采出水已經(jīng)成為當(dāng)前油氣開采中降本的主要關(guān)注點(diǎn)之一，本文將帶來一種釜底抽薪式的方法！

編譯 | TOM 驚蟄

產(chǎn)出水是指在油氣生產(chǎn)期間被帶到地面的天然水，采出水是迄今為止油氣行業(yè)產(chǎn)量最大的副產(chǎn)品。雖然已建油氣產(chǎn)區(qū)的地層水產(chǎn)量存在顯著差異，但據(jù)估計(jì)，每采出一桶石油，將采出4至10桶地層水。

地層水通常含有鹽、細(xì)菌、有機(jī)化學(xué)物質(zhì)以及其他污染物。雖然一些公司會將地層水用于水力壓裂或農(nóng)業(yè)生產(chǎn)，但這并不總是一種經(jīng)濟(jì)的選擇。大部分地層水的處理方式還是簡單粗暴，直接被注入地下廢水處理井。

據(jù)估計(jì)，到2018年，美國油氣上游行業(yè)將在水資源管理方面投入347億美元。存儲、轉(zhuǎn)移、運(yùn)輸、處理處置地層水的物流網(wǎng)絡(luò)復(fù)雜，占了水管理成本的89%。在單口井的使用壽命中，地層水的成本總計(jì)可達(dá)600萬美元，相當(dāng)于一口井運(yùn)營成本的一半。這些費(fèi)用預(yù)計(jì)還會增加。

地層水的處理與處置仍是油氣行業(yè)的重要課題，但從源頭解決這一問題，限制水產(chǎn)量的措施卻很少。對于采出水管理提出的挑戰(zhàn)，理想的解決辦法是在不妨礙油氣生產(chǎn)的情況下減少地層水的采出量。目前的技術(shù)，如凝膠或膨脹化學(xué)品，可以限制地層水的產(chǎn)出，但它們也限制了油氣的流動(dòng)。

Hexion的研究人員決心開發(fā)出一種既能降低地層水產(chǎn)量，又能保持油氣產(chǎn)量的解決方案。OilPlus支撐劑等技術(shù)已經(jīng)證明能夠通過改變支撐劑的表面化學(xué)性質(zhì)，來改善富液儲層的水產(chǎn)量。利用改變表面化學(xué)的試驗(yàn)，開發(fā)出AquaBond地層減水專利技術(shù)。

事實(shí)證明，與鄰井相比，該技術(shù)可將產(chǎn)出水減少多達(dá)50％，同時(shí)提高了油氣產(chǎn)量。由于該技術(shù)與支撐劑相結(jié)合，因此該技術(shù)的減水性可以有效延長油井的使用壽命。利用該技術(shù)可以通過降低廢水管理成本來提高油井的盈利能力，最終降低桶油成本。

AquaBond地層減水技術(shù)改變了支撐劑充填層的相對滲透性，使油氣進(jìn)入，減少水的進(jìn)入。該充填物作為半透膜，選擇性地允許油氣滲透，同時(shí)排斥地層水。對支撐劑涂層官能團(tuán)進(jìn)行修改后，形成了疏水親油性的臨界表面張力。這就產(chǎn)生了一種驅(qū)動(dòng)力，使支撐劑充填層能夠吸收石油，同時(shí)減少水在支撐劑充填層中的流動(dòng)。

由于支撐劑充填層是一種多孔介質(zhì)，如果水是唯一與充填層接觸的流體，那么它就可以流過充填層。這可以防止在支撐劑充填層或地層表面/支撐劑充填界面出現(xiàn)水堵現(xiàn)象。通過修改上文描述的試驗(yàn)就可以證明這一點(diǎn)。將起始水/油比調(diào)節(jié)至5：1，因此在試驗(yàn)開始時(shí)僅有水與支撐劑芯柱接觸。用傳統(tǒng)樹脂涂覆的支撐劑進(jìn)行對比試驗(yàn)，即使在油與支撐劑芯柱接觸后，仍繼續(xù)注入水，大部分油仍留在儲層內(nèi)。

