Sensitivity Analysis of Multi-phase Seepage Parameters Affecting the Clayey Silt Hydrate Reservoir Productivity in the Shenhu Area,South China Sea

Natural gas hydrate(NGH)is an important future resource for the 21st century and a strategic resource with potential for commercial development in the third energy transition.It is of great significance to accurately predict the productivity of hydrate-bearing sediments(HBS).The multi-phase seepage parameters of HBS include permeability,porosity,which is closely related to permeability,and hydrate saturation,which has a direct impact on hydrate content.Existing research has shown that these multi-phase seepage parameters have a great impact on HBS productivity.Permeability directly affects the transmission of pressure-drop and discharge of methane gas,porosity and initial hydrate saturation affect the amount of hydrate decomposition and transmission process of pressure-drop,and also indirectly affect temperature variation of the reservoir.Considering the spatial heterogeneity of multi-phase seepage parameters,a depressurization production model with layered heterogeneity is established based on the clayey silt hydrate reservoir at W11 station in the Shenhu Sea area of the South China Sea.Tough+Hydrate software was used to calculate the production model;the process of gas production and seepage parameter evolution under different multi-phase seepage conditions were obtained.A sensitivity analysis of the parameters affecting the reservoir productivity was conducted so that:(a)a HBS model with layered heterogeneity can better describe the transmission process of pressure and thermal compensation mechanism of hydrate reservoir;(b)considering the multi-phase seepage parameter heterogeneity,the influence degrees of the parameters on HBS productivity were permeability,porosity and initial hydrate saturation,in order from large to small,and the influence of permeability was significantly greater than that of other parameters;(c)the production potential of the clayey silt reservoir should not only be determined by hydrate content or seepage capacity,but also by the comprehensive effect of the two;and(d)time scales need to be considered when studying the effects of changes in multi-phase seepage parameters on HBS productivity.

Rate transient analysis methods for water-producing gas wells in tight reservoirs with mobile water

Tight gas reservoirs with mobile water exhibit multi-phase flow and high stress sensitivity.Accurately analyzing the reservoir and well parameters using conventional single-phase rate transient analysis methods proves challenging.This study introduces novel rate transient analysis methods incorporating evaluation processes based on the conventional flowing material balance method and the Blasingame type-curve method to examine fractured gas wells producing water.By positing a gas-water two-phase equivalent homogenous phase that considers characteristics of mobile water,gas,and high stress sensitivity,the conventional single-phase rate transient analysis methods can be applied by integrating the phase's characteristics and defining the phase's normalized parameters and material balance pseudotime.The rate transient analysis methods based on the equivalent homogenous phase can be used to quantitatively assess the parameters of wells and gas reservoirs,such as original gas-in-place,fracture half-length,reservoir permeability,and well drainage radius.This facilitates the analysis of production dynamics of fractured wells and well-controlled areas,subsequently aiding in locating residual gas and guiding the configuration of well patterns.The specific evaluation processes are detailed.Additionally,a numerical simulation mechanism model was constructed to verify the reliability of the developed methods.The methods introduced have been successfully implemented in field water-producing gas wells within tight gas reservoirs containing mobile water.

Prediction of immiscible gas flooding performance:a modified capacitance-resistance model and sensitivity analysis

Reservoir performance prediction is one of the main steps during a field development plan.Due to the complexity and time-consuming aspects of numerical simulators,it is helpful to develop analytical tools for a rapid primary analysis.The capacitance-resistance model(CRM)is a simple technique for reservoir management and optimization.This method is an advanced time-dependent material balance equation which is combined with a productivity equation.CRM uses production/injection data and bottom-hole pressure as inputs to build a reliable model,which is then combined with the oil-cut model and converted to a predictive tool.CRM has been studied thoroughly for water flooding projects.In this study,a modified model for gas flooding systems based on gas density and average reservoir pressure is developed.A detailed procedure is described in a synthetic reservoir model using a genetic algorithm.Then,a streamline simulation is implemented for validation of the results.The results show that the proposed model is able to calculate interwell connectivity parameters and oil production rates.Moreover,a sensitivity analysis is carried out to investigate effects of drawdown pressure and gas PVT properties on the new model.Finally,acceptable ranges of input data and limitations of the model are comprehensively discussed.

