Estimation of petrophysical parameters using seismic inversion and neural network modeling in Upper Assam basin,India

Estimation of petrophysical parameters is an important issue of any reservoirs. Porosity, volume of shale and water saturation has been evaluated for reservoirs of Upper Assam basin, located in northeastern India from well log and seismic data. Absolute acoustic impedance (AAI) and relative acoustic impedance (RAI) are generated from model based inversion of 2-D post-stack seismic data. The top of geological formation, sand reservoirs, shale layers and discontinuities at faults are detected in RAI section under the study area. Tipam Sandstone (TS) and Barail Arenaceous Sandstone (BAS) are the main reservoirs, delineated from the logs of available wells and RAI section. Porosity section is obtained using porosity wavelet and porosity reflectivity from post-stack seismic data. Two multilayered feed forward neural network (MLFN) models are created with inputs: AAI, porosity, density and shear impedance and outputs: volume of shale and water saturation with single hidden layer. The estimated average porosity in TS and BAS reservoir varies from 30% to 36% and 18% to 30% respectively. The volume of shale and water saturation ranges from 10% to 30% and 20% to 60% in TS reservoir and 28% to 30% and 23% to 55% in BAS reservoir respectively.     

Porosity prediction of lower cretaceous unconventional resource play,south Indus Basin,Pakistan, using the seismic spectral decomposition technique

Incised-valley shale systems are renowned as the fruitful exploration domains. However, the stratigraphic heterogeneity is significant, and thus, identifying the porous compartments within the thin-bedded and fractured shale system is one of the unconventional stratigraphic challenges. We present an innovative scheme for the exploration of the porous unconventional resources within the south Indus basin, Pakistan. The continuous wavelet transforms (CWT) exclusively detects the porous shales within the complete fractured system as compared to the full spectrum seismic data interpretation tool. The seismic amplitude, instantaneous frequency, and reflection strength tools show some tuning effects due to lithology and fluids. However, the tuning block of 28 Hz envelope sub-bands in conjunction with instantaneous phase tool accurately mark out the shale-plugged pinch out reservoirs. The synthetic wedge model based on the conventional seismic wavelet resolves the shale bed (incised-valley shale-filled lens) of about 23 m thickness, but shows limited imaging capability due to frequency band limitation for the porous shale locale. The acoustic impedance based on instantaneous spectral porosity modeling using the tuning volume of 28 Hz CWT has spectacularly resolved the thin-beds (gas shows) within the porosity range of 20 to 30%, which may have implications for future exploration of unconventional stratigraphic plays.     

Well log data analysis for lithology and fluid identification in Krishna-Godavari Basin,India

Well log analysis provides the information on petrophysical properties of reservoir rock and its fluid content. The present study depicts interpretation of well log responses such as gamma ray, resistivity, density and neutron logs from six wells, namely W-1, W-2, W-9, W-12, W-13 and W-14 under the study area of Krishna-Godavari (K-G) basin. The logs have been used primarily for identification of lithology and hydrocarbon-bearing zones. The gamma ray log trend indicates deposition of cleaning upward sediment. Coarsening upward, clayey-silty-sandy bodies have been evidenced from the gamma ray log. Gas-bearing zones are characterised by low gamma ray, high deep resistivity and crossover between neutron and density logs. Total 14 numbers of hydrocarbon-bearing zones are identified from wells W-9, W-12, W-13 and W-14 using conventional log analysis. Crossplotting techniques are adopted for identification of lithology and fluid type using log responses. Crossplots, namely P-impedance vs. S-impedance, P-impedance vs. ratio of P-wave and S-wave velocities (Vp/Vs) and lambda-mu-rho (LMR), have been analysed to discriminate between lithology and fluid types. Vp/Vs vs. P-impedance crossplot is able to detect gas sand, brine sand and shale whereas P-impedance vs. S-impedance crossplot detects shale and sand trends only. LMR technique, i.e. λρ vs. μρ crossplot is able to discriminate gas sand, brine sand, carbonate and shale. The LMR crossplot improves the detectability and sensitivity of fluid types and carbonate lithology over other crossplotting techniques. Petrophysical parameters like volume of shale, effective porosity and water saturation in the hydrocarbon-bearing zones in these wells range from 5 to 37%, from 11 to 36 and from 10 to 50% respectively. The estimated petrophysical parameters and lithology are validated with limited core samples and cutting samples from five wells under the study area.     

