Turbidite Reservoirs in the Dongying Sag,Bohai Bay Basin:Interactions between Carbonate Cementation and Hydrocarbon Charge

Turbidite sandstones have become increasingly significant in hydrocarbon exploration.Carbonate cementation occur commonly in turbidite reservoirs developing within the Paleocene lacustrine basins,Northeastern China.This study utilizes core data,thin section data and production data to investigate the interaction between the carbonate cementation and hydrocarbon charge within turbidite reservoirs in the Niuzhuang Sub-sag of the Dongying Sag,Bohai Bay Basin,East China.The results reveal that the carbonate cementation is mainly developed at the top and bottom of the turbidite sandbodies,and even forms carbonate cement shells.Three stages of hydrocarbon accumulation are identified based on fluid inclusion analysis:stage I(27.5–24.6 Ma),stage II(14.0–5.0 Ma),and stage III(5.0–0 Ma).The interaction between the carbonate cementation and hydrocarbon charge has significant controls on the formation of a turbidite reservoir.The temporal relations and intensity relations between the two factors should be considered significantly.Moreover,hydrocarbon charge during the early stage can inhibit the carbonate cementation,favoring the hydrocarbon accumulation in turbidite reservoirs.Many deep-lacustrine turbidite sandbodies surrounded by source rocks with abnormal high pressure,are also favorable for hydrocarbon accumulation.These results suggest that some deeply buried turbidite sandbodies with similar geological settings have high potential for hydrocarbon exploration.

Mechanism of carbonate cementation and its influence on reservoir in Pinghu Formation of Xihu Sag

Carbonate cements are the most abundant authigenic mineral and impact on physical properties greatly in sandstone reservoir.In this paper,Pinghu Formation of Xihu Sag was taken as a target.Characteristics,distribution and formation of carbonate cements were investigated via optical microscopy,cathodoluminescence(CL),electron probe and in-situ carbon-oxygen isotope.The results showed that carbonate cements varied in types and shapes.Calcite/dolomite mainly present as poikilotopic cements,while ferrocalcite/ferrodolomite/ankerite generally present as pore-filling cements.Carbon isotope(δ^(13)C)values of carbonate cements were ranging from–7.77‰to–2.67‰,with an average of–4.52‰,while oxygen isotope(δ^(18)O)values were ranging from–18.94‰to–12.04‰,with an average of–14.86‰.Theδ^(13)C/δ^(18)O indicated that the paleo-fluid of carbonate cement was mainly freshwater.Organic carbon mainly came from organic matter within mature source rocks,and inorganic carbon came from dissolution of carbonate debris and early carbonate cements.Distinctiveδ^(13)C/δ^(18)O values manifest that carbonate cements with different types formed in different periods,which make different contributions to the reservoir properties.Calcite/dolomite formed during eodiagenesis(70–90℃)and early mesodiagenesis stage(90–120℃),and were favorable to reservoir owing to their compacted resistance and selective dissolution.Ferrocalcite/ferrodolomite/ankerite formed during middle-late mesodiagenetic stage(above 120℃),and were unfavorable to reservoir due to cementing the residual intergranular pores.Hence,in order to evaluate the reservoir characteristics,it is of significantly important to distinguish different types of carbonate cements and explore their origins.

Characteristics of carbonate cementation in clastic rocks from the Chang 6 sandbody of Yanchang Formation, southern Ordos Basin

Densification of reservoir is an important factor that restricts oil and gas exploration from low porosity and extra-low permeability reservoirs. Carbonate cementation was heavily developed in Chang 6 sandbody, a facies of underwater distributary channel in delta front, of Upper Triassic Yanchang Formation in Fuxian area, southern Ordos Basin, and the cementation is one of the major factors that affect quality of reservoir. Based on the macro-microcosmic petrology and geochemistry features, the genesis of densification of carbonate-cemented reservoir was systematically discussed. The carbonate cementation can be classified into endogenous and exogenous, and the essential differences between them are that they were formed in different fluids and in different diagenesis periods. With the aid of identification of thin sections, analyses on electron probe, trace and rare-earth elements, carbon and oxygen isotope, we propose that the endogenous fluid for cementation came from the rock itself during early diagenetic stage. The minerals related to endogenous fluid had good shapes. The reservoir property was enhanced with porosity increasing by 3%-8% because of later dissolution by endogenous fluid. The exogenous fluid might be water combining with CO 2 , likely released from organic matter-rich mudstone. Calcite cement, in form of substrate cementation, was precipitated from the fluid and filled in the remaining pores of sandstones in late diagenetic stage as variations of physical and chemical conditions. The exogenous cement reduced rock porosity, damaged reservoir property, affected some oil enrichment, and seriously caused Chang 6 reservoir densification. Some of the dense layers that formed on top of sandbody could have served as diagenetic traps, and thus the exogenous cementation area could be favorable for oil exploration.

