Sedimentary architecture and distribution of intra-platform shoal in sequence framework of Permian Changxing Formation in central Sichuan Basin,SW China

Based on the comprehensive analysis of core, thin section, logging and seismic data, this study carried out the identification and comparison of Permian Changxing Formation sequences, clarified the typical sedimentary architectures of intra-platform shoal, investigated the vertical and horizontal development and distribution of intra-platform shoal in each sequence, and thus established the sedimentary evolution model of shoal body. The study results are reflected in four aspects.First, there are two complete third-order sequences(SQ1 and SQ2) in Changxing Formation in central Sichuan Basin. SQ1 is generally thick in the north and thin in the south, and SQ2 shows a thickness differentiation trend of “two thicknesses and three thinnesses”. Second, the Changxing Formation in central Sichuan Basin mainly develops intra-platform shoal, inter-shoal sea and intra-platform depression subfacies. In the vertical direction, the intra-platform shoal mainly presents two typical sedimentary sequences: stable superposed and high-frequency interbedded. Third, the stable superimposed sedimentary sequence is developed in the shoal belt at the edge of intra-platform depression, which is composed of two shoal-forming periods and located in the highstand systems tracts(HSTs) of SQ1 and SQ2. The high-frequency interbedded sedimentary sequence is developed in the southern shoal belt of intra-platform depression, which is composed of four shoal-forming periods and mainly located in the HST of SQ2. Fourth, during the SQ1 deposition, the intra-platform shoal was mainly developed at the edge of the intra-platform depression on the north side of the study area, and the inter-shoal sea subfacies was mainly developed on the south side. During the SQ2 deposition, the intra-platform shoal was widely developed in the area, forming two nearly parallel intra-platform shoal belts. The study results provide direction and ideas for exploration of Changxing Formation intra-platform shoal reservoirs in central Sichuan Basin.

Natural gas characteristics and gas-source comparisons of the Lower Triassic Feixianguan Formation,Eastern Sichuan Basin,China

There is great controversy regarding the origin and source of natural gas in the Lower Triassic Feix-ianguan Formation in the Eastern Sichuan Basin.This seriously restricts the study of natural gas dy-namics in the Feixianguan Formation and thus hampers natural gas exploration in the region,so further study is urgently required.Using experimental tests of natural gas composition,stable isotopes,and noble gas isotopes with gas chromatography(GC)and mass spectrometry(MS)studies of source rock and reservoir asphalt saturated hydrocarbons,the natural gas geochemical characteristics,the genetic identification and a gas-source comparison of the Feixianguan Formation were studied.Then,con-strained by the thermal history,the histories of gas generation and expulsion were restored by basin simulation technology.Finally,a gas accumulation model was established for the Feixianguan Formation.The results showed that(1)the H_(2)S-rich and H2S-poor gas reservoirs of the Feixianguan Formation are distributed on the east and west sides of the Kaijiang-Liangping trough in the Eastern Sichuan Basin,respectively.The carbon and hydrogen isotope compositions of the natural gas in the gas reservoirs are generally heavy and have typical characteristics of high-maturity dry gas reservoirs.(2)The natural gas of the Feixianguan Formation is organic thermogenic gas,which is mainly oil-type gas generated by the secondary cracking of crude oil.The gas-generating parent material is mainly type II kerogen.(3)The natural gas of the Feixianguan Formation in the Eastern Sichuan Basin was mainly generated by argil-laceous source rocks of the Upper Permian Longtan Formation.(4)Natural gas accumulation occurred as follows:the paleo-structure heights were filled with crude oil in the Early Jurassic,and paleo-oil res-ervoirs were formed in the Feixianguan Formation;during the Middle-Late Jurassic,the paleo-oil res-ervoirs were cracked when the reservoir temperatures rose above 160 C,and paleo-gas reservoirs were formed.Since the end of the Late Jurassic,the paleo-gas reservoirs have been adjusted and reformed to form the present-day natural gas reservoirs.These results provide a basis for studying natural gas accumulation dynamics of the Feixianguan Formation in the Eastern Sichuan Basin.

