Nested approaches to modelling swamp and fluvial channel distribution in the Upper Juandah Member of the Walloon Coal Measures, Surat Basin

Laterally discontinuous coal measures are common in alluvial settings due to interaction with fluvial systems. Under these conditions it is difficult to accurately represent coalbeds and interburden sandstone bodies in static and dynamic models at a regional scale. These challenges are compounded in the Walloon Coal Measures by non-uniform drill spacing, which varies from clustered to sparse and insufficient outcrop exposures available to constrain the correlations. To address these issues, this study investigates a nested approach to facies modelling of the Upper Juandah Member of the Jurassic Walloon Coal Measures in the Surat Basin, Queensland, which contains some 3,600 wells, of which half were analysed for lithofacies distributions. This approach contrasts the application of truncated Gaussian simulation, object modelling and multiple-point geostatistical simulation. First, a regional scale structural model was developed based on the correlation of sub units within the basin and the lithofacies were then interpreted from normalised wireline logs. Then geometries of individual facies were defined from two local scale models (~6 × 6 km2) where dense drilling, 3D seismic and paleocurrent analysis data were available to constrain the models. Three training images, generated by object modelling, an analogue of one part of the Ob River, and an interactive method were subsequently used to model primary channels, channels and crevasse splays, respectively. Truncated Gaussian simulation was used in modelling the distribution of marginal and coal swamp. The final model is a combination of the model with primary channels and channels, and the model with marginal and coal swamp. This approach is the first trial in modelling swamp and channel distributions at a regional scale by integrating data from local models, depositional analogues and paleo-flow interpretation in the Surat Basin.

PREDIKSI DISTRIBUSI SAND MENGGUNAKAN PEMODELAN GEOSTATISTIK

Gambaran distribusi fasies dan heterogenitas geologi yang representatif sangat diperlukan dalam pengelolaan aktivitas eksplorasi dan eksploitasi migas di bawah permukaan. Telah dilakukan pemodelan distribusi sand pada formasi Missisauga, lapangan Penobscot dengan menggunakan tiga algoritma berbasis grid yaitu Sequential Indicator Simulation (SIS) dan Truncated Gaussian Simulation (TGS) dan Multipoint Geostatistic (MPG). SIS dan TGS yang merupakan algoritma yang berbasis variogram, mampu menghasilkan model yang merepresentasikan korelasi spasial antar sumur dengan cukup baik namun belum secara optimal menangkap geometri fasies akibat sifat dari variogram yang hanya bisa memodelkan kontinuitas spasial antara dua lokasi pada satu waktu. TGS lebih unggul dibandingkan SIS pada aspek keterhubungan lateral dari sand channel dan distribusi fasies terlihat lebih well-ordered (sand-shalysand-shale).. MPG yang merupakan metode yang didasarkan pada data singkapan menawarkan korelasi lateral yang lebih baik.

Application of Truncated Gaussian Simulation Algorithm in Alluvial Fan Reservoir Architecture Modeling

This article counted the distribution regularity and the spread pattern of each tertiary architecture through detailed study of alluvial fan reservoir architecture of the sealing core drilling well in the Karamay group which under the sixth middle area of Karamay oilfield. The tertiary architecture of middle-fan subfacies are: braided channel, sheetfloot microfacies and gritfloot microfacies. Truncated Gaussian simulation algorithm can be used to simulate the middle-fan subfacies of alluvial fan for they have an obvious zone law. Described the distribution regularity and spread pattern of middle-fan subfacies architecture effectively. Figured out the contact relationship among different architectural units preferably. It has a certain reference for other oilfields with the same type reservoir of architecture modeling.