Analysis on Impacts and Co-Abatement Effects of Implementing the Low Carbon Cement Standard

Based on the MAP-CGE model,this paper simulated the impacts on the output,energy consumption and pollutant emissions of different cement production processes when implementing a low carbon cement standard in China.It also calculated the impacts on the marginal abatement cost and equilibrium price of the cement industry,and analyzed the co-abatement effects of different pollutants.The results showed that implementing the low carbon cement standard will be beneficial in promoting an upgrading of cement production processes,and strengthening the energy conservation and emission reduction in the cement industry.If there is no change in the existing technology,the cement industry will reduce SO2emissions by 1.17 kg and NOxemissions by 4.44 kg per ton of CO2emission reduction.Implementing low carbon cement standard can also promote NOxabatement in the cement industry.However,the cement industry will bear the abatement costs,and their equilibrium price will increase slightly.

Resistance Responses of Carbon Fiber Cement to Cycled Compressive Stresses

The stress-resistance relationship of carbon fiber cement was studied.Attention has been paid to explore the improvement of the stress-resistance sensitivity under cycled stress restriction.The prismy carbon fiber cement sensors were pre-fabricated.The factors such as contents of carbon fibers.silica fume,dispersant and the w/c were taken into account.The electrical resistance variations with the dynamic and static loads were simulated using a strain-controlled test machine.The test results show that there is an optimal fiber content,with which the compression-sensitivity achieves a high level.The addition of silica fume can improve the sensitivity.Under the optimal test conditions,the measured resistances can greatly correspond with the changes of the load.

Electrical resistance stability of high content carbon fiber reinforced cement composite

The influences of curing time, the content of free evaporable water in cement paste, environmental temperature, and alternative heating and cooling on the electrical resistance of high content carbon fiber reinforced cement (CFRC) paste are studied by experiments with specimens of Portland cement 42.5 with 10 mm PAN-based carbon fiber and methylcellulose. Experimental results indicate that the electrical resistance of CFRC increases relatively by 24% within a hydration time of 90 d and almost keeps constant after 14 d, changes hardly with the mass loss of free evaporable water in the concrete dried at 50 °C, increases relatively by 4% when ambient temperature decreases from 15 °C to ?20 °C, and decreases relatively by 13% with temperature increasing by 88 °C. It is suggested that the electric resistance of the CFRC is stable, which is testified by the stable power output obtained by electrifying the CFRC slab with a given voltage. This implies that such kind of high content carbon fiber reinforced cement composite is potentially a desirable electrothermal material for airfield runways and road surfaces deicing.

Effects of Carbonation on Micro Structures of Hardened Cement Paste

In order to investigate the effects of carbonation on the microstructure of cement concrete,the carbonation depth and microstructure of cement paste with 0.3,0.4 and 0.5 water/cement ratio after 7,14,21 and 28 d accelerated carbonation were studied respectively.The results showed that with the increase of waterto-cement ratio and carbonation age,the carbonation depth was deepened with faster early carbonation speed and slower later carbonation rate.Carbonation densified the structure of hardened cement stone with refinement of pore structure and reduced porosity.Then,during the carbonation process from the surface to the inside of carbonation area,it was prone to form micro-cracks extending to the interior specimen,resulting in cement paste carbonation depth uneven.It is further illustrated that the color reaction method using phenolphthalein solution combined with X-CT and X-ray diffraction analysis is much more reasonable to evaluate the cement concrete carbonation degree.Moreover,during carbonation process sulfur element in cement paste migrated to the area un-carbonated and the concentrated shape of sulfur element is consistent with the coloring region in carbonation interface.Finally it was identified that carbonation not only reduced the p H value in cement concrete but also made prone to crack in carbonation zone,which increased the probability of reinforcement corrosion.

