Steam fingering at the edge of a steam chamber in a heavy oil reservoir

The steam‐assisted gravity drainage (SAGD) process is one of the key in situ recovery processes being used today to recover heavy oil and bitumen. In this process, steam injected through a horizontal well, flows convectively towards the outer edges of a depletion chamber. At the edges of the depletion chamber, the steam releases its latent heat to the cool oil sand and raises its temperature. The heated oil is mobile and flows under the action of gravity to a horizontal production well located several metres below the injection well. It remains unclear what is the exact mechanism of chamber growth. Some have suggested that in addition to heat conduction, it is by convective steam flow in the form of pointed fingers at the edges of the chamber which penetrate the oil sand. In theory published by Butler [Butler, J. Can. Petroleum Technol. 1987;26(3):70–75], it was determined that the fingers can be as long as 6 m for Athabasca bitumen reservoirs. In this research, a new theory is derived and provides predictions of the rise rate which compare better to estimates derived from field thermocouple data and physical model experimental observations than values obtained from Butler's theory. The results suggest that in the absence of mobile water, heat conduction rather than steam fingers at the chamber edge is the dominant heat transfer mechanism.     

Stability of the edge of a SAGD steam chamber in a bitumen reservoir

Steam-Assisted Gravity Drainage (SAGD) is a key in-situ recovery process being used today to extract oil from bitumen reservoirs. In SAGD, an oil-depleted chamber of steam grows within the oil sands formation along a pair of horizontal wells and heats bitumen-laden oil sands at its edge. The viscosity of bitumen drops by up to five orders of magnitude when heated to above 200 °C and mobilized bitumen at the chamber edge flows under gravity to a production well located at the base of the chamber. If the steam chamber does not grow uniformly along the wellpair, then bitumen recovery is less than ideal. To raise the thermal efficiency, and consequently the economics, of the process, efficient heat transfer from chamber to the oil sands must occur and the chamber must grow uniformly along the entire length of the wellpair. If steam fingers develop at the edge of the chamber, then the heat transfer area enlarges and raises the thermal efficiency of the process since more heat is directed to the oil sands. In this research, the stability of the interface between the steam chamber and oil sands is examined by using linear stability theory. The results show that the stability is controlled by the difference between the energy content-weighted Darcy–Rayleigh numbers of the steam/water phases (displacing fluid) and the oil phase (displaced fluid). Also, the results show that at typical SAGD steam saturation temperatures, the chamber edge is unstable providing the steam quality at the edge exceeds about 50%.     

On fingering of steam chambers in steam‐assisted heavy oil recovery

Western Canadian oil sands reservoirs are among the largest petroleum accumulations in the world. Given original oil viscosity up to 5,000,000 mPa‐s, these oils are currently recovered from these reservoirs using steam which heats the oil to ～250°C with reduced viscosities <10 mPa‐s. A key issue faced by thermal recovery processes is the uniformity of the steam chamber within the reservoir. Nonuniformities of the chamber arise from multiphase flow instabilities in the porous media where fingering has been explained by penetration of low viscosity steam into viscous oil. Here, fine‐grid thermal reservoir simulation reveals that fingering takes place in the gas phase beyond the chamber edge in a zone created by gas exsolution due to elevated temperature beyond the edge of the steam chamber. The results suggest that nonuniform chambers will occur in perfectly homogeneous reservoirs which implies that uniform chambers along wells may be impossible to achieve. © 2015 American Institute of Chemical Engineers AIChE J, 62: 1364–1381, 2016     

稠油油藏蒸汽辅助重力泄油参数优化研究

在SAGD开采过程中,蒸汽腔的形成与发育直接影响着最终开发效果的好坏,在泄油过程中,蒸汽腔的大小、泄油能力不断在改变,蒸汽—油界面不断在移动,为防止蒸汽突破进入生产井或者热油积聚在蒸汽腔底部压迫蒸汽腔,必须对蒸汽腔的扩展状况以及油层温度场、压力场以及含油饱和度场进行动态模拟。本文应用STARTS数值模拟软件,对注采井间进行局部加密,精细模拟井间温度、压力场,对直井—水平井组合的SAGD技术的布井参数、注采参数等进行了优化设计,并对开发效果进行了预测。验证了运用数值模拟方法研究蒸汽辅助重力泄油技术开发效果的可行性和蒸汽辅助重力泄油技术开发超稠油油藏的可行性。     

A new analytical model to predict heavy oil production rate in the SAGD process

An analytical model for predicting the oil production rate in the steam-assisted gravity drainage (SAGD) process is presented in this article. The suggested correlation is found based on Butler's original work. It considers the most effective parameters of the process that emphasize the influence of gravity drainage and that are grouped together in the form of the Rayleigh's number. The present model introduces three coefficients (i, j, and k) into the equation, which are determined by minimizing an objective function based on the difference between the six experimental SAGD datasets and the calculated results. The tool chosen for the minimization is the genetic algorithm (GA). After the initial evaluation, the same approach is used for other reservoir characteristics to ensure the robustness of the new equation. Having considered various simulation outcomes with an average error of 8.9% makes this model a credible one for predicting the SAGD production rates. The novelty of the new predictive model lies within its unique approach, making it quite fast and applicable to a wide range of reservoirs with low associated estimation inaccuracies.     

