裂縫性儲(chǔ)層充氮?dú)馇菲胶忏@井流體參數(shù)設(shè)計(jì)圖版與實(shí)例

楊 虎

( 中國(guó)石油新疆油田公司工程技術(shù)研究院 )

裂縫性儲(chǔ)層充氮?dú)馇菲胶忏@井流體參數(shù)設(shè)計(jì)圖版與實(shí)例

楊 虎

( 中國(guó)石油新疆油田公司工程技術(shù)研究院 )

充氣鉆井是發(fā)現(xiàn)和保護(hù)油氣藏、防止裂縫性儲(chǔ)層井漏、提高機(jī)械鉆速的重要技術(shù)手段.通過實(shí)驗(yàn)資料和計(jì)算論證,闡述了井筒環(huán)空與鉆柱內(nèi)兩相流體呈現(xiàn)出的流型特征.同時(shí),建立了充氣鉆井井筒流動(dòng)模型和數(shù)值解法,計(jì)算并繪制出常用井身結(jié)構(gòu)的氣液流體參數(shù)設(shè)計(jì)圖版.準(zhǔn)噶爾盆地百泉1井充氮?dú)忏@井試驗(yàn)采用了新建的井筒氣液兩相流體注入?yún)?shù)設(shè)計(jì)圖版.根據(jù)二疊系裂縫性儲(chǔ)層漏失壓力和坍塌壓力,確定鉆井流體安全密度窗口,設(shè)計(jì)該井氮?dú)庾⑷雲(yún)?shù)和欠平衡專用設(shè)備需求量.該井的成功實(shí)踐充分證實(shí)充氮?dú)忏@井具有地層適應(yīng)性強(qiáng)、壓力控制范圍大、可有效避免裂縫性儲(chǔ)層井漏,利于勘探發(fā)現(xiàn).同時(shí),新建的設(shè)計(jì)圖版完全滿足常規(guī)井眼條件下充氮?dú)忏@井的工程設(shè)計(jì)和現(xiàn)場(chǎng)作業(yè).

裂縫性儲(chǔ)層;充氣液;流體參數(shù);設(shè)計(jì)圖版;應(yīng)用實(shí)例

充氣鉆井是指鉆井時(shí)將一定量的可壓縮氣體通過充氣設(shè)備注入到鉆井液中作為循環(huán)介質(zhì)的鉆井技術(shù),是發(fā)現(xiàn)和保護(hù)油氣藏、防止裂縫性儲(chǔ)層井漏、提高機(jī)械鉆速的重要技術(shù)手段,常用注入氣體主要是空氣和氮?dú)?充氣液是以氣體為分散相、液體為連續(xù)相,并加入穩(wěn)定劑而成為氣液混合均勻穩(wěn)定的體系,主要適用于地層壓力系數(shù)為0.7～1.1的易漏低壓儲(chǔ)層.充氣鉆井液經(jīng)過地面的除氣設(shè)備后,氣體從鉆井液中脫離,保證鉆井泵的正常工作.充入氣體的目的是為了減小鉆井液密度,從而降低流體液柱對(duì)井底的靜壓力,通過充入氣量的改變,可隨時(shí)調(diào)整鉆井液的密度以平衡地層壓力,從而實(shí)現(xiàn)近平衡或欠平衡鉆井.

1 充氣液管流的流動(dòng)型態(tài)

不同流動(dòng)性質(zhì)的兩相流體同時(shí)在管道內(nèi)流動(dòng),將產(chǎn)生不同相交界面構(gòu)型(簡(jiǎn)稱兩相流流型),其兩相流動(dòng)特性不僅與每一相的流態(tài)有關(guān),也與兩相交界面的變化和組合有關(guān).實(shí)驗(yàn)表明[1-4],在垂直管兩相流動(dòng)條件下經(jīng)常出現(xiàn)泡狀流、彈狀流、攪拌流、環(huán)狀流、霧狀流5種流型.

