Early in my career, my colleagues in the exploration department had especially large tables, upon which they spread large seismic sections with many wiggles (which seemed to make sense to them but not me) so that they could identify potential exploration targets. This has changed over time, especially with the advent of 3D seismic.
In this month’s column, I wish to focus on the innovative ways that have emerged in exploration. That is where our journey starts, as we would not have a thriving oil and gas industry without the geoscientists who continuously find hydrocarbon accumulations that can be developed, produced, and brought to the market. The advent of huge computing capability and the availability of high-capacity telecommunications facilities make the early exploration processes sound as if they were of the Stone Age, particularly to today’s young geoscientist sitting behind large desktop screens viewing and manipulating data. I give the example of the application of 2D, 3D, and 4D seismic coupled with new acquisition and processing techniques to illustrate what innovation can do and has contributed to our industry.
Prior to the advent of seismic data, the search for hydrocarbons was based on observation of surface phenomena (outcrops, seeps, etc.). The use of seismic waves to define the subsurface emerged in the early 1900s following observation of waves that were created by earthquakes. Some innovative scientists saw the potential of how surface-induced waves could be used to better define the geology of the Earth and, through the data obtained, provide a better picture of the subsurface structure and the potential for hydrocarbon accumulation.
The first well to find oil through the use of seismic was drilled in Brazoria County, Texas, in 1924. Subsequently, thousands of prospects all over the world were identified and drilled based on this technology, which was innovative when first used (Seismic, 1999). The early explorationists were trained to “eyeball” potential accumulations by using their experience to evaluate seismic sections that were displayed as a 2D plane to generate maps that were used to drill exploration wells.
There are a number of elements in the planning of any seismic program: the specifications for and positioning of the source that will generate the sound waves; the equipment for recording the sound waves; the technology and workflow for processing the data; and the interpretation of the acquired data. While the early growth in hydrocarbon exploration benefited from 2D, the methodology had its limitations. The lines were set kilometres apart and acquired with single or multiple sources, and a single line of receivers could only display limited information, as each line was processed individually and independently. Clearly, these lines were relatively cheap to acquire and the turnaround of the data was relatively short. However, since the data produced a cross-section of the subsurface in two dimensions only, the success rates of early exploration wells were low and various innovators sought ways to improve the acquisition and interpretation of data. Improvements made in instrumentation, computing power, and data processing techniques greatly increased the resolution of seismic data and the quality of the subsurface images, and hence improved success rates of exploration wells. However, the technique still yielded little information about the physical properties of the reservoirs or the pore fluids that were trapped in them.
The application of 3D seismic was a significant development in our industry. The first survey was shot in 1967. Five years later, a collaborative survey was carried out on the Bell Lake field in southwestern New Mexico to evaluate how the results could be correlated with and matched to existing well data. The early results of 3D were a breath of fresh air to the industry. The grid spacing of 25 m (compared with 1 to 2 km for 2D) permitted a much denser collection of data, which allowed the interpretation of the data in cross-sections of varying orientation, including horizontal and oblique (CGGVeritas). Information on faulting and fracturing, bedding plane orientation, the presence of pore fluids, complex geologic structure, and detailed stratigraphy were made possible from 3D seismic data sets.
A number of parallel innovations further enhanced the application of 3D. Among these were the introduction of global positioning systems for positioning the seismic source and the exponential growth in processing capacity of computers. In recent years, advances in electronics, battery design, and wireless communications have provided yet another boost to the 3D seismic acquisition method. Large increases in the number of recording channels and wide-azimuth spreads have enabled development of depth imaging algorithms for complex structure and subsalt. These intensive workflows have enabled improved exploration and development success in challenging deep water, subsalt, and fold-and-thrust belts, and elsewhere. Cable-less seismic acquisition in rugged terrain and environmentally sensitive areas, nodal-based seafloor systems, and micro-seismic monitoring are other recent technologies that have broadly expanded the power of 3D seismic prospecting, both in conventional and unconventional re-source plays.
Advances in workstation and software capabilities have also resulted in visualization options that make it possible for interpreters to view and collaborate in ways only dreamed of previously, including the use of purpose-built rooms in which projection of 3D data onto all surfaces has ushered virtual reality into interpretation.
The advantages of 3D have been extended by the introduction of 4D, which consists of periods of time-spaced 3D seismic surveys acquired to reveal how reservoir and fluid properties have changed over time. This can enable identification of hydrocarbons that may have been bypassed and the positioning of additional wells for production or injection for greatly enhanced recovery. In addition, recent innovations include multi-azimuthal 3D seismic data acquisition and processing techniques. The result is more hi-fidelity subsurface data for the geoscientist to interpret. The placing of sensors on sea floors is a more recent technique that has further enhanced the quality of data obtained from offshore surveys (Maver, 2001).
All of this has allowed the full team of geoscientists, reservoir, and production engineers to work more closely than ever to ensure that industry extracts the maximum volumes from hydrocarbon accumulations.
The world needs more from what we have.
- CGGVeritas. http://www.cggveritas.com/default.aspx?cid=1&lang=1
- Maver, Kim Gunn. 2001. Ocean Bottom Seismic: Strategic Technology for the Oil Industry. EAGE Fast Break.http://www.rxt.com/getfile.php/Filer/dec11_st_maverr.pdf
- 1999. Seismic Technology: Evolution of a Vital Tool for Reservoir Engineers. JPT. http://www.spe.org/jpt/print/archives/1999/02/JPT1999_02_seismic_tech.pdf