A laboratory study of hot WAG injection into fractured and conventional sand packs

Gas injection is the second largest enhanced oil recovery process,next only to the thermal method used in heavy oil fields.To increase the extent of the reservoir contacted by the injected gas,the gas is generally injected intermittently with water.This mode of injection is called water-alternating-gas(WAG).This study deals with a new immiscible water alternating gas(IWAG) EOR technique,"hot IWAG" which includes combination of thermal,solvent and sweep techniques.In the proposed method CO2 will be superheated above the reservoir temperature and instead of normal temperature water,hot water will be used.Hot CO2 and hot water will be alternatively injected into the sand packs.A laboratory test was conducted on the fractured and conventional sand packs.Slugs of water and CO2 with a low and constant rate were injected into the sand packs alternatively;slug size was 0.05 PV.Recovery from each sand pack was monitored and after that hot water and hot CO2 were injected alternatively under the same conditions and increased oil recovery from each sand pack and breakthrough were measured.Experimental results showed that the injection of hot WAG could significantly recover residual oil after WAG injection in conventional and fractured sand packs.     

低渗透油藏气驱注采比和注气量设计

注采比合理性对气驱生产效果影响较大。基于物质平衡原理、达西定律和油气分流理论、气驱增产倍数和气驱油墙描述等概念与成果,考虑并量化了注入气溶解、油藏流体膨胀、注入气成矿固化、储层压敏效应、天然裂缝疏导和干层吸气、注气井组和外部液量交换、气油比构成等因素,分别建立了基于采出油水两相地下体积的气驱注采比计算公式(2P公式)和基于采出油气水三相地下体积的气驱注采比计算公式(3P公式),给出了单井日注气量计算方法。应用新方法,研究代表性特低渗透油藏二氧化碳驱项目注采比变化情况,连续注气气窜后应按照3P公式计算的气驱注采比进行配注;水气交替注入按照2P公式计算的气驱注采比进行配注基本可行。     

气水交替改善CO2驱油效果的适应界限*

针对低渗特低渗透油藏CO2驱油效果差、气窜现象严重等特点,开展了CO2驱气水交替注入(WAG)方式改善CO2驱油效果研究,评价了岩心渗透率及其非均质性对气水交替驱油效果的影响;选取天然露头和人造非均质岩心,对气水交替的注入速率、注入参数及注入量进行优选,进行了WAG驱的适应性评价。研究表明,对于0.5×10^-3、1×10^-3和5×10^-3μm^2的低渗特低渗均质岩心,气水交替驱能够实现良好的流度控制作用,延长CO2的窜逸时间,且渗透率越低,气窜时间越晚;渗透率级差为5、10和50的非均质性岩心,渗透率级差越小,气水比越高,提高采收率效果越好。渗透率级差大于10时,气窜时间明显提前,特别是当级差大于50时,气水段塞无法有效启动低渗基质中的剩余油,快速气窜而无经济效益。利用气水交替在适应界限范围内可显著降低CO2流度,延长CO2窜逸时间,启动基质中的剩余油,提高剩余油采收率。图16表2参20。     

国外CO2驱油防止粘性指进和重力超覆工艺

在简述粘性指进和重力超覆的基础上，对国外采取的工艺措施进行了调研。针对广泛使用的水气交替注入(WAG)法，介绍了设计原则、注入方案及存在的不足。泡沫注入法是在WAG法的基础上发展起来的，其关键在于表面活性剂的筛选和使用。最后简要介绍了国外最新研究的稠化泡沫的原理和试验效果。     

水气交替方法在GGY油田长6油层的应用

根据鄂尔多斯盆地GGY油田区域注水开发存在的问题开展的室内外注气实验,对水气交替驱油技术在该油田的应用进行了分析,并与现场实验相结合,提出对本区超低-特低渗透储层水气交替驱的一些初步认识。     

Slug Water Alternating Gas Flow Processes Behavior in the Vicinity of Discontinuous Shales

Abstract

Gas injection is the second largest enhanced oil recovery process practiced in the world. To increase the macroscopic sweep efficiency, the gas is generally injected intermittently with water either simultaneously or as slugs. This mode of injection, called water alternating gas (WAG), is being widely used in the oil fields. This experimental and numerical study is aimed at understanding mechanisms of oil recovery following slug first-contact miscible WAG (FCMWAG) injection in the presence of discontinuous shales. A particular objective is to quantify the accuracy of numerical simulation when modeling slug FCMWAG displacements in these heterogeneous systems.

