During the past two years the shale gas exploration in Southern Sichuan basin received some exciting achievements. Data of a new appraisal well showed that the gas producrtions of vertical well and horizontal well are ~1.5 × 104 m3/day/well (with maximum ~3.5 × 104 m3/day/well) and ~12.5 × 104 m3/day/well (with maximum ~40 × 104 m3/day/well), respectively, indicating a good gas potential in this area. Eight core samples from the reservoir were investigated by using a carbon sulfur analyzer, microphotometry, x-ray diffractometry, field-emission scanning electron microscopy (FE-SEM), mercury injection porosimetry (MIP), and low-pressure nitrogen adsorption to obtain a better understanding of the reservoir characteristics of the Upper Ordovician-Lower Silurian organic-rich shale. Results show that the total organic carbon (TOC) content ranges from 0.5% to 5.9%, whereas the equivalent vitrinite reflectance (VRr) is between 2.8% and 3.0%. Pores in the studied samples were observed in three modes of occurrence, namely, interparticle pores, intraparticle pores, and intraparticle organic pores. The total porosity (P) ranges from 1.6% to 5.3%, and MIP data sets suggest that pores with throats larger than 20 nm contribute little to the pore volume. Low-pressure N2 adsorption isotherms indicate that the total specific surface area (SBET) ranges from 9.6 m2/g to 18.9 m2/g, and the pore volume (V) ranges from 0.011 cm3/g to 0.020 cm3/g. The plot of dV/dW versus W shows that the fine mesopores (pore size(BJH) < 4 nm) mainly contribute to the pore volume. The P, SBET, and V show a good positive correlation with TOC and a weak positive correlation with the total clay mineral content, thus indicating that the nanopores are mainly generated by the decomposition of organic matter. The reservoir characteristics of the Upper Ordovician-Lower Silurian organic-rich shale are comparable with commercial shale gas plays in North America. The sample gas contents with TOC >2% are more than 3.0 m3/ton. The observation can be a good reference for the future exploration and evaluation of reservoir in this area.
The low cost of the injected solvent, which can be also recovered and recycled, and the applicability of VAPEX technique in thin reservoirs are among the main advantages of VAPEX process compared to thermal heavy oil recovery techniques. In this research, an extensive experimental investigation is carried out to first evaluate the technical feasibility of utilization of various solvents for VAPEX process. Then the effect of drainage height on the stabilized drainage rate in VAPEX process was studied by conducting series of experiments in two large-scale 2D VAPEX models of 24.5 cm and 47.5 cm heights. Both models were packed with low permeability Ottawa sand (#530) and saturated with a heavy oil sample from Saskatchewan heavy oil reservoirs with viscosity of 5650 mPa s. Propane, butane, methane, carbon dioxide, propane/carbon dioxide (70%/30%) and propane/methane (70%/30%) were considered as respective solvents for the experiments, and a total of twelve VAPEX tests were carried out. Moreover, separate experiments were carried out at the end of each VAPEX experiment to measure the asphaltene precipitation at various locations of the VAPEX models. It was found that injecting propane would result in the highest drainage rate and oil recovery factor. Further analysis of results showed stabilized drainage rate significantly increased in the larger physical model.
To investigate the relationship between the structural characteristics and seepage flow behavior of rough single rock fractures, a set of single fracture physical models were produced using the Weierstrass-Mandelbrot functions to test the seepage flow performance. Six single fractures, with various surface roughnesses characterized by fractal dimensions, were built using COMSOL multiphysics software. The fluid flow behavior through the rough fractures and the influences of the rough surfaces on the fluid flow behavior was then monitored. The numerical simulation indicates that there is a linear relationship between the average flow velocity over the entire flow path and the fractal dimension of the rough surface. It is shown that there is good a agreement between the numerical results and the experimental data in terms of the properties of the fluid flowing through the rough single rock fractures.
