PENENTUAN LINGKUNGAN PENGENDAPAN UNTUK INTERPRETASI PERUBAHAN NILAI RESISTIVITAS AIR BERDASARKAN DATA BAWAH PERMUKAAN PADA FORMASI TALANGAKAR, LAPANGAN “GWEN” CEKUNGAN JAWA BARAT UTARA

Abstract

One of measured physical character since logging is resistivity. The magnitude of resistivity of a rock depend on the character it self, such as porosity, salinity, types of rock. Besides, contains of fluid also determine magnitude of resistivity rate. When formation has porous character and contain salt water then resistivity would low either, while formation contain hydrocarbon then it would higher. Litology, which arranged a formation would deposited in difference sedimentation environment. It would causes water resistivity value becomes difference for each sedimentation environment, therefore, a research should be perform to identify relationship of water resistivity value alteration to sedimentation environment. “GWEN” Field is exploration field in Cipunegara Block, which to be concession area of PT. Pertamina EP Jakarta. The exploration target in this area focussed in Talangkar Formation. Wells in research area in â€"GWEN"€ field consists of A1, A2, A3, A4, and A5 well, it is arranged by rocks such sandstone, limestone, slime stone, and flake. Based on litology data, it would identify that all five wells deposited based on log pattern, so that it could predicted. There perform petrophysic analysis for each system tract phase in order to identify water resistivity value so that model could make which figure relationship between water resistivity value alterations with sedimentation environment. Based on the model, resulted that water resistivity value is 0.01-0,0055  m, includes sedimentation environment of border neritic, sedimentation environment that has water resistivity value of 0,056 – 0,055  m categorized in delta sedimentation environment, sedimentation environment which has water resistivity value 0,056 – 0,7  m categorized in fluvial sedimentation environment. Higher water resistivity value indicates higher salinity value in an area. Salinity of sedimentation environment, which lean toward land are lower, so that it could causes water resistivity value get higher, vice versa. Keywords : log,water resistivity, depositional environment.