致密砂岩气藏在开发过程中普遍存在产水现象,容易造成井筒积液、产量快速递减甚至停产等问题,认识致密砂岩地层水赋存规律,从而评价产水规律及其对产能的影响,是致密气规模化开发必须解决的关键问题.以中国海油鄂尔多斯盆地矿区盒八段致密储层为研究对象,选取典型岩心8块,每一块岩心均依次开展了孔渗分析、核磁共振实验、高压驱替实验和恒速压汞实验,从而揭示致密砂岩束缚水饱和度及与之一一对应的微观孔喉量化关系.实验结果表明,临兴矿区盒八段致密储层束缚水饱和度整体在40％～70％,且赋存在小于0.1μm的孔隙内以及较大孔隙的亲水表面上;束缚水饱和度随着喉道半径平均值、渗透率的增加而降低,具有较好的线性关系.本文所提出的方法为定量评价致密砂岩气藏的产水能力提供了基础依据和指导.

致密砂岩气井产能预测受气水两相流特征和裂缝渗流参数影响大,相比于数值模拟,基于解析模型的产能预测计算快、应用较广,但传统的解析模型在处理两相渗流方程非线性问题时简化过大,造成动态分析结果误差较大.针对这一问题,考虑了储层和裂缝中的气水两相流动特征,利用三线性流模型表征压裂缝及储层应力敏感性,建立了致密砂岩气井气水两相产能预测模型.将流动物质平衡方程与牛顿迭代法结合,利用平均地层压力逐步更新渗流模型非线性参数,并通过逐次迭代将气水两相模型线性化,获得了模型的半解析解.通过与商业数值模拟软件结果对比以及矿场实例应用验证了模型的准确性,并绘制了气水两相产能预测曲线,分析了敏感性参数对产能的影响规律.研究结果表明,所建立的半解析求解方法能够高效地处理气水两相非线性渗流问题,快速准确地获取致密气井产能预测曲线;致密储层产水严重影响了气井产能,合理的裂缝参数对提高气井产能至关重要;气藏开发过程中应合理控制生产压差,降低应力敏感效应对致密气井产能的影响.

针对层内水来源的产水气井动态储量评价,分析了现有动态储量评价方法在产水致密气井中的适应性,对比了不同水气比现有方法计算误差,在此基础上,建立了层内水来源的产水气井气水两相流流动物质平衡方程,形成了此类井动态储量求解流程,并运用理论模拟方法对新方法及流程进行验证.结果表明:层内水产出对气井储量评价特征曲线形态影响较小,但对储量计算结果具有一定影响;当水气比小于5 m3/104 m3,相对误差约5％,认为现有方法仍适用,但大于该值则不适用;新方法能有效减小误差,经验证,水气比11 m3/104 m3时误差在1.4％,能够满足工程应用的需要.所提方法应用于鄂尔多斯盆地东缘临兴区块,为该区产能准确认识、井距优化部署提供了新方法.

The most recent study shows that a rigorous Darcy flow does not exist in hydraulic fractures due to the effect of viscous shear from fracture walls, and the Brinkman equation can be a more accurate method to characterize the fracture flow (Teng et al., 2020). For Darcy flow, the fracture permeability is equivalent to the proppant-pack permeability, whereas, for the Brinkman flow, the fracture permeability is related to the fracture width as well as to the proppant-pack properties. In this work, the authors conducted a comprehensive study of the effect of Brinkman flow on the performance of fractured wells by use of a proposed semi-analytical model. In addition to the Brinkman flow, this proposed semi-analytical model also can account for the geomechanical effect to describe the stress-dependent proppant-pack properties and fracture width. The calculated results in this work show that the fracture permeability is lower than the proppant-pack permeability ascribing to the effect of Brinkman flow. As the production proceeds, the Brinkman flow will play a more important role in influencing the fluid transport within propped fractures. The effect of Brinkman flow on the well performance is significant only if the geomechanical effect is considered. If the fracture volume is sufficiently large or the proppant-pack permeability is sufficiently high, a longer fracture can be more favorable for improving the well productivity. If the Darcy parameter (defined in Eq. (22)) of the hydraulic fracture is less than 0.001, the long-term cumulative production of the fractured wells will not be influenced by the Brinkman flow. If the Darcy parameter is larger than 0.001, the effect of Brinkman flow cannot be neglected unless the Darcy-flow dimensionless conductivity is sufficiently large.

