水平坑井における PI (産出指数) モデルおよび試算例について

抄録

A well production performance program for a horizontal well is now being developed. This program contains two main parts, inflow performance of reservoir fluids into a horizontal wellbore using three productivity index equations and well outflow performance using an empirical pressure drop correlation.
The productivity index equations used in the program are (1) a modified vertical well equation, (2) the Peaceman's equation and (3) the Babu and Odeh's equation.
A case study was carried out using the program with reservoir and well data in order to investigate the effects of four parameters on the horizontal well performance; (1) three productivity index equations, (2) horizontal well length, (3) completion tubing size in the horizontal well, and (4) vertical/horizontal permeability ratio (k_v/k_h) in the reservoir.
Conclusions of the case study are as follows;
(1) There are little differences among the calculation results of the three PI equations, especially if the horizontal well length is more than 500m for this case.
(2) Oil production rate is not proportional to the horizontal well length. The reduced drawdown due to turbulent flow along the wellbore may result in the total production rate reaching a certain critical value as a function of wellbore length.
(3) A larger diameter tubing reduces the pressure drop in the horizontal wellbore, which results in more uniform influx profile of reservoir fluids into the horizontal wellbore than a smaller diameter tubing.
(4) Vertical/horizontal permeability ratio (k_v/k_h) has the strongest effect on the well performance among the four parameters. If k_v/k_h is small, it needs a long horizontal well to produce oil at a high rate.