An Experimental Investigation of Fracture Tilt Angle Effects on Frequency and Stability of Liquid Bridges in Fractured Porous Media

Abstract

Liquid bridges are believed to play an important role in improving the recovery of fractured reservoirs. However, little is known about the stability of liquid bridges in fractured media at the pore scale. In this work, a glass micromodel representing a stack of two blocks was used at different tilt angles to monitor the frequency and stability of liquid bridges formed during free-fall gravity drainage as a function of tilt angle. It was observed that by increasing the tilt angle, the liquid bridge frequency decreased but its stability increased. This resulted in higher ultimate recovery. In addition, it was found that during the first half of the experiments, the number of bridges was higher but their stability was lower than during the second half of the tests. Moreover, no more than one stable liquid bridge was observed at tilt angles above 20°, and the bridge cross-sectional area was gradually decreased as the stability was maintained. A sequence of bridges that were formed and broken one after the other results in a higher drainage rate than a single bridge with stability equal to the overall stability of the sequence.     

A New Approach to the Modeling of a Simple Re-infiltration Gravity Drainage Process in Naturally Fractured Reservoirs

Abstract

One of the most important concerns regarding prediction of production performance in naturally fractured reservoirs is the issue of re-infiltration phenomena.

In this study, the modeling of a simple re-infiltration process with no effect of capillary continuity between blocks is presented by extending the gravity drainage mechanism for a single block.

First, a qualitative analysis of the gravity drainage process through porous media was conducted and the role of gravity and capillary forces was investigated.

Then a model for one-dimensional gravity drainage in a single block was developed in dimensionless form, a modified version of which can be found in the literature. Then, using the method of separation of variables, the corresponding partial differential equation was solved for a single block with certain boundary and initial conditions.

The upper boundary is a no-feed boundary and at the lower boundary the gas saturation is always zero. At the initial condition, the gas saturation is equal to zero throughout the block.

In order to model the simple re-infiltration process, the above-mentioned problem for concept was used and, based on the fact that the blocks of a stack governed by simple re-infiltration process act as single block, using a MATLAB program (The MathWorks, Inc., Natick, MA), the rate of drainage and cumulative production as function of time were obtained. The results are in very good agreement with the nature of the process in an actual case. This method can be extended to solve the problem of a stack of N blocks.     

The Applicability of Expanding Solvent Steam-Assisted Gravity Drainage (ES-SAGD) in Fractured Systems

Abstract

The aim of this contribution is to evaluate the performance of an expanding solvent steam assisted gravity drainage (ES-SAGD) process in naturally fractured systems. Steam-assisted gravity drainage (SAGD) and ES-SAGD processes have been investigated in both conventional and fractured reservoir models and the effect of networked fractures on the recovery mechanism and performance of ES-SAGD has been investigated. Operational parameters such as steam quality, vertical distances between wells, and steam injection temperature have been also evaluated. Finally, to study the effect of a well's horizontal offset, a staggered ES-SAGD well configuration has been compared to a stacked ES-SAGD.     

采用新标度方程预测再渗吸作用下天然裂缝性储集层重力泄油采收率

通过数值模拟对比单孔隙介质和双孔隙介质模型模拟结果,验证了再渗吸对天然裂缝性油藏的显著影响,提出了再渗吸作用下基质岩块泄油过程新的控制方程;利用检测分析,得到了适用于再渗吸作用下标度基质岩块采收率曲线的无因次方程;通过方案设计,针对具有不同岩石和流体性质的实验方案,确定了该方程的适用范围,并对各方案进行了模拟.结果 表...     

The Lessons Learned From Miscible Gas Flooding in Naturally Fractured Reservoirs: Integrated Studies,and Pilot and Field Cases

Abstract

Suitable methods have to be employed for secondary and tertiary oil recovery from the naturally fractured reservoirs (NFRs). The miscible gas injection has shown some promising results for enhancing oil recovery from NFRs. However, proper design of the field-scale miscible gas injection projects in NFRs is still a major challenge. The authors evaluate the technical issues of the miscible gas injection in NFRs. The classification of NFRs and their production characteristics, the mechanisms of oil production in NFRs, and significant findings of integrated studies, pilot and field trials, and commercial field projects of the miscible gas injection in NFRs are reviewed. Finally, important issues are identified, which need detailed investigations for the design and performance assessment of the field projects. It is hoped that this paper will serve as a helpful reference for the engineers interested in miscible gas injection process in NFRs.     

