Application of Seismic Imaging Technique Based on VSPWhile Drilling in Fracture-cavity Carbonate Reservoir

Abstract

Several Ordovician carbonate fractured-cavity type oil and gas fields have been found in the Tarim Basin. With the continuous development and pro duction of the reservoirs, the small and medium sized fractured-cavity systems have becomethe maintargets. In the process of exploration and development, due to the influence of inaccuracy velocity, it is difficult to obtain satisfactory imaging results in seismic data processing, which often leads to the failure of drilling. The seismic imaging technique based on VSP while drilling is an important technical means to avoid drilling risk and improving the drilling success rate of fracture cavity carbonate reservoirs in the Tarim Basin. The core problem is how to use the VSP data while drilling to improve the accuracy of the surface seismic velocity model and further promote the accuracy of seismic data imaging and guide the adjustment of drilling trajectories. Therefore, the correction method for the well driven seismic velocity model was proposed. Based on the traditional pre-stack depth migration imaging technology, this technology uses VSP logging velocity and drilling information while drilling for rapidly vertical high-precision velocity modeling near wellbores, interpolation and extrapolation of 3D spatial velocity models based on structural model constraints, as well as global grid tomographic velocity optimization and migration imaging, which can rapidly modify the 3D seismic velocity model and effectively improve the spatial imaging and location accuracy of the fracture and cave body, and optimize the drilling trajectory in time, finally improve the drilling success rate. After practical application of the technology in fracture-cavity carbonate rocks in the Tarim Basin, the update and iteration time of the velocity model greatly shortened and can meet the accuracy and timeliness requirements of VSP While Drilling processing. As a result, the drilling success rate has been greatly improved.