Effect of carbon nanotube on physical and mechanical properties of natural fiber/glass fiber/cement composites

The objective of this investigation was to introduce a cement-based composite of higher quality. For this purpose new hybrid nanocomposite from bagasse fiber,glass fiber and multi-wall carbon nanotubes（MWCNTs）were manufactured. The physical and mechanical properties of the manufactured composites were measured according to standard methods. The properties of the manufactured hybrid nanocomposites were dramatically better than traditional composites. Also all the reinforced composites with carbon nanotube, glass fiber or bagasse fiber exhibited better properties rather than neat cement.The results indicated that bagasse fiber proved suitable for substitution of glass fiber as a reinforcing agent in the cement composites. The hybrid nanocomposite containing10 % glass fiber, 10 % bagasse fiber and 1.5 % MWCNTs was selected as the best compound.

Hydrothermally induced diagenesis: Evidence from shallow marinedeltaic sediments, WilhelmØya, Svalbard

Sedimentary basins containing igneous intrusions within sedimentary reservoir units represent an important risk in petroleum exploration. The Upper Triassic to Lower Jurassic sediments at Wilhelm?ya(Svalbard) contains reservoir heterogeneity as a result of sill emplacement and represent a unique case study to better understand the effect of magmatic intrusions on the general burial diagenesis of siliciclastic sediments. Sills develop contact metamorphic aureoles by conduction as presented in many earlier studies. However, there is significant impact of localized hydrothermal circulation systems affecting reservoir sediments at considerable distance from the sill intrusions. Dolerite sill intrusions in the studied area are of limited vertical extent(～12 m thick), but created localized hydrothermal convection cells affecting sediments at considerable distance(more than five times the thickness of the sill)from the intrusions. We present evidence that the sedimentary sequence can be divided into two units:(1) the bulk poorly lithified sediment with a maximum burial temperature much lower than 60-70 ℃,and(2) thinner intervals outside the contact zone that have experienced hydrothermal temperatures(around 140 ℃). The main diagenetic alteration associated with normal burial diagenesis is minor mechanical plastic deformation of ductile grains such as mica. Mineral grain contacts show no evidence of pressure dissolution and the vitrinite reflectance suggests a maximum temperature of ～40 ℃. Contrary to this, part of the sediment, preferentially along calcite cemented flow baffles, show evidence of hydrothermal alteration. These hydrothermally altered sediment sections are characterized by recrystallized carbonate cemented intervals. Further, the hydrothermal solutions have resulted in localized sericitization(illitization) of feldspars, albitization of both K-feldspar and plagioclase and the formation of fibrous illite nucleated on kaolinite. These observations suggest hydrothermal alteration at T> 120-140 ℃ at distances considerably further away than expected from sill heat dissipation by conduction only, which commonly affect sediments about twice the thickness of the sill intrusion. We propose that carbonate-cemented sections acted as flow baffles already during the hydrothermal fluid mobility and controlled the migration pathways of the buoyant hot fluids. Significant hydrothermally induced diagenetic alterations affecting the porosity and hence reservoir quality was not noted in the noncarbonate-cemented reservoir intervals.

Determinationofelasticmodulus of claystone:Nano-/micro-indentation andmeso-compression tests used to investigate impact of alkaline fluid propagation over 18 years

Micro-mechanical properties of a claystone were tested after undergoing alkaline perturbation on site(Tournemire,CD borehole)for 18 years.In a saturated context and outside the excavation disturbed zone(EDZ),the claystone exhibits a 11.6-mm black rim at the cement/paste interface,which shows a different mechanical behaviour from the rest of the claystone.Three sets of measurements of elastic modulus were performed using:(i)nano-indentation tests with a constant indentation depth of 2 mm,(ii)microindentation tests with a constant indentation depth of 20 mm,and(iii)meso-compression tests with a constant displacement of 200 mm.The increase of the modulus of deformability in the black rim is between 15 GPa and 20 GPa according to the scale.Moreover,an overall decrease of the modulus of deformability from the smallest to the largest scale is observed in each zone.In view of the mineralogy and petrographic observations,higher values of modulus of deformability in the black rim are related to carbonate content and its distribution.Precipitation of cementitious carbonates as inclusions and very thin partings leads to hardening of the claystone.

