Sedimentary, Diagenetic and Accumulation Characteristics of an Offshore Oil-gas Field—a Case Study of Huizhou Depression, Pearl River Mouth Basin, South China Sea

In the Z21 oil-gas field, a total of six depositional lithofacies and two depositional elements were identified based on core observation. Three main diagenetic processes, namely mechanical compaction, cementation, and dissolution of Miocene Zhujiang Formation sandstones were identified according to thin section and scanning electron microscope (SEM) of core samples. Cementations mainly contain silica cementation, carbonate cementation, clay minerals and pyrite. A total of three main pore types, residual primary intergranular pores, secondary dissolution pores and micropores, were identified. Sand sheet deposited in low-energy environment and is characterized by relatively low porosity and permeability values. Lager grain-sized sandstones are of higher quality compared to smaller-sized sandstones. Mechanical compaction, calcite cementation and clay mineral cementation play a key role in reducing porosity and permeability, whereas dissolution of feldspar and debris contribute significantly to improving the reservoir quality. The gas charge occurs prior to oil charge, forming a gas cap in the structural high and an oil ring in the lower formation. Irreducible water stored in the lenticular sandstone of low-porosity and permeability reservoir may convert to movable water as the drill and production perform.

Cement Paste Mixture Proportioning with Particle Packing Theory: An Ambiguous Effect of Microsilica

Recently, the research of innovative building materials is focused on applying supplementary materials in the form of micro- and nanopowders in cementitious composites due to the growing insistence on sustainable development. Considering above, in paper, a research on the effect of microsilica and SiO2 nanoparticles addition to cement paste, designed with Andreasen and Andersen (AA) packing density model (PDM), in terms of its physical and mechanical properties was conducted. Density, porosity, compressive strength, hardness, and modulus of indentation were investigated and compared regarding different amount of additives used in cement paste mixes. Microstructure of the obtained pastes was analyzed. The possibility of negative influence of alkali-silica reaction (ASR) on the mechanical properties of the obtained composites was analyzed. The results of the conducted investigations were discussed, and conclusions, also practical, were presented. The obtained results confirmed that the applied PDM may be an effective tool in cement paste design, when low porosity of prepared composite is required. On the other hand, the application of AA model did not bring satisfactory results of mechanical performance as expected, what was related, as shown by SEM imaging, with inhomogeneous dispersion of microsilica, and creation of agglomerates acting as reactive aggregates, what as a consequence caused ASR reaction, crack occurrence and lowered mechanical properties. Finally, the study found that the use of about 7.5% wt. of microsilica is the optimum in regards to obtain low porosity, while, to achieve improved mechanical properties, the use of 4 wt. % of microsilica seems to be optimal, in the case of tested cement pastes.

A Study of Unconventional Gas Accumulation in Dannevirke Series (Paleogene) Rocks, Canterbury Basin, New Zealand

<p>This thesis aims to assess the potential of unconventional gas accumulation of Danevirke aged (65-43 Ma) mudrock of the Canterbury Basin, South Island, New Zealand. Unconventional hydrocarbon resources contained in low-porosity, low-permeability rocks are potentially a large source of natural gas. Recent developments throughout the United States and increasingly so in Australia, signify a shift in exploration efforts from conventional natural gas targets towards unconventional shale gas plays and basin centred gas systems. Despite extensive international progress made in this field of exploration, little is known about New Zealand unconventional hydrocarbon systems. The Canterbury Basin is approximaty 360,000km² in area and is located approximately between 44°S and 46°S. The deepest part of the basin is located offshore and is known as the Clipper Sub-Basin, which exhibits economic basement depths of 6500m. The Clipper Sub-Basin is a late Cretaceous syn-rift horst and graben feature which trends north east-south west and is bound basinward by the Benreoch High and landward by the Canterbury Bight High. Dannevirke aged transgressive rocks overlay these structures and intermittently exhibit gas-charged intervals in low porosity facies. Elevated gas concentrations are recorded in four exploration wells in the Clipper Sub-Basin from gas chromatograph readings (up to 2 .7/00.4%). These high-gas zones correspond to intervals of elevated quartz (up to 72wt%), whereas non-gaseous intervals corresponded to quartz values as low as 30wt%. Scanning electron microscopy results do not reveal biogenic silica populations in the cutting samples examined. High silica is related to diagenetic silica transformations of mica, various clay minerals, pyrite and silica transformations. Although no visible porosity is observed in thin sections, FMI wireline analysis illustrate natural fractures predominately occur in siliceous intervals, where resistive fractures can account up to one fracture per 10m of stratigraphic thickness. These fissile or laminated brittle lithologies are likely hydrocarbon conduits or accumulation intervals for wet gas. RockEval pyrolysis results indicate the siliceous mudrocks are organic le-n, comprising an immature gas-prone source rock which averages 1.5% total organic carbon. Findings made in this research are compared to the. Whangai Formation, considered in this study to be a comparable shale gas system and also to the Monterey Formation of the United States which is a known basin centred gas system. Dannevirke aged sediments found in the Clipper Sub-Basin appear to constitute the requisites of a near-to-source, direct type., basin centred gas system. Implications of this study open up the possibility that New Zealand's widespread Paleocene-Eocene mudrocks are capable of natural gas accumulation and therefore viable natural gas exploration targets in New Zealand.</p>