活断层的地震响应特征与瞬时地震属性

活断层探测是断层活动性评判的基础,也是天然地震灾害预防的依据,而浅层地震勘探是活断层探测的有效方法之一;而目前利用浅层地震方法评判断层活动性的能力亟待提高.通过构建了不同宽度破碎带的活断层理论模型,采用二维粘弹性波动方程有限差分法进行了波场响应特征模拟,运用希尔伯特变换方法提取了瞬时频率和相位属性.结果表明:地震水平叠加剖面和瞬时属性相结合可有效获取穿过第四系活断层的响应特征和实现断层活动性评判;当相干噪声达到30%时,水平叠加和瞬时频率属性剖面已难以追踪第四系中弱反射信号,而瞬时相位属性剖面仍可有效追踪;在实际活断层判定中,水平叠加、瞬时频率与瞬时相位地震属性剖面均可判断断层的存在,而穿过第四系的断层 (或破碎带) 特征瞬时相位属性最为明显和突出,水平叠加剖面次之,瞬时相位地震属性是判定断层活动性的重要和有效的属性.      

万昌地区永二段水下滑塌扇内上倾尖灭砂体识别

上倾尖灭型油气藏是岩性油气藏的基本类型之一.对上倾尖灭砂体的识别是岩性油气藏勘探的任务之一.在对比单一利用地震资料、地震属性和波阻抗反演等方法进行砂体识别的优缺点后, 提出运用波阻抗和瞬时相位相叠合的新方法对砂体进行识别.运用此方法, 对万昌地区水下滑塌扇内部上倾尖灭砂体进行了精细解释和分析.得出以下结论: (1)通过钻井岩心识别沉积相类型, 结合均方根振幅属性和同沉积断层分布情况, 可以准确地确定伊通盆地万昌地区永二段水下滑塌扇的分布范围; (2)用波阻抗和瞬时相位属性联合的方法对水下滑塌扇内部上倾尖灭砂体进行识别取得了较好的效果, 万昌地区WC1井附近水下滑塌扇内至少有两期最具油气勘探价值的上倾尖灭砂体.      

Midale油田奥陶系白云岩储层格架与油藏特征

综合三维地震、钻井、岩心和薄片资料分析了该油藏的储层展布格架、油藏构造及演化、油藏类型和控制因素等。在钻井剖面对比图上依据密度和中子测井,将白云岩储层可划分为4个小层。第1、2小层由于位于圈闭构造的较高部位因而通常含油。第3、4小层可能由于在某处与第1、2小层连通,虽然也具低幅度构造和更大的厚度及孔隙度,但多为水层;又因其容易侧向尖灭,故有可能形成地层圈闭。三维地震解释和正演模型均表明,当第1、2小层较厚时,常对应于强振幅和高频反射;当第3、4小层较厚且4个小层并存时会在原储层反射位置下方多出一个波峰同相轴,而且第3、4小层的尖灭通常伴随着该同相轴的终止。这一点有助于寻找与第3、4小层上倾尖灭有关的圈闭。Midale油藏的空间分布受局部低幅度构造和储层小层发育状况的双重控制。油藏驱动机制可能为边水和底水两种类型的结合。根据地震剖面上的地层关系和由三维地震资料所做的古构造演化图来看,油藏低幅度构造的形成与后期地层在前寒武基岩古隆起上的披覆及该隆起在后期多次不整合发生期间的重新活动有关。圈闭雏形形成于早志留到中泥盆世,最终定型于晚白垩世。区域构造演化和油气运移研究表明,有利的油气聚集带位于某些靠近油源区的古鼻隆的东北翼。     

构造曲率与振幅曲率在地震资料解释中的应用

通过对曲率属性的分析对比,寻找适合研究区的曲率,从而提高解释的精度和效率。振幅曲率与构造曲率在数学上是相互独立的,通过对地震振幅数据的二阶微分求取可以得到振幅曲率属性。针对断层以及地质异常体在常规地震剖面上表现为同相轴的变化、扭曲、振幅突变等特征,利用曲率属性上表现为线性构造,进行断层以及地质异常体的识别,同时总结了曲率属性在解释应用中应注意的问题。振幅曲率不但能反映构造特征,同时能够突出由地质因素造成的振幅差异,从而反映地质特点,对刻画地质体的轮廓、分层结构、断裂系统等非常有效。应用实例表明,曲率属性能够有效识别出断裂发育分布,利用振幅曲率断层的轨迹,沉积体边界刻画得清晰、连续,利于解释,可减少解释多解性。     

