scholarly journals Characteristics and formation mechanisms of silicified carbonate reservoirs in well SN4 of the Tarim Basin

2018 ◽  
Vol 36 (4) ◽  
pp. 820-849 ◽  
Author(s):  
Donghua You ◽  
Jun Han ◽  
Wenxuan Hu ◽  
Yixiong Qian ◽  
Qianglu Chen ◽  
...  
Keyword(s):  
Tarim Basin ◽  
Hydrothermal Fluid ◽  
High Salinity ◽  
Carbonate Reservoirs ◽  
High Yield ◽  
Formation Mechanisms ◽  
Lower Section ◽  
Yingshan Formation ◽  
Low Salinity ◽  
Homogenization Temperatures

High-yield natural gas was discovered in well SN4 in the Ordovician Yingshan Formation in the Tarim Basin. The gas is found in unusual, silicified, carbonate reservoirs. According to the degree of silicification, the silicified reservoirs can be divided into a lower section of silicified carbonates, a middle section of limestone, and an upper section of silicified carbonates. The silicified carbonates are mainly composed of quartz and calcite, in which the reservoir space mostly occurs as vugs, inter-crystalline pores of quartz, and partial fractures. Porosity varies widely, ranging from 3 to 20.5% with strong heterogeneity. The homogenization temperatures of fluid inclusions in quartz and calcite show that the silicification temperatures were 150–190°C, with characteristics of high temperature/low salinity and low temperature/high salinity. The 87Sr/86Sr ratios of secondary calcite are 0.709336–0.709732, which are significantly higher than that of concurrent seawater, indicating that the hydrothermal fluid originated from the deep clastic strata or the basement (sialic rock). The δ13C values of the secondary calcite are similar to that of the surrounding limestone, indicating that the carbon in the secondary calcite is derived from the limestone strata, and that the secondary calcite is the product of dissolution and re-precipitation resulting from interaction between the silica-bearing hydrothermal fluids and surrounding limestones. The silicification of silica-bearing hydrothermal fluid was significantly controlled by strike-slip faults. The fluids ascending along the fault zone and branch faults interacted with the surrounding limestone in the Yingshan Formation. As a result, a large amount of quartz and secondary calcite were formed together with various types of secondary pores, resulting in excellent reservoirs.

Carbon-Isotope, Diatom, and Pollen Evidence for Late Holocene Salinity Change in a Brackish Marsh in the San Francisco Estuary

2001 ◽  
Vol 55 (1) ◽  
pp. 66-76 ◽  
Author(s):  
Roger Byrne ◽  
B. Lynn Ingram ◽  
Scott Starratt ◽  
Frances Malamud-Roam ◽  
Joshua N. Collins ◽  
...  
Keyword(s):  
San Francisco ◽  
High Salinity ◽  
Carbon Isotopic Composition ◽  
Brackish Marsh ◽  
San Francisco Estuary ◽  
Freshwater Inflow ◽  
Water Diversion ◽  
Freshwater Flow ◽  
Low Salinity ◽  
Carbon Isotopic

AbstractAnalysis of diatoms, pollen, and the carbon-isotopic composition of a sediment core from a brackish marsh in the northern part of the San Francisco Estuary has provided a paleosalinity record that covers the past 3000 yr. Changes in marsh composition and diatom frequencies are assumed to represent variations in freshwater inflow to the estuary. Three periods of relatively high salinity (low freshwater inflow) are indicated, 3000 to 2500 cal yr B.P., 1700 to 730 cal yr B.P., and ca. A.D. 1930 to the present. The most recent period of high salinity is primarily due to upstream storage and water diversion within the Sacramento–San Joaquin watershed, although drought may also have been a factor. The two earlier high-salinity periods are likely the result of reduced precipitation. Low salinity (high freshwater flow) is indicated for the period 750 cal yr B.P. to A.D. 1930.

