TrueDepth prestack depth migration: an essential tool for mitigating drilling risk

The utilisation of non-seismic data in the structural imaging arena has been shifting its importance from an afterthought to an essentially a priori ingredient. The necessity to image complex subsurface structures that are at the right depth, at the correct geographical loca¬tion and with the correct geometry and topology has become paramount for a successful business model that combines drilling, geosteering, completion, fracking and re-fracking, as well as production and EOR efforts. This article can be thought of as an update and continu¬ation on our 2013 First Break publication (Stein et al., 2013) that introduced the concept of TrueDepth. Here we will describe the new developments in the technology suite, primarily spawned by our experiences processing many surveys around the world that pointed to some shortcomings in the original ideas and implementation. Particularly important has been the development of a new workflow that increases the efficiency and robustness of the techniques. The new workflow incorporates several new pieces of technology making the resulting images more accu¬rate. The new technologies include a global delta anisotropy tool, a tomography capable of inverting for velocity and anisotropy, and 3D QC visualisation techniques. We will finish the article by demonstrating the value of the new workflow and technologies by applying them to a real case history. It has become increasingly obvious that an accurate depth prediction, as well as a very detailed description of the geomet¬ric and topological nature of the reservoirs, is paramount for a cost-effective exploration and production effort. It has always been accepted that the incorporation of non-seismic data into the imaging effort is essential to the outcome. The shift in this mindset that has occurred in the last few years is that such data is not only valuable as a calibration or QC tool, but that it can, and we would argue it must, be part of the input data and combined with the seismic in our algorithms to produce exceptionally accurate results. This philosophy is at the core of the TrueDepth methodology; the use of a priori information in the imaging process. For a detailed description of the geophysical and math¬ematical basis of TrueDepth as well as some earlier examples, we will refer the reader to our earlier publications (Stein et al., 2013; Stein, 2014; Hellman et al., 2015; Baptiste et al., 2015).