2nd EAGE Conference on Reservoir Geoscience

Shifting Neogene depositional environment in the Malay-Tho Chu Basin and the mechanism

Geologically of Indonesia is an active magmatism path that has the potential to produce metal mineralization so that it is one of the countries that explores metal deposits. Metal mineralization is generally caused by hydrothermal activity associated with volcanic rocks. Complex hydrothermal alteration can result in changes in mineralogy, texture, and chemical content of rocks, one of which is the abundance of copper metal in the Purwoharjo area. This research was conducted to determine the distribution of Cu content in hematite minerals.

Both high resolution FWI models and broadband seismic data can provide the low frequency component of elastic property generation, enabling well information to be a control point. Accordingly reservoir geoscientists can confidently derive reliable elastic attributes such as acoustic impedance and Vp/Vs ratios away from well locations.

The sandstone reservoirs are major reservoirs in siliciclastic basin worldwide. Therefore, a good understanding of the development of internal rock properties are extremely important, especially factors such as porosity and permeability, in turn controlled by mineral composition, rock texture and diagenetic processes. This project studied the E and F formations in three wells in the Cuu Long Basin, with the aim of better defining controls on porosity and permeability, not just in terms of depositional character, but also diagenetic overprints. The core samples were analyzed via thin section observation, scanning electron microscopy (SEM), X-Ray diffraction (XRD), Capillary Pressure (PC) and Helium Porosity-Permeability measurements, together with petrophysical evaluation. The E formation was deposited in a fluvial-lacustrine environment that is characterized by claystone/shale interbedded with sandstone, with reduced depositional permeability in the finer-grained intervals. The XRD and SEM indicate rock quality in the sandstone reservoirs were influenced by a variety of authigenic minerals, such as carbonate cements, quartz overgrowths, zeolite and laumontite clays, all of which tend to reduce porosity and permeability. The F formation was deposited in a higher energy setting. This was mostly a braided channel environment indicated by a blocky shape in the wireline across the sandy interval and typically good primary porosity and permeability. In the E formation, XRD and SEM studies show that, as in the F formation, the porosity and permeability are strongly controlled by diagenetic evolution. Pore throats in the E and F sandstones are either minimized in size by intense compaction and a combination of pore-filling minerals including; calcite cements, authigenic clays and quartz overgrowths, leading to negative relationships with porosity and permeability. However, this negative relationship is not as clear in the interval with calcite cementation in E formation.

The recent drilling successes in Green Dragon structure in Nam con Son basin, offshore Vietnam have confirmed that this structure is potentially commercial discoveries with recoverable reserve nearly 41.8 mmbbl of oil based on wireline logging and MDT (Modular Formation Dynamic Tester) data. The seismic interpretation and prospect-time structure map reveal that Green Dragon structure is a 4- way dip anticlinical structure are thought to be result of transpression devirved from strike-slip or/and normal faulting. This anticlinical feature of the Green Dragon structure provided trap for series of hydrocarbon bearing sandstone units. According to petrophysical interpretation, total 12 commercial hydrocarbon bearing zones was identified. The hydrocarbon bearing zones were located below interbedded shale beds which worked as top seals. The existence of hydrocarbon accumulations indicates the sealing capacity of these inter-bedded shale formations holding hydrocarbon columns. However, the hydrocarbon thicknesses of reservoir units are different. This might be derived whether from difference in sealing capacity of top sealing beds or difference in hydrocarbon charging to each level. Hence, the top sealing capacity needs to be evaluated critically. This study presents an integrated approach using Mercury Injection Capillary Pressure (MICP) and petrographic analysis to assess the seal quality of the inter-bedded shale formations which are considered the intra-formation top seals of hydrocarbon bearing zones in Green Dragon structure. Based on the hydrocarbon column height at leak point derived from capillary pressure data, four seal types were identified. Furthermore, the result of scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis were interpreted to clarify the influence of clay minerals on seal capacity.

Reservoir data generated in the laboratory is often deceptive due to unwarranted sampling errors. Sometimes, it is not possible to sample from a representative rock type, if the size of the rock framework or pore body is bigger than the 1.5” core plug size. Error may also be introduced in case of multiple rock types at the lamina scale being combined within a plug sample. Multi-scale imaging through X-Ray tomography is a good solution to these problems. CT image statistical parameters like - mean lightness (L values) and standard deviation of mean lightness (STDEV) in combination with wireline logs (NPHI) can successfully be used to classify different rock and pore types within a heterogeneous core. Hydraulic conductivity simulations can lead to decipher connectivity of pores within it. Plug samples from representative rock types can subsequently be used for producing high-resolution, multi-scale 2D and 3D images. Numerical simulations are performed on these images to generate petrophysical properties and two-phase fluid flow properties for each individual rock type. This technique is applied to a Cretaceous rudist limestone section of Minagish Oolite reservoir and successfully captured data for a high permeability, megascopic, connected vuggy rudist limestone, which was otherwise not possible to characterize through standard routine and special core analysis. Key words : Vuggy limestone, high permeability, X-Ray tomography, Minagish Oolite

The execution of the Blocks B&48/95 and 52/97 project has special meaning for Vietnam, providing clean energy to fuel the country’s economic growth and socio-economic development of the Mekong Delta area. However, unlike conventional gas fields in the Northeast and Southeast areas offshore Vietnam, Blocks B&48/95 and 52/97 have a unique and complex geology with thousands of separate gas accumulations in fault-bounded clastic reservoirs. Gas composition includes variable quantities of CO2 and N2 that combined generally increase with depth from 5% up to 50%. To meet the obligatory sales gas specification of below 23% inert gas at power plants without CO2 removal equipment in surface production facility, it faces many challenges and uncertainties. The Operator developed a robust plan, tool and process ready to manage uncertainty and be able to quickly respond to the changes that may happen. It is an evergreen process which requires close integration between subsurface, drilling & completion, operation and planning. This paper summarizes the challenges and proposes a systematic methodology to overcome the challenges and to manage uncertainties for meeting the sales gas specifications.

A quasi-static model having homogeneous, isotropic, elastic material overlaying vicoelastic material of SLS due to a sudden movement along a very long, inclined to the free surface, strike slip fault of finite width have been studied in this work. Analytically solutions for displacement, stresses and strains are obtained before and after fault movement using a technique involving the use of Green’s functions and integral transforms. Assuming that tectonic forces maintain a shear strain far away from the fault. The effect of aseismic fault movement across it is found to depend on distance, dimension, relative position and other characteristic of the fault and inclination have been studied. The study of such earthquake fault dynamical models help us to understand mechanism of the lithosphere-asthenosphere boundary.

Reservoir characterization is a challenging task of integrating various data. The ultimate objective is to find an efficient way to process and harness the value of information that have already been acquired and interpreted. The idea is to use Machine Learning as a data driven approach towards achieving this. However, within the realm of Machine Learning, various algorithms and model optimization has a strong influence on the results. This process is equally important to make sure that the outcome is resonable and aids in our understanding of the subsurface. The target of this study is to investigate how the different algorithms and optimization impacts the results we are seeking.