A series of well-characterized laboratory experiments in two-dimensional heterogeneous bead packs were carried out. Slug FCMWAG displacement experiments were performed in the porous media containing discontinuous shale. Slug injection was carried out at a WAG ratio of 1:1 with slug sizes of 5 and 50% PV. All experiments were then modeled using IMPES finite difference simulator without using history matching (all simulations used directly measured porous media properties as inputs) to quantify the accuracy of the simulation when modeling the slug FCMWAG displacements in a porous media with a discontinuous shale.

The large water slug (50% PV) displacement outperformed the 5% PV slug process because the large water slug injected ahead of solvent significantly reduced the extent of fingering and the bypassed oil around the shale barrier. Simulation of the slug WAG experiments showed good agreement for the oil recovery. However, a discrepancy in the physics of the fluid flow during the displacements, especially downstream and upstream of the shale barrier, was observed in the fluid cut curves. Simulation predicted less fingering and fewer breakdowns of the injected slugs.     

Recovery Improvement Using Water and Gas Injection Scenarios

Abstract

Water and miscible gas injection scenarios are considered in an Iranian oil reservoir for the purpose of recovery improvement. Firstly reservoir fluid modeling and modeling of a slim tube test were performed. Then, water alternating gas (WAG) injection was evaluated by optimizing the WAG half cycle and WAG ratio. Alternatively, hybrid WAG and separate injection of water and gas in the top and bottom of the reservoir were also investigated. The numerical simulation results showed that the optimum WAG, with half cycle of 1.5 years and WAG ratio of one, gave the highest recovery factor. Moreover, economic evaluation of these scenarios indicated that WAG had the highest net present value and was the most interesting scenario for improving the recoveries.     

CO2驱水气交替注入参数正交试验设计模拟

结合ECLIPSE软件的PVTi和E300模块,建立了榆树林特低渗透油藏三维三相油藏数值模拟模型。在历史拟合基础上,根据正交试验设计原理,考虑水气交替注气量、段塞大小、气水比、注气速度和后续水驱注入速度5个参数,以增油量和换油率为评价指标,进行正交试验设计。通过对试验结果的直观和方差分析,得到注入参数对评价指标影响的主次顺序,优选出水气交替注入参数的最佳组合方案,为现场CO2驱水气交替注入参数的优化提供理论指导和技术支持。     

The effect of capillary-trapped CO2 on oil recovery and CO2 sequestration during the WAG process

This study investigated capillary-trapped CO₂ depending on the consideration of hysteresis effect in relative permeability for various water-alternation-gas (WAG) operating conditions to ascertain the oil production process. From the simulation results of CO₂ WAG flooding method, the trapped CO₂ led to prevent water-flow, in which CO₂ acts as a gas blocker near the well. It caused the injection pressure increase during water injection period. As the trapped CO₂ in pores increased, the reservoir pressure was also increased and maintained above minimum miscibility pressure (MMP). Ultimately, it was concluded that the reservoir was kept under miscible conditions throughout WAG process, reducing residual oil and increasing oil recovery.     

水驱后特低渗透油藏氮气驱驱油特性分析

特低渗透油藏水驱采收率低,注入压力高,而氮气在特低渗油藏具有良好的注入性。本文在特低渗透岩心水驱后分别进行了常规的注氮气、水驱后水气交替、水驱后脉冲注氮气驱替实验。实验结果表明:特低渗储层微观非均质性导致气体在大孔道易形成窜流,水驱后常规注氮气提高采收率的效果有限。水气交替通过多轮次的注入使油藏中不同相态流体的分散程度提高,在优势流动通道中形成毛管阻力,促使后续注入气体进入局部致密区,可有效提高采收率16.37%;脉冲注气通过周期性注气方式,在局部高渗区和局部低渗区间形成压力扰动与交互渗流,使流体在地层中不断地重新分布,从而启动油层低渗区原油,提高采收率15.94%。此外,脉冲注气的注气压力比较低,与水气交替开采方式比较注入性提高。图6表1参12