薄层稠油油藏SAGD物理模拟研究

紧密围绕杜84块兴Ⅰ组油藏的地质特点与开发现状,依据相似原理设计建立了比例物理模型,开展SAGD比例物理模拟实验,探讨了薄层稠油双水平井SAGD开采中蒸汽腔的形成和发育过程,生产特征和开发效果,预测了盖层的热损失,可为开发方案编制提供借鉴。     

Optimization strategies and impact of low oil price on long term SAGD projects

Steam assisted gravity drainage (SAGD) has been known as a commercially proven high ultimate recovery process for bitumen and heavy crudes. It is an energy intensive process, which is economical when oil price is above certain value. When the oil price goes below the economic threshold of project, steam injection can be decreased or completely stopped for a certain period of time, and can resume thereafter when the condition alters. The objective of this study is to provide comprehensive information about the effect of steam injection interruptions on thermal project performance. An optimization strategy for the SAGD process, in cases where steam injection interruption occurs, is discussed using actual reservoir models of different geological formations. An economical model is used to evaluate operating strategy effect on the net present value (NPV) of the project. The parameters, like shut-in period, initial steam injection period, etc, are optimized for Athabasca type oil sand reservoirs. The results show several key mechanisms exist in the life cycle of the SAGD process that must be included to reflect the field scale behaviour; otherwise, the mechanistic simplicity of the models could lead to directional and semi-quantitative conclusions. Among the mechanisms, temperature effect on basic petrophysical properties of reservoir rocks was found to have an important role in the oil recovery, and considerably impacts the results of optimization. When the steam injection is interrupted, an optimum shut-in period can be determined to maximize the oil recovery. The optimum length of steam injection interruption depends on the initial steam injection period.     

Heavy oil recovery efficiency using SAGD,SAGD with propane co-injection and STRIP-SAGD

Primary oil recovery methods in heavy oil basins generally extract 5–10% of the available resource, with the vast majority left in the ground and recoverable only through Enhanced Oil Recovery (EOR) methods. Traditional EOR methods, such as SAGD and solvent-assisted SAGD, generate steam in surface facilities and inject it underground to mobilize the oil for production. However, these methods can have considerable energy losses that significantly impact process performance. In contrast, the Solvent Thermal Resource Innovation Process (STRIP) technology, which uses down hole combustion of methane to produce CO₂ and steam, reduces the operating and capital costs of surface facilities, saving more than 50% of the energy typically required for thermal production. In this work, simulations of conventional SAGD, SAGD with a non-condensing solvent (propane), and STRIP-SAGD for a typical bitumen reservoir in the Fort McMurray region in Alberta, Canada were performed using the combined software system ADGPRS/GFLASH. SAGD simulations used steam injection with a quality of 0.8 while STRIP simulations injected a vapor–liquid mixture with a quality of 0.8. Furthermore, both solvent-based EOR methods required longer operation periods than conventional SAGD to recover a similar amount of oil. However, when compared on the basis of cumulative oil produced for the same overall energy input, it is shown that STRIP-SAGD recovered more oil per kJ of energy input to the reservoir than either SAGD or SAGD with propane co-injection.     

Displacement of bitumen from reconstituted oil sands by aqueous solutions

A simple method has been developed for modelling the recovery of bitumen from packed beds of oil sand by water or caustic solution displacement. Batches of reconstituted oil sand were prepared by intimately mixing predetermined amounts of sand, water, and bitumen, thereby permitting the composition of the oil sand to be controlled and varied within a wide range. Dilution of the bitumen with hexadecane facilitated the mixing process and allowed experiments to be performed at low temperatures while maintaining oil-water viscosity ratios comparable to those prevailing at the higher temperatures encountered during hot water or steam displacements in the field. The effects of a wide range of compositional and operational variables were studied using a two-level fractional factorial design technique and the findings are discussed. Of particular interest are the observations that the density and initial connate water saturation of the oil sand exert significantly more effect on bitumen recovery efficiency for the case of water displacement than for caustic solution displacement.     

