杜江民,傅 強(qiáng),劉東明,劉旭輝
(1.西北大學(xué)地質(zhì)學(xué)系/大陸動(dòng)力學(xué)國家重點(diǎn)實(shí)驗(yàn)室,陜西西安 710069;2.石家莊經(jīng)濟(jì)學(xué)院資源學(xué)院,
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蘇東區(qū)塊盒8段儲(chǔ)層微觀孔隙結(jié)構(gòu)特征研究
杜江民1,2,傅 強(qiáng)3,劉東明3,劉旭輝3
(1.西北大學(xué)地質(zhì)學(xué)系/大陸動(dòng)力學(xué)國家重點(diǎn)實(shí)驗(yàn)室,陜西西安 710069;2.石家莊經(jīng)濟(jì)學(xué)院資源學(xué)院,
河北石家莊 050031;3.中國石油集團(tuán)測井有限公司生產(chǎn)測井中心,陜西高陵 710201)
鄂爾多斯盆地蘇東區(qū)塊盒8段儲(chǔ)層是典型的致密砂巖儲(chǔ)層, 影響儲(chǔ)層質(zhì)量的因素較為復(fù)雜。以鑄體薄片、掃描電鏡和物性分析等資料為基礎(chǔ),對儲(chǔ)層微觀孔隙結(jié)構(gòu)特征進(jìn)行了定性分析,同時(shí)應(yīng)用恒速壓汞方法對儲(chǔ)層微觀孔隙結(jié)構(gòu)進(jìn)行了定量表征。研究結(jié)果表明:蘇東區(qū)塊盒8段低滲儲(chǔ)層物性主要受喉道控制,而不是孔隙;平均喉道半徑越大,微觀均值系數(shù)越小,相對大喉道越多,排驅(qū)壓力越低,儲(chǔ)層微觀孔隙結(jié)構(gòu)一般越好,反映儲(chǔ)層微觀孔隙結(jié)構(gòu)品質(zhì)越好。因此,喉道是影響致密砂巖儲(chǔ)層質(zhì)量的主要微觀地質(zhì)因素。
鄂爾多斯盆地 盒8 儲(chǔ)層微觀孔隙結(jié)構(gòu) 恒速壓汞 喉道
大量的油氣田開發(fā)實(shí)踐和研究成果表明,儲(chǔ)層微觀孔隙結(jié)構(gòu)是影響油田高效開發(fā)的關(guān)鍵因素,微觀孔隙結(jié)構(gòu)的非均質(zhì)性直接反映油藏的品質(zhì)及制約著驅(qū)油效率和開發(fā)效果(付曉燕等,2006;屈雪峰等,2006;任大忠等,2014;孫衛(wèi)等,2006)。鄂爾多斯盆地蘇東區(qū)塊盒8段儲(chǔ)層是典型的致密砂巖儲(chǔ)層,較常規(guī)儲(chǔ)層具有低孔低滲、孔喉結(jié)構(gòu)復(fù)雜、可動(dòng)流體賦存特征復(fù)雜和單井產(chǎn)量低等特點(diǎn)。因此,需通過鑄體薄片、掃描電鏡、物性分析和高壓壓汞、恒速壓汞等多種方法綜合定量表征蘇東區(qū)塊盒8段典型的致密砂巖儲(chǔ)層微觀孔隙結(jié)構(gòu)特征,揭示影響低滲透儲(chǔ)層微觀孔隙結(jié)構(gòu)品質(zhì)的主要因素,為進(jìn)一步擴(kuò)大鄂爾多斯盆地蘇東區(qū)塊的生產(chǎn)規(guī)模提供有利依據(jù)。
蘇東區(qū)塊處于鄂爾多斯盆地陜北斜坡中部,見圖1。盒8段儲(chǔ)層是該區(qū)的主力氣層,沉積環(huán)境為辮狀河三角洲前緣亞相。通過鑄體薄片、掃描電鏡、圖象粒度、X-衍射黏土分析、恒速壓汞實(shí)驗(yàn)等分析發(fā)現(xiàn),其巖性以巖屑石英砂巖、石英砂巖為主,含少量巖屑砂巖;孔隙以各類溶蝕孔(占40.77%)和晶間微孔(占41.41%)為主,原生粒間孔(占6.53%)和微裂隙(占1.20%)含量較少;粘土礦物絕對含量平均值為7.73%,其中以伊利石、高嶺石為主,伊/蒙間層、綠泥石含量相對很少;主流喉道半徑平均值為0.754μm ,孔喉半徑比平均值為268.3,說明大孔隙被小喉道所包圍;巖性致密,儲(chǔ)層樣品氣測孔隙度平均值為11.03%,氣測滲透率平均值為0.298×10-3μm2。
本次研究采用的是中國石油勘探開發(fā)研究院廊坊分院滲流所引進(jìn)的美國ASPE—730型恒速壓汞實(shí)驗(yàn)設(shè)備,實(shí)驗(yàn)溫度為恒溫23℃。利用恒速壓汞可獲得巖樣的有效孔隙體積和有效喉道體積,統(tǒng)計(jì)巖樣可動(dòng)流體飽和度與單位體積有效孔隙、喉道體積關(guān)系,從而探索影響儲(chǔ)層質(zhì)量的主要微觀地質(zhì)因素(朱永賢等,2008;高輝等,2011;高永利等,2011;崔連訓(xùn)等,2012;高輝等,2012;師調(diào)調(diào)等,2012)。
