Formation Evaluation Using LWD NMR, LWD Electrical Imaging and Triple Combo Data - A Case Study from India

Abstract

Abstract Logging While Drilling (LWD) Nuclear Magnetic Resonance (NMR), LWD Electrical Imaging along with Conventional Triple Combo LWD services were deployed in Mumbai Offshore field in India. LWD NMR data gives a rock independent porosity measurement which seem to verify the other measurements which in turn increases the data confidence. Depending on rock quality and wettability NMR data might give some good insight in fluid saturations. Furthermore, NMR data gives a permeability Index (also while drilling) which can be useful for selecting pressure stations while drilling, it might also be useful for completion design and production/injection rate calculations. LWD Electrical Imaging tool from provides detailed reservoir characterization, structural classification, and wellbore integrity management in Realtime. In this well, The NMR permeability seemed to be related to total porosity; high porosity gave high permeability and low porosity gave low permeability, i.e., a synthetic perm curve based on Neutron density aligned quite well with NMR perm. The Hydrocarbon saturation appeared to be highest in the upper part of the section but both Archie saturation and NMR saturation indicate a nearly monotonically decreasing Hydrocarbon saturation towards end of well. In the upper part the T2 peak was positioned at around 1000ms but gradually moved towards a shorter T2 time with depth. Towards bottom the T2 peak had moved down to about 2-300ms and water saturation appeared to be high. Electrical imaging was used to demarcate the bed boundaries, Dip Picking and Fracture identification. Quick-Look Interpretation of the image data provides evidence of vuggy carbonaceous formation with presence of continuous conductive fractures scattered across the drilled interval. This made the use of permeability model and saturation calculation more complicated. The conventional triple combo helped to steer the well and be in the zone of interest. The paper in depth discusses the deployments of LWD NMR and LWD Electrical Imaging in the field, Associated challenges, and value these services brought to the operator.