Diagenetic fluid evolution and water-rock interaction model of carbonate cements in sandstone: An example from the reservoir sandstone of the Fourth Member of the Xujiahe Formation of the Xiaoquan-Fenggu area, Sichuan Province, China

Carbonate cement is the most abundant cement type in the Fourth Member of the Xujiahe Formation in the Xiaoquan-Fenggu area of the West Sichuan Depression. Here we use a systematic analysis of carbonate cement petrology, mineralogy, carbon and oxygen isotope ratios and enclosure homogenization temperatures to study the precipitation mechanism, pore fluid evolu- tion, and distribution of different types of carbonate cement in reservoir sand in the study area. Crystalline calcite has relatively heavy carbon and oxygen isotope ratios （δ13C = 2.14%o, 8180 = -5.77‰）, and was precipitated early. It was precipitated di- rectly from supersaturated alkaline fluid under normal temperature and pressure conditions. At the time of precipitation, the fluid oxygen isotope ratio was very light, mainly showing the characteristics of a mixed meteoric water-seawater fluid（ δ180 = -3‰）, which shows that the fluid during precipitation was influenced by both meteoric water and seawater. The calcite cement that fills in the secondary pores has relatively lighter carbon and oxygen isotope ratios （δ13C = -2.36%0, 8180 = -15.68‰）. This cement was precipitated late, mainly during the Middle and Late Jurassic. An important material source for this carbonate cement was the feldspar corrosion process that involved organic matter. The Ca2＋, Fe3＋ and Mg2＋ ions released by the clay mineral transformation process were also important source materials. Because of water-rock interactions during the buri- al process, the oxygen isotope ratio of the fluid significantly increased during precipitation, by about 3‰. The dolomite ce- ments in calcarenaceous sandstone that was precipitated during the Middle Jurassic have heavier carbon and oxygen isotope ratios, which are similar to those of carbonate debris in the sandstone （δ13C = 1.93%o, δ180 = -6.11‰）, demonstrating that the two are from the same source that had a heavier oxygen isotope ratio （δ180 of about 2.2‰）. The differences in fluid oxygen isotope ratios during cement precipitation reflect the influences of different water-rock interaction systems or different wa- ter-rock interaction strengths. This is the main reason why the sandstone containing many rigid particles （lithic quartz sand- stone） has a relatively negative carbon isotope ratio and why the precipitation fluid in calcarenaceous sandstone has a relatively heavier oxygen isotope ratio.

Multisourced CO_(2) Injection in Fan Delta Conglomerates and Its Influence on Reservoir Quality: Evidence from Carbonate Cements of the Baikouquan Formation of Mahu Sag, Junggar Basin, Northwestern China

Sandy-conglomerate reservoir has gradually become a major target of oil and gas exploration.Complex diagenetic process and diagenetic fluid play a significant role in affecting reservoir heterogeneity.Carbonate cements form at various stages of the diagenesis process and record various geological fluid information.Recently,one-billion-ton sandy conglomerate oil field was exposed in Triassic Baikouquan Formation,Mahu sag,Junggar Basin.Therefore,an integrated study applying casting thin sections,cathodeluminescence,fluorescence,carbon and oxygen stable isotopes,electronic probe microanalysis and aqueous fluid inclusions measurements was performed in order to identify the types of carbonate mineral and its representative diagenetic environment and discuss the influences of different CO_(2) injections on reservoir quality.The main findings are as follows:The reservoir is mainly composed of 70.33%conglomerate and 16.06%coarse-grained sandstone.They are characterized by low compositional maturity and abundant lithic debris.Four types carbonate cements are identified according to the petrological and geochemical characteristics,including two types of Mn-rich calcite,ferroan calcite,siderite and dawsonite.They display an unusual broad spectrum ofδ^(13)C values(-54.99‰to+8.8‰),suggesting both organic and inorganic CO_(2) injections.The δ^(13)C values of siderite are close to 0,and its formation is related to meteoric water.Theδ^(13)C values of ferroan calcite and the occurrence of dawsonite indicate the trace of inorganic mantle-derived magmatic fluids.Theδ^(13)C values and trace elements of Mn-rich calcite record the information of hydrocarbon-bearing fluids.The fluid inclusions measurement data and reservoir properties and oil-test data show that the oil content of reservoir is not only affected by the formation time of different cements,but also by the relative content of dissolution and cementation.For these reservoirs altered by carbonate cements,it does not cause poor oil-bearing due to blockage of secondary minerals.

Controlling of cements and physical property of sandstone by fault as observed in well Xia503 of Huimin sag,Linnan sub-depression