井筒兩相流流型變化通常取決于兩相流體流量、流體性質(zhì)和井眼幾何參數(shù)等.對(duì)于充氣欠平衡鉆井,氣、液兩相的流量分別為10～50m3/min和0.189～1.325m3/min.Barnea[1]和Lage[3]等繪制的環(huán)空兩相流流型分布見圖1.由圖1可知,井口附近的環(huán)空氣體在施加一定井口回壓后,環(huán)空流型由環(huán)狀流或攪拌流轉(zhuǎn)變?yōu)閺棤盍?可有效避免井口附近的高速氣流對(duì)地面管線造成損壞.因此,對(duì)于多數(shù)充氣鉆井(井深1500～5500m),井口附近環(huán)空上部以彈狀流為主,攪拌流或環(huán)狀流出現(xiàn)的幾率很小,可視為彈狀流處理,而井筒環(huán)空下部主要以泡狀流為主[1-4].

綜合國(guó)外多位學(xué)者的試驗(yàn)研究[1-5],筆者認(rèn)為充氣欠平衡鉆井環(huán)空兩相流流型主要為泡狀流和彈狀流.這一點(diǎn)與Jiménez、Sunthankar等[6-7]的環(huán)空充氣鉆井液主要出現(xiàn)泡狀流和彈狀流的實(shí)驗(yàn)結(jié)果一致.若采用鉆柱注氣方式進(jìn)行欠平衡鉆水平井(井深大于1000m),則全部斜井段和水平井段在高液柱壓力作用下呈泡狀流.

圖1 環(huán)空氣液兩相流流型隨壓力變化曲線

對(duì)于向下氣液兩相管內(nèi)流,Barnea[1]和Lage[3]等在大氣壓狀態(tài)下的小尺寸實(shí)驗(yàn)中發(fā)現(xiàn)管內(nèi)兩相流只有環(huán)狀流、彈狀流和泡狀流.與環(huán)空兩相流相似,氣體折算速度較高時(shí)會(huì)出現(xiàn)環(huán)狀流.然而,充氣欠平衡鉆井氣、液兩相流體同時(shí)由井口注入,井口注入壓力通常高于6.9MPa,其高壓和高攪拌剪切力使鉆柱內(nèi)氣體分散于連續(xù)的液體之中,很難出現(xiàn)環(huán)狀流.

綜合國(guó)內(nèi)外多位學(xué)者的研究成果[4-9],筆者認(rèn)為充氣鉆井鉆柱內(nèi)兩相流流型以泡狀流和彈狀流為主.將常規(guī)充氣欠平衡鉆井管內(nèi)兩相流折算速度的計(jì)算數(shù)據(jù)標(biāo)注在Caetano[8]和Lage[4]繪制的管內(nèi)兩相流流型分布圖(圖2),圖中水平分布的3個(gè)黑色圓圈自左至右分別代表井底、井筒中部和井口處的氣、液流量組合下的流型分布情況.

2 環(huán)空氣液兩相流數(shù)學(xué)模型

筆者曾經(jīng)在文獻(xiàn)[9-11]中多次闡述了充氣鉆井井筒兩相流各種流型的流動(dòng)模型和數(shù)值解法.針對(duì)注入氣液比較高(10∶1)的充氣鉆井進(jìn)行模擬計(jì)算,井深約小于200m的環(huán)空含氣率超過50%,氣液比超過1∶1,此時(shí)才會(huì)出現(xiàn)彈狀流.通常,充氣鉆井應(yīng)用于中深井或深井,當(dāng)井深超過1800m,環(huán)空含氣率降至5%,氣液比僅為0.05∶1.因此,將整個(gè)環(huán)空充氣液視為泡狀流管流可以滿足充氣鉆井工程設(shè)計(jì)和作業(yè)的精度要求.

圖2 欠平衡鉆井鉆柱內(nèi)兩相流流型分布

2.1 假設(shè)條件

(1)環(huán)空中鉆井流體可能混合有巖屑和地層流體(天然氣、原油或地層水),模型假設(shè)環(huán)空鉆井流體為兩相流(氣體混合物和液體+巖屑混合物).假設(shè)環(huán)空混合氣體返速相同,環(huán)空注入液體和地層產(chǎn)出液體返速相同.

(2)模型中所有與位移有關(guān)的參數(shù)(包括井深、速度、壓力等)均為沿井眼的測(cè)量深度進(jìn)行計(jì)算[9],因此模型適用于水平井.