Expanding Polymer Injectivity Tests on a Second Giant Carbonate UAE Oil Reservoir at High Salinity & High Temperature Conditions.

2021 ◽  
Author(s):  
S.A. Baloch ◽  
J.M. Leon ◽  
S.K. Masalmeh ◽  
D. Chappell ◽  
J. Brodie ◽  
...  
Keyword(s):  
High Temperature ◽  
Polymer Solution ◽  
High Salinity ◽  
Laboratory Data ◽  
Experimental Studies ◽  
Carbonate Reservoirs ◽  
Field Conditions ◽  
Sweep Efficiency ◽  
Tertiary Butyl ◽  
Solution Preparation

Abstract Over the last few years, ADNOC has systematically investigated a new polymer-based EOR scheme to improve sweep efficiency in high temperature and high salinity (HTHS) carbonate reservoirs in Abu Dhabi (Masalmeh et al., 2014). Consequently, ADNOC has developed a thorough de-risking program for the new EOR concept in these carbonate reservoirs. The de-risking program includes extensive laboratory experimental studies and field injectivity tests to ensure that the selected polymer can be propagated in the target reservoirs. A new polymer with high 2-acrylamido-tertiary-butyl sulfonic acid (ATBS) content was identified, based on extensive laboratory studies (Masalmeh, et al., 2019, Dupuis, et al., 2017, Jouenne 2020), and an initial polymer injectivity test (PIT) was conducted in 2019 at 250°F and salinity >200,000 ppm, with low H2S content (Rachapudi, et al., 2020, Leon and Masalmeh, 2021). The next step for ADNOC was to extend polymer application to harsher field conditions, including higher H2S content. Accordingly, a PIT was designed in preparation for a multi-well pilot This paper presents ADNOC's follow-up PIT, which expands the envelope of polymer flooding to dissolve H2S concentrations of 20 - 40 ppm to confirm injectivity at representative field conditions and in situ polymer performance. The PIT was executed over five months, from February 2021 to July 2021, followed by a chase water flood that will run until December 2021. A total of 108,392 barrels of polymer solution were successfully injected during the PIT. The extensive dataset acquired was used to assess injectivity and in-depth mobility reduction associated with the new polymer. Preliminary results from the PIT suggest that all key performance indicators have been achieved, with a predictable viscosity yield and good injectivity at target rates, consistent with the laboratory data. The use of a down-hole shut-in tool (DHSIT) to acquire pressure fall-off (PFO) data clarified the near-wellbore behaviour of the polymer and allowed optimisation of the PIT programme. This paper assesses the importance of water quality on polymer solution preparation and injection performance and reviews operational data acquired during the testing period. Polymer properties determined during the PIT will be used to optimise field and sector models and will facilitate the evaluation of polymer EOR in other giant, heterogeneous carbonate reservoirs, leading to improved recovery in ADNOC and Middle East reservoirs.

Spatial and seasonal variability of emergent aquatic insects and nearshore spiders in a subtropical estuary

2019 ◽  
Vol 70 (4) ◽  
pp. 541 ◽  
Author(s):  
Martha J. Zapata ◽  
S. Mažeika P. Sullivan
Keyword(s):  
Aquatic Insects ◽  
High Salinity ◽  
Aquatic Insect ◽  
Freshwater Ecosystems ◽  
Dispersal Ability ◽  
Insect Community ◽  
Insect Communities ◽  
Low Salinity ◽  
Subtropical Estuary ◽  
Adult Aquatic Insects

