查看更多>>摘要：Understanding the distribution of the fracture system in the reservoir scale could significantly benefit coalbed methane(CBM)development.Coal fractures are controlled by multiple factors,among which the influence of macrolithotypes has been widely studied.However,few studies have explained their relationship from the perspective of mechanics.Furthermore,the macrolithotypes are controlled by coal facies and thus a relationship between coal facies and fracture system characteristics is likely to be built,which could largely facilitate the prediction of fracture system development in a CBM reservoir,especially for those having ultra-thick coal seams.In the current research,mechanical properties,in combination with in-situ and laboratory observations,are carried out for different coal macrolithotypes from ultra-thick lignite reservoirs to reveal their influence on coal fracture development in Erlian Basin,China.In this basin,xylitic coal and detritic coal are mainly developed,and the former has better developing natural fractures which appears to be caused by its weaker mechanical strength as identified by the mechanical tests including the compressive,shear,and tensile strength.Moreover,coal facies based on petrography and palynology tests were analyzed to clarify the spatial distribution of macrolithotypes in the reservoir.The results show that in an ideal coal-forming cycle,the coal seams occur starting from the detritic coal,to xylitic coal,and fusitic coal at last upwards in order.In a realistic sag,however,multilayer individual xylitic coal intervals are likely to exist,especially for ultra-thick lignite.In this situation,coal facies analysis could explain xylitic coal distribution,thereby predicting the fracture system development.
查看更多>>摘要：Biosurfactant production is one of the most efficient mechanisms in microbial enhanced oil recovery(MEOR)processes.This work investigates the production of biosurfactants by indigenous bacteria isolated from Egyptian oil fields,and how to optimize these produced biosurfactants for MEOR.59 Egyptian oil reservoirs were screened to evaluate the potential applicability of MEOR processes,based on their rock and fluid properties.Results showed that 8 reservoirs from the Gulf of Suez and 3 reservoirs from the Western Desert had the potential to MEOR.Combined analysis of morphological,and biochemical characterization was performed on the 11 bacterial strains isolated from different crude oil samples collected from the reservoirs that have the potential to MEOR process to identify their types.Bacillus spp,a bacilli species that can produce biosurfactants,was selected for further studies.To optimize the surface activity of the produced biosurfactant,ten different reported nutrient media,and a new proposed nutrient media were examined.Bacillus spp has shown the ability to produce a very active biosurfactant that reduced the surface tension of water from 71.8 ± 1.9 mN/m to 25.7 ± 1.2 mN/m,and the interfacial tension of water against kerosene from 48.4 ±2.1 mN/m to 0.38 ± 0.07 mN/m at Critical Micelle Concentration(CMC)of 0.04 ± 0.01 g/l,in a medium supplemented by the new proposed nutrient medium H.The growth rate of Bacillus spp was studied,and it was found it reached its maximum(OD600nm 2.59 ± 0.16)after 24 h of incubation.Biosurfactant production has no significant change in its surface activity over a wide range of temperature range up to 120 ℃,which means the studied species Bacillus spp is a thermophilic bacterium.Bacillus spp grew well in the presence of high salt concentration up to 20%(w/v)NaCl,the optimal surface activity was obtained in the range of 0-2%(w/v)NaCl,and at pH 7.The emulsification activity of the produced biosurfactant was examined,and it reached the maximum(69.6 ± 1.5%)against kerosene at temperature 25 ℃,Salinity 0%(w/v)NaCl(distilled water),and pH 7.The produced biosurfactant was purified and extracted by acid precipitation method,and the biosurfactant yield of the purified compound was found to be 2.8 ± 0.3 g/l.Finally,the core-flooding experiments were conducted to investigate the effect of produced biosurfactants by Bacillus subtilis in oil recovery.The obtained results reveal the potential of Bacillus spp to grow in the new proposed medium H and produce effective and efficient biosurfactants that enhanced oil recovery by 25.19-39.35% of additional oil over the water flooding residual oil saturation in the studied cores and retain more than 60% of its surface activity under harsh conditions and that are relevant to Microbial Enhanced Oil Recovery,MEOR.
