Water scaling predication for typical sandstone geothermal reservoirs in the Xi'an Depression

The Xi'an Depression in the Guanzhong Basin of western China has been suggested to contain geothermal resources that could aid China in achieving carbon neutrality and optimizing energy structure.However,the high concentration of total dissolved solids(TDS)and scale-forming ions in geothermal water from the depression causes severe scaling problems in harvesting geothermal energy.To reduce scale-related problems,accurate identification of scale types and prediction of scaling during geothermal energy utilization are crucial.This study starts with identifying the types and trends of scaling in the study area,using index-based discriminant methods and hydrogeochemical simulation to calculate and analyze the mineral saturation index of water samples from some wellheads and of reconstructed fluid samples of geothermal reservoirs.The results indicate that the scales are mostly calcium carbonate scales rather than sulfate scales as a result of temperature changes.Several portions of the geothermal water systems are found to have distinct mineral scaling components.Quartz and chalcedony are formed in low temperature areas,while carbonate minerals are in high temperature areas.Despite the low iron content of geothermal water samples from the study area,scaling is very common due to scaling-prone iron minerals.The findings can be used to evaluate geothermal drainage systems and guide anti-scaling during geothermal energy utilization in similar settings.

A new NMR-data-based method for predicting petrophysical properties of tight sandstone reservoirs

Evaluating the permeability and irreducible water saturation of tight sandstone reservoirs is challenging.This study uses distribution functions to fit measured NMR T_(2)distributions of tight sandstone reservoirs and extract parameters for characterizing pore size distribution.These parameters are then used to establish prediction models for permeability and irreducible water saturation of reservoirs.Results of comparing the fit of the T_(2)distributions by the Gauss and Weibull distribution functions show that the fitting accuracy with the Weibull distribution function is higher.The physical meaning of the statistical parameters of the Weibull distribution function is defined to establish nonlinear prediction models of permeability and irreducible water saturation using the radial basis function(RBF)method.Correlation coefficients between the predicted values by the established models and the measured values of the tight sandstone core samples are 0.944 for permeability and 0.851 for irreducible water saturation,which highlight the effectiveness of the prediction models.

Effect of Pisha sandstone on water infiltration of different soils on the Chinese Loess Plateau

The infiltration of water into soil is one of the most important soil physical properties that affect soil erosion and the eco-environment, especially in the Pisha sandstone area on the Chinese Loess Plateau. We studied the one-dimensional vertical infiltration of water in three experimental soils, created by mixing Pisha sandstone with sandy soil, irrigation-silted soil, and loessial soil, at mass ratios of 1：1, 1：2, 1：3, 1：4, and 1：5. Our objective was to compare water infiltration in the experimental soils and to evaluate the effect of Pisha sandstone on water infiltration. We assessed the effect by measuring soil bulk density（BD）, porosity, cumulative infiltration, infiltration rate and saturated hydraulic conductivity（Ks）. The results showed that Pisha sandstone decreased the infiltration rate and saturated hydraulic conductivity in the three experimental soils. Cumulative infiltration over time was well described by the Philip equation. Sandy soil mixed with the Pisha sandstone at a ratio of 1：3 had the best water-holding capacity. The results provided experimental evidence for the movement of soil water and a technical support for the reconstruction and reclamation of mining soils in the Pisha sandstone area.

Mechanical behavior of sandstone during post-peak cyclic loading and unloading under hydromechanical coupling

This paper investigates mechanical behaviours of sandstone during post-peak cyclic loading and unloading subjected to hydromechanical coupling effect, confirming the peak and residual strengths reduction laws of sandstone with water pressure, and revealing the influence of water pressure on the upper limit stress and deformation characteristics of sandstone during post-peak cyclic loading and unloading.Regarding the rock strength, the experimental study confirms that the peak strength σ_(p) and residual strength σ_(r) decrease as water pressure P increases. Especially, the normalized strength parameters σ_(p)/σ_(pk) and σ_(r)/σ_(re) was negatively and linearly correlated with the P/σ_(3). Moreover, the Hoek-Brown strength criterion can be applied to describe the relationship between effective peak strength and effective confining stress. During post-peak cyclic loading and unloading, both the upper limit stress σ_(p(i)) and crack damage threshold stress σ_(cd(i)) of each cycle tend to decrease with the increasing cycle number. A hysteresis loop exists among the loading and unloading stress–strain curves, indicating the unloading deformation modulus E_(unload) is larger than the loading deformation modulus E_(load). Based on experimental results,a post-peak strength prediction model related to water pressure and plastic shear strain is established.

