Electronic Theses and Dissertation

Kegiatan pemetaan geologi dilakukan dengan cakupan area kavling seluas 24 km², yang berada di Desa Alue Dua, Kecamatan Makmur, Kabupaten Bireuen, Provinsi Aceh. Lokasi Penelitian secara geologi berada pada Formasi Julurayeu yang berkaitan dengan petroleum sistem yang termasuk kedalam Cekungan Sumatra Utara. Cekungan ini berpotensi sebagai caprock sehingga menarik untuk mengetahui karakterisitk batuan mudstone pada Formasi Julurayeu (QTjr). Metode yang digunakan dalam penelitian ini berupa metode pemetaan geologi, Analisis Stratigrafi/Sedimentary Log dan analisis petrografi serta blue dye, yang nantinya ditunjuk untuk mendapatkan informasi mengenai karakterisitk mudstone serta nilai persentase porositas, ketebalan, struktur sedimen, dan hubungan antar lapisan yang akan dianalisis menghasilkan kolom stratigrafi terukur (Measure Section). Secara keseluruhan kondisi geologi daerah penelitian berada pada Formasi Julurayeu (QTjr) yang tersusun atas litologi endapan sungai, batupasir tufaan, lempung berlignit, dan batulumpur yang berumur Pliosen – Plistosen, Hasil yang di dapatkan dari penelitan berupa peta Geomorfologi yang terdapat 5 satuan bentang alam yang terdapat pada daerah penelitian, yaitu Satuan Tubuh Sungai (Fluvial F1), Zone Point Bar (Fluvial F4), Lereng Landai Hingga Curam (D1), Topografi Bergelombang dengan kekar (S2) dan Perbukitan Antiklin dan Sinklin (S9). Peta Geologi terdiri atas Satuan Batupasir Karbonatan QTjr, Satuan Batulanau QTjr dan Satuan Batupasir QTjr. Struktur yang terdapat dalam lokasi penelitian berupa struktur lipatan antiklin dan kekar. Hasil pengamatan kolom stratigrafi didapatkan fasies antara lain, Fasies Inter-Bedded Calcareus Sandstone and Calcareus Siltstone, Fasies Inter-Bedded Calcareus Sandstone and Siltstone, Fasies inter-Bedded Medium Sandstone and Siltstone, Fasies Inter-Bedded Sandstone and Calcareus Sandstone. lingkungan pengendapan pada daerah penelitian berada di lingkungan transisi antara darat dan laut, di mana terjadi pencampuran air tawar yang berasal dari sistem fluvial dengan air asin dari laut, yaitu berupa lingkungan pengendapan estuari/paralik. karakterisitk litologinya mudstone pada daerah penelitian di dominasi oleh matriks yang memiliki ukuran butir lanau (0,0039 – 0,031mm) menurut ukuran butir. Dari hasil uji analisis petrografi, batulanau karbonatan (mudstone) pada daerah penelitian menunjukkan nilai porositas buruk (poor) sebesar 10–20%, jika dilihat dari karakteristik batuan penutup (caprock), nilai porositas tersebut tergolong tinggi untuk dapat berfungsi sebagai penghalang migrasi hidrokarbon yang efektif, Jika dilihat dari hasil analisis porositas, batuan mudstone pada daerah penelitian yang menunjukkan bahwa karakteristik batuan penudung (caprock) pada daerah penelitan tergolong kurang efektif (buruk).

Geological mapping was conducted over a concession area of approximately 24 km², located in Alue Dua Village, Makmur District, Bireuen Regency, Aceh Province. Geologically, the study area is situated within the Julurayeu Formation, which is associated with the petroleum system of the North Sumatra Basin. This basin has potential as a caprock, making it important to investigate the mudstone characteristics of the Julurayeu Formation (QTjr). The methods applied in this study include geological mapping, stratigraphic analysis/sedimentary logging, petrographic analysis, and blue dye analysis. These methods were used to obtain information on mudstone characteristics, including porosity percentage, thickness, sedimentary structures, and interlayer relationships, which were analyzed to produce a measured stratigraphic section. Overall, the geological condition of the study area is dominated by the Julurayeu Formation (QTjr), which consists of fluvial deposits, tuffaceous sandstone, lignite-bearing clay, and mudstone, and is dated to the Pliocene–Pleistocene. The results of the study include a geomorphological map identifying five geomorphological units within the study area, namely: River Channel Unit (Fluvial F1), Point Bar Zone (Fluvial F4), Gentle to Steep Slopes (D1), Undulating Topography with Joints (S2), and Anticlinal and Synclinal Hills (S9). The geological map consists of the Carbonate Sandstone Unit (QTjr), Siltstone Unit (QTjr), and Sandstone Unit (QTjr). Geological structures observed in the study area include anticlinal folds and joints. Stratigraphic column observations identified several facies, including Interbedded Calcareous Sandstone and Calcareous Siltstone Facies, Interbedded Calcareous Sandstone and Siltstone Facies, Interbedded Medium Sandstone and Siltstone Facies, and Interbedded Sandstone and Calcareous Sandstone Facies. The depositional environment of the study area represents a transitional setting between terrestrial and marine environments, characterized by the mixing of freshwater from fluvial systems and saline marine water, corresponding to an estuarine/paralic depositional environment. Lithologically, the mudstone in the study area is dominated by a matrix with silt-sized grains (0.0039–0.031 mm). Petrographic analysis indicates that the carbonate siltstone (mudstone) exhibits poor porosity values ranging from 10–20%. From a caprock perspective, this porosity range is considered relatively high, reducing its effectiveness as a barrier to hydrocarbon migration. Based on the porosity analysis results, the mudstone in the study area is therefore classified as having poor caprock effectiveness.