Wawan Gunawan A. Kadir

Fractal geometry of the sumatra active fault system and its geodynamical implications

Abstract The Sumatra active fault system is a 1650 km long northwest trending dextral active strikeslip fault which accommodates the oblique convergence between the Indo-Australian and the Eurasian plates. It consists of 11 fault segments connected northward to the Andaman extensional back arc basin and southward to the extensional fault zone of the Sunda Strait. The geometries of the 11 segments are quantified using a fractal approach and it is found that their fractal dimensions (D) range from 1.00 ± 0.03 to 1.24 ± 0.03. Larger D values are associated with more irregular fault geometry. There are six discontinuities, reflected by sharp changes of fractal dimensions, observed along the segments. The locations of the discontinuities correspond to sites of major structural breaks in Sumatra mainland and its fore arc and back arc. The discontinuities and variations of D values suggest that the Sumatra mainland is not rigid. Instead it appears to be segmented into several blocks which may correlate to the segmentation in the Sumatra fore arc. This segmentation may explain the large discrepancy among the displacements and velocities of the Andaman Sea opening, the Sumatra fault motion and the Sunda Strait opening. This research also demonstrates the applicability of the fractal approach for analyzing the variations of fault geometry due to geodynamic processes.

Time-lapse Microgravity Application for Estimating Fluid Density Changes of Multilayer Reservoir Using DSMVD Technique

The fluid density changes parameter in a reservoir during production and injection fluid activities is very interesting to be analyzed. Through this parameter it can be identified the reservoir mass changes and its impact on the effectiveness of production and injection wells in a reservoir. One of the indirect monitoring technologies has been widely used to observe this parameter is a time-lapse microgravity method. For the case of a single-layer reservoir such as carbonate reservoir, the fluid density changes can be estimated easily because the gravity response measured on the surface directly reflects the fluid density changes in the targeted reservoir. This is in contrast to the case of a multilayer reservoir such as sandstone reservoir, the fluid density changes of each layer becomes more difficult to be predicted, because it depends on the processing technique used, also requires the completeness of supporting data such as volume of reservoir fluid production and injection during a period of gravity measurement on the surface.

Using gravity fault identification data in Bandung basin

The Bouguer anomaly map of the Bandung Basin, Indonesia was used to identify the existence of the subsurface features of this area and to identify possible faults and types. Based on the regional map the gravity of the research area has a high gravity anomaly in the western area of research associated with intrusive rocks. The middle-high anomaly is in the middle area from west to east which then turns toward the northeast. There are two low anomalies that exist in the northern area of research associated with a volcanic fan from its northern direction. Another low anomaly is in the eastern part of the study area with a thick sedimentary sediment. In identifying the structure is done by processing residual gravity data, SVD map and assisted by the structure map of seismotectonic. There were found seven faults identified with six normal faults and a reverse.The Bouguer anomaly map of the Bandung Basin, Indonesia was used to identify the existence of the subsurface features of this area and to identify possible faults and types. Based on the regional map the gravity of the research area has a high gravity anomaly in the western area of research associated with intrusive rocks. The middle-high anomaly is in the middle area from west to east which then turns toward the northeast. There are two low anomalies that exist in the northern area of research associated with a volcanic fan from its northern direction. Another low anomaly is in the eastern part of the study area with a thick sedimentary sediment. In identifying the structure is done by processing residual gravity data, SVD map and assisted by the structure map of seismotectonic. There were found seven faults identified with six normal faults and a reverse.

Inverse Modeling of Gravity Data with Two Layers Density in Sedimentary Basin Structure

Study of sedimentary basin structure and basement variation in the subsurface using gravity methods are very common in early stage of hydrocarbon exploration. Most of inverse modeling are designed with several series of juxtaposed vertical prism in the subsurface. In this study, we utilize two layers of vertical prism below each gravity stations to represent homogeneous density of sedimentary layer and basement in the subsurface. In order to reach best miss-fit data we used iterative calculation utilizing differences between observed and calculated data. Performance of iterative calculation will attempt to find solution of interface density in the subsurface. In this paper, we use two synthetic data of symmetrical sedimentary basin model for inversion performance test. The performance test will evaluate the effect of initial model, exploration well data, topographic data, and noisy data effect. Based on synthetic data test, the performance of iterative method provide small order of miss-fit data with residual solution model of noisy data in the range -44 to 35 meters. Real data application identified three shallow sedimentary layer and two deeper sedimentary layer in the study area.

Integration of 4D Microgravity, Geology and Production Data to Monitor Water Injection in Improved Oil Recovery Project, Diamond Field

Water injection is common technology applied to maintain the reservoir pressure under Improved Oil Recovery (IOR) scheme. Reservoir pressure maintenance is required to sustain the oil production and maximize oil recovery. Water injection is to be technically and economically designed, properly implemented and thoroughly evaluated. When the water injection is commenced, it is essential to conduct technical evaluation to monitor its effectiveness in order to achieve the goal and objectives. Understanding the reservoir fluid dynamics including the injected water movement is the key for optimizing the water injection. Production, geological and geophysical data are to be integrated to portray the reservoir fluid saturation changes. A comprehensive analysis of time lapse (4D) microgravity, production and geology is used to evaluate the water injection performance. The 4D microgravity that passively surveyed at the arranged stations is easy to operate, competitive and technically accepted. Several time-lapse microgravity that was surveyed in water injection IOR, Diamond field, would provide different time lapse microgravity anomaly for further analysis. This research applies forward modeling of microgravity anomaly to match with the reservoir production performance. The outcomes from this joint study would then be used to support continuous water injection optimization and improvement. Other than subsurface integration, from surface operation point of view, water injection improvement also involves surface discipline which consists of production operations and construction that responsible for surface facilities operations and construction.