Fengrui Sun

Numerical simulation of superheated steam flow in dual-tubing wells

In this paper, a novel model is presented to estimate the thermophysical properties of superheated steam (SHS) in dual-tubing wells (DTW). Firstly, a mathematical model comprised of the mass conservation equation, momentum balance equation and energy balance equation in the integral joint tubing (IJT) and annuli is proposed for concentric dual-tubing wells (CDTW), and in the main tubing (MT) and auxiliary tubing (AT) for parallel dual-tubing wells (PDTW). Secondly, the distribution of temperature, pressure and superheat degree along the wellbores are obtained by finite difference method on space and solved with iteration technique. Finally, based upon the validated model, sensitivity analysis of injection temperature is conducted. The results show that: (1) effect of injection temperature difference between MT and AT on temperature profiles is weak compared with that between the IJT and annuli. (2) Temperature gradient in IJT and annuli near wellhead is larger than that in MT and AT. (3) Superheat degree in both CDTW and PDTW increases with the increase in injection temperature in IJT and MT, respectively. (4) Superheat degree in IJT and MT decreases rapidly near wellhead, but the superheat degree in annuli and AT has an increase. (5) Thermal radiation and convection are the main ways of heat exchange between MT and AT. This paper gives engineers a novel insight into what is the flow and heat transfer characteristics of SHS in DTW, and provides an optimization method of injection parameters for oilfield.

The heat and mass transfer characteristics of superheated steam in horizontal wells with toe-point injection technique

Little efforts were done on the heat and mass transfer characteristics of superheated steam (SHS) flow in the horizontal wellbores. In this paper, a novel numerical model is presented to analyze the heat and mass transfer characteristics of SHS in horizontal wellbores with toe-point injection technique. Firstly, with consideration of heat exchange between inner tubing (IT) and annuli, a pipe flow model of SHS flow in IT and annuli is developed with energy and momentum balance equations. Secondly, coupled with the transient heat transfer model in oil layer, a comprehensive mathematical model for predicting distributions of pressure and temperature of SHS in IT and annuli is established. Then, type curves are obtained with numerical methods and iteration technique, and sensitivity analysis is conducted. The results show that (1). The decrease in SHS temperature in annuli caused by heat and mass transfer to oil layer is offset by heat absorbtion from SHS in IT. (2). SHS temperature in both IT and annuli increases with the increase in injection pressure. (3). IT heat loss rate decreases with the increases in injection pressure. (4). Increasing pressure can improve development effect.

A brief communication on the effect of seawater on water flow in offshore wells at supercritical state

At present, the study of supercritical water (SCW) flow in wellbores is at the starting stage. In this paper, a simple but useful model is developed to study the effect of seawater on the thermophysical properties of SCW in offshore vertical wellbores. Firstly, based on the momentum and energy balance equations, a flow model describing SCW flow in a tube is established. Then, coupled with transient heat transfer model in seawater and formation, and thermophysical parameters of SCW, a comprehensive mathematical model is established. In order to solve the model, the governing equations are expressed in the form of difference equations. The straight forward numerical method is adopted to solve the model from wellhead to well-bottom. In the process of solving, iterative technique is used to control the calculation accuracy. Finally, type curves of SCW flow in offshore wellbores and sensitivity analysis are discussed. Results show that (a) the flow of seawater results in a rapid decline in the temperature/enthalpy of SCW in wellbores. (b) Heat loss is the dominant factor of physical parameter distribution in wellbores when the injection rate is relatively small. (c) Heat loss has an obvious influence on temperature drop when SCW is sparse in volume. (d) The SCW pressure decreases with increasing of injection temperature.

