A New Era In Land Seismic: The Near Surface Challenge

Summary

A new era in land seismic is at hand. Growing energy demand will spur greater efforts in exploration and development into regions of the world where hydrocarbons occur in land environments. Interpreters will require accurate near surface solutions for mapping low-relief structures and stratigraphic traps, and to improve data quality for placing horizontal wells. This will require solutions to the near surface challenges, such as energy penetration, scattering, source generated noise, surface generated multiples, statics, and source and receiver coupling. Solutions to these problems will become possible due to advances in seismic acquisition, including simultaneous source acquisition and wireless seismic driven ultra-high channel systems. Advances in seismic processing technology for processing the resulting huge data volumes will be made possible by continual growth in computational capability. These advances will for the first time allow acquisition of true 3D seismic data. This will not only result in better imaging of the subsurface, but will allow the near surface to be addressed as an imaging problem with better description of velocities and suppression of surface related noise.

Introduction

We start by stating the obvious – the difference between land and marine data is the near surface. The near surface dictates how data acquisition differs between land and marine environments, and it is the cause of lower data quality on land. Energy penetration, scattering, source generated noise, surface generated multiples, statics, and source and receiver coupling are some of the long standing near surface issues that continue to present challenges for land seismic imaging. In arid environments, the near surface can be up to 2,000 ft thick with sand dunes and topography.

In the recent past, the seismic technology focus has been on the marine environment, particularly deep water. However, we are about to enter a new, exciting era in land seismic due to four key trends: 1) world growth in energy demand, 2) exploration and development focus on low-relief structures, stratigraphic traps, and horizontal well placement, 3) advances in seismic acquisition technology, and 4) advances in seismic processing due to continually expanding computer capability.

The history of technology development in our industry is a history of developing approximate solutions. To this day, we still do not collect true 3D seismic data. For example, 3D surveys are typically not full azimuth and field arrays are used to attenuate noise, which otherwise would be recorded aliased. Most everything we work on as technology developers is some type of approximate solution primarily due to limitations in acquisition and secondarily due to limitations in processing. The biggest advances in our industry have come in acquisition, from refraction to reflection, to high fold, to 3D. These acquisition advances allowed developments in processing, such as CDP stack and migration. Perhaps the best example of an excellent technology development that is an approximation is DMO. The knowledge of how to implement pre-stack migration existed prior to the development of DMO. But due to limitations in processing capability, DMO was an excellent temporary, approximate solution.