湯小燕,張偉杰,龔愛(ài)華,劉之的
(1.西安科技大學(xué) 地質(zhì)與環(huán)境學(xué)院,陜西 西安 710054;2.中國(guó)石油集團(tuán)測(cè)井有限公司 長(zhǎng)慶事業(yè)部,陜西 高陵 710201;3.西安石油大學(xué) 地球科學(xué)與工程學(xué)院,陜西 西安 710065)
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扶余油田注水開(kāi)發(fā)過(guò)程中儲(chǔ)層孔隙結(jié)構(gòu)變化特征*
湯小燕1,張偉杰2,龔愛(ài)華2,劉之的3
(1.西安科技大學(xué) 地質(zhì)與環(huán)境學(xué)院,陜西 西安 710054;2.中國(guó)石油集團(tuán)測(cè)井有限公司 長(zhǎng)慶事業(yè)部,陜西 高陵 710201;3.西安石油大學(xué) 地球科學(xué)與工程學(xué)院,陜西 西安 710065)
研究油田注水開(kāi)發(fā)過(guò)程中儲(chǔ)層孔隙結(jié)構(gòu)及演化特征,對(duì)于制定剩余油開(kāi)發(fā)方案意義重大。利用不同含水期密閉取心井的薄片、掃描電鏡、壓汞及物性等分析化驗(yàn)資料,在翔實(shí)分析儲(chǔ)層孔隙結(jié)構(gòu)特征的基礎(chǔ)上,利用統(tǒng)計(jì)分析手段查明了該油田注水開(kāi)發(fā)過(guò)程中儲(chǔ)層孔隙結(jié)構(gòu)演化特征。研究結(jié)果表明,扶余油田儲(chǔ)層孔隙類(lèi)型主要為粒間孔與粒間溶孔,膠結(jié)物主要為泥質(zhì);由于注入水的沖刷影響,致使孔隙中的粘土礦物分散及漂移,進(jìn)而導(dǎo)致膠結(jié)類(lèi)型由中低含水期孔隙-接觸式轉(zhuǎn)變?yōu)楦吆诘目紫妒?;注水開(kāi)發(fā)對(duì)孔隙半徑均值和中值的影響較小;最大、平均孔隙半徑相同的情況下,滲透性隨著水淹程度加大,滲透率增大,而孔隙半徑中值、孔隙半徑均值變化較小。
扶余油田;注水開(kāi)發(fā);孔隙結(jié)構(gòu);演化特征
儲(chǔ)層孔隙結(jié)構(gòu)控制著儲(chǔ)滲性能的同時(shí),決定了油氣藏產(chǎn)能的大小[1-2]。查明注水開(kāi)發(fā)過(guò)程中儲(chǔ)層孔隙結(jié)構(gòu)的演化特征對(duì)研究油水兩相滲流機(jī)理和剩余油分布至關(guān)重要[3-5]。前人針對(duì)不同油田研究過(guò)注水開(kāi)發(fā)對(duì)儲(chǔ)層孔隙結(jié)構(gòu)的影響[6-9],取得的共性認(rèn)為,油層在注水開(kāi)發(fā)后,巖石中的粘土礦物等膠結(jié)物含量減少,孔隙度變大,滲透率提高。然而截止時(shí)日,扶余油田尚且沒(méi)有開(kāi)展過(guò)注水開(kāi)發(fā)過(guò)程中儲(chǔ)層孔隙結(jié)構(gòu)及演化特征的相關(guān)研究,致使該區(qū)注水開(kāi)發(fā)后油水滲流規(guī)律、剩余油分布認(rèn)識(shí)不清,這給剩余油開(kāi)發(fā)方案制定帶來(lái)不便?;诖?,通過(guò)詳實(shí)分析密閉取心井的薄片、掃描電鏡、壓汞及物性等化驗(yàn)分析資料,深入剖析注水開(kāi)發(fā)過(guò)程中儲(chǔ)層孔隙結(jié)構(gòu)及演化特征,以期為該油田后期開(kāi)發(fā)方案的有效制定提供地質(zhì)依據(jù)。
