Sains Malaysiana 49(9)(2020): 2065-2072

http://dx.doi.org/10.17576/jsm-2020-4909-04

Implementation 3D Inversion of Gravity Data to Identify Potential Hydrocarbon Reservoir Zones in West Timor Basin

(Implementasi Songsangan 3D pada Data Graviti untuk Mengenal Pasti Potensi Zon Reservoir Hidrokarbon di Lembangan Timor Barat)

MOHAMMAD SYAMSU ROSID* & CICILIA BUDI SARASWATI

Physics Department, FMIPA Universitas Indonesia, Depok 16424, Indonesia

Diserahkan: 15 Januari 2020/Diterima: 10 Mei 2020

ABSTRACT

A gravity survey has been carried out in the area of West Timor, East Nusa Tenggara to identify the existence of basin structures. The existence of reservoirs and trap structures are two important parameters in hydrocarbon exploration. Geologically, Timor possibly an area known to have a very complex geological structure. This complexity can be the main factor that causes the demotivation of geologists in exploring hydrocarbons. There are many indications of hydrocarbons in the form of oil and gas seeps on the surface, especially in East Timor. But most of them are not confirmed in the field, and only a few are even found in West Timor. The method used in this study is analyzing and 3D inversion modeling gravity data. The analysis was carried out using spectrum analysis and the second vertical derivative of the complete Bouguer anomaly (CBA). From the gravity parameters confirmed by geological data, the results indicate that in the study area there are basin and basement structures thought to be formed from unconformably of andesite igneous rock and tight send sediment with a density value of about 2.5 gr/cm³. The average basement depth is about 5.5 km with its forming structure is the reverse/thrust fault with Northeast to Southwest its strike orientation. While in the southern part, especially in the central basin area, there is indicated a layer of sand sediment that is quite thick with a density value of about 2.2 gr/cm³ and has the potential to become a hydrocarbon reservoir.

Keywords: East Nusa Tenggara; gravity method; hydrocarbon exploration; Timor basin

ABSTRAK

Suatu survei graviti telah dijalankan di daerah Timor Barat, Nusa Tenggara Timur untuk mengenal pasti keberadaan struktur lembangan di situ. Keberadaan reservoir dan struktur perangkap adalah dua parameter penting dalam eksplorasi hidrokarbon. Secara geologi, Timor mungkin merupakan satu daerah yang diketahui memiliki struktur geologi yang sangat kompleks. Kekompleksan ini menjadi faktor utama yang menyebabkan motivasi para geologis berkurang dalam melakukan eksplorasi hidrokarbon di sana. Banyak ditemukan petunjuk hidrokarbon dalam bentuk rembesan minyak dan gas di permukaan terutama di daerah Timor Timur. Tetapi kebanyakan daripada mereka tidak dapat dipastikan di lapangan dan hanya beberapa bahkan ditemukan di wilayah Timor Barat. Kaedah yang digunakan dalam kajian ini adalah melakukan analisis data graviti dan pemodelan songsangan 3D. Analisis dilakukan dengan menggunakan analisis spektrum dan turunan menegak kedua daripada anomali Bouger lengkap (CBA) data graviti. Daripada parameter graviti yang dipastikan oleh data geologi, hasilnya menunjukkan bahawa di kawasan kajian terdapat struktur lembangan dan dasar yang diduga terbentuk daripada batuan beku andesit yang tidak selaras dengan endapan pasir keras dengan ketumpatan ialah 2.5 g/cm³. Purata kedalaman dasar ini sekitar 5.5 km dan membentuk struktur sesar tujah dengan arah jurusnya Timur laut ke Barat daya. Sementara di bahagian Selatan, terutama di pusat lembangan, menunjukkan adanya lapisan endapan pasir yang cukup tebal dengan ketumpatan 2.2 g/cm³ dan berpotensi untuk menjadi reservoir hidrokarbon.

Kata kunci: Eksplorasi hidrokarbon; kaedah graviti; lembangan Timor; Nusa Tenggara Timur

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*Pengarang untuk surat-menyurat; email: syamsu.rosid@ui.ac.id