查看更多>>摘要：The permeability of the coal reservoir is affected by the stress caused by water production and matrix shrinkage caused by methane desorption,and its change rate is mainly affected by the elastic parameters of coal,namely Young's modulus(E)and Poisson's ratio(v).E and v will change with the change of coal water saturation,which will affect the reservoir permeability,but there is little research on it.Therefore,in this study,triaxial compression experiments were carried out on high volatility bituminous coal samples with different water saturation to obtain the variation law of E and v with water saturation.Combined with gas permeability experiments of coal samples with different water saturation and finite element method,the influence of E and v on permeability change were analyzed based on the P&M permeability evolution model.The results showed that E decreases linearly with the increase of water saturation,while v increases linearly,and the change rate was affected by the fracture of coal and stress.The existence of fractures makes the mechanical properties of coal show great heterogeneity,resulting in the reduction of water action,and the stress will close the fractures to be as a whole,more prone to elastic deformation and greater deformation.The change of E and v will lead to a decrease of permeability faster or slower,which depends on the initial E and v and their change rate.Because the effects of E and v on permeability are different and nonlinear,the control effects of E and v on permeability are also different,depending on the E and v value.The quantitative numerical analysis showed that the variation of E can increase permeability change range by at least 32%.When the E is less than 3000 MPa and greater than 4000 MPa,the influence degree is greater,more than 60%,which means that the change of E has a significant control effect on permeability change.The change of v has little effect on the permeability change range with the maximum permeability change range is only 31%.The permeability of coal reservoir generally exceeds 3000 MPa,which means that more attention should be paid to the influence of E and v change with water production on permeability,especially the change of E.
查看更多>>摘要：The upper Permian Longtan Formation(LTF)shale is a new shale gas exploration and development focus in China,which was formed in a transitional depositional environment.Because of the difference in the sedimentary environment between marine-continental transitional shale and marine shale,the enrichment characteristics and mechanism of organic matter(OM)are very different.Because of a weak research foundation,the enrichment mechanism of OM in the LTF shale in the Sichuan Basin is still unclear.In this paper,shale samples of the upper Permian LTF from the Well F5 were collected,and the abundance,source and sedimentary environment of organic matter were studied by using paleoclimate,detrital input,redox,paleoproductivity and sedimentation rate parameters.The results show that the TOC content of the LTF shale is high(average = 3.04%)and reaches the high to overmature stage(average = 2.46%),indicating a favorable source rock.The LTF shale was deposited in a humid and hot climate,which was conducive to the growth and prosperity of a large number of plants.The source of organic matter was mainly terrestrial plant fragments.The sedimentary environment of the LTF shale was oxic,it had a high sedimentation rate,which reduced the oxidation rate of OM,promoted the rapid deposition of OM,and ensured the preservation of organic matter.In summary,the enrichment of OM of LTF shale in the Sichuan Basin was affected by the sedimentary environment,which was complicated.The main controlling factors were detrital input,redox conditions and sedimentation rate.
查看更多>>摘要：The evaluation of Hungarian tight gas formations requires the use of innovative interpretation technologies because of diverse geological environment,heterogeneous dataset including several variables measured with different accuracies,and reservoirs under varying petrophysical conditions.Conventional well logging methods based on the use of limited number of wireline logs make only a quick-look interpretation,in which a limited number of unknowns is determined,and there is a non-negligible risk for occurrence of ambiguity.In order to increase the overdetermination(data-to-unknowns)ratio and the estimation accuracy and reliability,all suitable well logs are to be jointly processed in a more effective manner.To estimate the total organic carbon content together with porosity,water saturation,shale content and rock matrix volumes with higher accuracy,a new inversion methodology is introduced that is tested in tight gas reservoirs.A differential evolution algorithm-based interval inversion method is developed that is combined by nano-permeability and high precision porosity laboratory measurements for the detection and evaluation of Hungarian tight gas reservoirs.Spectral gamma-ray,neutron-porosity and electric resistivity logs are jointly analyzed using the interval inversion approach.By solving a highly overdetermined inverse problem,the effective porosity,water-and gas saturation,shale and sand content,as well as the kerogen volume are estimated in a reliable inversion procedure.The silt and clay content of Miocene tight gas formations are separated and both determined by inversion,while the total organic carbon content is derived from the inversion results.The permeability log is directly derived from the inverted porosity values using the local porosity versus permeability relation established by multi-well core analysis.The combination of in situ wireline log data analysis and porosity and nano-permeability laboratory measurements is shown to be advantageous for a more reliable interpretation of unconventional hydrocarbon formations.An added advantage of the interval inversion method is the calculation of depth dependent errors of the estimated petrophysical quantities.It is shown that total organic carbon and other volumetric parameters can be determined with high accuracy in one interpretation procedure.In the Derecske basin,East Hungary,gas indications are confirmed by interval inversion,that were previously made it probable according to measurements made on poor core samples and rather noise-sensitive local well logging inversion procedure.The joint evaluation of new core data and original wireline logs using the proposed methodology may reveal further potential tight gas resources in the studied area.The Hungarian case study confirms that the suggested workflow may serve a new alternative for an improved evaluation of tight gas formations in different other hydrocarbon fields.