Variability in the density and distribution of adult aquatic insects is an important factor mediating aquatic-to-terrestrial nutritional subsidies in freshwater ecosystems, yet less is understood about insect-facilitated subsidy dynamics in estuaries. We surveyed emergent (i.e. adult) aquatic insects and nearshore orb-weaving spiders of the families Tetragnathidae and Araneidae in a subtropical estuary of Florida (USA). Emergent insect community composition varied seasonally and spatially; densities were lower at high- than low-salinity sites. At high-salinity sites, emergent insects exhibited lower dispersal ability and a higher prevalence of univoltinism than low- and mid-salinity assemblages. Orb-weaving spider density most strongly tracked emergent insect density rates at low- and mid-salinity sites. Tetragnatha body condition was 96% higher at high-salinity sites than at low-salinity sites. Our findings contribute to our understanding of aquatic insect communities in estuarine ecosystems and indicate that aquatic insects may provide important nutritional subsidies to riparian consumers despite their depressed abundance and diversity compared with freshwater ecosystems.

scholarly journals Precious Metal Enrichment at the Myra Falls VMS Deposit, British Columbia, Canada

Geosciences ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 422
Author(s):  
Daniel Marshall ◽  
Carol-Anne Nicol ◽  
Robert Greene ◽  
Rick Sawyer ◽  
Armond Stansell ◽  
...  
Keyword(s):  
Fluid Inclusion ◽  
Precious Metal ◽  
Metal Enrichment ◽  
Sea Floor ◽  
North West ◽  
Low Salinity ◽  
Volcanogenic Massive Sulphide ◽  
Igneous Fluids ◽  
Homogenization Temperatures ◽  
Water Depths

Gold, present as electrum, in the Battle Gap, Ridge North-West, HW, and Price deposits at the Myra Falls mine, occurs in late veinlets cutting the earlier volcanogenic massive sulphide (VMS) lithologies. The ore mineral assemblage containing the electrum comprises dominantly galena, tennantite, bornite, sphalerite, chalcopyrite, pyrite, and rarely stromeyerite, and is defined as an Au-Zn-Pb-As-Sb association. The gangue is comprised of barite, quartz, and minor feldspathic volcanogenic sedimentary rocks and clay, comprised predominantly of kaolinite with subordinate illite. The deposition of gold as electrum in the baritic upper portions of the sulphide lenses occurs at relatively shallow water depths beneath the sea floor. Primary, pseudosecondary, and secondary fluid inclusions, petrographically related to gold, show boiling fluid inclusion assemblages in the range of 123 to 173 °C, with compositions and eutectic melt temperatures consistent with seawater at approximately 3.2 wt % NaCl equivalent. The fluid inclusion homogenization temperatures are consistent with boiling seawater corresponding to water depths ranging from 15 to 125 m. Slightly more dilute brines corresponding to salinities of approximately 1 wt % NaCl indicate that there is input from very low-salinity brines, which could represent a transition from subaqueous VMS to epithermal-like conditions for precious metal enrichment, mixing with re-condensed vapor, or very low-salinity igneous fluids.

scholarly journals Bulk and Surface Aqueous Speciation of Calcite: Implications for Low-Salinity Waterflooding of Carbonate Reservoirs

SPE Journal ◽  
2017 ◽  
Vol 23 (01) ◽  
pp. 84-101 ◽  
Author(s):  
Maxim P. Yutkin ◽  
Himanshu Mishra ◽  
Tadeusz W. Patzek ◽  
John Lee ◽  
Clayton J. Radke
Keyword(s):  
Ionic Strength ◽  
Ion Exchange ◽  
Crude Oil ◽  
Surface Charge ◽  
Double Layer ◽  
Carbonate Reservoir ◽  
Carbonate Reservoirs ◽  
Diffuse Double Layer ◽  
Low Salinity ◽  
Low Salinity Waterflooding

