Fasies Litologi dan Lingkungan Pengendapan Batupasir "CR" dan "YB" Formasi Air Benakat, Lapangan Rhamayanti, Subcekungan Jambi, Sumatera Selatan

RHAMAYANTI PUTRI, Dr. Ir. Jarot Setyowiyoto, M.Sc

2014 | Skripsi | TEKNIK GEOLOGI

Tugas Akhir Jurusan Teknik Geologi Fasies, Stratigrafi dan Petrofisik Pada Batupasir �CR� dan �YB� Formasi Air Benakat, Lapangan Rhamayanti, Subcekungan Jambi, Sumatra Selatan Oleh: Rhamayanti Putri, NIM. 09/281635/TK/35101 Pembimbing: Dr. Ir. Jarot Setyowiyoto, M.Sc. 2014 Abstrak Formasi Air Benakat (ABF) merupakan target kedua dari eksplorasi pertama di Cekungan Sumatera Selatan, setelah Formasi Talang Akar. Kompleksitas struktur ABF berupa flower structure, juga geometri dan ukuran reservoar yang kecil, menjadi alasan ditinggalkannya formasi ini meskipun berhasil ditemukan minyak bumi sekitar 626 MMBO. Hal demikian menjadi daya tarik tersendiri untuk dilakukan penelitian pada ABF daerah penelitian. Tujuan penelitian adalah untuk menganalisis fasies dan lingkungan pengendapan reservoar ABF pada Lapangan Rhamayanti serta menganalisis petrofisiknya. Analisis fasies dan lingkungan pengendapan batuan dilakukan dengan mengamati karakter litologi (warna, ukuran butir, tekstur dan komposisi batuan) pada deskripsi cutting dan sidewall core (SWC), diintegrasikan dengan elektrofasiesnya. Analisis petrofisik meliputi perhitungan volume lempung, porositas dan saturasi air berdasarkan data log, dengan menggunakan beberapa metode. Berdasarkan hasil analisis fasies, lingkungan pengendapan dan petrofisik, daerah penelitian memiliki dua reservoar, yaitu Reservoar �CR� dan Reservoar �YB�. Reservoar �CR� berupa batupasir fasies offshore bar yang terdeposisi pada lower shoreface, dengan porositas yang sangat baik (31,55%) dan saturasi air sebesar 46,36%, ketebalan bersih 76 cm. Reservoar �YB� berupa batupasir fasies crevasse splay yang terdeposisi pada delta plain, dengan porositas yang sangat baik (32,15%), saturasi air sebesar 53,81% dan ketebalan bersih 850 cm.

Lithology Facies and Depositional Environment of �CR� and �YB� Sandstones Air Benakat Formation, Rhamayanti Field, Jambi Subbasin, South Sumatra By: Rhamayanti Putri, NIM.09/281635/TK/35101 Lecturer: Dr. Ir. Jarot Setyowiyoto, M.Sc. 2014 Abstract Air Benakat Formation (ABF) was the secondary target of the first oil and gas exploration in South Sumatra Basin, after Talang Akar Formation. Eventhough the exploration succeed for finding reserve as much as 626 MMBO, ABF then became abandoned because of structure complexity in form of flower structure, also the geometry and size of its reservoir were relatively small. Nevertheless, this facts arose main attraction for researching ABF of Rhamayanti Field with purposes are analyzing facies, depositional environment and petrophysic of ABF reservoir. Facies and depositional environment analysis were conducted by ways of observed the character of lithology (including colour, grain size, texture and composition) that is contained on cutting and sidewall core (SWC) descriptions belonging to PT. Pertamina EP. The results then integrated with its electrofacies. Petrophysic analysis includes of shale volumes, porosities and water saturations calculations based on log data with several methods. According to facies, depositional environment and petrophysic analysis, research area has two reservoirs, named �CR� Reservoir and �YB� Reservoir. �CR� Reservoir in form of offhore bar sandstone deposited on lower shoreface, has porosities relatively very great (31,55%), water saturation amounted to 46,36% and net sand 76 cm. Meanwhile, �YB� Reservoir in form of crevasse splay sandstone deposited on delta plain, has porosities relatively very great (32,15%), water saturation amounted to 53,81% and net sand 850 cm. Based on results of sequence stratigraphy and dynamic sedimentation analysis, �CR� Reservoir was formed in TST 1, when relative sea level rise/stillstand become relative fall and the sea wave high. �YB� Resevoar was formed in late LST 1, when relative sea level fall become relative rise very slow.

Kata Kunci : Kata kunci: Formasi Air Benakat, Fasies batupasir crevasse splay, Fasies batupasir offshore bar, Petrofisik.