Numerical investigation on the fatigue failure characteristics of waterbearing sandstone under cyclic loading

The strength of sandstone decreases significantly with higher water content attributing to softening effects.This scenario can pose a severe threat to the stability of reservoirs of pumped storage power stations developed from abandoned mines,especially when subjected to the cyclic loading condition caused by the repeated drainage and storage of water(fatigue damage).Based on this,it is essential to focus on the fatigue failure characteristics.In this study,the mineral composition of the used sandstone of Ruineng coal mine in Shanxi Province,China,was first tested to elucidate the rock softening mechanism after absorbing water.Next,a numerical model for replicating the mechanical behavior of water-bearing sandstone was established using twodimensional particle flow code(PFC2D)with a novel contact model.Then,16 uniaxial cyclic loading simulations with distinct loading parameters related to reservoir conditions(loading frequency,amplitude level,and maximum stress level)and different water contents were conducted.The numerical results show that all these three loading parameters affect the failure characteristics of sandstone,including irreversible strain,damage evolution,strain behavior,and fatigue life.The influence degree of these three parameters on failure behavior increases in the order of maximum stress level,loading frequency,and amplitude level.However,for the samples with different water contents,their failure characteristics are similar under the same loading conditions.Furthermore,the failure mode is almost unaffected by the loading parameters,while the water content plays a significant role and causing the transformation from the tensile splitting with low water content to the shear failure with higher water content.

Potential Role of Feldspathic Sandstone as a Natural Water Retaining Agent in Mu Us Sandy Land,Northwest China

This paper analyzed the water-retention mechanism of feldspathic sandstone(fine-(<1 mm diam.)and gravel-sized(2-3 cm diam.)in Mu Us Sandy Land,Northwest China.The objective of this study is to study the effect of feldspathic sandstone amendment on water retention in sandy land.The results showed that as the proportion of fine feldspathic sandstone in the sandy land soil increased,the soil texture changed from sand to silt loam,the capillary porosity gradually increased from 26.3%to 44.9%,and the soil saturated hydraulic conductivity decreased from 7.10 mm/min to 0.07 mm/min.Feldspathic sandstone gravel formed micro-reservoirs in the sandy land soil,playing the role of a′water absorbent′and′water retaining agent′in sandy land.Amendment with feldspathic sandstone can increase water retention in the arable layer of sandy land by 67%.This study provides a theoretical basis for the amelioration of sandy land on a large scale.It can be concluded that amendment with feldspathic sandstone can improve the physical properties of sandy land soil and increase soil water retention.

Weathering of Pisha-Sandstones in the Wind-Water Erosion Crisscross Region on the Loess Plateau

Two types of pisha-sandstones of purple sandstones and gray sandstones,widely distributing in the wind-water erosion crisscross region of China,were selected and used in laboratory experiments for a better understanding of the drying-wetting-freezing weathering process resulting from the apportionment of water or salt solution to rock samples.Weathering experiments were carried out under the conditions of environment control(including temperature,moisture and salt solution).All rock samples were frequently subjected to 140 drying-wetting-freezing cycles.The influences of weathering process were evaluated.It was found that the different treatments of moisture and salt solution applications could affect the nature of the weathering products resulting from drying-wetting-freezing.It was also observed that salt solution could effectively alleviate the weathering of pisha-sandstones.Although not all the observations could be explained,it was apparent that simulated environmental factors had both direct and indirect effects on the weathering of rocks.