利用地震属性进行砂岩储层横向预测

地震属性分析技术一直是地震特殊处理和地质解释的主要研究内容。随着相关理论的发展,地震属性分析技术已经应用到油气勘探开发的各个阶段。S盆地南部处于勘探开发的前期,具有井少、二维地震测网较稀、储层预测难的特点。由于沉积地层的变化能引起地震波在动力学和运动学上的相应变化,因此利用地震属性能较好地进行储层特征的定性研究,即通过地震多种属性分析,进行研究区内砂岩储层横向预测。其研究技术路线实际上为先找储层,再进行初步油气检测,最后进行勘探目标优选。根据这个技术路线,地震属性的研究则相应地以三个方面的分析为主:即利用振幅属性来寻找砂体富集区,利用有效带宽判断砂层的均质性,再利用频率属性判断其含气性。地震属性分析方法的应用在早期天然气勘探开发具有可以推广的普遍意义。     

应用测井资料的"三瞬"属性进行地层划分及对比研究

地层划分及对比是油气田勘探开发一项重要且存在难题的工作,提出应用 Hilbert-Huang变换方法提取常规测井资料(自然伽马、声波时差等)的"三瞬"属性特征进行地层划分及对比,即"瞬时频率"、"瞬时振幅"、"瞬时相位"3个属性,揭示了测井数据各深度处的频率特性,可以清晰反映出频率变化的结构特征.依据不同属性的振荡异常刻度层序边界,不同频率成分的属性振荡周期变化特征刻度不同规模的层序旋回周期特征,进而利用"三瞬"属性信息进行地层对比,刻画地层内部特征.利用这些属性异常可以清晰地找到对应地层序列中不同级别的界面,进而实现对各级层序划分,在各级层序格架控制下,进行各级地层等时对比.提取测井资料的三瞬属性为高分辨率层序地层研究提供了一种新的方法思路,为推动高分辨率层序地层学的发展具有重要意义.     

塔里木盆地塔中北斜坡奥陶系鹰山组深部优质岩溶储层的形成与分布

塔中地区是塔里木盆地的重点勘探区域,奥陶系鹰山组蕴藏了丰富的油气资源。鹰山组发育大套台地相碳酸盐岩,以高能相的台内滩沉积为主。鹰山组埋藏较深,但岩溶储层呈大面积厚层状分布。早奥陶世塔中I号断裂使得塔中隆起隆升并遭受强烈剥蚀形成下奥陶统鹰山组顶部风化壳,以孔洞型和裂缝-孔洞型储层为主。通过古地貌恢复、地震属性分析和地震测井联合波阻抗反演技术和方法识别溶洞发育带和断层裂缝发育带,确定出有利储层的分布范围。研究认为,岩性岩相是岩溶型储层发育的重要基础,层间岩溶控制了储层的成层性和横向展布规模,断裂和裂缝网络是岩溶水的主要渗滤通道,埋藏岩溶形成大量有效的缝洞空间,极大地提高了储集性能。研究发现,优质储层主要分布在鹰山组顶面以下120m地层厚度范围内,横向有一定连通性,在断层、构造裂缝和溶蚀作用下形成统一的储集体,呈准层状展布。     

D-S证据理论在地震属性中的应用

在利用复地震道分析技术提取出地震信号局部变化的三瞬属性(瞬时振幅;瞬时相位和瞬时频率)的基础上,采用D—S改进算法对三瞬属性进行多传感器的证据融合,得到三种属性所占的权重,并根据相应权重,经过数据融合可以得到最终融合结果。这样有效融合了三种地震属性中有利于进行地震薄互层分析的地震信息,与单一的复地震道分析相比,更能有效地反映出地震信号的局部变化。最后通过对实际的地震资料进行了处理,发现D—S信息融合技术体现的地震波属性的变化,比单一属性更能清楚地反映出地质体的地质现象及表达的沉积过程。     

