Characterization of the generalized permeability jail in tight reservoirs by analyzing relative-permeability curves and numerical simulation

This study comprehensively characterizes the boundary values of generalized permeability jail in tight reservoirs through relative-permeability curve analysis,numerical simulation,and economic evaluation.A total number of 108 relative-permeability curves of rock samples from tight reservoirs were obtained,and the characteristics of relative-permeability curves were analyzed.The irreducible water saturation(Swi)mainly ranges from 20% to 70%,and the residual gas saturation(Sgr)ranges from 5% to 15% for 55% of the samples.The relative-permeability curves are categorized into six types(Category-Ⅰ to Ⅵ)by analyzing the following characteristics:The relative permeability of gas at Swi,the relative permeability of water at Sgr,and the relative permeability corresponding to the isotonic point.The relative permeability curves were normalized to facilitate numerical simulation and evaluate the impact of different types of curves on production performance.The results of simulation show significant difference in production performance for different types of relative-permeability curves:Category-Ⅰ corresponds to the case with best well performance,whereas Categories-Ⅴ and Ⅵ correspond to the cases with least production volume.The results of economic evaluation show a generalized permeability jail for Categories-Ⅳ,Ⅴ,and Ⅵ,and the permeability jail develops when the relative permeability of gas and water is below 0.06.This study further quantifies the range of micro-pore parameters corresponding to the generalized permeability jail for a tight sandstone reservoir.

Test of the Relative Permeability Curve of a Gas and Oil Condensate System and its Effect on the Recovery of Oil and Gas

The relative permeability curve has been measured with simulation oil (refined oil) and gas (nitrogen or air) at room temperature and a lowpressure, both of which are very important parameters for depicting the flow of fluid through porous media in a hydrocarbon reservoir. This basic measurement is often applied in exploitation evaluation, but the underground conditions with high temperature and pressure, and the phase equilibrium of oil and gas, are not taken into consideration when the relative permeability curve is tested. There is an important theoretical and practical sense in testing the diphase relative permeability curve of the equilibrium of oil and gas under the conditions of high temperature and pressure. The test method for the relative permeability curve is proposed in this paper. The relative permeability of the equilibrium of oil and gas and the standard one are tested in two fluids, and the differences between these two methods are stated. The research results can be applied to the simulation and prediction of CVD in long cores and then the phenomenon can better explain that the recovery of condensate gas rich in condensate oil is higher than that of CVD test in PVT. Meanwhile, the research shows that the relative permeability curve of equilibrium oil and gas is sensitive to the rate of exploitation, and the viewpoint proves that an improved gas recovery rate can properly increase the recovery of condensate oil.

Classification Study on Relative Permeability Curves

The classification method of relative permeability curves is rarely reported, when relative permeability curves are applied;if the multiple relative permeability curves are normalized directly, but not classified, the calculated result maybe cause a large error. For example, the relationship curve between oil displacement efficiency and water cut, which derived from the relative permeability curve in LD oilfield is uncertain in the shape of low water cut stage. If being directly normalized, the result of the interpretation of the water flooded zone is very high. In this study, two problems were solved: 1) The mathematical equation of the relationship between oil displacement efficiency and water cut was deduced, and repaired the lost data of oil displacement efficiency and water cut curve, which solve the problem of uncertain curve shape. After analysis, the reason why the curve is not available is that relative permeability curves are not classified and optimized;2) Two kinds of classification and evaluation methods of relative permeability curve were put forward, the direct evaluation method and the analogy method;it can get the typical relative permeability curve by identifying abnormal curve.

A Method for Calculating Oil Field Relative Permeability Curve by Using Water Drive Characteristic Curve in High Water Cut Stage

With the production of strong bottom water reservoir, it will soon enter the ultra-high water cut stage. After entering the ultra-high water cut period, the main means of stable production is liquid extraction. Large liquid volume has a certain impact on the physical property distribution and fluid seepage law of the oilfield. The relative permeability curve measured according to the industry standard is not used for the prediction of development indicators and the understanding of the dynamic law of the oilfield. In order to understand the characteristics of water drive law in high water cut stage of water drive oilfield, starting from the water drive characteristic curve in high water cut stage, the method for calculating the relative permeability curve is deduced. Through numerical simulation verification and fitting the actual production data, it is confirmed that the obtained relative permeability curve is in line with the reality of the oilfield, It can provide some guiding significance for understanding the production law and water drive law of strong bottom water reservoir in ultra-high water cut stage.

