--> Reducing Depth Uncertainty in Deep and Ultra-Deep Water Exploration Wells With Seismic While Drilling

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Reducing Depth Uncertainty in Deep and Ultra-Deep Water Exploration Wells With Seismic While Drilling


Exploration wells, by definition, carry intrinsic uncertainties prior to drilling and logging. 3D seismic data and velocities underlie well planning activities such as target identification, mud weight windows and casing shoe depths. These well design parameters are based on estimated uncertainty ranges which are amplified in deep-water settings. The use of seismic while drilling (SWD) to measure seismic velocities and record real-time look ahead seismic images to reduce uncertainties and optimize drilling decisions is presented. In 2017 Woodside conducted a five-well drilling campaign offshore Myanmar. The use of seismic while drilling in these exploration wells is examined. Operations were executed from a drillship. Transparent acquisition, sea-bed checkshots, impact of a riserless environment and employing Marine Mammal Observation procedures as standard practice are discussed. A unique dual tool configuration set-up for SWD was employed to acquire checkshots whilst drilling, as well as lookahead vertical seismic profile images to confidently establish seismic markers ahead of the bit. The main objective was to mitigate uncertainty and risk in the shallow large diameter hole sections where traditional wireline measurements are not run, especially in a riserless environment. Seismic while drilling enabled the drilling team to optimize the casing shoe depth in order to maximize shoe strength and also allowed VSP acquisition with no separate wireline run being required. Velocity uncertainties in the overburden can have a large impact on deeper mapped targets. In deep water drilling, large hole sizes are usually drilled riserless and coupled with a large diameter of 26 inches, are not traditionally logged with wireline. SWD conveyed as part of the logging while drilling assembly allows acquisition of important velocity measurements and seismic images under these conditions to optimize the well construction process and provide an updated depth prognosis while drilling.