Discovery and inspiration of large-and medium-sized glutenite-rich oil and gas fields in the eastern South China Sea:An example from Paleogene Enping Formation in Huizhou 26 subsag,Pearl River Mouth Basin

Based on the practice of oil and gas exploration in the Huizhou Sag of the Pearl River Mouth Basin,the geochemical indexes of source rocks were measured,the reservoir development morphology was restored,the rocks and minerals were characterized microscopically,the measured trap sealing indexes were compared,the biomarker compounds of crude oil were extracted,the genesis of condensate gas was identified,and the reservoir-forming conditions were examined.On this basis,the Paleogene Enping Formation in the Huizhou 26 subsag was systematically analyzed for the potential of oil and gas resources,the development characteristics of large-scale high-quality conglomerate reservoirs,the trapping effectiveness of faults,the hydrocarbon migration and accumulation model,and the formation conditions and exploration targets of large-and medium-sized glutenite-rich oil and gas fields.The research results were obtained in four aspects.First,the Paleogene Wenchang Formation in the Huizhou 26 subsag develops extensive and thick high-quality source rocks of semi-deep to deep lacustrine subfacies,which have typical hydrocarbon expulsion characteristics of"great oil generation in the early stage and huge gas expulsion in the late stage",providing a sufficient material basis for hydrocarbon accumulation in the Enping Formation.Second,under the joint control of the steep slope zone and transition zone of the fault within the sag,the large-scale near-source glutenite reservoirs are highly heterogeneous,with the development scale dominated hierarchically by three factors(favorable facies zone,particle component,and microfracture).The(subaqueous)distributary channels near the fault system,with equal grains,a low mud content(<5%),and a high content of feldspar composition,are conducive to the development of sweet spot reservoirs.Third,the strike-slip pressurization trap covered by stable lake flooding mudstone is a necessary condition for oil and gas preservation,and the NE and nearly EW faults obliquely to the principal stress have the best control on traps.Fourth,the spatiotemporal configuration of high-quality source rocks,fault transport/sealing,and glutenite reservoirs controls the degree of hydrocarbon enrichment.From top to bottom,three hydrocarbon accumulation units,i.e.low-fill zone,transition zone,and high-fill zone,are recognized.The main area of the channel in the nearly pressurized source-connecting fault zone is favorable for large-scale hydrocarbon enrichment.The research results suggest a new direction for the exploration of large-scale glutenite-rich reservoirs in the Enping Formation of the Pearl River Mouth Basin,and present a major breakthrough in oil and gas exploration.

Stress corrosion cracking behavior of buried oil and gas pipeline steel under the coexistence of magnetic field and sulfate-reducing bacteria

Magnetic field and microorganisms are important factors influencing the stress corrosion cracking(SCC)of buried oil and gas pipelines. Once SCC occurs in buried pipelines, it will cause serious hazards to the soil environment. The SCC behavior of X80 pipeline steel under the magnetic field and sulfate-reducing bacteria(SRB) environment was investigated by immersion tests, electrochemical tests, and slow strain rate tensile(SSRT) tests. The results showed that the corrosion and SCC sensitivity of X80 steel decreased with increasing the magnetic field strength in the sterile environment. The SCC sensitivity was higher in the biotic environment inoculated with SRB, but it also decreased with increasing magnetic field strength, which was due to the magnetic field reduces microbial activity and promotes the formation of dense film layer. This work provided theoretical guidance on the prevention of SCC in pipeline steel under magnetic field and SRB coexistence.

Sedimentary build-ups of pre-salt isolated carbonate platforms and formation of deep-water giant oil fields in Santos Basin,Brazil