Review of the chronostratigraphic charts in the Sinú-San Jacinto basin based on new seismic stratigraphic interpretations

Disperse and punctual studies; absence of integration of data ranging from local to regional focus; interpretations based only on lithostratigraphic features; and interpretation of data premised on an allochthonous origin of the Caribbean plate, are some of factors that increase the confusion and uncertainty in understanding the Sinú-San Jacinto Basin. The sedimentary record of Upper Cretaceous to Eocene has been traditionally interpreted as the record of deep-water settings. However, recently these sediments have been related to shallow marine and deltaic settings. Second problematic point is about the deposition environment of the Oligocene to Late Miocene succession. Some studies suggest canyons, turbidites and sediments deposited in deep-water settings. However, recent studies propose deltaic and shallow marine settings. The last stratigraphic problem is related to the controversial fluvial vs. shallow marine interpretations of the Pliocene sediments. Based upon seismic stratigraphic analysis in recent and reprocessed 2D seismic data, integrated with well data, we propose chronostratigraphic charts for the northern, central and southern zones of the Sinú-San Jacinto Basin. Twenty seismic facies based on amplitude, continuity, frequency and geometry of seismic reflectors and twelve seismic sequences were recognized. The seismic stratigraphic analysis in this study suggests that the sediments of Upper Cretaceous to Paleocene/Eocene were associated to continental to shallow marine settings. Lagoons, coastal plain and carbonate platform dominated during this period. The Oligocene to Middle Miocene record was characterized by deep-water deposition, whereas the Late Miocene to recent sedimentation was characterized by falling base level, characterized by deltaic and fluvial deposits. Five syn-rift sequences with wedge-shaped geometry were identified in this study. Three Triassic to Jurassic syn-rift sequences were characterized by seismic facies typical of fluvial to lacustrine and flood plain sedimentation. Two Cretaceous to Paleocene syn-rift sequences were characterized by seismic facies related to lagoons to coastal plain settings. Normal high-angle faults with a northeast-southwest direction related to rifting processes controlled the development of these sequences. The sheet-drape post-rift section was characterized by passive margin settings in the northern part of the Sinú-San Jacinto Basin and by diachronic tectonic inversion of older normal faults during Cenozoic, predominantly in the central and southern zones. The stratigraphic record related to the Mesozoic to Early Cenozoic rifting; the shallow marine sedimentation during Eocene and the tectono-stratigraphic continuity across the northern Colombia and northwestern Venezuela is coherent and well explained by the in situ origin of the Caribbean plate and is not explained by the “allochthonous” model.     

井间资料约束下地震波阻抗反演方法研究

采用多井约束的随机逆反演方法,结合井间地震反射成像与测井资料,首先对反射成像后的井间地震数据进行测井约束的波阻抗反演,进而从反演剖面中抽取一定量的反演道作为虚拟井数据,结合测井数据对地面地震数据进行井地联合反演。理论数据和实际数据的试算表明,井地联合反演可以为地面地震测井约束反演提供更多的约束条件,从而提高了地面地震反演的精度。     

用于地震反射界面识别的瞬时相位复合属性

复地震道技术采用Hilbert变换通过求解实地震信号的解析信号,可将反映地震信号局部变化情况的地震波的瞬时振幅、瞬时相位和瞬时频率等信息分离开,瞬时相位是一种独立于地震振幅,并且不受其影响的地震属性参数,因此瞬时相位能更好地反映构造几何形态的细节.通过理论模型分析发现,瞬时振幅与极性反转前后地震记录的瞬时相位一阶差分之和进行加权,得到的复合属性可以较为准确、可靠地识别地震反射界面的位置,具有较好的应用效果.     

