彭 松，郭 平

(“油氣藏地質(zhì)及開(kāi)發(fā)工程”國(guó)家重點(diǎn)實(shí)驗(yàn)室，西南石油大學(xué)，成都 610500)

縫洞型碳酸鹽巖凝析氣藏注水開(kāi)發(fā)物理模擬研究

彭 松，郭 平

(“油氣藏地質(zhì)及開(kāi)發(fā)工程”國(guó)家重點(diǎn)實(shí)驗(yàn)室，西南石油大學(xué)，成都 610500)

與一般砂巖凝析氣藏不同，縫洞型碳酸鹽巖凝析氣藏發(fā)育有大小不同、形狀各異的裂縫和孔洞，使其具有非均質(zhì)性強(qiáng)，流體流動(dòng)規(guī)律復(fù)雜等特征。如何提高該類氣藏的采收率是值得研究的問(wèn)題。技術(shù)成熟的注水技術(shù)具有開(kāi)發(fā)成本低、水氣流度比好、水驅(qū)波及效率高等優(yōu)點(diǎn)。以塔中86井為例，采用露頭碳酸鹽巖經(jīng)過(guò)人工技術(shù)制成全直徑縫洞型巖心，在原始地層條件下(140.6 ℃，58 MPa)完成注水開(kāi)發(fā)物理模擬實(shí)驗(yàn)。結(jié)果表明，采用注水保壓方式開(kāi)發(fā)高含凝析油的縫洞型碳酸鹽巖凝析氣藏效果較好；凝析油的采收率受縫洞連通方式、縫洞充填與否、壓力保持水平等因素的影響。

縫洞型碳酸鹽巖；凝析氣藏；高含凝析油；注水；高溫高壓；全直徑巖心；物理模擬

縫洞型碳酸鹽巖凝析氣藏是經(jīng)多期構(gòu)造運(yùn)動(dòng)與古巖溶共同作用形成的一種特殊類型的氣藏，其儲(chǔ)集空間以縫洞和裂縫—孔洞為主，具有構(gòu)造復(fù)雜、儲(chǔ)層非均質(zhì)性強(qiáng)、雙孔隙網(wǎng)絡(luò)及滲流規(guī)律復(fù)雜等特征，是當(dāng)前最復(fù)雜特殊的氣藏之一。如何提高縫洞型碳酸鹽巖凝析氣藏(尤其高含凝析油時(shí))的采收率是一個(gè)值得研究的問(wèn)題。注水作為一項(xiàng)成熟的技術(shù)，具有開(kāi)發(fā)成本低、水氣流度比好、水驅(qū)波及效率高等優(yōu)點(diǎn)，國(guó)內(nèi)外諸多學(xué)者針對(duì)注水開(kāi)發(fā)砂巖凝析氣藏[1-9]及縫洞型碳酸鹽巖油藏[10-25]做過(guò)一系列研究，但未涉及到高含凝析油的縫洞型碳酸鹽巖凝析氣藏。故本文以塔中86井(凝析油含量533 g/m3，地層溫度140.6 ℃，地層壓力58 MPa，露點(diǎn)壓力55.4 MPa，最大反凝析液量壓力31 MPa)為例設(shè)計(jì)并完成了縫洞型碳酸鹽巖凝析氣藏注水開(kāi)發(fā)物理模擬實(shí)驗(yàn)。本次研究填補(bǔ)了這方面的空白，取得的研究成果對(duì)于縫洞型碳酸鹽巖凝析氣藏的高效開(kāi)發(fā)具有一定的指導(dǎo)意義。

圖1 全直徑巖心實(shí)驗(yàn)流程

1 實(shí)驗(yàn)條件

1.1 實(shí)驗(yàn)裝置

本次實(shí)驗(yàn)在高溫高壓全直徑巖心驅(qū)替裝置上完成，實(shí)驗(yàn)流程如圖1所示。

1.2 巖心制備

由于縫洞型儲(chǔ)層的重點(diǎn)研究對(duì)象是縫和洞，對(duì)基質(zhì)要求較低，且實(shí)際取得的全直徑巖心通常不具有縫洞代表性，達(dá)不到實(shí)驗(yàn)要求，故采用野外取來(lái)的碳酸鹽巖露頭按文獻(xiàn)[26]中的方法制作縫洞型巖心。首先選擇一塊邊長(zhǎng)30 cm左右的方塊碳酸鹽巖巖心，進(jìn)行人造自然單縫，使縫面大致平行于方塊的任意一條棱且貫穿整塊巖心；然后用直徑為4 in的鉆頭鉆取全直徑巖心，長(zhǎng)度10～25 cm，保持縫盡量位于全直徑巖心中央；最后根據(jù)實(shí)際情況對(duì)全直徑巖心內(nèi)部進(jìn)行造洞。本次實(shí)驗(yàn)研究制作的巖心如圖2所示。