Shale oil and gas reservoirs are developed by MFHWs. After large-scale hydraulic fracturing, it is hard to forecast the production rate using the theoretical method. In the engineering application field, the empirical method of DCA is often used to forecast the production rate of shale oil and gas produced by MFHWs. However, there are some problems in using DCA, like how to find out the proper decline model and switch point of two contiguous flowing periods and how to deal with the unsteady operation condition which causes a lot of uncertainty in production forecast. In order to solve these problems, firstly, a straight line model, representing the linear flow period in the life cycle of shale oil and gas produced by MFHWs, in the Q,lg q coordinate system is proven to be theoretically proper. Secondly, the duration of the linear flow period is verified to be over 10~15 years by using an analytical model to do the calculation with the method of Monte Carlo random sampling taking a large amount of parameter combinations of Eagle Ford shale oil and gas reservoirs into calculation. And a field data analysis of Barnett and Eagle Ford also shows that the duration of linear flow period can be more than 10~15 years. Thus, a method of production forecast taking advantage of the straight line feature in the Q,lg q coordinate system is raised. After practical use, it is found that the method is robust and can increase the forecast efficiency and decrease the manual error. Moreover, it can increase the accuracy of production forecast and deal with some unsteady operation conditions. Therefore, this new method has good promotional value in the engineering field.

由于致密气、煤层气二者的赋存机理与开发方式存在着很大的不同,业界对于两气合采干扰及开发效果仍存在着较大的顾虑.为了充分认识致密气-煤层气(两气)合采存在的层间干扰问题及进一步探讨两气合采可行性,从两气合采层间干扰机理入手,分析了不同机理对合采层间干扰的影响,结合数值模拟方法总结了两气合采干扰控制因素.研究结果表明:①合采过程会出现层间水倒灌现象,但相对于整个开发过程持续时间短;②影响合采效果的关键因素是致密储层水锁效应强度,物性参数差异影响合采时各层产能贡献比例,但对最终合采效果的影响可忽略.基于此,提出了两气合采选层原则:①非产水致密层不宜与煤层合采;②物性参数差异性不作为合采选层的考虑因素;③产水致密层可与煤层合采,但需确定技术经济可采参数界限值.基于研究结果,创建了"六图版四象限"两气合采快速选层法,能够运用于现场两气合采层系快速优选.

The oil and gas fields are commonly developed with a group of production wells. Therefore, it can be essential for the industries to predict the performance of the production wells in order to optimize the development strategies. In practice, it frequently happens that we only hope to study the performance of a single production well. In such cases, it can be time consuming to run the reservoir simulation with the entire reservoir model to study the well performance. Hence, it can be preferred to determine the control volume (or drainage volume) of the target well from the entire reservoir and run the simulation with the small control volume to reduce the simulation cost. However, an irregular layout of the production wells and the heterogeneity of reservoir properties, which can be commonly observed in real field cases, can induce a stringent barrier for one to determine the control volumes. At present, we are still lacking a method to determine the control volumes of the production wells considering well distribution and reservoir heterogeneities. In order to overcome such a barrier, the authors proposed a new approach to divide the entire reservoir into small control volumes on the basis of the fast marching method (FMM). This approach is validated by comparing the simulation outputs of the target well calculated only with the determined control volume to those calculated with the entire reservoir model. The calculated results show that using the control volume that is determined with the proposed method to calculate the well performance can yield results that agree well with the results that are calculated with the entire reservoir model. This indicates that this proposed method is reliable to determine the control volume of the production wells. In addition, the calculated results in this work show that changing fracture length exerts a slight influence on the control volumes if the length of all fractures is increased, whereas, if only one of the fracture lengths is increased, the control volume of the corresponding well will be significantly increased. The number of the production wells and the distribution of the production well can noticeably influence the control volumes of the production wells. The findings of this study can help for optimizing the well spacing, estimating the ultimate recovery, and reducing the computational cost.