(3)井筒流體穩(wěn)定流動(dòng)時(shí),流體溫度沿井深為線性分布.

2.2 數(shù)學(xué)模型

根據(jù)機(jī)械能守恒定律,環(huán)空穩(wěn)定泡狀流的流動(dòng)總壓降由重力壓降、摩阻壓降和加速壓降組成[12]:

重力壓降為:

摩阻壓降為:

采用Beggs[13]和Brill[14]的推薦方法,加速壓降為:

式中 ρG、ρL、ρm、ρR--分別為氣體、液體、混合流體及地層巖石的密度,kg/m3;

DIC、DOT--分別為井眼或套管內(nèi)徑、鉆柱

外徑,m;

Dh--環(huán)空水力直徑,m;

Qm--混合物流量,m3/s;

HL--真實(shí)含液率,無因次;

USG--液體折算速度,m/s;

Um--混合物兩相流流速, m/s;

VDR--機(jī)械鉆速,m/s;

fF--范寧摩阻系數(shù),可由Gunn和Darling

推薦方法計(jì)算得出[2].

2.3 數(shù)值解法

考慮到鉆井流體沿環(huán)空流道為一維穩(wěn)定流動(dòng),可利用數(shù)值迭代解法進(jìn)行計(jì)算[15].由于是穩(wěn)態(tài)模型,算法中無需考慮時(shí)間因素.將環(huán)空流道進(jìn)行一維迭代網(wǎng)格劃分,根據(jù)計(jì)算精度要求設(shè)定計(jì)算步長(zhǎng)為5～20m;邊界條件為井口溫度和井口壓力;迭代計(jì)算路徑為井口→環(huán)空→井底.

3 環(huán)空氣液參數(shù)設(shè)計(jì)圖版

上述環(huán)空流體數(shù)學(xué)模型及數(shù)值解法,可通過計(jì)算機(jī)程序化進(jìn)行充氣鉆井的參數(shù)設(shè)計(jì).然而,多數(shù)設(shè)計(jì)人員和工程作業(yè)人員并沒有配備相應(yīng)計(jì)算軟件,且該類數(shù)值計(jì)算繁瑣,往往由地面流體參數(shù)迭代出井底參數(shù),需要多次試算.為了方便工程設(shè)計(jì)和現(xiàn)場(chǎng)作業(yè),針對(duì)常用的井身結(jié)構(gòu)和套管程序,計(jì)算不同氣體流量、不同井深的環(huán)空井底壓力(表1),并且繪制出相應(yīng)井身結(jié)構(gòu)的氣體流量的設(shè)計(jì)圖版(圖3).在確定了最大井底壓降和設(shè)計(jì)井深后,可由此圖版確定氣體流量并選擇注氣設(shè)備.

表1 φ216mm井眼不同氣體流量時(shí)環(huán)空井底壓力計(jì)算值

表1中計(jì)算條件如下:井深不大于5000m;鉆桿外徑為127mm;上層套管外徑為244.5mm;上層套管內(nèi)徑為222.4mm;液體流量為1.20m3/min;液體黏度為15mPa.s;液體密度為1.10g/cm3;機(jī)械鉆速為2m/h;巖屑直徑為4mm;巖屑密度為2.6g/cm3;井口回壓為100kPa.

由于井底壓力是液柱壓力和摩阻壓力的矢量和,若氣液比過高,環(huán)空摩阻將抵消氣體產(chǎn)生的液柱壓降[9-11].因此,圖版曲線密集區(qū)中氣體流量對(duì)井底壓降的貢獻(xiàn)較小.為節(jié)約成本,建議設(shè)計(jì)時(shí)不宜在曲線密集區(qū)選擇設(shè)計(jì)點(diǎn),應(yīng)在稀疏區(qū)選擇氣體流量和液體流量的最優(yōu)組合.

