CHANNEL DEPOSIT GEOMETRY CHARACTERIZATION OF GAS RESERVOIR IN SHALLOW ZONE NATA FIELD MAHAKAM BLOCK EAST BORNEO

• Main Author: Mesra Sjahbunan, Putra
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/77957
• Institution: Institut Teknologi Bandung

Nata is a giant gas and condensate field that located at the eastern side of the modern Mahakam Delta. This field is located in between Peciko-Bekapai field (operated by Total Indonesie) in the south, and Attaka field (operated by Chevron) in the north. This field have formed elongated in median axis, trending northeast - southwest with an estimated length of about 75 km with a width of about 15 km of covering an area of approximately 1130 km2 Reservoirs interval in Nata field are divided into two zone by 1a/MF6 marker as a regional marker, that are Nata Main Zone and Nata Shallow Zone. Nowadays, Nata development has been continued to produce gas in shallow zone interval, that in previous development had been considered as a drilling hazard because of its gas. Shallow Zone is an interval filled of fluvial and delta stacking deposit, deposited in upper miocene – pliocene. Core data showing two type of channel deposits, that are fluvial channel and distributary channel, but its lateral distribution haven’t been known yet. In the other hand, reservoir modelling is planned using deterministic approach which needs geometry parameters of reservoir targets in Nata Shallow Zone. Seismic data gives a lateral picture of reservoir distribution in blue over red anomaly, that caused by gas filled inside the reservoir. This anomaly shows two different shape of geometry. Measuring those anomaly will give amount of data that can be analyzed by statistical method. Based on statistical analysis, there are 3 groups of data, explaining particular channel deposit. Group A has width/thickness ratio in between 6 – 36, average sinuosity is 1.17 and average thickness is 16 m, interpreted as fluvial channel deposit. Group B has width/thickness ratio in between 7 – 26, average sinousity is 1.04, and average thickness is 13 m, interpreted as upper delta plain distributary channel. Group C has width/thickness ratio in between 20 – 165, averege sinuosity is 1.17 and average thickness 5 m, interpreted as lower delta plain distributary channel. Channel deposit geometry is affected by depositional trend and stratigraphy that developed in Nata field. Depositional trend in Nata Shallow Zone is relatively northwest-southeast trend, than east-west trend. This trend afffected width/thickness ratio, that is bigger in southern side. Observation in core, statistic data and seismic proved that sequence stratigraphy change in Nata Shallow Zone gave an impact to a reservoar geometry