantages of this method to match ordinary black oil PVT data and makes it an ideal method to implement as an automatic EOS tuning algorithm for black oils.     

Numerical simulation of non-Archie electrophysical property of saturated rock with lattice Boltzmann method

The electrophysical property of saturated rocks is very important for reservoir identification and evaluation. In this paper, the lattice Boltzmann method （LBM） was used to study the electrophysical property of rock saturated with fluid because of its advantages over conventional numerical approaches in handling complex pore geometry and boundary conditions. The digital core model was constructed through the accumulation of matrix grains based on their radius distribution obtained by the measurements of core samples. The flow of electrical current through the core model saturated with oil and water was simulated on the mesoscopic scale to reveal the non-Archie relationship between resistivity index and water saturation （I-Sw）. The results from LBM simulation and laboratory measurements demonstrated that the I-Sw relation in the range of low water saturation was generally not a straight line in the log-log coordinates as described by the Archie equation. We thus developed a new equation based on numerical simulation and physical experiments. This new equation was used to fit the data from laboratory core measurements and previously published data. Determination of fluid saturation and reservoir evaluation could be significantly improved by using the new equation.     

Hydrocarbon accumulation characteristics of beach-bar sandstones in the southern slope of the Dongying Sag, Jiyang Depression, Bohai Bay Basin, China

A number of beach-bar sandstone reservoir beds are developed in the upper fourth member of the Eocene Shahejie Formation （Es4s） on the southern slope of the Dongying Sag.Based on the analysis of seismic and logging data,with characterization and petrographic studies of core and cutting samples,this paper analyzes the hydrocarbon accumulation characteristics in two typical blocks of the Boxing and Wangjiagang oilfields,especially reservoir bed heterogeneity and migration conditions that influence oil and gas distribution,calculates the index of reservoir bed quality （IRQ） with a mathematical method,and discusses the relationship between driving force and resistance of hydrocarbon accumulation.Taking into account the characteristics of thin interbeds in beach-bar sandstones,an experimental model simulated the characteristics of hydrocarbon migration and accumulation in thin interbedded sandstones with reservoir bed heterogeneity.The results showed that hydrocarbon distribution and properties were extremely non-uniform.Reservoir bed and migration conditions controlled hydrocarbon accumulation in beach-bar sandstones.IRQ is above 0.4 in the main hydrocarbon region.Sand body distribution,structural configuration and fault systems controlled the direction of regional migration and location of hydrocarbon accumulation.Simulation experiments indicated that the change of driving force for hydrocarbon migration affected selective accumulation mechanisms.Hydrocarbon moved vertically along fault zones to the reservoir and resulted in the distribution of hydrocarbon in the reservoir.Two kinds of hydrocarbon accumulation models exist in the study area.One is a hydrocarbon accumulation model controlled by reservoir bed heterogeneity and the second is a hydrocarbon accumulation model controlled by a complex migration system with faults connecting sandbodies.Finally,different exploration strategies should be adopted for the detailed exploration for beach-bar sandstone reservoirs according to different geological backgrounds.     

The tectonic fracture modeling of an ultra-low permeability sandstone reservoir based on an outcrop analogy: A case study in the Wangyao Oilfield of Ordos Basin, China

