Formation Evaluation in Carbonates with LWD Logs in High Angle Wells in Presence of Heavy Hydrocarbons

Complex carbonate reservoirs present unique challenges for measuring porosity, deriving permeability, and assessing producibility. While drilling a complex carbonate reservoir offshore Brazil, to be developed using horizontal , geosteered wells, an operator required a Logging while Drilling (LWD) analysis to characterize producible zones. The operator used magnetic resonance service to obtain real-time LWD measurements in a several challenging horizontal wells. The NMR LWD measurements evaluate pore-size distribution to estimate formation properties and consequently determine the best stimulation treatment and completion optimization. A multi-sensor LWD collar is also run in conjunction to evaluate rock and fluid properties and obtain accurate lithology description, porosity and continuous permeability. Presence of relatively heavy hydrocarbon type (18-20 API with viscosity of 12 cP) represented a special challenge, affecting the traditional NMR interpretation approach. Utilizing a sequential multi-mineral application methodology together with NMR data, fluids were split into five categories: clay bound water, capillary irreducible water, un-flushed formation oil, filtrate and movable water. An integrated permeability thickness profile was computed allowing classification of each zone potential and size accordingly the stimulation plan. The predictions were confirmed by stimulation execution, resulting in very fast pressure decays over the intervals characterized to have the highest permeability.