研究區(qū)位于松遼盆地南部中央坳陷區(qū)東緣華字井階地扶余三號(hào)構(gòu)造上,工區(qū)內(nèi)斷層多,薄層狀油層較為發(fā)育,油藏埋藏淺。油藏主要受構(gòu)造控制,屬于中孔中高滲構(gòu)造砂巖油藏。縱向上儲(chǔ)層物性非均質(zhì)性強(qiáng),橫向上巖性變化大[10]。研究區(qū)目的層為泉四段扶余油層。泉四段地層巖性主要是細(xì)砂巖、粉砂巖、粉砂質(zhì)泥巖及泥巖[11]。
研究區(qū)塊位于油田西部,東西2側(cè)為斷層遮擋。該區(qū)地質(zhì)儲(chǔ)量348.0×104t;泉四段頂面構(gòu)造形態(tài)為西傾單斜構(gòu)造,東西2側(cè)被南北向斷層遮擋。油水分布主要受構(gòu)造控制,全區(qū)統(tǒng)一的油水界面-330 m.主要發(fā)育扶余油層,局部鉆遇楊大城子(圖1)。
圖1 扶余油田X區(qū)塊井位圖Fig.1 Well location map of X block in Fuyu oil field
研究區(qū)沉積期環(huán)境變化劇烈,在陸相~三角洲過(guò)渡環(huán)境下發(fā)育3種亞相。由下向上經(jīng)過(guò)曲流河、三角州平原、三角洲前緣多次變遷。近期完鉆密閉取心井巖心描述揭示,研究區(qū)砂巖交錯(cuò)層理、槽狀交錯(cuò)層理、斜層理、平行層理及水下韻律層理均較發(fā)育。砂巖碎屑礦物成分包括石英、長(zhǎng)石、巖塊;膠結(jié)物以泥質(zhì)為主,灰質(zhì)次之;儲(chǔ)層巖石分選性中等一好;磨圓度為次棱。砂巖成分以巖屑質(zhì)長(zhǎng)石砂巖、長(zhǎng)石質(zhì)巖屑砂巖為主,表明巖石成分成熟度較低。
巖心物性分析表明,扶余油田泉四段以中孔中滲儲(chǔ)層為主,孔隙度在14.3%~28.5%之間,平均23.2%;滲透率在0.9×10-3~992.3×10-3μm2之間,平均95.75×10-3μm2;泥質(zhì)含量在5.1%~40%之間,平均21.74%.
該區(qū)塊自投產(chǎn)以來(lái),通過(guò)溶解氣驅(qū)、注水開(kāi)發(fā)等生產(chǎn)方式,已累積產(chǎn)油90.12×104t.目前以線(xiàn)性注采井網(wǎng)分注合采方式生產(chǎn)[12],綜合含水率高達(dá)96%.
孔隙結(jié)構(gòu)是指儲(chǔ)集層巖石孔隙及喉道的形態(tài)、大小、分布及其相關(guān)組合關(guān)系[11,13-14]。充分利用研究區(qū)注水開(kāi)發(fā)中后期密閉取心井的薄片等化驗(yàn)分析資料,對(duì)其儲(chǔ)層的孔隙結(jié)構(gòu)進(jìn)行系統(tǒng)剖析。
基于前人的研究成果,并結(jié)合研究區(qū)內(nèi)鑄體薄片、掃描電鏡等巖心分析資料可知,儲(chǔ)層孔隙空間一方面經(jīng)歷了溶蝕加大,另一方面次生礦物的充填使其孔隙變小[10]。由于本區(qū)強(qiáng)烈的自生礦物形成和充填作用,粘土薄膜覆蓋在孔隙壁表面,使其凹凸不平,進(jìn)而堵塞了孔隙喉道,致使該油藏采收率較低[15-17]。
鑄體薄片統(tǒng)計(jì)結(jié)果顯示(表1),扶余油層孔隙度變化比較大,滲透率從低滲到高滲,變化比較大。面孔率變化區(qū)間為7.93%~16.90%,整體上來(lái)看,儲(chǔ)層面孔率變化較大。從孔喉比以及各種孔隙參數(shù)來(lái)看,孔隙屬于中高孔類(lèi)型。
