張汝生李克智黃志文
1.中國石化石油勘探開發(fā)研究院;2.中國石化海相油氣藏開發(fā)重點(diǎn)實(shí)驗(yàn)室;3.中國石化華北分公司
定北區(qū)塊致密氣儲(chǔ)層水平井壓裂參數(shù)優(yōu)化
張汝生1,2李克智3黃志文1,2
1.中國石化石油勘探開發(fā)研究院;2.中國石化海相油氣藏開發(fā)重點(diǎn)實(shí)驗(yàn)室;3.中國石化華北分公司
水平井多級(jí)分段壓裂是鄂爾多斯北部定北氣田致密氣藏開發(fā)的有效手段。由于儲(chǔ)層較深、物性較差,在定北區(qū)塊盒1氣層的前期壓裂施工過程中不斷出現(xiàn)砂堵和超壓的現(xiàn)象,施工成功率低。為了探索前期加砂困難的原因,優(yōu)化壓裂設(shè)計(jì),開展了支撐劑導(dǎo)流能力評(píng)價(jià)實(shí)驗(yàn)、支撐劑在裂縫中通過性物理實(shí)驗(yàn)和攜砂液運(yùn)移規(guī)律數(shù)值模擬等研究。實(shí)驗(yàn)結(jié)果表明,近井多裂縫及動(dòng)態(tài)縫寬與支撐劑粒徑不匹配等因素是導(dǎo)致施工加砂困難的主要原因。對(duì)定北盒1儲(chǔ)層支撐劑體系、施工排量和砂比進(jìn)行了優(yōu)化,現(xiàn)場(chǎng)應(yīng)用6口井45段,施工成功率達(dá)到97.8%,解決了定北區(qū)塊盒1儲(chǔ)層水平井壓裂加砂困難的問題,提高了壓裂效果,為相關(guān)致密氣儲(chǔ)層水平井的壓裂工藝提供技術(shù)參考。
鄂爾多斯盆地;致密氣藏;水平井;壓裂;參數(shù)優(yōu)化
水平井壓裂技術(shù)已經(jīng)成為低滲、特低滲油氣田勘探和開發(fā)的主要手段[1]。水力壓裂可以在儲(chǔ)層中形成支撐劑充填裂縫,為油氣從儲(chǔ)層流入井筒提供一條滿足油氣產(chǎn)出的高導(dǎo)流的裂縫通道,以保證水平井壓裂工藝成果。目前,國內(nèi)外學(xué)者和研究機(jī)構(gòu)針對(duì)致密儲(chǔ)層水平井分段壓裂的優(yōu)化設(shè)計(jì)開展了大量工作,形成了通過應(yīng)力干擾確定水平井壓裂段間距的優(yōu)化方法,水平井壓裂與注采井網(wǎng)相適配的施工參數(shù)優(yōu)化方法,基于地質(zhì)工程一體化的水平井壓后產(chǎn)能預(yù)測(cè)方法[2-11]。在保障致密儲(chǔ)層水力壓裂工藝效果方面,尤其是對(duì)施工壓力持續(xù)上升甚至砂堵無法完成施工的情況,李國鋒、楊安林等人通過提高液體攜砂性能、降低壓儲(chǔ)層濾失對(duì)工藝進(jìn)行了相關(guān)優(yōu)化[12-13]。目前致密儲(chǔ)層水平井壓裂優(yōu)化方法中,對(duì)于裂縫中支撐劑鋪置對(duì)產(chǎn)能的影響研究,有金智榮等人應(yīng)用的組合加砂技術(shù),在薄互層大型壓裂中有效運(yùn)用,提高了壓裂效果[14];有溫慶志等人采用平板裂縫模擬系統(tǒng),模擬了支撐劑在裂縫中的動(dòng)態(tài)沉降和砂堤形成的可視化過程,但對(duì)粒徑優(yōu)化和支撐劑在裂縫中的通過性研究尚未開展[15]。
在定北區(qū)塊盒1儲(chǔ)層特征分析和前期壓裂施工難點(diǎn)分析的基礎(chǔ)上,考慮不同支撐劑粒徑和鋪砂濃度的裂縫導(dǎo)流能力,建立了支撐劑通過性的物理模擬實(shí)驗(yàn)方法,同時(shí)利用數(shù)值模擬方法分析了攜砂液在裂縫中的流動(dòng)規(guī)律,從而優(yōu)化了定北盒1儲(chǔ)層水平井壓裂用支撐劑體系的設(shè)計(jì),開展了現(xiàn)場(chǎng)應(yīng)用。
Reservoir characteristics of Dingbei Block and difficulty analysis of early fracture
位于鄂爾多斯盆地北部的定北區(qū)塊盒1儲(chǔ)層埋藏深、溫度高、物性差,屬特低孔、特低滲油氣藏,產(chǎn)能較低,只有通過壓裂改造才能獲得工業(yè)氣流。該區(qū)塊與大牛地以及蘇里格氣田成藏條件相似,上古生界發(fā)育巖性圈閉氣藏,自上而下發(fā)育盒3、盒2、盒1、山2、山1、太2和太1段7套氣層??v向疊合,橫向連片都較好,儲(chǔ)層結(jié)構(gòu)復(fù)雜:泥巖互層現(xiàn)象明顯。定北盒1儲(chǔ)層埋藏深度3 650~3 820 m、地層溫度124~135℃、儲(chǔ)層平均孔隙度為6.76%、平均滲透率0.41 mD、儲(chǔ)層非均質(zhì)性強(qiáng),局部儲(chǔ)層鉆井漏失、儲(chǔ)層地應(yīng)力高,儲(chǔ)層巖石彈性模量為3.9×104MPa,泊松比為0.19。
定北盒1儲(chǔ)層前期直井壓裂在中高砂比階段易形成砂堵,施工成功率低(82.1%)、平均砂比低(17%),在定北區(qū)塊盒1氣層開展了首口水平井分段壓裂試驗(yàn),該井采用裸眼預(yù)制管柱完井,多級(jí)管外封隔器分段壓裂,共施工9段,施工成功率僅為77.8%。前期壓裂施工出現(xiàn)加砂困難、施工壓力高、砂堵井多等技術(shù)問題。
