Advanced Materials Research Vols. 1010-1012

Abstract: Hydrocarbon contamination to subsurface from petroleum spills and underground tank leaking has become more and more concerned. In this study, the vertical migration processes of diesel was simulated in a scaled beach sand aquifer model using a cylinder Plexiglas tank and monitored by self-made automatic resistivity monitoring system. It was shown that the resistivity change curves were dissimilar among unsaturated zone, capillary fringe and saturated zone. Through the measurements of the soil samples, the water content and oil content variability were consistent with the resistivity changes. From the sharp point of resistivity change curves, the thickness of the accumulated oil zone could be estimated. It provides an effective method to dynamically monitor the light oil plume migration in ground aquifer after leaking and determine the location of the oil lens.

Abstract: At present, there are still some disputes on the influence of pressure on the relative permeability of oil and water phase in low permeable reservoirs. This text carried out the displacement experiments to study the influences of effective stress and displacement pressure on the relative permeability. The results indicate that: with the decreasing of displacement pressure, the relative permeability of oil and water and the displacement efficiency become poor; the lower the permeability is, the worse the effective permeability and displacement efficiency are; low permeable reservoirs have strong stress sensitivity, the relationship between permeability and effective stress follows power function; when the reservoir energy drops, the effective stress of rock increases, which causes the physical property worse, and meanwhile the flooding pressure decreases, which ultimately reduce the displacement efficiency, so high energy preserving level is the guarantee of improving the flooding efficiency. The results also indicate that the displacement pressure gradient should consider the actual producing pressure gradient after meeting the requirement of π number, otherwise, the testing displacement efficiency may be larger than the actual. The studying results provide theoretical references for high efficiency development of low permeable oilfields.

Abstract: A type of X80 grade high strength and toughness pipeline steel was designed and researched. The strengthening mechanism of the steel was analyzed by SEM, TEM and XRD, and the CO₂ corrosion behavior of the steel was simulated by high-temperature and high-pressure autoclave. The result shows that the microstructure of the base metal is mainly acicular ferrite with a small amount of granular bainite. Acicular ferrite consists of laths which occlude and interweave with each other, and there are many dislocation and carbonitrides distributing in acicular ferrite, which made the pipeline steel have good strength and toughness. Under the simulation of the actual working conditions, the activity of reactants is low at 30°C, so the corrosion rate is smaller at this temperature; the maximum of corrosion rate occurs at 60°C; when the temperature increases to 90°C, the corrosion rate is lower than that of 60°C, that is because hindering corrosion effect which take by the acceleration deposit of corrosion product is better than the acceleration corrosion reactions.

Abstract: Sweep efficiency is a very important parameters for development effect evaluation and dynamic analysis of oilfield. For low permeability oilfield, well pattern thickening is one of the most effective means of improving development effectiveness. In this paper, a corrected calculation method is given and well spacing density is introduced as a parameter for the formula correction. The curve of volumetric sweep efficiency and well spacing density was achieved through the formula and statistical data. After the infill adjustment, increasing multiple of sweep efficiency can be calculated. Using the actual data of Changqing oilfield to calculate, result show that the deviation is 1.1% .

Abstract: Plume is closely related to the presence of gas hydrates which can often be found in plume development area. By acoustic detection, plumes of bubbles in the seawater from shallow gas have been found by marine surveying instruments in some areas over the world. Based on the existed theory of plume porosity, acoustic echo profile of sedbed seep plumes are numerically calculated. Within the simulation results, according to the pattern of gas bubble change and movement in the seawater, process of methane plumes generation is simulated and directs the distribution of bubble radius and plume boundary as depth. Acoustic features of plume bubbles seeping from shallow gas are shown to be consistent with the field results.

