A Novel Approach for Near Wellbore Stimulation and Deposits Removal Utilizing Thermochemical Reaction

Organic and inorganic deposits play a major issue and concern in the wellbore of oil wells. This paper discusses the utilization of a new and novel approach utilizing a thermochemical recipe that shows a successful impact on both organic and inorganic deposits, as an elimination agent, and functions as stimulation fluid to improve the permeability of the near wellbore formation. The new recipe consists of mixing nitrite salt with sulfamic acid in the wellbore at the target zone. The product of this reaction includes heat, acidic salt, and nitrogen gas. The heat of the reaction is enough to liquefy the organic deposits, and the acidic salt will tackle the carbonate scale in the tube and will increase the permeability of the near wellbore area. The nitrogen gas is an inert gas; it will not affect the reaction and will help to flow back the well after the treatment. The experimental work shows an increment in the temperature by 65 °C when mixing the two chemicals. The test was conducted at room conditions and the temperature reached around 90 °C. Adding another 65 °C to the wellbore temperature is enough to melt asphaltene and wax, the acidic salt tackles carbonate scale. As a result, the mixture works on eliminating both the organic and inorganic deposits. The permeability of the limestone sample shows an increment of 65% when treated by the mixture of the reaction recipe. The uniqueness of the new thermochemical recipe is the potential of performing three objectives at the same time; the heat of the reaction removes the organic deposits in the wellbore, the acidic salt tackles carbonate scale, and improves the permeability of the near wellbore zone.

Modeling Transient Flow in CO2 Injection Wells by Considering the Phase Change

A transient model to simulate the temperature and pressure in CO2 injection wells is proposed and solved using the finite difference method. The model couples the variability of CO2 properties and conservation laws. The maximum error between the simulated and measured results is 5.04%. The case study shows that the phase state is primarily controlled by the wellbore temperature. Increasing the injection temperature or decreasing the injection rate contributes to obtaining the supercritical state. The variability of density can be ignored when the injection rate is low, but for a high injection rate, ignoring this may cause considerable errors in pressure profiles.

Validation of analytical model and identification of salt effect on wellbore temperature in underbalanced drilling

Understanding the behavior of the borehole temperature recovery process, which influences drilling operations, requires an adequate estimation of fluid temperature. The presence of salt in a saline formation changes the composition of the annular fluid and has a significant impact on the fluid temperature distribution during drilling operations. As a result, while drilling a saline formation, it is vital to examine the key parameter that determines an accurate estimate of fluid temperature. Using python software and statistical quantitative methods, this study proposes a simplified user-friendly computational system that analyzes the drilling fluid systems performance evaluation and selection optimization.The fluid temperature distribution of X Field in China was analyzed using Shan mathematical model as a base model. When compared to MWD data from the field, the model predicted the temperature distribution of the field with less than 10% error. An adjustment factor was introduced to the base model to accommodate for changes in annular fluid composition while drilling a saline formation. The findings show that salt concentration has an impact on fluid temperature distribution during drilling. The fluid temperature at the wellbore condition changes by at least 7% with both high and low adjustment factors. Because the salt in the formation inflow dissolves in the drilling fluid near the annulus, the rheology of the fluid combination changes.

Investigation and application of wellbore temperature and pressure field coupling with gas–liquid two-phase flowing

With the development of gas well exploitation, the calculation of wellbore with single-phase state affected by single factor cannot meet the actual needs of engineering. We need to consider the simulation calculation of complex wellbore environment under the coupling of multiphase and multiple factors, so as to better serve the petroleum industry. In view of the problem that the commonly used temperature and pressure model can only be used for single-phase state under complex well conditions, and the error is large. Combined with the wellbore heat transfer mechanism and the calculation method of pipe flow pressure drop gradient, this study analyzes the shortcomings of Ramey model and Hassan & Kabir model through transient analysis. Based on the equations of mass conservation, momentum conservation and energy conservation, and considering the interaction between fluid physical parameters and temperature and pressure, the wellbore pressure coupling model of water-bearing gas well is established, and the Newton Raphael iterative method is used for MATLAB programming. On this basis, the relationship between tubing diameter, gas production, gas–water ratio, and wellbore temperature field and pressure field in high water-bearing gas wells is discussed. The results show that the wellbore temperature pressure coupling model of high water-bearing gas well considering the coupling of gas–liquid two-phase flow wellbore temperature pressure field has higher accuracy than Ramey model and Hassan & Kabir model, and the minimum coefficients of variation of each model are 0.022, 0.037 and 0.042, respectively. Therefore, the model in this study is highly consistent with the field measured data. Therefore, the findings of this study are helpful to better calculate the wellbore temperature and pressure parameters under complex well conditions.

New LWD Image Improvement Method to Mitigate Interpretation Risks

With the advancement of LWD (Logging While Drilling) hardware and acquisition, the imaging technology becomes not only an indispensable part of the drilling tool string, but also the image resolution increases to map layers and heterogeneity features down to less than 5mm scale. This shortens the geological interpretation turn-around time from wireline logging time (hours to days after drilling) to semi-real time (drilling time or hours after drilling). At the same time, drilling motion is complex. The depth tracking is on the surface referenced to the surface block movement. The imaging sensor located downhole can be thousands of feet away from the surface. Mechanical torque and drag, wellbore friction, wellbore temperature and weight on bit can make the downhole sensor movement motion not synchronized with surface pipe depth. This will cause time- depth conversion step generate image artifacts that either stop real-time interpretation of geological features or mis-interpret features on high resolution images. In this paper, we present several LWD images featuring distortion mechanism during the drilling process using synthetic data. We investigated how heave, depth reset and downhole sensor stick/slip caused image distortions. We provide solutions based on downhole sensor pseudo velocity computation to minimize the image distortion. The best practice in using Savitsky-Golay filter are presented in the discussion sections. Finally, some high-resolution LWD images distorted with drilling-related artifacts and processed ones are shown to demonstrate the importance of image post-processing. With the proper processed images, we can minimize interpretation risks and make drilling decisions with more confidence.

Numerical Simulation of Natural Convection and Calculation of Heat Transfer Coefficient in Wellbore Annulus during Deep-Water Gas Well Testing

Most of the current prediction model of wellbore temperature for deep-water gas well does not consider the influence of natural convection in annulus on the heat dissipation of the system, resulting in a lower prediction accuracy of temperature. In this study, three-dimensional simulation on the heat transfer by natural convective of testing fluid in annulus was performed. The mechanism of heat transfer are studied for different values of Rayleigh number (Ra) and Bingham number (Bn). The results show that the occurrence of natural convection in the annulus can significantly increase the heat loss of the fluid in the tubing. With the increases in Ra or decreases in Bn, the convective transport in annulus gradually strengthens, and the heat transfer coefficient gradually increases. However, when the Bingham number increases to about 100, the heat transfer mode in annulus becomes a single heat conduction. Based on the simulation results, a new correlation of heat transfer coefficients in annulus was proposed. The introduction of this correlation can significantly improve the prediction accuracy of wellbore temperature during deep water gas well testing, and lay a foundation for the prevention and control of hydrate and wax formation in wellbore.