查看更多>>摘要：Spontaneous imbibition(SI)refers to displacement of non-wetting phase by wetting phase fluids in porous media which driven by capillary force.Spontaneous imbibition plays an important role in terms of increasing hydrocarbon recovery in low-permeability and tight reservoirs.In this study,we derived a new analytical model of spontaneous imbibition height in low-permeability reservoir considering effective viscosity,surface roughness,slip and gravity effects in a single tortuous capillary tube.Firstly,analytical solutions of imbibition height are derived in a single tortuous rough capillary tube with and without gravity effects.Moreover,our analytical model shows satisfactory match with experimental results from literatures in typical low-permeability core samples.Finally,sensitivity studies are conducted to discuss the effect of surface fractal dimension,effective viscosity,contact angle,interfacial tension,pore sizes and slip length on imbibition height,respectively.The results show that imbibition height inversely proportional to surface fractal dimension,effective viscosity,and contact angle on rough surface.Higher surface fractal dimension,effective viscosity and contact angle decrease imbibition height significantly.On the contrary,the imbibition height is proportional to pore radius,IFT,and slip length.Neglecting the slip effect results in underestimation of imbibition height in nanopore sizes,and insignificant changes are observed for micro-pore sizes.The presented models have clear physical meaning in every parameter on the imbibition height performance.
查看更多>>摘要：The structure of subsurface fault networks,which has a significant effect on hydrocarbon migration,is inherently difficult to recognize and map.3D seismic surveys provide an opportunity to map the fault system within a carbonate reservoir of Xinchang in the western Sichuan Basin,China.We calculated attributes from the seismic reflection data that covers an area of 1330 km~2,including variance,edge detection,dip-magnitude and dip azimuth.We focused on the Triassic Leikoupo Formation of dolostone,at ~6 km depth,adjacent to the Longmen Shan thrusting range.The mapped attributes display(1)a primary network of faults in an orthogonal pattern in the anticline,striking East-West and North-South,and(2)a secondary,conjugate fault set in the fold limb,striking Northeast and Northwest with a length range of 1-10 km.The latter set of conjugate faults are confined to a 300 m-thick layer of dolostone,diminishing into underlaying unit of anhydrite.We envision that the conjugate fault networks and associated fractures enhance gas charging and reflect a model of self-sourced migration and accumulation in the Leikoupo Formation.These results are significant for sweet-spot evaluation of carbonate reservoirs in the Sichuan Basin,and provide insights for understanding the migration of subsurface fluids.
Liyana Nadiah OsliMohamed R.ShalabyMd Aminul Islam
15页
查看更多>>摘要：The characteristics of the source rocks in the early to late Miocene Belait Formation of Brunei Darussalam have been evaluated through the application of Rock-Eval and biomarker analyses,as well as by organic petro-graphical examination.Analyses have been performed on coal,coaly shale/carbonaceous claystones and shale samples from the Formation,retrieved from outcrops across the Brunei-Muara district,and covering a wide lateral extension of the Formation.The geochemical results indicate that the coal and some carbonaceous samples(with TOC from 14.1% to 67.7%)from the Belait Formation have"good to excellent"generating potential,quantity and quality,due to their high S2 and TOC values,which are consistent with the intermediate hydrogen index(HI)values ranging from 144 to 258 mg HC/g TOC.Organic material of"fair to good"quantity,quality and hydrocarbon generating potential is recorded for the coaly shale samples in the Belait Formation.Non-coal samples generally have the lowest potential as source rocks,due to their low TOC,HI and S2 values.Within the Formation,the coal layers together with a number of coaly shale and shale layers contain type III(gas prone)and type II-III(mixed oil and gas)kerogens.This is proven by the dominance of huminite,often of fluorescent varieties,which is confirmed though maceral analysis,as well as a trend of n-alkanes skewed towards heavier compounds.Evidence of the possible generation of liquid hydrocarbon is offered by the fact that liptinite is the second most abundant maceral group in most of the samples,as well as by the perhydrous nature of part of the huminite.Furthermore,kerogen type IV(dry gas)has been identified in a majority of the coaly shale samples.Facies analysis of the Belait Formation through the use of maceral indices and biomarkers data indicates that the coals were deposited in a mangrove setting in a lower delta plain,where mainly herbaceous and arboreal plants were growing.The depositional conditions were predominantly oxic,with a possible marine influence,and hence brackish conditions.All samples are found to be thermally immature to early mature,with T_(max)values ranging from 356 ℃ to 441 ℃,huminite reflectance values of up to 0.46% and high carbon preference index(CPI)values.
