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看阿根廷如何循环利用压裂废水

2016-01-15浏览次数:1659   来源:石油圈  作者:Bob Chen
  【石油机械网】阿根廷的Vaca Muerta等页岩油气田已经开始勘探和开发,商业化过程必须使用大量的水进行水力压裂。
 阿根廷的Vaca Muerta等页岩油气田已经开始勘探和开发,商业化过程必须使用大量的水进行水力压裂。自上世纪60年代,水力压裂增产措施在于阿根廷石油与天然气生产中广泛使用,目前已经应用于五个产油气盆地和多种类型的储层和油藏。本文论述了页岩气藏水资源管理方面的经验,室内实验研究了处理和未经处理的返排水,并评估其作为压裂液的可行性。

看阿根廷在页岩油气藏开采中如何玩水

水资源和增产措施:由于Vaca Muerta的经济潜力巨大,已成为阿根廷的开发重点。开发Neuquén盆地最初所用的水源主要来自河流、湖泊、水库和地下水,产出水不适合人类或农业使用。

对Vaca Muerta页岩油气田的六种水力压裂裂缝类型、13口井和65条水力压裂裂缝进行分析,发现每级压裂的平均水量随着流体层的不同而不同。油井平均用水量为1300m3,湿气井是1850m3,干燃气井是2180m3通常 Vaca Muerta页岩油气田中直井完井用水量约为6500m3,水平井约为14500m3

水资源运输

在过去的五年里,为了阿根廷页岩气的可持续发展,水资源管理和运输能力取得了实质性进步。目前最常用的存储系统是移动压裂罐和圆形水罐。

第一口直井

看阿根廷在页岩油气藏开采中如何玩水

Vaca Muerta页岩油气田第一口井设计包含四级水力压裂,需要7600m3的水。评估了各种方案后,决定在增产井附近安装一个由管道和储水器组成的传输系统。在同一个区域的可提供水资源水井(低矿化度地下水)附近可安置一个圆形水罐。铺设直径为4英寸的管道,连接水井和储水器,储水器周围安装两个圆形的储罐。

直井和水平井

Vaca Muerta页岩油气田的第二口直井同样设计了四级水力压裂,需8000m3的水。为了增加该井产能,设计者决定在该井附近新钻一口水井,并且采用与第一口井相同的水管理方案。第一口水平井的完井由六级压裂组成,需要13000m3的水。为直井建造的部分基础设施可用于该水平井。由于需水量大,所以必须增加一个容量更大的新圆形水罐。

看阿根廷在页岩油气藏开采中如何玩水

室内研究评估了采用非传统水作为压裂液的不同方案。测试包括:

1. 水(物理/化学)分析
2. 粘土膨胀和抑制测试
3. 评价并改进液体支撑剂的运输能力
4. 凝胶残渣和悬浮固态物总量(TSS)引起的伤害
5. 返排液、产出水和净化水的使用和再利用

物理/化学分析:返排液和产出水具有相似的性质,但与淡水略有差别。这些水比重大、pH低、固溶物总量(TDS)和悬浮固态物总量高、钙、镁、钠、钾、铁、钡浓度明显较高。

粘土抑制剂测试:在Vaca Muerta页岩油气田的勘探阶段,新区的每一口井都例行测试了毛细管吸收时间,其目的是了解储层的水敏程度并优选粘土稳定剂的种类和浓度。

以下粘土稳定剂已经通过测试并应用:石油圈原创www.oilsns.com

    季铵盐(液体)
    无机盐、氯化钾(固体)
    近期新型超低分子量的阳离子有机聚合物取代了季铵盐

混合水(未处理的返排液):第一个测试采用常规压裂液(瓜尔胶/硼酸)和水的混合物。测试结果并不令人满意,这是因为凝胶水合物及其交联问题导致流体在地面和井底条件下不稳定。此外,尽管硼酸系统通常在高pH值条件下起作用,但是增加系统的pH值会产生丝状 
物、絮凝和沉淀。

净化水(返排液):根据之前的结果,决定评估含有100%净化返排水的流体,对流体进行的pH值和交联剂浓度作出微小改变。在含有混合水的流体和100%净化处理后的返排水之间可观察到粘度降低现象。

看阿根廷在页岩油气藏开采中如何玩水

携带支撑剂的能力:进行了两种类型的测试分析其携带能力。第一个是在静态条件下的测试(沉降),第二个是利用泥浆粘度计的动态条件下的测试。沉降测试显示,总体而言Vaca Muerta页岩油气田目前使用的瓜尔胶/硼酸系统在两小时后失去携砂能力。泥浆粘度测试表明聚物配方采用了100%非传统处理水,尽管其粘度值低,但具有良好的携带支撑剂能力。