Water breaks through along fractures is a major concern in tight sandstone reservoirs with a bottom aquifer. Analytical models fail to handle the three-dimensional two-phase flow problem for partially penetrating inclined fractures, so time-consuming numerical simulation are often used for this problem. This paper presents an efficient semianalytical model for this problem considering three-dimensional fractures and two-phase flow. In the model, the hydraulic fracture is handled discretely with a numerical discrete method. The three-dimensional volumetric source function in real space and superposition principle are employed to solve the model analytically for fluid flow in the reservoir. The transient flow equations for flow in three-dimensional inclined fractures are solved by the finite difference method numerically, in which two-phase flow and stress-dependent properties are considered. The eventual solution of the model and transient responses are obtained by coupling the model for flow in the reservoir and discrete fracture dynamically. The validation of the semianalytical model is demonstrated in comparison to the solution of the commercial reservoir simulator Eclipse. Based on the proposed model, the effects of some critical parameters on the characteristics of water and oil flow performances are analyzed. The results show that the fracture conductivity, fracture permeability modulus, inclination angle of fractures, aquifer size, perforation location, and wellbore pressure drop significantly affect production rate and water breakthrough time. Lower fracture conductivity and larger inclination angle can delay the water breakthrough time and enhance the production rate, but the increment tends to decline gradually. Furthermore, water breakthrough will occur earlier if the wellbore pressure drop and aquifer size are larger. Besides, the stress sensitivity and perforation location can delay the water breakthrough time.

Two-phase (gas+water) flow is quite common in tight sandstone gas reservoirs during flowback and early-time production periods. However, many analytical models are restricted to single-phase flow problems and three-dimensional fracture characteristics are seldom considered. Numerical simulations are good choices for this problem, but it is time consuming in gridding and simulating. This paper presents a comprehensive hybrid model to characterize two-phase flow behaviour and predict the production performance of a fractured tight gas well with a three-dimensional discrete fracture. In this approach, the hydraulic fracture is discretized into several panels and the transient flow equation is solved by the finite difference method numerically. A three-dimensional volumetric source function and superposition principle are deployed to capture the flow behaviour in the reservoir analytically. The transient responses are obtained by coupling the flow in the reservoir and three-dimensional discrete fracture dynamically. The accuracy and practicability of the proposed model are validated by the numerical simulation result. The results indicate that the proposed model is highly efficient and precise in simulating the gas/water two-phase flow and evaluating the early-time production performance of fractured tight sandstone gas wells considering a three-dimensional discrete fracture. The results also show that the gas production rate will be overestimated without considering the two-phase flow in the hydraulic fracture. In addition, the influences of fracture permeability, fracture half-length, and matrix permeability on production performance are significant. The gas production rate will be higher with larger fracture permeability at the early production period, but the production curves will merge after fracturing fluid flows back. A larger fracture half-length and matrix permeability can enhance the gas production rate.

页岩超低渗、强非均质性以及复杂缝网特征使得解析模型法产量预测参数输入不确定性大,生产历史拟合多解性强,产量预测难度大.基于页岩气井生产长时间段呈线性流动的特点,开展线性流分析和解析模型产量预测工作,提出首先通过线性流分析解释确定解析模型参数初值和范围、再进行历史拟合和产量预测的思路和方法流程.研究表明:根据页岩气流动阶段诊断可以初选解析模型;运用流动物质平衡方法可确定动用储量和气藏尺寸;采用线性流不确定性分析可以确定渗透率和裂缝半长等参数范围.该方法可提高解析模型历史拟合和产量预测精度,同时提高了工作效率,经8口井应用测试结果表明:方法提高单井历史拟合速率40％以上,提高产量预测精度18.1％.

页岩油气产量受地质、工程等多重因素影响,常规产量预测方法难以反映其真实生产特征,因此引入了机器学习方法进行页岩油气产量预测.以美国Eagle Ford页岩某区块400余口生产井地质、油藏、工程数据为学习样本,对人工神经网络模型进行训练和优化,确定了最佳模型参数;结合交叉验证等手段改进了训练方法,提高计算效率和预测精度,得到了初始产量、递减率、递减指数等产量递减参数与地质、油藏、工程参数之间的关系模型,进而形成了基于静态参数的页岩油气单井产量预测技术.实例应用表明,投产5年内,本文模型产量预测精度可达90％.在没有生产数据或生产数据较少情况下,本文模型预测产量具有突出优势.