New analytical equations for productivity estimation of the cyclic CO2-assisted steam stimulation process considering the non-Newtonian percolation characteristics

The research course in the estimation of productivity of cyclic steam stimulation wells can be divided into three stages: (a) the mobility of heavy oil in the cold area is neglected, (b) the mobility of heavy oil in the cold area is considered—however, it is Newtonian fluid seepage, and (c) it is conserved as non-Newtonian fluid seepage in the cold area. However, the distribution of the value of starting pressure gradient in the heated area where heavy oil is still non-Newtonian fluid is neglected. In this paper, a new model is developed for productivity estimation of cyclic steam stimulation wells with consideration of the non-Newtonian fluid flow behaviors in the heated area where the temperature is higher than the turning point. New percolation equations are developed based on the new proposed concept of “the transition region” in the heated area. The results show that: (1) when the non-Newtonian fluid characteristic is neglected, the predicted results from the new model match the results from the numerical simulator perfectly, and (2) in oil field, the non-Newtonian fluid characteristic cannot be neglected. When the non-Newtonian fluid characteristic is considered in the model, the average oil production in each cycle can match the filed data better than Yang et al.’s model. This new model laid a basic reference for oil companies and researchers involved in the area when they are designing the well pattern, spacing or estimating the productivity of oil wells.

Effect of physical heating on productivity of cyclic superheated steam stimulation wells

Previous works have focused on the single factor analysis of the effects of chemical reactions of superheated steam with oil and rock minerals on the oil well productivity. However, the relationship between the factors and the contributions to productivity is still unknown. In this paper, the contribution of physical heating of superheated steam to well productivity is studied with the numerical method. Results show that: (a) the heat in the area has a very limited increase when the temperature of superheated steam continues to increase. (b) At the starting stage, the oil is heated to a higher temperature and the mobility is increased. The elastic energy becomes the dominant factor controlling the productivity of the oil well in the following stage. (c) The chemical reactions of superheated steam with oil and rock minerals are the dominant factors contributing to the productivity.

Enhanced gas recovery by CO2 sequestration in marine shale: a molecular view based on realistic kerogen model

Injection of CO2 into shale reservoir is regarded as one potential scenario for CO2 sequestration and enhanced gas recovery (CS-EGR). In this work, a realistic molecular model of kerogen in Chinese Silurian marine black shale was generated using molecular dynamics (MD) simulations. The competitive adsorption of CH4 and CO2 was simulated by the grand canonical Monte Carlo (GCMC) method under different reservoir pressures, temperatures, geological depths, CO2 mole ratios, and moisture contents of kerogen model. Results show that CO2/CH4 adsorption selectivity decreases with increasing reservoir pressure, indicating that CS-EGR can be more efficient if CO2 injection is conducted at the late development stage. The temperature has a negative effect on the selectivity, which indicates that thermal stimulation has an adverse effect on the efficiency of CS-EGR. Also, the selectivity decreases with increasing geological depth, suggesting that shallow shale formations are more suitable for CS-EGR. At low pressures, the selectivity increases with increasing CO2 mole ratio, while at high pressures, the selectivity decreases with the increase of CO2 mole ratio. This result suggests that CO2 mole ratio should be dynamically adjusted with the production so as to adapt to the changing reservoir pressure. At higher pressure condition, both the amounts of CO2 sequestration and CH4 desorption increase with the increase of CO2 mole fraction. However, the adsorption stability of CO2 weakens with increasing injection amounts of CO2. Moreover, the adsorption selectivity decreases initially, and then increases with the moisture content of kerogen. Thus, the performance of CS-EGR may be improved by increasing the kerogen moisture content for Silurian shale gas reservoirs. This study gains enhanced insights on the effect of reservoir pressure, temperature, geological depth, CO2 mole ratio, and kerogen moisture content on CO2/CH4 competitive adsorption, and the results can provide applicable guidances for CS-EGR in shale gas reservoirs.

Comments on: The flow and heat transfer characteristics of compressed air in high-pressure air injection wells [Arabian Journal of Geosciences (2018) 11: 519]

High pressure has been widely used in the petroleum industry. The commended paper presented a model that can be used to simulate air flow in a vertical wellbore. The novelty and usefulness of the model is good, and the paper deserves to be published in the Arabian Journal of Geosciences. However, we pointed out some critical points that should be noticed by the authors as well as the following researchers who are involved in this area. The comments will show usefulness in pointing out future research direction in wellbore modeling.