Reservoir Fluid Geodynamics using Logging-While-Drilling Downhole Fluid Analysis: A North Sea Case Study

Abstract

Abstract We present a case study of the application of Fluid Mapping While Drilling (FMWD) to acquired logging-while-drilling downhole fluid analysis (FMWD-DFA) in the development stage of a North Sea reservoir. An extensive Wireline DFA (WL-DFA) dataset and Reservoir Fluid Geodynamics (RFG) study helped characterize fluid variations in the exploration and appraisal stages of this field revealing a complex reservoir charge history that results in fluid variations throughout the field and furthermore revealing connections between reservoir quality/productivity and in-situ fluid properties. In the development stage, knowledge acquired in the previous field phases guided well placement decisions and FMWD-DFA was used actively in well construction to validate and enhance the fluid model in this field. FMWD pressure and DFA measurements were acquired in five development wells in the field: three horizontals and two high-angle pilots. DFA measurements provide fluid composition and optical density, which correlates directly with the asphaltene content of the oil. Asphaltene gradients are modeled to assess thermodynamic equilibrium conditions and investigate lateral and vertical connectivity. DFA and other data streams integrated by the RFG analysis provided the base model: a relatively recent secondary migration of light hydrocarbon into the reservoir that resulted in different realizations of the mixing process depending on distance from the charge plane and rate of mixing. Well trajectories were designed to target sweet spots based on appraisal data; however, some level of uncertainty remains when entering the development stage. FMWD-DFA was used to understand fluid property variations throughout the field that may be associated to geological factors or resulting from fluid mixing processes that may yield localized asphaltene instability. FMWD pressure and mobility measurements complement this model and enable an assessment of current levels of pressure depletion from production in a neighboring field in hydraulic communication through a shared aquifer. This field example shows integration of DFA technology from different acquisition platforms at different stages of the life of the field. It illustrates how this technology is used to improve the understanding of the complex fluid variations in this field and make development decisions such as optimizing well design by ensuring placement within reservoir sweet spots.