Comparison of basic features and origins of oolitic shoal reservoirs between carbonate platform interior and platform margin locations in the Lower Triassic Feixianguan Formation of the Sichuan Basin,southwest China

The oolitic shoal reservoirs of the Lower Triassic Feixianguan Formation carbonates in the Sichuan Basin of southwest China are an important target for gas exploration in the basin.Their occurrence,like other cases worldwide,can be divided into two locations in general,i.e.,platform interior and platform margin locations.Their differences of reservoir features and origins,however,have not been investigated comprehensively due to different exploration degrees.This issue is addressed in this paper,to provide basic data and information for the basin＇s hydrocarbon exploration and for the study of carbonate platform sedimentology and reservoir geology worldwide.We compared the features of these two types of reservoirs in detail,including the depositional and diagenetic features,pore types and petrophysical features.Based on the comparison,the origin of the reservoirs was further discussed.It is shown that the reservoirs in platform interior and platform margin locations differ significantly.The interior carbonates were deposited in moderate to high energy settings and the dominant lithologic type was limestone,which was weakly compacted and intensely cemented and has undergone meteoric dissolution.Pore types include intragranular dissolution and moldic pores,with low porosities（6%） and low permeabilities（0.1 mD）.By contrast,the platform margin carbonates were deposited in relatively high energy settings and mainly consisted of dolostones with some limestones.The rocks were strongly compacted but incompletely cemented.As a result,some primary intergranular pores were preserved.Both meteoric solution and burial solution have taken place.There are various types of pore spaces including intergranular and intercrystalline solution pores and residual intergranular pores.This type of reservoir generally has better petrophysical properties（9% porosity and 0.1 mD permeability） and pore-throat structures than the interior reservoirs.These differences were influenced by both primary depositional features and secondary diagenesis.For the interior carbonate reservoirs,early meteoric dissolution,weak compaction and strong cementation are important controlling factors.By contrast,the factors controlling the formation of the margin carbonate reservoirs mainly include dolomitization,preservation of primary pores and burial dissolution.

Characteristics and genesis of the Feixianguan Formation oolitic shoal reservoir, Puguang gas field, Sichuan Basin, China

The Lower Triassic Feixianguan Formation at the well-known Puguang gasfield in the northeastern Sichuan Basin of southwest China produces a representa- tive oolitic reservoir, which has been the biggest marinesourced gasfield so far in China （discovered in 2003 with proven gas reserves greater than 350× 10^8 m3）. This study combines core, thin section, and scanning electron microscopy observations, and geochemical analysis （C, O, and Sr isotopes） in order to investigate the basic characteristics and formation mechanisms of the reservoir. Observations indicate that platform margin oolitic dolomites are the most important reservoir rocks. Porosity is dominated by intergranular and intragranular solution, and moldic pore. The dolomites are characterized by medium porosity and permeability, averaging at approximately 9% and 29.7 mD, respectively. ^87Sr/^86Sr （0.707536-0.707934） and δ^13CpDB （1.8 ‰--3.5 ‰） isotopic values indicate that the dolomitization fluid is predominantly concentrated seawater by evaporation, and the main mechanism for the oolitic dolomite formation is seepage reflux at an early stage of eodiagenesis. Both sedimentation and diagenesis （e.g., dolomitization and dissolution） have led to the formation of high-quality rocks to different degrees. Dolomite formation may have little contribution, karst may have had both positive and negative influences, and burial dissolution-TSR （thermochemical sulfate reduction） may not impact widely. The preservation of primary intergranular pores and dissolution by meteoric or mixed waters at the early stage of eogenesis are the main influences. This study may assist oil and gas explorationactivities in the Puguang area and in other areas withdolomitic reservoirs.