Due to inherent limits of data acquisition and geophysical data resolution, there are large uncertainties in the characterization of subsurface fractures. However, outcrop analogies can provide qualitative and quantitative information on a large number of fractures, based on which the accuracy of subsurface fracture characterization can be improved. Here we take the tectonic fracture modeling of an ultra-low permeability sandstone reservoir based on an outcrop analogy, a case study of the Chang6t~ Formation of the Upper Triassic Yanchang Group of the Wangyao Oilfield in the Ordos Basin of China. An outcrop at the edge of the basin is a suitable analog for the reservoir, but the prerequisite is that they must have equivalent previous stress fields, similar final structural characteristics, relative timing and an identical depositional environment and diagenesis. The relationship among fracture density, rock type and bed thickness based on the outcrop is one of the most important fracture distribution models, and can be used to interpret fracture density in individual wells quantitatively. Fracture orientation, dip, geometry and scale, also should be described and measured in the outcrop, and can be used together with structure restoration and single well fracture density interpretation to guide fracture intensity prediction on bed surfaces and to constrain the construction of the 3D fracture geometry model of the subsurface reservoir. The application of the above principles shows the outcrop-based tectonic fracture models of the target ultra-low permeability sandstone reservoir are consistent with fractures inferred from microseismic interpretation and tracer tests. This illustrated that the fracture modeling based on the outcrop analogy is reliable and can reduce the uncertainty in stochastic fracture modeling.     

Current State of Oil Sands Development and Utilization in China

Oil sands, also known as sand asphalt, are a kind of sandstone or other kinds of stone than contains natural asphalt. Oil sands from different regions of the world have different compositions. Being one of the non-conventional oil resources, oil sands is distributed widely in the globe with a recoverable resources of about 651 billions of barrels, accounting for 32% of world＇s total recoverable oil and gas resources. Oil-rich countries include Canada, Russia, Venezuela, and USA. Among them, Canada owns most of oil sands in the world. Oil sands have been an important replacement for conventional energy resources.[第一段]     

Generating geologically realistic 3D reservoir facies models using deep learning of sedimentary architecture with generative adversarial networks

This paper proposes a novel approach for generating 3-dimensional complex geological facies models based on deep generative models. It can reproduce a wide range of conceptual geological models while possessing the flexibility necessary to honor constraints such as well data. Compared with existing geostatistics-based modeling methods, our approach produces realistic subsurface facies architecture in 3D using a state-of-the-art deep learning method called generative adversarial networks (GANs). GANs couple a generator with a discriminator, and each uses a deep convolutional neural network. The networks are trained in an adversarial manner until the generator can create “fake” images that the discriminator cannot distinguish from “real” images. We extend the original GAN approach to 3D geological modeling at the reservoir scale. The GANs are trained using a library of 3D facies models. Once the GANs have been trained, they can generate a variety of geologically realistic facies models constrained by well data interpretations. This geomodelling approach using GANs has been tested on models of both complex fluvial depositional systems and carbonate reservoirs that exhibit progradational and aggradational trends. The results demonstrate that this deep learning-driven modeling approach can capture more realistic facies architectures and associations than existing geostatistical modeling methods, which often fail to reproduce heterogeneous nonstationary sedimentary facies with apparent depositional trend.     

CURRENT STATE AND PROSPECTS OF SINO-CANADA ENERGY COOPERATION

Canada is abundant in oil sands. The most present statistics indicates that Canada owns the proven reserves of oil sands as much as 175 billion barrels and is producing oil from sands at the rate of over 100 million barrel/day. Boosted by surging international oil price, large-scale development of oil sands in Canada attracts more and more attention from the industry. During the past two years, several Chinese oil giants had also invested in Canada＇s energy sector, promoting the Sino- Canada energy cooperation into a new stage. Therefore, it is safe to conclude that the energy cooperation between the two countries has good foundation and brilliant future.[第一段]     

A static resistance model and the discontinuous pattern of hydrocarbon accumulation in tight oil reservoirs

In exploration for tight oil, the content and saturation of hydrocarbon in the tight reservoir is a key factor for evaluating the reserve. Therefore, it is necessary to study the geological history of hydrocarbon accumulation and the tight oil charging process. However, kinetic models used for petroleum development are not applicable for petroleum exploration. In this study, a static resistance model[ is proposed after analyzing resistances in ultra-slow flow in porous media. Using this model, the disco~atinuous pattern of oil charging is reproduced through incompressible Navier-Stokes equations, the phase field method and the finite element method. This study also explains macroscopic percolation behavior with microscopic flow mechanisms and discusses some issues in ultra-slow flow in a micro/nano pore-throat network. The resistance analysis reveals that capillary resistance and dissipation resistance are dominant factors in the mechanism of oil accumulation in tight reservoirs. Numerical simulations show that pressure thresholds exist and result in discontinuous oil charging. Generally, it is proven that the static model is more applicable than kinetic models in describing oil accumulation in tight reservoirs.     