The Influence Law of Oil Relative Permeability on Water Cut

Water cut is a key evaluation parameter for reservoir development evaluation. Relative permeability curve reflects reservoir characteristics and fluid characteristics. It is important to figure out the influence law of oil relative permeability on water cut. Based on the 269 relative permeability curves of Bohai oilfields, the distribution of oil index of Bohai oilfields were studied. On the basis, combined with Corey expression of relative permeability and fractional flow equation, the theoretical relationship between oil index and water cut increasing rate was established. Three end points of water cut increasing rate curve were proposed and the influence law between three end points and oil index was studied. The results show that the oil index has a linear relationship with three end points. When the value of water oil mobile ratio is large than 1, with the increase of oil index, maximum value of water cut increasing rate gradually increase. When the value of water oil mobile ratio is less than 10, oil index has great effect on recovery percent when water cut increasing rate reaches to the maximum value as well as water cut when water cut increasing rate reaches to the maximum value. The application of SS field shows that the theoretical value is consistent with the field data.

A Statistical Model for the Relative Hydraulic Conductivity of Water Phase in Unsaturated Soils

Permeability coefficients of fluids occupying the pore space of a porous medium have significant influence on the flow of these fluids through the porous medium. In the case of unsaturated soils, in addition to other parameters such as void ratio, void distribution, particle size distribution and initial density the degree of saturation also affects the permeability coefficient of water. The degree of saturation, in unsaturated soil, is directly related to the matric suction of the soil through soil water characteristic curve. Matric suction is one of the two stress state variables widely used to characterize the deformation behavior of unsaturated soils. Therefore, it can be stated that both flow and deformation behaviors of unsaturated soil are affected by the permeability coefficient of water. Numerical modeling of coupled deformation-flow behavior of unsaturated soil requires a mathematical equation that relates the permeability coefficient to the degree of saturation. Since the parameters that affect the permeability coefficient of water in unsaturated soil have similar direct or indirect effects on the soil water characteristic curve, permeability can be effectively predicted using the soil water characteristic curve as done in statistical models. In this paper, a statistical model is proposed for the permeability of water in unsaturated soil using soil water characteristic curve of the soil. The calibrated parameters of the soil water characteristic curve are directly used in the prediction of permeability with- out additional calibration using measured permeability data. The predictive capability of the new equation is verified by matching the measured data of eight different soils found in the literature.

Study on gas-liquid relative permeability experiments of fractured-porous reservoirs

For carbonate reservoirs,gas-water and oil-gas relative permeability curve are of importance for parameters calculation in oil-field development,dynamic analysis and numerical reservoir simulation.The oil-gas/gas-water relative permeability curves were measured with unstable method under normal temperature and low pressure,using fifteen artificial fractured cores.The shape and change characteristics of gas/water and oil/gas relative permeability curve were mainly analyzed.The results showed that for the relative permeability curve of water driving gas.The saturation of equal permeability point,the saturation range of two-phase flow region and the displacement efficiency has a good power-function relation with core permeability.In addition,the saturation of equal permeability point,the saturation range of two-phase flow region and the displacement efficiency will decrease with the increasing of core permeability.However,for oil-gas relative permeability curves,the saturation of equal permeability point,the saturation range of two-phase flow region and the displacement efficiency will increase with the increasing of core permeability.It should be noted that the gas relative permeability presents a straight line in the normalized relative permeability curve,which indicates that the main flow is dominated by fracture with low displacement efficiency.The research results provide theory basis for fracture-vuggy carbonate reservoir development and new research idea for the further study of this kind of reservoir.

相对渗透率定量预测新方法

在压汞测试的基础上 ,利用分形几何学原理和方法 ,建立了毛管压力曲线分形模型和相对渗透率的分形预测模型。在毛管压力曲线分形模型和分数维的基础上 ,能准确确定任意含水饱和度 ,提高了饱和度的预测精度。在此基础上 ,利用建立的相对渗透率分形预测模型 ,可求得任意含水饱和度下的润湿相相对渗透率和非润湿相的相对渗透率。

鄂尔多斯盆地东南部长6储层岩电关系特征

鄂尔多斯盆地东南部延长组长6储层以低孔低渗特低渗为特征,长6岩心岩电实验分析结果表明,岩电关系复杂,其中孔隙度-地层因素(F)关系中,a、m参数变化范围大,具有相对高a值低m值的特点,同时,含水饱和度(S_w)-电阻率增大系数(I)关系除常规直线关系外,相当一部分储层含水饱和度(S_w)-电阻率增大系数(I)表现为分段线性函数关系,n参数大多小于2.0.

