張 雄, 耿宇迪, 焦克波, 侯 帆, 羅攀登
(中國(guó)石化西北油田分公司工程技術(shù)研究院,新疆烏魯木齊 830011)
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塔河油田碳酸鹽巖油藏水平井暫堵分段酸壓技術(shù)
張雄, 耿宇迪, 焦克波, 侯帆, 羅攀登
(中國(guó)石化西北油田分公司工程技術(shù)研究院,新疆烏魯木齊 830011)
針對(duì)塔河油田裸眼水平井“封隔器+滑套”分段酸壓費(fèi)用高、作業(yè)周期長(zhǎng)、分段工藝復(fù)雜、分段工具可靠性低、工具留井后處理難度大等問(wèn)題,通過(guò)“纖維+顆?!睆?fù)合暫堵代替“封隔器+滑套”分段,完成單段酸壓后注入“纖維+顆粒”復(fù)合段塞,在裂縫端口架橋形成具有一定封堵強(qiáng)度的暫堵層,迫使裂縫從下一段起裂,實(shí)現(xiàn)無(wú)工具分段酸壓。通過(guò)室內(nèi)試驗(yàn)優(yōu)選出耐溫120 ℃的暫堵纖維,120 ℃下其在清水及鹽酸中2 h的溶解率小于40%,可保證持續(xù)暫堵效果,最終溶解率100%,不傷害儲(chǔ)層;優(yōu)化了纖維和顆粒的尺寸及質(zhì)量分?jǐn)?shù),質(zhì)量分?jǐn)?shù)為1.0%~2.0%、長(zhǎng)度為6~8 mm的纖維+質(zhì)量分?jǐn)?shù)為0.5%、直徑為1.0 mm的顆粒其暫堵壓力大于9 MPa。該技術(shù)在塔河油田應(yīng)用8井次,施工暫堵壓力6.6~9.0 MPa,單井改造后產(chǎn)能大幅度提高,施工費(fèi)用降低,累計(jì)增油5.6×104t。研究結(jié)果表明,水平井暫堵分段酸壓技術(shù)無(wú)需分段工具,解決了塔河油田碳酸鹽巖水平井酸壓工具下入和后期處理困難等問(wèn)題。
碳酸鹽巖油藏;水平井;暫堵;分段酸壓;塔河油田
塔河油田縫洞型碳酸鹽巖儲(chǔ)層埋藏深、溫度高、非均質(zhì)性強(qiáng),自然投產(chǎn)率很低,酸壓已成為儲(chǔ)層改造的重要方式[1-7]。該油田碳酸鹽巖油藏水平井儲(chǔ)層改造主要應(yīng)用“封隔器+滑套”分段酸壓技術(shù)[8-9],存在費(fèi)用高、作業(yè)周期長(zhǎng)、分段工藝復(fù)雜、對(duì)分段工具要求高、分段工具可靠性低、工具留井后處理難度大等缺點(diǎn)[10-11]。
為此,塔河油田提出了用“可降解聚丙烯腈纖維+聚合物顆粒”(以下簡(jiǎn)稱“纖維+顆?!?暫堵代替“封隔器+滑套”分段的技術(shù)思路,通過(guò)室內(nèi)試驗(yàn)優(yōu)選纖維種類及顆粒直徑,并評(píng)價(jià)不同纖維及顆粒質(zhì)量分?jǐn)?shù)對(duì)不同縫寬的暫堵壓力[12-15],確定了暫堵縫寬、纖維及顆粒質(zhì)量分?jǐn)?shù)等參數(shù)值,再應(yīng)用相關(guān)軟件模擬得到所需縫寬下的排量作為暫堵段塞注入排量,并根據(jù)儲(chǔ)集體與井筒距離確定每一段酸壓壓裂液及酸液的用量[16-17],形成碳酸鹽巖油藏水平井暫堵分段酸壓技術(shù)。8井次的現(xiàn)場(chǎng)應(yīng)用表明,該技術(shù)可實(shí)現(xiàn)水平井無(wú)工具分段酸壓,并能大幅度節(jié)省酸壓費(fèi)用、提高碳酸鹽巖儲(chǔ)集體溝通率。
在應(yīng)用“封隔器+滑套”進(jìn)行分段酸壓時(shí),封隔器及滑套下入過(guò)程中常因遇阻而下入困難,且施工過(guò)程中會(huì)存在封隔器無(wú)法坐封或滑套無(wú)法正常打開等問(wèn)題,導(dǎo)致分段酸壓不能順利進(jìn)行甚至失敗,而用“纖維+顆粒”代替“封隔器+滑套”的暫堵分段酸壓技術(shù),可完全避免上述問(wèn)題,且施工結(jié)束后可降解聚丙烯腈纖維和聚合物顆粒會(huì)自動(dòng)溶解,不傷害儲(chǔ)層。
該技術(shù)的基本原理為:在第一段酸壓完成后,注入攜帶“纖維+顆?!钡膲毫岩憾稳稳哼M(jìn)入第一段酸壓形成的裂縫端口時(shí),纖維及顆粒不斷架橋堆積并壓實(shí),形成具有一定暫堵壓力的阻擋層,迫使液體轉(zhuǎn)向進(jìn)入第二段儲(chǔ)層;然后提高排量進(jìn)行第二段儲(chǔ)層的酸壓施工,從而達(dá)到分段酸壓的目的。