圖2 制成的縫洞型全直徑巖心照片長(zhǎng)度：11.117 cm；直徑：9.965 cm；孔隙度：16.83%；滲透率：48.26×10-3 μm2

1.3 流體制備

參照行業(yè)標(biāo)準(zhǔn)SY/T5543—2002，按凝析油含量533 g/m3、地層溫度140.6 ℃、露點(diǎn)壓力55.4 MPa，采用現(xiàn)場(chǎng)取得的塔中86井的油樣及氣樣配制凝析氣。地層水根據(jù)現(xiàn)場(chǎng)分析資料在室內(nèi)自行配制，總礦化度為137 900 mg/L，水型為CaCl2型。

2 實(shí)驗(yàn)內(nèi)容

基于未填砂及填砂(模擬孔洞被外來(lái)固相介質(zhì)充填)的人造縫洞巖心設(shè)計(jì)了如下9組實(shí)驗(yàn)：

(1)衰竭實(shí)驗(yàn)4組(未填砂及填砂時(shí)水平衰竭、垂直衰竭各1組)：衰竭到10 MPa(廢棄地層壓力)；

(2)水平水驅(qū)實(shí)驗(yàn)3組(保持露點(diǎn)壓力注水，未填砂和填砂各1組；保持最大反凝析液量壓力注水，巖心未填砂1組)：巖心水平夾持，壓力衰竭到露點(diǎn)壓力(最大反凝析液量壓力)時(shí)開(kāi)始注水，水突破后不出油結(jié)束注水，最后衰竭到10 MPa；

(3)垂直水驅(qū)實(shí)驗(yàn)2組(未填砂和填砂各1組)：巖心垂直夾持，上部采氣，壓力衰竭到最大反凝析液量壓力時(shí)開(kāi)始從下部注水，水突破后不出油結(jié)束注水，最后衰竭到10 MPa。

3 實(shí)驗(yàn)結(jié)果及分析

圖3及表1中的數(shù)據(jù)顯示：(1)注水開(kāi)發(fā)時(shí)的凝析油最終采出程度遠(yuǎn)高于衰竭開(kāi)發(fā)時(shí)。因?yàn)樗ソ唛_(kāi)發(fā)過(guò)程中，大量析出的凝析油滯留于孔洞底部無(wú)法采出，致使凝析油采出程度低；(2)注水開(kāi)發(fā)時(shí)，絕大部分凝析油是在注水突破前采出的；(3)雖然注水開(kāi)發(fā)時(shí)的凝析油采出程度整體較高，但是不同實(shí)驗(yàn)條件下的凝析油最終采出程度有著較大差別。下面就注水開(kāi)發(fā)縫洞型碳酸鹽巖凝析氣藏時(shí)影響凝析油采收率的因素做分析。

圖3 凝析油采出程度與地層壓力的關(guān)系曲線

實(shí)驗(yàn)填砂與否巖心夾持方式凝析油采出程度/%注水前衰竭注水保壓衰竭至10MPa水平衰竭垂直衰竭保持露點(diǎn)壓力(55.4MPa)注水保持最大反凝析液量壓力(31MPa)注水未填砂水平15.95填砂水平16.44未填砂垂直14.64填砂垂直15.55未填砂水平1.6672.679.95填砂水平1.555.2761.39未填砂水平11.0955.3357.45未填砂垂直10.8363.0563.05填砂垂直10.9950.0452.99

3.1 注水越早凝析油采收率越高

表1中數(shù)據(jù)顯示，未填砂巖心水平夾持時(shí)，保持55.4 MPa(露點(diǎn)壓力)注水時(shí)的凝析油采出程度比保持31 MPa(最大反凝析液量壓力)注水時(shí)高17.27%。從圖4中可看出，保持露點(diǎn)壓力注水過(guò)程中，無(wú)凝析油析出，注入多少水就驅(qū)替出多少體積的凝析氣，生產(chǎn)氣油比維持在原始?xì)庥捅人?，凝析油采出程度與累積注水量間呈現(xiàn)較好的線性關(guān)系。而保持最大反凝析液量壓力注水之前，反凝析出的油量達(dá)到最大值并滯留于孔洞的底部，氣相中的凝析油含量減少，當(dāng)液面抬升至水平縫面之前凝析油產(chǎn)量低，采出程度低；累積注水0.4 HCPV后，析出的凝析油被抬升至水平縫面后沿裂縫通道采出，產(chǎn)油量迅速升高，當(dāng)注水突破后油氣產(chǎn)量急劇下降直至不出油，較為復(fù)雜的油氣水三相滲流使得其凝析油采收率相對(duì)較低。上述分析表明，越早注水，地層壓力保持水平越高，凝析出的油量越少，凝析氣中的凝析油含量就越高，最終采出程度也越高。