圖1 研究區(qū)地理位置與構(gòu)造圖Fig.1 Geographical location and structure diagram of the study area 1-蘇里格氣田;2-地名;3-研究區(qū);4-構(gòu)造帶;5-斷裂1-Sulige gas field; 2-Names; 3-Study area; 4-Tectonic belt;5-Fracture
2.1 孔隙半徑分布特征
由恒速壓汞實(shí)驗(yàn)得出,蘇東區(qū)塊盒8段儲(chǔ)層有效孔隙半徑分布較為分散,平均喉道半徑分布范圍
窄,集中在0.544~0.999μm之間,平均為0.753μm。從統(tǒng)計(jì)結(jié)果來看,平均孔隙半徑與物性基本沒有相關(guān)性(圖2a、b),表明孔隙不是控制低滲透儲(chǔ)層物性的主要因素。
2.2 喉道半徑特征
鑄體薄片和掃描電鏡觀察表明,研究區(qū)盒8段儲(chǔ)層樣品以縮頸狀、彎片狀或片狀喉道為主。因此,可用毛細(xì)管壓力的理論公式(2-1)(何更生,1993),結(jié)合壓汞曲線計(jì)算這類儲(chǔ)層喉道半徑下限。
毛細(xì)管壓力的理論公式:
(2-1)
式中:Pc為毛細(xì)管壓力,MPa;r為毛管半徑,μm;σ為氣水界面張力,N/m;θ為潤濕角,°。實(shí)驗(yàn)中恒速壓汞技術(shù)的最高進(jìn)汞壓力約為6.2MPa,水銀的界面張力為485mN/m,潤濕角為140°,求得的最小喉道半徑約為0.12μm。
從統(tǒng)計(jì)結(jié)果來看,樣品平均喉道半徑與孔隙度正相關(guān)性一般(相關(guān)系數(shù)0.334),與滲透率正相關(guān)性很好(相關(guān)系數(shù)0.731),表明半徑大于0.12μm的喉道對低滲透儲(chǔ)層滲透率具有顯著的控制作用,同時(shí)對孔隙度也具有一定的控制作用,但不明顯(圖3a,b);平均喉道半徑與主流喉道半徑正相關(guān)性很好(相關(guān)系數(shù)0.971),說明平均喉道半徑越大,相對大喉道對儲(chǔ)層滲透率貢獻(xiàn)值越大,其中當(dāng)平均喉道半徑大于1.5μm時(shí),主流喉道半徑大于平均喉道半徑(圖3c);尤其當(dāng)平均喉道半徑小于1.45μm,滲透率小于1×10-3μm2。時(shí),平均喉道半徑越小,其與滲透率的散點(diǎn)相對越集中且相關(guān)性趨勢線越陡,表明滲透率受喉道控制作用越明顯(圖3b)。
圖2 平均孔隙半徑與儲(chǔ)層物性相關(guān)關(guān)系Fig.2 Relationship between the average pore radius and reservoir property
圖3 喉道半徑比與孔隙半徑、平均喉道半徑關(guān)系Fig.3 Relationship between average throat radius with porosity, permeability, mainstream throat radius
2.3 孔喉半徑比分布
從統(tǒng)計(jì)結(jié)果來看(圖4a、b),樣品平均喉道半徑與孔隙半徑具有正相關(guān)關(guān)系,但相關(guān)性比較差,相關(guān)系數(shù)僅為0.39,說明孔隙大小對該儲(chǔ)層孔喉比控制作用較弱;然而平均喉道半徑與喉道半徑具有較好的負(fù)相關(guān)關(guān)系(相關(guān)系數(shù)0.90),相關(guān)性較強(qiáng)。從圖中可以看出,半徑大于0.12μm的喉道對該儲(chǔ)層孔喉比具有顯著的控制作用,其主要表現(xiàn)在平均喉道半徑越大,平均孔喉半徑比越小,越利于油氣田開發(fā)(齊亞東等,2013;高輝等,2008);尤其當(dāng)平均喉道半徑大于1.20μm,孔喉比小于180時(shí),平均喉道半徑越大,其與孔喉半徑比的散點(diǎn)圖越集中,且相關(guān)性趨勢線較陡,說明喉道對孔喉半徑比的控制作用越明顯;而當(dāng)孔喉比大于180,平均喉道半徑小于1.20μm時(shí),孔喉半徑比的散點(diǎn)圖較分散,且相關(guān)性趨勢變化較緩慢,說明小孔-微細(xì)喉類型孔喉結(jié)構(gòu),喉道對孔喉半徑比的控制作用較小。