产量递减规律与水驱特征曲线的关系

建立了不同条件下Arps、Logistic产量递减方程与不同水驱特征曲线之间的对应关系,使得这2个油田开发基本规律不再完全孤立、互不相关。研究表明:在油田渗流条件保持基本不变的条件下,符合某一递减方程的油相渗流特征,若能与水相渗流特征一起构成某一种水驱特征曲线的油水相渗比值关系式,那么产量递减方程与水驱特征曲线之间存在必然的联系:在油田渗流条件发生变化的条件下,若Qw+nO。保持为某一常数,那么水驱特征曲线I～Ⅲ的产量递减方程均服从双曲递减,水驱特征曲线Ⅳ[m=1]产量递减方程服从调和递减;若Qw+nQ。=kexp（st）,水驱特征曲线Ⅳ[m=1]的产量递减方程服从Logistic产量递减。

基于参数优选的储层渗透率深度置信网络模型预测初探

储层渗透率是储层产能的一个重要影响因素。针对常规测井渗透率模型在孔隙连通性差的低渗砂岩储层预测精度不高的问题,提出利用深度置信网络算法结合常规测井曲线预测储层渗透率的方法。该方法利用灰色关联法对测井曲线进行了关联度分析,依据相关度排序选取了特征敏感测井曲线,结合深度置信网络的有监督学习调优与对比散度算法进行数据挖掘,建立了渗透率的预测模型。该模型在以往BP神经网络的基础上改善了局部优化的问题,提高了网络模型的训练效率与预测精度。预测模型的平均相对误差为9.1%,相比常规渗透率模型,降低了20%左右。通过对实际资料的处理应用,结合误差分析,表明该方法能够有效地提高低渗透储层渗透率的预测精度。

高水头抽水蓄能电站高压岔管围岩非线性渗流分析及渗透稳定性研究

针对抽水蓄能电站钢筋混凝土岔管承载的高内水压力导致围岩高渗压差、高水力梯度等问题,以高压岔管围岩渗流控制为目标,结合现场高压压水试验及其解析模型,定量分析高渗压下岔管围岩的渗流参数,基于单裂隙花岗岩非达西渗流室内试验成果,拟合Forchheimer非达西渗流方程影响因子与渗透率之间的指数型关系式。在此基础上,采用Forchheimer非达西渗流方程、Signorini型变分不等式和自适应罚函数相结合的方法,推导非达西渗流控制方程组及其有限元计算格式,并将其应用于阳江抽水蓄能电站高岔区围岩渗流规律研究。结果表明:高压岔管内水外渗导致防渗排水措施和导水断层附近区域产生了强烈的非达西渗流;采用非达西渗流理论计算的渗漏量明显小于达西渗流理论计算值,且差值伴随着流场非线性的增强而增大。研究成果对于高水头抽水蓄能电站岔管区防渗设计与控制具有参考价值。

Displacement behavior and mechanism of long-term water flooding in sandstone oil reservoirs

Sandstone oil reservoirs with huge bottom water and high permeability are generally developed with high flow rate.After long-term water flooding(LTWF),the water flooding characteristics are quite different from that of original reservoir.In this paper,the effects of the PV number,viscosity,and displacement rate during LTWF are studied through experiments.The mechanism is analyzed based on analysis of changes in oil composition,rock mineral composition and wettability.The oil-water relative permeability curves,oil recovery and wettability were obtained with new experiments methods,which avoids the oil metering error by measuring oil and water separately.The research indicates that when the viscosity increases,the water phase permeability decreases,the residual oil saturation increases,and the water content rate increases earlier.A higher water flooding rate results in a higher ultimate recovery.A higher asphaltene content results in a higher viscosity and more oil-wet reservoir conditions.After LTWF,the wettability tends to water-wet,which is more favorable for heavy oil recovery.Moreover,LTWF reduces the clay content,which creates a more water-wet surface and a larger reservoir pore throat environment.This research provides insightful characteristics of offshore sandstone oil reservoirs,which can be used to enhance oil recovery.

新型水驱特征曲线在低渗透油藏的应用

在油田开发过程中,采出程度、可采储量和含水率变化的预测是评价油田开发效果的重要指标,现有的计算方法大多适用于中、高渗透油藏,在低渗透油藏指标预测过程中存在较大差异。针对该类问题,以吴起油田低渗透油藏为研究对象,运用了一种新型水驱特征曲线公式,该公式综合了纳扎洛夫和西帕切夫水驱特征曲线特点,利用理论推导与数理统计的方法,得出了适用于吴起油田的含水率和采出程度关系图版。研究结果表明:新型水驱特征曲线能够有效反映低渗透油藏含水变化规律,通过数据拟合确定出待定参数,从而确定出低渗透油藏含水率与累计产量的关系式,通过关系式建立的曲线与生产数据曲线符合度高,低渗透油藏含水上升率变化呈先上升后下降的规律。该研究对低渗透油藏的开发部署方案编制中的开发指标预测具有一定指导意义。