Cement content of carbonate in tight sandstone near section is much the fault of well Xia503, in the Huimin sag in Linnan sub-depression higher than that of the normal sandstones far away from In order to understand the origin and its impact on fault sealing, analyses of the whole-rock minerals, casting thin sections, cathodoluminescence, isotope and physical properties are conducted on cores from well Xia503. It is found that c~ L3C varies from 0.1%o to 0.6%o with the average value of 0.42%o, c~ LSO varies from -13.5%o to -12.3%c with the average of-13.1%~., and C-O isotope plotting points are distributed in the low to moderate temperature area of the hydrothermal dolomite. According to the occupied relationship, cathodoluminescence, and C-O isotope feature, the carbonate cementation could be divided into four stages： calcites, dolomite, ankerite, and ferrocalcite. It is discovered that the carbonate cementation is negatively related to reservoir physical property, with the porosity of 4.8%, permeability of 0.37 roD, and displacement pressure of 1.97 MPa in the tight sandstone, which have increased by almost one order of magnitude compared to the porosity of 14.3%, permeability of 3.73 mD, and displacement pressure of 0.27 MPa in the normal sandstone, which is far away from the fault. Regardless of the lithology of the counterpart wall of the fault, only the displacement pressure difference caused by carbonate cementation between the tight sandstone and the normal sandstone could seal 41 m high oil column.

Effect and quantitative evaluation of CO_2 derived from organic matter in coal on the formation of tight sandstone reservoirs

Tight reservoirs are widely distributed, especially in coal measure strata. Identification of the densification mechanism of the tight sandstone reservoirs is critical in effectively exploring and exploiting tight gasoil resources. In this study, the gas for mation from type III organic matter in coal was kinetically modeled for the whole diagenetic stage, from the shallow buried biogas generation stage to the deep buried thermal gas generation stage. The results demonstrated that during hydrocarbon formation, quantities of nonhydrocarbon gases, such as CO2, were generated. The proportion of CO2 is about 50%70% of that of the C15, which far exceeds the CO2 content （05%） in the natural gas in the sedimentary basins. Geological case study analysis showed that a considerable part of the ＂lost＂ gaseous CO2 was converted into carbonate cement under favorable envi ronments. Under the ideal conditions, the volume of the carbonate cement transformed from total CO2 generated by 1 m3 coal （Junggar Basin Jurassic, TOC 67%） can amount to 0.32 m3. Obviously, this process plays a very important role in the for mation of tight sandstone reservoirs in the coal measures. Our results also show that the kinetic generation processes of Ci5 and CO2 are asynchronous. There are two main stages of CO2 generation, one at the weak diagenetic stage and the other at the overmature stage, which are different from largescale multistage hydrocarbon gas generation. Therefore, we can understand the mechanism of tight gas charging by determining the filling time for a tight gas reservoir and the key period of CO2 genera tion. Further analysis and correlation studies of a specific region are of great significance for determining the mechanism and modeling gas charging in tight reservoirs. It should be noted that the formation of tight sandstone reservoirs is the combined result of complex organicinorganic and waterrockhydrocarbon interactions. The details of spatial and temporal distributions of the carbonate cement derived from the organic C02, which combines with metal ions （Ca/Mg/Fe） in the formation water, should be further investigated.

A novel stimulation strategy for developing tight fractured gas reservoir

Conventional stimulation methods such as matrix acidizing,acid fracturing,or proppant fracturing have resulted in products that perform poorly and/or fail within months.Other options,such as water fracs with light sand,give better results but are prohibitively expensive.Mineral composition,brittleness index,stress regime,and petrophysical properties,which are favorable for creating complex fracture networks,can be obtained by geochemical and geomechanical analysis.The extended Reshaw and Pollard criterion shows that hydraulic fractures tend to be arrested by pre-existing natural fractures,and complex fracture networks would be created during fracturing.Additionally,the critical stressed faults theory indicates that the pre-existing natural fractures tend to slip with the shear mode as the pore fluid pressure increases.Rotating disk experiments and conductivity tests with artificial sheared plates have shown that flow channels can be etched at the location of scratches on fracture surfaces.Meanwhile,the carbonate cement in natural fractures can be chelated to form wormhole likely flow channels.Complex fracture networks with sufficient acid etched conductivity can be generated by water fracs with acid.A novel and economical volume stimulation strategy known as network acid fracturing has provided Tarim Oil Company the means to develope ultra-deep,ultra-high pressure,high temperature,and ultralow permeability but fractured gas reservoirs.Post-stimulation production performances of numerous wells with network acid fracturing are comparable to those with stimulated reservoir volumes.

Substantial global carbon uptake by cement carbonation

Subject Code:D03With the support by the National Natural Science Foundation of China and the Chinese Academy of Sciences,the research team led by Prof.Xi Fengming(郗凤明)at the Institute of Applied Ecology,Chinese Academy of Sciences(IAE CAS),uncovered the global carbon uptake by cement materials,which was published in Nature Geoscience(2016,9:880—883).Until recent research,cement material was widely considered as an import carbon source.