查看更多>>摘要：Fractures play an important role in hydrocarbon storage and migration in basement buried hills.Taking the South Jinzhou oilfield(JZS oilfield)as an example,based on the data from cores,thin sections,seismic,logging,and experimental analysis,we clarified the genetic types and characteristics of fractures in the JZS crystalline basement oilfield and discussed controlling factors and their significance to petroleum geology.Tectonic and non-tectonic fractures are present in the study area,in which tectonic fractures are predominant.Tectonic fractures show three dominant directions with E-W,NE-SW,and NW-SE trends;among them,fractures with E-W trends are best developed.Most of the fractures are oblique,with a dip angle between 45° and 60°.The shear-compression zone trigged by strike-slip faults in-plane is favorable for fracture development.The granitic rocks with low compressive strength are more prone to fracture than diabase.Meteoric water and organic acids promote dissolution along fractures,expanding the tectonic fractures further.The fractures can increase the permeability of crystalline basement rocks by 10~3 times compared with the matrix.The dissolution along fractures can effectively improve the storage capacity of the crystalline basement rocks.Furthermore,there are a large number of fractures developed below the oil-water contact,which are important lateral migration channels for hydrocarbons.
查看更多>>摘要：Borno(Chad)Basin is an intra-cratonic rift basin located at the southwestern terminal of the West Africa Rift System.Despite its reported low petroleum potential,oil seepages have recently been found in the basin from its oldest and lowest stratigraphic unit,the Bima Sandstone.The lack of source beds below this reservoir sandstone makes it challenging to classify the basin petroleum system elements(PSEs)in their normal order and to predict the origin of the oil seepages in the region.Coupled structural analysis(2D Move)and petroleum system modeling(PetroMod)were employed to investigate the structural and hydrocarbon evolution of the basin to reassess its PSEs,hydrocarbon potential and migration trends.The structural model shows that the basin has extended up to 2900 km since the Late Cretaceous.The extension controlled by regional tectonic activities has affected the West and Central Africa Rift System and caused some localized tectonic disturbance in the form of igneous underplating and magmatic intrusion,leading to regional uplift.The magmatic sill intruded into the Late Cretaceous source rock formations increased the heat flow for the study area to a peak value of 128 mW/m2.This anomalous high heat flow value is 38 mW/m2 above the regional average and 18 mW/m2 above the average value for a non-volcanic rift margin.Essential petroleum system elements for trapping and accumulation of hydrocarbons were missing as a result of the uplift during the Late Cretaceous,creating hiatus and diverting sediments to other parts of the basin.The PetroMod model result indicates three zones of oil generation:Early Oil,Main Oil,and Late Oil in the Fika Shale and the Gongila source formations.Source rocks became mature at a relatively shallow burial depth of 900 m due to transient heating from the magmatic sill intrusion in the Late Cretaceous.Oil migrated updip to the surface through fault breakouts.The modeling results show no significant entrapment of conventional hydrocarbons in the study area.The findings improve our understanding of the Borno Basin petroleum system setting and offer new insight on the petroleum exploration potential in the region.
查看更多>>摘要：The hydraulic fracture aperture packed by proppants determines the fracture conductivity and is pivotal to oil and gas production.After hydraulic fracturing,the fracture width decreases owing to proppant embedment,deformation,and crushing.However,the analysis of fracture width reduction based on the mechanical properties of the proppant pack is limited.In this study,an experiment is designed to obtain the apparent Young's modulus,which represents the rigidity of the entire pack,and steel sheets are used to replace rock samples to eliminate heterogeneity and weaken the effect of proppant embedment.Subsequently,the effects of proppant type,concentration,and size on the apparent Young's modulus are discussed.Finally,the controlling factors and mechanisms of fracture width reduction are determined.The results indicate that the fracture width decreases linearly with increasing closure pressure for the ceramsite pack,and that the apparent Young's modulus is associated with the fracture aperture variation,which is governed by proppant embedment and deformation.The apparent Young's modulus increases as the proppant concentration increases or the proppant size decreases,whereas the proppant size imposes a more prominent effect.However,the mixed-size ceramsite pack shows only slight improvements in terms of propping ability.This study provides new insights into factors governing proppant pack deformation.
查看更多>>摘要：Slick water fracturing fluids with high viscosity and minimal friction pressure losses are commonly employed in hydraulic fracturing technology.The conventional method of conducting hydraulic fracturing operations using high-viscosity fluids is not always suitable in complex geological conditions because hydraulic fracturing in low-productive formations creates fractures that resemble radial fractures,lowering the impact's efficiency and profitability due to inefficient use of materials and reagents.As such,the goal is to limit the height of the fracture development and increase their length.In this work,we developed a low viscosity fracturing fluid with high proppant transport ability in order to minimize the specific pressure in the fracture and control its height.The hydrophobizing effect of surfactant was investigated,and criteria for employing it in hydraulic fracturing fluid formulation were created.We also developed a fracture model that we used to run simulation experiments in order to determine the nature of the fracturing fluid dispersion.Model simulations of hydraulic fracturing were performed utilizing proppant mesh sizes of 30/60,20/40,and 16/20.Our experimental results have demonstrated that utilizing a capillary suspension,it is possible to generate a stable formulation of hydraulic fracturing fluid with an effective settling capacity by adding PLA fibers as a reinforcing filler to the formulation.
