Shale Porosities from Well Logs on Haltenbanken (Offshore Mid-Norway) Show No Influence of Overpressuring

Hermanrud, Christian; Wensaas, Lars; Teige, Gunn M. G.; Bolås, Hege M. Nordgård; Hansen, S. M.; Vik, E.

doi:10.1306/m70615c4

Cited by 34 publications

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“…As a test of the hypothesis of Hermanrud et al (1998), and, by implication, Bowers (2001), the resistivity log should react in a similar manner to the sonic log, that is, a response to sediment unloading. This paper focuses primarily on two wells, B-11 in the Bekapai Field and SEM-39 in the Semberah Field.…”

Section: Methodsmentioning

confidence: 99%

“…It also has utility in interpreting pore pressure, and is commonly used for this purpose, more often in association with Eaton (1975), where disequilibrium compaction is present. The hypothesis tested here is based on observations by Hermanrud et al (1998) where log responses in the intra-Jurassic shales, Norway, revealed that neutron and density logs do not show a significant difference in porosity between shales that are low vs. high in overpressure, whereas the sonic and resistivity responses show higher (apparent) porosity differences. It is suggested that the porosity is unaffected by differences in pore pressures, but that the sonic and resistivity logs are reacting to textural changes induced in the shales by overpressure rather than high porosities due to undercompaction.…”

Section: Introductionmentioning

confidence: 97%

“…As it seems that the resistivity log is also reacting to overpressure in these published studies by Hermanrud et al (1998) and Bowers (2001), it is proposed in this paper that resistivity data could be utilized in a similar way to sonic data to produce an approach to interpret pore pressure when unloading is present. This has not been previously investigated and published.…”

Section: Introductionmentioning

confidence: 99%

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The Resistivity Log and Its Role in Understanding Sediment Unloading in the Lower Kutai Basin, Indonesia

O’Connor,

Ramdhan,

Arifin

et al. 2023

Indonesian J. Geosci.

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High overpressure is a critical drilling issue in the Lower Kutai Basin. Typical pore pressure prediction approaches involve an empirical relationship, such as Eaton’s method using sonic log data. In areas with high geothermal gradients, such as the Lower Kutai Basin, there is evidence for additional overpressure from gas generation such that sediment unloading must be considered to interpret pore pressure correctly. In this paper a repeatable deterministic model is presented for pore pressure from sonic data and, using selected wells from the Lower Kutai Basin, also the use of the resistivity log in a similar model. In the Lower Kutai Basin, sonic logs are often absent from the logging suite or otherwise running over limited intervals, making an alternative log-based prediction method particularly valuable. As a caveat, shallow freshwater encroachment is reported in the Lower Kutai Basin, means the shallow resistivity data can be problematic to use to define both top of overpressure and a normal compaction trend. Care must therefore be taken if resistivity is to be used for the interpretation of unloaded pore pressure, and chiefly applied and this likely to be more successful where encroachment is less pronounced, such as pro-delta shales. Assuming the additional care needed in using resistivity data, this paper suggests that resistivity can be a useful tool for pore pressure prediction in unloaded shale at elevated temperatures within the Lower Kutai Basin. At present the technique has been applied to only a limited dataset due to data availability limitations, but it is hoped with further refinement it will form a helpful additional approach in the pore pressure prediction toolkit. Keywords: pore pressure, resistivity, unloading, Lower Kutai Basin

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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The Resistivity Log and Its Role in Understanding Sediment Unloading in the Lower Kutai Basin, Indonesia

O’Connor,

Ramdhan,

Arifin

et al. 2023

Indonesian J. Geosci.

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“…The comprehensive compaction curve (Figure 3) plotted for all 10 members in the study area (Chang 1-10), shows a trend that, from Chang 1 to Chang 4 + 5, the acoustic travel time decreases, while the deep lateral resistivity increases, the formation density increases, and the neutron porosity decreases; below Chang 4 + 5, from Chang 6 to Chang 8, the acoustic travel time, resistivity, density, and neutron porosity show reverse behavior and are synchronized. Only when this synchronization occurs can the segmented compaction of mudstone be confirmed (Fertl and Timko, 1972;Hermanrud et al, 1998). Thus, it can be confirmed that Chang 1 to Chang 4 + 5 is a normal compaction segment, and Chang 6 to Chang 8 is an under-compaction segment.…”

Section: Segmentation Of Mudstone Compactionmentioning

confidence: 97%

Reservoir Forming Dynamics of Differential Accumulation of Tight Oil in the Yanchang Formation Chang 8 Member in the Longdong Area, Ordos Basin, Central China

Yang

Liu

2022

Front. Earth Sci.

