Determination of groundwater solute transport parameters in finite element modelling using tracer injection and withdrawal testing data

The groundwater tracer injection and withdrawal tests are often carried out for the determination of aquifer solute transport parameters.However,the parameter analyses encounter a great difficulty due to the radial flow nature and the variability of the temporal boundary conditions.An adaptive methodology for the determination of groundwater solute transport parameters using tracer injection and withdrawal test data had been developed and illustrated through an actual case.The methodology includes the treatment of the tracer boundary condition at the tracer injection well,the normalization of tracer concentration,the groundwater solute transport finite element modelling and the method of least squares to optimize the parameters.An application of this methodology was carried out in a field test in the South of Hanoi city.The tested aquifer is Pleistocene aquifer,which is a main aquifer and has been providing domestic water supply to the city since the French time.Effective porosity of 0.31,longitudinal dispersivity of 2.2 m,and hydrodynamic dispersion coefficients from D=220 m^(2)/d right outside the pumping well screen to D=15.8 m^(2)/d right outside the tracer injection well screen have been obtained for the aquifer at the test site.The minimal sum of squares of the differences between the observed and model normalized tracer concentration is 0.00119,which is corresponding to the average absolute difference between observed and model normalized concentrations of 0.0355(while 1 is the worst and 0 is the best fit).

Effect of freeze-thaw cycle on hydraulic conductivity of compacted clayey soil

When filling embankment dams in cold regions,engineers must solve two freeze–thaw cycle(FTC)-induced soil problems.First,compacted soil constituting the dam is subjected to the FTC during dam construction.Second,loose soil material(LSM),which is subjected to the FTC,fills the dam.To investigate the effects of the aforementioned two problems on the hydraulic conductivity of compacted clayey soil,a series of permeation tests on clayey soil compacted before and after FTC were conducted in this study.The results showed that for the first problem,the hydraulic conductivity of compacted clayey soil subjected to one FTC significantly increases by two to three orders of magnitude because FTC-induced cracks can cause preferential flow in the permeation process.For the second problem,when the FTC number is less than a critical number,the FTC of the LSM may result in the development of united soil particles,thereby increasing the effective porosity ratio and hydraulic conductivity of the compacted soil.It was discovered that the hydraulic conductivity of compacted soil can increase by one to three times when the LSM is subjected to 10 FTCs.When the FTC number exceeds a critical number,the effective porosity ratio and hydraulic conductivity of the compacted soil may decrease with the FTC of the LSM.This should be investigated in future studies,and the results can be used to improve engineering management processes when filling embankment dams during winter in cold regions.

Clogging Process Caused by Organic Particle Accumulation and Biofilm Growth in Subsurface Wastewater Infiltration System

Substrate clogging is the worst operational problem for subsurface wastewater infiltration system (SWIS), nevertheless quantitative understanding of the clogging process is currently very limited. In this study, the developing process of clogging caused by organic particle accumulation and biofilm growth was investigated in two groups of lab-scale SWIS, which were fed with glucose (dissolved organic matter) and starch (particulate organic matter) influent and filled with the same substrate made of 50% brown soil and cinder at a weight of 50%. Results showed that in glucose-fed systems the growth of biofilm in the substrate pores certainly caused remarkable reduction of effective porosity, especially for the high concentration organic wastewater, whereas its influence on infiltration rate was negligible. In comparison with biofilm growth, organic particles accumulation could rapidly reduce infiltration rate and the clogging occurred in the upper layer in starch-fed systems and the most important contribution of biofilm growth to clogging was accelerating the occurrence of clogging.

Petrophysical interpretations of subsurface stratigraphic correlations,Baram Delta,Sarawak,Malaysia

Petrophysical well log data help to predict hydrocarbon reserves before field development which involves huge financial commitment.In this study,reservoir characterization was performed with a view to obtain information on the geological formation type and petrophysical parameters.Wireline log data obtained from five wells were used to develop a 3D model of X-field in the Baram Delta which was in turn evaluated using the PETREL software.Suites of gamma ray,sonic,density,resistivity and neutron logs aided the delineation and correlation of the sandstone formation.Fourteen hydrocarbon-bearing sands were defined from well log data and divided into two-reservoir zones,shallow and deep.Well correlation assisted in the delineation of the reservoir sands across the wells.The quality of the reservoir formation was evaluated from average petrophysical properties:with an average thickness of 62 m,an average porosity of 0.19,an average net-to-gross ratio of 0.068,an average V-shale of 0.45,and an average water saturation of 0.95.A rollover anticline structure was identified across the field using the fault as a description tool.Variation of petrophysical parameters and uncertainty in the reservoir properties were included to predict the effect on the volume of oil in place.This study revealed that the discovered hydrocarbon reserve resource accumulations in the Field X for the fourteen-mapped reservoir sands have a total proven reserve resource estimate of 740MMSTB at P90,655MMSTB at P50 and 593MMSTB at P10.Reservoirs A and B are the only intervals with the highest recoverable oil,a volume of 256MMSTB at P90,215MMSTB at P50 and 181MMSTB at P10,respectively.These analyses facilitated an improved reservoir description of shaly sandstone,which contributes to better planning of hydrocarbon re-development and future recovery,and thereby improving the energy supply security of the regions.