為了保證施工過(guò)程中連續(xù)暫堵,并達(dá)到有效分段的目的,需要優(yōu)選溶解速度緩慢并能最終完全溶解的纖維,且塔河油田產(chǎn)層起裂壓力差主要集中在5~9 MPa,需要對(duì)“纖維+顆粒”的暫堵壓力進(jìn)行評(píng)價(jià),以優(yōu)選出暫堵壓力大于9 MPa的暫堵組合。
2.1纖維優(yōu)選
2.1.1優(yōu)選原則
根據(jù)施工需求,制定了纖維優(yōu)選原則:1)耐酸,避免與酸接觸后快速溶解而失去暫堵能力;2)由于單段酸壓施工時(shí)間約為2 h,為了確保施工時(shí)的持續(xù)暫堵效果,纖維2 h溶解率需小于40%;3)最終可完全降解,避免傷害儲(chǔ)層。
2.1.2試驗(yàn)方法
取清水和20%HCl溶液各100 mL,分別加入2 g纖維,置于密閉聚四氟乙烯罐內(nèi);將滾子爐加熱至120 ℃恒溫,放入盛有樣品的聚四氟乙烯罐,在一定時(shí)間(0.5,1.0,2.0,4.0,6.0和8.0 h)后取出,過(guò)濾、烘干并稱重,然后計(jì)算纖維溶解率。
2.1.3試驗(yàn)結(jié)果
1—3號(hào)纖維的溶解試驗(yàn)結(jié)果如圖1所示。
圖1 不同纖維的溶解試驗(yàn)結(jié)果Fig.1 Results of dissolution experiments for different fibers
從圖1可以看出,120 ℃溫度下,在清水及20%鹽酸中,1號(hào)纖維的2 h溶解率大于80%,2號(hào)纖維的2 h溶解率大于60%,3號(hào)纖維的2 h溶解率為31%且最終溶解率達(dá)到100%。因此,選擇3號(hào)纖維用于暫堵分段酸壓的暫堵材料。
2.2暫堵壓力評(píng)價(jià)
在線性材料中加入合適直徑的顆粒有利于架橋,并可提高暫堵強(qiáng)度。因此,暫堵段塞采用“線性纖維+顆?!钡膹?fù)合物,根據(jù)縫寬大小確定顆粒直徑[18],當(dāng)縫寬為2.0 mm時(shí),可選用直徑為1.0 mm的顆粒與纖維進(jìn)行復(fù)合暫堵。
2.2.1試驗(yàn)方法
采用工作液動(dòng)態(tài)濾失儀(見(jiàn)圖2)進(jìn)行試驗(yàn),試驗(yàn)步驟為:1)配制好壓裂液,將不同質(zhì)量分?jǐn)?shù)的長(zhǎng)6~8 mm的纖維及直徑1.0 mm的顆?;烊雺毫岩褐?,裝入攪拌池;2)在巖心夾持器中放入具有不同寬度(寬度為2.0和3.0 mm)裂縫的巖心;3)開始驅(qū)替,監(jiān)測(cè)注入壓力,以評(píng)價(jià)其暫堵壓力。驅(qū)替后的巖心如圖3所示。
圖2 工作液動(dòng)態(tài)濾失儀Fig.2 Dynamic filter for fracturing fluid
圖3 驅(qū)替后帶裂縫巖心Fig.3 Core with cracks after displacement
2.2.2試驗(yàn)結(jié)果
縫寬分別為2.0和3.0 mm時(shí),不同質(zhì)量分?jǐn)?shù)的纖維及顆粒復(fù)合的暫堵壓力見(jiàn)表1。
表1不同質(zhì)量分?jǐn)?shù)纖維及顆粒復(fù)合的暫堵壓力
Table 1Temporary plugging pressure produced by different fibers and particle mass fraction
縫寬/mm纖維質(zhì)量分?jǐn)?shù),%顆粒質(zhì)量分?jǐn)?shù),%暫堵壓力/MPa2.01.02.00.15.90.36.80.59.10.16.30.37.00.510.03.02.00.5不能有效暫堵
由表1可知:質(zhì)量分?jǐn)?shù)為1.0%~2.0%的纖維+質(zhì)量分?jǐn)?shù)為0.5%的顆粒組合其暫堵壓力大于9 MPa,可用于塔河油田產(chǎn)層的暫堵分段酸壓,但現(xiàn)場(chǎng)施工時(shí)需降低注入排量,將裂縫縫寬控制在2.0 mm以內(nèi),以保證暫堵效果。
