Wax deposition can reduce flow channel, increase the resistance and decrease fluid producing intensity in oil pipelines, which bring a critical operational challenge for the oil development. The prediction of temperature field and wax deposition location is the basis in thermal washing and wax removal. In this paper, the wells of sucker rod pump in Da Qing oil field is selected as the research object, a new method is proposed to predict temperature field and wax deposition location based on heat-fluid coupling method. The regularities of temperature distribution and wax deposition location are simulated with different fluid producing intensities and moisture contents. With the migration of produced liquid, the temperature decreases from bottom to upward, while the decline rate becomes less and less. With the increase of fluid producing intensity and moisture content, the temperature is increasing and the wax deposit location becomes shallower. In contrast to the calculated and measured results, the coincidences rate distribution is in the range of 95.61-97.86%. The results have a significance to the thermal washing plan formulation.
In this work, the intensive theoretical study and laboratory tests are conducted to evaluate the craters morphology via the flat-ended indenter test, relationship of indentation hardness (HRI) and uniaxial compressive strength (UCS). Based on the stress distribution, failure process and Mohr–Coulomb failure criterion, the mathematical mechanical models are presented to express the formation conditions of “pulverized zone” and “volume break”. Moreover, a set of equations relating the depth and apex angle of craters, the ratio of indentation hardness and uniaxial compressive strength, the angle of internal friction and Poisson’s ratio are obtained. The depth, apex angle of craters and ratio of indentation hardness and uniaxial compressive strength are all affected by the angle of internal friction and Poisson’s ratio. The proposed models are also verified by experiments of rock samples which are cored from Da Qing oilfield, the percentage error between the test and calculated results for depth, apex angle of craters and the ratio of HRI and UCS are mainly in the range of –1.41%–8.92%, –5.91%–3.94% and –8.22%–13.22% respectively for siltstone, volcanic tuff, volcanic breccia, shale, sand stone and glutenite except mudstone, which demonstrates that our proposed models are robust and effective for brittle rock.
Background:Since the fragile anisotropy of shale, it is difficult to carry out laboratory experiments of geostress by shale cores. The existing geostress calculation model that is based on the homogeneous hypothesis also cannot meet the accuracy requirement. Therefore, it is necessary to establish the new geostress calculation model and test methods which are suitable for shale and provide the effective guidance for drilling and fracturing. Methods:Firstly, the triaxial stress experiments were carried out. It showed that the mechanical parameters had strong difference between parallel and vertical bedding direction. The characteristics of transversely isotropic were shown obviously. Then, the geostress calculation model which considers the mechanical parameters of anisotropy in different direction was established by the constitutive relation of transversely isotropic materials. Finally, it was assumed that there is no relative displacement between formations in the process of deposition and the late tectonic movement; the prediction method for the shale geostress was established by the adjacent homogeneous formation. The sensitivity factors and influence laws were analyzed for the horizontal bedding shale geostress. Results:The results showed that the shale geostress was controlled by the elastic parameters of its own and the adjacent beds'. Conclusion:The research can provide the theoretical basis and easy way for calculating the shale geosterss.
Wax deposition in oil pipelines brings a critical operational challenge in the oil development, and the indirect thermal washing is a most common and effective method of wax cleaning. The temperature field in thermal washing is the basis for making a reasonable plan to wash and remove wax well. In this paper, the wells of sucker rod pump in Da Qing oil field are selected as research objects, a new method which is based on heat-fluid coupling method is proposed for predicting temperature field during the thermal washing process. The temperature field of the annulus of tubing and casing and the temperature field of the annulus of rod and tubing are simulated with different thermal washing parameters. In the indirect thermal washing, the temperature in annulus of tubing and casing gradually decreases from wellhead to the bottom, while the temperature in the annulus of rod and tubing increases from bottom to the wellhead. With the increase of temperature and flow rate of thermal washing fluid, the temperature in annulus of tubing and casing and the temperature in annulus of rod and tubing are both increasing, but the rise rate is different at different depths. Compared to the measured results, the coincidences rate is in the range of 93.67%–99.31%. The research results can guide effectively the thermal washing operation.
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