RESERVOIR CONNECTIVITY STUDY OF G057B & G058B ZONES IN NILAM FIELD, KUTEI BASIN, EAST KALIMANTAN

• Main Author: RORYM CHERDASA, JERES
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/16169
• Institution: Institut Teknologi Bandung

Awibengkok geothermal field, also known Salak field is located 60 km from Jakarta in West Java Province, Java Island, Indonesia. The consession of Awiengkok field including the proven field lies in a highland on the southwestern flank of the Gunung Salak volcano (2211m absl). Physiographyly Awibengkok field is located in Bogor zone based on Van bemelen 1951 and the main structure trend in this field are northeast and northwest trend. Based on regional stratigraphy for West Java area, Awibengkok field is deposited with pleistocene-recent volcanic deposit. The geothermal system in Awibengkok field is a liquid-dominated, fracture-controlled reservoir with benign chemistry and low-to-moderate non-condensable gas content. The geothermal systems it self hosted mainly by andesitic-to-rhyodacitic rocks, and floored by Miocene marine sedimentary rocks cut by igneous intrusions.<p>Fluid flow in the geothermal field is very much related with the fracture pattern developed in the area and fracture reservoirs are very complicated and difficult to evaluate. In geothermal filed which dominated by fracture reservoir need an effective evaluation, precise prediction and planning to handle those kind of situation. To help the evaluation and planning in awibengkok geothermal field the fracture and geomechanics analysis ended with geological and fracture distribution model is being done in this study.<p>Geomechanic model is the integrated study of the state of stress, pore pressure and physical properties of reservoirs, natural fractures/faults, cap rocks and the formations in the overburden. The primary parameters controlling these interactions are the state of in-situ stress, rock strength, bedding orientation and properties, pore pressure and distribution of fractures and faults, wellbore trajectory, and mud weight.<p>Several methods have been developed in order to determine parameter of geomechanics model. Vertical Stress is calculated by integrating rock density from depth of interest to the surface, pore pressures determined by direct measurement from DST or RFT test. The approach used in most soft rock (low strength) geology cases to characterize relative minimum horizontal stress magnitude for each formation bed or layer using the available xLOT test, Laboratory measurement of rock strength can be physically achieved through testing of a core sample extracted from the formation either the Uniaxial Core test or the Triaxial Core Test. The azimuth of maximum horizontal stress is obtained from breakout and tensile fracture observation on image log, while the maximum horizontal stress magnitude can be estimated from borehole failure data.<p>Geomechanics analysis at AWI 1-2 well results shown the Vertical stress gradient is 1.122 psi/ft, the pore pressure gradient is 0.32 psi/ft, the stress horizontal minimum gradient is 0.54 psi/ft, the orientation of stress horizontal maximum is within N 300-370 E or NE-SW trend, and the horizontal stress magnitude gradient is 0.93 psi/ft. For AWI 2-1 results shown the Vertical stress gradient is 1.069 psi/ft, the pore pressure gradient is 0.32 psi/ft, the stress horizontal minimum gradient is 0.54 psi/ft, the orientation of stress horizontal maximum is within N 350-470 E or NE-SW trend, and the horizontal stress magnitude gradient is 0.89 psi/ft. Based on geomechanics analysis on those two wells, the principal stress works in this area is Sh min (?3) < SH Max (?2) < Sv (?1), based on Anderson 1951, this principal stress regime is reflecting normal stress rezime.<p>Image log interpretation at AWI 1-2 and AWI 2-2 wells showing 3 types of fracture: conductive fracture, resistive fracture and tensile fracture. The dominant trend for conductive fracture or open fracture is northeast-southwest trend, the resistive fracture or filled fracture present with a chaotic trend due to the several paragenesis system in the area, but the major trend is still northeast-southwest trend. The dip angle for both fractures is varied from 35-85 degree. For tensile fracture have a dominant trend northeast-southwest with dip angle allign the borehole.<p>Simplyfied stratigraphy consists of Upper formation, Middle formation, RDM formation, lower formation, sedimentary basement and intrusion is being used to build the geological model. The fault model is being interpreted using present geological and structural map, microearthquake data, and RDM formation distribution from each well. The interpreted fault plane is assumed being a vertical plane, the reason for this assumption is due to the geomechanics analysis result that showing in this area is reflecting normal stress rezime where normal fault will be present, and from fracture analysis the fracture present mainly having a steep dip angle.<p>Fracture modeling is build with Discrete Fracture Network algorithm from PETREL software. The algorithm from the software is being developed more to strain concept compare than stress concept, so the fracture distribution mainly will be guide with proximity to fault and maximum curvature concept. The fracture will be intensively present as closer to the fault and at the peak of the curvature. To minimize the uncetainty from the modeling, the modelings were run with 4 different parameters especially in the fracture dip geometry as a result for sensitivity analysis.<p>Fracture modeling result shows 0-5% value with mean value 1.5% for fracture porosity and 0-6 mD with mean value 0.1mD for fracture permeability. As a comparison result for the fourth model is the steep the angle for the fracture the more disconnected they are and as compensation from these condition, the fracture porosity and permeability are getting smaller. The similarity from the fourth model is showing an intensive fracture zone trending northeast-southwest, this high intensive fracture zone is the main fracture zone which controlling the production in this area, and it's already proven by the well test in the area. Based on the modelling result,it being suggested to drill the well path going to the east from the well head to hit the intensive fracture zone.