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Tight oil is usually accumulated near source rocks after short-distance migration. For the Chang 8 member tight oil reservoir in the Longdong area of the Ordos Basin, however, the tight oil accumulation does not completely follow the source control theory, which states that richer tight oil is found in zones closer to the source rock. The causes behind such differential accumulation need to be investigated. On the basis of previous studies, this paper accurately restores the oil migration dynamics in the main reservoir-forming period by using the latest paleo-hydrodynamic restoration technology through mudstone compaction analysis. The oil migration dynamics are then compared with the start-up pressure gradient of the transport layer along the potential oil migration path during the main reservoir-forming period. Finally, combined with the paleo-structural characteristics during the main reservoir-forming period, the causes for the differential accumulation of tight oil in the Chang 8 member of the Longdong area are analyzed. The results show that: 1) during the main reservoir-forming period, tight oil in the Chang 8 member tended to and could migrate from the north and northeast to the southwest and has accumulated in the nose-like paleo-structure in the southwest; and 2) following the main reservoir-forming period, as the reservoir formation was compacted and the fluid pressure and hydrocarbon generation capacity reduced, oil accumulated nearer the source rock, and to a lesser extent than it did during the reservoir-forming period. In these two stages, changes in the intensity of oil migration dynamics dominated the differential accumulation of tight oil. This study provides a new perspective for similar efforts.

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“…Measured pressure data, mud weight and well logs can reflect the relationship between formation pressure and depth (Hermanrud et al, 1998;Tingay et al, 2013). The principle of the equilibrium depth method is that in a set of strata with the same properties, regardless of the formation temperature, where strata at different depths have the same porosity, the skeleton stress between rock particles will be the same.…”

Section: Pressure Evolution 421 Pressure Characteristicsmentioning

confidence: 99%

Fluid Charging and Paleo‐pressure Evolution in the Ledong Slope Zone of the Yinggehai Basin, South China Sea

Zhao

Huang

et al. 2023

Acta Geologica Sinica (Eng)

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Large numbers of gas reservoirs have been discovered in overpressure basins. Fluid charging has a close relationship with paleo‐pressure evolution, affecting the migration of gas reservoirs. To study fluid charging and the related pressure system, we analyzed burial histories and fluid inclusion (PVTx) simulations and conducted basin modeling of the Ledong Slope Zone in the Yinggehai Basin as an example. On the basis of fluid‐inclusion assemblages (FIAs), homogenization temperature (Th), final melting temperature (Tm, ice) and Raman spectroscopy in fluid inclusions, there are three stages of fluid charging: during the first and second stage, methane‐dominated fluid was charged at 2.2–1.7 Ma and 1.7–0.9 Ma, respectively. In the third stage, CO2‐rich hydrothermal fluid was charged since 0.9 Ma. It could be concluded from the well‐logging data that the disequilibrium compaction in the Yinggehai Fm., along with the fluid expansion and clay diagenesis in the Huangliu and Meishan formations, resulted in the overpressure in the Ledong slope zone. The evolution of paleo‐pressure was affected by the sedimentation rate of the Yinggehai Fm., as well as the hydrocarbon generation rate. Additionally, the Ledong Slope Zone is less affected by diapir activity than the nearby diapir area. Based on fluid inclusions, paleo‐pressure, basin modeling and geological background, the gas migration history of the Ledong Slope Zone can be divided into four stages: in the first stage, excess pressure was formed around 5 Ma; from 2.2 to 1.7 Ma, there was a reduction in the charging of hydrocarbon fluid and steadily increasing excess pressure; during the 1.7–0.9 Ma period a large amount of hydrocarbon was generated, excess pressure increasing significantly and hydraulic fractures forming in mudstones, With gas reservoirs developing in structural highs; since 0.9 Ma, CO2‐rich hydrothermal fluid accumulated in reservoirs adjacent to faults and the pressure coefficient remained stable. The research results are helpful in the study of fluid migration and accumulation mechanisms in overpressure basins.

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Shale Porosities from Well Logs on Haltenbanken (Offshore Mid-Norway) Show No Influence of Overpressuring

Cited by 34 publications

References 0 publications

The Resistivity Log and Its Role in Understanding Sediment Unloading in the Lower Kutai Basin, Indonesia

The Resistivity Log and Its Role in Understanding Sediment Unloading in the Lower Kutai Basin, Indonesia

Reservoir Forming Dynamics of Differential Accumulation of Tight Oil in the Yanchang Formation Chang 8 Member in the Longdong Area, Ordos Basin, Central China

Fluid Charging and Paleo‐pressure Evolution in the Ledong Slope Zone of the Yinggehai Basin, South China Sea

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