Rare earth element geochemistry of groundwater from a deep seated sandstone aquifer,northern Anhui province,China

Deep coal mines in northern Anhui province,China,provide opportunities for tracing the distribution and fractionation of rare earth elements(REEs) in deep seated environments.Major ions,as well as REE concentrations were measured in groundwater from a sandstone aquifer located between-400 and-280 m.Our results indicate that this groundwater consists of Cl HCO3-Na or Cl CO3-Na water types with warm temperature(30.1-31.4 °C),circumneutral pH(7.27-8.61) and high levels of total dissolved solids(TDS = 1306-2165 mg/L).Concentrations of REEs in groundwater are high as expressed by their Nd concentrations(0.0086-0.018 lg/L).Except for weak heavy REEs(HREE) enrichment relative to light REEs(LREE),the similarity of REE distribution patterns between groundwater and aquifer rock indicate that enrichment of REEs is considered to be controlled by aquifer rock,as well as by their minerals,whereas the fractionation of REEs is controlled by HREE enriched minerals and,to a lesser extent,by inorganic REE complexes.Ce anomalies normalized to Post Archean Average Shale(PAAS) and aquifer rock are weak,which probably reflect the contribution of reduced conditions in combination with pH,rather than a signature of aquifer rock.

Pore-Throat Combination Types and Gas-Water Relative Permeability Responses of Tight Gas Sandstone Reservoirs in the Zizhou Area of East Ordos Basin, China

With the aim of better understanding the tight gas reservoirs in the Zizhou area of east Ordos Basin,a total of 222 samples were collected from 50 wells for a series of experiments.In this study,three pore-throat combination types in sandstones were revealed and confirmed to play a controlling role in the distribution of throat size and the characteristics of gas-water relative permeability.The type-I sandstones are dominated by intercrystalline micropores connected by cluster throats,of which the distribution curves of throat size are narrow and have a strong single peak(peak ratio>30%).The pores in the type-II sandstones dominantly consist of secondary dissolution pores and intercrystalline micropores,and throats mainly occur as slice-shaped throats along cleavages between rigid grain margins and cluster throats in clay cement.The distribution curves of throat size for the type-II sandstones show a bimodal distribution with a substantial low-value region between the peaks(peak ratio<15%).Primary intergranular pores and secondary intergranular pores are mainly found in type-III samples,which are connected by various throats.The throat size distribution curves of type-III sandstones show a nearly normal distribution with low kurtosis(peak ratio<10%),and the micro-scale throat radii(>0.5μm)constitute a large proportion.From type-I to type-III sandstones,the irreducible water saturation(Swo)decreased;furthermore,the slope of the curves of Krw/Krg in two-phase saturation zone decreased and the two-phase saturation zone increased,indicating that the gas relative flow ability increased.Variations of the permeability exist in sandstones with different porethroat combination types,which indicate the type-III sandstones are better reservoirs,followed by type-II sandstones and type-I sandstones.As an important factor affecting the reservoir quality,the pore-throat combination type in sandstones is the cumulative expression of lithology and diagenetic modifications with strong heterogeneity.

Assessment of groundwater suitability for different activities in Toshka district,south Egypt

Globally,groundwater has globally emerged as a crucial freshwater source for domestic,irrigation,and industrial needs.The evaluation of groundwater quality in the Toshka region is imperative to ensure its suitability for the extensive agricultural and industrial activities underway in this promising,groundwater-dependent development area.This is particularly significant as Egypt increasingly relies on groundwater reserves to address freshwater deficits and to implement mega-development projects in barren lands.In this study,fifty-two samples were collected from the recently drilled wells tapping into the Nubian Sandstone Aquifer(NSA)in the Toshka region.Groundwater quality was assessed through hydrochemical analysis,Piper diagram,and various indicators such as Na%,SAR,RSC,KR,MH and PI.The hydrochemical analysis revealed improved groundwater quality characteristics,attributed to continuous recharge from Lake Nasser.The Piper diagram categorised most of the water samples as"secondary salinity"water type.Almost all wells proved suitable for irrigation with only two wells unsuitable based on MH values and six wells based on KR values.Considering Total Hardness(TH)values,all samples were classified as"Soft",indicating their suitability for domestic and industrial purposes.Water Quality Index(WQI)results concluded that all samples met WHO and FAO guidelines for drinking and irrigation,respectively.Spatial distribution maps,constructed using GIS,facilitate the interpretation of the results.Regular monitoring of quality parameters is essential to detect any deviation from permissible limits.

