Introduction to special section: Interpretation for unconventional resources

Abstract

Interpretation for unconventional resources introduces a broad range of issues and objectives that are markedly different from those encountered when interpreting for conventional plays. There are of course many commonalities. Structural interpretation is still a strong driver, particularly to assist in geosteering horizontal wells with long extended reach. Structural attributes can also aid the analysis of the stress field and can inform the interpretation of microseismic data.Beyond this, however, there's a greater prize to be pursued: characterization of the unconventional reservoir with a goal of optimizing field development. Given the size of reserves that are involved and the magnitude of the capital investment, enhancing the efficiency of reservoir development through early and ongoing reservoir characterization can result in enormous financial gains and economic returns.Industry is still at an early stage in understanding how the key characteristics of an unconventional reservoir are manifested in the seismic domain and how the relevant information can be extracted from a 3D seismic data set. Intuitively, the key variables that characterize an unconventional reservoir can be identified and listed: total organic content, hydrocarbon filled porosity, permeability, presence or absence of open fractures, formation brittleness, formation stress, fluid properties, and lateral heterogeneity of the reservoir.Seismic attribute analysis offers the promise of providing insight on these properties. This would have a major economic impact in evaluating unconventional plays in the exploration phase and in ranking areas to drill in the development phase. Many operators are testing this approach over their acreage, but the accuracy that's needed is high. These reservoirs have low porosity and permeability. A variation of just 1 p.u. (porosity unit) in many cases can mark the difference between an economic and uneconomic well. This is the level of accuracy we must seek in our seismic prognosis.This special section of Interpretation presents a set of papers that shows where we are in the pursuit of this goal. The first two papers outline interpretation workflows for unconventional resources. Rebec et al. discuss the use of seismic data to reduce risk and improve production in unconventional plays. This requires careful preplanning based on the nature of the play, acquiring the right seismic program, processing the seismic data correctly, extracting the optimum information and then transforming the information into business value. The authors discuss these criteria and focus on extracting the optimum information with examples from the Marcellus and Niobrara plays.Leiceaga et al. address how integration of prestack seismic, rock physics, horizontal drilling, and hydraulic fracture monitoring may be used to help evaluate hydrocarbon production capacity in unconventional plays such as tight or shale formations. The workflow presented in this paper demonstrates how several pieces of the geoscience puzzle may be fit together to ...