Micropore structure characteristics and quantitative characterization methods of lacustrine shale-A case study from the member 2 of Kongdian Formation, Cangdong sag, Bohai Bay Basin

To better understand the micropore characteristics of lacustrine shale and develop quantitative methodsfor characterizing lacustrine shale, the reservoir space types, structures and spatial distribution patternsof effective pores in the shale of Member 2 of Kongdian Formation in Cangdong sag are studied usingcores, thin sections, scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM),nuclear magnetic resonance (NMR), whole-rock X-ray diffraction (XRD) data, etc. Various shale porositycalculation methods are evaluated. The study results show that the reservoir spaces of the shale mainlyinclude three types, i.e., matrix pores, organic pores and fractures. Flaky pore throats formed bydissolution-induced pores and mould pores can improve the pore connectivity. NMR effective porosity ofthe shale varies from 0.59% to 4.42% with an average of 2.38%, accounting for 49.54% of the total NMRporosity and 34.53% of the gas porosity. The shale is divided into the unimodal-type felsic shale, bimodaltype felsic shale, carbonate shale and mixed shale. The different lithologies exhibit linear correlationsamong NMR, gas and effective porosities. The shale has effective porosity of 0.56%-4.53% with an averageof 2.12%. Furthermore, the shale reservoir is divided into four classes: Class I reservoir with effectiveporosities of more than 2.5%;Class II1 reservoir with effective porosity of 2.0%-2.5%;Class II2 reservoirwith effective porosity of 1.5%-2%;and Class III reservoir with effective porosity of less than 1.5%.

Reservoir and development characteristics of the Da'anzhai tight oil in Sichuan Basin,SW China

The oil in the Jurassic Da'anzhai reservoirs in the Sichuan Basin is unconventional tight oil,which accumulated in or near source rocks,and did not experience extensive migration in a large-scale long distance.The first submember,second submember and third submember of Da'anzhai Member are dominated by shell limestone which is widely and continuously distributed,and are typical near-source lacustrine shell limestone tight reservoirs.Complex lithology,multiple types of reservoir space and complicated pore structure are developed in these reservoirs.The effective reservoir space mainly includes micro-pores and micro-fractures with strong fabric selectivity.The petrophysics experiment reveals that the average connected matrix porosity of tight oil reservoir in Jurassic Da'anzhai Member is about 2.13%,lower than that of other tight oil reservoirs but higher than the average effective porosity(0.97%)from previous single alcohol-saturated method.According to production performance data,the Da'anzhai shell limestone reservoir is not a simple porous or fractured reservoir,but has complex porethroat-fracture association or storage-seepage mode.Because the development of fossil shells controls the development of micro-fractures,fluids are difficult to enter into but easy to escape from the reservoirs.Although the pore-throat is fine,the sorting is poor and the displacement pressure is high,the movable fluid saturation and mercury ejection efficiency of the reservoir in the Da'anzhai Member is only slightly lower than that of some storage-seepage modes,and higher than that of Oil-bearing Group 7 of Yanchang Formation in the Ordos Basin.The reservoir in the Da'anzhai Member is one of the few tight oil reservoirs with high natural productivity.The tight oil in the shell limestone of the Da'anzhai Member has great development potential,but its extensive and effective development also has some challenges,such as high seepage resistance of matrix and ineffective single development mode.The development mode of the Da'anzhai tight oil should draw lessons from the Bakken Formation in North America and Oil-bearing Gourp 7 of Yanchang Formation in the Ordos Basin,and thus,effective development technologies based on volume fracturing and fine operation for shell limestone tight oil in the Da'anzhai Member in Sichuan Basin are developed to realize the development of profit and scale.

Pore structure complexity and its significance to the petrophysical properties of coal measure gas reservoirs in Qinshui Basin,China

The pore structure of continuous unconven-tional reservoirs(CURs)in coal measures was investigated using different technologies for 29 samples(9 coal samples,9 shale samples,and 11 sandstone samples)from Qinshui Basin,China.Results show that coals have relatively high porosities and permeabilities ranging from 4.02%to 5.19%and 0.001 to 0.042 mD,respectively.Micropores(<2 nm)are well-developed in coals and contribute to the majority of pore volume(PV)and specific surface area(SSA).The porosities and permeabilities are between 1.19%-4.11%,and 0.0001-0.004 mD of sand-stones with a predominance of macropores(>50 nm).However,shales are characterized by poorly petrophysical properties with low porosity and permeability.Macropores and mesopores(2-50 nm)are well-developed in shales compared with micropores.For coals,abundant organic matters are expected to promote the development of micropores,and clay minerals significantly control the performance of mesopores.For shales and sandstones,micropores are mainly observed in organic matters,whereas clay minerals are the important contributor to mesopores.Moreover,micropore SSA significantly deter-mines the adsorption capacity of CURs and sandstones have the best pore connectivity.The permeability of CURs is positively associated with the macropore PV since macropores serve as the main flow paths for gas seepage.Additionally,we also proposed that effective porosity has a significant effect on the permeability of CURs.The findings of this study could enhance the understanding of the multiscale pore structure of CURs and provide insights into the mechanisms that control gas storage,transport,and subsequent co-production for continuous unconventional natural gas(CUNG)in the Qinshui Basin and other coal-bearing basins worldwide.