针对页岩油气产能影响因素具有参数多、关系复杂、难以量化评价的特点,利用因子分析、多元回归等方法,对某页岩区块数百口生产井的地质、油藏、工程等数据进行数据分析.研究从数据关联角度,将产能影响参数归纳为泄流范围、储层特征和改造强度等相互独立的三类,利用这三类参数可以对研究区特征进行详细刻画;同时研究中结合多元回归等方法,对产能的影响因素进行量化评价,确定了不同产区的产能主控因素.结果表明,在各方面条件均优的情况下,泄流范围对产能影响权重占40％,储层特征占40％,改造强度占20％.当储层含油气性好,物性好,储层能量足时,储层特征的影响程度会有所提高,反之,则泄流范围影响处于主导地位.改造强度影响程度则随着储层中人工裂缝密度和复杂程度的增加而提高.

全球能源低碳化的背景下,油气行业正面临着传统能源消费增速放缓、碳成本日益增高、高碳资产持有风险升高、油气价格持续受到抑制等多重压力.选择了行业内大型国际油气公司作为样本,研究各公司的低碳战略特点及实践成效,了解国内外油气行业应对能源低碳转型的举措和效果,为我国油气行业更好地贯彻国家生态文明建设要求和执行能源安全新战略要求提供参考和借鉴.

本文从层间干扰机制出发,分析了倒灌现象、物性差异以及开发方式对层间压力干扰的影响,并运用数值模拟手段进行合采生产特征和控制因素分析,研究表明:合采时出现短时的水倒灌现象,对开发效果影响不大,但倒灌后形成的水锁效应强弱是影响合采的关键;渗透率等物性差异不影响合采效率,但渗透率、解吸压力、工作制度等是影响两气合采经济性的重要参数.

Two-phase flow of oil and gas is quite common in the reservoir during the depletion of liquid-rich shale gas and tight light-oil. Many analytical models proposed for multistage fractured horizontal wells completed in unconventional reservoirs are restricted to single phase flow problem. In this paper, an approximate semianalytical method is proposed to handle the complexities of phase change, pressure dependent PVT properties, two-phase flow behavior and complex fracture networks. The black oil model is used to model phase change and two-phase flow of oil and gas. The secondary fractures in the stimulated reservoir volume and the reservoir beyond the main fractures are considered in the physical model to make long-term production forecasts. The forecasted producing GOR is used to decrease the equations of the two-phase flow model, so only the flow equations of primary phase are used to develop the mathematic model. Then an approximate method is used to linearize the model and the analytical solution is obtained in Laplace space for constant pressure inner boundary problem. The Duhamel's principle is applied to correct the production rate under variable flowing pressure inner boundary, and a procedure is proposed for history matching of field production data and making forecasts. Finally, the semianalytical model is validated with two simulation examples, the average relative error is shown to be less than 10%. After that, two field examples are used to show its utility.

产能预测是页岩油气资产评估、开发方案设计等工作的重要前提,但由于页岩储层特低孔低渗及多级压裂的特点,常规油气产能预测方法在页岩油气中的适应性不强.为此,深入分析了页岩油气产能预测中存在的问题,提出了页岩油气产能预测新思路,推荐了产能预测方法流程.研究结果表明:① 常规方法不适合页岩油气产能预测主要在于页岩渗透率极低不具备产能试井需达到拟稳态流动的条件,产量递减规律认识不清尤其是后期产量递减规律认识不够,多套产能预测模型选择困难,流动机理无定论致数值模拟不确定性大等;② 页岩油气产能预测中应转变思路,重点关注4个方面:重视生产数据的挖掘并找寻产量与地质、油藏工程参数的关系,采用多种方法综合评价并互为补充验证,注重不确定性产能预测方法以降低评估风险,加强生产动态分析并开展储层及裂缝参数反演加深参数认识;③ 针对有无生产数据、生产数据多少等不同情况建立产能预测推荐流程,有选择地开展多方法综合评价,以实现页岩油气产能预测目标.

