Pemodelan Fasies 3 Dimensi Batupasir 'X', Formasi Banuwati, Lapangan 'FRD', Blok Southeast Sumatera (SES), Cekungan Sunda

Muhamad Rival Ferdiansah, Ir. Rahmadi Hidayat, S.T., M.Eng., Ph.D., IPP; Ir. Jarot Setyowiyoto, M.Sc., Ph.D., IPU., ASEAN Eng.

2026 | Skripsi | TEKNIK GEOLOGI

Cekungan Sunda merupakan salah satu cekungan sedimen Tersier penghasil hidrokarbon di Indonesia yang telah berproduksi sejak tahun 1969. Produksi hidrokarbon di cekungan ini terus mengalami tren penurunan sehingga diperlukan eksplorasi dan pengembangan lebih lanjut. Formasi Banuwati merupakan sedimen pengisi awal Cekungan Sunda dan belum banyak dieksplorasi karena dikenal sebagai batuan induk di cekungan ini, padahal batupasir formasi ini menunjukkan keberadaan hidrokarbon berdasarkan data mud log dan batuan inti di Lapangan ‘FRD’. Akan tetapi, persebaran dari batupasir formasi ini belum banyak diketahui. Penelitian ini bertujuan untuk mengetahui fasies dan lingkungan pengendapan dari Formasi Banuwati serta mengetahui persebaran Batupasir ‘X’ dengan membangun model fasies 3 dimensi. Data yang digunakan adalah data batuan inti, log sumur, mud log, dan peta struktur kedalaman. Metode yang digunakan dalam membangun model fasies 3 dimensi adalah object modeling dalam bentuk fluvial channel. Berdasarkan analisis data batuan inti dan log sumur, didapatkan 9 litofasies mulai dari konglomerat–batupasir, batulempung, dan batubara. Asosiasi fasies di Formasi Banuwati dibagi menjadi channel, abandonment channel, dan floodplain di lingkungan sungai teranyam serta asosiasi fasies shallow lake dan deep lake di lingkungan lakustrin. Formasi Banuwati terdiri dari 12 parasikuen dan 2 system tract, yaitu lowstand system tract (LST) dan transgressive system tract (TST) yang mengalami proses transgresi dari lingkungan sungai teranyam menjadi lingkungan lakustrin. Interval Batupasir ‘X’ berada di marker FS1–FS2 yang memiliki lingkungan sungai teranyam. Parameter channel dalam membangun model fasies 3 dimensi object modeling didapatkan dari data sumur, peta gross depositional environment, dan analog sungai modern. Berdasarkan pemodelan fasies 3 dimensi, terdapat 2 fasies yaitu sand yang mewakili channel dan shale yang mewakili floodplain dan abandoonment channel. Model fasies 3 dimensi yang telah dibuat dilakukan validasi dengan membandingkan antara korelasi sumur dengan intersection model. Persebaran fasies berdasarkan model 3 dimensi adalah sebagai berikut, fasies sand atau channel menebal di utara daerah penelitian dengan orientasi barat–timur, sedangkan persebaran fasies shale yang mewakili floodplain berada di tengah dan selatan daerah penelitian atau berada di sekitar dari fasies sand atau channel. Persebaran shale abandonment channel berada di dalam sela-sela fasies channel akibat proses abandonment active channel sebelumnya.

The Sunda Basin is one of the Tertiary sedimentary basins in Indonesia that has produced hydrocarbons since 1969. However, hydrocarbon production in this basin has shown a declining trend over the years, indicating the need for further exploration and development. The Banuwati Formation represents the initial syn-rift sediment fill of the Sunda Basin and has not been extensively explored because it is commonly known as the main source rock of the basin. Nevertheless, sandstone intervals within this formation have shown hydrocarbon indications based on mud log and core data obtained from the ‘FRD’ Field. The spatial distribution of these sandstones, however, remains poorly understood. This study aims to analyze the facies and depositional environment of the Banuwati Formation and to determine the distribution of the ‘X’ Sandstone interval through the construction of a 3-dimensional facies model. The data used include core data, well log data, mud log data, and structural depth maps. The 3-dimensional facies model was constructed using the object modeling method in the form of fluvial channels. Based on the analysis of core and well log data, 9 lithofacies were identified, ranging from conglomerate–sandstone, claystone, to coal. Facies associations within the Banuwati Formation are divided into channel, abandonment channel, and floodplain within a braided river system, as well as shallow lake and deep lake facies within a lacustrine environment. The Banuwati Formation consists of 12 parasequences and 2 system tracts, namely the lowstand system tract (LST) and transgressive system tract (TST), indicating a transgressive process from braided river to lacustrine deposition. The ‘X’ Sandstone interval is located within the FS1–FS2 marker, representing a braided river environment. Channel parameters for the 3-dimensional facies object modeling were derived from well data, gross depositional environment maps, and modern river analogs. The 3-dimensional facies model consists of two facies, sand representing the channel and shale representing the floodplain. The 3-dimensional facies model that has been created was validated by comparing well correlations with the intersection model. The distribution of facies based on the 3-dimensional model is as follows sand or channel facies thicken in the north of the study area with a west-east orientation, while the distribution of shale facies representing floodplains is in the center and south of the study area or around sand facies. The distribution of abandonment channel shale is between channel facies due to the abandonment process of the previous active channel.

Kata Kunci : Cekungan Sunda, Formasi Banuwati, pemodelan fasies 3 dimensi, batupasir, sungai teranyam