A Fluid Properties while Drilling Rapid Identification Method under Oil-Based Drilling Fluid Conditions for Low Porosity and Low Permeability Reservoirs in the Xihu Sag

In order to achieve rapid identification while drilling of fluid properties for low porosity and low permeability reservoirs in the Xihu Sag under oil-based drilling fluid conditions, a delay-resistivity logging comparison identification method was proposed. The fluid loss test of oil-based drilling fluid was carried out, and its fluid loss characteristics in the low porosity and low permeability reservoirs were studied. The characteristics of resistivity change after the drilling fluid filtrate intruded into the different depths and types of formations during the resistivity LWD under oil-based drilling fluid conditions were analyzed. The study found that there was a certain fluid loss in the oil-based drilling fluid, and the amount of fluid loss showed a certain relationship with in-situ physical properties, along with pressure difference and time. The oil-based drilling fluid filtrate was not conductive, and if it invaded the reservoir, and the oil and gas were displaced, the resistivity of LWD and re-tested one were basically the same. If the formation water was displaced, the re-tested resistivity increased, and it could be greater than the resistivity of LWD. Therefore, based on the high intrusion characteristics of oil-based drilling fluids, according to the time-lapse logging concept, a method was proposed to that could quickly identify the fluid properties by comparing the difference between the shallow real-time resistivity and the re-tested resistivity. This method was successfully applied in the field, and the obtained fluid properties rapid identification results were consistent with the results of subsequent cable formation test pumping, indicating that this new technique was feasible and in addition, could potentially have widespread applications.