Summary Low-salinity waterflooding (LSW) is ineffective when reservoir rock is strongly water-wet or when crude oil is not asphaltenic. Success of LSW relies heavily on the ability of injected brine to alter surface chemistry of reservoir crude-oil brine/rock (COBR) interfaces. Implementation of LSW in carbonate reservoirs is especially challenging because of high reservoir-brine salinity and, more importantly, because of high reactivity of the rock minerals. Both features complicate understanding of the COBR surface chemistries pertinent to successful LSW. Here, we tackle the complex physicochemical processes in chemically active carbonates flooded with diluted brine that is saturated with atmospheric carbon dioxide (CO2) and possibly supplemented with additional ionic species, such as sulfates or phosphates. When waterflooding carbonate reservoirs, rock equilibrates with the injected brine over short distances. Injected-brine ion speciation is shifted substantially in the presence of reactive carbonate rock. Our new calculations demonstrate that rock-equilibrated aqueous pH is slightly alkaline quite independent of injected-brine pH. We establish, for the first time, that CO2 content of a carbonate reservoir, originating from CO2-rich crude oil and gas, plays a dominant role in setting aqueous pH and rock-surface speciation. A simple ion-complexing model predicts the calcite-surface charge as a function of composition of reservoir brine. The surface charge of calcite may be positive or negative, depending on speciation of reservoir brine in contact with the calcite. There is no single point of zero charge; all dissolved aqueous species are charge determining. Rock-equilibrated aqueous composition controls the calcite-surface ion-exchange behavior, not the injected-brine composition. At high ionic strength, the electrical double layer collapses and is no longer diffuse. All surface charges are located directly in the inner and outer Helmholtz planes. Our evaluation of calcite bulk and surface equilibria draws several important inferences about the proposed LSW oil-recovery mechanisms. Diffuse double-layer expansion (DLE) is impossible for brine ionic strength greater than 0.1 molar. Because of rapid rock/brine equilibration, the dissolution mechanism for releasing adhered oil is eliminated. Also, fines mobilization and concomitant oil release cannot occur because there are few loose fines and clays in a majority of carbonates. LSW cannot be a low-interfacial-tension alkaline flood because carbonate dissolution exhausts all injected base near the wellbore and lowers pH to that set by the rock and by formation CO2. In spite of diffuse double-layer collapse in carbonate reservoirs, surface ion-exchange oil release remains feasible, but unproved.

scholarly journals Fluid Inclusion and Oxygen Isotope Constraints on the Origin and Hydrothermal Evolution of the Haisugou Porphyry Mo Deposit in the Northern Xilamulun District, NE China

Geofluids ◽  
2017 ◽  
Vol 2017 ◽  
pp. 1-19 ◽  
Author(s):  
Qihai Shu ◽  
Yong Lai
Keyword(s):  
Fluid Inclusion ◽  
Meteoric Water ◽  
Early Time ◽  
Low Oxygen ◽  
Potassic Alteration ◽  
Low Salinity ◽  
Oxygen Isotopic ◽  
Homogenization Temperatures ◽  
Porphyry Mo Deposit ◽  
Positive Correlations

The Haisugou porphyry Mo deposit is located in the northern Xilamulun district, northeastern China. Based on alteration and mineralization styles and crosscutting relationships, the hydrothermal evolution in Haisugou can be divided into three stages: an early potassic alteration stage with no significant metal deposition, a synmineralization sericite-chlorite alteration stage with extensive Mo precipitation, and a postmineralization stage characterized by barren quartz and minor calcite and fluorite. The coexistence of high-salinity brine inclusions with low-salinity inclusions both in potassic alteration stage (~440°C) and locally in the early time of mineralization stage (380–320°C) indicates the occurrence of fluid boiling. The positive correlations between the homogenization temperatures and the salinities of the fluids and the low oxygen isotopic compositions (δ18Ofluid < 3‰) of the syn- to postmineralization quartz together suggest the mixing of magmatic fluids with meteoric water, which dominated the whole mineralization process. The early boiling fluids were not responsible for ore precipitation, whereas the mixing with meteoric water, which resulted in temperature decrease and dilution that significantly reduced the metal solubility, should have played the major role in Mo mineralization. Combined fluid inclusion microthermometry and chlorite geothermometer results reveal that ore deposition mainly occurred between 350 and 290°C in Haisugou.

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