塔河油田碳酸鹽巖油藏水平井暫堵分段酸壓技術(shù)在該油田應(yīng)用8井次,施工暫堵壓力6.6~9.0 MPa,累計(jì)增油5.6×104t,有效提高了長(zhǎng)裸眼水平井的“甜點(diǎn)”動(dòng)用率,對(duì)于裸眼井段周圍存在多個(gè)“甜點(diǎn)”的水平井有很好的適應(yīng)性,能大幅度提高單井改造后的產(chǎn)能,并降低施工費(fèi)用。下面以塔河油田A井為例介紹該技術(shù)的現(xiàn)場(chǎng)應(yīng)用情況。
3.1A井概況
A井位于斷溶破碎帶,裸眼井段長(zhǎng)355.00 m,測(cè)井解釋和井筒應(yīng)力剖面顯示該井段存在3個(gè)對(duì)應(yīng)的“甜點(diǎn)”,有必要進(jìn)行分段酸壓提高井段動(dòng)用率,且“甜點(diǎn)”之間的應(yīng)力差為6~7 MPa,適合采用“纖維+顆?!睆?fù)合暫堵分段,因此設(shè)計(jì)2個(gè)暫堵段塞分3段進(jìn)行酸壓。
3.2壓裂液及酸液用量?jī)?yōu)化
A井3個(gè)“甜點(diǎn)”處儲(chǔ)集體與井筒的距離分別為93.00,98.00和87.00 m,采用壓裂模擬軟件FracproPT對(duì)施工壓裂液及酸液用量進(jìn)行了模擬優(yōu)化,結(jié)果見(jiàn)表2。
表2不同壓裂液及酸液用量下的裂縫長(zhǎng)度模擬結(jié)果
Table 2Simulation results for crack lengths with different fracturing fluid and acid volumes
壓裂液注入量/m3高溫膠凝酸注入量/m3動(dòng)態(tài)縫長(zhǎng)/m有效縫長(zhǎng)/m導(dǎo)流能力/(D·cm)200200118.1095.00322.0250200121.0097.00311.0250240122.90101.00362.0250280124.50103.00334.0300280126.00105.00371.0
由表2可知:當(dāng)采用250 m3壓裂液+240 m3膠凝酸時(shí),有效縫長(zhǎng)達(dá)101.00 m,可有效溝通3個(gè)“甜點(diǎn)”處的儲(chǔ)集體,因此確定每一段的用液量為250 m3壓裂液+240 m3膠凝酸。
3.3暫堵段塞設(shè)計(jì)
采用3層暫堵:1)采用轉(zhuǎn)向酸進(jìn)行預(yù)充填暫堵,轉(zhuǎn)向酸與巖石反應(yīng)形成凝膠,室內(nèi)測(cè)得轉(zhuǎn)向酸比常規(guī)稠化酸暫堵壓力高2.0 MPa(見(jiàn)圖4);2)采用質(zhì)量分?jǐn)?shù)為1.0%、長(zhǎng)度為6~8 mm的纖維與質(zhì)量分?jǐn)?shù)為0.5%、直徑為1.0 mm的顆粒形成主暫堵層(暫堵壓力試驗(yàn)結(jié)果見(jiàn)圖5);3)采用質(zhì)量分?jǐn)?shù)為1.0%的纖維在縫口壓實(shí)形成致密低滲層,不僅有一定的暫堵效果,還可防止主暫堵層中的顆粒返排。
圖4 轉(zhuǎn)向酸暫堵壓力試驗(yàn)結(jié)果Fig.4 Test results for temporary plugging pressures with diverting acid
圖5 1.0%纖維+0.5%顆粒的暫堵壓力試驗(yàn)結(jié)果Fig.5 Test results for temporary plugging pressures with 1.0% fiber and 0.5% particles
3.4暫堵排量?jī)?yōu)化
根據(jù)2.2.2的試驗(yàn)結(jié)果,施工中需要控制排量,保證裂縫寬度在2.0 mm以下。采用壓裂軟件FracproPT模擬了不同排量下的縫寬,結(jié)果如圖6所示。
圖6 不同排量下的縫寬Fig.6 The crack width under different flow rates
從圖6可以看出:當(dāng)排量為1.5 m3/min時(shí),縫寬為2.0 mm。因此,確定施工時(shí)纖維及顆粒暫堵段塞排量小于1.5 m3/min,以利于暫堵。
3.5施工概況
A井奧陶系一間房組6 980.00~7 335.00 m井段分3段進(jìn)行了酸壓施工,施工規(guī)模1 735.0 m3,加入纖維1.4 t,加入顆粒0.3 t,停泵20 min,壓力從4.0 MPa降至3.6 MPa(見(jiàn)圖7),壓裂后日產(chǎn)油108.3 t。