Effects of physical parameter range on dimensionless variable sensitivity in water flooding reservoirs

The similarity criterion for water flooding reservoir flows is concerned with in the present paper. When finding out all the dimensionless variables governing this kind of flow, their physical meanings are subsequently elucidated. Then, a numerical approach of sensitivity analysis is adopted to quantify their corresponding dominance degree among the similarity parameters. In this way, we may finally identify major scaling law in different parameter range and demonstrate the respective effects of viscosity, permeability and injection rate.

Productivity Analysis Method of Abnormal High-Pressure Gas Reservoir in Ying-Qiong Basin

Ying-Qiong Basin in the west of South China Sea contains plenty of abnormal high-pressure gas reservoirs, whose stress sensitivity is crucial for well productivity. To explore the influence of stress sensitivity on production, the variable outlet back pressure stress sensitivity experiments were applied to test core sample permeability under different burden pressure and obtain the relational expression of power function of core stress sensitivity. Afterwards, new productivity equation is deduced in consideration of reservoir stress sensitivity, and the affection of stress sensitivity on production is analyzed. The result demonstrates close link between stress sensitivity and productivity, since single well production decreases dramatically when reservoir stress sensitivity has been taken into account. This research is constructive for well-testing data interpretation in stress sensitive gas reservoirs.

Isotopic characteristics and source analysis of atmospheric ammonia during agricultural periods in the Xichuan area of the Danjiangkou Reservoir

Nitrogen deposition is an important means of exogenous nitrogen input in reservoir water.Agricultural activities around the reservoir lead to a sharp increase in the concentration of ammonia in the atmosphere,which poses a threat to the reservoir water body.Clarifying the contribution of agricultural ammonia release to atmospheric NH_(x)(gaseous NH_(3)and particulate NH_(4)^(+)),in the reservoir area can provide a theoretical foundation for local reactive nitrogen control.We collected atmospheric NH_(3)and NH_(4)^(+)samples during the agricultural periods and analyzed the isotopic characteristics of atmospheric NH_(x)and the contribution rates of different ammonia sources in the Xichuan area of the Danjiangkou Reservoir.The results showed that the initialδ~(15)N values of NH_(3)(-30.0‰to–7.2‰)and particulate NH_(4)^(+)(–33‰to+4.9‰for finer and coarser particles,respectively)are different,and their contribution ratios from dissimilar ammonia sources are also different,among which NH_(4)^(+)is more susceptible to meteorological factors.However,since the atmospheric NH_(x)in the Xichuan area is mainly gaseous NH_(3),the final sources of atmospheric ammonia nitrogen source depend on gaseous NH_(3).Agricultural sources(59%-74%)were the main NH_(3)sources in this area.Among them,the fertilizer use emission was dominant;it had the highest contribution rate in summer during the agricultural period and a more prominent impact in areas with less human interference.Reasonable regulation of the application of high-ammonia releasing fertilizer,especially during the agricultural period in summer,is an effective way to reduce the threat of atmospheric ammonia to water health.

Sensitivity analysis for the total nitrogen pollution of the Danjiangkou Reservoir based on a 3-D water quality model

Inter-basin water deal of nitrogen are great transfers containing a great threats to human health, biodiversity, and air and water quality in the recipient area. Danjiangkou Reservoir, the source reservoir for China＇s South-to-North Water Diversion Middle Route Project, suffers from total nitrogen pollution and threatens the water transfer to a number of metropolises including the capital, Beijing. To locate the main source of nitrogen pollution into the reservoir, especially near the Taocha canal head, where the intake of water transfer begins, we constructed a 3-D water quality model. We then used an inflow sensitivity analysis method to analyze the sig- nificance of inflows from each tributary that may contribute to the total nitrogen pollution and affect water quality. The results indicated that the Han River was the most significant river with a sensitivity index of 0.340, followed by the Dan River with a sensitivity index of 0.089, while the Guanshan River and the Lang River were not significant, with the sensitivity indices of 0.002 and 0.001, respectively. This result implies that the concentration and amount of nitrogen inflow outweighs the geographical position of the tributary for sources of total nitrogen pollution to the Taocha canal head of the Danjiangkou Reservoir.