A New Equation for the Determination of a Well Drainage Area in Naturally Fractured Reservoirs

Abstract

In reservoir study, the relationship between the reservoir performances and well bore is a key for any well completion design and well production optimization. In order to estimate the behavior of reservoir pressure with different production flow rates, the well drainage area is necessary. The well drainage area is estimated from well test under pseudo-steady-state production when the change of reservoir pressure with time is constant. The MBH method is used to estimate well drainage area and its shape in conventional reservoirs. But for the case of naturally fractured reservoirs, a small amount of research has been done on the determination of well drainage area and shape. There are a few limited methods to determine the drainage area of a well in naturally fractured reservoirs that have been presented in recent years. The authors compare the available methods with a new developed equation for determination of the drainage area of a well in naturally fractured reservoir. The presented new equation is easy to apply and it has high accuracy.     

Pressure Data Analysis in Two Phase Naturally Fractured Reservoirs With a Pseudo Steady State Flow Regime Using the TDS Technique

The matrix-to-fracture interporosity parameter (λ), and fracture storativity (ω) are subject to changes during the life of an oil field. This depends entirely on the nature of saturation condition both in fractures and matrix blocks. Failure to consider two-phase flow parameters will result in inaccurate estimation of reservoir parameters. Because of the high amount of this type of behavior in many reservoirs worldwide, developing appropriate method is very important. A new procedure is presented for analyzing transient test in naturally fractured reservoirs with pseudo steady state two-phase (oil and water) flow using direct synthesis technique (TDS) to determining reservoir parameters. TDS is a modern technique that utilizes the characteristic lines and points found on the pressure and pressure derivative log-log plot. These points and lines are then used with appropriate equations to solve directly for desired reservoir parameters. The proposed methodology is successfully verified by its application to field simulated pressure data and a step-by-step procedure for calculating these parameters is included.     

天然裂缝性油藏的离散裂缝网络数值模拟方法

针对裂缝性油藏中大裂缝、微细裂缝和孔隙等多种储渗介质共存的现象,将大裂缝作为控制流体流动的一维实体,组成离散裂缝网络,进行显式表示,将孔隙和微细裂缝组成的系统作为基岩介质,建立了天然裂缝性油藏两维两相数值模拟模型。采用加权余量法,建立有限元方程并进行了求解。对油藏有无裂缝及大裂缝的方位、长度和分布对水驱油的影响进行了研究。结果表明：大裂缝的存在会严重改变水驱油藏中注入水前缘的前进方向和速度,大裂缝与注采井间连线夹角越小及长度越大,都会导致注入水窜进越严重,从而使得油井见水早,含水率高;多条大裂缝的存在会造成剩余油分布的极度非均质及剩余油富集区的形成。     

Scaling miscible displacement in fractured porous media using dimensionless groups

Scaling of miscible and immiscible displacement in porous media using inspectorial analysis leads us to better understanding of the process. Less has been listed about fractured reservoirs especially with the fracture flow conditions taken into consideration. We derived dimensionless groups using Inspectional Analysis for the miscible displacement in fractured porous media when there is flow through fracture. The solvent–solute transfer between fracture and adjunct matrix is only due to diffusion/flux transfer. Based on the dimensionless groups derived we proposed a new dimensionless group for better defining the effectiveness of the process. The newly proposed group, Matrix-Fracture Diffusion Number (N_M-FD), will be critical in evaluating the performance of enhanced oil recovery, CO₂ sequestration and contaminant transport problems. Laboratory scale experiments were performed for validation and physical interpretation of the (N_M-FD).     