阿根廷压裂废水循环的启示

储水系统主要是可移动的压裂储存器和圆形罐,这种系统通常用在增产的井场,大多数水是由卡车运输。为了支持Vaca Muerta页岩油气田的完井工作,建立完整的水资源管理方案,包括使用靠近井场水源、管道传输系统和存储系统。要实现大规模开发,必须有一个综合的水资源管理计划,要考虑到河流、湖泊、水井以及与其他地区运营商的合作。

Vaca Muerta页岩气的非传统水源分析(返排液/产出水)表明其含有大量的TDS、TSS和高浓度的钙、镁、钠、钾、铁、钡离子,处理这样的水会导致重要的TSS和铁元素减少。在压裂处理中使用这些水表明不需要使用额外的粘土稳定剂。利用处理后的水研制出了具有低聚合物分子量和低pH值得新压裂液配方。该压裂液适用在不同PH条件下,沉淀物也不会降低裂缝的传导能力,并且沉淀测试和泥浆粘度测试中表现出良好的携带能力。在未来压裂措施中,处理和重复利用非传统的水将大大减少页岩井淡水需求,并且减少了注入废弃井中的液量。

英文原文
 

 

 

Recently, exploration and development of shale plays in Argentina, such as the Vaca Muerta, have begun. To achieve commercial production, this type of reservoir must be stimulated by hydraulic fracturing using large volumes of water.This paper discusses aspects of water logistics necessary during the well-completion phase, fracture-treatment designs applied in Vaca Muerta, and laboratory studies performed on flowback and produced water to help evaluate the potential
for water reuse.

Introduction

Well stimulation using hydraulic fracturing has been used widely for producing oil and gas reservoirs in Argentina since the 1960s. This stimulation technique has been applied in the five hydrocarbon producing basins shown in Fig. 1, as well as in a variety of formations and types of reservoirs, such as conventional, tight, and, more recently, shale. The majority of shale exploration and development has been in the Vaca Muerta formation, but work has also been assessed in other formations, such as Los Molles, Cacheuta, D-129, and Agrio. Experience gained related to water management in these shale plays during the completion of more than 40 wells (more than 200 hydraulic fractures) by different operators is presented in the paper. Furthermore, laboratory studies were conducted on treated and untreated flowback water, and assessment of its use as fracturing-fluid water is presented.

Water Sources and Stimulation

Given the economic potential of the Vaca Muerta play, the focus lies on this reservoir. The primary sources of water in the Neuquén basin used to develop these hydrocarbon resources are rivers (Neuquén, Limay, and Colorado), lakes, reservoirs (Cerro Colorado and Pellegrini), or groundwater sources, such as wells with low salinity. These types of wells for water supply need a permit from the regulatory authority, and produced water is not suitable for human consumption orŽfarming.

Types of Systems. The following systems used fresh water and contained chemical additives to perform various functions:
SW—Contained a friction reducer and friction-reducer breaker
LG—Contained a gelling agent, buffer, and breaker
XL—Consisted of a buffer, gelling agent, crosslinker, and breaker
Additionally, each of the fluid systems also typically contained a biocide, clay inhibitors, and surfactant additives.

Types of Treatment. The most common hydraulic-fracturing treatments performed in different plays in Argentina were hybrid fracturing designs. The greatest volumes of water by stage correspond to reservoirs of gas and wet gas in hybrid treatment designs for both SW/LG (Los Molles) and SW/LG/XL (VacaŽMuerta).

A statistical analysis regarding the type of hydraulic fracture in Vaca Muerta was performed for six fields, A, B, C, D, E, and F. Thirteen wells and more than 65 hydraulic fractures were analyzed. In general, average water volume per stage varied according to the fluid reservoir; for oil wells, the average water volume was 1300 m3; it was 1850 m3 for wetgas and 2180 m3 for gas wells. The fracturing treatments were primarily hybrid SW/XL, although some cases used SW/LG/XL. LG was commonly used as a contingency in the transition from SW to XL. Normally, the completion of a Vaca Muerta well involved a total water volume of approximately 6500 m3 for vertical wells and approximately 14 500 m3 for horizontal wells.

Logistics

During the past 5 years, there has been substantial progress related to water management and logistics for sustainable development of Argentina’s shale plays. A variety of water-storage systems and methods for transferring water have been used in the Neuquén basin, primarily in the Vaca Muerta.

Currently, the most common storage systems used are mobile fracture tanks and circular tanks. Pit usage is restricted for environmental reasons.

