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Integrated geophysical applications and well datasets play an important role in understanding reservoir distribution and decision making for a robust development plan. A technical assessment was completed in a gas field in the North Malay Basin to describe the reservoir heterogeneity in the Early Miocene to Late Oligocene reservoir intervals. The field is a North-South oriented plunging anticline with stratigraphic trap configuration, discovered in 2007 by Well-X1. The assessment has resulted in a proposal of an appraisal well in 2014, Well-X2ST to delineate the northern hydrocarbon extent and to assess the hydrocarbon potential in the exploration interval of deeper sequences. The new well datasets were acquired and the results were utilized to further evaluate the field.
This paper focuses on the deepest reservoir sequence, DS12, encountered by the appraisal well in the eastern flank of the Malaysia-Thailand Joint Development Area (MTJDA). Rock physics modeling and seismic attribute datasets with well log and pressure data integration were utilized to better understand sand distribution for the upcoming development planning. Due to the thinly bedded nature of the reservoirs, the seismic could not be fully utilized to evaluate internal stacking geometries. This was further complicated by attenuation from the overlying thick shale. However, attribute analysis was effective to determine overall sand presence where the bed thickness ranges from 10 to 15 meters and the seismic detection limit is approximately 8 meters.
Rock property analysis was performed to calibrate both acoustic impedance and Vp/Vs to gamma ray for indication of sand presence. The Vp/Vs derivative was used instead of acoustic impedance because of the extra information obtained in both the elastic and AVO domain. In addition, rock physics modeling was performed to differentiate gas from wet sand and shale. The seismic datasets were used to qualitatively condition a geologic model to better distribute sand presence for well planning optimization. Development wells are planned to target good quality sands to maximize recovery efficiency
The success of proving the deepest reservoir sequence in the eastern flank of MTJDA, utilizing geophysical application and well data integration, have resulted in an improved understanding to outline deep reservoir distribution in the surrounding area and mitigate uncertainties in the development plan.
Adnan, M. Mohd (Carigali-PTTEPI Operating Company) | Ismail, W. Wan (Carigali-PTTEPI Operating Company) | Kaewtapan, J. (Carigali-PTTEPI Operating Company) | Setiawan, A. S (Carigali-PTTEPI Operating Company) | Tanprasat, S. (Carigali-PTTEPI Operating Company)
A comprehensive technical evaluation was conducted after the completion of six exploration and appraisal wells to assess the future petroleum potentials in North Malay Basin, offshore Malaysia-Thailand Joint Development Area (MTJDA). This paper focuses on major discoveries and findings from key wells, namely Well-E3, Well-A2ST, and Well-T3 to better understand the petroleum potentials for the subsequent development planning.
Well-E3 and Well-A2ST were drilled to investigate the stratigraphic trap play in the eastern flank of MTJDA and to explore the hydrocarbon potential in deeper depositional sequence below DS10 interval. The seismic dataset and amplitude analyses were used to identify channel fairways and qualitatively predict sand presence for well planning optimization. Both wells encountered gas-bearing sands with proven stratigraphic trap style, requires channel orientation oblique with the axial anticline structure. Full integration of well log dataset, formation pressure test and seismic attribute analyses have proven the exploration intervals with gas-bearing sands discoveries. In addition, rock physics analysis was performed to differentiate gas from wet sand and coals.
Well-T3 was drilled in the western flank to appraise the seismic anomaly associated with hydrocarbon sand and to investigate the CO2 content in the southernmost extension of hydrocarbon accumulation. The anomaly is observed as two distinct sand fairways of channel-bar complex. The northern lobe was dissected by deep seated fault system with high CO2 content. The southern lobe appears to be free from deep seated fault system. Well-T3 was drilled in the area where CO2 pathways was expected to have no connection with deep seated fault system and lower CO2 content than the main area. Formation pressures, samples and seismic anomaly supported the hypothesis that the northern and southern culminations are not connected with significant stratigraphic heterogeneity interpreted. An important oil discovery was also observed from pressure gradient and samples as the first oil discovery in the western flank.
Full integration of the well log dataset, formation pressures, seismic attribute analyses and rock physics modeling have resulted in an improved understanding of reservoir distribution and reduced the degree of uncertainty in reservoir connectivity, thus allowing a more robust development strategy. The new discoveries of proven stratigraphic trap in the eastern flank with deeper hydrocarbon culminations and proven oil discovery in the western flank with enhanced understanding of CO2 content have triggered more future petroleum potentials in MTJDA acreage.