In response to the problems of unclear distribution of deep-water pre-salt carbonate reservoirs and formation conditions of large oil fields in the Santos passive continental margin basin,based on comprehensive utilization of geological,seismic,and core data,and reconstruction of Early Cretaceous prototype basin and lithofacies paleogeography,it is proposed for the first time that the construction of pre-salt carbonate build-ups was controlled by two types of isolated platforms:inter-depression fault-uplift and intra-depression fault-high.The inter-depression fault-uplift isolated platforms are distributed on the present-day pre-salt uplifted zones between depressions,and are built on half-and fault-horst blocks that were inherited and developed in the early intra-continental and inter-continental rift stages.The late intra-continental rift coquinas of the ITP Formation and the early inter-continental rift microbial limestones of the BVE Formation are continuously constructed;intra-depression fault-high isolated platforms are distributed in the current pre-salt depression zones,built on the uplifted zones formed by volcanic rock build-ups in the early prototype stage of intra-continental rifts,and only the BVE microbial limestones are developed.Both types of limestones formed into mound-shoal bodies,that have the characteristics of large reservoir thickness and good physical properties.Based on the dissection of large pre-salt oil fields discovered in the Santos Basin,it has been found that both types of platforms could form large-scale combined structural-stratigraphic traps,surrounded by high-quality lacustrine and lagoon source rocks at the periphery,and efficiently sealed by thick high-quality evaporite rocks above,forming the optimal combination of source,reservoir and cap in the form of“lower generation,middle storage,and upper cap”,with a high degree of oil and gas enrichment.It has been found that the large oil fields are all bottom water massive oil fields with a unified pressure system,and they are all filled to the spill-point.The future exploration is recommended to focus on the inter-depression fault-uplift isolated platforms in the western uplift zone and the southern section of eastern uplift zones,as well as intra-depression fault-high isolated platforms in the central depression zone.The result not only provides an important basis for the advanced selection of potential play fairways,bidding of new blocks,and deployment of awarded exploration blocks in the Santos Basin,but also provides a reference for the global selection of deep-water exploration blocks in passive continental margin basins.

Enhancing economic sustainability in mature oil fields:Insights from the clustering approach to select candidate wells for extended shut-in

Fluctuations in oil prices adversely affect decision making situations in which performance forecasting must be combined with realistic price forecasts.In periods of significant price drops,companies may consider extended duration of well shut-ins(i.e.temporarily stopping oil production)for economic reasons.For example,prices during the early days of the Covid-19 pandemic forced operators to consider shutting in all or some of their active wells.In the case of partial shut-in,selection of candidate wells may evolve as a challenging decision problem considering the uncertainties involved.In this study,a mature oil field with a long(50+years)production history with 170+wells is considered.Reservoirs with similar conditions face many challenges related to economic sustainability such as frequent maintenance requirements and low production rates.We aimed to solve this decision-making problem through unsupervised machine learning.Average reservoir characteristics at well locations,well production performance statistics and well locations are used as potential features that could characterize similarities and differences among wells.While reservoir characteristics are measured at well locations for the purpose of describing the subsurface reservoir,well performance consists of volumetric rates and pressures,which are frequently measured during oil production.After a multivariate data analysis that explored correlations among parameters,clustering algorithms were used to identify groups of wells that are similar with respect to aforementioned features.Using the field’s reservoir simulation model,scenarios of shutting in different groups of wells were simulated.Forecasted reservoir performance for three years was used for economic evaluation that assumed an oil price drop to$30/bbl for 6,12 or 18 months.Results of economic analysis were analyzed to identify which group(s)of wells should have been shut-in by also considering the sensitivity to different price levels.It was observed that wells can be characterized in the 3-cluster case as low,medium and high performance wells.Analyzing the forecasting scenarios showed that shutting in all or high-and medium-performance wells altogether results in better economic outcomes.The results were most sensitive to the number of active wells and the oil price during the high-price period.This study demonstrated the effectiveness of unsupervised machine learning in well classification for operational decision making purposes.Operating companies may use this approach for improved decision making to select wells for extended shut-in during low oil-price periods.This approach would lead to cost savings especially in mature fields with low-profit margins.

Fault diagnosis and analysis of main sea water pump based on vibration monitoring in offshore oil field

The main sea water pump is the key equipment for the floating production storage and offloading （FPSO）. Affected by some factors such as hull deformation, sea water corrosion, rigid base and pipeline stress, the vibration value of main sea water pump in the horizontal direction is abnormally high and malfunctions usually happen. Therefore, it is essential to make fault diagnosis of main sea water pump, By conventional off-line monitoring and vibration amplitude spectrum analysis, the fault cycle is found and the alarm value and stop value of equipment are set, which is helpful to equipment maintenance and accident prevention.

