Tapping the remaining oil with horizontal wells is routinely used in high water-cut oilfields. However, it faces serious challenges in complex fluvial reservoirs with stacked sand body, horizontal interlayers, lateral barrier and complex water flooding conditions. Moreover, the depth uncertainty of the target interval, limited number of offset wells, rapid change of thickness, thin target intervals, and variable fluid contact have also increased the risks of the horizontal well placement. In order to locate the optimal positions of the horizontal wells, get the maximum recovery, reduce the risk of water flooding, minimize the drilling time, we propose a comprehensive well planning and optimization method based on multidisciplinary innovative techniques. New techniques from geology, geophysics, and drilling engineering are assembled to efficiently perform the challenging task.
Firstly, an improved interwell 3D correlation technique was proposed to characterize the single sand body. The technique can depict the vertical hierarcy of reservoir. Secondly, we propose a lateral boundary delineation technique based on seismic geometrical attribute. Combined with ant tracking algorithm, we are able to extract the 3D lateral discontinuous surfaces. Based on above technique, we can build detailed architecture model fast and optimize the positions of horizontal wells. Considering the geological uncertainty, the boundary mapping tool is used to optimize the well trajectories in real time to avoid the water flooded zone and shale zone, and to stay in the sweet zone.
We applied the integrated workflow in Q oilfield in Bohai Bay basin, East China. 112 horizontal wells are drilled. The drilling results proved that boundary mapping tool can achieve smooth landing of well path and delineate the accurate geometry and thickness variation of sand body which reduces the depth uncertainty of seismic horizon explanation, and keeps the horizontal well trajectories away from oil-water contact. The production results show that 86% horizontal wells have achieved low water-cut and high oil production rate. The total production rate of Q oil field has increased by 2.5 times.