How to effectively develop tight-gas carbonate reservoir and achieve high recovery is always a problem for the oil and gas industry. To solve this problem, domestic petroleum engineers use the combination of the successful experiences of North American shale gas pools development by stimulated reservoir volume (SRV) fracturing with the research achievements of Chinese tight gas development by acid fracturing to propose volume acid fracturing technology for fractured tight-gas carbonate reservoir, which has achieved a good stimulation effect in the pilot tests. To determine what reservoir conditions are suitable to carry out volume acid fracturing, this paper firstly introduces volume acid fracturing technology by giving the stimulation mechanism and technical ideas, and initially analyzes the feasibility by the comparison of reservoir characteristics of shale gas with tight-gas carbonate. Then, this paper analyzes the validity and limitation of the volume acid fracturing technology via the analyses of control conditions for volume acid fracturing in reservoir fracturing performance, natural fracture, horizontal principal stress difference, orientation of in-situ stress and natural fracture, and gives the solution for the limitation. The study results show that the volume acid fracturing process can be used to greatly improve the flow environment of tight-gas carbonate reservoir and increase production; the incremental or stimulation response is closely related with reservoir fracturing performance, the degree of development of natural fracture, the small intersection angle between hydraulic fracture and natural fracture, the large horizontal principal stress difference is easy to form a narrow fracture zone, and it is disadvantageous to create fracture network, but the degradable fiber diversion technology may largely weaken the disadvantage. The practices indicate that the application of volume acid fracturing process to the tight-gas carbonate reservoir development is feasible in the Ordovician Majiagou Formation of lower Paleozoic, which is of great significance and practical value for domestic tight-gas carbonate reservoir development and studies in the future.
Nowadays, the non-hydrocarbon gases are the main sources for gas injection projects in different countries. The main advantages of the flue gas injection are low cost, readily available sources (which consists mainly of N2 and CO2) and low compressibility in comparison with other gases like CO2 or CH4 (for a given volume at the same conditions). In addition, it occupies more space in the reservoir and it is an appropriate way for CO2 sequestering and consequently reducing greenhouse gases. In the aforementioned method, N2 and/or CO2 is injected into the oil reservoir for miscible and/or immiscible displacement of remaining oil.
Moreover, a key parameter in the designing of a gas injection project is the minimum miscibility pressure (MMP) which is commonly calculated by running simulation case or implementing conventional correlations. From technical viewpoints, the lower MMP values are more flavor for miscible gas injection process due to lower injection pressure and consequently lower maintenance and lower injection costs.
The main aim of this research is to investigate various gas injection methods (N2, CO2, produced reservoir gas, and flue gas) in one of the northern Persiangulf oil fields by a numerical simulation method. Moreover, for each scenario of gas injection technical and economical considerations are took into account. Finally, an economic analysis is implemented to compare the net present value (NPV) of the different gas injection scenarios in the aforementioned oil field.
In this work, a series of experiments were carried to investigation of rheological behavior of crude oil using waxy crude oil sample in the absence/presence of flow improver such as ethylene-vinyl acetate copolymer. The rheological data covered the temperature range of 5-30 °C. The results indicated that the performance of flow improver was dependent on its molecular weight. Addition of small quantities of flow improver, can improve viscosity and pour point of crude oil. Also, an Artificial Neural Network (ANN) model using Multi-Layer Perceptron (MLP) topology has been developed to account wax appearance temperature and the amount of precipitated wax and the model was verified using experimental data given in this work and reported in the literature. In order to compare the performance of the proposed model based on Artificial Neural Network, the wax precipitation experimental data at different temperatures were predicted using solid solution model and multi-solid phase model. The results showed that the developed model based on Artificial Neural Network can predict more accurately the wax precipitation experimental data in comparison to the previous models such as solid solution and multi-solid phase model with AADs less than 0.5%. Furthermore, the number of parameters required for the Artificial Neural Network (ANN) model is less than the studied thermodynamic models.
Based on fractal geometry, fractal medium of coalbed methane mathematical model is established by Langmuir isotherm adsorption formula, Fick's diffusion law, Laplace transform formula, considering the well bore storage effect and skin effect. The Laplace transform finite difference method is used to solve the mathematical model. With Stehfest numerical inversion, the distribution of dimensionless well bore flowing pressure and its derivative was obtained in real space. According to compare with the results from the analytical method, the result from Laplace transform finite difference method turns out to be accurate. The influence factors are analyzed, including fractal dimension, fractal index, skin factor, well bore storage coefficient, energy storage ratio, interporosity flow coefficient and the adsorption factor. The calculating error of Laplace transform difference method is small. Laplace transform difference method has advantages in well-test application since any moment simulation does not rely on other moment results and space grid.