Improving the Predictive Capability of Popular SWCCs by Incorporating Maximum Possible Suction

Soil-water characteristic curve (SWCC) that represents the relationship between the soil moisture and matric suction is one of the important constitutive models required for numerical modeling of unsaturated soils. An effective SWCC model should be capable of calculating the moisture-suction variation for the entire range of degree of saturation. Applicability of popular SWCC models such as Brooks and Corey, van Genuchten, and Fredlund and Xing is limited, especially in low (< 20%) degree of saturation range. In this study, all these models are modified by incorporating maximum suction as one of the model parameters, so that these models can be effectively used over the entire range of degree of saturation. The Fredlund et al (1994) permeability function is also modified based on the modification to the Fredlund and Xing SWCC model. The applicability of the improved models is investigated by calibrating the SWCC of various types of soil and presented in this paper. Based on this study it can be concluded that the modified models are flexible enough to fit the experimental data for the entire range of degree of saturation.

Electrical responses and classification of complex waterflooded layers in carbonate reservoirs: A case study of Zananor Oilfield, Kazakhstan

Experiments of electrical responses of waterflooded layers were carried out on porous,fractured,porous-fractured and composite cores taken from carbonate reservoirs in the Zananor Oilfield,Kazakhstan to find out the effects of injected water salinity on electrical responses of carbonate reservoirs.On the basis of the experimental results and the mathematical model of calculating oil-water relative permeability of porous reservoirs by resistivity and the relative permeability model of two-phase flow in fractured reservoirs,the classification standards of water-flooded layers suitable for carbonate reservoirs with complex pore structure were established.The results show that the salinity of injected water is the main factor affecting the resistivity of carbonate reservoir.When low salinity water(fresh water)is injected,the relationship curve between resistivity and water saturation is U-shaped.When high salinity water(salt water)is injected,the curve is L-shaped.The classification criteria of water-flooded layers for carbonate reservoirs are as follows:(1)In porous reservoirs,the water cut(fw)is less than or equal to 5%in oil layers,5%–20%in weak water-flooded layers,20%–50%in moderately water-flooded layers,and greater than 50%in strong water-flooded layers.(2)For fractured,porous-fractured and composite reservoirs,the oil layers,weakly water-flooded layers,moderately water-flooded layers,and severely water-flooded layers have a water content of less than or equal to 5%,5%and 10%,10%to 50%,and larger than 50%respectively.

CO2 flooding strategy to enhance heavy oil recovery

CO_(2) flooding is one of the most promising techniques to enhance both light and heavy oil recovery.In light oil recovery,the production pressure in CO_(2) flooding in general keeps constant in order to maintain the miscibility of injected CO_(2) and crude oil;while in heavy oil recovery,a depleting pressure scheme may be able to induce foamy oil flow,thus the oil recovery could be further enhanced.In this study,different pressure control schemes were tested by 1-D core-flooding experiments to obtain an optimized one.Numerical simulations were conducted to history match all experimental data to understand the mechanisms and characteristics of different CO_(2) flooding strategies.For the core-flooding experiments,1500 mD sandstone cores,formation brine and a heavy oil sample with a viscosity of about 869.3 cp at reservoir condition(55℃ and 11 MPa)were used.Before each CO_(2) flooding test,early stage water-flooding was conducted until the water cut reached 90%.Different CO_(2) injection rates and production pressure control strategies were tested through core-flooding experiments.Experimental results indicated that a slower CO_(2) injection rate(2 ml/min)led to a higher recovery factor from 31.1%to 36.7%,compared with a high CO_(2) injection rate of 7 ml/min;for the effects of different production strategies,a constant production pressure at the production port yielded a recovery factor of 31.1%;while a pressure depletion with 47.2 kPa/min at the production port yielded 7%more oil recovery;and the best pressure control scheme in which the production pressure keeping constant during CO_(2) injection period,then depleting the model pressure with the injector shut-in yielded a recovery factor of 42.5%of the initial OOIP.For the numerical simulations study,the same oil relative permeability curve was applied to match the experimental results to all tests.Different gas relative permeability curves were obtained when the production pressure schemes are different.A much lower gas relative permeability curve and a higher critical gas saturation were achieved in the best pressure control scheme case compared to other cases.The lower gas relative permeability curve indicates that foamy oil was formed in the pressure depletion processes.Through this study,it is suggested that the pressure control scheme can be optimized in order to maximize the CO_(2) injection performance for enhanced heavy oil recovery.