Characteristics,classification and KNN-based evaluation of paleokarst carbonate reservoirs:A case study of Feixianguan Formation in northeastern Sichuan Basin,China

The Feixianguan Formation reservoirs in northeastern Sichuan are mainly a suite of carbonate platform deposits.The reservoir types are diverse with high heterogeneity and complex genetic mechanisms.Pores,vugs and fractures of different genetic mechanisms and scales are often developed in association,and it is difficult to classify reservoir types merely based on static data such as outcrop observation,and cores and logging data.In the study,the reservoirs in the Feixianguan Formation are grouped into five types by combining dynamic and static data,that is,karst breccia-residual vuggy type,solution-enhanced vuggy type,fractured-vuggy type,fractured type and matrix type(non-reservoir).Based on conventional logging data,core data and formation microscanner image(FMI)data of the Qilibei block,northeastern Sichuan Basin,the reservoirs are classified in accordance with fracture-vug matching relationship.Based on the principle of cluster analysis,K-Nearest Neighbor(KNN)classification templates are established,and the applicability of the model is verified by using the reservoir data from wells uninvolved in modeling.Following the analysis of the results of reservoir type discrimination and the production of corresponding reservoir intervals,the contributions of various reservoir types to production are evaluated and the reliability of reservoir type classification is verified.The results show that the solution-enhanced vuggy type is of high-quality sweet spot reservoir in the study area with good physical property and high gas production,followed by the fractured-vuggy type,and the fractured and karst breccia-residual vuggy types are the least promising.

Formation Mechanism of the Changxing Formation Gas Reservoir in the Yuanba Gas Field,Sichuan Basin,China

In a very gentle platform-margin paleogeographic environment, platform-margin reef flat facies carbonate reservoir rocks were developed in the Changxing Formation of Yuanba field. Later weak structural evolution and diagenetic evolution caused the Changxing Formation to form lithologic traps, with good reservoirs such as dissolved bioclastic dolostone and dissolved pore dolostone. The Changxing Formation gas reservoir is a pseudo-layered porous lithologic gas reservoir under pressure depletion drive, with high H2S and moderate CO2 contents. This paper predictes that the conducting system for the Changxing Formation gas reservoir is possibly composed of the pores and microfractures in the Changxing Formation reservoir, the top erosional surface of the Changxing Formation, as well as the micropores and microfractures in the underlying formations. The Changxing Formation reservoir has experienced 3 hydrocarbon charging stages. This paper suggests that diffusion is the major formation mechanism for this gas reservoir. In the Middle and Late Yanshanian, the Yuanba area entered the major gas charging stage. The gas migrated mainly through diffusion and with the assistance of seepage flow in small faults and microfractures from the source rocks and the other oil-bearing strata to the Changxing Formation carbonate reservoir rocks, forming lithologic gas pools. In the Himalayan Epoch, the lithologic traps were uplifted as a whole without strong modification or overlapping, and were favorable for gas preservation.

Geochemical characteristics and diagenetic systems of dolomite reservoirs of the Changxing Formation in the eastern Sichuan Basin, China

In order to discuss the relationship between dolomite reservoirs and diagenetic systems of the Changxing Formation, we studied carbon, oxygen and strontium stable isotopes, iron, manganese and strontium trace elements and the Mg/Ca （mol%） ratio, dolomite order degree, and determined that burial dolomitization is the key to controlling the distribution of high quality dolomite reservoir in the Changxing Formation in the eastern Sichuan Basin. The dolomite of the Changxing Formation is divided into four diagenetic systems： （1） penecontemporaneous stage syngenetic brine diagenetic system, （2） early diagenetic stage strata seal brine diagenetic system, （3） middle-late diagenetic stage mixed hot brine diagenetic system and （4） tectonic uplift stage mixed hydrothermal fluid diagenetic system. New understanding of the controlling factors and distribution of dolomite reservoir development is discussed. Reef shoal facies belts controlled regional reservoir distribution and the scale of development. Burial dolomitization of a strata seal brine diagenetic system is the foundation of reservoir development, mainly developing pore reservoir. Burial dolomitization of mixed hot brine diagenetic system expanded the reservoir distribution and improved the reservoir quality, mainly developing pore-vug reservoir. Fracturing and dissolution of a mixed hydrothermal fluid diagenetic system is the key to improving the reservoir quality, mainly developing pore-vug-crack complex reservoirs.

