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.

ANALISIS ELEMEN HINGGA NONLINIER BALOK GESER BETON MEMADAT MANDIRI DAN BETON MUTU TINGGI

<p align="center"><strong>Abstrak</strong></p><p class="11daftarpustaka"> </p><p class="11daftarpustaka">Indonesia merupakan negara yang rentan terhadap bencana gempa bumi. Banyak rumah atau gedung di Indonesia dibangun dengan menggunakan material beton bertulang. Kerusakan geser pada elemen beton bertulang tersebut sangat berbahaya, hal ini dikarenakan kerusakan ini terjadi secara tiba-tiba dan biasanya terjadi secara eksplosif. Analisis nonlinier elemen hingga tiga dimensi balok beton memadat mandiri dan beton mutu tinggi dengan pemadatan mekanis dilakukan dengan software MSC Marc/Mentat. Baja dimodelkan dengan tertanam di beton. Kriteria kegagalan Linier Mohr-Coulomb digunakan untuk beton dan Von Mises untuk baja tulangan. Hasil kurva hubungan beban-lendutan untuk kedua balok beton memadat mandiri dan beton mutu tinggi pemadatan mekanis hampir sama dengan hasil kurva eksperimen di daerah elastic, namun setelah melewati fase elastik, kurva analisis berbeda sedikit dengan kurva eksperimen. Hasil analisis teoritis kekuatan beton hampir sama dengan hasil analisis elemen hingga balok beton tanpa tulangan. Hasil analisis kontak juga memperlihatkan terjadi kontak dan perlepasan pada bidang kontak baja tumpuan beban dan tumpuan balok dengan beton.</p><p class="11daftarpustaka"> </p><p class="11daftarpustaka">Kata kunci: <em>beton memadat mandiri,</em><em> mutu tinggi, elemen hingga, MSC Marc/Mentat</em><em></em></p><p class="11daftarpustaka"> </p><p align="center"><strong> </strong></p><p align="center"><strong>Abstract</strong></p><p class="11daftarpustaka"> </p><p class="11daftarpustaka">Indonesia is a country that is prone to earthquakes. Many houses or buildings in Indonesia are built using reinforced concrete material. Shear damage to reinforced concrete elements is very dangerous, because this damage occurs suddenly and usually occurs explosively. The nonlinear three-dimensional finite element analysis of self-compacting concrete beam and high strength concrete beam by mechanical compaction were carried out using the MSC Marc/Mentat software. Steel is modeled by being embedded in concrete. The Mohr-Coulomb Linear failure criterion is used for concrete and Von Mises for reinforcing steel. The results of the load- deflection curves for both self-compacting and mechanical compaction high-strength concrete beams are almost the same as those of the experimental curves in the elastic area, after elasticity, the analysis curve differs slightly from the experimental curve. The results of the theoretical analysis of the strength of the concrete are almost the same as the results of the analysis of the finite element concrete beams without reinforcement. The results of the contact analysis also showed that there was contact and detachment in the contact area of the load bearing steel and the beam support with the concrete.</p><p class="11daftarpustaka"> </p><p class="11daftarpustaka">Keywords: <em>self-compacting concrete, high strength, finite element, MSC Marc/Mentat</em><em></em></p>

Structural diagenesis in ultra-deep tight sandstones in Kuqa depression, Tarim Basin, China

The Lower Cretaceous Bashijiqike Formation of Kuqa depression is ultra-deeply buried sandstone in fold-and-thrust belts. Few researches link diagenetic processes with structure. To fill this gap, a comprehensive analysis integrating diagenesis with structure pattern, fracture and in situ stress is performed following a structural diagenetic approach. The results show that the pore spaces include residual intergranular pores, intergranular and intragranular dissolution pores, and micro-fractures. The sandstones experienced a high degree of mechanical compaction, and compaction is limited in well-sorted rocks or abundant in rigid quartz grains. The most volumetrically important diagenetic minerals are calcites. The framework grains experienced a varied degree of dissolution, and intergranular and intragranular dissolution pores are formed. Special aims are paid on the dissolution associated with the fracture planes. Most natural fractures are cemented by carbonate cements, which limit fluid flow. In addition, presences of fracture enhance dissolution, and the fracture planes are enlarged by dissolution. Cementation and dissolution can occur simultaneously in fracture surfaces, and the enlarged fracture surfaces can be cemented by late-stage cements. The in situ stress magnitudes are calculated using well logs. The horizontal stress difference (Δσ) determines the degree of mechanical compaction, and rocks associated with low Δσ experienced a low degree of compaction, and there contain preserved intergranular pores. Natural fractures are mainly related to the low Δσ layers. The presences of intergranular and intragranular dissolution pores are mainly associated with the fractured zones. The high quality reservoirs with intergranular pores or fractures are related to low Δσ layers. The structural diagenesis researches above help the prediction of reservoir quality in ultra-deep sandstones, and reduce the uncertainty in deep natural gas exploration in Kuqa depression.

