부산대학교 도서관

As part of the Gorgon Stage 2 project, a total of four production wells were installed at a new manifold within the Jansz-Io gas field. A key well construction challenge was the placement of the 12 ¼″ section total depth (TD). Due to the presence of reservoir depletion, the mud weight required to drill the sandstone would be insufficient to prevent wellbore collapse in the Barrow Shale immediately above the reservoir. Hence, the casing design called to isolate the entire Barrow Shale interval by placing the 9 ⅝″ production liner shoe immediately inside the reservoir. To avoid damaging the high-quality sandstone in the upper reservoir, it was desired to limit the reservoir penetration to less than 1m true vertical depth (TVD) at 80° inclination. Chevron recognised several challenges in landing the wells, which included: seismic uncertainty of the reservoir top, poor resistivity contrast and the lack of significant markers in the overburden. Conventional methods such as near-bit gamma ray carried high risk because the sensor offset to bit is close to the penetration limit. Therefore, a new approach of integrating a deep directional resistivity (DDR) tool and an at-bit resistivity measurement to make the casing point decision was proposed. With this new approach, all four wells were landed, with actual reservoir penetration less than 1m TVD. The real-time data from the DDR tool allowed the operator to efficiently drill the section, only reducing the rate of penetration immediately prior to entering the reservoir. The at-bit resistivity tool, drilling parameter changes and cuttings identification were beneficial to confirm reservoir entry and call section TD.