Optimizing Horizontal Well Placement and Reservoir Inflow in Thin Oil Rim Reservoirs Improves Recovery and Extends the Life of an Aging Field
Authors: Kartoatmodjo G. , Bahri C. , Badawy A. , Ahmad N. , Moreno J. , Wu B. , Zulkhifly F. , Bela S. Magna , AlShuraiqi H. , Moreno J. C. , Friede T. 
Published: December 2009

Planning of infill drilling in oil rim reservoirs is a challenging task. In the case of thin oil rims with large gas caps, early gas breakthrough and gas cycling can cause serious problems, especially in a co-mingled production environment and heterogeneous geological conditions. For the last years, high resolution geological models have been widely used to plan new wells trajectories. However, the dynamic behavior of the reservoirs was widely ignored. These effects are related for instance to interference phenomena which directly impact the optimum number of infill wells during the concept selection in a field development stage. High resolution geological models together with reservoir simulation models using parallel computing allow a more sophisticated workflow to optimize horizontal well placement.

Interactive well planning was initially used to optimize the horizontal well location within the 3-D reservoir model, ensuring a smooth trajectory, near placement to the current oil-water contact, and steer away from the gas cap to delay gas breakthrough. The wells were then translated into the dynamic simulation model where a detailed modeling of both reservoir inflow and well bore hydraulics were used to optimize the flow at well completion level. An iterative process was used to maximize the well production by balancing the pressure drop along the horizontal section in order to maximize oil production and minimize gas-oil-ratios at well and field level. As a result the number of drainage points needed to effectively recover the existing oil was reduced from 20 to 4, realizing 75% of the total infill potential.

This paper describes the workflow for optimization of horizontal well performance during the field development planning stage of an offshore oil rim brownfield. The field is highly constrained with gas production, which constitutes about 90% of the total field production. Crestal gas re-injection is ongoing as a pressure maintenance effort. Most wells are completed in commingle horizontal wells. Successful infill wells must be placed and completed appropriately to reduce gas and therefore maximize oil production. Among the parameters studied for the field development plan are: type of well, well completion options, offset from fluid contacts and well orientation.

This paper also describes wellbore dynamic behavior that has not been extensively covered in the literatures. It illustrates the challenges of placing and optimizing production along the horizontal section of the wells and how an efficient control of completion and depletion levels is used to optimize and accelerate oil production in an aging oil rim field. Extensive reservoir simulation on a full field model was utilized for the initial well placement study. In parallel, geosteering feasibility assessment was conducted and tied to the reservoir simulation results. These were the basis for the subsurface team to determine the most suitable wellbore trajectories and conformance requirements. At the same time, a comprehensive sand production prediction study was carried out, including laboratory work and mechanical earth modeling to investigate sanding tendency for various completion scenarios on the shallow and deeper reservoirs. Decision and risk analysis completes the full cycle of resevoir engineering, well placement and well completion has been rigorously evaluated.