高含水期水平井提高水驅(qū)采收率機(jī)制

肖 康,姜漢橋,李俊鍵

(1.中國(guó)石油大學(xué)石油工程學(xué)院,北京 102249；2.中國(guó)石油勘探開(kāi)發(fā)研究院采油所,北京 100083)

高含水期水平井提高水驅(qū)采收率機(jī)制

肖 康1,姜漢橋1,李俊鍵2

(1.中國(guó)石油大學(xué)石油工程學(xué)院,北京 102249；2.中國(guó)石油勘探開(kāi)發(fā)研究院采油所,北京 100083)

以孤島油田地質(zhì)及開(kāi)發(fā)動(dòng)態(tài)特征為基礎(chǔ),應(yīng)用水驅(qū)油相似原理,建立三維大型物理膠結(jié)正韻律多層模型。當(dāng)井組物理模型生產(chǎn)至高含水階段,應(yīng)用水平井以及直井在剩余油富集區(qū)進(jìn)行挖潛,并結(jié)合數(shù)值模擬方法,研究不同儲(chǔ)層參數(shù)以及工作制度條件下,水平井相對(duì)于直井?dāng)U大波及系數(shù)與提高驅(qū)油效率對(duì)提高采收率的貢獻(xiàn)程度。結(jié)果表明:應(yīng)用水平井進(jìn)行高含水期剩余油挖潛,相對(duì)直井有著較大的優(yōu)勢(shì)；水平井相對(duì)于直井主要是通過(guò)擴(kuò)大波及系數(shù)來(lái)提高水驅(qū)采收率,并且儲(chǔ)層條件以及工作制度對(duì)波及系數(shù)與驅(qū)油效率的貢獻(xiàn)率差異程度有著較大影響；隨著含水率的上升,波及系數(shù)與驅(qū)油效率貢獻(xiàn)率差異程度逐漸減小,但二者貢獻(xiàn)率比值始終大于1。

油藏；水平井；高含水；物理模擬；數(shù)值模擬；波及系數(shù)；驅(qū)油效率

目前,大部分油田已進(jìn)入高含水階段,局部區(qū)塊甚至進(jìn)入了特高含水階段,但由于油藏非均質(zhì)性、開(kāi)發(fā)方式等原因,仍然存在未被波及或動(dòng)用程度較少的剩余油富集區(qū)[1-2]。應(yīng)用水平井作為挖潛的主要技術(shù)手段,可以有效提高剩余儲(chǔ)量控制程度以及采收率[3-5]。眾多學(xué)者對(duì)高含水期水平井挖潛原理及效果進(jìn)行了研究[6-11]。但是,針對(duì)水平井提高水驅(qū)采收率的機(jī)制,即水平井相對(duì)直井?dāng)U大波及系數(shù)與提高驅(qū)油效率關(guān)系的研究較少。因此,筆者以孤島油田地質(zhì)及動(dòng)態(tài)開(kāi)發(fā)特征為基礎(chǔ),建立具有正韻律特征的三維大型物理膠結(jié)模型,進(jìn)行水平井高含水期挖潛試驗(yàn),并結(jié)合油藏?cái)?shù)值模擬方法,研究在不同地質(zhì)條件以及工作制度下,水平井相對(duì)直井?dāng)U大波及系數(shù)與提高驅(qū)油效率對(duì)提高采收率貢獻(xiàn)程度。

1 物理模擬試驗(yàn)

基于三維物理模型,在對(duì)不同挖潛方式動(dòng)用效果進(jìn)行評(píng)價(jià)的基礎(chǔ)上[12-15],考察水平井波及系數(shù)與驅(qū)油效率的關(guān)系。

計(jì)算水平井相對(duì)直井?dāng)U大波及系數(shù)與提高驅(qū)油效率對(duì)提高采收率的貢獻(xiàn)率的基本原理見(jiàn)圖1。

圖1 波及系數(shù)與驅(qū)油效率貢獻(xiàn)率示意圖Fig.1 Schematic diagram of sweep and displacement efficiency contribution

首先確定挖潛井處于特定含水階段,模擬每個(gè)網(wǎng)格飽和度相對(duì)挖潛初始時(shí)的變化量。因模型在驅(qū)替及飽和度探針檢測(cè)過(guò)程中存在不可避免的誤差,所以當(dāng)網(wǎng)格飽和度變化大于5%時(shí),即認(rèn)為此網(wǎng)格被波及。

其次,在已得到的直井波及區(qū)域內(nèi),分別計(jì)算直井與水平井在挖潛階段其特定含水率下相對(duì)挖潛初始時(shí)所提高的采收率,二者之差與水平井相對(duì)直井所提高整體采收率的比值即為驅(qū)油效率貢獻(xiàn)率。

用1減去驅(qū)油效率貢獻(xiàn)率,為波及系數(shù)貢獻(xiàn)率,即為水平井波及區(qū)大于直井波及區(qū)的區(qū)域,計(jì)算式為