Geochemical characteristics of the Permian Changxing Formation reef dolomites,northeastern Sichuan Basin,China

The recent discovery of deep and ultra-deep gas reservoirs in the Permian Changxing Formation reefs, northeastern Sichuan Basin is a significant development in marine carbonate oil ＆ gas exploration in China. Reef dolomites and their origins have been major research topics for sedimentologists and oil ＆ gas geologists. The petrography, trace element and isotope geochemistry of the reef dolomites indicated that the dolomites are characterized by low Sr and Mn contents, relatively low Fe contents, very similar δ13C and 6180 values and very different 87Sr/86Sr ratios. Although the calculated results of the fluid mixing suggested that a mixture with 85%-95% meteoric water and 50/o- 15% seawater seemed to be the dolomitizing fluids of the reef dolomites, the low Mn contents, relatively low Fe contents, high δ13c values and high homogenization temperatures of the dolomites did not support that there were large proportions of meteoric water in the dolomitization process, and the 87Sr/86Sr ratios which were close to coeval seawater also did not support the possibility of the mixture of deep-burial circulated fluids from clastic rocks. High temperature deep-burial circulated seawater with low Mn and Fe contents, high Sr content and high δ13C values from the dissolution of widely distributed Triassic evaporites during the burial diagenetic processes （including dehydration of water-bearing evaporites） could have been the dolomitizing fluids of the reef dolomites.

Prestack inversion identification of organic reef gas reservoirs of Permian Changxing Formation in Damaoping area, Sichuan Basin, SW China

Organic reef reservoirs in the platform margin of Kaijiang-Liangping trough in Damaoping area, Sichuan Basin are thin in single layer, fast in lateral variation, and have small P-impedance difference from the surrounding rock, it is difficult to identify and predict the reservoirs and fluid properties by conventional post-stack inversion. Through correlation analysis of core test data and logging P-S wave velocity, this work proposed a formula to calculate the shear wave velocity in different porosity ranges, and solved the issue that some wells in the study area have no S-wave data. AVO forward analysis reveals that formation porosity is the main factor affecting the variation of AVO type, the change of water saturation cannot affect the AVO type, but it has an effect on the change range of AVO. Through cross-plotting analysis of elastic parameters, it is found that fluid factor is a parameter sensitive to gas-bearing property of organic reef reservoir in the study area. By comparing results of post-stack impedance inversion, post-stack high frequency attenuation property, pre-stack simultaneous inversion and AVO anomaly analysis of angle gathers, it is found that the gas-bearing prediction of organic reef reservoirs by using fluid factor derived from simultaneous pre-stack inversion had the highest coincidence rate with actual drilling data. At last, according to the characteristics of fluid factor distribution, the favorable gas-bearing area of the organic reef reservoir in Changxing Formation was predicted, and the organic reef trap at the top of Changxing Formation in Block A of Damaoping area was sorted out as the next exploration target.

The Geochemical Characteristics of Stable Carbon and Oxygen Isotope and Analysis of Diagenetic Environment --A Case Study of Upper Permian Changxing Formation Dolostone in Northeast of Sichuan

四川盆地东北部上二叠统长兴组白云岩为重要的优质储层,近年来,长兴组白云岩成岩环境或成因问题成为研究者讨论的热点话题。在岩石学研究的基础上,运用稳定碳、氧同位素,对研究区长兴组白云岩进行综合研究表明,白云石化具有多期次的特点,按照成岩环境划分为蒸发环境下的准同生白云岩和埋藏条件下的早、中、晚期成岩白云岩。并划分为早、中、晚成岩阶段,结合碳、氧同位素分析结果进一步表明晚成岩阶段白云岩是构造热液白云石化的结果。

Reservoir Prediction Restricted by Sequence Stratigraphy--A Case Study of Bioclastic Shoal Reservoir in Changxing Formation of Jiannan Area

