Development of a green oil field was started in 2014 with a horizontal well pattern targeting the underwater distributary-channel sand reservoir of the braided-channel deltaic sediment. In this geological environment, the complex uncertainties appear as the irregular superposition of sand bodies and interbeds, lateral changes in sand reservoir property and thickness, and the high structural dip uncertainty. In appraisal wells, the laminated edge water sand reservoir consists of multiple irregular and thin (0.5 to 5.6 m) sand layers and shaly and calcareous interbeds. The crucial points for success in this development are to manage uncertainties and accurately identify the laminated reservoir profile for optimal well placement along discontinuous sweet sand layers and to update the reservoir model for the future development plan optimization.
To manage the uncertainties and challenges, a deep directional electromagnetic resistivity logging-while-drilling tool was introduced to provide a High-definition (HD) Multilayer Bed Boundary Detection Service. The prejob feasibility study revealed this HD service's capability in this complex multilayer environment by delineating the profiles of multiple layers (more than three) simultaneously from a distance of up to 15 ft. The perfect application result of this HD service in the first well proved this service as the effective approach to enhance the reservoir understanding and place the horizontal wells optimally along discontinuous sweet sand layers. Accordingly, a significant start was made to initiate the development breakthrough in this specific underwater distributary-channel laminated reservoir. The success of multiple subsequent wells further validated the high efficiency of this approach.
Several key outcomes have been observed during the execution and upon the completion of the wells as the highlights of this HD service for this complex reservoir, as follows:
The HD resistivity automated multilayer inversion could simultaneously reveal up to four boundaries and five layers vertically to clearly identify the subsurface multilayer resistivity profile in real time including several sand bodies.
Enhanced understanding of the laminated reservoir helped in proactively landing the smooth trajectory into the uncertain sweet zone and to identify remotely the lateral reservoir thickness variation and its vertical heterogeneity to control the smooth trajectory within the best zone while close to the target top for the maximum oil recovery.
The updating of the reservoir model accordingly helped the assessment of the reserve and the optimization of the future development plan.
The implementation of this efficient approach is the key enabler to place efficiently the smooth trajectory along the best position within the sweet zone to develop profitably this specific laminated channel sand reservoir.