Digitized Outcrop Geomodeling of Ramp Shoals and its Reservoirs： as an Example of Lower Triassic Feixianguan Formation of Eastern Sichuan Basin

Numerous hydrocarbon accumulations are found in ramp crest shoals worldwide and therefore this depositional setting has a high potential of being the hydrocarbon reservoir. In this paper, we combined digital outcrop geology and traditional geological mapping to build an outcrop-based geocellular model of the ramp-crest shoal complex of the Lower Triassic Feixianguan Formation in the Eastern Sichuan Basin. The outcrop model serves as an analogue for the subsurface reservoir of the Feixianguan Formation and illustrates the complexity of the lithofacies types, stratigraphic architecture, and reservoir heterogeneities at a scale below conventional subsurface data resolution. The studied ramp -crest shoal complex consists of thirteen types of lithofacies that can be grouped into three facies-groups corresponding to subtidal intraclastic shoal, sub- to inter-tidal oolitic shoal, and tidal flat depositional environments respectively. The stratigraphic architecture of the shoal complex shows mostly a strong progradation of the high energy facies associated with an overall decrease of accommodation space associated with relative sea level still stand. Two reservoir facies associations have been recognized. The first one consists of supratidai dolomudstone and upper intertidal partially dolomitized oolitic packstone with anhydrite or nodules. These facies were deposited above the high energy oolitic grainstones and occurs as thin-bedded and laterally continuous layers, characterized by high porosity and low permeability. The second reservoir facies association is composed of intertidal crystalline dolomite and subtidal intraclastic bindstone that occurs stratigraphically below the oolitic grainstones. These deposits consist of massive laterally discontinuously beds, and are characterized by high porosity and high permeability. Both types of reservoir facies tend to be stacked vertically and migrated laterally with the progradation of the shoal complex. The construction of the outcrop-based 3D geological model provide a description and quantification of the facies distribution within a robust stratigraphic framework and the style and amount of reservoir heterogeneities associated with a ramp-crest shoal complex reservoir such as the one found in Lower Triassic Feixianguan Formation and Cambrian Longwangmiao Formation in Sichuan Basin or other ramp-crest reservoir worldwide.

Primary Intergranular Pores in Oolitic Shoal Reservoir of Lower Triassic Feixianguan Formation,Sichuan Basin,Southwest China:Fundamental for Reservoir Formation and Retention Diagenesis

The Lower Triassic Feixianguan （飞仙关） Formation oolitic shoal reservoir in the Sichuan （四川） basin （Southwest China） is currently an exploration and research highlight in China. The reservoir is widely believed to be formed mainly by burial dissolution and/or dolomitization on the basis of primary intergranular pores. In this study, through a comprehensive geological study on the whole basin, the dissolution and dolomitization are suggested not to be the fundamental factor of reservoir formation and there thus may be a possible new fundamental mechanism-the preservation of primary intergranular pores, i.e., the retention diagenesis. Based on this, a complex and multi-stage reservoir evolution and formation model is proposed. In the model, the depositional environment is the basis of reservoir initial formation. Subsequently, early compaction and shallow burial cementation result in the primary reservoir differentiation. Then, multi-stage burial dissolution alters and adjusts the reservoir. Because the last stage gaseous hydrocarbons have little diagenetic impact, the reservoir is formed finally. Therefore, this study presents a possible new fundamental mechanism and evolution model for the reservoir formation. The results can be applied in the regional reservoir predication and shaping exploration strategies, and provide reference for the study of shoal reservoirs in other areas.

Sedimentary diagenesis of rudist shoal and its control on reservoirs: A case study of Cretaceous Mishrif Formation, H Oilfield, Iraq

Based on the core, cast thin section, whole rock analysis, conventional physical properties and high pressure mercury intrusion test, the sedimentary diagenesis characteristics of rudist shoal in Cretaceous Mishrif Formation of H Oilfield, Iraq and its control on the reservoir were studied. The rudist shoal of the Mishrif Formation develops in the high-stand systems tract and is distributed in the high places of paleogeomorphology on the edge of platform with strong hydrodynamic force. According to the relative sea level changes, lithologic evolution and sedimentary structure characteristics of the rudist shoal, the single rudist shoal is divided into four lithologic sections: A, B, C and D, that is, low-angle cross-bedding pelletoids-rudist packstone, low-angle cross-bedding and parallel bedding arene-rudist grainstone, parallel bedding rudist gravel limestone, and horizontal bedding carbonaceous mudstone. The complete sedimentary sequence of a single rudist shoal is often disrupted. Several rudist shoals superimpose to form thick rudist shoal sediment. The single rudist shoal thickness and lithologic sections assemblage change regularly in vertical direction. The rudist shoal has the characteristics of "strong dissolution, weak cementation and strong compaction", forming pore-type reservoir with intergranular pores, intergranular dissolved pores, mold pores, and dissolved pores. With mainly coarse pore throats larger than 5 μm, the reservoir is of medium-high porosity and high permeability. There is lithological reverse cycles inside single shoals and between single shoals, with content of mud crystals decreasing from the bottom to the top, dissolution increasing, cementation decreasing in strength, pore throats getting larger, and physical properties turning better. The rudist shoal of MB2-1 at the top of the high-stand systems tract has the largest thickness, moreover, subject to the strongest atmospheric freshwater leaching, this layer has the most significant dissolution and the largest pore throat, so it is the best reservoir of the Mishrif Formation.

