Automatic, Geological Layer-Constrained Seismic-Well Tie Through Blocked Dynamic Warping
A blocked dynamic warping (BDW) method has been developed for an automatic, optimal seismic-well tie that honors geologically consistent velocity constraints. Well log to seismic tying is a key step in many interpretation workflows and builds a connection for these major types of data to identify the geological formation in the seismic data for oil and gas exploration. A typical workflow for a seismic-well tie first includes using well logs to generate a reflection series in the depth domain, which is then converted to time with a primitive time-depth curve. This time-domain reflection series is subsequently convolved with a wavelet to obtain a synthetic seismic trace. By matching the synthetic data with a real seismic along the well via time shifts, we can update the time-depth curve to determine which horizon to pick. In practice, both the time-depth curve and well logs can be blocked following geological boundaries given by lithology, fluid content or sedimentation, etc., and it is preferred that the blocking be retained while tying.
Automatic methods for matching are desirable, especially when the task involves tying for multiple well logs. Studies have emerged that explore the use of dynamic time warping (DTW) for automatic tying. However, none of the studies have taken geological layering into consideration. Additionally, while these algorithms are great at matching the character of the synthetic to the seismic, they tend to create interval velocities that are not geologically realistic.
Blocked dynamic warping also modifies DTW to effectively constrain the modeling integrity within geological layers. BDW is able to allow for a constant or linearly variable interval velocity inside each block—typically a geological layer. With an optimal correlation between synthetic seismograms and surface seismic, this algorithm returns not only an automatically updated time-depth curve, but an updated interval velocity model that still retains the original geological velocity boundaries. In other words, the algorithm finds the optimal solution for tying the synthetic to the seismic while restricting the interval velocity changes to coincide with the initial input blocking. This paper demonstrates the application of the BDW technique on a hand-crafted example, as well as to tying the well log and seismic in an actual field.
AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016