Study On Thermodynamic Calculation In Wellbore For SAGD Circulation Startup

Steam assisted gravity drainage is an effective technique for the development of heavy oil and ultra heavy oil.The effect of circulating preheating is an important factor affecting the development of steam assisted gravity drainage.The distribution of the steam thermal properties along the wellbore has a direct influence on the cycle preheating.Therefore,it is of great practical significance to study the distribution law of the steam along the wellbore by means of establishing the mathematical models for fluid flow and heat transfer.In this paper,the mathematical model of the flow and heat transfer in the horizontal section is established based on the structure and the reservoir characteristics of the horizontal section.In the model,the phase transition and the heat transfer between the flow and the back flow are considered.The model is solved by programming,and the variation law of steam thermal properties along the path is obtained.Sensitivity analyses are made on the circulation velocity and the dryness of A point in the bottom hole.The results show that the pressure drop and temperature drop along the horizontal section are mainly occurred in the long oil pipe.The lower steam flow rate and dryness are favorable to the heat transfer between the annulus and the reservoir,but the uniformity of heat dissipation is poor.Based on the theory that the dry degree is greater than or equal to 0 when the steam returns to A point,we get the optimal parameter chart.Based on the theory of linear heat source and superposition principle,a model of heat communication judgment during circulation preheating is established.And sensitivity analysis of horizontal interval is carried out.The time required for cyclic preheating increases obviously with the increase of well spacing.In this paper,a mathematical model of double tube flow and heat transfer in vertical wells is established for the wellbore above the horizontal section.The distribution of steam thermal properties along the path is calculated by programming.The results show that high circulating flow rate and high steam dryness easily lead to a larger pressure drop along the path.The change of steam dryness along the flow decreases with the increase of the circulating flow rate.When the circulating flow rate is low,the steam in the long pipe near the wellhead is easy to become superheated steam with the increase of the steam dryness at A point.When the circulating flow rate is low,the steam in the short pipe near the wellhead is easy to become water with the decrease of the steam dryness at A point.The results provide a theoretical basis for the regulation and optimization of the preheating of SAGD.