表1 扶余油田鑄體薄片孔隙參數(shù)統(tǒng)計(jì)表
圖2 扶余油田巖石薄片F(xiàn)ig.2 Rock thin section in Fuyu oil field (a)J27(437.49~437.77 m) (b)J27(424.03~424.30 m)
由巖石薄片鑒定可知,圖2(a)為含內(nèi)碎屑細(xì)粒長(zhǎng)石,孔隙發(fā)育,連通性好;顆粒77%,填隙物6%,孔隙17%,顆粒內(nèi)細(xì)砂80%,中砂15%,填隙物中泥質(zhì)2%,高嶺石1%,鐵白石2%,孔隙中粒間孔6.7%,粒間溶孔10%,孔徑30~120 μm,配位數(shù)2~4.圖2(b)為細(xì)粒巖石長(zhǎng)石巖屑砂巖,長(zhǎng)石多被溶蝕,顆粒多點(diǎn)-線(xiàn)接觸;顆粒81%,填隙物9%,孔隙10%,顆粒內(nèi)細(xì)砂90%,其余為中砂,填隙物中泥質(zhì)4%,高嶺石2%,白云石、鐵白石2%,孔隙中粒間孔4%,粒間溶孔5.5%,孔徑10~60 μm,配位數(shù)2~3.從巖石薄片鑒定(圖2(a)圖2(b))可以發(fā)現(xiàn),巖石中細(xì)砂、中砂顆粒約占80%,膠結(jié)物主要為泥質(zhì)。
圖3 扶余油田密閉取心井面孔率與深度關(guān)系圖Fig.3 Relationship between the face rate and depth of closed coring wells in Fuyu oil field
薄片分析表明,該地區(qū)以巖屑長(zhǎng)石砂巖和巖屑砂巖為主,由于長(zhǎng)石砂巖孔隙發(fā)育,長(zhǎng)石巖屑砂巖面孔率一般較高;盡管巖屑砂巖中長(zhǎng)石多被溶蝕,但由于巖屑砂巖中填隙物含量高、孔隙發(fā)育較差,巖屑砂巖的面孔率也相對(duì)較低。由深度與面孔率關(guān)系圖可知(圖3),各井的面孔率差異較大,但總體上呈現(xiàn)隨著深度增加,面孔率有減少的趨勢(shì)。經(jīng)歷壓實(shí)、膠結(jié)作用后,絕大多數(shù)井原生粒間孔含量仍然較高,但也能為油田注水開(kāi)發(fā)提供流體流動(dòng)的滲流通道。
系統(tǒng)分析密閉取心井的鑄體薄片、掃描電鏡等資料可知,研究區(qū)內(nèi)儲(chǔ)層孔隙主要有4類(lèi):原生粒間孔、縮小原生粒間孔、長(zhǎng)石溶蝕孔、晶間微孔(圖4),次生粒間孔隙是主要的儲(chǔ)集空間。
3.1孔隙結(jié)構(gòu)
基于壓汞資料統(tǒng)計(jì)分析,獲得表2所示的孔隙半徑、物性及排驅(qū)壓力參數(shù)統(tǒng)計(jì)表。由表2可得到以下2點(diǎn)認(rèn)識(shí)。
圖4 扶余油田儲(chǔ)層巖石鑄體薄片與掃描電鏡照片F(xiàn)ig.4 Cast thin section and scanning electron microscope pictures of the reservoir rocks in Fuyu oil field (a)原生粒間孔 (b)縮小原生粒間孔 (c)長(zhǎng)石溶蝕孔 (d)晶間微孔
3.1.1全區(qū)孔隙半徑都比較小
壓汞資料表明,研究區(qū)內(nèi)儲(chǔ)層的平均孔隙半徑為1.62~6.12 μm,孔隙半徑中值為0.59~1.63 μm,最大孔隙半徑為6.31~15.67 μm,孔隙半徑均值為1.38~4.69 μm.扶余油田孔隙類(lèi)型以粒間孔和微孔隙為主,孔隙半徑大小的分布范圍為0.04~18 μm,其中微孔隙占25%~36%.
