PEMODELAN GEOLOGI BAWAH PERMUKAAN FASIES BATUPASIR SOKANG FORMASI ARANG, CEKUNGAN NATUNA TIMUR

Widyo Permono, ST, Salahudin Husein, S.T., M.Sc., Ph.D.

2011 | Tesis | S2 Teknik Geologi

Daerah penelitian berada di bagian selatan Cekungan Natuna Timur yang merupakan salahsatu cekungan potensial penghasil hidrokarbon gas. Akan tetapi, aktivitas eksplorasi pada tipe reservoar batupasir belum berlangsung maksimal. Penelitian ini dilakukan guna mengetahui karakteristik fasies batupasir, konfigurasi, dan model geologi bawah permukaan fasies Batupasir Sokang pada bagian atas Formasi Arang. Pemodelan geologi bawah permukaan fasies Batupasir Sokang ini dilakukan dengan mengintegrasikan hasil analisis heterogenitas skala kecil yang memuat informasi model fasies batupasir Sokang dan hasil analisis heterogenitas skala besar yang menggambarkan kondisi geologi bawah permukaan. Fasies batupasir Sokang pada bagian atas Formasi Arang teridentifikasi sebagai tipe fasies Distributary Channel dan fasies Distributary Mouth Bars. Fasies Distributary Channel mempunyai kisaran porositas 3,72 – 32,70 % dan ketebalan 14,87 - 48,84 kaki. Penyebaran fasies Distributary Channel berada pada kondisi sub-lingkungan Delta Plain dengan geometri mengikuti pola alur channel berorientasi relatif Baratdaya – Timurlaut. Sedangkan tipe fasies Distributary Mouth Bars mengindikasikan kisaran porositas 7,14 – 36,12 % dengan variasi ketebalan dari 21,75 – 114,59 kaki. Penyebaran fasies Distributary Mouth Bars berada pada kondisi sub-lingkungan Delta Front dengan pelamparan ke arah cekungan membaji terhadap fasies Distal Delta Front.

Study area is located in the southern part of the East Natuna Basin, which is one of the potentially gas-producing basins. However, exploration activity on the sandstones reservoir is not maximized. This research was conducted to determine the characteristics of sandstone facies, subsurface configuration, and subsurface geological model of Sokang Sandstone facies at the top of Arang Formation. Subsurface geological modeling of Sokang Sandstone facies is done by integrating the analysis of small-scale heterogeneity that contain information Sokang Sandstone facies model and the results of large-scale heterogeneity analysis that describes the subsurface geological conditions. Sokang Sandstone facies at the top of Arang Formation are identified as Distributary Channel facies and Distributary Mouth Bars facies. Distributary Channel facies have porosities range from 3.72 to 32.70% and a thickness of 14.87 to 48.84 feet. The Distributary Channel facies are deposited in Delta Plain sub-environment with geometric of channels trending Southwest – Northeast. Whereas, the Distributary Mouth Bars facies indicates the range of porosity from 7.14 to 36.12% with a thickness variation from 21.75 to 114.59 feet. Distributary Mouth Bars facies are deposited in Delta Front sub-environments and tends to wedge against with Distal Delta Front facies towards the basin.

Kata Kunci : Batupasir Sokang, Formasi Arang, Cekungan Natuna Timur, reservoir batupasir, model fasies, model geologi.