Patent ID: 8606522
Filing Date: 2013-12-10
Classification: E21B

Abstract:
1. A method for determining current gas saturation in a near-wellbore zone of a wellbore in a volatile oil formation, the method comprising: measuring formation parameters and formation fluid parameters before starting production, wherein (i) the formation parameters and the formation fluid parameters are measured by at least one of a logging tool, core testing, and fluid testing, and (ii) the formation parameters and the formation fluid parameters are selected from a group consisting of formation porosity, rock mineral composition, water saturation, water composition, formation gas PVT-data, formation gas composition, and bubble point, determining an expected gas saturation value and a composition of a gas-oil mixture in a near wellbore zone by hydro-dynamic modeling the gas-oil mixture using the measured formation parameters, the formation fluid parameters, and phase permeability functions, creating a numerical model to simulate neutron logging signal change during production using the measured formation parameters, the formation fluid parameters, the expected gas saturation value, and the determined gas-oil mixture composition, starting production of the wellbore, performing neutron logging using a neutron logging tool and measuring neutron logging signals after a decrease in well productivity, comparing the measured neutron logging signals with the simulated neutron logging signals, and determining the current gas saturation by adjusting the phase permeability functions until a match is obtained between the measured neutron logging signals and the simulated neutron logging signals.