對(duì)定北區(qū)塊盒1儲(chǔ)層某口井的小型壓裂測(cè)試數(shù)據(jù)進(jìn)行G函數(shù)分析(關(guān)于時(shí)間t的函數(shù),t的單位為s),如圖1所示。分析結(jié)果表明,該儲(chǔ)層地層閉合應(yīng)力在64~67 MPa之間,儲(chǔ)層巖石彈性模量高,巖石呈現(xiàn)塑性特征;壓裂液造縫效率低,瓜膠壓裂液造縫效率為38%;造縫階段的施工凈壓力小于4 MPa;而G函數(shù)壓力導(dǎo)數(shù)曲線呈現(xiàn)出的“駝峰狀下降”則表明壓后近井存在多裂縫。因此可以判斷,縫內(nèi)凈壓力小、近井裂縫復(fù)雜、動(dòng)態(tài)縫寬較窄等原因是導(dǎo)致壓裂施工加砂困難的主要原因。
圖1 定北區(qū)塊盒1儲(chǔ)層壓裂測(cè)試曲線Fig.1 Fracturing test curve of He 1 reservoir in Dingbei Block
通過對(duì)定北前期壓裂技術(shù)難點(diǎn)的分析,明確了需要從施工參數(shù)、支撐劑選擇和泵注程序共3個(gè)方面開展優(yōu)化研究工作。在保證導(dǎo)流能力的前提下,優(yōu)選較小粒徑的支撐劑,保證支撐劑在裂縫中的順利運(yùn)移和鋪置,同時(shí)要控制平均砂比范圍和最高砂比值;通過優(yōu)化排量、砂比等施工參數(shù),提高縫內(nèi)凈壓力,增加動(dòng)態(tài)縫寬,進(jìn)而提高壓裂施工成功率。
Flow conductivity evaluation and proppant optimization
針對(duì)定北區(qū)塊前期壓裂所應(yīng)用的支撐劑40/70目、30/50目和20/40目陶粒的單粒徑和復(fù)合粒徑,進(jìn)行了短期導(dǎo)流能力和長期導(dǎo)流實(shí)驗(yàn)評(píng)價(jià)。短期導(dǎo)流能力的測(cè)試閉合壓力分別是52.2 MPa、69 MPa和89.1 MPa,鋪砂濃度分別是10 kg/m2和5 kg/m2,具體實(shí)驗(yàn)結(jié)果見表1。長期導(dǎo)流能力的測(cè)試閉合壓力是69 MPa,鋪砂濃度是5 kg/m2,測(cè)試結(jié)果如圖2所示。
由表1可知,前期壓裂所應(yīng)用的30/50目陶粒在69 MPa下平均導(dǎo)流能力達(dá)到51.9 D·cm,40/70目的支撐劑導(dǎo)流能力為37.32 D·cm,是30/50目導(dǎo)流能力的72%。由圖2可知,現(xiàn)場(chǎng)用40/70目陶粒長期導(dǎo)流能力是30/50目陶粒的66.5%,長期導(dǎo)流能力達(dá)到22.99 D·cm。
針對(duì)30/50目和40/70目的復(fù)合粒徑支撐劑開展了導(dǎo)流能力測(cè)試,測(cè)試閉合壓力分別是52.2 MPa、69 MPa和89.1 MPa,鋪砂濃度是10 kg/m2,測(cè)試結(jié)果見表2。結(jié)果表明,定北盒1儲(chǔ)層現(xiàn)場(chǎng)采用較小粒徑陶粒支撐劑的導(dǎo)流能力為54.48~87.04 D·cm,完全滿足氣井生產(chǎn)需要,可以采用30/50目陶?;?0/50目和40/70目復(fù)合粒徑陶粒。
表1 不同粒徑支撐劑導(dǎo)流能力測(cè)試結(jié)果Table 1 Flow conductivity test results of the proppants with different grain sizes
圖2 不同粒徑支撐劑長期導(dǎo)流能力測(cè)試結(jié)果Fig.2 Long-term flow conductivity test results of the proppants with different grain sizes
表2 不同復(fù)合粒徑支撐劑導(dǎo)流能力測(cè)試結(jié)果Table 2 Flow conductivity test results of the proppants with different composite grain sizes
Sand carrier flow simulation and sand ratio optimization
為了分析盒1儲(chǔ)層壓裂施工過程中出現(xiàn)的超壓和砂堵現(xiàn)象,基于FLUENT流體計(jì)算軟件建立支撐劑固相顆粒體系和壓裂液液相體系的雙流體模型,具體模型參數(shù)見表3。同時(shí)運(yùn)用大型可視化實(shí)驗(yàn)裝置開展了物理模擬實(shí)驗(yàn)對(duì)模型進(jìn)行驗(yàn)證,該模擬方法中裂縫剖面支撐劑鋪置體積分?jǐn)?shù)的變化即可反應(yīng)出實(shí)際施工過程中裂縫中支撐劑的砂濃度變化。實(shí)際模擬結(jié)果表明,當(dāng)裂縫內(nèi)攜砂液的運(yùn)移及沉降受液體黏度、攜砂液的砂比和施工排量影響明顯,當(dāng)動(dòng)態(tài)裂縫寬度為5 mm時(shí),砂比大于30%時(shí)支撐劑在裂縫內(nèi)沉降速度快,從而造成支撐劑在裂縫中局部的體積分?jǐn)?shù)增加(如圖3所示),即裂縫中的砂濃度過高即出現(xiàn)縫內(nèi)砂堵。