Terminal Fan and Its Impact on Reservoir Quality of 2+3 Reservoir of Upper Second Member of Shahejie Formation,West Zone of Dongpu Depressio

正Introduction The 2+3 reservoir are two of the important sets of oil and gas reservoir intervals in Pucheng Oilfield.The latest resources assessment result indicated that oil-gas resources is plentiful where total petroleum resources is1298.24×104 tons and that of nature gas is 17.31×108cubic meters.Since they were put into exploration and development,2+3 reservoir in south district of Pucheng Oilfield had been drilled in 109 wells.67 wells have obtained the oil and gas flows.However,exploration of the 2+3 reservoir is complicated and stable oil production is difficult to be maintained in some wells in the discovered oil fields.The most essential reason for this,except for the complex geological structure     

Limitation of fault-sealing and its control on hydrocarbon accumulation—An example from the Laoyemiao Oilfield of the Nanpu Sag

Based on previous studies on the internal structures of fault belts, the fault belts in the Laoyemiao Oilfield of the Nanpu Sag can be divided into three units, a crushed zone, an upper induced fracture zone and a lower induced fracture zone according to the log response characteristics. The upper induced fracture zone is characterized by the development of pervasive fractures and has a poor sealing or non-sealing capability. It therefore can act as pathways for hydrocarbon migration. The lower induced fracture zone consists of fewer fractures and has limited sealing capability. The crushed zone has a good sealing capability comparable to mudstone and can thus prevent lateral migration of fluid. Through physical modeling and comparing laboratory data with calculated data of oil column heights of traps sealed by faults, it is concluded that the fault-sealing capability for oil and gas is limited. When the oil column height reaches a threshold, oil will spill over from the top of reservoir along the lower induced fracture zone under the action of buoyancy, and the size of reservoir will remain unchanged. Analysis of the formation mechanisms of the fault-sealed reservoirs in the Nanpu Sag indicated that the charging sequence of oil and gas in the reservoir was from lower formation to upper formation, with the fault playing an important role in oil and gas accumulation. The hydrocarbon potential in reverse fault-sealed traps is much better than that in the consequent fault-sealed traps. The reverse fault-sealed traps are favorable and preferred exploration targets.     

A time domain induced polarization relaxation time spectrum inversion method based on a damping factor and residual correction

Relaxation time spectra （RTS） derived from time domain induced polarization data （TDIP） are helpful to assess oil reservoir pore structures. However, due to the sensitivity to the signal-to-noise ratio （SNR）, the inversion accuracy of the traditional singular value decomposition （SVD） inversion method reduces with a decrease of SNR. In order to enhance the inversion accuracy and improve robustness of the inversion method to the SNR, an improved inversion method, based on damping factor and spectrum component residual correction, is proposed in this study. The numerical inversion results show that the oscillation of the RTS derived from the SVD method increased with a decrease of SNR, which makes it impossible to get accurate inversion components. However, the SNR has little influence on inversion components of the improved method, and the RTS has high inversion accuracy and robustness. Moreover, RTS derived from core sample data is basically in accord with the pore-size distribution curve, and the RTS derived from the actual induced polarization logging data is smooth and continuous, which indicates that the improved method is practicable.     

立足国际竞争，加快海洋石油企业标准与国际接轨的进程

The reservoir geochemistry is used to analyse reservoir fluid heterogeneity in Yacheng 13-1 gasfield,and the mixed gas sources of the field are studied in combination with homogenization temperature of fluid inclusions and organic-facies of souce rocks.It can be concluded that there is a mixing of gases which derived from two different hydrocarbon kitchens and generated in various maturation stages in Yacheng 13-1 field.From the south block(3 and 6 well areas) to the north block(4well area to 1 and 2 well areas),the gas shows a gradual decrease in features of oil-prone organic matter(contribution of hydrobios),a gradual increase in features of coal-forming facies(contribution of terrigenous sediment)and a rise in thermal maturity.     

