Interpretation of fractures and joint inversion using multicomponent seismic data — Marcellus Shale example

Evaluating and exploiting unconventional complex oil and gas reservoirs such as the Marcellus Shale gas reservoirs within the Appalachian Basin in Pennsylvania, USA, have gained considerable interest in recent years. Technologies such as conventional 3D seismic, horizontal drilling, and hydraulic fracturing have been at the forefront of the effort to exploit these resources. Recently, multicomponent seismic technologies have been integrated into some resource evaluation and reservoir characterization activities of low-permeability rock systems. We evaluated how multicomponent seismic technology provides value to reservoir characterization in shale gas exploration. We improved fault interpretations and natural fracture identifications by means of P-SV1 and P-SV2 integrated interpretation. In addition, using P-P-/P-SV-joint inversion, we extracted key parameters, such as VP∕VS ratio and density, that improve stratigraphic interpretation and rock-property descriptions of shale gas reservoirs. Introduction The Devonian Marcellus Shale is a natural-gasbearing rock distributed across parts of Pennsylvania, Ohio, West Virginia, and New York. This shale was deposited in a shallow sea that covered these states nearly 400 million years ago. Some of the organic material trapped in the Marcellus matured (changed chemically with heat and pressure) into natural gas. Natural gas now present in the low-porosity Marcellus Shale remains mostly trapped between grains and in natural fractures already present in the shale (Enomoto et al., 2011). The Marcellus Shale is positioned at the base of the Hamilton Group and is divided into three major members, consisting of two organically rich members separated by the Cherry Valley limestone. The Lower Marcellus member sits on a sequence boundary/transgressive surface of erosion, thought to be a third-order depositional sequence composed of a lower, upward-increasing gamma-ray transgressive systems tract (TST) and an upper, upward-decreasing gamma-ray regressive systems tract (RST). A maximum flooding surface constitutes the highest gamma-ray shale (Figure 1). The Upper Marcellus Member comprises another third-order sequence consisting of a basal regressive surface of erosion, a relatively thin, mainly limestone TST, and a thicker RST (Lash and Engelder, 2011; Slatt and Rodriquez, 2012). Total organic carbon (TOC) values range up to approximately 10% wt. in the well used in Figure 1, but some wells in the area can have TOC values as high as 20% wt. (Bowker and Grace, 2010). Previous investigators (Freeman, 2010; Koesoemadinata et al., 2011) use conventional P-wave (P-P) technology to investigate the Marcellus Shale. Although P-P data can be useful in subsurface structural analysis, there has been little progress in using P-P data for reservoir fracture prediction. Joint interpretation of P-P and P-SV data has more advantages in analyzing subsurface structures, lithology distributions, and pore-fluid saturates than do interpretations solely based on P-P data (Stewart, 2010; DeAngelo and Hardage, 2013). In particular, P-SV data are more sensitive than P-P data to rock defects that are 2D in nature. A P-P/P-SV joint inversion technique can simultaneously use wireline log, seismic, and geologic data to extract key rock parameters, such as Poisson’s ratio, P-P to P-SV velocity ratio, and density, and thus provide more detailed and constrained interpretation of fractured shale-gas reservoirs. Robust matching of P-P and P-SV reflection events is required to build a viable initial inversion model based on P-P and P-SV data (Yue et al., 2010). China University of Geosciences, School of Energy Resources, Beijing, China and Sinopec International Petroleum Exploration and Production Corporation, Beijing, China. E-mail: [email protected]. The University of Texas at Austin, Bureau of Economic Geology, Austin, Texas, USA. E-mail: [email protected]; bob.hardage@ beg.utexas.edu. Manuscript received by the Editor 27 September 2013; revised manuscript received 27 January 2014; published online 22 April 2014. This paper appears in Interpretation, Vol. 2, No. 2 (May 2014); p. SE55–SE62, 10 FIGS. http://dx.doi.org/10.1190/INT-2013-0146.1. © 2014 Society of Exploration Geophysicists and American Association of Petroleum Geologists. All rights reserved. t Special section: Multicomponent seismic interpretation Interpretation / May 2014 SE55 D ow nl oa de d 04 /2 5/ 14 to 1 29 .1 16 .2 32 .2 33 . R ed is tr ib ut io n su bj ec t t o SE G li ce ns e or c op yr ig ht ; s ee T er m s of U se a t h ttp :// lib ra ry .s eg .o rg /