Donghe Sandstone Subtle Reservoir Exploration and Development Technology in Hade 4 Oilfield

Hade 4 oilfield is located on the Hadexun tectonic belt north of the Manjiaer depression in the Tarim basin, whose main target layer is the Donghe sandstone reservoir, with a burial depth over 5,000m and an amplitude below 34m, at the bottom of the Carboniferous. The Donghe sandstone reservoir consists of littoral facies deposited quartz sandstones of the transgressive system tract, overlapping northward and pinching out. Exploration and development confirms that water-oil contact tilts from the southeast to the northwest with a drop height of nearly 80m. The reservoir, under the control of both the stratigraphic overlap pinch-out and tectonism, is a typical subtle reservoir. The Donghe sandstone reservoir in Hade 4 oilfield also has the feature of a large oil-bearing area (over 130 km2 proved), a small thickness (average efficient thickness below 6m) and a low abundance (below 50 × 104t/km2). Moreover, above the target layer developed a set of igneous rocks with an uneven thickness in the Permian formation, thus causing a great difficulty in research of the velocity field. Considering these features, an combination mode of exploration and development is adopted, namely by way of whole deployment, step-by-step enforcement and rolling development with key problems to be tackled, in order to further deepen the understanding and enlarge the fruits of exploration and development. The paper technically focuses its study on the following four aspects concerning problem tackling. First, to strengthen the collecting, processing and explanation of seismic data, improve the resolution, accurately recognize the pinch-out line of the Donghe sandstone reservoir by combining the drilling materials in order to make sure its distribution law; second, to strengthen the research on velocity field, improve the accuracy of variable speed mapping, make corrections by the data from newly- drilled key wells and, as a result, the precision of tectonic description is greatly improved; third, to strengthen the research on sequence stratigraphy and make sure the distribution law of the Donghe sandstone; and fourth, with a step- by-step extrapolation method, to deepen the cognition of the leaning water-oil contact, and by combining the tectonic description and drilling results, to make sure little by little the law of change of the water-oil contact. The exploration and development of the Donghe sandstone subtle reservoir in Hade 4 oilfield is a gradually perfected process. From 1998 when it was discovered till now, the reservoir has managed to make a benign circle of exploration and development, in which its reserve has gradually been enlarged, its production scale increased, and, in a word, it has used techniques necessary for this subtle reservoir in the Tarim basin.

Daily Variation of Natural Emission of Methane to the Atmosphere and Source Identification in the Luntai Fault Region of the Yakela Condensed Oil/Gas Field in the Tarim Basin,Xinjiang,China

The static flux chamber method was applied to study natural emissions of methane to the atmosphere in the Luntai fault region of Yakela Condensed Oil/Gas Field in the Tarim Basin, Xinjiang Municipality, northwestern China. Using an online method, which couples together a gas chromatography/high-temperature conversion/isotope ratio mass spectrometry （GC/C/MS）, 13^C/12^C ratios of methane in flux chambers were measured and showed that methane gases are liable to migrate from deep oil/gas reservoirs to the surface through fault regions and that a part of the migrated methane, which remains unoxidized can be emitted into the atmosphere. Methane emission rates were found to be highest in the mornings, lowest in the afternoons and then increase gradually in the evenings. Methane emission rates varied dramatically in different locations in the fault region. The highest methane emission rate was 10.96 mg/m^2·d, the lowest 4.38 mg/m^2, and the average 7.55 mg/ m^2·d. The 13^C/12^C ratios of the methane in the flux chambers became heavier as the enclosed methane concentrations increased gradually, which reveals that methane released from the fault region might come from thermogenic methane of the deep condensed oil/gas reservoir.

Kinetic Performance of Oil-field Produced Water Treatment by Biological Aerated Filter

The biological aerated filter （BAF） was used to treat the oil-field produced water. The removal efficiency for oil, COD, BOD and suspended solids （SS） was 76.3%-80.3%, 31.6%-57.9%, 8.6.3%-96.3% and76.4%--82.7%, respectively when the hydraulic loading rates varied from 016m·h^-1 to 1.4m·h^-1. The greatest partof removal, for example more than 80% of COD removal, occurred on the top 100cm of the media in BAF. The kinetic .performance of BAF indicated that the relationship of BOD removal efficiency with the hydraulic loadingrates, in biological aerated filters could be described by c1/c1=l-exp（-2.44/L^0.59）. This equation could be used topredict the B OD.removal efficiency at different hydraulic loading rates.

Geological emission of methane from the Yakela condensed oil/gas field in Talimu Basin, Xinjiang, China

A static flux chamber method was applied to study natural emissions of methane into the atmosphere in the Yakela condensed oil/gas field in Talimu Basin, Xinjiang, China. Using an online method, which couples a gas chromatography/high-temperature conversion/isotope ratio mass spectrometry (GC/C/MS) together, the 13C/12C ratios of methane in the flux chambers were measured. The results demonstrated that methane gases were liable to migrate from deep oil/gas reservoir to the surface through microseepage and p...

