Application of Seismic Attributes in Estimating Gas Resources in Complex Fluvial Channel Reservoirs

Abstract

The purpose of this paper is to show the reserve estimation procedures used by KUFPEC on the NW Shelf of Australia production license WA-49-L, which is currently under development as part of the Chevron's Wheatstone LNG project. The gas in the WA-49-L permit was discovered in a combination of structural and stratigraphic traps of a regional fluvial channel sand complex within the Triassic Mungaroo Formation. These channel sands contain gas trapped on a large structural ridge with up-dip terminations below a regional, angular unconformity and overlain by the Cretaceous Muderong Shale. Some of the deeper channel sands are trapped against the bounding fault of the ridge. These channel sands are stacked as a result of amalgamation of numerous channels, with the individual sand thickness of up to 60 meters but typically in the 15 to 30 meters range. These channel sands are discrete with individual gas-water-contacts, and clearly visible on seismic and inversion data as low impedance, Class 3 AVO (amplitude versus offset) anomalies.The estimation of gas resources is delineated by 20 wells drilled through April 2011 on WA-49-L. Limitations of the seismic frequency content result in channel thicknesses of less than 5 meters not being visible. Seismic inversion attributes are used to estimate gas sand probability, sand thickness and porosity. Rather than using large scale net-to-gross assumptions commonly used in the industry for reserves calculations, KUFPEC used maps of individual sand bodies based on the inversion impedance amplitudes and gas sand probability (GSP) attributes to compute each sands' likely range of resources values.

Turbidite Dynamics and Hydrocarbon Reservoir Formation in the Tano Basin: A Coastal West African Perspective

“…Gamma ray logs have also been used to identify and characterize sand bodies in the EMK field within the Niger Delta region, while seismic reflection data has been used to investigate subsurface fluid flow features and their correlation with hydrocarbon systems in Egypt's Alamein basin [15] [16] [17] [18]. Other studies have focused on characterizing reservoirs in different regions, including fluvial reservoirs in the Laohekou Oilfield, China, fluvial channel systems and gas sand reservoirs in Australia's Carnarvon Basin, and submarine channels and valleys in the eastern Mediterranean Sea [19] [20] [21]. These studies highlight the importance of understanding sedimentation mechanisms and geological structure in deep-water environments, as well as the significance of various tools and data for reservoir characterization and exploration.…”

Using recursive inversion as input for gross-rock volume extraction from lithology prediction volumes: How bad can it be?

“…Many of the gas bearing reservoirs have associated class three AVO anomalies conformable with structure, resulting in "bright spot" and occasional flatspot DHIs. AVO seismic inversion and lithology prediction is commonly used to define both reservoir channel fairways and de-risking exploration (Lamont et al, 2008;Tilbury et al, 2009;Al-Duaij et al, 2013). It has been shown that lithology prediction seismic cubes can be used to directly estimate the sand volume within a stratigraphic interval of the Mungaroo Formation by calculating geobodies with a certain prediction threshold (Shadlow et al, 2018).…”

Quantitative Interpretation: Use of Seismic Inversion Data to Directly Estimate Hydrocarbon Reserves and Resources

“…The subjectivity is due to channel edges not always being readily identifiable, thin channel associated reservoir not always being recognised and intra-channel heterogeneities affecting the amplitude response. In addition, the predominant class 3 AVO effect exhibited by the Mungaroo reservoirs (Al-Duaij et al 2013) complicates the interpretation of channels near the fluid contacts. Seismic inversion data is commonly used in conjunction with reservoir static and dynamic modelling to help constrain reserve assessments, and has been effectively used both on the Julimar Brunello complex (Al-Duaij et al 2013) and on the Gorgon Field to the southwest (Van Der Weiden, Nayak, & Swinburn, 2012).…”

“…In addition, the predominant class 3 AVO effect exhibited by the Mungaroo reservoirs (Al-Duaij et al 2013) complicates the interpretation of channels near the fluid contacts. Seismic inversion data is commonly used in conjunction with reservoir static and dynamic modelling to help constrain reserve assessments, and has been effectively used both on the Julimar Brunello complex (Al-Duaij et al 2013) and on the Gorgon Field to the southwest (Van Der Weiden, Nayak, & Swinburn, 2012). In addition, there are several case studies in which inversion data has been used to de-risk exploration (Di Luca, et al, 2014), calculate net pay , or use stochastic inversion to assess sand connectivity in a simulation model (Moyen & Doyen, 2009).…”