為了證明該技術(shù)在油田的有效性，在德克薩斯州Panhandle羅伯茨縣與亨普希爾縣的Granite Wash地層進(jìn)行了試驗(yàn)。一家油氣公司在兩口水平井中使用了AquaBond技術(shù)，并將其與11口鄰井水平井進(jìn)行了比較。試驗(yàn)井利用該技術(shù)，泵入23%的40/70地層減水劑支撐劑尾漿，以及剩余的都是未涂覆壓裂砂。三口鄰井采用了23%的40/70統(tǒng)樹脂涂層支撐劑尾漿，另外八口鄰井采用了100%未涂覆的壓裂砂。

數(shù)據(jù)集中所有井的完井細(xì)節(jié)類似：垂深接近11000英尺，水平段4000英尺，井底靜態(tài)溫度為180華氏度。所有井的支撐劑用量約為230萬磅。在整個(gè)作業(yè)期間，采用傳統(tǒng)樹脂涂層支撐劑的鄰井與采用未涂覆壓裂砂的鄰井表現(xiàn)大致相同。采用AquaBond技術(shù)的井的含水率比鄰井低30%。平均累積產(chǎn)水量降低了43%，對產(chǎn)出總液量并無影響。

在水力壓裂作業(yè)中，不需要特殊設(shè)備就可以實(shí)現(xiàn)地層減水。地層減水方案概述如下:利用與傳統(tǒng)支撐劑相同的方法，將之泵入井下；按照常規(guī)的回流程序，壓裂液返回地面；油氣與地層水接觸到化學(xué)變化的支撐劑填充層；AquaBond技術(shù)使油氣比水更優(yōu)先流動(dòng)；采出更多的油氣（更少的水）至地面。

作業(yè)后分析可以根據(jù)產(chǎn)量數(shù)據(jù)優(yōu)化未來的完井設(shè)計(jì)。根據(jù)地層特征、預(yù)期減水效果和/或水問題的嚴(yán)重程度，可以采用領(lǐng)漿、尾漿或全支撐劑設(shè)計(jì)。該技術(shù)還可以作為現(xiàn)有高含水井重復(fù)壓裂的補(bǔ)救措施，并已成功應(yīng)用于該領(lǐng)域。由于其靈活性與易用性，該技術(shù)應(yīng)被視為壓裂設(shè)計(jì)中很重要的一部分，并納入有效的水管理策略。

實(shí)驗(yàn)測試結(jié)果表明，AquaBond技術(shù)可使油比水優(yōu)先流出。這些測試已經(jīng)重復(fù)多遍，使用了來自北美不同地區(qū)的不同原油與采出水的樣本。通過改變水/油比也改變了測試。當(dāng)進(jìn)行實(shí)驗(yàn)室測試時(shí)，只有水與含有AquaBond技術(shù)（或固結(jié)支撐劑充填層）的芯柱接觸時(shí)，不會發(fā)生水堵現(xiàn)象。

該技術(shù)已用于Permian區(qū)塊，Bakken頁巖區(qū)塊, Granite Wash地層以及Haynesville頁巖區(qū)塊。采用與傳統(tǒng)支撐劑相同的方法，無需特殊設(shè)備。以Granite Wash地層為例，說明了該技術(shù)可以在不影響總流體產(chǎn)量的前提下，降低地層水產(chǎn)量。

Produced water, or formation water, is naturally occurring water that is brought to the surface during oil and gas production. It is by far the largest by-product for the industry. While there is significant variation in the amount of formation water generated from established oil-and-gas-producing regions in the country, it is estimated that for every barrel of oil recovered, 4 to 10 bbl of formation water will be produced.

THE PROBLEM

Formation water often contains salts, bacteria, organic chemicals and other contaminants.1?Although some companies will treat the water for re-use in hydraulic fracturing or agriculture, this is not always an economical option. Most of the formation water is disposed of by injecting it into subterranean wastewater disposal wells.

The U.S. upstream industry will spend an estimated $34.7 billion on water management in 2018. A complex logistical network accounts for storing, transferring, trucking, treating and disposing of formation water, and totals 89% of water management costs.2?Over the life of an individual well, formation water costs can total $6 million, representing up to half of a well’s operating expense.3?These costs are predicted to increase.

Formation water handling and disposal continue to be important topics in the oil and gas industry, but little is being done to limit water production by addressing the issue at the source. An ideal solution to the challenges presented by the management of produced water would include reducing the amount of formation water generated without hindering hydrocarbon production. Current technologies, such as gels or swelling chemicals, can limit formation water production, but they restrict the flow of hydrocarbons.