3.2 縫洞垂直連通時(shí)凝析油采收率相對(duì)較高

圖5表明，保持最大反凝析液量壓力注水時(shí)，巖心垂直夾持(縫洞垂直連通)時(shí)的凝析油采出程度高于水平夾持(縫洞水平連通)時(shí)，這是由于縫洞水平連通時(shí)，裂縫平面將洞分割成上(0.4 HCPV)、下(0.6 HCPV)兩部分，當(dāng)注入水的液面升至裂縫平面后會(huì)突破(累積注水0.7 HCPV)，注入水只占據(jù)了縫面下部的孔洞空間，而縫面上部的洞中仍聚集有凝析氣，即俗稱的“閣樓氣”；當(dāng)縫洞垂直連通時(shí)，受重力分異作用影響，注入水在洞底部聚積，隨著注水量增加，油相逐漸往洞頂移動(dòng)，氣相也不斷被驅(qū)出，最終注入水占據(jù)了0.9 HCPV的縫洞空間，故其凝析油采出程度相對(duì)較高。上述分析表明，縫洞連通方式會(huì)對(duì)注水效果產(chǎn)生一定的影響，縫洞垂直連通時(shí)，注水突破前累積注入水量較高，水驅(qū)波及體積大，凝析油采出程度相對(duì)較高。

圖4 不同壓力下的氣油比及產(chǎn)量對(duì)比巖心未填砂

圖5 不同縫洞連通方式注水實(shí)驗(yàn)氣油比及產(chǎn)量對(duì)比

圖6 填砂與未填砂巖心注水實(shí)驗(yàn)對(duì)比曲線

3.3 縫洞充填后凝析油采收率有所降低

從圖6中可清晰看出，縫洞巖心填砂后各注水階段的產(chǎn)油量均低于未填砂時(shí)，其凝析油采出程度也相應(yīng)較低。分析認(rèn)為縫洞巖心填砂后，非連續(xù)的洞變成了連續(xù)多孔介質(zhì)，氣、水的流體性質(zhì)差異使得注入水容易在連續(xù)多孔介質(zhì)中滲流，并將部分凝析氣封存在孔隙中；其次，巖心填砂后表面積增大，從而增加了多相滲流阻力，所以相同注水條件下，填砂巖心的凝析油采出程度不及未填砂巖心。

4 結(jié)論

(1)與衰竭開(kāi)發(fā)相比，注水開(kāi)發(fā)縫洞型碳酸鹽巖凝析氣藏時(shí)的凝析油采出程度高、開(kāi)發(fā)效果較好。

(2)縫洞垂直連通時(shí)，水驅(qū)波及體積大，凝析油采出程度相對(duì)較高。

(3)地層壓力越高時(shí)注水，凝析油采收率越高。

(4)孔洞被充填時(shí)，凝析油采收率有所降低。

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(編輯 黃 娟)

Physical simulation of exploiting fractured-vuggy carbonate gas condensate reservoirs by water injection

Peng Song, Guo Ping

(State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, Sichuan 610500, China)

Due to the development of fissures and cavities with different sizes and shapes, fractured-vuggy carbonate gas condensate reservoirs are distinct from the general sand gas condensate reservoirs, hence are characterized by strong heterogeneity and complicated flow regularity. To these reservoirs, it is a question of concern that which developing strategy is benefit to maximize the recoveries of oil and gas. As a mature technology, water injection possesses advantages such as lower cost, better gas-water mobility ratio, and higher sweep efficiency. Taking well TZ86 as a target, we accomplished a physical simulation research under initial reservoir conditions (140.6 ℃,58 MPa) by using an artificial fractured-vuggy full-diameter core which was made from an outcrop of carbonate rock. The experimental results show that the effectiveness of exploiting fractured-vuggy carbonate gas condensate reservoirs by water injection is significant. The factors such as the connectivity pattern between fissure and cavern, the pressure maintenance level of water injection, and cavern whether or not filling have effects on the recovery of condensate oil.

fractured-vuggy carbonate rock; gas condensate reservoir; high content of condensate oil; water injection; high temperature and high pressure; full-diameter core; physical simulation

1001-6112(2014)05-0645-05

10.11781/sysydz201405645

2013-05-07；

2014-07-20。

彭松(1986—)，男，博士生，從事油氣藏工程研究。E-mail: winter_melon@126.com。

郭平(1965—)，男，教授，從事油氣藏工程、油氣相態(tài)、氣田開(kāi)發(fā)研究。E-mail: guopingswpi@vip.sina.com。

高校博士點(diǎn)基金“高溫高壓多組分凝析氣非平衡相態(tài)理論模型研究”(20115121110002)資助。

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