表3 數(shù)值模擬參數(shù)Table 3 Numerical simulation parameters
圖3 裂縫中支撐劑鋪置體積分?jǐn)?shù)Fig.3 Dynamic change of placement volume fraction of the proppants in the fracture
Proppant passing ability evaluation in the fracture and particle size optimization
前期定北區(qū)塊盒1儲(chǔ)層壓裂支撐劑主要采用20/40目陶粒為主,加砂后期出現(xiàn)超壓或砂堵機(jī)率大的情況后,利用自主研制的復(fù)雜裂縫導(dǎo)流能力測(cè)試系統(tǒng)進(jìn)行了復(fù)雜裂縫中支撐劑通過性實(shí)驗(yàn)。該實(shí)驗(yàn)研究在預(yù)制復(fù)雜裂縫內(nèi),不同加載邊界、注入排量、縫寬和液體黏度等條件下,研究流體注入壓力變化和支撐劑的展布情況,并以此來評(píng)價(jià)支撐劑的通過性。實(shí)驗(yàn)分別在6 mm和3 mm的大巖心裂縫中對(duì)20/40目和40/70目的支撐劑通過性進(jìn)行評(píng)價(jià),結(jié)果如圖4和圖5所示。施工壓力超壓的原因在于20/40目支撐劑在流動(dòng)通道上砂粒堆積,因而造成超壓。增加壓裂液黏度,降低支撐劑粒徑,可有效提高支撐劑在裂縫中的通過性。
圖4 清水中不同粒徑支撐劑通過性泵注壓力曲線Fig.4 Pumping pressure curve of passing ability of proppants with different grain sizes in the clear water
圖5 膠液中不同粒徑支撐劑通過性泵注壓力曲線Fig.5 Pumping pressure curve of passing ability of proppants with different grain sizes in the liquid cement
Design optimization and field application
為了提高壓裂液的攜砂性,降低壓裂作業(yè)對(duì)儲(chǔ)層的傷害,在優(yōu)化支撐劑粒徑的同時(shí),對(duì)壓裂液體系也進(jìn)行了優(yōu)化,優(yōu)化后的壓裂液基液黏度為72 mPa·s,交聯(lián)時(shí)間100~160 s可控,殘?jiān)?14 mg/L。
通過壓裂模擬分析,施工排量對(duì)裂縫高度、寬度具有明顯作用,為保障攜砂液階段支撐劑安全泵入,盒1層合理施工排量范圍在5.0~6.0 m3/min。以造長縫、提高裂縫導(dǎo)流能力為優(yōu)化目標(biāo),根據(jù)定北盒1儲(chǔ)層基礎(chǔ)數(shù)據(jù),建立壓裂模型,對(duì)5%—10%—15%—20%—25%—30%—35%—40%砂比進(jìn)行模擬。在注入總液量不變的情況下,隨著砂比提高,動(dòng)態(tài)縫長變化不大,支撐縫長先增加后減??;隨著平均砂比增加,裂縫導(dǎo)流能力顯著增大,在導(dǎo)流能力滿足要求的基礎(chǔ)上,結(jié)合模擬計(jì)算結(jié)果,優(yōu)化平均砂比為20%?,F(xiàn)場(chǎng)應(yīng)用中,對(duì)定北盒1儲(chǔ)層6口水平井開展了壓裂設(shè)計(jì)優(yōu)化,排量為5.2~5.8 m3/min,前置液比例37%~43%,平均砂比達(dá)到19%~21%,水平井壓裂施工成功率達(dá)到97.8%。
Conclusions
(1)在壓裂液性能提升的基礎(chǔ)上,縫內(nèi)凈壓力小、動(dòng)態(tài)縫寬較窄、支撐劑在裂縫口通過性差、在裂縫內(nèi)沉降速度快是定北區(qū)塊盒1儲(chǔ)層壓裂施工砂堵和超壓的主要原因。
(2)建立的裂縫內(nèi)支撐劑通過性評(píng)價(jià)實(shí)驗(yàn)結(jié)果和施工參數(shù)測(cè)試結(jié)果表明,提高壓裂液基液黏度,優(yōu)化排量范圍5~6 m3/min,,前置液比例范圍35%~45%,支撐劑粒徑為40/70目,施工最高砂比不超過35%,平均砂比20%,優(yōu)化后6口水平井壓裂施工順利,施工成功率達(dá)到97.8%。
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(修改稿收到日期 2017-01-17)
〔編輯 李春燕〕
Horizontal well fracturing parameter optimization for the tight gas reservoir in Dingbei Block
ZHANG Rusheng1,2,LI Kezhi3,HUANG Zhiwen1,2
1.Research Institute of Petroleum Exploration Development,SINOPEC,Beijing100083,China;