3.1.2不同沉積微相孔隙半徑不同
砂體孔隙半徑受沉積微相控制較為嚴(yán)重。由表2可知,點(diǎn)砂壩的物性最好,孔隙度和滲透率均較大,最大孔隙半徑高達(dá)15.67 μm;分流河道、決口扇及天然堤次之,均大于8 μm;其它微相的孔隙半徑則相對(duì)較小。
3.2膠結(jié)類(lèi)型
圖5 扶余油田密閉取心井膠結(jié)類(lèi)型柱狀圖Fig.5 Cementation type column of sealed coring well in Fuyu oil filed
研究區(qū)J6,J7井為注水開(kāi)發(fā)前的密閉取心井,含水率約為20%;其余各井為注水開(kāi)發(fā)過(guò)程中密閉取心井,其中J8,J9,J10井含水率約為40%左右,J15,J19,J21,J22,J23含水率約為70%左右,J24,J25,J26,J27,J28含水率約為95%左右。利用研究區(qū)注水開(kāi)發(fā)前后不同含水期的密閉取心井薄片分析資料,對(duì)膠結(jié)類(lèi)型的變化特征進(jìn)行分析。由圖5可知,隨著油田含水率的升高,膠結(jié)類(lèi)型發(fā)生了明顯的變化。油田開(kāi)發(fā)初期及中低含水期,儲(chǔ)層的膠結(jié)類(lèi)型以接觸式為主;隨著注水量增大,含水率達(dá)到85%時(shí),儲(chǔ)層的膠結(jié)類(lèi)型逐漸轉(zhuǎn)化為孔隙-接觸式、接觸-孔隙式;當(dāng)含水率上升到95%時(shí),儲(chǔ)層的膠結(jié)類(lèi)型則以孔隙式為主。儲(chǔ)層的膠結(jié)類(lèi)型演化過(guò)程受注水量的影響較為嚴(yán)重,注入水的沖刷分散了孔隙中的粘土礦物,并將其漂移、攜帶出儲(chǔ)層,從而導(dǎo)致膠結(jié)類(lèi)型轉(zhuǎn)變?yōu)榭紫妒侥z結(jié),向孔隙方向轉(zhuǎn)換。
表2 扶余油田儲(chǔ)集層孔隙半徑數(shù)據(jù)表
3.3孔隙半徑與粒度中值之間的關(guān)系
利用特強(qiáng)水淹J25,J26,J27井所取的巖樣,共計(jì)開(kāi)展了29個(gè)樣品的壓汞、粒度分析實(shí)驗(yàn)。利用交會(huì)圖分析技術(shù),構(gòu)建了圖6所示的粒度中值與孔隙半徑關(guān)系圖。由該圖可知,特強(qiáng)水淹儲(chǔ)層中,隨著粒度中值增大,其孔隙也隨之增大。這也進(jìn)一步說(shuō)明,隨著注水開(kāi)發(fā)過(guò)程中含水率增大、儲(chǔ)層水洗程度加大,注入水將泥質(zhì)等膠結(jié)物攜帶出儲(chǔ)層,顆粒表面的清潔度變好,孔喉網(wǎng)絡(luò)的連通性變好,致使儲(chǔ)層粒度中值與孔隙半徑具有較好的正相關(guān)性。
圖6 特強(qiáng)水淹粒度中值與孔隙半徑關(guān)系圖Fig.6 Relationship between the median pore radius and pore radius
圖7 高/特高含水階段孔隙半徑與滲透率關(guān)系圖Fig.7 Relationship between pore radius and permeability at high/ultra high water cut stage
3.4孔隙半徑與滲透率之間的關(guān)系
利用含水85%時(shí)與含水95%時(shí)密閉取心井壓汞和物性分析資料,構(gòu)建了圖7所示的孔隙半徑與滲透率交會(huì)圖。由該圖可知,孔隙半徑與滲透率相關(guān)性較好,且呈現(xiàn)出隨著含水升高,最大孔隙半徑和平均孔隙半徑增大的態(tài)勢(shì),而孔隙半徑中值和孔隙半徑均值的增幅相對(duì)較小。最大孔隙半徑和平均孔隙半徑相同時(shí),滲透率隨孔隙半徑增大而增大,且增幅較大。究其原因,注水開(kāi)發(fā)時(shí)孔隙中的泥質(zhì)膠結(jié)物被攜帶出儲(chǔ)層,于是儲(chǔ)層的孔隙度和滲透率將增大;孔隙半徑中值和孔隙半徑均值的變化較小,表明注水開(kāi)發(fā)對(duì)其影響也較小,反之也說(shuō)明了注水開(kāi)發(fā)對(duì)小孔隙和大孔隙的影響均較大。
為了進(jìn)一步探討儲(chǔ)層孔隙結(jié)構(gòu)隨水淹程度的變化規(guī)律,將壓汞分析數(shù)據(jù)以特強(qiáng)水淹、中水淹、弱水淹3個(gè)級(jí)別的水淹程度分類(lèi)進(jìn)行分析,通過(guò)滲透率與最大孔隙半徑、平均孔隙半徑、孔隙半徑均值、孔隙半徑中值相關(guān)性分析可知(圖8),最大孔隙半徑小于14 μm平均孔隙半徑小于6 μm時(shí),相同最大、平均孔隙半徑情況下,滲透性隨著水淹程度加大,滲透率增大,而孔隙半徑中值、孔隙半徑均值也有變化,但變化不大。
圖8 不同水淹級(jí)別孔隙半徑與滲透率對(duì)比關(guān)系圖Fig.8 Comparison of pore radius and permeability under different water flooding level
