Utilization of UDAR LWD Technology for Seismic Data Validation in a Complex Sand Injectite Environment

Abstract The intricate architecture of the remobilized and injectite sand (RIS) complex in the Balder field, significant velocity variations within the overburden geology, a rugose carbonate underlying strata and production related effects have made seismic imaging and interpretation challenging. The use of Ultra Deep Azimuthal Resistivity (UDAR) technology to calibrate and validate multiple seismic data sets, including the recently acquired and processed Ocean Bottom Node (OBN) seismic data, has become an essential tool in the field's development. The introduction of UDAR Logging While Drilling (LWD) technology enabled mapping of RIS, along with fluid contacts, from sub-seismic to seismic scale. In this paper, 1D/3D UDAR and formation evaluation log data from recently drilled horizontal wells in the Balder field were integrated with 4D and legacy streamer seismic data, as well as with newly acquired OBN seismic survey. The main objective was to correlate remobilized sand bodies, mapped by UDAR inversions, to validate the newly improved clearer definition of the RIS geometries on the OBN seismic. During the drilling of producer wells, the real-time integration of 1D/3D UDAR and log data with OBN seismic data has shown a very good correlation in terms of reservoir mapping and sand thickness resolution, compared to the previously used streamer seismic. The use of full-azimuth design and improved velocity modelling has led to the suppression of noise and consequent improvement in the imaging of both seismic and sub-seismic scale sand features with varying strike and dip, especially the steeply inclined injectite dykes (>20 deg inclination). Better understanding of target sand morphology and connectivity in the area has facilitated informed well trajectory adjustments during geosteering for optimal well placement, when absence and end of a sand body is confirmed by UDAR data. Post-drill, the reservoir characterization work for static model updates utilizes interpretation of sand bodies on UDAR inversions, to further refine the net sand estimation for more accurate sand thickness prediction across the Balder field. The mapped top and base of the sands from UDAR data in the horizontal wells provide a dense set of varying sand thicknesses and facies for seismic calibration. UDAR helps to identify contact movements, undrained zones, depth control and the interpretation of 4D seismic signatures. The paper therefore contributes to the continuous improvement in the understanding of UDAR use and accurate seismic imaging of sand injectites on OBN data for de-risking reservoir targets and helping to provide optimal well placement in challenging, complex injectite environments. The calibration of the seismic data sets and interpretation using UDAR data should ultimately lead to geologically realistic static models for infill drilling, dynamic simulations, and reserve estimation.