The tight reservoirs are characterized by the low permeability,fracturing increment and so on,the longterm non-stable linear flow is caused for the oil and gas wells,so the specialized curve method is widely used in these wells to interpret the permeability,fracture parameters and so forth and moreover to predict the production.However,in the actual application of the well,the following so many problems are met:“negative intercept” phenomenon for the characteristic curve of the root mean square of the time,variable rate-variable pressure,oil and gas phases,multi-linear portions and so on.With the help of a large number of the data test,theoretical analysis and method demonstration,the faced conditions in the field application were understood.The study shows that the reasons of the “negative intercept” occurrence are maybe the rather lower initial formation pressure or the earlier defined start time of the production;the variable rate-variable pressure problem can be settled by the material balance time and linear superposition pseudo-time,especially for the gas wells,the second time is suggested for the oil well;the well with oil and gas production can be treated by the discounted production or two-phase pseudo-function;the obvious features are necessary in the log-log curve for the multi-linear portion diagnosis;in terms of the analysis procedure,the flowing material balance (FMB) method is recommended to calculate the reserves and fracture half-length,and then the permeability can be calculated as well.

The productivity of shale gas well is often with high uncertainty because of the uncertainties in the characterization of formation properties, fracture properties, gas adsorption, and flow mechanisms. This paper provides an efficient method to probabilistically forecast shale gas production by combining the Markov chain Monte Carlo method (MCMC) and a semi-analytical model. A trilinear flow model is used to predict shale gas production with the consideration of gas desorption and multiple flow mechanisms. The parameters in the model are sampled with the MCMC. A workflow is proposed to predict the gas production and characterize the uncertainties. To make the study results helpful for the field use, a field case from a shale gas field in Southwestern China is applied in the analysis. In this case, we chose ten uncertain parameters to study their effects on eventual ultimate recoveries. Shale gas production is shown to be closely related to the properties of formation, fracture, and flow mechanisms. The fracture half-length and BHP have strong effects on gas production, particularly the production within 5 years. BHP also influences the production after 5 years because of the gas PVT properties and gas adsorption. The results also show that enough iteration number is needed to get a reasonable uncertainty quantification. The sensitivity analysis shows that at least 2000 iterations are required for this case. After that, the probable production could be predicted with a range rather than only one value, and P10, P50, and P90 can be obtained. For the case studied in this paper, there is 90% probability that the EUR for a well is ranging from 0.62 × 10 8 to 1.48 × 10 8 m 3 .

页岩油气产量预测是页岩油气区块进行规模开发前的重点和难点工作之一.在对产量预测技术分析的基础上,提出了2种产量预测方法.一是基于页岩气流动机理及水平井特有的多级压裂改造方式提出了页岩气分段式典型曲线产量预测新方法,认为页岩气累计产量和产量半对数曲线呈现三段式特征,利用数值模拟方法验证了三段式规律,Eagle Ford和Barnett页岩气矿区现场实际应用也论证了三段式规律.二是基于生产动态数据及解析模型提出了不确定性产量预测方法,即以单井生产动态数据为基础,利用线性流理论,采用RTA软件,对储层渗透率及裂缝半长参数进行不确定性反演分析,从而获得储层及裂缝参数的概率分布,再利用RTA软件解析模型实现不确定性产量预测.本文新方法可为页岩油气产量预测提供指导.

Rate transient analysis (RTA)is a type of theoretical analysis method to quickly evaluate the parameters of shale oil-gas reservoirs including the permeability,hydraulic fracture half-length,SRV volume,recoverable reserves and EUR based on production data.When analyzing the actual data of a certain overseas shale oil-gas field,due to the irregular dynamic data and imperfect theory,a great uncertainty exists in RTA results.This will cause errors in the judgment of well production state,thus misleading the formulation of development strategies.Aiming at the problems of multiple solutions and false solutions easily appearing in the process of RTA,a research was conducted in terms of optimizing interpretation method and perfecting analysis theory in this study,and two methods were proposed,i.e.,the constrained solution method including linear flow analysis and analytical model fitting and compound linear flow interpretation method,which can improve the reliability of interpretation results.Moreover,the two methods showed good application effect in analyzing the typical wells of a certain shale oil-gas block,of which the interpretation permeability was basically consistent with test permeability.On this basis,it was found that the hydraulic fracture half-length of some producing wells was less than the designed well spacing,so that well pattern infilling could be locally adjusted according to analysis results.