Comparative Study of Basins within Palaeogene Seaway in East China and Cretaceous Seaway in North America and Its Reservoir Significance

The well known Cretaceous seaway in North America was recognized in the middle of the last century and the Palaeogene seaway in East China was proposed by the author recently.The two seaways located on the opposite sides of North Pacific Ocean may be not a coincidence,and a comparative study was made in this paper.The results show that the two seaways inundated basins share several similarities particularly in basin origin,filling processes and reservoir facies. It is suggested that reservoir facies of estuarine sandstone and shelf bar sandstone related to sea level fluctuation,which are well developed in the Cretaceous seaway covered basins in North America might have been also developed here in Palaeogene seaway inundated basins in East China.Therefore it is worth paying more attention to finding these new reservoir facies on this side of the Pacific ocean.Evidences of sedimentology and ichnology indicate that good prospects are likely.     

Novel empirical correlations for estimation of bubble point pressure, saturated viscosity and gas solubility of crude oils

Knowledge of petroleum fluid properties is crucial for the study of reservoirs and their development. Estimation of reserves in an oil reservoir or determination of its performance and economics requires a good knowledge of the fluid physical properties. Bubble point pressure, gas solubility and viscosity of oils are the most important parameters in use for petroleum and chemical engineers. In this study a simple-to-use, straight-forward mathematical model was correlated on a set of 94 crude oil data. Three correlations were achieved based on an exponential regression, which were different from conventional empirical correlations, and were evaluated against 12 laboratory data other than those used for the regression. It is concluded that the new exponential equation is of higher precision and accuracy than the conventional correlations and is a more convenient mathematical formulation.     

The sensitivity of the array resistivity log to mud filtrate invasion and its primary five-parameter inversion for improved oil water recognition

In order to improve reservoir fluid recognition, the sensitivity of array resistivity response to the difference of the invasion properties in both oil-bearing layers and water layers is analyzed. Then the primary inversion is carried out based on the array resistivity log. The mud invasion process is numerically simulated based on the oil-water flow equation and water convection diffusion equation. The results show that the radial resistivity of a fresh mud-invaded oil-bearing layer presents complex distribution characteristics, such as nonlinear increase, increasing to decreasing and low resistivity annulus, and the resistive invasion profile of a water layer is monotonic. Under specific conditions, array resistivity log can reflect these changes and the array induction log is more sensitive. Nevertheless, due to the effect of factors like large invasion depth, reservoir physical and oil-bearing properties, the measured apparent resistivity may differ greatly from the actual mud filtrate invasion profile in an oil-bearing layer. We proposed a five-parameter formation model to simulate the complex resistivity distribution of fresh mud-invaded formation. Then, based on the principle of non-linear least squares, the measured array resistivity log is used for inversion with the Marquardt method. It is demonstrated that the inverted resistivity is typically non-monotonic in oil-bearing layers and is monotonic in water layers. Processing of some field data shows that this is helpful in achieving efficient reservoir fluid recognition.     

The evolution and present status of the study on peak oil in China

Peak oil theory is a theory concerning long-term oil reserves and the rate of oil production. Peak oil refers to the maximum rate of the production of oil or gas in any area under consideration. Its inevitability is analyzed from three aspects. The factors that influence peak oil and their mechanisms are discussed. These include the amount of resources, the discovery maturity of resources, the depletion rate of reserves and the demand for oil. The advance in the study of peak oil in China is divided into three stages. The main characteristics, main researchers, forecast results and research methods are described in each stage. The progress of the study of peak oil in China is summarized and the present problems are analyzed. Finally three development trends of peak oil study in China are presented.