The Effects of Different Ratios of Feldspathic Sandstone and Sand Compound Soil on Water-stable Aggregates in 4 Years Crop Planting

To study the formation process of feldspathic sandstone and sand compound soil in the Mu Us Desert,1∶ 1,1∶ 2 and 1∶ 5 ratios of feldspathic sandstone and sand were mixed to obtain compound soil to plant crops,and analyze the rules of changes in water-stable aggregates of the compound soil among the 4 years crops growing process. The results showed,before crop planting,the order of mass percent of> 0. 25 mm and 0. 25-2. 00 mm water-stable aggregates in three kinds of compound soil was 1∶ 1 > 1∶ 2 > 1∶ 5,showing that the overall content was low; the mass percent of > 0. 25 mm water-stable aggregates remained at 18. 38%-28. 22%; the mass percent of 0. 25-0. 50 mm,0. 50-2. 00 mm,2. 00-5. 00 mm,and > 5. 00 mm water-stable aggregates was close with each other in each kind of compound soil. After4 years of planting,the mass percent of > 0. 25 mm water-stable aggregates in 1∶ 2 compound soil increased significantly and exceeded other2 kinds of compound soil,reached 32. 34%; the main components of > 0. 25 mm water stable aggregates in 1∶ 1,1∶ 2,and 1∶ 5 compound soil were 0. 25-0. 50 mm( 53. 54%),0. 25-0. 50 mm( 59. 43%),0. 05-2. 00 mm( 52. 16%),aggregates; 0. 25-2. 00 mm aggregates increased significantly in all three kinds of compound soil,with the highest increase in 1∶ 2 compound soil; the organic matters of 1∶ 2 compound soil were significantly correlated with 0. 25-0. 50 mm and 0. 25-2. 00 mm water-stable aggregates. The results showed that the ratio of 0. 25-2. 00 mm aggregates in the three kinds of compound soil was increased after 4 years of crop planting and 1∶ 2 compound soil was most favorable for the formation of aggregates.

Water Saturation Dependence on CO₂Sorption Potential of Sandstones

For the assessment of the carbon dioxide (CO2) storage potential of water-filled reservoir rocks (i.e., saline aquifers), it should be first important step for a thorough understanding of the effect of water content on CO2/water/rock interactions during CO2 injection. The purpose of this study is to examine the CO2 sorption amount for Kimachi sandstone and Berea sandstone at different water content using the manometric method at temperature of 50?C and pressures of up to 20 MPa. Our results document that a significant quantity of CO2 was sorbed on the two types of sandstone on all water-saturated bases, which corresponded to the amount adsorbed on the air-dry basis. Also, all the wet samples had significantly higher sorption capacity than the theoretical values calculated from the solubility model based on dissolution of CO2 in pore water and the pore-filling model, which assumes that the pore volume unoccupied by water is filled with CO2. Furthermore, the observations indicated a certain degree of correlation between the sorbed amount and the water content, except at pressures below the critical point for Berea sandstone. This investigation points out that CO2 sorption is a possible mechanism in CO2 geological storage even under water-saturated conditions and that the mechanism of sorption on silica and silicate minerals plays an essential role in the reliable and accurate estimation of the CO2 storage capacity of water-saturated reservoirs.

Development of High Viscous Oil in Sandstone Reserviors During the High Water Cut Stage，Gudao Oilfield

The oi!bearing area of Gudao Oilfield covers 80.9 square kilometers.with 373 million tons of oil in place.It is a large drape anticlinal.Neogene Gu-dao Formation is main oil-beraing reservoir devel-oped with dip gentle from 30'to 1°30'in general.The main oil-bearing sequences can be divided into 6 sand groups and 34 layers in detail.in which the Ng°-Ng°sand groups are the main payzones in which oil in place accounts for 97.2%of the total.