裂缝性油气藏采收率：100个裂缝性油气田实例的经验总结

通过对世界上100个裂缝性油气藏的综合评价,研究储集层及流体本身的性质(包括孔隙度、渗透率、黏度、可动油比例、含水饱和度、润湿性及裂缝分布特征等)和驱动机制及油藏管理战略(优化日产量和采用不同类型的提高采收率技术)对其最终采收率的影响。将裂缝性油气藏分为4类：I类的基质几乎没有孔隙度和渗透率,裂缝是储存空间和流体流动的通道;Ⅱ类的基质有较低的孔隙度和渗透率,基质提供储存空间,裂缝提供流动通道;Ⅲ类(微孔隙)的基质具有高孔隙度和低渗透率,基质提供储存空间,裂缝提供流动通道;Ⅳ类(大孔隙)的基质具有高的孔隙度和渗透率,基质提供储存空间和流动通道,裂缝仅增加渗透率。对26个Ⅱ类油气藏和20个Ⅲ类油气藏的开采历史的研究表明：Ⅱ类油气藏的采收率受水驱强度和最优日产量控制,日产量过高会很容易破坏Ⅱ类油气藏,一些Ⅱ类油气藏如果管理得当,采收率可以很高,不需要二次或三次采油;Ⅲ类油气藏的采收率主要受岩石和流体本身性质的影响,特别是基质渗透率、流体重度、润湿性以及裂缝强度等,不进行二次或三次采油不可能完全开采,往往需要采用一些提高采收率的专门技术。以往将Ⅱ类和Ⅲ类裂缝性油气藏归为一类,认识它们的区别将有助于选择更好的开发策略。     

海拉尔盆地乌南次凹南屯组致密储层黏土矿物特征及其地质意义

海拉尔盆地乌南次凹南屯组储层黏土矿物含量高,严重影响油气的开发。 利用乌南次凹 767 个岩心样品的扫描电镜及 X 射线衍射资料,研究了黏土矿物的类型和组合关系,以及其分布特征与成因。 结果表明,蒙脱石含量低且仅存在南二段上部,伊利石含量高且在整个南屯组都有分布;自下而上发育的黏
土矿物组合有 S+K+I+I/S , K+I+C+I/S+C/S , I+C+I/S+C/S , I+K+I/S 及 I+C+I/S 等;火山物质的水解蚀变及长石的溶蚀作用均是造成黏土矿物含量增高的主要因素。     

Sensitivity Analysis to Operational Parameters of the Offset Well During Fast-SAGD Process in Naturally Fractured Reservoir

Few studies were done to investigate performance of the Fast steam-assisted gravity damage (SAGD) recovery method especially in naturally fractured reservoirs (NFR). The authors studied some cyclic steam stimulated operational parameters effects on the Fast-SAGD performance in NFR. A synthetic 2D homogenous model was constructed by Computer Modelling Group's (CMG) and simulated using the STARS module. Comparison between SAGD and Fast-SAGD recovery methods in this model shows great increase in the oil production but small increase of thermal efficiency in the Fast-SAGD recovery method. Simulation outcomes represent 17% increment in ultimate recovery factor but small reduction in steam-oil ratio. Results show that increasing the number of offset cycles and injection period yield increment in the oil production. Increasing the offset injection rate causes growth in the oil production, but has an optimal value. By increasing the distance between the offset well and SAGD well pairs up to a certain value, oil production increases but decreases after that point. This is due to the ability of the fractures in making connection between the steam chambers in higher distances. When production bottom-hole pressure decreases, the heated oil in near well region is subjected to more pressure drop and causes more oil to be produced. More offset wells result in higher production but simultaneously lower recovery factors. Increasing and decreasing soak time as the last investigated parameter did not affect the trend of production anyway.     