Influence of diagenetic features on petrophysical properties of fine-grained rocks of Oligocene strata in the Lower Indus Basin, Pakistan

Nari Formation is considered as one of the most important oil and gas exploration targets. These fine-grained tight sandstone reservoirs face enormous challenges due to their extremely low matrix porosity and permeability. Hence, in this regard, the study was carried out to collect the high-quality data on petrophysical properties along with mineralogy and microstructural characteristics and diagenesis. The experiments performed includes the petrographic study and scanning electron microscopy, and X-ray diffraction analyses. Besides, the measurement of petrophysical properties was carried out to assess the likely influence of the reservoir quality. The petrographic analysis shows predominantly fine- to medium-grained grey samples along with calcite, clay, lithic fragments and iron oxides. Further, the thin-section observations revealed that the quartz is a principal mineral component in all the analysed samples ranging from 52.2 to 92.9%. The bulk volume of clay minerals that range from 5.3 to 16.1% of. The porosity and permeability measured range from 5.08 to 18.56% (average 7.22%) and from 0.0152 to 377 mD (average 0.25 mD), respectively. The main diagenetic processes that affected the sandstones of Nari Formation are mechanical compaction, grain deformation, cementation and quartz dissolution and have played a significant role in influencing the quality of the reservoir rock. Overall, it appears that the primary petrophysical properties (porosity and permeability) were decreased due to the mechanical compaction, lithification, cementation, and framework grain dissolution. Based on the integrated mineralogical, microstructural analysis, and the laboratory-based petrophysical properties, the samples exhibited poor porosity, permeability, and moderate clay content, which indicate that the Nari Formation is a poor quality reservoir.

Petrography, Provenance And Diagenesis Of Murree Group Exposed along Basohli- Bani Road, Kathua District, Jammu and Kashmir

Sandstones of Murree Group of rocks exposed along Bani- Basohli road, Kathua District in Jammu were analyzed for petrography, petrofacies and provenance. These sandstones are classified as sublithic arenites and have been derived from mixed provenance including plutonic basement, sedimentary and metasedimentary rocks. Different types of quartz grains and other constituent minerals suggest the source from lower and middle and upper rank metamorphic terrains of the continental block-recycled orogen and subduction zone complex. The imprints of shallow burial diagenesis suggest low mechanical compaction probably just before cementation leading to moderate packing and reduction of porosity.

Diagenesis and Porosity Evolution of the Pachmarhi Sandstones (Early Triassic), Satpura Gondwana Basin, Central India

This study deals with the diagenetic history of the Pachmarhi Sandstones of Satpura Gondwana Basin, Central India. The sandstones are classified as quartz-arenite and sub-arkose type. Monocrystalline quartz grains dominate the detrital mineralogy followed by polycrystalline quartz grains, feldspars (more alkali-feldspar than plagioclase), rock fragments, detrital mica and heavy minerals. The diagenetic signatures observed in the Pachmarhi Sandstones include mechanical compaction, cementation (Fe-oxide, quartz overgrowths, calcite, matrix and clay minerals), replacement and dissolution of feldspar and calcite cement. The most commonly observed type of secondary porosity is dissolution of feldspars. The porosity loss is mainly due to cementation by pore occlusion and by early stage of mechanical compaction. In addition, several clay minerals occurred as pore-filling and pore-lining cements. The nature of various types of grain- to grain contacts suggests early cementation and consequent minor compaction. Among the various cements, calcite is the earliest followed by iron oxide while silica cementation occurred probably at a late stage. The carbonate cement formed during burial by dissolution and re-precipitation represents redistributed calcite which was buried with the sandstone. The iron cement was perhaps derived from weathering and leaching of ferromagnesian minerals of overlying Deccan traps. Silica cement was derived from the corrosion of quartz and feldspar grains. Types of grain contacts, minus-cement porosity and porosity reduction indicate a shallow depth of burial conditions for these sandstones.

Hepatic Polarization Accelerated by Mechanical Compaction Involves HNF4α Activation

There remain few data about the role of homeostatic compaction in hepatic polarization. A previous study has found that mechanical compaction can accelerate hepatocyte polarization; however, the cellular mechanism underlying the effect is mostly unclear. Hepatocyte nuclear factor 4 alpha (HNF4α) is crucial for hepatic polarization in liver morphogenesis. Therefore, we sought to identify any possible involvement of HNF4α in the process of hepatocyte polarization accelerated by mechanical compaction. We first verified in the nonhepatic cell model HEK-293T, and the hepatic cell model primary hepatocytes that the mechanical compaction on cell aggregates simulated by using transient centrifugation can directly activate the expression of HNF4α promoters. Moreover, data using primary hepatocytes showed that the HNF4α expression is positively associated with the levels of compaction force: 2.1-folds higher at the mRNA level and 2.1-folds higher at the protein level for 500 g vs. 0 g. Furthermore, activated HNF4α expression is associated with the enhanced biliary canalicular formation and the increased production of albumin and urea. Pretreatment with Latrunculin B, an inhibitor of F-actin, and SHE78-7, an inhibitor of E-cadherin, which both interrupt the pathway of mechanical transduction, partially but significantly reduced the HNF4α expression and production of albumin and urea. In conclusion, HNF4α can be actively involved in the hepatic polarization in the context of environmental mechanical compaction.