Investigation of solid particle erosion-related failures in once-through steam generators (OTSGs) in oil sands in-situ production: The limitations of the API RP 14E guideline in OTSG design or operational decision-making

The required steam for steam-assisted gravity drainage (SAGD) oil sands operations is generated using a once-through steam generator (OTSG) that is fed with relatively poor quality process water. Industries have reported possible solid particle erosion-related failure in the OTSG boiler tubes because of the transport of precipitated dense inorganic particles. However, the presence of other damage mechanisms, e.g. corrosion, flow accelerated corrosion (FAC), often masks the evidence of erosive wear. Also, industries set an upper limit operating velocity for the OTSG using the API RP 14E guideline, which provides no quantitative erosion rates to determine an operating envelope. This study presents a computational fluid dynamics (CFD) analysis of erosion damage in a SAGD OTSG boiler tube. The results revealed that API RP 14E may not be an effective decision-making tool for operating the OTSG system. For example, a 10% increase in velocity, even at conditions below the API RP 14E threshold, showed a decrease in the failure time of the boiler tubes by 40%–50%.     

Design,construction and operation of lab scale cylindrical steam assisted gravity drainage model for heavy oil recovery

Based on a theoretical background [1,2], a lab scale cylindrical SAGD (steam assisted gravity drainage) model was designed, constructed and operated. There are six different parts in the apparatus: (1) water supplier, (2) steam generator, (3) SAGD cylindrical model, (4) cooling system, (5) constant pressure maintaining system and (6) production system. Temperature, pressure and steam injection rate were controlled by computer, and product (mixture of oil and water) was collected/separated manually. Extra heavy oil (<10 cp at 200 °C) and glass bead (diameter 1.5 mm) were mixed homogeneously for making porosity of 0.3 and applied for simulating oil sand. For obtaining optimum operation conditions of SAGD apparatus, several attempts were made. When the steam at high temperature (160–180 °C), high pressure (8–9 atm) was injected with 20–25 cc/min, cSOR (cumulative steam to oil ratio) of about 5 was obtained with oil recovery of 78.8%.     

油气工况下提升管出口旋流快分系统性能的数值研究

为促进旋流快分(SVQS)系统的工业应用、准确评估其性能,参照国家标准设计了一系列不同密度、黏度的油气模型,并采用商用软件FLUENT 2019 R3对一套Φ600 mm×3150 mm的SVQS系统进行了流动模拟和可行性验证。用单因素变量法分别研究了油气性质对系统无量纲切向速度和压降的影响;用标量输运方程分析了油气在系统内的停留时间分布规律。结果表明,无量纲切向速度随油气密度增加或黏度降低而变大;无量纲最大切向速度随油气密度增加或黏度减小而呈对数递增,最大为0.912;密度越大、黏度越小的油气在SVQS系统内的平均停留时间越短,最短可达6.279 s;压降、阻力系数不仅与系统的结构参数相关,也与油气黏度呈对数关系。拟合得到了与油气参数相关的无量纲切向速度、压降和阻力系数函数式,具有较好的普适性,可为SVQS系统的结构优化提供参考。     

低油价形势下改善稠油热采开发效果对策研究

针对胜利油田边底水能量强、原油黏度高、油层厚度薄、储层物性差、强水敏等油藏特征,以及稠油油藏热采开发成本高的特点,分析了当前低油价形势下稠油热采无效直井的治理对策。通过研究,提出了强边水油藏一线井提液二线井调剖、优化注汽参数、组合吞吐、分层注汽和氮气补充地层能量等技术措施,有针对性地解决了高含水井、无效益井的问题。现场应用表明,该系列技术对策有效提高了热采直井的开发效果,取得了良好的经济效益。     

热采井抗高温长效水泥固井技术研究与现场应用

稠油油藏大多采用热力降粘的方式开采,主要是采用蒸汽热采的方法。注蒸汽热采一般为蒸汽吞吐,后期转为蒸汽驱,因此热采稠油井的固井必须适合和满足蒸汽吞吐和蒸汽驱开采方式。后期注蒸汽开采时,由于地层的保温效果很差,高温蒸汽在注入过程中能量通过水泥环很快耗散到地层中,导致稠油油藏达不到注蒸汽热采的效果,严重影响稠油油藏的开发效果。在注蒸汽开采过程中,水泥石在高温蒸汽环境中强度衰减严重,导致水泥环破裂损坏,使原本封固好的环空失效,引发油气水窜,严重缩短油井寿命。针对稠油油藏固井存在的问题,须研究开发一种适用于封固稠油热采井的长效固井技术,使该固井技术具有水泥浆热容高、保温效果好,可延缓蒸汽注入过程中能量损失;水泥浆具有良好的强胶结性能,大大改善固井第二界面胶结强度,有效防止油气水窜的发生,提高浅层水泥封固段长期封固效果;水泥石强度高,抗高温性能好,其强度在高温下衰减缓慢,可经受稠油热采高温蒸汽的侵蚀的优点。有效解决稠油热采井在高温驱替环境下固井质量差、油井寿命短的问题,为稠油油藏勘探开发提供有力的技术支撑。     