式中,Ef為挖潛井處于某一含水階段下模型采出程度；Soij為第i層的第j個(gè)網(wǎng)格的含油飽和度；Soiji為挖潛初始時(shí)含油飽和度；φ為孔隙度；Cdi、Csi分別為驅(qū)油效率、波及系數(shù)貢獻(xiàn)率；Ehiv、Eviv分別為直井波及區(qū)內(nèi)水平井、直井的采出程度；Ehi、Evi分別為應(yīng)用水平井、直井挖潛的模型整體采出程度。

以試驗(yàn)飽和探針?biāo)玫降娘柡投葦?shù)據(jù)為基礎(chǔ),通過(guò)插值方法得到不同含水階段波及系數(shù)與驅(qū)油效率對(duì)提高采收率貢獻(xiàn)程度(表1)。由表1可以看出,水平井相對(duì)于直井,主要是靠擴(kuò)大波及系數(shù)來(lái)提高水驅(qū)采收率。當(dāng)水平井垂直注入井連線(xiàn)向平行注入井連線(xiàn)過(guò)渡時(shí),擴(kuò)大波及系數(shù)的貢獻(xiàn)率逐漸減小；并且隨著含水率的上升,擴(kuò)大波及系數(shù)的貢獻(xiàn)率逐漸減小,而提高驅(qū)油效率的貢獻(xiàn)率逐漸升高。但是在高含水時(shí)期,擴(kuò)大波及系數(shù)與提高驅(qū)油效率貢獻(xiàn)率比值一般都大于1,因此在注入體積倍數(shù)較高時(shí),相對(duì)于提高驅(qū)油效率,擴(kuò)大波及系數(shù)仍然占主導(dǎo)地位。

表1 水平井相對(duì)直井?dāng)U大波及系數(shù)與提高驅(qū)油效率貢獻(xiàn)率Table 1 Contribution of sweep and displacement efficiency with horizontal well compared to vertical well

2 數(shù)值模擬

2.1 建立模型

以膠結(jié)模型水驅(qū)油試驗(yàn)以及實(shí)際現(xiàn)場(chǎng)動(dòng)態(tài)資料為基礎(chǔ),建立數(shù)值模擬模型,其中數(shù)值模型尺寸、工作制度等與物理試驗(yàn)?zāi)Ｐ捅３忠恢?網(wǎng)格數(shù)為54× 62×3=10044個(gè),并對(duì)模型進(jìn)行精細(xì)擬合,擬合情況見(jiàn)圖2。

由圖2可以看出,建立的數(shù)值模型與試驗(yàn)結(jié)果基本保持一致,因此可以在試驗(yàn)基礎(chǔ)上利用建立的數(shù)值模型進(jìn)行不同地質(zhì)特征及工作制度下水平井相對(duì)直井提高采收率機(jī)制研究,研究區(qū)含水率為75%～98%。

圖2 數(shù)值模擬擬合試驗(yàn)Fig.2 Numerical simulation matching experiment

2.2 挖潛機(jī)制

2.2.1 儲(chǔ)層縱向滲透率級(jí)差

模型目標(biāo)區(qū)塊儲(chǔ)層類(lèi)型屬于河流相儲(chǔ)層,其縱向滲透率基本呈正韻律發(fā)育特征,高含水期縱向非均質(zhì)性對(duì)剩余油分布有著較大的影響。圖3為不同縱向滲透率級(jí)差下水平井提高采收率機(jī)制。可以看出,隨含水率上升,同一級(jí)差下的波及系數(shù)與驅(qū)油效率的貢獻(xiàn)率比值(Csi/Cdi)逐漸減小,不同滲透率級(jí)差下二者比值的差異下降。挖潛井含水率達(dá)到98%時(shí),波及貢獻(xiàn)率仍大于驅(qū)油效率貢獻(xiàn)率,此時(shí),隨著儲(chǔ)層滲透率級(jí)差的增大,貢獻(xiàn)率比值逐漸減小,而水平井與直井的采收率比值(RH/RV)逐漸增大。當(dāng)級(jí)差大于8時(shí),比值變化趨于平緩。

圖3 不同縱向滲透率級(jí)差下水平井提高采收率機(jī)制Fig.3 Mechanism of improving water drive recovery with horizontal well under different permeability contrast

2.2.2 挖潛時(shí)機(jī)

不同挖潛時(shí)機(jī)含水率示意圖見(jiàn)圖4。不同挖潛時(shí)機(jī)(用含水率表示)下水平井提高采收率結(jié)果如圖5所示。

圖4 不同挖潛時(shí)機(jī)含水率示意圖Fig.4 Water cut curve at different potential tapping time

由圖5可以看出,隨含水率上升,同一挖潛時(shí)機(jī)下的波及系數(shù)與驅(qū)油效率貢獻(xiàn)率比值逐漸減小,不同挖潛時(shí)機(jī)下二者比值的差異下降。挖潛井含水率達(dá)到98%時(shí),二者比值仍大于1,隨著挖潛時(shí)機(jī)的延后,波及系數(shù)與驅(qū)油效率的貢獻(xiàn)率比值逐漸增大,而水平井與直井采收率的比值則逐漸減小,當(dāng)挖潛時(shí)機(jī)含水率大于90%時(shí),貢獻(xiàn)率比值與采收率比值變化都趨于平緩。