Research on Water Sensitivity and Velocity Sensitivity of Loose Sandstone Reservoir in China Offshore Oilfield

Aiming at the development characteristics of Bohai P oilfield, formation mechanism of reservoir damage was analyzed by mines of mineral composition, micro-pore structure, and seepage mechanism. Microscopic petrological observations and laboratory core experiments show that the content of clay minerals such as the Imon mixed layer and kaolinite is high with high porosity and good pore roar structure;the water sensitivity is medium to strong, The lower the salinity of injected water, the greater the drop in core permeability;the velocity-sensitive damage is strong, and permeability increases with the increase in flow velocity, and a large number of particles are observed in the produced fluid under the microscope. Aiming at the contradiction of velocity sensitivity between core permeability increase and the permeability decrease near the wellbore, the velocity sensitivity seepage model of “long-distance migration and blockage near the well” is proposed, and the permeability and formation distribution formula are deduced. The calculated value is close to the test value of actual pressure recovery test. The research results of water sensitivity and velocity sensitivity provide important guidance for Bohai P oilfield to improve production and absorption capacity and reservoir protection.

Hydrogeological feasibility of mine water deep geological storage in Baotashan coarse sandstone:A case study in Ordos Basin

For the sake of mine water drainage and sustainable groundwater protection,the new approach of mine water deep geological storage(MWDGS)is highly necessary to save water resources in the semi-arid region of China.However,up to now,little academic research has been done on mine water geological storage.Given this situation,the hydrogeological feasibility of MWDGS was explored in Baotashan coarse sandstone(BCS)of Jurassic measure in Ordos Basin.The results show that the white-gray BCS with a fragile skeleton of quartz(41.4%),feldspar(21.1%),and clay minerals(16.4%)provides the potential variable-void for mine water;and its hydro-chemical type of BCS aquifer is CO_(3)-Na and Cl-Na.As the burial depth increases,the strong alkaline groundwater is in stagnant and poor recharge-runoff-discharge condition.The lab test shows that the pores whose diameter is over 10μm could be treated as the main storage of mine water;and the effective porosity varies from 1.36%to 3.46%.When mine water is injected,the strong hydrodynamics of mine water storage would change the permeability significantly and about 0.201%soluble solids would be dissolved.Partial clay minerals obstruct the pores and induce the saturated phase of high permeability to evolve into steady phase of lower permeability.Under the condition of nonhydraulic fracturing during continuous storage,the heterogeneous anisotropic medium obtained by Transition PRObability GeoStatistics(TPROGS)shows that the capacity of BCS aquifer is 0.455 to 1.226Mm^(3)for 1 km^(2)in the study area.The simulation shows that the groundwater mound in well-scale and mine-scale would be formed.The groundwater quality characteristics of“Three Zone”would occur around and gradually drop to approximate the original brine within 10 years.The hydrogeological feasibility reveals that this approach is useful for the well design and groundwater environment management during the mine water deep geological storage project in the Ordos basin.

Comparison of different spectral decompositions for non-marine deep water sandstone reservoir prediction in the Xingma area

It is difficult to identify and predict non-marine deep water sandstone reservoir facies and thickness,using routine seismic analyses in the Xingma area of the western Liaohe sag,due to low dominant frequencies,low signal-to-noise ratios,rapid lateral changes and high frequencies of layered inter-bedding.Targeting this problem,four types of frequency spectral decomposition techniques were tested for reservoir prediction.Among these,the non-orthogonal Gabor-Morlet wavelet frequency decomposition method proved to be the best,was implemented directly in our frequency analysis and proved to be adaptable to non-stationary signals as well.The method can overcome the limitations of regular spectral decomposition techniques and highlights local features of reservoir signals.The results are found to be in good agreement with well data.Using this method and a 3-D visualization technology, the distribution of non-marine deep water sandstone reservoirs can be precisely predicted.

