Publications

This case study describes use of logging-while-drilling (LWD) resistivity at the bit and near-bit gamma ray to perform pre-modeling for the best tool configuration to determine a core point near the top of a gas reservoir. The service was successfully utilized in an Australian well. Resistivity at the bit assists in the identification of a formation top at the time of bit penetration and, together with other data obtained while drilling, can increase the confidence in picking a core point. This practice can result in significant rig-time savings by reducing the risk of circulating bottom hole cuttings up to determine if the reservoir section has been reached. If conventional LWD resistivity is used to determine a core point, more of the target interval is drilled because the sensors are located a greater distance behind the bit. The near-bit gamma ray measurement delivers reliable data from a short distance behind the bit. This data can be used to sense-check the interpretation of the at-bit resistivity data. During well planning, two geological models were used for estimating tool response: a complex model and a much simpler one. Modeling was performed by using various bottom hole assembly (BHA) configurations and mud resistivity values. The reservoir navigation application can also be used for determining casing points, maximizing hole section lengths, and eliminating casing strings by stopping abnormal pressure zones and running casing. Keywords: LWD Measurements, Resistivity at the Bit, Near-Bit Gamma Ray.