THE SOLUTION

Researchers at Hexion were determined to develop a solution that would reduce formation water production, while maintaining oil and gas output. Technologies, such as OilPlus proppants, have demonstrated the ability to improve production in liquid-rich reservoirs by altering the surface chemistry of the proppant.5?The lessons learned from tailoring surface chemistry were leveraged to develop the patented AquaBond formation water reduction technology.

Fig. 2. Schematic of the AquaBond technology test apparatus.

This technology has proven to reduce produced water by as much as 50%, while improving oil and gas production compared to offset wells. Since the technology is bonded to proppant, the water-reducing property stays effective for the life of the well. Utilization of the technology can increase well profitability by reducing costs associated with wastewater management, ultimately leading to a lower cost per barrel of oil equivalent (boe).

HOW IT WORKS

The AquaBond formation water reduction technology alters the relative permeability of the proppant pack to admit hydrocarbons and reduce the admission of water. The pack acts as a semi-permeable membrane to selectively allow hydrocarbons to penetrate while excluding formation water.

Modifications to the functional groups of the proppant coating result in a tailored critical surface tension that is hydrophobic and oleophilic at the same time,?Fig. 1.?This creates a driving force that tends to admit oil into the proppant pack, while reducing the flow of water through the proppant pack.

AVOIDING A “WATER BLOCK”

Since the proppant pack is a porous medium, water can flow through the pack, if it is the only fluid in contact with the pack. This prevents a water block scenario from occurring in the proppant pack or at the formation surface/proppant pack interface. This was proven by modifying the previously described test. The starting water/oil ratio was adjusted to 5:1, so only water was in contact with the proppant core at the start of the test.?Figure 4?is a picture of the AquaBond technology proppant core at the start of the modified test. The control test with traditional resin-coated proppant continued to flow water, even after oil contacted the proppant core, leaving a majority of the oil in the reservoir cell.

Fig. 4. AquaBond technology proppant core is only in contact with water at the beginning of the 5:1 water/oil ratio test. This core flows water until the oil (dyed blue) makes contact.

CASE STUDY

To prove that this technology is effective in the field, a trial was conducted in the Granite Wash formation of Roberts and Hemphill counties in the Texas Panhandle. A single operator utilized AquaBond technology on two horizontal wells, which were compared to 11 nearby offset horizontal wells. The wells utilizing this technology consisted of a 23% tail-in of 40/70 formation water-reducing proppant and a balance of uncoated frac sand. Three of the offset wells used a 23% tail-in of 40/70 traditional resin-coated proppant, and eight wells used 100% uncoated frac sand.

Completion details were similar for all wells in the data set: true vertical depth (TVD) was approximately 11,000 ft, with a lateral length of 4,000 ft, and bottomhole static temperature was 180°F. All wells used approximately 2.3 million lb of total proppant.

Over the entire period, the traditional resin-coated proppant offsets and the uncoated frac sand wells performed about the same. The AquaBond technology wells had a 30% lower water cut, compared to the offsets. Average cumulative water production was reduced 43%, and no impact to total fluid production was observed.

HOW TO USE THE TECHNOLOGY

The formation water-reduction technology requires no special equipment for use in hydraulic fracturing. The formation water reduction plan is outlined below:

Post-job analysis can be used to optimize future completion designs, based on production data. Lead-ins, tail-ins or total proppant designs can be utilized, depending on formation characteristics, desired water reduction and/or severity of water issue. The technology also can be used as a remedial treatment for refracturing existing high-water-cut wells and has been used successfully in this application. Due to its flexibility and ease of use, the technology should be considered as a responsible part of any frac design incorporating an effective water management strategy.

CONCLUSION

Laboratory tests demonstrate that AquaBond technology will preferentially flow oil over water. These tests have been repeated multiple times, using different crude oil and produced water samples from various regions throughout North America. Testing also has been modified by varying water/oil ratios. When performing laboratory tests with only water in contact with the core incorporating AquaBond technology (or consolidated proppant pack), it was demonstrated that a water block will not occur.

This technology has been utilized in the Permian basin, Bakken shale, Granite Wash formation, and the Haynesville shale. It is applied using the same method as traditional proppants and requires no special equipment. The case study in the Granite Wash demonstrates how this technology can reduce the production of formation water without impacting total fluid production.?

備注：數(shù)據(jù)僅供參考，不作為投資依據(jù)。