圖3 常規(guī)三開φ216mm井眼充氣鉆井環(huán)空氣體流量設(shè)計(jì)圖版

4 應(yīng)用實(shí)例

百泉1井位于準(zhǔn)噶爾盆地西部隆起克百斷裂帶百口泉鼻隆,完鉆井深為4998m,采用三開井身結(jié)構(gòu),主探目的層為二疊系風(fēng)城組(P1f),風(fēng)城組主要巖性為砂礫巖和白云質(zhì)粉砂巖,局部夾薄層碳質(zhì)泥巖,孔洞、裂縫非常發(fā)育[16-17].該井三開井眼采用密度為1.11～1.13g/cm3的鉀鈣基聚磺鉆井液,鉆至風(fēng)城組3070～3656m時(shí),由于儲(chǔ)層裂縫發(fā)育、承壓能力低,井漏頻發(fā)13次.雖然采取架橋材料、剛性材料及注灰等堵漏措施,仍無法避免井漏[18].為此,后續(xù)井段(3656～4998m)開展充氮?dú)忏@井試驗(yàn).

4.1 鉆井設(shè)計(jì)

從風(fēng)城組井壁穩(wěn)定性、儲(chǔ)層壓力系統(tǒng)、儲(chǔ)層潛在傷害等方面,開展百泉1井充氮?dú)忏@井的可行性論證[19-21],認(rèn)為風(fēng)城組滿足充氮?dú)忏@井的適應(yīng)性要求,包括:①利用鄰井百56井測(cè)井和試油數(shù)據(jù),評(píng)價(jià)風(fēng)城組孔隙壓力系數(shù)為0.9～1.1;②百泉1井風(fēng)城組井眼力學(xué)穩(wěn)定性較好,預(yù)測(cè)水基聚合物鉆井液浸泡下坍塌壓力系數(shù)為0.5～0.9;③反演風(fēng)城組巖石單軸抗壓強(qiáng)度為100～160MPa,黏聚力為13.0～25.5MPa,巖石可鉆性差.

利用百泉1井鉆井基本數(shù)據(jù)和建立的設(shè)計(jì)圖版,設(shè)計(jì)出三開φ215.9mm井眼內(nèi)氣體和液體的最佳流量范圍.結(jié)合地面鉆井設(shè)備(鉆井泵等)的性能,設(shè)計(jì)出充氮?dú)忏@井的相關(guān)技術(shù)參數(shù)(表2).圖4為百泉1井三開充氮?dú)忏@井地面設(shè)備配置及工藝流程.

表2 百泉1井充氮?dú)忏@井技術(shù)參數(shù)

圖4 百泉1井充氮?dú)忏@井專用設(shè)備與工藝流程

4.2 效果評(píng)價(jià)

百泉1井自井深3656m開始充氮?dú)忏@井,未發(fā)生井漏.當(dāng)鉆進(jìn)至3769m停止注氣后,仍發(fā)生漏速為33.6m3/h的井漏.充氮?dú)忏@進(jìn)至4105.43m,氣測(cè)全烴峰值為0.28%～1.08%,分離器遠(yuǎn)端火炬點(diǎn)火,焰高2～5m.由此證實(shí),充氮?dú)忏@井技術(shù)能有效保護(hù)低壓裂縫性儲(chǔ)層并防止井漏.

如表3所示,百泉1井在3656～4998m的風(fēng)城組采用間歇分段充氮?dú)忏@井.充氮?dú)忏@井總進(jìn)尺為952m,平均機(jī)械鉆速為1.36m/h;常規(guī)鉆井總進(jìn)尺為390m,平均機(jī)械鉆速為0.80m/h;同一層組內(nèi)充氮?dú)忏@井的機(jī)械鉆速較常規(guī)鉆井提高了8.6%～48.3%,提速效果明顯.然而,百泉1井的試驗(yàn)表明,針對(duì)巖石強(qiáng)度及可鉆性不同的地層,充氮?dú)忏@井提速的效果存在差異.利用百泉1井測(cè)井資料反演了巖石強(qiáng)度參數(shù)和可鉆性極值(表4),可見與風(fēng)三段相比,風(fēng)一段和風(fēng)二段的抗壓強(qiáng)度和內(nèi)摩擦角更高,研磨性更大,可鉆性極值高出0.9～2.2.風(fēng)二段充氮?dú)忏@井的提速效果不明顯進(jìn)一步說明對(duì)于超硬研磨性地層(單軸抗壓強(qiáng)度大于150MPa),小幅度降低井底巖石圍壓(百泉1井充氮?dú)夂缶讐航禐?.5～7.2MPa)對(duì)破巖效率改變不大[22-23].而對(duì)于中硬砂礫巖且裂縫發(fā)育的風(fēng)三段,充氮?dú)忏@井的提速比例近50%.