Production optimization in a fractured carbonate reservoir with high producing GOR

The Gas-Oil Ratio(GOR)is a crucial production parameter in oil reservoirs.An increase in GOR results in higher gas production and lower oil production,potentially leading to well shut-ins due to economic infeasibility.This study focuses on a real fractured oil field that requires urgent production operations to reduce the producing GOR.In this study,the static model for the field was developed using commercial software,involving steps such as data collection,fault modeling,meshing,and statistical analysis to prepare for dynamic simulation.The dynamic model incorporates geometry,gridding,and rock properties from the static model,utilizing a dual-porosity approach for the naturally fractured reservoir and the Peng-Robinson equation for fluid phase behavior.Initial reservoir conditions,production history,and rock-fluid interactions were defined,with relative permeability curves indicating a water-wet reservoir and low critical gas saturation affecting the GOR.To better understand the relationship between reservoir and production parameters,a detailed sensitivity analysis was performed using the Response Surface Methodology(RSM).Following the sensitivity analysis,a history matching process was conducted using the Designed Exploration and Controlled Evolution(DECE)optimizer to validate the model for future forecasts.Six operational scenarios were defined to decrease the production GOR and enhance final recovery from the field.The results indicate that the water injection scenario is effective in preventing the GOR increase by maintaining reservoir pressure,thereby sustaining production over a longer period.This scenario also improves oil recovery by approximately 6%compared to the base case.Finally,optimization was carried out using the DECE optimizer for each scenario to fine-tune the operational parameters.The goal was to maximize oil revenue for each scenario during the optimization process.This study stands out as one of the few that provides a comprehensive analysis of production behavior and development planning for a real fractured reservoir with high producing GOR.

缝洞型碳酸盐岩气藏斜井Blasingame产量递减模型

为了更准确地认识缝洞型碳酸盐岩气藏产量递减规律,假设气藏顶底边界和外边界封闭,储集层水平等厚,建立了斜井三孔单渗和三孔双渗的Blasingame产量递减模型。采用拉普拉斯变化等数学方法求解模型,得到井底压力解并将其代入转换方程后获得递减产量解,再通过数值反演得到真实空间下的产量解。绘制且对比了斜井三孔单渗和三孔双渗Blasingame产量递减曲线,并对斜井三孔双渗的产量递减曲线进行了参数敏感性分析。结果表明:斜井三孔双渗产量递减曲线位置在初期比单渗的产量递减曲线位置更低,且窜流凹子更浅;裂缝渗透率比值越大,窜流凹子越深、曲线位置越低;窜流系数越大,窜流发生越早、曲线位置左移;基质弹性储容比越大,基质向裂缝窜流的窜流凹子越宽越深、溶洞向裂缝窜流的窜流凹子越窄越浅;斜井长度越长、井斜角越大,产量递减曲线位置越高且曲线向左移动;结合现场实例井解释,斜井三孔双渗模型比斜井三孔单渗模型拟合效果更好、解释结果更可靠。建立的单双渗模型和绘制的Blasingame产量递减曲线可预测碳酸盐岩气藏斜井的产量递减规律。

Sensitivity analysis of reservoir risk in marine gas hydrate drilling

It is easy to change the original temperature state of marine gas hydrate reservoir by drilling,which leads to uncontrollable decomposition of gas hydrate and release of large amount of gas.The decomposition gas will further escape and expand,and the reservoir will break and collapse due to its weak cementation characteristic,which will easily lead to a series of other potential risks.Therefore,in this study,based on the drilling process of marine gas hydrate,we establish the theoretical model and numerical calculation method of wellbore temperature field,analyze the influence on wellbore temperature of drilling fluid displacement,density,viscosity and injection temperature,and seawater depth.Then the sensitivity laws of reservoir risk in marine gas hydrate drilling are obtained.The results show that with the increase of drilling fluid displacement,density,viscosity and injection temperature,the temperature in lower well section and bottom hole will increase,making the increasing amplitude of temperature in hydrate reservoir larger and the scope of influence on hydrate reservoir stability bigger.Moreover,drilling is more likely to raise the temperature of reservoirs in shallow seawater depth,posing greater risks.Thus,engineering measures to avoid risks caused by rising reservoir temperature in marine gas hydrate reservoir drilling are presented.This study is of great significance to ensure the safety of marine gas hydrate reservoir drilling.

Effectiveness and sensitivity analysis of solution gas re-injection in Baikouquan tight formation,Mahu sag for enhanced oil recovery

To address the fast productivity decline of the horizontal wells and low oil recovery during natural depletion in Baikouquan formation,the approach of solution gas re-injection was proposed with the primary objective of further developing this formation.Herein,a field-scale numerical compositional reservoir model was built up based on the formation properties and then the effects of permeability,fractures and formation stress on the production dynamics were thoroughly investigated.A sensitivity analysis,which can correlate the oil recovery with these parameters,was also performed.The results showed that the re-injection of solution gas could remarkably retard the production depletion of the horizontal wells thereby improving the oil production.The oil recovery rate increased with permeability,fracture half-length,fracture conductivity,and formation dip.With regard to the fracture distribution,it was found that the interlaced fracture outperformed the aligned fracture for the solution gas re-injection.The influence of the formation stress should be carefully considered in the production process.Sensitivity analysis indicated that the formation dip was the paramount parameter,and the permeability,fracture half-length,and fracture conductivity also played central roles.The results of this study supplement earlier observations and provide constructive envision for enhanced oil recovery of tight reservoirs.