Bioclastic shoal reservoir in Changxing Formation of Jiannan area is characterized by small thickness and strong heterogeneity. The uncertainty of the reservoir distribution pattern has confined the effective development of this area, so the accurate bioclastic shoal reservoir prediction would be the key to achieve development breakthroughs. Based on drilling, well-log, seismic and core analysis data, this article conducted exquisite sequence stratigraphic classification and established isochronal regional stratigraphic framework of Changxing Formation in Jiannan area. The reservoir seismic corresponding features were determined by exquisite calibrating bioclastic shoal reservoir in Changxing Formation. Therefore, seismic processing methods, such as multiple attribute analysis and amplitude inversion, were applied to attain more reliable reservoir prediction results, which indicated the distribution of vertical reservoir in SSQ2, the IV sequence order and the distribution of horizontal reservoir around Well J43 and JZ1 in the platform margin of the study area.

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.

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.

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.

Formation mechanism of reservoir oolitic dolomite in Lower Triassic Feixianguan formation, northeastern Sichuan Basin, southwest China

A series of marine natural gas fields were recently discovered in oolitic dolomites of the Lower Triassic Feixianguan formation, northeastern Sichuan Basin, southwest China. The mechanism forming these reservoir dolomites is debatable, limiting the ability to characterize these reservoir successfully. Based on the investigation of the representative Dukouhe, Luojiazhai, and Puguang areas, this issue was addressed by examining the distribution, petrology, and geochemistry of the dolomites, the most comprehensive study to date was provided. Dolomitization occurred at a very early stage of diagenesis, as shown by the petrological features of the rock fabric. Vadose silt, which is composed primarily of dolomitic clasts, is found in the primary and secondary pores of the oolitic dolomite. This indicates that the overlying strata were subjected to dolomitization when the Feixianguan formation was located in the vadose zone. Therefore, it may be inferred that the dolomitization which occurred before the formation was exposed to meteoric conditions. The spatial distribution and geochemical characteristics of the dolomite indicate that dolomitization occurred as a result of seepage reflux. The degree of dolomitization decreases with increasing distance from the evaporative lagoon. Furthermore, the type and porosity of the dolomite vary in different zones of the upward-shoaling sequence, with the porosity gradually decreasing from the highest layer to the lowest layer. This reflects a close relationship between dolomitization and seawater evaporation during the formation of the dolomite. Geochemical analysis provided further evidence for the relationship between the dolomitization fluid and the coeval seawater. The 87Sr/86Sr and 813C isotopes, as well as the abundances of trace elements, Fe and Mn, indicate that seawater concentrated by evaporation acted as the dolomitization fluid. These results also show that dolomitization most likely occurred in a semi-closed diagenetic environment. Therefore, the main mechanism of oolitic dolomite formation is seepage reflux, which occurred at an early stage of diagenesis.

The Major Controlling Factors and Different Oolitic Shoal Reservoir Characteristics of the Triassic Feixianguan Formation,Eastern Longgang Area,NE Sichuan Basin,SW China

Based on comprehensive analyses of occurrence,petrological observation,pore structure and geochemistry,the different reservoir characteristics and reservoir evolutionary pathways between different oolitic shoal reservoir types of the Feixianguan Formation on the west side of the Kaijiang-Liangping Trough have been studied.There exist three stages of high-energy slope break belts in the Feixianguan period,the corresponding three stages of oolitic shoals gradually migrating in the direction of the trough.Three types of oolitic shoal reservoirs,namely,residual-oolitic dolomite,mold-oolitic dolomite and sparry oolitic limestone,were formed during sedimentary-diagenetic evolution,the pore types being intergranular dissolved pore,mold pore(or intragranular dissolved pore)and residual intergranular pore,respectively.The petrology,physical properties and pore structure of the different types of oolitic shoal reservoirs are quite different.Residual-oolitic dolomite reservoirs have the best quality,while sparry oolitic limestone reservoirs have the poorest.Combined with analyses of trace elements,rare earth elements and carbon-oxygen isotopes,it is suggested that the formation of residual-oolitic dolomite reservoirs is jointly controlled by penesaline seawater seepage-reflux dolomitization and hydrothermal dolomitization.Mold-pore oolitic dolomite reservoirs are controlled by penesaline seawater seepage-reflux dolomitization and meteoric water solution.The burial dissolution of organic acid not only further improves the reservoir qualities of previously formed oolitic dolomite reservoirs,but also preserves residual intergranular pores in the sparry oolitic limestone reservoirs.