四川盆地东部地区二叠系茅口组孤立浅滩的发现及天然气勘探潜力

中二叠统茅口组长期以来一直是四川盆地天然气勘探的重点层系之一,茅口组天然气勘探开发先后以四川盆地南部地区岩溶缝洞型石灰岩储层和四川盆地中部地区滩相白云化储层为主要目的层系。为了寻找并落实茅口组下一个天然气勘探方向,在勘探程度相对较低的四川盆地东部(以下简称川东)地区开展了大量基础研究工作,在重新梳理地层格架的基础上,对茅口组沉积、储层及成藏条件进行了系统分析,指出了该区孤峰段硅质岩下茅二下亚段孤立浅滩的存在,最后明确了茅口组天然气的勘探潜力。研究结果表明:(1)川东地区在茅口组孤峰段事件性硅质岩沉积之前,宣汉—万州地区茅二下亚段发育碳酸盐岩孤立浅滩,面积可达6500 km^(2);(2)在宣汉—万州地区茅二下亚段发现了滩相基质孔储层,其中发育于茅二下亚段底部的孔隙型白云岩储层厚3~12 m,发育于茅二下亚段中上部的孔隙型石灰岩储层厚5~18 m;(3)川东地区茅口组滩相储层成藏条件优越,其中烃源岩主要为下伏上奥陶统五峰组—下志留统龙马溪组厚层页岩,且与烃源岩沟通的断裂发育,区域盖层主要为孤峰段硅质岩及吴家坪组海相泥岩、页岩,保存条件良好。结论认为,川东地区茅口组孤立浅滩的发现和良好的成藏组合条件,将进一步加快该区天然气勘探开发进程,茅口组大面积分布的高能浅滩有望成为下一个天然气勘探开发重要领域。

鄂尔多斯盆地东北部奥陶系马四段白云岩储层特征及主控因素

米探1井等多口探井在鄂尔多斯盆地东北部奥陶系马四段白云岩中获得高产天然气流,展示出该区域马四段具有良好的勘探前景。然而对盆地东北部马四段是否发育规模白云岩储层还存在争议,白云岩储层分布不清制约了下一步勘探部署。基于岩心、薄片、场发射扫描电镜及地球化学特征等资料,对盆地东北部奥陶系马四段白云岩储层特征及其发育控制因素开展了系统研究,并预测了盆地东北部奥陶系马四段白云岩储层分布。研究结果表明:(1)盆地东北部奥陶系马四段白云岩发育潮坪型白云岩储层、丘滩型白云岩储层和生物扰动型白云岩储层,3类白云岩储层储集空间主要为晶间孔,含少量微裂缝,平均孔隙度分别为4.77%、5.12%和2.52%。(2)白云岩储层的形成与丘滩体、生物扰动作用和白云石化作用相关。白云石化作用是潮坪型白云岩储层晶间孔形成的关键,丘滩体和白云石化作用控制了丘滩型白云岩储层发育,生物扰动作用和白云石化作用控制了生物扰动型白云岩储层发育。(3)盆地东北部神木—靖边地区在奥陶纪马四期位于低隆起带上,有利于丘滩体发育和生物扰动作用、白云石化作用的发生,形成的白云岩储层可为天然气富集提供规模储集空间。

