Pemodelan Log Teoritis Berbasis Litologi Untuk Karakterisasi Formasi Di Lapangan Poseidon, Cekungan Browse, Australia

Nur Akhiralimi, Dr.rer.nat. Wiwit Suryanto, S.Si.,M.Si.

2026 | Tesis | S2 Ilmu Fisika

Interpretasi log sumur di wilayah hidrokarbon laut dalam, seperti Cekungan Browse di Australia, menghadapi tantangan besar akibat heterogenitas litologi yang kompleks, terutama pada reservoir Formasi Plover yang terbentuk dalam sistem deltaik hingga laut dangkal. Penelitian ini mengembangkan model log teoritis berbasis litologi untuk lima jenis log sumur: gamma ray (GR), densitas, neutron, sonik, dan resistivitas yang diterapkan pada empat sumur di Lapangan Poseidon (Boreas-1, Kronos-1, Poseidon-1, dan Poseidon-2) menggunakan pendekatan forward modeling deterministik satu dimensi. Pendekatan ini menghubungkan komposisi litologi dengan parameter petrofisika menggunakan persamaan fisika batuan klasik, meliputi pencampuran volumetrik linier, persamaan densitas massa, persamaan sonik Wyllie, dan persamaan resistivitas Archie. Hasil analisis perbandingan log teoritis dan log observasi serta validasi kuantitatif menggunakan RMSE, R², MAE, dan MBE, menunjukkan bahwa model mampu merepresentasikan tren dan pola makro dalam log observasi di semua sumur dengan deviasi yang dapat dipertanggungjawabkan secara ilmiah, dengan RMSE densitas berkisar 0,09–0,30 g/cc dan RMSE sonik 11,23–16,54 microsecond/ft. Deviasi yang teridentifikasi dimanfaatkan sebagai informasi diagnostik; anomali resistivitas positif pada Formasi Plover mengkonfirmasi keberadaan gas, sementara MBE GR yang positif mencerminkan perbedaan mineralogi lempung aktual dengan asumsi model. Model ini menunjukkan potensi untuk mengatasi dua tantangan utama interpretasi log sumur, yaitu keterbatasan data inti pada interval tertentu dan ambiguitas akibat tumpang tindih respons log antar litologi, sekaligus memberikan implikasi signifikan terhadap penentuan litologi dominan, identifikasi zona reservoir, dan penilaian kualitas batuan reservoir Lapangan Poseidon, Cekungan Browse.

The well log interpretation in deepwater hydrocarbon regions, such as the Browse Basin in Australia, faces major challenges due to complex lithological heterogeneity, particularly in the Plover Formation reservoirs formed in deltaic to shallow marine systems. This study develops lithology-based theoretical log models for five well log types: gamma ray (GR), density, neutron, sonic, and resistivity, applied to four wells in the Poseidon Field (Boreas-1, Kronos-1, Poseidon-1, and Poseidon-2) using a one-dimensional deterministic forward modeling approach. This approach relates lithological composition to petrophysical parameters using classical rock physics equations, including linear volumetric mixing, the mass density equation, the Wyllie sonic equation, and the Archie resistivity equation. The results of the comparative analysis of theoretical and observational logs, as well as quantitative validation using RMSE, R², MAE, and MBE, indicate that the model is able to represent macro trends and patterns in observation logs in all wells with scientifically accountable deviations, with density RMSE ranging from 0,09 to 0,30 g/cc and sonic RMSE ranging from 11,23 to 16,54 microsecond/ft. The identified deviations are used as diagnostic information; positive resistivity anomalies in the Plover Formation confirm the presence of gas, while positive GR MBE reflects differences between the actual clay mineralogy and model assumptions. This model has shown potential to address two main challenges in well log interpretation, namely the limited core data at certain intervals and ambiguity due to overlapping log responses between lithologies, while providing significant implications for determining the dominant lithology, identifying reservoir zones, and assessing the quality of reservoir rocks in the Poseidon Field, Browse Basin.

Kata Kunci : Cekungan Browse, Forward Modeling, Karakterisasi Formasi, Log Sumur, Model Log Teoritis Berbasis Litologi