A model for nitrogen injection in horizontal wells of tight oil reservoirs

Abstract

ABSTRACT In the petroleum industry, nitrogen is often used to improve the recovery of unconventional oil and gas resources such as heavy oil, tight oil, and shale oil. When nitrogen is injected into the oil and gas layers along the horizontal section of the wellbore, its pressure and temperature and other physical parameters all change with coordinates and time. These changes of pressure and temperature will have certain impact on the recovery efficiency. Therefore, it is necessary to simulate the non-isothermal variable mass pipe flow process of nitrogen in the horizontal wellbore. Based on the principles of conservation of energy and momentum, this paper establishes a nitrogen flow model in the horizontal wellbore by coupling sub-models such as the reservoir suction model. Results show that: (a) when the number of grids reaches 100, the degree of agreement between the predicted pressure value and the measured value of the model has met the requirements of engineering calculation accuracy. (b) when the injection pressure is lower than 2.7 MPa, the temperature gradient at the heel end and toe end of the wellbore is similar, while when the injection pressure is high (equal to 2.9 MPa), the temperature gradient at the toe end of the wellbore is significantly higher than that at the heel end.