A Study of Unconventional Gas Accumulation in Dannevirke Series (Paleogene) Rocks, Canterbury Basin, New Zealand

<p>This thesis aims to assess the potential of unconventional gas accumulation of Danevirke aged (65-43 Ma) mudrock of the Canterbury Basin, South Island, New Zealand. Unconventional hydrocarbon resources contained in low-porosity, low-permeability rocks are potentially a large source of natural gas. Recent developments throughout the United States and increasingly so in Australia, signify a shift in exploration efforts from conventional natural gas targets towards unconventional shale gas plays and basin centred gas systems. Despite extensive international progress made in this field of exploration, little is known about New Zealand unconventional hydrocarbon systems. The Canterbury Basin is approximaty 360,000km² in area and is located approximately between 44°S and 46°S. The deepest part of the basin is located offshore and is known as the Clipper Sub-Basin, which exhibits economic basement depths of 6500m. The Clipper Sub-Basin is a late Cretaceous syn-rift horst and graben feature which trends north east-south west and is bound basinward by the Benreoch High and landward by the Canterbury Bight High. Dannevirke aged transgressive rocks overlay these structures and intermittently exhibit gas-charged intervals in low porosity facies. Elevated gas concentrations are recorded in four exploration wells in the Clipper Sub-Basin from gas chromatograph readings (up to 2 .7/00.4%). These high-gas zones correspond to intervals of elevated quartz (up to 72wt%), whereas non-gaseous intervals corresponded to quartz values as low as 30wt%. Scanning electron microscopy results do not reveal biogenic silica populations in the cutting samples examined. High silica is related to diagenetic silica transformations of mica, various clay minerals, pyrite and silica transformations. Although no visible porosity is observed in thin sections, FMI wireline analysis illustrate natural fractures predominately occur in siliceous intervals, where resistive fractures can account up to one fracture per 10m of stratigraphic thickness. These fissile or laminated brittle lithologies are likely hydrocarbon conduits or accumulation intervals for wet gas. RockEval pyrolysis results indicate the siliceous mudrocks are organic le-n, comprising an immature gas-prone source rock which averages 1.5% total organic carbon. Findings made in this research are compared to the. Whangai Formation, considered in this study to be a comparable shale gas system and also to the Monterey Formation of the United States which is a known basin centred gas system. Dannevirke aged sediments found in the Clipper Sub-Basin appear to constitute the requisites of a near-to-source, direct type., basin centred gas system. Implications of this study open up the possibility that New Zealand's widespread Paleocene-Eocene mudrocks are capable of natural gas accumulation and therefore viable natural gas exploration targets in New Zealand.</p>

Compaction of crushed salt for safe containment – overview of the KOMPASS project

In Germany, rock salt formations are possible host rock candidates for a repository for heat-emitting radioactive waste. The safety concept of a repository in salt bases on a multibarrier system consisting mainly of the geological barrier salt and geotechnical seals ensuring safe containment. Crushed salt will be used for backfilling of cavities and sealing measures in drifts and shafts due to its favourable properties and its easy availability (mined-off material). The creep of the rock salt leads to crushed salt compaction with time. Thereby, the crushed salts' porosity is reduced from the initial porosity of 30 %–40 % to a value comparable to the porosity of undisturbed rock salt (≤1 %). In such low porosity ranges, technical impermeability is assumed. The compaction behaviour of crushed salt is rather complex and involves several coupled THM processes (Kröhn et al., 2017; Hansen et al., 2014). It is influenced by internal properties like humidity and grain size distribution, as well as boundary conditions such as temperature, compaction rate or stress state. However, the current process understanding has some important gaps referring to the material behaviour, experimental database and numerical modelling. It needs to be extended and validated, especially in the low porosity range. The objective of the KOMPASS project was development of methods and strategies for the reduction of deficits in the prediction of crushed salt compaction leading to an improvement of the prognosis quality. Key results are as follows (KOMPASS Phase 1, 2020): selection of an easily available and permanently producible synthetic crushed salt mixture, acting as a reference material for generic investigations; development and proof of different techniques for producing pre-compacted samples for further investigations; establishment of a tool of microstructure investigation methods to demonstrate the comparability of grain structures of pre-compacted samples with in-situ compacted material for future investigations; execution of various laboratory experiments using pre-compacted samples, e.g. long-term creep tests which deliver reliable information about time- and stress-dependent compaction behaviour; development of a complex experimental investigation strategy to derive necessary model parameters considering individual functional dependencies. Its technical feasibility was successfully verified; benchmarking with various existing numerical models using datasets from three different triaxial long-term tests. The result was not entirely satisfactory; however, the number of influencing factors is small and further validation work has to be done. Overall, the KOMPASS project has made significant progress in the approaches to solving the outstanding question, building the basis for further investigations.

