[Society of Exploration Geophysicists Proceedings of the 11th SEGJ International Symposium, Yokohama, Japan, 18-21 November 2013 - Yokohama, Japan (18 November to 21 November)] Proceedings of the 11th SEGJ International Symposium, Yokohama, Japan, 18-21 November 2013 - Vertical Gradient Modeling of Borehole Gravity and Its Application for Identifying the Subsurface Layer Boundaries and Estimating the Reservoir Porosity in the ABC Field