CHARACTERISTICS OF SANDSTONE AND RESERVOIR POTENTIAL OF NGRAYONG FORMATION IN TUBAN AND MADURA AREAS, NORTH EAST JAVA BASIN, INDONESIA
HTWE, PAIKE, Sugeng Sapto Surjono, Dr
2016 | Disertasi | S3 Teknik GeologiWilayah studi adalah Pulau Madura dan Daerah Tuban, yang terletak di Cekungan Timur Laut Pulau Jawa. Formasi Ngrayong yang berumur Miosen Tengah adalah reservoir minyak bumi yang penting di cekungan Timur Laut Jawa. Hal ini sudah banyak dikenal di bagian Anticlinal Blok Tuban dan Pulau Madura. Formasi Ngrayong terutama terdiri dari batupasir quartzarenit di daerah Tuban, batupasir dan batu kapur berpasir di Pulau Madura. Tujuan dari penelitian ini adalah untuk mengidentifikasi potensi reservoir di wilayah studi berdasarkan karakteristik dan geometri lithofacies dan variasi lingkungan pengendapan. Di Daerah Tuban, Formasi Ngrayong terdiri dari enam lithofacies; facies batupasir berlapistebal (Sc), fasies batupasir laminasi laminer (Sl), facies batupasir silang siur (Sx), fasies batubara (C), facies lapisan tipis batu pasir (Sf) dan fasies batulempung (Fm). Dapat diklasifikasikan enam lithofacies di Daerah Madura yaitu facies lapisan batu pasir berbutir kecil (Sm), fasies batu pasir heterolithic (Sh), fasies batulanau abu-abu gelap (Fc), fasies serpih abu-abu (Fs), fasies batupasir berbutir halus (Sf) dan facies kapur berpasir (Lgb). Tiga asosiasi lithofacies dan satuan pengendapan telah dikelompokkan ke dalam Formasi Ngrayong di Daerah Tuban dan Daerah Madura. Asosiasi lingkungan pantai di dan facies lapisan batu pasir (Sc), fasies batupasir lapisan sejajar (Sl), facies batupasir silang siur (Sx) dan faceis batubara (C) Daerah Tuban terdapat di lingkungan pantai dan tepi pantai. Asosiasi lapisan atas yang dangkal di Pulau Madura diwakili oleh facies batu pasir heterolithic (Sh), facies lapisan batu pasir berbutir kecil (Sm), fasies batupasir berbutir halus (Sf) dan fasies kapur berpasir (Lgb) dan facies lapisan tipis batu pasir (Fs) terakumulasi di sekitar Tuban dididominasi lingkungan laut dangkal. Asosiasi rendah lapisan dangkal di Pulau Madura terdiri dari facies batulanau abu-abu gelap (Fc) dan fasies serpih abu-abu (Fs), dan facies batulumpur (Fm) di bagian selatan dari Blok Tuban adalah deposito laut dangkal yang lebih rendah. Di Daerah Tuban, lapisan batupasir tebal berupa batupasir menengah sampai kasar. Porositas batupasir ini berkisar antara 42,18% dengan permeabilitas 260.02mD. Analisis petrofisika dari batupasir laminasi paralel menunjukkan porositas 30,90-36,13% dan permeabilitas 93,80-97,02 mD. Batupasir ini terdiri dari kuarsa berbutir halus yang disemen oleh mineral lempung. Perlapisan menyilang batupasir berbutir sedang, termasuk buruk untuk dengan butir feldspar disemen oleh mineral sedikit tanah liat. Batupasir ini memiliki porositas 39,60-40,70% dan permeabilitas 180,00-238,42 mD.Lapisan batupasir tipis diwakili oleh butir halus, dengan lapisan pasir dan batu lempung. Porositas batupasir ini berkisar 15,01-17,20% dengan permeabilitas 33.90-35.13mD. Di Pulau Madura, lapisan batupasir berbutir menengah bercampur dengan butiran pasir tersortasi sedang,. Berdasarkan analisis petrofisika, porositas batupasir ini adalah 25,27-29,68% dengan permeabilitas 54,87-57,53 mD. Batupasir Heterolithic terutama terdiri dari rbutir halus, cukup untuk cukup baik diurutkan pasir. Porositas dan permeabilitas batupasir ini dari 21,83% menjadi 27,71% dan dari 50.84mH ke 52.22mD. Bataulanau abu-abu gelap yang terkandung sortasi sangat baik. Sifat petrofisika hanya 11,49% porositas dan permeabilitas 5.47mD. Batupasir berbutir halus termasuk butir halus dan butiran pasir memiliki sortasi buruk. Porositas ini berbutir halus pasir adalah 16,74-21,03% dengan permeabilitas 15.77- 45.11mD. Berdasarkan karakteristik batupasir, reservoir yang baik ditemukan di lapisan batu pasir tebal di Tuban. Batupasir terlaminasi paralel, batu pasir lapisan menyilang di Tuban berlapis berbutir pasir di Pulau Madura memiliki karakteristik yang baik untuk reservoar. Potensi reservoir batupasir heterolithic dan batupasir berbutir halus dari Pulau Madura yang terbukti memiliki karakteristik yang baik. Namun lapisan batupasir tipis di aearah Tuban dan batulanau abu-abu gelap dari Pulau Madura memiliki kualitas reservoir yang rendah.