1)研究區(qū)儲(chǔ)層孔隙類(lèi)型主要為粒間孔與粒間溶孔,其面孔率隨著深度增加,呈減少趨勢(shì)。隨著注水開(kāi)發(fā)的逐漸推進(jìn),儲(chǔ)層膠結(jié)類(lèi)型由中低含水期的接觸式逐漸演化為中高含水期的孔隙-接觸式和孔隙式;
2)油田高含水期,孔隙半徑大小與粒度中值呈現(xiàn)正相關(guān),滲透率與孔隙半徑中值及主要流動(dòng)孔隙半徑均值亦呈現(xiàn)出正相關(guān)。孔隙結(jié)構(gòu)相同的情況下,隨著油田注水開(kāi)發(fā)中后期含水率升高,儲(chǔ)層的物性明顯變好,而且滲透率增大更為明顯。
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Reservoir pore structure and evolution characteristics in the process of water injection development in Fuyu Oilfield
TANG Xiao-yan1,ZHANG Wei-jie2,GONG Ai-hua2,LIU Zhi-di3
(1.CollegeofGeologyandEnvironment,Xi’anUniversityofScienceandTechnology,Xi’an710054,China;2.ChangqingBusinessDivision,ChinaPetroleumLoggingLtd.,Xi’an710201,China;3.SchoolofEarthSciencesandEngineering,Xi’anShiyouUniversity,Xi’an710065,China)
It is of great significance to make the remaining oil development plan that studies the pore structure and the evolution characteristics in the process of water injection development.Making use of testing data of thin section,scanning electron microscopy,mercury intrusion and physical property in different water cut period of pressure coring well,the reservoir pore structure characteristics are analyzed in-depth and systematically,and the reservoir pore structure and evolution characteristics are found during the oilfield waterflood development using statistical analysis method.Research results show that the reservoir pore types in Fuyu oilfield are intergranular pore and intergranular dissolved pore,and cement is mainly argillaceous;Due to injection water scouring effect,it cause the clay content in pore to separate and drift,and result in cementation types translate pore-contact in the low and medium water cut period into pore type in high water cut period;In the process of water injection development,the influence of the water injection development on median and the mean radius is small,then on the other hand,the influence on the maximum pore and small pore is the bigger;For the same maximum and average pore radius,the permeability increases with the watered-out degree increasing,the changes of median pore radius and pore radius are small.
Fuyu oilfield;water injection development;pore structure;evolution characteristics
10.13800/j.cnki.xakjdxxb.2016.0409
1672-9315(2016)04-0507-07
2016-03-20責(zé)任編輯:李克永
國(guó)家自然科學(xué)基金(41502159)
湯小燕(1977-),女,四川廣安人,博士,副教授,E-mail:tangxiaoyanlmj@sina.com
TE 122
A