Sequence Stratigraphy and Sedimentary Facies of Feixianguan Formation in the Kaijiang-Liangping Area of Sichuan Basin, China

The Feixianguan formation in the Kaijiang-Liangping basin has been the focus of extensive research on multiple aspects. Based on field survey, core observation, laboratory analysis and seismic data interpretation, the sequence stratigraphy and sedimentary facies of the Kaijiang-Liangping area are studied. Four sequence boundaries and three maximum flooding surfaces of the Feixianguan formation are detected in this area. Three third-order sequences are identified as first sequence (SQ1), the second sequence (SQ2), and the third sequence (SQ3) in which SQ1 corresponds to the member 1 of the Feixianguan formation, SQ2 corresponds to the member 2, and SQ3 corresponds to the member 3 and member 4. Member 1, 2, 3 and 4 are lithologic sections divided by predecessors. On the basis of this sequence division and their sedimentary marks, the facies of the Feixianguan formation can be divided into open platform and evaporate platform categories. The open platform is composed of three subfacies identified as platform bank or basin marginal bank, interbank, and platform basin. Thus, a sedimentary evolution model is established. According to the sedimentary and seismic characteristics of the Kaijiang-Liangping area, we determine that two oolitic bank models, the aggradation model and the progradation model, are developed in this area. The aggradation model is developed in the Longgang region, which includes the basin marginal bank as a favorable exploring zone. The progradation model is developed in the Jiulongshan and Longhui areas, besides the basin marginal bank, the favorable exploration zones also include the oolitic bank developing areas of the inner basin.

Porosity Formation and Evolution of the Deeply Buried Lower Triassic Feixianguan Formation, Puguang Gas Field, NE Sichuan Basin, China

The deeply buried shoal dolomite reservoirs of the Lower Triassic Feixianguan Formation, giant Puguang Gas Field, NE Sichuan Basin, are exceptionally porous. The influences of diageneses on pore evolution are studied. Through petrologic investigation, diagenetic phases are divided into four stages, i.e., near-surface, pre-oil window, oil window, and gas window. The Adobe Photoshop system is used to quantify the rock texture components, porosity constitutions and the influences of diageneses on reservoir porosity. Porosity evolution curves are quantitatively recovered. The Feixianguan reservoir porosities are mainly created by early meteoric dissolution, dolomitization, and organic acids dissolution. Dissolution during deep burial is insignificant. Pores are formed in near-surface and pre-oil window stages and effectively preserved till present. This result may be of great significance to the further exploration of deeply buried carbonate reservoirs not only in NE Sichuan Basin, but also around the world.

四川盆地五百梯地区长兴组古地貌恢复及地震预测

四川盆地五百梯地区长兴组地层分布范围广、勘探潜力大,但存在礁滩储层厚度薄、礁滩体刻画难、演化规律不明显、非均质性强等问题,增加了储层预测的多解性。对此,从生物礁岩石学特征及储层特征研究出发,提出了生物礁储层的纵向发育规律和部位,并利用生物礁储层的地震异常特征,刻画礁滩体优质储层横向展布特征,并重点分析了古地貌对礁滩储层发育特征的关键性控制作用,最后结合古地貌恢复及储层反演等方法,对礁滩储层进行综合评价,并总结形成了长兴组礁滩体储层地震识别模式,降低了礁滩储层预测的多解性。研究发现,长兴组沉积前已形成了海槽雏形,长兴组早中期形成了台缘及台内二排礁区域高地貌基本格局,到长兴组沉积末期海槽特征明显,古地貌高部位是储层发育的最有利区域,优势储层主要集中在台缘外带及台内二排礁局部区域,该认识为四川盆地长兴组台内礁勘探提供了重要的依据及借鉴意义。

