Compartment Analysis Using Fault Seal Prediction in Miocene Carbonate Reservoir of Banggai Basin and Its Implication to Field Development
Research area is located in collision zone between Banggai-Sula Spur and Sulawesi Ophiolite Belt. The collision happened in Neogene time. Banggai-Sula Spur is part of northward drifting Australia Continent. Australia–SE Asia collision began in the Early Miocene when the Sula Spur collided with the North Sulawesi volcanic arc. Subduction rollback began at about 15 Ma into the Jurassic Banda Embayment causing extension of the Sula Spur (Hall, 2012). Banggai-Sula Spur then collided with ophiolite belts and another associated rocks of East Sulawesi. During the drifting of the Banggai-Sula Microcontinent to collision with Sulawesi Ophiolite Belts in Miocene, depositional environment in Banggai-Sula appears as shallow to deep marine which is good for carbonate growth, reefal to clastic, thus this carbonate acts as main reservoir rock in the research area. This carbonates sequence continued to deposited as the Banggai-Sula collided with Sulawesi Ophiolite Belt. The collision affected the reservoir to be thrusted and faulted. In this research area, hydrocarbon entrapment is controlled by fault dominated resulted from compressional event. Fault capacity may act as a conduit or a barrier for hydrocarbon flow. Therefore research about fault seal becomes the key instrument in this field. The objective of this reserach is to analyze compartments in order to optimize development scenarios in producing field. Generally, a static hydrocarbon column held across a fault is caused by aquifer and buoyancy pressure of fluids (applied against the capillary entry pressure of fault rocks and juxtaposed stratigraphies) reaching equilibrium across the fault over geological time (Fisher et al. 2001). The geometrical relationships of faults, their sealing properties, and the geometry and petrophysical properties of faulted blocks have been used by many researchers to quantify the effects faults can have on migration pathways and entrapment of hydrocarbons within sedimentary basins (Yoshioka 1986; Knipe 1992; Fulljames et al. 1997; Freeman et al. 1998). However, modelling the sealing effects of faults based on the geometry and petrophysical properties of the faulted blocks and the parameters of deformation is deterministic (Hesthammer & Fossen 2000; James et al. 2004; Bjorlykke et al. 2005; Ligtenberg 2005). Due to the rarely presence of impermeable layer in carbonate platform reservoir, fault seal analysis method that being used in this research was generating shale gouge ratio, which were confirmed by cut offs of porosity-vshale, porosity-permeability, and permeability-SGR. These cut offs were made to determine the minimum limit of hydrocarbon flow through faults in carbonate reservoir. To confirm connectivity of the compartments, pressure test analysis was performed on wells separated by faults. The pressure difference may confirm compartmentalization in reservoir. The results are showing different characteristics of each fault. Porosity with 5% cut off and vshale with 25% cut off becomes the minimum value for flowing hydrocarbon in reservoir. Then the value of porosity cut off was associated in porosity-permeability relationship to obtain the minimum limit of permeability for flowing hydrocarbon, which is 5mD. Then this permeability value is used in permeability-SGR crossplot. From the generated crossplot, the minimum SGR value is 0.25. based on the analysis, the faults were categorized as sealing faults, partial sealing faults, and leaking faults. These results also confirmed by RFT pressure analysis which performed in wells separated by faults. This Research highlights the possibility for carbonate reservoir compartments in adjacent fault blocks to be hydrocarbon bearing, water bearing zone or connectivity of the reservoir itself. Thus it is important for developing oil and gas fields with faulted reservoir.
AAPG Datapages/Search and Discovery Article #90336 ©2018 AAPG Asia Pacific Region, The 4th AAPG/EAGE/MGS Myanmar Oil and Gas Conference, Myanmar: A Global Oil and Gas Hotspot: Unleashing the Petroleum Systems Potential, Yangon, Myanmar, November 13-15, 2018