表3 百泉1井充氮?dú)忏@井提速效果統(tǒng)計(jì)

表4 百泉1井風(fēng)城組巖石力學(xué)參數(shù)和可鉆性極值

5 結(jié)論

(1)研究認(rèn)為充氮?dú)忏@井環(huán)空頂部(井深小于200m)以彈狀流為主,大部分環(huán)空為泡狀流(包括分散泡狀流).通常,充氮?dú)忏@井應(yīng)用于中深井或深井,將整個(gè)環(huán)空充氣液視為泡狀流管流可以滿足充氮?dú)忏@井工程設(shè)計(jì)和作業(yè)的精度要求.

(2)為方便工程設(shè)計(jì)和現(xiàn)場(chǎng)作業(yè),針對(duì)常用的井身結(jié)構(gòu)和套管程序,計(jì)算并繪制出氣液注入流量的設(shè)計(jì)圖版.設(shè)計(jì)人員可由設(shè)計(jì)井底壓力和充氣鉆井井段,依據(jù)圖版確定氣體流量和注氣設(shè)備.現(xiàn)場(chǎng)技術(shù)人員也可由地面氣體流量和液體流量等參數(shù),依據(jù)設(shè)計(jì)圖版反算井底壓力,及時(shí)調(diào)整作業(yè)參數(shù).

(3)百泉1井充氮?dú)忏@井解決了裂縫性低壓儲(chǔ)層的惡性井漏難題,保護(hù)和發(fā)現(xiàn)風(fēng)城組油氣同層2層、油水同層3層,機(jī)械鉆速提高8.6%～48.3%.對(duì)于單軸抗壓強(qiáng)度大于150MPa的超硬高研磨深部地層,建議采用氣體或泡沫鉆井技術(shù)來提高機(jī)械鉆速.

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Hydraulic parameter design chart of aerated nitrogen underbalanced drilling and application in fractured reservoirs

Yang Hu
( Research Institute of Engineering Technology, PetroChina Xinjiang Oilfield Company )

Aerated nitrogen drilling is an important technical method for discovering and protecting oil and gas reservoirs, controlling mud loss in fractured reservoirs, and improving ROP. Using experimental data and calculation demonstration, the fluid patterns of gas-liquid two-phase flow in wellbore annulus and drill string while drilling were analyzed, the wellbore fluid flowing model and numerical solution during aerated drilling were established, and the gas-liquid flowing parameter design chart for conventional wellbore structures was developed and used the aerated nitrogen drilling test in Well Baiquan 1 in the Junggar Basin. In the field test, the safe density window of the drilling fluid was selected,and nitrogen injection parameters and underbalanced drilling equipment were designed according to the leakage and collapse pressures of the Permian fractured reservoirs. The successful application of this method in Well Baiquan-1 has fully proved that the aerated nitrogen drilling technology has wide formation adaptability, larger pressure control range, and effective reduction of lost circulation in fractured reservoirs, thus it is beneficial to reservoir exploration and discovery. Moreover, the new design chart can completely satisfy the requirements for engineering design and field operation in aerated nitrogen drilling in conventional wellbores.

fractured reservoir, aerated drilling fluid, flow parameter, design chart, application case

TE22

A

10.3969/j.issn.1672-7703.2017.06.014

中國(guó)石油科技重大專項(xiàng)"新疆油田、吐哈油田勘探開發(fā)增產(chǎn)關(guān)鍵技術(shù)"(2012E-31).

楊虎(1974-),男,新疆克拉瑪依人,博士,2007年畢業(yè)于中國(guó)石油大學(xué)(北京),高級(jí)工程師,現(xiàn)主要從事地質(zhì)力學(xué)、復(fù)雜深井、特殊工藝井的理論與技術(shù)研發(fā)工作.地址:新疆克拉瑪依市勝利路87號(hào)中國(guó)石油新疆油田公司工程技術(shù)研究院方案規(guī)劃所,郵政編碼:834000.E-mail: yanghu@petrochina.com.cn

2016-11-16;修改日期:2017-08-18