圖7 A井分段酸壓施工曲線Fig.7 Operation curve of sectional acid fracturing in the Well A
第一暫堵段塞注入后,在排量不變的情況下,井口壓力增加6.6 MPa;第二暫堵段塞注入后,在排量不變的情況下,井口壓力增加7.0 MPa,顯示出良好的暫堵效果。采用FracproPT進(jìn)行了G函數(shù)擬合,顯示存在3條不同的裂縫濾失及張開閉合。根據(jù)施工曲線計(jì)算,3段延伸壓力梯度分別為0.015 6,0.013 3和0.014 4 MPa/m,顯示溝通3套不同的儲(chǔ)集體。以上結(jié)果表明,A井暫堵分段酸壓施工成功。
3.6效果分析
鄰井B井、C井的振幅變化率與A井相似(見(jiàn)圖8),且地震剖面顯示均為“雜、亂、弱”的反射特征(見(jiàn)圖9)。B井、C井采用籠統(tǒng)酸壓后,初期用φ4.0 mm油嘴自噴生產(chǎn),日產(chǎn)油量分別為61.0和65.0 t。A
井進(jìn)行暫堵分段酸壓后,初期用φ4.0 mm油嘴自噴生產(chǎn),日產(chǎn)油量108.3 t,比B井和C井分別高77.5%和66.6%。
圖8 A井、B井和C井的振幅變化率Fig.8 Amplitude variation rate of the Well A,B and C
圖9 A井、B井和C井地震剖面反射特征Fig.9 Features of seismic reflection in the Well A,B and C
鄰井D井采用“封隔器+滑套”分3段酸壓,總費(fèi)用1 134萬(wàn)元,而采用“纖維+顆?!睍憾路侄嗡釅旱腁井總費(fèi)用僅592萬(wàn)元,費(fèi)用降低47.8%。A井暫堵分段酸壓效果表明,水平井暫堵分段酸壓技術(shù)具有較大的增油及經(jīng)濟(jì)優(yōu)勢(shì)。
1) 塔河油田碳酸鹽巖儲(chǔ)層壓裂起裂壓力差主要集中在5~9 MPa,試驗(yàn)顯示質(zhì)量分?jǐn)?shù)1.0%~2.0%、長(zhǎng)度為6~8 mm的纖維+質(zhì)量分?jǐn)?shù)為0.5%、直徑為1.0 mm的顆粒復(fù)合時(shí)暫堵壓力大于9 MPa,可滿足該油田暫堵分段酸壓的需求。
2) 現(xiàn)場(chǎng)應(yīng)用表明,塔河油田碳酸鹽巖油藏水平井暫堵分段酸壓技術(shù)具有顯著的增油效果及較好的經(jīng)濟(jì)效益。
3) 水平井暫堵分段酸壓技術(shù)可實(shí)現(xiàn)無(wú)井下分段工具分段酸壓,解決了塔河油田碳酸鹽巖水平井工具下入困難和后期處理難度大等問(wèn)題,并具有施工風(fēng)險(xiǎn)低、周期短等優(yōu)勢(shì)。
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[編輯令文學(xué)]
The Technology of Multi-Stage Acid Fracturing in Horizontal Well for Carbonate Reservoir by Temporary Plugging Ways in the Tahe Oilfield
ZHANG Xiong, GENG Yudi, JIAO Kebo, HOU Fan, LUO Pandeng
(EngineeringTechnologyResearchInstitute,SinopecNorthwestOilfieldCompany,Urumqi,Xinjiang, 830011,China)
During the course of multi-stage acid fracturing in open hole of horizontal wells in the Tahe Oilfield, “packer+slide sleeve” methods are featured with high operation costs, long working cycle, complicated stage fracturing, low reliability of relevant tools, difficult to handle the tools left in the hole etc. To eliminate these problems, “fiber+particles” composite