川中古隆起北斜坡寒武系龙王庙组油气成藏特征及演化模式

利用测井、录井、岩心分析化验等资料,对川中古隆起北斜坡下寒武统龙王庙组油气成藏条件、油气充注特征及成藏演化模式展开了深入研究。研究结果表明:(1)川中古隆起北斜坡下寒武统龙王庙组天然气具备良好的成藏条件,下伏筇竹寺组烃源岩在北斜坡腹部及西侧裂陷槽存在2个生烃中心,其TOC平均值分别为1.90%和3.46%,有机质以Ⅰ型干酪根为主,可提供充足且优质的烃源;龙王庙组内部发育的颗粒滩体岩溶储层与上覆高台组厚层致密泥质云岩,构成了优势储-盖组合;区内广泛发育的油源断裂可作为纵向优势运移通道高效输导油气。(2)研究区龙王庙组具3期成藏特征:晚三叠世末期(约214~206 Ma)发生第1期充注,大量成熟油聚集形成古油藏;早侏罗世末期(约193~186 Ma)发生第2期充注,表现为“多油少气”混合充注;中侏罗世末期(约170~164 Ma)发生第3期充注,大量油裂解气充注储层并聚集形成现今气藏。(3)研究区龙王庙组油气成藏演化可划分为4个阶段:加里东早期—二叠纪前少量低熟油充注阶段、二叠纪—三叠纪大量成熟油充注形成古油藏阶段、中侏罗世—白垩纪古油藏被破坏形成裂解气藏阶段以及晚白垩世至今气藏调整阶段。

四川盆地蓬溪-武胜台凹西侧长兴组成藏主控因素

蓬溪-武胜台凹为开江-梁平海槽同期构造产物,其两侧的油气勘探一直未取得较大突破,成藏特征认识也不够清晰。文中在系统梳理烃源岩、储层、构造等成藏条件基础上,结合最新钻探成果,开展了成藏主控因素研究。结果表明,长兴组成藏具有3个基本条件,即多套优质烃源岩的发育,规模发育的礁滩储层,通源断层提供的油气垂向进入长兴组的通道。长兴组油气富集规律取决于2个要素:1)源储匹配。源储匹配不佳决定了长兴组未能大规模成藏,多套烃源岩中仅筇竹寺组在生、排烃期上与断层活动期的匹配较好,其余烃源岩对长兴组供烃有限;由于延伸至长兴组的断层较少,源储间有效通道缺乏又进一步导致了气源不足。2)生物礁滩储层发育状况。生物礁滩储层的连续发育促成了垂侧向复合输导体系的形成,在此基础上有限的烃类会逐步向斜坡高部位运移聚集,气水分布受构造影响较大,非“一礁一藏”。据此研究结果,优选了4个勘探有利区。

印模法古地貌恢复在岩溶丘滩相有利区评价中的应用:以川中古隆起北斜坡灯影组二段为例

四川盆地寒武系-震旦系裂陷槽东侧川中古隆起北斜坡灯影组二段岩溶丘滩相储层非均质性强,主控因素复杂,成为制约北斜坡地区下一步天然气勘探目标优选的关键因素。利用三维连片地震数据,基于最新探井钻井、测井等资料,创新思路,提出用灯影组沉积后期的岩溶地貌来刻画滩相储层有利区,把上覆地层沧浪铺底作为基准层,采用印模法进行微幅古地貌分析,刻画了灯二岩溶期地貌特征。在此基础上,精细研究了储层的地震响应特征,建立了地震相分类模式,利用波形分类方法进行岩溶丘滩相储层发育有利区预测。成果揭示灯二段岩溶丘滩相储层发育规律呈与侵蚀槽展布方向相同的北西-南东向展布,与实际钻井和地质认识一致。相较之常规用的残厚法,该方法更加考虑了沉积特征和地质规律,减少了地震预测的多解性,且可达到半定量预测效果,为古隆起北斜坡单斜构造背景下研究岩溶滩相储层有利区提供了有利指导。

