Confirming Reservoir Geometry and Exploration Opportunity through 5D Interpolation PSDM in The Sub-ophiolite Zone, Banggai Sula Basin, Central Sulawesi

In 2020, Pertamina EP made another gas discovery in Banggai-Sula Basin. However, the prediction missed the top of formation by several hundred meters and therefore increased the uncertainty in the actual amount of the discovered gas resources. The previous geological model was based on 3D Pre-Stack Depth Migrated seismic data from 2018. With only one well as data control, plus complex structure and the proximity to the Batui thrust, the velocity has not been modeled correctly. To reduce the uncertainty, a reprocessed seismic data is required to help building an updated geological model. The newly drilled well, WOL-002, provides new velocity information for PSDM reprocessing. It is however located below an ophiolite layer when signals are very weak. To improve the signal to noise ratio, a powerful yet time-consuming 5D Interpolation is employed. This step significantly improves image quality especially below the thrust. Since this project is tightly time constrained, a careful parameterization has been done for improving processing efficiency. As a result, the imaging can be finished ahead of schedule. Reflector’s depth is confirmed using not only velocity data from well W-20 but also from the neighboring field. New interpretation based on the 2020 reprocessing suggests a larger structure in the subsurface compared to the previous model. This newly processed 3D seismic is also used for identifying new prospect closer toward the thrust zones.

Unrest at the Laguna del Maule volcanic field 2005–2020: renewed acceleration of deformation

The Laguna del Maule volcanic field in Chile has been exhibiting unrest since 2005. New GPS and InSAR data reveal a second episode of accelerated deformation beginning in late 2016 and continuing through May 2020, with an uplift rate > 290 mm/year between 2019 and 2020. To explain the spatial and temporal pattern of deformation, we apply a dynamic model of viscous magma flowing through a conduit into a fluid-filled reservoir surrounded by a heterogeneous, viscoelastic crust. A Monte Carlo procedure optimizes the ellipsoid reservoir geometry and the inlet pressure history. The two episodes of accelerating uplift are each modeled with a pressure increase rate of $\sim $ ∼ 9 MPa/year. Since 2016, 0.10 km3 of magma was injected into the system for a total of 0.37 km3 since 2005.

Mathematical description of a bounded oil reservoir with a horizontal well

Horizontal wells are more productive compared to vertical wells if their performance is optimized. For a completely bounded oil reservoir, immediately the well is put into production, the boundaries of the oil reservoir have no effect on the flow. The pressure distribution thus can be approximated with this into consideration. When the flow reaches either the vertical or the horizontal boundaries of the reservoir, the effect of the boundaries can be factored into the pressure distribution approximation. In this paper we consider the above cases and present a detailed mathematical model that can be used for short time approximation of the pressure distribution for a horizontal well with sealed boundaries. The models are developed using appropriate Green’s and source functions. In all the models developed the effect of the oil reservoir boundaries as well as the oil reservoir parameters determine the flow period experienced. In particular, the effective permeability relative to horizontal anisotropic permeability, the width and length of the reservoir influence the pressure response. The models developed can be used to approximate and analyze the pressure distribution for horizontal wells during a short time of production. The models presented show that the dimensionless pressure distribution is affected by the oil reservoir geometry and the respective directional permeabilities.

Mathematical description of a bounded oil reservoir with a horizontal well

When horizontal wells are compared with verticals wells, their production is always higher. If their performance can be improved, they can even be more productive. Considering a horizontal well in a completely bounded oil reservoir, when the well has been producing for some time and the effect of the boundaries is evident on the flow, the pressure distribution can be approximated by considering the effects of the boundaries on the flow. Considering when a pseudosteady state flow is attained this study presents a mathematical model for approximating pressure distribution for late time for a horizontal well in an oil reservoir with sealed boundaries. We use appropriate Source and Green’s functions to develop the model. The model developed show that when the flow reaches all the boundaries a pseudosteady state flow is attained and thus pressure distribution is influenced by the oil reservoir geometry especially its width and length. Considering that the thickness of the oil reservoir will be small compared to the length of the well, the oil reservoir width and length will determine the pressure response. This will influence the flow period occurring. By considering all aspects of the flow, the model can be applied to approximate the pressure distribution for as long as the well can continue producing.

DEPOSITIONAL PROCESSES AND FACIES ARCHITECTURE OF BALIKPAPAN SANDSTONE FORMATION, APPLICATION OF 3D DIGITAL OUTCORP MODEL (DOM) TO IDENTIFY RESERVOIR GEOMETRY AND DISTRIBUTION IN DELTAIC SYSTEM

In recent years, digitalization of the outcrop technique is a powerful tool - for detailed analysis on the geo-software. Thus, the integration between outcrops and subsurface data for reducing the subsurface uncertainties. This provides the impetus to propose and accomplish a holistic understanding of the architecture and geometry of the deltaic system and to provide an exhaustive analysis of their sedimentary processes. This study investigates the temporal and spatial distribution of deltaic sandstone using a combination of 3D Digital Outcrop Model (DOM) application and traditional geologic mapping of Balikpapan Formation in the Kutei Basin. Our study has successfully revealed that DOM is an excellent method to better understand the depositional process and facies architecture within the heterogeneity of deltaic system. The classification scheme presented in this study is also applicable to other sedimentological settings worldwide.

Experimental evidence for bifurcation angles control on abandoned channel fill geometry

The nature of abandoned channels' sedimentary fills has a significant influence on the development and evolution of floodplains and ultimately on fluvial reservoir geometry. A control of bifurcation geometry (i.e., bifurcation angle) on channel abandonment dynamics and resulting channel fills, such as sand plugs, has been intuited many times but never quantified. In this study, we present a series of experiments focusing on bedload transport designed to test the conditions for channel abandonment by modifying the bifurcation angle between channels, the flow incidence angles and the differential channel bottom slopes. We find that disconnection is possible in the case of asymmetrical bifurcations with high diversion angle (≥30∘) and quantify for the first time an inverse relationship between diversion angle and sand plug length and volume. The resulting sand plug formation is initiated in the flow separation zone at the external bank of the mouth of the diverted channel. Sedimentation in this zone induces a feedback loop leading to sand plug growth, discharge decrease and eventually to channel disconnection. Finally, the formation processes and final complex architecture of sand plugs are described, allowing for a better understanding of their geometry. Although our setup lacks some of the complexity of natural rivers, our results seem to apply at larger scales. Taken into account, these new data will improve fluvial (reservoir) models by incorporating more realistic topography and grain size description in abandoned channels.

Pressure behaviour of a horizontal well sandwiched between two parallel sealing faults

Generally, reservoir fluid flow is governed by diffusivity equation and solution to this equation helps to investigate pressure behaviour under certain reservoir and wellbore boundary conditions. In this paper however, the analytical solution method of Green and Source function is deployed to determine the performance of a horizontal well located between two parallel sealing faults, assuming simple rectangular reservoir geometry. Also, the dimensionless pressure and derivative approach is applied for all computations as it prevents the problem of unit conversions, reduces longer expressions and it helps to handle numerical values. The pressure expression derived from this work reveals that a maximum of two flow periods occur for the stated reservoir model. It was found out that an inverse relationship exists between dimensionless pressure and dimensionless length while pressure increased with thickness. Also high vertical permeability shortens the effect of the early radial flow period experienced by the horizontal well, thereby increasing productivity index. Finally, it was discovered that increased perforation length reduces the production potential of the horizontal well. Keywords: Dimensionless pressure, pressure derivatives, heterogeneity, pressure performance, reservoir and wellbore characterization.