2.Key Laboratory of Marine Oil and Gas Reservoir Development,SINOPEC,Beijing100083,China;
3.North China Branch of SINOPEC,Zhengzhou450006,Henan,China
Horizontal well multi-stage segmental fracturing is the effective method for the development of the tight gas reservoir in Dingbei gas field in the north of Ordos.Due to deep burial of the reservoir and poor physical property,sand plug or overpressure phenomena continuously appear in the process of earlier fracturing operation in He 1 gas reservoir in Dingbei Block with low operation success ratio.In order to clarify the reason for the difficulties to add sand in the earlier stage and optimize the fracturing design,the researches on proppant flow conductivity evaluation experiment,physical experiment of the proppant passing ability in the fracture and numerical simulation of sand carrier migration rules and etc.have been developed.The experimental results show that the factors of many fractures in the reservoir,dynamic fracture width and mismatch of the proppant sizes are the main reasons for the difficulties of adding sand in the fracturing operation.Therefore,the proppant system,operational discharge capacity and sand ratio of He 1 reservoir in Dingbei block are optimized,and the field application of 6 wells and 45 well sections show that the operational success ratio reaches 97.8%.Thus,the difficult problem of adding sand in horizontal well fracturing in He 1 reservoir of Dingbei Block has been solved and the fracturing effect has been improved,which provide the technical reference to horizontal well fracturing technology for the relative tight gas reservoir.
Ordos Basin;tight gas reservoir;horizontal well;fracturing;design parameter optimization
張汝生,李克智,黃志文.定北區(qū)塊致密氣儲(chǔ)層水平井壓裂參數(shù)優(yōu)化[J].石油鉆采工藝,2017,39(2):249-253.
TE21
:A
1000-7393(2017)02-0249-05
10.13639/j.odpt.2017.02.022
: ZHANG Rusheng,LI Kezhi,HUANG Zhiwen.Horizontal well fracturing parameter optimization for the tight gas reservoir in Dingbei Block[J].Oil Drilling &Production Technology,2017,39(2): 249-253.
張汝生(1970-),1995年畢業(yè)于四川大學(xué)應(yīng)用化學(xué)專業(yè),獲碩士學(xué)位,現(xiàn)從事采油工程技術(shù)研究工作,高級(jí)工程師。通訊地址:(100083)北京市海淀區(qū)學(xué)院路31號(hào)中石化勘探院采油所。E-mail:zhangrsh.syky@sinopec.com