First Vertical Well

The completion of the first well in Vaca Muerta consisted of four hydraulicfracture stages, requiring of 7600 m3 of water. Alternatives were evaluated for the logistics and water management, and it was decided to install a transfer system through pipes and a water-storage location close to the well to be stimulated. A water well (groundwater with low salinity) in the same field was used for source water. A circular tank for water storage was located in the vicinity. The operator performed the laying of 4-in. pipe from the water well to the water storage location, where two circular tanks were installed.

Vertical and Horizontal Well

The second vertical well in Vaca Muerta consisted of four hydraulic-fracture stages, requiring 8000 m3 of water. For the stimulation of this well, it was decided to drill a new water well close to the wellsite and apply the same water-management strategy.

The first horizontal-well completion consisted of six fracture stages, consuming 13 000 m3 of water. Part of the infrastructure built for the vertical well was used for the horizontal well. Because of the amount of water needed, a new circular tank with greater capacity was required.

Laboratory studies evaluated different alternatives for the use of nontraditional waters as fracturing fluids. The tests „included:
1. Detailed water (physical/chemical) analysis
2. Clay-swelling and -inhibition testing
3. evaluation and development of XL fluids proppant-transport capacity
4. Damage by gel residue and total suspended solids (TSS)
5. Use and Reuse of Flowback,Produced, and Treated Water
Physical/Chemical Analysis. Flowback and produced water have similar characteristics, which differentiate them from fresh water. In general, these waters have higher values of specific gravity, lower pH values, higher levels of total dissolved solids (TDS) and TSS, and significant Ca, Mg, Na, K, Fe, B, and Ba„concentrations.

Action as Clay Inhibitor. During the exploration phase of the Vaca Muerta, a routine capillary-suction-time test was performed for each well in a new field; the intention was to understand the degree of water sensitivity and select the best clay stabilizer and concentration.

The following clay stabilizers have been tested and used in these fields:
Quaternary ammonium salt (liquid)
Inorganic salt, KCl (solid)
New ultralow-molecular-weight cationic organic polymer recently applied to replace the quaternary ammonium salts

Fracturing Fluid. Referring to the XL fluid tests performed, the base fluid used was fresh water and the system used guar/borate. The pumping of large volumes of SW or linear gel before an XL gel has a cooling effect, which makes the XL systems subject to background temperatures of approximately 120°F and spacing of approximately 30 to 45 minutes.

Blend of Water (Flowback Untreated). The first test performed used the normal fracturing fluid (guar/borate) with a mixture of waters. The results were not satisfactory because of gel-hydration and -crosslinking problems that resulted in unstable fluids at surface and bottomhole conditions. Moreover, increasing the pH of the system generated filaments, flocculants, and precipitates, although borate systems usually work in high pH.

Treated Water (Flowback). The previously obtained results led to the decision to evaluate the fluid with 100% treated flowback water. Slight changes in pH adjustment and concentration of the crosslinker were made to the fluid.

A reduced viscosity profile was observed between the fluids formulated with blends of water and those formulated with 100% treated flowback water.

Proppant-Transport Capacity. Two types of tests were conducted to analyze transport capacity. The first was a conditional static (settling) test, and the second was under dynamic conditions with a slurry viscometer. The settling test revealed that, overall, the guar/ borate system currently used in operations in the Vaca Muerta lost its carrying capacity after the first 2 hours. The slurry viscometer test indicated that lowpolymer fluid formulations using 100% nontraditional treated water demonstrated good proppant-transport capacity, despite having low viscosity values.

Conclusions

In general, hybrid fracturing-treatment designs dominate the fluid types used in Argentina’s shale plays. The waterstorage systems that have been primarily used are mobile fracturing storage and circular tanks, which are usually at the wellsite being stimulated. Most water is delivered by transport trucks. An integrated water-management plan was developed to support well completions in Vaca Muerta using sources of water close to the wellsite, pipeline transfer systems, and a storage system. For a large scale development, an integrated water management plan must be implemented, taking into account rivers, lakes, water wells, and synergies with other regional operators. Nontraditional water sources analyzed (flowback/produced) for the Vaca Muerta revealed substantial TDS and TSS and significant Ca, Mg, Na, K, Fe, and Ba concentrations. Treating such waters results in important reductions of TSS and Fe.content. The use of these waters in fracture treatments indicated that there is no need to use additional clay stabilizers. A new fracturing fluid, with low polymer loading and low pH, was developed that can be formulated with these waters. This system presents the advantages of working in a range of pH in which precipitates do not generate reduced conductivity in the fracture pack. It generates a good carrying capacity, as seen by settling tests and slurry- viscometer testing. Treatment and reuse of nontraditional water for future fracturing treatments greatly mitigate the issue of freshwater requirements for shale wells and reduce volumes to be injected in disposal wells.


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