Pemodelan 3D Lingkungan Pengendapan Interval 'MAX', Formasi Sepinggan, Lapangan 'Upside Down', Cekungan Kutai, Kalimantan Timur

Clearesta Dian Maria Banurea, Ir. Jarot Setyowiyoto, M.Sc., Ph.D. IPU., ASEAN.Eng.; Prof. Dr. Ir. Sugeng Sapto Surjono, S.T., M.T., IPU., ASEAN.Eng.

2026 | Skripsi | TEKNIK GEOLOGI

Formasi Sepinggan pada Lapangan ‘Upside Down’, Cekungan Kutai, Kalimantan Timur, merupakan satuan pembawa reservoir batupasir yang diendapkan pada sistem delta. Sebaran dan geometri fasies pada interval ‘MAX’ belum tergambar secara menyeluruh, sehingga menimbulkan ketidakpastian dalam interpretasi reservoir. Penelitian ini bertujuan menentukan lingkungan pengendapan interval ‘MAX’ serta membangun model tiga dimensi sebaran fasiesnya. Penelitian dilakukan melalui integrasi data bawah permukaan pada 22 sumur, meliputi log sumur, laporan mudlog dan sidewall core sebagai pembanding, lalu dikelompokkan menjadi asosiasi fasies berdasarkan pola elektrofasies dan kedudukan stratigrafinya. Kerangka sekuen stratigrafi non-marin disusun dan dikorelasikan melalui empat penampang. Pemodelan tiga dimensi dilakukan dengan metode object-based modeling pada grid 25 × 25 meter lalu divalidasi melalui uji validasi. Penelitian mengidentifikasi empat fasies litologi (batupasir, batulempung, serpih dan batubara) yang dikelompokkan menjadi empat asosiasi fasies, yaitu distributary channel, crevasse splay, interdistributary bay, dan floodplain. Kerangka sekuen terbagi menjadi dua low-accommodation system tract dan dua high-accommodation system tract yang dibatasi dua subaerial unconformity dan dua maximum rate of accommodation. Model memperlihatkan channel meluas dan saling berhubungan, dengan akurasi uji sumur buta 74,5?n nilai Cohen’s Kappa 0,491 yang tergolong moderate. Interval ‘MAX’ terendapkan pada lingkungan delta plain yang berubah dari upper delta plain di bagian bawah menjadi lower delta plain ke arah atas, dengan sebaran fasies dikendalikan kerangka sekuen stratigrafi non-marin. Model ini dapat menjadi dasar penafsiran arsitektur dan konektivitas fasies pada interval ‘MAX’.

The Sepinggan Formation in the 'Upside Down' Field, Kutai Basin, East Kalimantan, is a sandstone reservoir-bearing unit deposited within a deltaic system. The facies distribution and geometry of the 'MAX' interval remain poorly constrained, causing uncertainty in reservoir interpretation. This study aims to determine the depositional environment of the 'MAX' interval and to construct a three-dimensional model of its facies distribution. The study integrated subsurface data from 22 wells, comprising wireline logs and mudlog reports, with sidewall core as a comparison. Lithofacies were determined and subsequently grouped into facies associations based on electrofacies patterns and stratigraphic position. A non-marine sequence stratigraphic framework was established and correlated across four cross sections. Three-dimensional modelling was performed using the object-based modelling method on a 25 × 25 metre grid, then validated through blind well testing. Seven lithofacies were identified and grouped into four facies associations, namely distributary channel, crevasse splay, interdistributary bay, and floodplain. The framework comprises two low-accommodation systems tracts and two high-accommodation systems tracts, bounded by two subaerial unconformities and two maximum rate of accommodation surfaces. The model shows channel bodies that are widespread and interconnected. The 'MAX' interval was deposited in a delta plain environment, shifting from upper delta plain in the lower part to lower delta plain upward, with facies distribution governed by the non-marine sequence stratigraphic framework. The model provides a basis for interpreting facies architecture and connectivity within the 'MAX' interval.

Kata Kunci : Formasi Sepinggan, delta plain, asosiasi fasies, sekuen stratigrafi non-marin, object-based modeling.