2.2.3 夾層滲透率

圖6為不同夾層滲透率下水平井提高采收率機(jī)制。由圖6可以看出,隨著含水率上升,同一滲透率下的波及系數(shù)與驅(qū)油效率貢獻(xiàn)率比值逐漸減小,并且不同滲透率下二者比值的差異也下降。但挖潛井含水率達(dá)到98%時(shí),比值仍大于1,此時(shí)夾層滲透率約為20×10-3μm2,貢獻(xiàn)率比值達(dá)到最大,而夾層滲透性向0過(guò)渡時(shí),比值遞減較快,而向200×10-3μm2過(guò)渡時(shí),比值遞減較慢；采收率比值在含水率為98%時(shí)的變化規(guī)律,正好與效率貢獻(xiàn)率比值相反。

圖5 不同挖潛時(shí)機(jī)下水平井提高采收率機(jī)制Fig.5 Mechanism of improving oil recovery with horizontal well under different potential tapping time

圖6 不同夾層滲透率下水平井提高采收率機(jī)制Fig.6 Mechanism of improving oil recovery with horizontal well under different interlayer permeability

2.2.4 夾層規(guī)模

夾層規(guī)模影響著剩余油分布,進(jìn)而對(duì)水平井相對(duì)

直井提高采收率產(chǎn)生影響。夾層規(guī)模示意圖見(jiàn)圖7。

圖7 夾層規(guī)模示意圖Fig.7 Schematic diagram of interlayer scale

不同夾層規(guī)模下水平井提高采收率機(jī)制見(jiàn)圖8。由圖8可以看出,隨著含水率上升,同一夾層規(guī)模下波及系數(shù)與驅(qū)油效率貢獻(xiàn)率比值逐漸減小,不同夾層規(guī)模下二者比值的差異下降。但挖潛井含水達(dá)到98%時(shí),貢獻(xiàn)率比值仍大于1,此時(shí),隨著夾層規(guī)模增大,波及系數(shù)與驅(qū)油效率貢獻(xiàn)率比值逐漸減小,而水平井與直井采收率比值逐漸增大,但貢獻(xiàn)率比值與采收率比值變化都逐漸趨于平緩。

圖8 不同夾層規(guī)模下水平井提高采收率機(jī)制Fig.8 Mechanism of improving oil recovery with horizontal well under different interlayer scale

3 結(jié) 論

(1)水平井主要通過(guò)擴(kuò)大波及系數(shù)來(lái)提高采收率。但波及系數(shù)與驅(qū)油效率的貢獻(xiàn)率差異程度隨儲(chǔ)層參數(shù)以及工作制度變化而變化。

(2)隨著含水率上升,即水驅(qū)程度的深入,水平井相對(duì)直井?dāng)U大波及系數(shù)的貢獻(xiàn)率比值逐漸下降,但在高含水時(shí)期,波及系數(shù)與驅(qū)油效率貢獻(xiàn)率比值仍然大于 1；在貢獻(xiàn)率比值減小的過(guò)程中,水平井與直井采收率比值呈增大的趨勢(shì)。

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(編輯 李志芬)

Mechanisms of improving oil recovery efficiency by horizontal well in high water-cut stage

XIAO Kang1,JIANG Han-qiao1,LI Jun-jian2

(1.College of Petroleum Engineering in China University of Petroleum,Beijing 102249,China；
2.Oil Production Institute,Research Institute of Petroleum Exploration&Development,PetroChina, Beijing 100083,China)

Based on the geological and production performance data in Gudao Oilfield,a large scale artificial consolidated multi-layer model reflecting the normal rhythm was established according to the similar principle of waterflooding.Considering different reservoir parameters and working system,horizontal and vertical wells were used to tap the potential respectively when well group physical model reaches high water-cut stage.And combined with numerical simulation,mechanisms of both sweep and displacement efficiency contributing to improving oil recovery with horizontal well compared with vertical well were studied.The results show that the effect of horizontal well tapping remaining oil is better than that of vertical well.Contribution of sweep efficiency to improving oil recovery with horizontal well compared with vertical well occupies main position,and difference between sweep efficiency and displacement efficiency contribution is affected by reservoir parameters and working system.With the increase of water cut,though the contribution differentiation degree between sweep efficiency and displacement efficiency becomes smaller and smaller,contribution ratio of sweep efficiency to displacement efficiency is always more than 1.

reservoir；horizontal well；high water-cut；physical simulation；numerical simulation；sweep efficiency；displacement efficiency

TE 327

A

1673-5005(2013)03-0110-05

10.3969/j.issn.1673-5005.2013.03.019

2012-07-10

國(guó)家科技重大專(zhuān)項(xiàng)(2011ZX05009- 006；2011ZX05030-005)

肖康(1987-),男,博士研究生,主要從事油田開(kāi)發(fā)調(diào)整及油藏?cái)?shù)值模擬研究。E-mail:xiaokang870224@163.com。