The study areas, Madura Island and Tuban Area, are located in the North-East Java Basin. The early Middle Miocene Ngrayong Formation is an important petroleum reservoir in North-East Java Basin. It is well exposed in the anticlinal part of Tuban Block and Madura Island. The Ngrayong Formation is mainly composed of quartzarenite sandstones in Tuban Area and sandstones and sandy limestone in Madura Island. The purpose of the present study is to identify the potential reservoirs of the study areas based on the characteristics and geometry of lithofacies and the variation of depositional environments. In Tuban Area, Ngrayong Formation comprises six principal sedimentary lithofacies; thickly bedded sandstone facies (Sc), parallel laminated sandstone facies (Sl), cross-bedded sandstone facies (Sx), coal facies (C), thinly bedded sandstone facies (Sf) and mudstone facies (Fm). It can be classified six lithofacies in Madura Area, too. These are thickly bedded medium grained sandstone facies (Sm), heterolithic sandstone facies (Sh), dark grey siltstone facies (Fc), grey shale facies (Fs), fine grained sandstone facies (Sf) and sandy limestone facies (Lgb). The three lithofacies associations and depositional units have been grouped into Ngrayong Formation in both Tuban and Madura Areas. The intertidal environment association composed of thickly bedded sandstone facies (Sc), parallel laminated sandstone facies (Sl), cross-bedded sandstone facies (Sx) and coal faceis (C) in Tuban Area is deposited in near shore to tidal flat environment. The subtidal environment association represented by thickly bedded medium grained sandstone facies (Sm), heterolithic sandstone facies (Sh), fine grained sandstone facies (Sf) and sandy limestone facies (Lgb) in Madura Island and thinly bedded sandstone facies (Fs) in Tuban Area is accumulated on tide dominated shoreface environment. The outer shelf association comprised dark gray siltstone facies (Fc) and grey shale facies (Fs) in the Madura Island, and mudstone facies (Fm) in the southern part of Tuban Block is deep shallow shelf or offshore deposits. In Tuban Area, thickly bedded sandstones are composed of moderately sorted, medium to coarse quartz grains. Porosity of these sandstones is ranging from 42.18% with permeability of 260.02mD. The pertophysic analysis of parallel laminated sandstones shows porosity 30.90 - 36.13% and permeability 93.80 - 97.02 mD. These sandstones consist of moderately- to moderately well sorted, fine grained quartz cemented by clay minerals. The cross-bedded sandstones include medium grained, poorly to moderately sorted quart and feldspar grains cemented by a little bit clay minerals. These sandstones have 39.60 - 40.70 % porosity and 180.00 - 238.42 mD permeability. Thinly bedded sandstones are represented by fine grained, poorly sorted sandstone interbedded with mudstones. The porosity of these sandstones samples is ranging from 15.01-17.20% with permeability 33.90-35.13mD. In Madura Island, the thickly bedded medium grained sandstones are combined with medium grained, poorly to moderately sorted sand grains. Based on petrophysics analysis, porosity of these sandstones is 25.27 - 29.68 % with 54.87 - 57.53 mD permeability. Heterolithic sandstones are mainly composed of fine grained, moderately to moderately well sorted sands. The porosity and permeability of these sandstones are from 21.83% to 27.71% and from 50.84mD to 52.22mD. The dark grey siltstones are contained very fine and poorly sorted grains. The petrophysics properties are only 11.49 % porosity and 5.47mD permeability. The fine grained sandstones include fine grain and poorly sorted sand grains. The porosity of these fine grained sandstone exhibit 16.74-21.03% with permeability 15.77- 45.11mD. Based on the characteristics of sandstones, the excellent reservoir properties are found in the thickly bedded sandstone in Tuban Area. The parallel laminated sandstone, cross-bedded sandstone in Tuban Area and thickly bedded medium grained sandstone in Madura Island have good to excellent reservoir characteristic. The reservoir potential of heterolithic sandstone and fine grained sandstones of Madura Island are fair to good characteristics. However, thinly bedded sandstones of Tuban Area and dark gray siltstones of Madura Island can be denoted only poor to fair reservoir quality.
Kata Kunci : RESERVOIR POTENTIAL OF NGRAYONG FORMATION
