Shallow Gas Features Based on Interpretation of Bottom Profilling Records at Topang Delta, Meranti Regency, Riau Province Kenampakan Gas Dangkal dari Hasil Interpretasi Rekaman Penampang Bawah Permukaan Dasar Laut di Delta Topang, Kabupaten Meranti, Provinsi Riau

Purnomo Raharjo, Willyan Djaja, Ediar Usman
2016 Bulletin of the Marine Geology   unpublished
One of the tasks in conducting a renewable energy research is finding a shallow gas contained commonly in river deltas. The location chosen is in Topang Delta" Meranti District, Riau Province in 2015. The research was conducted by using sub-bottom profiling (SBP) method. Biogenic gas indications could be observed in the SBP records in the forms of free reflector, acoustic plumes and acoustic blanket. The shallow biogenic gas at research area is trapped in A and B sequences. Sequence A is
more » ... equence A is characterized by plume gas and acoustic blanket, while B-type biogenic gas is showed by free-reflector feature of 10-15 meters depth. Sediment which does not have porocity such as old clay is required environment for anaerobic bacteria as catalyst in the formation of biogenic gas to be evolved. Old clay sediment is potential as a biogenic gas source rock afterwards migrated to a layer of sand as a reservoir rock. Some parts of biogenic gas does not appear to the surface because there have been traped in cap rock in form of young clay sediment. ABSTRAK : Salah satu tugas dalam melakukan penelitian energi terbarukan adalah pecarian gas dangkal yang biasa terdapat di delta-delta sungai. Lokasi yang terpilih adalah di delta Topang Kabupaten Kepulauan Meranti, Provinsi Riau pada tahun 2015. Penelitian yang dilakukan salah satunya menggunakan metoda sub bottom profilling (SBP). Indikasi gas biogenik tampak dalam rekaman subbottom profilling berupa reflektor bebas pantul, terobosan gas dan selimut akustik. Keterdapatan gas biogenik dangkal di lokasi penelitian terjebak dalam sekuen sedimen A dan B. Sekuen A dicirikan dengan kenampakan berupa terobosan gas dan selimut akustik, sedangkan biogenik gas tipe-B dicirikan dengan kehadiran reflektor bebas pantul dengan ketebalan 10-15 meter. Sedimen yang tidak memiliki porositas seperti lempung tua merupakan lingkungan yang dimungkinkan untuk bakteri anaerobik sebagai katalisator dalam pembentukan gas biogenik. Endapan lempung tua berpotensi sebagai batuan sumber biogenik gas kemudian bermigrasi ke lapisan sedimen pasir sebagai tempat tersimpannya gas biogenik. Sebagian gas biogenik tidak dapat muncul ke permukaan hingga lapisan atas karena terjebak dalam lapisan sedimen penutup berupa lempung muda. Kata Kunci : Delta Topang, Gas Biogenik, bebas pantul, terobosan gas, selimut akustik INTRODUCTION The occurrence of shallow gas in seabed sediment was recognized for a long time. Schuller (1952) was the first person to identify an effect on echosounder record on seabed sediment called "basin effect‰. Gas on marine sediment first reported by Emery and Hoggan (1958). Many researchers reported the occurrence of methane and other gases near seabed sediment. The purpose of this article is to give description of the occurrence of biogenic gas in seabed sediment based on sub-bottom profiling record analyses. Research area is located at Delta Topang Island, Meranti Regency, Riau Province (Figure 1).
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