Formation and distribution characteristics of Proterozoic–Lower Paleozoic marine giant oil and gas fields worldwide

There are rich oil and gas resources in marine carbonate strata worldwide.Although most of the oil and gas reserves discovered so far are mainly distributed in Mesozoic,Cenozoic,and upper Paleozoic strata,oil and gas exploration in the Proterozoic–Lower Paleozoic（PLP）strata—the oldest marine strata—has been very limited.To more clearly understand the oil and gas formation conditions and distributions in the PLP marine carbonate strata,we analyzed and characterized the petroleum geological conditions,oil and gas reservoir types,and their distributions in thirteen giant oil and gas fields worldwide.This study reveals the main factors controlling their formation and distribution.Our analyses show that the source rocks for these giant oil and gas fields are mainly shale with a great abundance of type I–II organic matter and a high thermal evolution extent.The reservoirs are mainly gas reservoirs,and the reservoir rocks are dominated by dolomite.The reservoir types are mainly karst and reef–shoal bodies with well-developed dissolved pores and cavities,intercrystalline pores,and fractures.These reservoirs arehighly heterogeneous.The burial depth of the reservoirs is highly variable and somewhat negatively correlated to the porosity.The cap rocks are mainly thick evaporites and shales,with the thickness of the cap rocks positively correlated to the oil and gas reserves.The development of high-quality evaporite cap rock is highly favorable for oil and gas preservation.We identified four hydrocarbon generation models,and that the major source rocks have undergone a long period of burial and thermal evolution and are characterized by early and long periods of hydrocarbon generation.These giant oil and gas fields have diverse types of reservoirs and are mainly distributed in paleo-uplifts,slope zones,and platform margin reef-shoal bodies.The main factors that control their formation and distribution were identified,enabling the prediction of new favorable areas for oil and gas exploration.

Effect of HCO_3^- concentration on CO_2 corrosion in oil and gas fields

The effect of HCO3^- concentration on CO2 corrosion was investigated by polarization measurement of potentiodynamic scans and weight-loss method, Under the conditions of high pressure and high temperature, the corrosion rate of steel X65 decreased with the increase of HCO3^- concentration, while pH of solution increased. SEM, EDS, and XRD results of the corrosion scales indir cated that the typical FeCO3 crystallite was found at low HCO3^- concentration but Ca（Fe,Mg）（CO3）2 was found at high HCO3^- con- centration. Ca^2＋ and Mg^2＋ are precipitated preferential to Fe^2＋ at high pH value. Potentiodynamic polarization curves showed that the cathodic current density decreases with the increase of HCO3^- concentration at low HCO3^- concentration. When the HCO3^- concentration reaches 0.126 mol/L, increasing HCO3^- concentration promotes cathodic reactions. Anodic behavior is an active process at low HCO3^- concentration and the anodic current density decreases with the increase of HCO3^- concentration. An evident active-passive behavior is exhibited in anodic process at 0.126 mol/L HCO3^-.

Investigation of the oil-seawater mixed flow under an electromagnetic field

The electromagnetic separation method is a new approach to treat ship-based marine oily wastewater,in which oil droplets are dispersed in seawater(oil-seawater mixed flow).In order to clarify the separation process and determine the separation characteristics,the flow field and volume fraction of the oil droplets of the oil-seawater mixed flow under an applied electromagnetic field with different operating conditions were investigated by 2D numerical simulations with the Eulerian model.The results show that:(1)the downward Lorentz force causes seawater to flow downwards and the oil droplets to move upwards due to the electromagnetic separation force in the effective section of the separation channel;(2)the volume fraction of the oil droplets at the top of the outlet section increases with the current density,magnetic field,and the diameter of the oil droplet and decreases with the inlet velocity of the oily seawater.The results provide useful guidance for the design of electromagnetic separation devices of the oil-seawater mixed flow.