查看更多>>摘要：Nano-material enhanced viscoelastic surfactant(VES)systems have attracted considerable attention as clean fracturing fluids due to their improved Theological properties compared to conventional VES systems.In this study,a pseudo-interpenetrating network VES(PINVES)fracturing fluid,which was composed of sodium oleate(NaOA),potassium chloride(KC1)and surface-modified cellulose nanofibril(SMCNF),was proposed.The rheological behavior of the PINVES fracturing fluid and the interaction mechanism between SMCNF and wormlike micelles(WLMs)were comprehensively studied.The zero-shear viscosity of PINVES increased with appropriate SMCNF addition but decreased with excess SMCNF addition.Meanwhile,the typical viscosity-flat of WLMs gradually disappeared when the concentration of SMCNF exceeded the optimum value.The optimum value was closely related to the functional groups on the surface of SMCNF.The SMCNF physically crosslinked the WLMs through hydrogen bonding but the sulfonic groups and hydrophobic groups on the surface of SMCNF destroyed the network of WLMs at relatively high SMCNF concentration.The network formed by SMCNF dominated the rheological behavior of the PINVES fracturing fluid simultaneously.In addition,due to the competition between the network of WLMs and the network of SMCNF,the PINVES fracturing fluid exhibited higher concentration dependence of surfactant in rheological behavior than conventional VES fracturing fluid.The SMCNF network also endowed the PINVES with better temperature-resistance.Furthermore,the relaxation time and elasticity of PINVES fracturing fluid increased with the increase in SMCNF concentration.The static proppant settling tests demonstrated that the addition of SMCNF improved the sand-carrying capability of PINVES fracturing fluid.The results of the study could provide some enlightenments on the application of SMCNFs in reservoir stimulation.
查看更多>>摘要：Cuttings removal out of the wellbore represents a real barrier for successful drilling operations.The performance of hole cleaning is determined by several factors.The current article provides a theoretical study of the impact of three operational parameters on cuttings transport in non-Newtonian drilling fluids.Computational fluid dynamics(CFD)is used to study the effect of drill pipe rotation speed(from 0 to 200 rpm),inclination angle(0-90°),and pipe eccentricity(0-0.8)on the cuttings transport ratio(CTR),cuttings volume concentration(CVT),and pressure drop.Response surface methodology(RSM)is employed to explore the two-factor interactions and to optimize the parameters by minimizing the CVT while maximizing the CTR.RSM is also used to generate statistical models to correlate the impact of the aforementioned three factors to the hole cleaning performance(represented by CVT,CTR,and pressure drop).Results revealed that many interactions exist between the tested operational parameters.The drill pipe rotation has the dominant effect on the performance of cuttings transportation,with the effect are more pronounced for highly deviated and horizontal wells.The results indicate that there are only a few cases of inadequate hole cleaning that drill-pipe rotation cannot control,and those cases are associated with the operation in vertical wellbore sections.Less effective cuttings transportation(i.e lower CTR)was observed when the hole angle deviated from the vertical.In addition,a significantly higher CVT(up to 73%)was recorded for eccentric pipes as compared to the concentric cases,primarily due to the reduced fluid velocity in the narrow gap of the eccentric annulus.As far as the pressure drop is concerned,lower pressure loss was obtained at lower rotation speeds and higher angles of inclination from the vertical.As the drill pipe rotational speed increased,the pressure drop decreased slightly until a critical rotatory speed was reached,thereafter,the pressure drop increased markedly.This trend was similar for all pipe eccentricities at any inclination angles,however,the critical rotadonal speed at which the pressure loss started to increase was found to be dependent on both the inclination angle and eccentricity.Operating at low drill pipe rotation speeds in a concentric annulus is recommended for vertical wells while higher speeds are favorable for more effective cuttings transport in horizontal wells.The CFD simulation results have been validated against experimental measurements for single and multiphase flow for different cases with/without drill pipe rotation at various inclination angles for both Newtonian and Non-Newtonian fluids.