脉冲渗吸水驱油机理实验研究与分析

由于裂缝性油藏储集空间物理性质的复杂性和特殊性,渗吸效果控制着低渗透裂缝性油藏水驱开发动态与开发效果,而脉冲渗吸驱油一直被认为是低渗透裂缝性油藏有效的开发方式。在室内实验研究的基础上,结合油藏工程等理论知识对脉冲渗吸驱油机理进行了研究,得出脉冲增压改善基质岩块孔隙中渗吸条件是脉冲注水方式提高渗吸驱油效率的根本原因。     

Well Test Analysis of Naturally Fractured Reservoirs with Unsteady State Behavior Using Direct Synthesis Technique

Abstract

This study proposes a new method for analyzing pressure transient in naturally fractured reservoirs (NFR). Parameter estimation is based on the direct synthesis technique.

The direct synthesis technique utilizes the characteristic intersection, maximum and minimum points, slopes, and starting time of various straight lines from a log–log plot of pressure and pressure derivative data. Applicability of the empirical expressions developed as a result of this work is demonstrated by successfully analyzing actual pressure transient data. The main advantage of direct synthesis method is for a case where there is no guarantee on the existence of an early-time unit slope line, and/or the late-time infinite acting radial flow line has not been seen due to inner and outer boundaries, lack of points, and severe noise problems. Application of this technique is presented for well test analysis in infinite-acting naturally fractured reservoirs with an unsteady state flow model. Both the effects of wellbore storage and skin are included in the analysis. Comparison between the results obtained in this work and already published results indicates good agreement.     

天然裂缝性碳酸盐岩封闭油藏产量递减规律研究及应用

建立了天然裂缝性碳酸盐岩封闭油藏渗流模型。考虑了封闭油藏定井底压力和变井底压力两种不同的内边界情形,并采用Laplace变换和Duhamel原理对数学模型进行了求解,得到了天然裂缝性碳酸盐岩封闭油藏的递减曲线,在曲线上产量出现两个明显的递减阶段和两个相对平缓的递减阶段,讨论了窜流系数和裂缝弹性储容比对天然裂缝性油藏递减曲线的影响。实例表明,实际产量资料与理论递减曲线的拟合可确定地层参数,预测产量变化。     

基于微流控模型的裂缝性储集层渗吸机理实验

针对岩心渗吸实验周期长和计量难度大等问题,设计了不同尺寸、不同边界条件的裂缝-基质微流控模型,并通过表面性质修饰对模型润湿性进行调控,开展了油-水、油-润湿改性体系、油-Winsor Ⅲ型表面活性剂体系的一系列渗吸实验并研究其渗吸机制.研究表明,在油-水、油-润湿改性体系渗吸过程中,油相通过海恩斯阶跃采出,毛细管回压是...     

裂缝型致密油藏分段压裂水平井伤害实验研究

红河油田长8油藏具有典型的低孔特低渗储层特点,储层孔喉细小,天然微裂缝发育,入井液易污染储层。裂缝发育区主要在断层带附近分布。红河油田长8油藏水平井在钻井、完井、压裂过程中,带入许多外来流体,外来流体通过断缝系统侵入储层易产生水锁伤害、粘土膨胀与运移伤害、沉淀堵塞伤害、压裂残渣伤害以及微裂缝发育引起压裂液大量滤失导致砂堵等多种伤害。通过对储层地质特征认识,储层伤害机理及因素分析,从而确定红河油田长8油藏伤害主要以水锁伤害为主。并提出抑制和解除水锁伤害的方法。     

Investigation of the Effect of Geometrical Properties of Networked Fractures on the Efficiency of Steam-Assisted Gravity Drainage Process

Abstract

Various fracture geometrical properties such as orientation, extension, discontinuity, dispersion, location, and networking were investigated. Results indicate improved oil recovery and sweep efficiency in the presence of vertical fractures. Longer vertical fractures seemed to have even more beneficial effects. Horizontal fractures revealed detrimental effects on oil recovery and the performance became worse for longer horizontal fractures. Discontinuous horizontal fractures caused a better performance especially when combined with continuous vertical fractures (networking). Vertical fractures helped the growth of the steam chamber in the vertical direction, which resulted in higher oil recovery. However, horizontal fractures seemed to inhibit growth of the steam chamber in the vertical direction, hence retarding oil recovery.