查看更多>>摘要：Low-cost,fast and accurate acquisition of multi-scale mechanical properties of shale is essential to realize the complex hydraulic fracture network and the optimization of multi-scale fracture efficiency of bottom hole rock.The macro-scale indentation test is used to study the mechanical parameters of the meso-scale across the scales.The rapid evaluation method of the shale mechanical parameters across the scales is established,which can be used as a method to obtain the mechanical parameters of shale quickly and accurately.The macro-indentation test experiment is carried out through the elastic contact hypothesis,the macro-micro mechanics theory,and the grid indentation experiment method.Considering the coupling effects of peak indentation fluctuations,contact stiffness(S),and the ratio of elastic work to total work(Wu/Wt),the cross-scale distribution character-istics of shale hardness(H)and elasdc modulus(E)are studied.The results showed that the elastic modulus and hardness showed a normal distribution on the whole,and the macroscopic indentation process of the rock was accompanied by the meso-scale indentation.For Longmaxi shale,the elastic modulus and hardness have large discreteness and heterogeneity.The kernel density values of elastic modulus and hardness were studied by using kernel density analysis method.Different factors have different effects on the fluctuation amplitude of elastic modulus and hardness.The fluctuation range of the S is the largest,and the fluctuation range of Wu/Wt is the smallest.At the meso-scale,the dispersion of hardness peak value is larger,and the dispersion of elastic modulus peak value is smaller than that of valley value.The S-Wu/Wt-E-H coupling response law presents a"striped"characteristic.The S-Fm-E-H coupling response law presents a"multi-point"distribution.The Fm-Wu/Wt-E-H coupling response law shows a"wave-like"distribution.The hardness of vertical bedding indentation is greater than that of parallel bedding.There is a good linear correlation between the elastic modulus and hardness.With the increase of the elastic modulus,the hardness increases.The research results are helpful to determine the parameters in the actual design of hydraulic fracturing and improving the rock breaking efficiency.
查看更多>>摘要：The production performance of coalbed methane(CBM)reservoirs with multiple-fractured horizontal well(MFHW)is difficult to solve since the governing equations of fluid flow are highly nonlinear and two-phase flow is involved.Based on the material balance equation(MBE)and the solution of MFHW in rectangular reservoir,the production performance curves of CBM reservoir are obtained using finite difference method and dichotomy method.The solution of the semi-analytical model is validated comparing with numerical solution.Subsequently,the effects of Langmuir volume,Langmuir pressure,fracture number,fracture conductivity and fracture interval on production performance are investigated in detail.Langmuir pressure is negatively correlated with gas production and cumulative gas production.In addition,the increase of fracture number,conductivity and interval all has positive influence on the actual production.With the increase of fracture number and fracture interval,the decline rate of water production and gas production increase.
查看更多>>摘要：Shale gas reservoir is characterized by complex pore structure,ultra-low permeability and a large number of natural fractures.Therefore,it is necessary to apply horizontal well drilling with hydraulic fracturing to stimulate the shale gas reservoirs by forming complex fractures network composed of main fractures(i.e.,hydraulic fractures)and branch fractures(i.e.,activated natural fractures).During shale gas fracturing,hydraulic fractures will initiate simultaneously,deflect under the stress interference with each other,activate adjacent natural fractures and connect with them.These complex behaviors of fractures propagation would greatly complicate the production prediction after shale gas fracturing.Currently,the majority of the production prediction models neglect the complexity of fractures network.Therefore,based on Fick's diffusion law,Langmuir isothermal adsorption equation and dual-medium seepage theory,this paper derived a productivity prediction model by considering complexity of fractures network,stress-sensitive effect and ad-desorption by using point source method,Duhamel principle and Laplace transform,and solved the model with perturbation theory,discrete superposition and Stehfest numerical inversion.Then,the production prediction model was verified by a field example analysis,and the influence of the morphology of main fractures and branch fractures on productivity is explored.It indicates that the main fracture shape has a great influence on the production,and the trapezoidal mode is closer to the production practice.The large deflection of main fractures,the high conductivity and large approaching angle of branch fractures are beneficial to improving the production of fractured shale gas horizontal wells.
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