temporary plugging operations have be used to replace the conventional “packer+slide sleeve” techniques. Upon completion of acid fracturing in a single interval, “fiber+particles” can be injected to generate barriers at opening of fracture, the crack initiation will be in the next section, hereby the sectional fracturing can be performed without staged tools. Through laboratory tests, the temporary plugging fibers with temperature resistance up to 120 ℃ have been deployed, its dissolution rate is below 40% in fresh water and hydrochloride acid under temperature of 120 ℃ for two hours, which keeps satisfactory temporary plugging effect and has ultimate dissolution rate of 100%, no damage to reservoir formations. Mass fractions of fibers and particle size were optimized, i.e. fiber length of 6-8 mm with mass fraction of 1.0%-2.0%, particle size of 1.0 mm with mass fraction of 0.5%, temporary plugging pressures>9 MPa. The techniques have been applied for 8 times in the Tahe Oilfield, with initial plugging pressures of 6.6-9.0 MPa, the single well production capacity has been raised significantly, and operation cost lowered, cumulative increase of oil 5.6×104t. Research results showed that temporary plugging and staged acid fracturing for horizontal wells did not require the staged tools, so it can eliminate the problem of running and pulling relevant tools that ever used in conventional operation in horizontal wells of carbonate formations in the Tahe Oilfield.
carbonate reservoir;horizontal well;temporary plugging;multi-stage acid fracturing;Tahe Oilfield
2015-10-21;改回日期:2016-04-29。
張雄(1986—),男,四川綿陽(yáng)人,2009年畢業(yè)于中國(guó)石油大學(xué)(北京)石油工程專業(yè),2012年獲中國(guó)石油大學(xué)(北京)油氣田開發(fā)工程專業(yè)碩士學(xué)位,助理研究員,主要從事儲(chǔ)層改造技術(shù)及理論研究。E-mail:zhangnoland@163.com。
國(guó)家科技重大專項(xiàng)“縫洞型碳酸鹽巖油藏高效酸壓改造技術(shù)”(編號(hào):2011ZX05014-006)資助。
doi:10.11911/syztjs.201604015
TE357.2
A
1001-0890(2016)04-0082-06
?油氣開發(fā)?