查看更多>>摘要：In the process of deep shale gas exploitation through horizontal drilling and large-scale multi-section hydraulic fracturing,the cement sheath can easily fail due to the high peak pressure and the frequent and violent fluctuations.In this paper,firstly,the deformation characteristics of the cement was studied based on the uniaxial and triaxial compression experiments at different temperature conditions.Then,mechanical model of cement sheath was set up.Based on Melan's shakedown theorem,shakedown load of the cement sheath under the periodic alternating loads is obtained and then converted to the internal pressure of the casing.Results shows that:(1)Compared with that at 25 ℃,the compression resistance and elastic modulus of cement reduced significantly under 130 ℃.The cement exhibits obvious plastic flow characteristics and can be regarded as a rational elastic-plastic material.(2)During the cyclic loading and unloading process,new plastic strains are continuously generated,the width of hysteresis loops is continuously reduced,and the hysteresis loop becomes denser,which indicates that the accumulation rate of plastic deformation is continuously decreasing.(3)The shakedown load is the smaller of the loading and unloading yield pressures,and reverse yielding tend to occur in the depths.(4)The shakedown load of the cement sheath has a positive linear and non-linear relationship with the cohesive force and the friction angle,respectively.(5)the shakedown load has a positive linear relationship with the external I pressure.The external pressure,as the most influence of the calculation result of the shakedown load,accounts I for close to 80%.The research could provide valuable theoretical and engineering guidance for the design and I construction of shale gas well cement.
查看更多>>摘要：Carbonate reservoirs hold a substantial amount of our existing oil reserves.However,waterflood recovery from these reservoirs is often low due to their oil-wet nature.Recent studies have shown that oil recovery from oil-wet carbonate reservoirs can be increased by wettability alteration using low salinity brines having carefully modified ionic compositions.In this study,we developed a multiphase,multicomponent,finite-difference reservoir simulator and incorporated an improved mechanistic model to model low salinity waterflood in carbonates.The model considers key geochemical reactions relevant to low salinity waterflooding as reported by many authors recently.However,our modeling approach differs in two ways.Firstly,our model assumes that geochemical reactions of injected brines with the rock take place only on water-wet surfaces of these rocks and at the three-phase contact line;compared to other existing models that consider reactions to occur on the entire rock surface for oil-wet rocks.Secondly,previous models consider organic acids as a single species.In reality,oil is likely to have a mixture of different organic acids of different polarity,chain length,etc.In our model,we consider the oil to have a mixture of different organic acids and studied its impact on wettability alteration and oil recovery.Using this model,single phase and oil recovery experiments reported in the literature were modeled.The effect of rock wettability on geochemical reactions of low salinity brines with carbonate rocks was studied.Similarly,the effect of organic acid distribution on wettability alteration and oil recovery was investigated.Our simulation results showed that the extent of reaction of low salinity brines with carbonate rocks decreased as the rock became more oil-wet due to a decrease in reactive surface area.For example,less delay in effluent sulfate ions was observed in case of oil-wet rocks.The water-wet regions grew as a result of wettability alteration at the three-phase contact line.The initial wettability,extent of wettability alteration,and oil recovery profiles were dependent on the organic acid distribution.Furthermore,the inclusion of only key geochemical reactions(dolomitization,sulfate adsorption,and anhydrite dissolution/precipitation)were found to be reasonable for modeling various experiments reported in the literature.The proposed model will help in improving our understanding of mechanisms responsible for wettability alteration.
Mehdi KhoshnoodkiaOmeid RahmaniMohammad Hossein Adabi
21页
查看更多>>摘要：The Bangestan reservoir,which occurs in the Ahwaz oilfield,consists of the middle Cretaceous limestone Ilam and Sarvak Formations that were deposited in the Zagros Basin.The reservoir is divided into ten Zones(A to J)formed in the upper Albian-Santonian and contains considerable hydrocarbon accumulations.The limestones were deposited on an extensive shallow carbonate platform on a passive margin and are dominated by rudist biostrome and grainstone facies.Paleogeographical changes mean that identification of the facies is complex.Seismic stratigraphy and isotopic data are used to better understand the structural and geological setting and develop an understanding of the sedimentary environment.The results show that the rudist biostrome facies extends to a shallow interior shelf as a patch reef,indicating a regressive trend.Petrographic studies on 3174 thin sections identified twelve microfacies in the Bangestan reservoir.In the Sarvak Formation,the dominant microfacies consist of rudist biostrome,shoal bar,and lagoon facies,with a high sedimentation rate in the basin,whereas the Ilam Formation involves open and deep-marine facies.Seismic tectono-stratigraphy shows that there are seven sedimentary sequences with mostly regressive cycles and six maximum flooding surfaces from the upper Albian to the Santonian.In addition,the Ahwaz oilfield had experienced pre-tectonic extension before the Early Cretaceous and post-tectonic extension after the Late Cretaceous.The isotopic data from the Bangestan reservoir demonstrate two important disconformities(Cenomanian-Turonian and post-Turonian)that had an important influence on the evolution of the area evolution.Sr geochronology confirms long-term exposure to two main disconformities within the Ahwaz Bangestan reservoir.
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