圖4 平均喉道半徑與孔隙度、滲透率、主流喉道半徑關(guān)系Fig.4 Relationship between throat radius ratio with poreradius, the average throat radius
2.4 微觀孔隙結(jié)構(gòu)參數(shù)特征
通過繪制研究區(qū)盒8氣層樣品平均喉道半徑與表征微觀孔隙結(jié)構(gòu)特征的各參數(shù)之間關(guān)系圖(圖5), 發(fā)現(xiàn)平均喉道半徑與喉道進(jìn)汞飽和度(圖5d)﹑總進(jìn)汞飽和度(圖5f)相關(guān)性很好,相關(guān)系數(shù)為0.86﹑0.92;與微觀均值系數(shù)(圖5a)、排驅(qū)壓力(圖5b)、分選系數(shù)(圖5c)相關(guān)性一般,相關(guān)系數(shù)分別為0.75﹑0.79、0.78;與孔隙進(jìn)汞飽和度(圖5e)相關(guān)性較差,相關(guān)系數(shù)為0.62。研究表明,該氣層孔隙半徑相差不大,平均喉道半徑對微觀孔隙結(jié)構(gòu)具有較明顯的控制作用,表現(xiàn)為喉道半徑越大,微觀均值系數(shù)越小,相對大喉道越多,排驅(qū)壓力越低,總體儲(chǔ)層微觀孔隙結(jié)構(gòu)越好,尤其當(dāng)平均喉道半徑小于1.50μm時(shí),表現(xiàn)為平均喉道半徑與儲(chǔ)層微觀孔隙結(jié)構(gòu)參數(shù)越集中,且相關(guān)性趨勢線越陡(圖5)。
圖5 平均喉道半徑與孔隙結(jié)構(gòu)參數(shù)相關(guān)關(guān)系Fig.5 Relationship between the average pore throat radius and pore parameters
儲(chǔ)層品質(zhì)指數(shù)可用氣測滲透率與氣測孔隙度比值的平方根表示(李先鵬,2008;陳科貴等,2014;李瑞等,2004),該參數(shù)目前已廣泛用于評(píng)價(jià)低滲透儲(chǔ)層微觀孔隙結(jié)構(gòu)品質(zhì)。大量油氣田生產(chǎn)實(shí)踐表明,低滲透砂巖儲(chǔ)層的儲(chǔ)層品質(zhì)指數(shù)在一定程度上能客觀地反映產(chǎn)層的產(chǎn)能情況。通過繪制研究區(qū)盒8段儲(chǔ)層滲透率、孔隙度以及平均喉道半徑與儲(chǔ)層品質(zhì)指數(shù)(RQI)之間的關(guān)系圖(圖6a、b、c),可以看出,平均喉道半徑與儲(chǔ)層品質(zhì)指數(shù)相關(guān)系數(shù)為0.87(圖6c),高于滲透率、孔隙度與儲(chǔ)層品質(zhì)指數(shù)的相關(guān)系數(shù)0.65、0.27(圖3d)。因此,儲(chǔ)層平均喉道半徑大小能更好地反映儲(chǔ)層品質(zhì)與產(chǎn)能的好壞。
(1)恒速壓汞測試表明,蘇東區(qū)塊盒8段低滲儲(chǔ)層物性主要受喉道控制,而不是孔隙,其中半徑大于0.12μm的喉道對滲透率控制作用顯著,但對孔隙度控制作用一般??缀戆霃奖仍叫?尤其當(dāng)平均喉道半徑小于1.60μm,滲透率小于2.00×10-3μm2時(shí),喉道半徑分布范圍越寬且相對大喉道越多,平均喉道半徑和主流喉道半徑越大且后者一般大于前者,滲透率越大。
圖6 儲(chǔ)層物性與儲(chǔ)層品質(zhì)參數(shù)(RQI)的關(guān)系Fig.6 Relationship between parameters of reservoir property and RQI
(2)蘇東區(qū)塊盒8段典型的致密砂巖儲(chǔ)層微觀孔隙結(jié)構(gòu)主要受半徑大于0.12μm的喉道控制,表現(xiàn)為平均喉道半徑越大,微觀均值系數(shù)越小,相對大喉道越多,排驅(qū)壓力越低,儲(chǔ)層微觀孔隙結(jié)構(gòu)一般越好,反映儲(chǔ)層微觀孔隙結(jié)構(gòu)品質(zhì)越好。
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Characteristics of Micro-Pore Structure of Reservoirs in He 8 Section of Shihezi Formation in the Sudong Block of Ordos Basin