Transient conduit permeability controlled by a shift between compactant shear and dilatant rupture at Unzen volcano (Japan)

The permeability of magma in shallow volcanic conduits controls the fluid flow and pore pressure development that regulates gas emissions and the style of volcanic eruptions. The architecture of the permeable porous structure is subject to changes as magma deforms and outgasses during ascent. Here, we present a high-resolution study of the permeability distribution across two conduit shear zones (marginal and central) developed in the dacitic spine that extruded towards the closing stages of the 1991–1995 eruption at Unzen volcano, Japan. The marginal shear zone is approximately 3.2 m wide and exhibits a 2-m wide, moderate shear zone with porosity and permeability similar to the conduit core, transitioning into a ~1-m wide, highly-sheared region with relatively low porosity and permeability, and an outer 20-cm wide cataclastic fault zone. The low porosity, highly-sheared rock further exhibits an anisotropic permeability network with slightly higher permeability along the shear plane (parallel to the conduit margin) and is locally overprinted by oblique dilational Riedel fractures. The central shear zone is defined by a 3-m long by ~9-cm wide fracture ending bluntly and bordered by a 15–40 cm wide damage zone with an increased permeability of ~3 orders of magnitude; directional permeability and resultant anisotropy could not be measured from this exposure. We interpret the permeability and porosity of the marginal shear zone to reflect the evolution of compactional (i.e., ductile) shear during ascent up to the point of rupture, estimated by Umakoshi et al. (2008), at ~500 m depth. At this point the compactional shear zone would have been locally overprinted by brittle rupture, promoting the development of a shear fault and dilational Riedel fractures during repeating phases of increased magma ascent rate, enhancing anisotropic permeability that channels fluid flow into, and along, the conduit margin. In contrast, we interpret the central shear zone as a shallow, late-stage dilational structure, which partially tore the spine core with slight displacement. We explore constraints from monitored seismicity and stick-slip behaviour to evaluate the rheological controls, which accompanied the upward shift from compactional toward dilational shear as magma approached the surface, and discuss their importance in controlling the permeability development of magma evolving from overall ductile to increasingly brittle behaviour during ascent and eruption.

Advances in Cased-Hole Formation Evaluation—The Access to Untapped Tight-Gas Resources in Mature Fields: A Case Study from the Dnieper-Donets Basin, Ukraine

The Sakhalin Field is located in the Dnieper-Donets Basin, east of Ukraine, and has been producing 7.7 billion cubic meters of natural gas in place from carboniferous rocks since the 1980s. Notwithstanding, it is strongly believed that significant untapped resources remain in the field, specifically those classified as tight intervals. Advances in wireline logging technology have brought, besides better accuracy on measurements behind the casing, a new measurement called fast neutron cross-section (FNXS), which has proved to be sensitive enough to the volume of gas in low-porosity formations. This enabled a quantitative interpretation for a better understanding of where these additional resources may lie in the Sakhalin Field. The methodology is based on advanced pulsed neutron spectroscopy logs to assess the essential formation properties such as lithology, porosity, and gas saturation and reduce the evaluation uncertainty in potential tight gas intervals. The advanced technology combines measurements from multiple detectors that represent independent formation properties such as formation sigma, thermal neutron porosity, FNXS, and elemental fractions. To address the lithology, the tool measures directly the rock elements required to determine representative mineralogy and matrix properties, which in turn are used to compensate for the matrix effects and obtain a reliable porosity and gas volume estimation. The methodology was tested on the upper Visean productive zones (Mississippian epoch) characterized by its low porosity (&lt;10 pu) and permeability (&lt;10 mD). In the past, those intervals have been overlooked because of inconclusive petrophysical interpretation based on basic openhole logs and their low production in some areas of the field. The necessity to finding new reserves has motivated the re-evaluation of possible bypassed tight-gas intervals by logging of mature wells behind casing in different sectors of the field. Advanced pulsed neutron spectroscopy logging behind casing uniquely identifies reserves in tight-gas intervals where basic open-hole interpretations were ambiguous. The gas production obtained from the perforated intervals supports the formation evaluation parameters estimated from the standalone interpretation of the pulsed neutron data. This work describes in detail the application of the alternative methodology and interpretation workflow to evaluate the formation through the casing. A concrete example is presented to illustrate the effectiveness of this approach in the revealing and development of tight gas reservoirs in mature fields in the Dnieper-Donets Basin.