Role of the 3D Seismic Technique in Improving Oilfield Economics

Abstract

Summary As the various disciplines interacting in our industry begin to recognize the need for an integrated approach, the three-dimensional (3D) seismic method has emerged to help reduce the uncertainty inherent in finding and recovering new reserves. The 3D method improves the accuracy of the subsurface information obtained from surface-recorded measurements over conventional seismic techniques by comprehending the spatial or 3D nature of the problem to be solved. The increased detail and accuracy obtained from the technique allow better definition and delineation of the structural (or stratigraphic) trap; hence, reservoir management can proceed with less uncertainty, enhancing the value of in-situ reserves. The most promising role for 3D techniques lies in the area of reservoir description. The 3D seismic method is uniquely capable of providing spatially continuous estimates of rock parameters. When it is providing spatially continuous estimates of rock parameters. When it is integrated with available well and core data, areal distribution of net pay, porosity, or hydrocarbon content across the reservoir can be derived pay, porosity, or hydrocarbon content across the reservoir can be derived and add significantly to the quality of information provided by the integrated database input to the reservoir simulation process. Fewer dry holes, better well placement, earlier production, and greater total hydrocarbons recovered are the result. Thus the 3D seismic method offers positive leverage on the net present value of the field. Introduction Any business venture can be conceptualized by the following graphic: The goal is to influence positively the relationship between the three variables to improve cash flow and, hence, the net present value (NPV) of the project. In our industry, this equates to reducing the number of dry holes or inefficiently located wells, obtaining optimum production from each well through effective well placement and reservoir management, and bringing placement and reservoir management, and bringing production on-stream as early as possible. production on-stream as early as possible. As the industry extends its search to more complex geologic environments and looks for smaller plays, the critical need to maintain or improve its cost-effectiveness remains, and the application of new techniques to support this objective must be a constant consideration. Figs. 1 and 2 provide an analysis of producing and dry-hole footage drilled in the U.S. over the last 30 years by industry phase. While it is expected that most of the producing footage has been drilled in the development producing footage has been drilled in the development phase, it is not intuitively obvious that in absolute footage, phase, it is not intuitively obvious that in absolute footage, more dry-hole footage is also drilled in this phase, and this suggests the opportunity to increase profits by reducing this unproductive expenditure. While approximately 80% of development wells are productive, individual well efficiency remains an area for productive, individual well efficiency remains an area for improvement. With sparse information, the placement of wells to optimize individual well productivity (within the context of total reservoir management) must be considered to have ample scope for improvements in efficiency. Improvements in both the quantity and the quality of information can only reduce uncertainty and enhance the decision-making process. The dual goals of improved success ratios and increased well productivity are keys to enhancing the value of insitu reserves. A breakdown of expenditure by major cost classification in the exploration and the development/production phase indicates that geology and geophysics account for phase indicates that geology and geophysics account for approximately 12% of exploration expenditure, much of it associated with conventional reflection seismic surveys. It is in this prediscovery phase that seismic methods have historically been used. Insignificant expenditure for geology and geophysics is associated with development and production. New technologies, however, such as vertical seismic profiling, seismic inversion, and 3D seismic techniques, have begun to play an emerging role in this environment, and 3D has proved its utility with more than 200 onshore and 300 proved its utility with more than 200 onshore and 300 offshore surveys, improving the cost-effectiveness of the development phase. The 3D seismic method particularly can play a central role because of its ability to provide high-resolution, continuous information of not only reservoir geometry, but also inferences on reservoir rock characteristics and variations in those characteristics across the reservoir. In addition, these seismic methods have progressed significantly in their ability to communicate information in terms familiar to the petroleum engineer. JPT P. 777