Analisis Fasies dan Interpretasi Lingkungan Pengendapan pada Interval FS ‘1’ – FS ‘6’, Blok ASIS, Cekungan Kutai, Kalimantan Timur

Salma Elcanza Asfuri, Ir. Rahmadi Hidayat, S.T., M.Eng. Ph.D., IPP ; Anwar Sadat, S.T., M. Si.

2026 | Skripsi | TEKNIK GEOLOGI

Interval FS1–FS6 di Blok “Asis”, Cekungan Kutai, merupakan interval pengendapan delta yang menunjukkan variasi fasies secara vertikal dan lateral. Heterogenitas fasies pada sistem delta menyebabkan karakteristik dan distribusi fasies sulit diinterpretasikan hanya berdasarkan log sumur konvensional. Penelitian ini bertujuan mengidentifikasi karakteristik dan distribusi asosiasi fasies serta menginterpretasikan evolusi sistem pengendapan melalui integrasi log sumur konvensional, batuan inti, dan log citra pada tiga sumur, yaitu SEA, LST, dan ASF. Metode penelitian meliputi analisis elektrofasies, interpretasi log citra, identifikasi litofasies, analisis biostratigrafi, korelasi antar-sumur, dan analisis sequence stratigraphy. Integrasi data digunakan untuk mengidentifikasi karakteristik asosiasi fasies, menganalisis distribusi fasies, serta merekonstruksi evolusi sistem pengendapan. Hasil penelitian mengidentifikasi sembilan litofasies yang dikelompokkan menjadi tiga asosiasi fasies, yaitu Lower Intertidal, Subtidal, dan Middle Intertidal. Asosiasi fasies tersebut menunjukkan perkembangan sistem tide-influenced delta dengan lingkungan pengendapan yang mencakup Delta Front hingga Lower Delta Plain. Analisis sequence stratigraphy mengidentifikasi Flooding Surface (FS) sebagai batas antarparasekuen, sedangkan Transgressive Surface (TS) dan Maximum Flooding Surface (MFS) digunakan sebagai key surface. MFS menjadi batas antara Transgressive Systems Tract (TST) dan Highstand Systems Tract (HST). Evolusi sistem pengendapan menunjukkan perubahan dari fase transgresif menuju fase highstand. Interval FS1–MFS menunjukkan retrogradational stacking yang ditandai deepening upward dan perkembangan lingkungan menuju kondisi yang lebih dalam hingga mencapai maximum flooding pada MFS. Setelah MFS, interval MFS–FS6 menunjukkan progradational stacking yang ditandai shallowing upward dan perkembangan lingkungan menuju kondisi yang lebih dangkal, terutama Lower Delta Plain. Dengan demikian, evolusi sistem pengendapan merepresentasikan perubahan dari fase transgresi menuju fase progradasi dalam sistem tide-influenced delta.

The FS1–FS6 interval in the “Asis” Block, Kutai Basin, represents a deltaic depositional interval characterized by vertical and lateral facies variations. Facies heterogeneity within the deltaic system makes facies characteristics and distribution difficult to interpret using conventional well logs alone. This study aims to identify the characteristics and distribution of facies associations and interpret the evolution of the depositional system through the integration of conventional well logs, core data, and image logs from three wells: SEA, LST, and ASF. The methods include electrofacies analysis, image-log interpretation, lithofacies identification, biostratigraphic analysis, well-to-well correlation, and sequence stratigraphic analysis. The integrated data were used to identify facies-association characteristics, analyze vertical and lateral facies distribution, and reconstruct the evolution of the depositional system. The results identified nine lithofacies grouped into three facies associations: Lower Intertidal, Subtidal, and Middle Intertidal. These facies associations indicate development within a tide-influenced delta system, with depositional environments ranging from Delta Front to Lower Delta Plain. Sequence stratigraphic analysis identified Flooding Surfaces (FS) as parasequence boundaries, while the Transgressive Surface (TS) and Maximum Flooding Surface (MFS) were used as key surfaces. The MFS separates the Transgressive Systems Tract (TST) from the Highstand Systems Tract (HST). The depositional evolution records a transition from a transgressive to a highstand phase. The FS1–MFS interval exhibits retrogradational stacking, characterized by deepening upward and progressive development toward relatively deeper environments, reaching maximum flooding at the MFS. Following the MFS, the MFS–FS6 interval exhibits progradational stacking, characterized by shallowing upward and development toward shallower environments, particularly the Lower Delta Plain. Overall, the depositional evolution represents a transition from transgression to progradation within a tide-influenced delta system. 

Kata Kunci : borehole image log, tide dominated delta, sequence stratigraphy, depositional system evolution, Kutai Basin.