Characteristics of Abnormal Pressure Systems and Their Responses of Fluid in Huatugou Oil Field,Qaidam Basin

Based on the comprehensive study of core samples, well testing data, and reservoir fluid properties, the construction and the distribution of the abnormal pressure systems of the Huatugou oil field in Qaidam Basin are discussed. The correlation between the pressure systems and hydrocarbon accumulation is addressed by analyzing the corresponding fluid characteristics. The results show that the Huatugou oil field as a whole has low formation pressure and low fluid energy; therefore, the hydrocarbons are hard to migrate, which facilitates the forming of primary reservoirs. The study reservoirs, located at the Xiayoushashan Formation （N1/2） and the Shangganchaigou Formation （N1） are relatively shallow and have medium porosity and low permeability. They are abnormal low-pressure reservoirs with an average formation pressure coefficient of 0.61 and 0.72 respectively. According to the pressure coefficient and geothermal anomaly, the N1 and N1/2 Formations belong to two independent temperature-pressure systems, and the former has slightly higher energy. The low-pressure compartments consist of a distal bar as the main body, prodelta mud as the top boundary, and shore and shallow lake mud or algal mound as the bottom boundary. They are vertically overlapped and horizontally paralleled. The formation water is abundant in the Cl^- ion and can be categorized as CaCl2 type with high safinity, which indicates that the abnormal low-pressure compartments are in good sealing condition and beneficial for oil and gas accumulation and preservation.

Optimization of operation conditions for extracting lithium ions from calcium chloride-type oil field brine

AI（OH）3 was prepared to extract lithium ions from calcium chloride-type oil field brine. The influences of four factors, namely temperature, Al3＋/Li＋ molar ratio, OH-/Al3＋ molar ratio, and contact time between AI（OH）3 and the brine, on the yield of lithium ions were investigated. It is found that their optimal values are 35℃, 4.5, 2.6, and 6 h, respectively. In the course of the experiment, the apparent pH value was observed. The results reveal that the apparent pH value has no remarkable influence on the yield of lithium ions. Meanwhile, the effects of the concentrations of calcium ions and magnesium ions in the brine on lithium recovery were studied. The results indicate that cal- cium ions have minor negative influence on the yield of lithium ions under optimal conditions, and magnesium ions slightly influence the yield of lithium ions.

Research and Application of CO₂Flooding Enhanced Oil Recovery in Low Permeability Oilfield

This paper discusses the new progress and field application of CO2 flooding in low permeability reservoirs enhanced oil recovery. The study shows that CO2 flooding can improve the oil recovery rate of low permeability oilfield by more than 10%. The practice shows that the liquid CO2 injection in low permeability reservoir is easier than water injection, and the reservoir generally has better CO2 storage.

Synergistic effect of magnetic field and nanocomposite pour point depressant on the yield stress of waxy model oil

Yield stress,as the key parameter to characterize the network strength of waxy oil,is important to the petroleum pipeline safety.Reducing the yield stress of waxy oil is of great significance for flow assurance.In this study,the effect of alternating magnetic field(intensity,frequency)on the yield stress of a waxy model oil with nanocomposite pour point depressant(NPPD)is systematically investigated.An optimum magnetic field intensity and frequency is found for the reduction in yield stress.When adding with NPPD,the heterogeneous nucleation of NPPD contributes to the reduction in yield stress for waxy model oil.Interestingly,the magnetic field is helpful for the modification of yield stress at a lower frequency and intensity before the optimal value;however,the modification is found to be weakened when the magnetic field is further increased after the optimal value.Possible explanation is proposed that the aggregation morphology of wax crystal would be altered and results in the release of wrapped oil phase from the network structure under the magnetic field.

Practice and theoretical and technical progress in exploration and development of Shunbei ultra-deep carbonate oil and gas field,Tarim Basin,NW China

In this review on the exploration and development process of the Shunbei ultra-deep carbonate oil and gas field in the Tarim Basin, the progress of exploration and development technologies during the National 13th Five-Year Plan of China has been summarized systematically, giving important guidance for the exploration and development of ultra-deep marine carbonate reservoirs in China and abroad. Through analyzing the primary geological factors of “hydrocarbon generation-reservoir formation-hydrocarbon accumulation” of ancient and superposed basin comprehensively and dynamically, we point out that because the Lower Cambrian Yuertusi Formation high-quality source rocks have been located in a low-temperature environment for a long time, they were capable of generating hydrocarbon continuously in late stage, providing ideal geological conditions for massive liquid hydrocarbon accumulation in ultra-deep layers. In addition, strike-slip faults developed in tectonically stable areas have strong control on reservoir formation and hydrocarbon accumulation in this region. With these understandings, the exploration focus shifted from the two paleo-uplifts located in the north and the south to the Shuntuoguole lower uplift located in between and achieved major hydrocarbon discoveries. Through continuing improvement of seismic exploration technologies for ultra-deep carbonates in desert, integrated technologies including seismic acquisition in ultra-deep carbonates,seismic imaging of strike-slip faults and the associated cavity-fracture systems, detailed structural interpretation of strike-slip faults, characterization and quantitative description of fault-controlled cavities and fractures, description of fault-controlled traps and target optimization have been established. Geology-engineering integration including well trajectory optimization,high efficiency drilling, completion and reservoir reformation technologies has provided important support for exploration and development of the Shunbei oil and gas field.