Investigation of the influences of asphaltene deposition on oilfield development using reservoir simulation

This paper investigates the deposition of asphaltenes in the porous medium of the studied field in Russia and predicts production profiles based on uncertainty evaluation. This problem can be solved by dynamic modeling, during which production profiles are estimated in two scenarios: with and without the activation of the asphaltene option. Calculations are carried out for two development scenarios: field operation under natural depletion and water injection into the aquifer as a reservoir pressure maintenance system. A full-scale compositional reservoir simulation model of the Russian oilfield was created. Within a dynamic simulation, the asphaltene option was activated and the asphaltene behavior in oil and porous medium was tuned according to our own special laboratory experiments. The model was also matched to production historical data, and a pattern model was prepared using the full-scale simulation model. Technological and the asphaltene option parameters were used in sensitivity and an uncertainty evaluation. Furthermore, probable production profiles within a forecast period were estimated. The sensitivity analysis of the pattern model to input parameters of the asphaltene option allowed determining the following heavy-hitters on the objective function: the molar weight of dissolved asphaltenes as a function of pressure, the asphaltene dissociation rate, the asphaltene adsorption coefficient and the critical velocity of oil movement in the reservoir. Under the natural depletion scenario, our simulations show a significant decrease in reservoir pressure and the formation of drawdown cones leading to asphaltene deposition in the bottom-hole area of production wells, decreasing their productivity. Water injection generally allows us to significantly reduce the volume of asphaltene phase transitions and has a positive effect on cumulative oil production. Injecting water into aquifer can keep the formation pressure long above the pressure for asphaltene precipitation, preventing the asphaltene deposition resulted from interaction of oil and water, so this way has higher oil production.

A new method to calculate the productivity index for vertical fractured well of tight gas reservoir

Generally the irreducible water saturation of low permeability gas reservoir is quite high which leads to the permeability stress sensibility and threshold pressure gradient. Under the assumption that permeability varies with experimental law of the pseudo pressure drop, according to concepts of perturbable ellipses and equivalent developing regulations, the calculation method of stable production of hydraulically fractured gas well in low permeability reservoirs is investigated with threshold pressure. And productivity curve is drawn and analyzed. The result shows that, permeability modulus and threshold pressure have effect on production of fractured gas well. The higher the permeability modulus and the threshold pressure, the lower the production is. Therefore, the impact of stress sensitive and threshold pressure must he considered when analyzing the productivity of vertical fracture well in low permeability gas reservoir.

干热岩压裂储层布井方式优选数值模拟

增强型地热系统(EGS)是从干热岩储层中提取热能的重要手段,而布井方式是影响其采热效果的关键因素,目前开展的布井方式研究较少考虑压裂储层开采模型的影响。建立了干热岩压裂储层采热的数值模型,通过不同位置的基质岩体温度下降幅度、热提取率、采出温度和采热功率对比分析了4种不同的布井方式对EGS采热性能的影响。结果表明:相较于直井,水平井的流体热交换的面积更大,能充分开发裂缝间的热量。在生产30 a时,考虑水力压裂裂缝连通的情况下,水平井一注两采模型的采热效率最高,其在垂直于井方向上温度波及范围约690 m,基质岩体平均温度下降38.09 K,热提取率为24.42%,采热功率为3.5 MW。研究成果为提高地热系统产热量、实现干热岩高效可持续开发提供了理论参考。

丹江口水库运行期非一致性洪水频率分析

汉江流域上游已建成投运诸多水库及引调水工程,显著改变了汉江流域径流的时空分布,导致洪水资料序列的非一致性。现将洪水系列资料延长至2023年,开展非一致性洪水频率分析,以水库系数和调水工程系数作为协变量,建立时变P-Ⅲ分布模型,定量估算丹江口水库运行期的设计洪水,并与原设计成果对比。结果表明:所选协变量符合水文客观规律,均可反映上游水利工程调蓄对丹江口坝址设计洪水的影响;丹江口水库运行期1000 a一遇设计洪峰流量和7 d洪量较原设计成果均削减31%左右;汉江上游水库调蓄对设计洪水的影响比调水工程更加显著。由于丹江口水库运行期设计洪量显著减少,在防洪标准不变的前提下可酌情提高水库的运行水位,这不仅有利于增加发电量,还可提高水资源利用效率和水库蓄满率。

