Comprehensive characterization of fractured igneous rock reservoirs and PS modeling with reference to hydrocarbon E&P in Wichian Buri Subbasin, Thailand | |
| Author | Chaiyaphruk Chaiyasart |
| Call Number | AIT Diss no.GE-22-01 |
| Subject(s) | Igneous rocks--Thailand--Wichian Buri Hydrocarbon reservoirs--Thailand--Wichian Buri |
| Note | A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Geotechnical and Earth Resources Engineering with area of specialization in Geosystem Exploration and Petroleum Geoengineering |
| Publisher | Asian Institute of Technology |
| Abstract | The hydrocarbon in shallow fractured igneous rock reservoirs is a rare type of petroleum system found in several countries, including Thailand. The Wichian Buri basin is in the Phetchabun province of central Thailand. The Wichian Buri (WB) sub-basin has been producing hydrocarbons since 1988 in clastic and 2006 in fractured reservoirs. The igneous intrusions of 11-16 Ma and 18-24 Ma could play a dual function in the petroleum system in this area. Understanding how the intruded shale maturity was enhanced, how the fractured igneous rock reservoir was formed by the intrusion process, how the HC was generated and migrated into it are all important aspects of this petroleum system. The goal of this research is to characterize the fractured igneous rock reservoir in the WB sub-basin using well log analysis, onedimensional petroleum system (1DPSM), reserve estimation, reservoir simulation modeling, and economic feasibility for exploration and production. The dissertation begins with literature review to better understand the regional geological conditions and those in the WB sub-basin. The first step of this study is to conduct an integrated geological evaluation of the igneous rock reservoir found in this basin. A field outcrop survey was conducted to collect rock samples and well cuttings for laboratory thin section analysis, determination of physical characteristics, and seismic data correlation. The outputs of the well log analysis included lithology identification, TOC, source rock thickness, petrophysical parameters for basin modeling, and volumetric calculation using Monte Carlo simulation. The quality of the seismic data was checked, and seismic interpretation of the source rock and igneous rock layers was also done for further one-dimensional petroleum system modeling (1DPSM) and volumetric calculations. Monte Carlo simulation was used to assess the stock of oil in situ (STOIP). To calculate the estimated ultimate recovery (EUR), a pressure plot was made for identification of the oil-water-contact (OWC) and a production decrease analysis with water breakthrough was carried out. The static reservoir model was constructed, and various dynamic reservoir models were running with historical matching with the actual production data. The final step was to examine Thailand's fiscal framework, define the cost unit and crude oil price, and then assess the SW1 concessionaire's economic viability. A comprehensive well log analysis was conducted to find out the petrophysical characteristics of the fractured igneous rock reservoirs, which are generally characterized by low GR of 20 – 38 API, RHOB of 2.64 - 2.69 g/cc and DT of 61-68 μs/ft. It is noted that the average porosity for fractured intrusive rocks located from 750 to 1,500 m is about 9% – 11%, for the shallow extrusive igneous rock reservoirs located around 300 m deep it is about 21.30% – 22.70%, while for deeper-located pre-Tertiary basalt reservoirs from 1500 to 1800 m deep is about 17.48%. Water saturation of these fractured reservoirs was calculated by Archie’s. Simandoux, Dual porosity, Waxman-Smits, and Indonesia models, respectively, varying from 51 to 97%. The source rock TOC was determined using well log analysis and the logR technique, with the shale zone baseline interval found at 1,038–1,080 m, corresponding to Δtbase =125 s/ft and Rbase = 4 ohm.m. The average TOC of the source rock from 1,332 to 1,500 m MDRKB was 1.84 wt%. The source rock's net to gross ratio is 10.71%, corresponding to a net thickness of 36.95 m. The rifting process formed the Wichian Buri sub-basin in the Early Oligocene and ended in the Middle Miocene when the post rift began. The 1DPSM temperature gradient is 2.5-5.5 Co/100 m. The source rock's vitrinite reflectance is 0.62 percent. The source rock's hydrogen index (HI) is 222 mgHC/gTOC, while the original hydrogen index (HI0) is 550-600 mgHC/gTOC. Based on 1DPSM results, the hydrocarbons generated, expulsed, and retained range from 2,179.1 to 3,178.6 MMSTB, 298.3 to 355.5 MMSTB, and 1,880.8 to 2,823.0 MMSTB. The percentage of HCexp to HGgen is 11.2% to 13.7% and that of HCret to HGgen is 86.3% to 88.8% for the source rock in the Wichian Buri sub-basin. The calculated HCexp, was corrected by multiplying it with an efficiency coefficient of petroleum system (PSeff), which for HI0 = 600 mgHC/gTOC, PSeff = 15% and N/G of source rock 10.71% was assessed as 53.33 MMSTB. This is supposed to be a conservative assessment, as if one uses higher HI0 and PSeff the remained HCIIP in the shallow fractured igneous rock reservoirs in the Wichian Buri sub-basin can be higher. All in all the findings by an integrated well log analysis and 1DPSM in this study helped to indicate that there is still a significant amount of HCIIP to be explored in future in this sub-basin with such special type of shallow fractured igneous intrusion reservoirs. The EUR was calculated using two different methods for one fractured reservoir named WBEXT-3, and namely: (i) production decline analysis and (ii) volumetric calculation using Monte Carlo simulation. It was found that by considering water breakthrough in the production decline analysis one could get a more realistic production projection for shallow fractured igneous rock reservoirs in the WB sub-basin. Regarding the reserve of fractured igneous rock reservoir, the cumulative oil (Np) until end of April 2017 is 4.165 MMSTB. The 1P STOIP was calculated using the production decline method, while the 2P and 3P STOIP were calculated using the volumetric calculation by Monte Carlo simulation. The 1P reserve is as small as 304 MSTB, while the 2P and 3P reserves, on the other hand, are much higher and equal to 4,204.73 and 5,585.4 MSTB respectively. In the field development plan, new wells were planned considering water flooding. The static reservoir models were successfully constructed for dynamic reservoir simulations. The total capital expenditure (CAPEX) was estimated MM$ 21.02 from new prospects and in-filled drilling around $MM 1.54 per well including well facilities & installation. The cost of waterflooding project was estimated MM$ 2.9, consisting of three major cost components, i.e.: i) study cost (MM$ 0.45); ii) well completion and onshore equipment (MM$ 2.0); iii) for well intervention, perforation, and sand screen installation (MM$ 0.45). The decommissioning cost plans for removing all surface equipment and well abandon around $MM 0.204 at the year-end period of SW1 concession. The average historical crude oil selling of SW1 block with API range from 22 to 35 without sulfur in WB field was different from WTI crude oil price market around 7.77 USD/STB relatively. The operation expenditure (OPEX) of crude oil trucking, variable cost, fixed cost, and G&A cost was estimated equal 7.04 $US/STB from actual cost over production of 2015 data. The results of economic model analysis are good for future field development of SW1 concession with the 3-5% discounted net cash flow $MM 17.63 - 21.09, $MM. |
| Year | 2023 |
| Type | Dissertation |
| School | School of Engineering and Technology (SET) |
| Department | Department of Civil and Infrastucture Engineering (DCIE) |
| Academic Program/FoS | Geotechnical Engineering (GE) |
| Chairperson(s) | Pham Huy Giao;Avirut Puttiwongrak (Co-Chairperson) |
| Examination Committee(s) | Chau, Kuo-Chieh;Noppadol Phien-Wej |
| Scholarship Donor(s) | Royal Thai Government Fellowship |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2023 |