Microbiostratigraphy, microfacies and sequence stratigraphy of upper cretaceous and paleogene sediments, Hendijan oilfield, Northwest of Persian Gulf, Iran

Hendijan oilfield is located on Northwest of Pesian Gulf offshore of Iran and geologically in the Dezful embayment. In this study, the paleosedimentary depositional environment of the Early Cenomanian to Late Eocene deposits of the Sarvak, Ilam, Gurpi, Pabdeh and JahrumPabdeh Formations was evaluated using microbiostratigraphy, microfacies and D-INPEFA curves which are an accurate method in sequence stratigraphy in terms of regression and transgression of the sea. Also, we used limited elemental geochemical data of oxygen and carbon isotopes in compare with palaeontological data to infer the upper part, 10 m, of the Sarvak Formation. Statistical correlation analyses of geochemical data from upper part of the Sarvak Formation enable inference of differences in paleoconditions at this part and Sarvak Formation, and another Formation, Ilam, was distinguished. Palaentilogical analysis using planktonic foraminifera and calcareous nannofossils enables inference about time scale of each Formation. Petrographic data and different sediment textures support those inferences resulted from Gamma ray logs as D-INPEFA curves about different paleo-conditions that occurred during the development of the studied Formations. Synthesis of the analyses leads to the final interpretation that upper Cretaceous, Sarvak, Ilam and Gurpi Formations, at the Hendijan oil field were formed in a carbonate ramp that was likely closed to the open sea, where Gurpi Formation was deposited, by a shallow barrier that allowed seawater recharge into the basin and deep marine basin where Paleogene sediments, Pabdeh and Jahrum-Pabdeh, were deposited.

Treatment of Oil Field Wastewater after Chemical Flooding by Fenton Oxidation Combined with Biodegradation

Wastewater after chemical flooding is difficult to be treated by biological methods due to the residual chemicals in the wastewater. Fenton oxidation, which has been widely applied to detoxifying hazardous organic compounds and improving the biodegradability of these compounds, can solve this problem. So, in this paper, Fenton oxidation was used to enhance the biodegradability of the wastewater after chemical flooding. The op- timum operating conditions for the Fenton oxidation process were 2.5 g/L Fe2 ＋ , 600 mg/L H202 and 30 rain of treatment time. The wastewater pre- treated by Fenton oxidation was treated by aerobic activated sludge. It was found that a small amount of H202 can significantly increase both the biodegradation rate and extent of the wastewater. The effluent CODc, and HPAM contents were 260 and 94 mg/L respectively after the aerobic bio- logical process with the biodegradation time of 24 h. After Fenton oxidation combining with biodegradation, the total CODc, removal efficiency was up to 90%, and polymer and oil degrading efficiencies were 95% and 92% respectively.

The effects of diagenesis on the petrophysical and geochemical attributes of the Asmari Formation,Marun oil field,southwest Iran

The distribution of good reservoir quality and its causes is the main challenges in carbonate reservoir characterization.This study investigates the effects of diagenetic processes on the reservoir quality of the carbonate successions of the Asmari Formation,in the Marun oil field,southwest Iran.The study applies an integrated approach including core petrography,petrophysical rock typing,stable carbon and oxygen isotopes as well as major and trace elements analyses.Petrographic studies and geochemical analyses express that the Asmari limestones have been affected mainly by compaction,dissolution,recrystallization,calcite and anhydrite cementation and dolomitization.Among those diagenetic overprints,dolomitization and dissolution played an important role to enhance the reservoir quality of the formation.Moreover,four types of dolomites were recognized and the rate of dolomitization increases toward the top of the Asmari carbonate successions.Possible models for dolomitization include mixing zone,brine reflux,seepage reflux and tidal pumping of seawater.Employing Flow Zone Index and Discrete Rock Type concepts led to classification of the Asmari reservoir into seven reservoir rock types.Integrating reservoir rock typing with petrographic studies and geochemical analyses also confirms that reservoir quality of the Asmari Fm.would have been mainly controlled by diagenetic processes.Moreover,stable isotopes,trace elements and facies analyses support the idea that carbonate intervals of the Asmari Formation were deposited in a warm,shallow-water environment under a saline condition.