Water-out performance and pattern of horizontal wells for marine sandstone reservoirs in Tarim Basin, NW China

Based on geological analysis,reservoir numerical simulation and production performance analysis,water-out performance and pattern of horizontal wells in Tarim marine sandstone reservoir were studied.Compared with continental sandstone reservoirs,the marine sandstone reservoirs in Tarim Basin were characterized by low oil viscosity,good reservoir continuity,and development of interbeds,which together with the large amount of horizontal wells,resulted in fast production rate and high recovery degree of the reservoirs.The main controlling factors of uneven water-out in horizontal wells were reservoir seepage barrier,injection-production well pattern,and dominant seepage channel.Thus 9 types in 4 categories of typical water-out pattern of horizontal wells in Tarim marine sandstone reservoirs were identified,and water-out management measures were proposed for them respectively according to their water-out mechanism and remaining oil distribution characteristics.Finally,the water-out pattern can be identified based on the inflection characteristics of derivative curve of water-oil ratio.This study of the water-out pattern can provide guidance for the adjustment policy of water injection in horizontal wells in marine sandstone reservoirs of Tarim Oilfield.

Evaluation and prevention of formation damage in offshore sandstone reservoirs in China

Reduction in water injectivity would be harmful to the waterflood development of offshore sandstone oil reservoirs. In this paper the magnitude of formation damage during water injection was evaluated by analyzing the performance of water injection in the Bohai offshore oilfield, China. Two parameters, permeability reduction and rate of wellhead pressure rise, were proposed to evaluate the formation damage around injection wells. The pressure performance curve could be divided into three stages with different characteristics. Analysis of field data shows that formation damage caused by water injection was severe in some wells in the Bohai offshore oilfield, China. In the laboratory, the content of clay minerals in reservoir rock was analyzed and sensitivity tests （including sensitivity to water, ftow rate, alkali, salt and acid） were also conducted. Experimental results show that the reservoir had a strong to medium sensitivity to water （i.e. clay swelling） and a strong to medium sensitivity to flow rate, which may cause formation damage. For formation damage prevention, three injection schemes of clay stabilizer （CS） were studied, i.e. continuous injection of low concentration CS （CI）, slug injection of high concentration CS （SI）, and slug injection of high concentration CS followed by continuous injection of low concentration CS （SI-CI）. Core flooding experiments show that SI-CI is an effective scheme to prevent formation damage and is recommended for the sandstone oil reservoirs in the Bohai offshore oilfield during water injection.

A Sand Control and Development Model in Sandy Land Based on Mixed Experiments of Arsenic Sandstone and Sand: A Case Study in Mu Us Sandy Land in China

Serious desertification caused by human activity and climate change,in addition to water loss and soil erosion related to arsenic sandstone in the Mu Us Sandy Land,lead to severe scarcity of soil and water resources,which causes worse local agricultural conditions accordingly.Many physical properties of arsenic sandstone is complementary with that of sand,arsenic sandstone is therefore supposed to be blended to enhance water productivity and arability of sandy land.Container experiments are carried out to study the enhancement of water holding capacity of the mixture,the blending ratio of arsenic sandstone and sand,and the proper size of the arsenic sandstone particles,respectively.The results of the experiments show that particle size of 4 cm with a ratio of 1∶2 between arsenic sandstone and sand are the proper parameters on blending.Both water content and fertility increase after blending.Water use efficiency in the mixture is 2.7 times higher than that in sand by the water release curves from experiments.Therefore,a new sand control and development model,including arsenic sandstone blending with sand,efficient water irrigation management and reasonable farming system,is put forward to control and develop sandy land so that water-saving agriculture could be developed.Demonstration of potato planting about 153.1 ha in area in the Mu Us Sandy Land in China indicates that water consumption is 3018 m3/ha in the whole growth period.It means that about 61%of irrigation water can be saved compared with water use in coarse sand without treatment.Recycle economic mode and positive feedback of sand resource-crop planting-soil resource are constructed,which changes sand into arable soil and make it possible to develop water-saving agriculture on it.The proposed model will be helpful for soil-water resources utilization and management in the Mu Us Sandy Land.

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.