Majalengka is a district in West Java which is located close to local faults and subduction zone, so that made this area has a high enough risk of earthquake hazards. Engineering Seismology Team of Meteorology Climatology and Geophysics Agency has been carried out microtremor and MASW survey in Majalengka. The combination of HVSR and MASW inversion methods is applied to obtain the value of the shear wave velocity (Vs), a combination of the two methods is expected to overcome the deficiency of each method. Results of the distribution of the value of the shear wave velocity can explain the subsurface conditions related to a vulnerability in the study area to seismic hazards. The results of HVSR and MASW inversion are 1-D (Vs) profiles at each measurement point, after that interpolated to obtain a 3-D Vs30 model. The results showed that Vs30 values in Majalengka District varied around 80 - 1500 m/s. Layers with low (Vs) values were relatively thick dominant in the north and northwest regions of the study area, soil types in this area were mostly composed of medium soils, a small part was composed of soft soil layers and rock layers. Therefore, in theory, the disaster in the north and northwest regions has a relatively higher vulnerability compared to other regions in Majalengka District.
The CD Carbonate in X-Field, East Java Basin has multiple reservoir targets with varying flow units, predominantly because of secondary porosity development from karst processes. Each of these reservoirs are relatively thin and the continuity of the karst within the reservoir is random. The amount of producible hydrocarbon will rest on the length of the drain section along the reservoir and the amount of karst intersected by the trajectory. Thus, maintaining the trajectory inside the carbonate reservoir while targeting the karst position is important for productivity. To maintain the production in the field, a new platform was built to the southeast of the first platform, aiming for a new development area. Five horizontal wells were planned as part of the second development phase. The first horizontal well is the most challenging one because of the high uncertainty of the structural dips along the lateral length triggered by the low seismic resolution and the limited nearby offset wells for control points. Moreover, the offset wells show inconsistent log properties that complicate the correlation to land into the targeted karst level within the reservoir. Initially, a pilot hole was planned to reduce the landing uncertainties; however, it was being challenged for cost efficiency. Therefore, a well placement strategy was proposed instead, including landing and geosteering using a new logging-while-drilling (LWD) combination of advanced high-definition reservoir mapping technology, high-resolution laterolog borehole imaging technology, and a multifunction LWD tool. In this paper we demonstrate the complete preparation of the well placement project, strategy, and evaluation using this new LWD combination for better interpretation of the reservoir. The deeper reading and higher resolution of the new reservoir mapping technology have permitted continuous mapping of the target reservoir, which typically has 35- to 50-ft thickness, to reduce the structural uncertainties from seismic. For the first time, it successfully revealed the karst network within the reservoir with greater details, identified by a blue-vein color spectrum of the resistivity inversion caused by seawater invasion or clay-filled karst. This high-definition karst mapping has helped to land the well precisely at the target karst sweet spot, improving the understanding of the karst characters along the trajectory, and providing higher confidence in the real-time geosteering decision. The high-resolution borehole image revealed the carbonate rock texture and karst/vugs appearance on a smaller scale, which was used to analyze the secondary porosity distribution and contribution along the trajectory using a quantitative image-based porosity analysis method. By integrating the high-definition reservoir mapping inversion interpretation and porosity analysis from a high-resolution borehole image, we were able to bridge the gap from seismic to reservoir scale, and finally to link the karst scale down to the vug pore sizes, for a better geological understanding and an improved geosteering strategy in the field.
The CD Carbonate of Ngimbang Formation in East Java basin was deposited in early Oligocene and divided into 5 reservoir targets for development. These reservoir targets were subdivided into different flow units, predominantly due to secondary porosity resulting from karst processes. Identifying these karst zones therefore became important for formation evaluation. Classic high resolution borehole images, combined with sonic, density and neutron logs, and NMR are the most commonly used tools to identify secondary porosity. However, due to the horizontal well design, conventional wireline logging was no longer possible thus Logging While Drilling (LWD) has become the primary data acquisition method. The LWD tool selection criteria have to meet both the geosteering and formation evaluation objectives by considering all drilling challenges. Even though all these measurements are currently available with LWD technology, the complexity of the long horizontal well trajectories and associated drilling risks have been assessed as being too high to run all the LWD services. Therefore, a different technique is required to identify karst zones and to determine saturation along the deeply-invaded karst intervals. A statistic-based correlation technique using principal component variance between advanced measurements from the multifunction LWD tool such as sigma, neutron capture spectroscopy, and standard measurements such as gamma ray, neutron porosity, density, caliper, and resistivity invasion profile is used to show an indication of karst- or matrix-dominated porosity. The spectroscopy provides accurate lithology volumes and information on grain properties. A simultaneous sigma–resistivity inversion technique is used to determine Archie's parameters in zones where the water salininty is known. The applicability and limitations of the technique are discussed for this particular reservoir environment. The combination of all these techniques along with information from state-of-the-art reservoir mapping technology has provided more complete characterization of the reservoir along the horizontal section.
The well within the context of this paper is carbonate formation in East Java basin deposited in late Oligocene to early Miocene. It is divided to 3 reservoir targets and potentially has different flow units, which believe predominantly due to secondary porosity. The well testing in exploration well drilled on the carbonate reservoir has commingled mixed between oil and water. Further appraisal well was necessary to be drilled to evaluate hydrocarbon saturation. The studied well was designed by combining the development and appraisal objective, therefore the deviation of the well was significantly high angle well. The conventional water saturation from resistivity based Archie did not give conclusive result because of fresh water environment and low contrast resistivity features. Utilizing nuclear magnetic resonance (NMR) log has been used for decades on carbonate evaluation through T2 (transversal relaxation time), and T1 (longitudinal relaxation time) for determination of pore type/system and differentiation of irreducible water from free fluid volume with applying fix pre-determined T2 cut-off. NMR log acquired while drilling gives the continuous T2 distribution which can be utilized to derive the poro-fluid facies on the porosity system from the measured actual T2distribution. The new technique based on statistical "factor analysis" search the peak response from each T2 distribution in depth level. Each changing on the T2 peak distribution on every depth will be recognized as actual cut off the T2 distribution and it will represent the poro-fluid facies constituents inside the T2 distribution. This paper will discuss the application the technique applied to the LWD NMR for determining poro-fluid facies analysis on the carbonate reservoir. The ultimate purpose is to identify the free fluid type presence on the porous rock. It will also discuss the advantages of this technique applied to the NMR acquired while drilling and use synthetic based mud to minimize the invasion and the ambiguity of filtrate invasion that may effect the free fluid determination on the rock.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.