STUDY ON THE LAW OF GAS CAP MIGRATION OF CARBONATE CONDENSATE OIL-GAS RESERVOIR WITH WEAK VOLATILE OIL BASED ON VARIATION OF CRUDE OIL DENSITY

Boilfield is a structural lithologic weak volatile oil-gas reservoir with condensate gas cap and edge-bottom water. With the development of oil ring, the formation pressure drops and the condensate gas cap expands outward, resulting in condensate oil appearance in the production wells near the oil-gas interface. Because of the serious degassing of weak volatile crude oil in oil-gas reservoirs, it is difficult to judge the source of gas and impossible to analysis the situation of gas cap by gas production alone. In this paper, by analyzing the change of crude oil density in condensate oil wells, combining with fracture cavity identification results and numerical simulation research, we established a set of methods to study gas cap migration in carbonate condensate oil-gas reservoirs. The results show that: (1) based on the change of crude oil density, the wells can be divided into three types: pure condensate oil model, black oil to mixed oil model, and condensate oil to mixed oil model; (2) after 15 years of development, the oil-gas interface in the north has dropped 21m along the fracture, which is the cause of the change of crude oil density in the three types of wells; (3) monitoring the crude oil density near the oil-gas interface can be used to study the gas cap migration law. The research results provide a new method for studying the migration law of gas cap in other similar reservoirs, which is of great significance.