四川盆地PS8井区灯影组四段丘滩体储层特征及成因机制

四川盆地震旦系灯影组四段是近期的重点勘探层位,PS8井灯影组四段试气获得高产,展示出灯影组四段天然气勘探的巨大潜力。基于钻井岩心、岩屑、薄片、分析化验和测井等资料,对PS8井区灯四段丘滩体储层特征及成因机制开展研究。结果表明:①PS8井区灯影组四段从裂陷槽向台内具有逐渐增厚的趋势,储集层岩性主要为藻凝块白云岩、藻叠层白云岩、砂屑白云岩;储集空间以溶蚀孔洞及裂缝为主,柱塞样孔隙度为0.86%~6.59%,平均3.58%,渗透率为0.00085~14.75mD,平均1.71mD,全直径孔隙度为1.15%~8.42%,平均3.84%,渗透率为0.003~16.8mD,平均2.16mD,属于低孔低渗型储层;②台缘带发育的微生物丘滩沉积是PS8井区灯影组四段优质储层发育的物质基础,表生期风化壳岩溶和埋藏期热液溶蚀作用是PS8井区灯影组四段储层大量溶蚀孔洞发育的关键因素。研究成果落实了研究区灯影组四段丘滩体储层特征,并明确了储层的成因机制,为后期储层发育分布预测提供了理论支撑,同时为评价方案的部署提供了地质依据。

川中-蜀南地区茅口组岩溶储层油气成藏条件与有利区带预测

四川盆地茅口组早期勘探一直聚焦蜀南和川东高陡构造带及裂缝发育区,近年来老井复查揭示川中-蜀南地区非构造高部位,特别是斜坡-向斜区的油气显示活跃,但是斜坡-向斜区油气储层分布及发育模式认识不清,区域茅口组岩溶储层油气勘探部署方向不明确。利用岩心观察、CT成像、测井解释、地震预测等方法,针对川中-蜀南地区茅口组岩溶储层开展攻关。结果表明:茅口组发育2套颗粒滩体,下部茅二段b亚段颗粒滩发育一种受水平潜流带控制的岩溶储层新类型,即孔隙-孔洞型,与茅口组上部茅二段a亚段至茅三段颗粒滩发育的裂缝-孔洞型岩溶储层一起,构成了川中-蜀南地区茅口组的有效岩溶储层;茅口组岩溶储层经历了3期油气充注过程,具有“现今背斜构造区早期规模富集、晚期差异调整,斜坡-向斜区原位保存”大面积成藏的特点;结合关键成藏期古地貌、颗粒滩体和现今构造,最终优选威远—古蔺一带附近茅口组2个有利勘探区带,同时建议油气勘探目标可从传统的仅为上部的裂缝-孔洞型岩溶储层类型拓展到上下2套储层兼顾,特别是不发育断裂且构造稳定的向斜区,新发现的孔隙-孔洞型碳酸盐岩储层是茅口组油气勘探的新领域,本研究可为四川盆地茅口组油气勘探提供新的思路。

Sedimentary Facies and Distribution of Reservoir Rocks from the Feixianguan Formation in the Daxian-Xuanhan Region, NE Sichuan

The Lower Triassic Feixianguan Formation in the Daxian-Xuanhan region, northeastern Sicbuan is interpreted to be a carbonate platform intermediate between the West Hubei-East Cbongqing marine basin and Guangyuan-Wangcang marine basin. Outcrops, well logs and seismic data have disclosed that three sedimentary facies can be identified for the formation： open platform, platform exposed shoal and restricted platform facies. During the early stage of deposition of the Feixianguan Formation, there existed a sedimentary framework all the same as the Late Permian one： open platform in the west, and platform exposed shoal, restricted platform and open platform eastwards. The gradual increase of the shoal area permitted eastward migration of the shoal facies. During the deposition of the third member of the Feixianguan Formation, the study area was invaded by temporary transgressions. Till the deposition of the fourth member of the formation, the study area was prevailed over the unified restricted platform deposits, as indicated by the sedimentary model for the typical carbonate platform shoal deposits. The reservoir rocks in the Feixianguan Formation consist mostly of solution opening dolostone, and the rock types are assembled by oolitic dolostone, residual oolitic dolostone and sucrosic residual oolitic medium- to coarse-grained dolostone. The deep and shallow dual laterologs show relatively high resistivity, clear amplitude differences and time difference saltation of acoustic waves in some intervals. The seismic responses are indicated by low-frequency and highly variable amplitudes and chaotic reflection configurations. The reservoir rocks are characterized by high porosity-high permeability and medium porosity-medium permeability, showing a marked correlation between porosity and permeability. Solution openings are extremely developed in the reservoir rocks, including cast pores, intergranular solution openings, intercrystal pores, intercrystal solution openings, solution openings （caves） and minute fissures. Macropores and coarse pore throats are common. The reservoir rocks are apparently controlled by sedimentary facies in distribution patterns. Vertically, they occur dominantly in the second and first members of the Feixianguan Formation, and laterally in the platform exposed shoals and restricted platforms, where good natural gas potential is expected.

