Systematic improvement in Tong's B-type water drive method

Abstract

Tong's B-type water drive method was proposed as early as the 1970s and has been widely applied in the dynamic prediction and effective evaluation of oilfield development. Through extensive applications and studies, many researchers found that the statistical constants in the formula of the Tong's B-type water drive method (also referred to as the Tong's B-type formula) are not applicable to multiple types of reservoirs, especially low-permeability ones, due to the limited range of reservoir types when the formula was conceived. Moreover, they put forward suggestions to improve the Tong's B-type formula, most of which focused on the research and calculation of the first constant in the formula. For oilfields in the development stages of high or ultra-high water cuts, it is widely accepted that different types of reservoirs have different limit water cuts. This understanding naturally makes it necessary to further modify the Tong's B-type formula. It is practically significant to establish the water drive formula and cross plot considering that the two constants in the formula vary with reservoir type. By analyzing the derivation process and conditions of the Tong's B-type formula, this study points out two key problems, i.e., the two constants 7.5 and 1.69 in the formula are not applicable to all types of reservoir. Given this, this study establishes a function between key reservoir parameters and the first constant and another function between key reservoir parameters and recovery efficiency. Based on the established two functions and considering that different types of oil reservoir have different limit water cuts, this study develops an improved Tong's B-type formula and prepares the corresponding improved cross plot. The results of this study will improve the applicability and accuracy of Tong's B-type water drive method in predicting the trend of water cut increasing for different types of oil reservoirs.