板桥区块长兴组不同储层类型及其勘探潜力评价

本文利用岩心、薄片、测井等资料按照不同的分类方法对板桥区块长兴组储层类型进行了划分。按照是否有造礁生物,划分为生物礁储层和生屑滩储层;按照起主导作用的储集空间类型划分为裂缝-孔隙型和孔隙-裂缝型储层。结合不同储层类型典型井的试油及生产情况,分析其勘探潜力,得到以下认识:(1)生物礁储层物性好,储层厚度大,累产气量大,含气性比生屑滩储层更好,勘探潜力更大。生屑滩储层孔隙度普遍较低,只有在裂缝较发育时,可获得较大的勘探潜力。(2)裂缝-孔隙型储层的含气性比孔隙-裂缝型储层更好,勘探潜力更大,即使测试产量不高,但累产气量大,生产效果好;而孔隙-裂缝型储层由于孔隙度低,储层致密,即使初始测试产量较高,但稳产能力不足,后期生产效果不好。

川东飞仙关组鲕粒滩岩性识别及其分布特征

【目的】为解决针对川东海槽南段西侧、台内等地区飞仙关组岩性变化不明确等问题。【方法】综合利用岩心、薄片、钻录井等多元地质数据对飞仙关组岩性类型及特征进行研究,提出以机器学习为基础的岩性测井智能识别方法,解决了老区岩性精细识别的技术难题,揭示了区内飞仙关组鲕粒滩岩性、分布及演化规律。【结论与结果】(1)飞仙关组主要由泥岩、泥晶灰岩、泥质灰岩、鲕粒灰岩、鲕粒云岩、泥晶云岩、膏质云岩、膏岩等岩性组成;(2)对比发现,改进的梯度提升决策树算法即随机梯度提升决策树(SGBDT)构建岩性模型优于其他算法,更适合碳酸盐岩复杂岩性识别;(3)鲕粒灰岩集中发育于开江—梁平海槽以南地区的飞一段—飞三段时期,鲕粒云岩集中发育于飞二段时期且分布分散;(4)区内鲕粒滩分布差异明显,飞一段时期主要发育于台地古地貌高点和台地边缘,飞二段时期多发育台缘鲕粒滩,少量发育台内古地貌高点鲕滩和点滩,飞三段时期主要发育台内点滩。

川西北上寺剖面下三叠统飞仙关组一段砾屑灰岩沉积特征及成因

广元上寺剖面早三叠世砾屑灰岩对上扬子地区P-T事件后的古环境变化研究具有重要的理论意义。本文以下三叠统飞仙关组一段格里斯巴赫亚阶的砾屑灰岩为研究对象,通过沉积学、岩石学方法,结合不同砾屑灰岩碳、氧同位素变化特征来分析其可能的成因。结果表明,这些砾屑灰岩可划分出4大类:剖面下部的Ⅰ型砾屑灰岩,形状不规则,大小混杂,缺乏板条状砾屑,推测为重力流成因;Ⅱ型砾屑灰岩(角砾状灰岩)砾屑直径大,含大量分米级板条状砾屑,推测为强度和频率急剧增加的风暴诱发的沉积;Ⅲ型砾屑灰岩(扁平砾屑灰岩)的砾屑平行于层面分布,平面上呈扁平状,垂向切片呈竹叶状,具有倒“小”字、菊花状构造和局部呈叠瓦状排列等特征,推测为机械-压溶复合成因;Ⅳ型砾屑灰岩显示为蠕虫状灰岩,代表着水动力条件相对较弱的环境,推测为生物-机械复合成因。风暴对先期沉积的灰岩的撕裂是扁平砾屑形成的基础,后期成岩过程中泥质填隙物与灰岩砾屑的差异压实是扁平砾屑灰岩形成的又一原因。蠕虫状灰岩可能为生物-风暴、成岩作用共同的结果,与扁平砾屑灰岩在成因上有一定的联系。上寺剖面飞一段碳酸盐岩碳同位素曲线显示出缓慢上升的趋势,角砾状灰岩(Ⅱ型砾屑灰岩)发育后期碳同位素发生正偏,指示着沉积环境的过渡转折,可能和这一时期风暴作用对海洋的影响致使浮游微生物繁盛有关。