Abstract: Typical tight gas reservoirs in the Su53 Gas Field, Ordos Basin, are the demonstration region for deploying horizontal wells. In order to provide foundation for evaluating the volume fracturing adaptability of horizontal wells, through using the amplitude difference data between deep investigate double lateral resistivity (Rd) and shallow investigate double lateral resistivity (Rs), and other conventional logging data, in combination with the response characteristics of fracture in the logging curve, reservoir fracture was quantitatively identified with the variable scale fractal technique, the vertical heterogeneity of fracture distribution was analyzed, and the relationship between fractal dimension value of fracture and initial deliverability of gas well was researched. The results indicate that, this method is applied to quantitatively identify and evaluate the fracture development degree of single-well is feasible; the relationship between fractal dimension value and fracture development degree is positively relative, fractal dimension value is bigger, the fracture is more developed; there is a good corresponding relationship between fractal dimension value and deliverability of gas well, fractal dimension value decreases with a decrease of deliverability.

Abstract: With its unique structure and properties, polymer surfactants have been used in chemical flooding. Compared with ordinary polymer, polymer surfactants have a higher recovery degree. However, remaining oil starting mechanism in different pores using different polymer surfactants after water flooding is still unclear. NMR (Nuclear Magnetic Resonance) has a good effect on determination of rock oil saturation and analysis of pore structure. In this paper, oil displacement experiment using kerosene which contains no hydrogen was conducted and the problem caused by the similarity between oil phase relaxation time and water relaxation time in large pores was overcome. Through the change of NMR relaxation time, oil distribution situation in different pores of ordinary polymer, refining III polymer surfactant, and Haibo III polymer surfactant after polymer flooding was measured accurately. This paper also quantitatively analyzed the contribution degree to oil recovery in pores of different sizes, and evaluated oil displacement effect of the above three kinds of oil displacement systems. The results show that when only the swept volume is considered, recovery degree of Haibo III polymer surfactant is higher, reaching 53.66%. In different systems, middle pores contribute most to recovery degree. At the same time, the remaining oil in middle pores and large pores accounts more, which is the main attack direction towards tapping the potential of remaining oil in the oilfield.

Abstract: Because of the high heterogeneity, late water flooding and irregular well network, the distribution law of residual oil reserve in Chang 6 reservoir becomes much complicated. Combining the geology with dynamics of the reservoir, volumetric and formation coefficient methods are adapted to calculated the residual reserves, and then the distribution laws and controlling factors are analyzed. The results indicate that: there are still large amounts of residual reserve in main layer Chang 6₂²; the residual reserve can be classified into three kinds, Class I and class II are distributed concentrative in main layer; the controlling factors include property, sedimentary facies, heterogeneity, well network controlling and geological structure and so on. Finally, according to the distribution laws and controlling factors, targeted measures are proposed. The studying results provide well foundations for improving recovery of residual oil reserves and the total recovery of the reservoir.

Abstract: The adsorption behavior of thiazole inhibitior on the surface of N80 carbon steel was studied by potentiodynamic polarization curves in heterogeneous NaCl solution at pH=4. The electrochemical parameters were fitted. The result shows that thiazole inhibitor is of anodic adsorption, and the inhibition efficiency increases with the concentration increasing (4.9×10^-4~1.9×10^-3mol/L), but decreases with the temperature increasing (30~60°C). The thermodynamics of this adsorption was also discussed. The result is shown that the adsorption is according with Langmuir adsorption isotherm formula in acidic condition, and adsorption is a spontaneous behavior.

Abstract: It is critical to understand whether the available drilling assembly could meet the requirements of drilling design during the design and drilling of horizontal wells. This paper pointed out several limitations on horizontal extension capability of horizontal wells and provided judging criteria of the limit of horizontal extension based upon the characteristics of horizontal wells, and set up the gap element model analyzing torque and dragged of whole drill strings in horizontal wells. According to the force analysis of drill strings in bores given the foundation for regularities in the distribution of torque and drag force along the axis, on the basis of those above mentioned models and theories, a software was made to calculate the torque and drag force of a well, which compared with the field data, the average discrepancies of theoretical values are below 20% that could meet the needs in field works.