稠油井分层稳恒注汽技术

注蒸汽吸汽不均问题是稠油非均质油藏蒸汽吞吐开发主要矛盾之一,多年来工艺技术人员研究应用选配注技术,通过分隔纵向油层,实施配汽,取得了较好的效。但是不能同时给两个油层注汽,只能先注下层,然后投球配注上层,蒸汽的热损失大,而且存在人为误差和蒸汽的浪费,同时在热采井口投球存在不安全隐患。针对这类问题,研制应用了分层稳恒注汽技术,将分层稳恒注汽管柱下入指定位置。注汽时,蒸汽通过稳恒注汽阀按设计注汽量进入油层,达到调整和改善油层的吸汽剖面,使油井各层位产能达到均衡动用,提高热采效果和采收率。     

Theoretical studies on the gravity drainage of heavy oil during in-situ steam heating

One concept for the in-situ production of oil from the tar sands involves the continuous injection of steam into a growing steam-saturated volume or steam chamber. Steam flow to the boundary of the chamber, condenses and gives up its heat to the surrounding oil sands. The condensate and heated oil flow by gravity to a production well located at the bottom of a chamber and are removed continuously. The well may consist of a horizontal slotted pipe. This paper describes the theory of operation of such a process and an equation is derived which predicts the rate of drainage.     

考虑储层非均质时注汽井内蒸汽流动规律

稠油热采水平井注蒸汽是一个复杂多变的过程，水平井沿程蒸汽热物性的预测对于储层的均匀动用十分关键。考虑储层渗透率、围压和蒸汽相变等条件的相互耦合影响，建立了预测水平井注汽流动的综合数学模型。与现场测井数据进行对比分析，验证了模型的准确度。模拟结果表明，单一变量条件下，水平井跟部注汽压力越大，注汽井内质量流量和蒸汽干度下降越快，当注汽压力由11 MPa降为8.5 MPa时，配汽距离增加1倍；在水平井相同位置处，跟部注汽干度越高，注汽井内质量流量越大，且蒸汽压力下降越快，注汽干度提高1倍时，压降也几乎增加1倍；跟部注汽流量越大，蒸汽压力下降越快，注汽流量提高1.75倍时压降提高了5.3倍，但管内蒸汽干度下降趋缓；储层渗透率越高，注汽井内的蒸汽干度下降越快。该模型可以为现场注汽提供理论支撑，有效提高配汽效果达到增产降耗。     

新型高效活性聚合物驱油剂的研究

本文介绍了一种用于油田三次采油的新型活性聚合物驱油剂。该种驱油剂具有以下特点:对稠油有降粘分散作用;耐温性好、可配合蒸汽开采;耐盐耐剪切;防止粘士膨胀,不会伤害地层;有固砂效果,在驱出原油的同时不会引起地层出砂。目前该产品已经建成1000t/a装置,已在油田应用,并取得了明显的经济效益和社会效益。     

互层状超稠油油藏调剖助排技术研究与应用

兴隆台超稠油油藏因为原油粘度高、纵向及平面上非均质性、井距近等因素影响,井间汽窜干扰、周期吞吐时间短等矛盾突出.为此,在原有技术的基础上,将高温暂堵调剖和驱油助排结合,研发了调剖助排技术,现场应用后,在抑制汽窜的同时,降低产出液粘度,改善了吞吐效果.在超稠油吞吐开发领域内,实现了整体的工艺创新.     

春风油田浅层超稠油开发效果评价

对春风油田薄浅层超稠油开发效果进行了评价研究。水平井蒸汽吞吐开发技术利用水平井增大泄油面积,蒸汽在水平井段上部形成蒸汽腔室,实现隔热保温驱油。矿场实践证实水平井蒸汽吞吐辅助氮气、降粘剂开发薄浅层超稠油是可行的。稠油产量周期内、周期间快速递减的规律不可改变,但可以通过技术配套和加强管理减缓递减。通过开发规律研究,为指标预测、开发决策提供了依据。对于较厚油层,可以采用蒸汽吞吐辅助氮气、降粘剂开发。春风油田已建成产能65万吨/年,累产油115万吨。