南方灌区沟渠塘库系统水平衡模拟模型研究

定量描述南方多水源灌区灌溉水转化机制是实现灌区水资源高效利用的基础。本文以湖北省漳河灌区内部的杨树垱流域为例,考虑其内部的空间异质性,对流域划分灌溉子区并对灌排系统进行水平和垂向概化,根据水量平衡原理研发多个水平衡子模块,构建沟渠塘库系统水平衡模拟模型。根据2021-2022年典型塘堰和内部水库的实测逐日水位资料,利用拉丁超立方抽样法和偏相关分析法对模型参数进行敏感性分析,并在不同流域尺度上对模型进行率定和验证。模拟结果的Nash-Sutcliffe系数(0.72~0.99)、均方根误差(0.09~0.20 m)和平均绝对误差(0.08~0.14 m)表明模型模拟效果较好,与传统灌区分布式水平衡模拟模型相比,该模型可以在满足较高精度的同时,更为全面地描述灌区水转化过程,为定量描述流域内灌溉系统的水转化过程提供新途径。

新疆阜康矿区四工河区块煤储层敏感性分析

为研究新疆阜康矿区四工河区块煤层气开采过程中渗透率对煤储层的损害程度,对该区A2和A5煤层开展了应力敏感性、速敏性、水敏性、酸敏性、碱敏性实验。结果表明:研究区储层具有中等偏强的应力敏感性、速敏性和偏弱的水敏性、酸敏性和碱敏性;伤害储层的主因为应力敏感性与速敏性;净围压的增大导致煤样塑性变形,随入口压力增加,煤样渗透率急剧下降。

龙凤山火山岩气藏经济有效开发下限研究

龙凤山气田火山岩气藏地质条件复杂,具有“喷发期次多、机构规模小、岩相变化快、流体性质多变”的特点,不同井区储层物性参数和气藏类型不同,致使经济评价时所用测算参数差异较大。以现金流量法为基础,针对不同气藏类型(井区)建立了经济评价模型,分析了敏感性因素。结合气藏生产特征,建立了不同井区不同水平段长度经济有效开发下限图版,并分析了不同条件下实现气田经济有效开发所应满足的基本物质条件,优选了经济有效开发区块。结果表明,储层中深是影响气田开发经济效益最重要的因素,北213井区储层中深3400 m,当水平段长度800 m时,经济有效开发初产下限3.4×10^(4)m^(3)/d、单井控制储量下限1.6×10^(8)m^(3)。在目前经济技术条件下,水平段长度800~1600 m时,北5井区期次1西部、北213井区和北217井区期次3东南部、北213井区期次4东北部和北218井区期次4西北部可作为部署水平井的目标区块。

庙沟水库复合土工膜受力变形敏感性分析

探究不同因素对庙沟水库土工膜受力变形的影响程度,对深入了解土工膜在实际工程环境中的性能,提高水库工程的安全性和可靠性至关重要。基于赫章县庙沟水库除险加固工程,采用数值模拟方法设计正交实验探究了黏土保护层不同参数对复合土工膜受力变形的影响程度,并采用极差分析法对正交试验结果进行分析。结果表明,复合土工膜竖向变形最大值受体积压缩模量系数变化的影响最为显著,弹性模量系数的变化对单宽拉应力和拉应变最大值的影响最为显著。

河北省娄里水库防洪效益分析及经济评价

娄里水库是洺河流域防洪体系的重要工程,主要任务为防洪,主要防洪保护对象为坝址下游的永年城区、洺河两岸村镇和耕地、大陆泽宁晋泊缓滞洪区。分析了娄里水库防洪效益,其中永年城区防洪效益采用最优等效替代法,其他地区直接防洪效益采用频率法进行计算,适当考虑间接防洪效益,在防洪效益分析的基础上进行经济评价。结果表明,娄里水库防洪效益显著,经济内部收益率等指标符合规范要求,经济可行。未来进行防洪效益分析时,还应充分考虑人民生命、生态和社会等非经济效益,完善现有防洪效益的分析计算方法。