DU Jiang-min1,2,F(xiàn)U Qiang3,LIU Dong-ming3,LIU Xu-hui3
(1.DepartmentofGeology,NorthwestUniversityandStateKeyLaboratoryforContinentalDynamics,Xi’an,Shanxi710069;2.CollegeofResources,ShijiazhuangUniversityofEconomics,ShijiazhuangHebei050031;3.ProductionLoggingCenterofLoggingInvestmentCo.,Ltd.,CNPC,Gaoling,Shannxi710201)
The reservoirs of He 8 section of the Shihezi Formation in the Sudong area of the Ordos basin are characterized by dense sandstone, where complex factors influence the quality of the reservoirs.Based on conventional methods such as casting slice, scanning electron microscope(SEM) and physical property analysis,characteristics of reservoir microscopic pore structure have been qualitatively analyzed, then quantitatively described by constant-rate mercury injection technique. The results show that the quality of reservoirs is mainly controlled by the throat rather than pore. The greater the average throat radius, the smaller the micro average coefficient. When there are more relatively large throats, the expulsion pressure is lower. Consequently microscopic pore structure of reservoirs is better, implying a good quality of microscopic pore structure. Therefore, throats are the primary microscopic geological factor which affects the quality of tight sandstone reservoirs.
Ordos Basin,He 8 section of Shihezi Formation,micro-pore structure of reservoir,constant-rate mercury;throat
2015-07-23;
2016-01-18;[責(zé)任編輯]陳英富。
國家自然科學(xué)基金項(xiàng)目(41302076)與河北省教育廳科研項(xiàng)目(QN2015255)聯(lián)合資助。
杜江民(1984年-),男,講師,博士研究生,主要從事石油地質(zhì)研究。E-mail:jiangmindu@163.com。
TE132.2
A
0495-5331(2016)02-0340-06
Du Jiang-min, Fu Qiang, Liu Dong-ming, Liu Xu-hui. Characteristics of Micro-Pore Structure of Reservoirs in He 8 Section of Shihezi Formation in the Sudong Block of Ordos Basin[J]. Geology and Exploration, 2016, 52(2):0340-0345