普光地区飞仙关组颗粒滩储层发育分布规律及控制因素

四川盆地二叠系—三叠系白云岩储层广泛发育,发现了普光、元坝、罗家寨等一系列大中型气田,但深层海相碳酸盐岩储层的规模和非均质性却成为限制深层油气藏勘探开发的关键因素之一。综合普光地区飞仙关组钻测井、岩心、岩石薄片、碳氧同位素等资料的研究发现:飞仙关组储层岩石类型主要为(残余)鲕粒白云岩、晶粒白云岩;储集空间类型主要为粒内溶孔、粒间(溶)孔、晶间(溶)孔、溶洞。其中,粒内溶孔平面上主要发育在古地貌高地,垂向上发育于旋回上部。飞仙关组优质储层形成与保存受控于高能鲕粒滩沉积、溶蚀作用、白云岩化作用和较好的保存条件。飞仙关组储层的非均质性主要与颗粒滩原始沉积和后期成岩有关,古地貌和海平面升降控制了储层平面和垂向的非均质性,古地貌较高区域以厚层高能鲕粒滩沉积为主,遭受较强的准同生溶蚀和白云岩化作用,具备较强的孔隙保存能力,现为优质储层。该研究进一步落实优质储层的分布,丰富普光气田滩相储层非均质性方面的研究成果,对相似碳酸盐岩储层的研究提供借鉴。

Reservoir characteristics and genetic differences between the second and fourth members of Sinian Dengying Formation in northern Sichuan Basin and its surrounding areas

This study investigated the characteristics and genesis of reservoirs in the 2^(nd) and 4^(th) members of Sinian Dengying Formation in northern Sichuan and its surrounding areas, on the basis of outcrop, drilling cores and thin section observation and geochemical analysis. The reservoirs of 2^(nd) member are distributed in the middle part of the stratum. The reservoir quality is controlled by supergene karst and the distribution of mound-shoal complex. The bedded elongated isolated algal framework solution-cave and the residual "grape-lace" cave, which are partially filled with multi-stage dolosparite, constituted the main reservoir space of the 2^(nd) member. There is no asphalt distribution in the pores. The pore connectivity is poor, and the porosity and permeability of the reservoir is relatively low. The reservoirs of 4^(th) member were distributed in the upper and top part of the stratum. The reservoir quality is controlled by burial dissolution and the distribution of mound-shoal complex. The bedded algal framework solution-pores or caves, intercrystalline pores and intercrystalline dissolved pores constituted the main reservoir space of the 4^(th) member. It's partially filled with asphalt and quartz, without any dolosparite fillings in the pores and caves. The pore connectivity is good. Most of the 4^(th) member reservoirs had medium-low porosity and low permeability, and, locally, medium-high porosity and medium permeability. Affected by the development of mound-shoal complex and heterogeneous dissolution, the platform margin along Ningqiang, Guangyuan, Jiange and Langzhong is the most favorable region for reservoir development. Deep buried Dengying Formation in the guangyuan and langzhong areas should be the most important hydrocarbon target for the future exploration.

