Evaluation of the drainage area of a well is an effort to obtain success in planning field development. The size of the drain area not only affects the production rate but will also affect the distribution of pressure and saturation as well as the physical properties of the fluid and reservoir rock. Determination of optimum well spacing is important in field development management. This paper presents observations on the effect of the drain area on the production rate, pressure drop, and recovery factor. Simulation of the well model with a cylindrical drain area is used for various sizes of drainage areas. Based on the analysis in this study, it is concluded that the size of the discharge area affects the production rate, recovery factor, and pressure drop. The decrease in pressure affects the release of dissolved gas as indicated by changes in the gas-oil ratio (GOR) curve and the peak of the GOR.

The study area is an oil and gas field that has a low resistivity reservoir zone in the Talang AkarFormation, South Sumatera Basin. The reservoir zone is composed of siltstone and sandstone that was depositedin a shallow to transitional marine environment. The aim of this study is to identify and determine the potential oflow resistivity reservoirs in the study formation. The data used in the study include well log, mud log, core data(porosity, permeability, petrography), formation water analysis, and biostratigraphy. The methodology includesqualitative analysis to determine reservoir potential zones (quick look interpretation) and the reason for low resistivityreservoirs, as well as quantitative analysis to calculate petrophysical parameters. The results of the quicklook analysis showed 77 low resistivity reservoir zones, but the petrophysical analysis identified 25 low resistivityreservoir zones as potential candidates for drill steam test (DST). Factors causing low resistivity reservoirs inthe study area include clay mineral content (kaolinite and illite), conductive minerals (pyrite and siderite), highsalinity formation water (10,000 ppm), very fine to medium sand grain size (0.063 - 0.5 mm) distribution ofclay minerals (laminated and dispersed clay), and thin laminates. The results of the petrophysical analysis showthat shale volume is less than 30%, porosity is greater than 14%, permeability is greater than 10 mD, and watersaturation is less than 70%.

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AbstrakObjek studi difokuskan pada Formasi Tapak yang terendapkan pada Miosen Akhir -Pliosen Akhir di Sub-Cekungan Banyumas. Pengungkapan serta rekonstruksi model lingkungan pengendapan purba didasarkan pada analisis detail sedimentologi dan stratigrafi yang meliputi tekstur, struktur sedimen, asosiasi fasies, paket sekuen pengendapan, kandungan fosil, geometri pelamparan secara vertikal maupun horisontal serta pengukuran arah arus purba pada daerah penelitian. Fasies yang berkembang pada Formasi ini cukup bervariasi yaitu lagoonal pond, tidal channel in foreshore facies, upper shorefaceshelf mud facies. Secara regional Formasi Tapak diendapkan dalam suatu sistem pada lingkungan pengendapan lagoon hingga laut dangkal. Pada daerah penelitian juga ditemukan batugamping terumbu yang terbentuk pada barrier reef. Dari Hasil pengukuran arus purba pada struktur sedimen trough crossbedding pada lokasi pengamatan Banyumas -14, terlihat bahwa arah umum dari transportasi sedimennya berasal dari Barat-Laut menuju ke Tenggara. Kata kunci: Sedimentologi; Stratigrafi; Lingkungan Pengendapan; Formasi Tapak. AbstractThe object of study is focused on The Tapak Formation deposited in Late Miocene -Late Pliocene in the Banyumas Sub-Basin. Reconstruction of the paleo-environment model is based on detailed analysis of sedimentology and stratigraphy which includes textures, sedimentary structures, facies associations, depositional sequence packages, fossil content, vertical and horizontal geometry and measurement of paleocurrents in the study area. Facies in this formation namely lagoonal pond, tidal channel in foreshore facies, upper shorefaceshelf mud facies. Regionally, The Tapak Formation was deposited in the lagoon deposition to the shallow sea environment. In the study area also found reef limestone formed on the barrier reef. From the results of paleocurrents measurements in the trough crossbedding sedimentary structure, it appears that the general direction of sediment transport originated from The Northwest to The Southeast.

Pemetaan digital dapat menghasilkan analogi digital dari singkapan sebagai representasi dan gambaran kondisi bawah permukaan pada daerah yang memiliki kesamaan karakteristik geologi. Penerapan metode ini memungkinkan interpretasi dan pengukuran fitur geologi secara digital untuk keperluan karakterisasi reservoar hidrokarbon. Selain itu, metode ini tidak memerlukan biaya tinggi seperti akuisisi seismik atau wireline logging, schingga eksplorasi hidrokarbon, khususnya untuk mengetahui karakter reservoar jauh lebih mudah dan murah. Penelitian ini dilakukan di wilayah Desa Binangun, Kabupaten Tuban, Jawa Timur, karena memiliki penyebaran Formasi Ngrayong yang cukup baik. Tujuan penelitian ini adalah memetakan secara digital singkapan batuan untuk memberikan gambaran awal karakteristik reservoar serta menghitung reservoar quality index (RQI). Metode pemetaan digital ini menggunakan kamera digital, quadcopter drone, dan perangkat global positioning system. Integrasi data pemetaan digital menghasilkan model fasies, properti (porositas dan permeabilitas), serta model RQI. Berdasarkan model RQI didapatkan tiga potential flow units, yakni high quality (porositas 25-35%, permeabilitas 500 mD), medium - high quality (porositas 27 - 30%, permeabilitas 90 - 500 mD) dan medium quality (porositas 24 - 33%, permeabilitas 85-95 mD). Metode pemetaan digital berhasil menggambarkan karakterisasi reservoar dan memberikan informasi lebih banyak pada daerah yang sedikit ataupun tidak memiliki data bawah permukaan, serta dapat mengurangi resiko dan ketidakpastian di bawah permukaan.