A novel imidazoline derivative, 2-methyl-4-phenyl-1-tosyl-4, 5-dihydro-1H-imidazole (IMI), was prepared and investigated as corrosion inhibitor for P110 carbon steel in 1.0 M HCl solution by weight loss measurements, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests. The inhibition efficiency increased with the rising concentration of IMI inhibitor. The test results and fitting data indicated that the IMI behaved as a mixed-type inhibitor and obeys the Langmuir adsorption isotherm. Scanning electron microscopy (SEM) was carried out to investigate the surface of carbon steel specimens, showing great protection from aggressive solution. Finally, inhibition mechanism of IMI on metal surface was further discussed.
Traditional reliability evaluation method for corroded pipeline exists the problem of not considering the associated defects. We therefore propose a new calculation method considering the associated defects. In this paper, the traditional and new methods are respectively used to calculate and contrastively analyze the failure probability of corroded pipeline; we then perform the research of residual life prediction for the corroded pipeline, followed by the sensitivity calculation of all random evaluation parameters. And then the Monte Carlo method (MCS) is applied to verify the rationality of the new method. The research results show that: the method considering associated defect is more objective, and truly react corroded pipeline's dynamic reliability changes; obtain new method to predict residual life of corroded pipeline; corrosion depth, radial corrosion rate have a significant impact on reliability of corroded pipeline considering associated defects. The calculation results of the method are more accurate, more time-saving.
In the centrifugal separations of drilling fluid, screw conveyor is a critical component to push and separate the sediment. The work performance and structural parameters of conveyor are immediately related to the production capability, the working life and the separating effect of the centrifuge. The existing researches always use the theoretical calculation of the approximate loads to analyze the strength of conveyor, and it cannot reflect the stress situations accurately. In order to ensure the precise mastery of the working performance, this article obtained pressure distribution under working conditions from CFX evaluation and gained equivalent stress and deformation under several load conditions by using the ANSYS Workbench platform to check the strength of conveyor. The results showed that the influence of centrifugal hydraulic pressure was less than that of centrifugal force on the strength and deformation of conveyor. Besides, the maximum equivalent stress occurred at the inside of the feed opening, while the maximum deformation occurred at the conveyor blade edge of taper extremity. Furthermore, whether considered the feed opening or not, the computing model had a great influence on the analysis results, and the simplified loads had a great influence on the deformation analysis results. The methods and results from this article can provide reference for the design and the improvement of screw conveyor.
More and more oilfields are using acoustic technology to enhance oil recovery. In order to know the mechanism of acoustic oil recovery technology, the sound radiator of a new downhole vibration device is modeled and analyzed. Based on the theoretical background, this paper firstly analyzes the acoustic mechanism for the oil reservoir and then makes a acoustic response analysis on the sound radiator model for frequency and time-domain investigation by using professional acoustic simulation software-LMS Virtual.lab Acoustics, finally calculates the acoustic transmission loss in the downhole oil reservoir. The research reveals that firstly, acoustic waves have influences on the oil & water fluidity in the oil reservoir, the oil pressure gradient and the interfacial tension of capillary; secondly, the acoustic radiation power and sound pressure of field point attain a peak on the natural frequency of the sound radiator; thirdly, with the acoustic impact, the sound pressure of oil reservoir would fluctuate so as to improve the oil recovery ratio; the last but not the least one is both the sound pressure of oil reservoir point and the transmission loss of rock have a positive correlation with the vibration frequency. Therefore, it is of great importance for the research of vibration frequency and structure optimization of sound radiator.
In order to effectively improve penetration rates and enhance wellbore quality for vertical wells, a new Automatic Vertical Drilling Tool (AVDT) based on Eccentric Braced Structure (EBS) is designed. Applying operating principle of rotary steering drilling, AVDT adds offset gravity block automatic induction inclination mechanism. When hole straightening happens, tools take essentric moment to be produced by gravity of offset gravity lock to control the bearing of guide force, so that well straightening is achieved. The normal tool's size of the AVDT is designed as 215.9 mm，other major components' sizes are worked out by the result of theoretical analysis, including the offset angle of EBS. This paper aims to introduce the structure, operating principle, theoretical analysis and describe the key components' parameters setting of the AVDT.