川东地区三叠系嘉陵江组邻水-丰都台凹的发现及油气勘探意义

地质历史时期的构造-沉积分异作用对大型含油气盆地内碳酸盐岩层系的沉积充填过程及成藏地质条件具有重要影响。通过覆盖全区的二维地震及钻测井资料,对川东地区三叠系嘉陵江组沉积时期隆凹格局及古地理演化进行了精细刻画。研究结果表明:(1)从地震剖面、地层及岩性组合等特征上识别出邻水-丰都台凹,其两侧坡度为1°~2°,且左侧坡度大于右侧坡度;(2)邻水-丰都台凹与其他古地质单元共同控制了嘉二段沉积时期川东地区的古地理格局及构造-沉积分异特征,嘉二段沉积早—中期,颗粒滩沿邻水-丰都台凹周缘发育,晚期台凹内则大面积发育膏质潟湖沉积;(3)邻水-丰都台凹及周缘微古地貌控制沉积早期颗粒滩分布,台凹周缘地貌高部位更易形成优质白云岩储层,持续干旱、蒸发环境致使沉积晚期台凹内形成区域盖层沉积;(4)总体来看,嘉二段具备良好的成藏地质条件,有望成为寻找滩相整装气藏的战略勘探层系,建议将邻水-丰都台凹周缘台内滩相发育带作为川东地区嘉陵江组下步勘探重点区之一。

川中龙女寺构造栖霞组薄储层预测地质模型

近年来,川中地区多口井在栖霞组钻获高产工业气流,展现出该层系巨大的勘探潜力,但较之川西北台缘带,位于台内的龙女寺地区栖霞组碳酸盐岩滩体规模小,储层厚度薄,远低于地震纵向分辨率,一直未取得较好的储层预测效果,严重制约着广大台内地区的油气勘探开发。为此,针对台内地区薄储层预测难点,综合利用岩芯、薄片、测井及地震等资料,以地质地球物理紧密结合的思路,对川中龙女寺地区栖霞组储层控制因素及预测地质模型进行研究,研究结果表明,该区域栖霞组储层主要为滩相白云岩储层,储集岩以晶粒云岩、云质灰岩为主,主要储集空间为晶间(溶)孔、溶洞,可见少量裂缝。控制栖霞组相对优质储层形成的主要因素为栖霞期古地貌位置、沉积微相及断裂发育情况,据此建立了“栖霞期古地貌高地+滩核和滩缘微相区+断裂发育区”的龙女寺栖霞组薄储层预测地质模型,并在此基础之上优选出储层发育有利区,为栖霞组台内地区油气勘探部署优选有利区带提供理论支撑。

四川盆地东北部飞仙关组台缘早期鲕滩带的发现及宣探1井天然气勘探突破意义

四川盆地东北部(以下简称川东北地区)下三叠统飞仙关组是四川盆地高含硫天然气勘探开发的重要层系之一,已在飞一段上部—飞二段取得了重要的勘探开发系列成果。为了进一步扩大该地区的天然气勘探开发局面,寻找新的有利勘探区带及油气富集区,通过对该区地震资料“双高”处理解释,结合490余口老井复查,开展了飞一段台缘早期鲕滩发育特征研究,预测了台缘早期鲕滩的分布规律,并结合宣探1井的钻探成果,分析了台缘早期鲕滩储层发育特征及高含硫天然气勘探潜力。研究结果表明:①研究区飞仙关组划分5个四级层序,台缘早期鲕滩发育于SSQ1—SSQ2层序,分布于渡口河—七里北地区,岩性主要为亮晶鲕粒石灰岩和残余鲕粒白云岩,具有礁滩叠置和鲕滩向台内不断迁移的特征;②台缘早期鲕滩储层分布于老君庙地区以东、渡口河地区以及渡口河—七里北之间的向斜区,储层平均厚度超过100 m;③宣探1井飞仙关组台缘早期鲕滩储层类型以Ⅱ和Ⅲ类为主,局部见Ⅰ类储层,总体为含气层和气层,为岩性气藏,试油效果良好。结论认为,宣探1井成功钻遇礁滩储层,证实飞仙关组发育台缘早期鲕滩带,这对于重新认识开江—梁平海槽两侧台缘礁滩勘探领域具有重大战略意义,开辟了川东北地区天然气勘探新领域,且预示该区仍具有非常好的天然气勘探潜力,同时也为克拉通边缘或内部海槽(台洼)两侧类似地区礁滩油气勘探开发提供了思路。