The research on division and correlation of stratigraphic sequence based on the “three instantaneous” attribute features of logging data

The stratigraphic division and correlation has important guiding significance to oil and gas field. This paper presents the application of Hilbert-Huang Transform to extract the “three instantaneous” attribute features of logging data (GR,AC) to perform the division and correlation of stratigraphic sequence, that is, the three properties of "instantaneous frequency", "instantaneous amplitude", "instantaneous phase" are extracted from logging data, which revealed the frequency characteristics of each depth of logging data and clearly reflected the structural characteristics of the frequency change. According to the oscillation anomalies of different attributes, we scale sequence boundaries, and use the variation characteristics of oscillation period of different frequency components attributes to scale the periodic characteristics of different scale sequence cycle, then use the “three instantaneous” attribute information for stratigraphic correlation, and for describing the internal features of formation. These attributes anomalies can be used to clearly find the different class interface of stratigraphic sequence, to achieve the sequence division at all levels, and under the control of sequence stratigraphic framework at all levels, we can do the isochronous stratigraphic correlation at all levels. The “three instantaneous” attribute extraction of logging data provides a new approach and idea for high resolution sequence stratigraphy analysis, and it has important significance for promoting the development of high-resolution sequence stratigraphy.     

Characterization of Architectural Elements of Ordovician Fractured-cavernous Carbonate Reservoirs,Tahe Oilfield,China

A new method for characterizing architectural elements of fractured-cavernous carbonate reservoirs was proposed, with application to an Ordovician reservoir in the Tahe Oilfield, Tarim basin. The new method integrates observations from outcrop analogs and concepts from modern karst theory for the mapping and modeling of fractured-cavernous reservoirs. In this paper, fractured-cavernous reservoirs were divided into 4 architectural element types—underground river caverns, sinkholes, discrete internal caverns, and faults. Architectural elements of the Ordovician reservoir in Tahe oilfield were identified and characterized by integrating well logs and seismic data. A new method constrained by faults, karst zones, and seismic acoustic impedance data, was introduced to build a 3D model of architectural elements of fractured-cavernous reservoir in the S48 unit of Tahe Oilfield. A porosity model was then derived from the architectural element model using facies-constrained method. The research provides a work-flow for the characterization of fracturedcavernous reservoirs and determining optimal methods for maximizing oil recovery in the study area or in similar areas.     

Continuous wavelet transforms of spectral decomposition analyses for fluvial reservoir characterization of Miano Gas Field,Indus Platform,Pakistan

Fluvial depositional systems constitute diverse host for the hydrocarbons all over the globe. Nevertheless, predicting the hydrocarbon sands within these assorted sand systems is a challenge for the prospect generation. We apply the continuous wavelet transform of spectral decomposition technique to a 3D seismic data of the Miano Gas Field in the Indus Platform, Pakistan. Full spectrum seismic attributes like the amplitude and root mean square (RMS) detect the reservoir sands down to a restricted reservoir compartment. Nonetheless, the continuous wavelet transforms can be advantageous in imaging and enactment of these clastic reservoirs within the whole reservoir zone. Rock physics reveal high-quality reservoir with an average porosity ～25% together with the discrimination of lithology/fluids, signifying the bright chances for ascertaining the potential stratigraphic reservoirs.     

Study on Sequence Stratigraphy of Zhujiang andZhuhai Formations, Zhu Ⅲ Subbasin, PearlRiver Mouth Basin, South China Sea

INTRODUCTIONThe Zhu m subbasin, about 11 000 kmZ in area, the western part of the Pearl River Mouth (PRM) basin, South ChinaSea (SCS), consists of nine sub-tectonic units: half-grabenWenchang A (HGWC-A), half-graben Wenchang B (HGWCB), half-graben Wenchang C (HGWC-C), half-graben Qionghai (HGQH), horst Qionghai (HQH), half-graben YangjiangA (HGYJ-A), half-graben Yangjiang B (HGYJ-B), low horstYangjiang (LHYJ) and horst Yangjiang (HYJ) (Fig. 1). According to the p…     

Structural style and early stage growth of inversion structures: 3D seismic insights from the Egersund Basin,offshore Norway

High-quality three-dimensional (3D) seismic reflection and borehole data from the Egersund Basin, offshore Norway are used to characterise the structural style and determine the timing of growth of inversion-related anticlines adjacent to a segmented normal fault system. Two thick-skinned normal faults, which offset Permian clastics and evaporites, delineate the north-eastern margin of the basin. These faults strike NNW-SSE, have up to 1900 m of displacement and are separated by an ESE-dipping, c. 10 km wide relay ramp. Both of these faults display exclusively normal separation at all structural levels and tip out upwards into the upper part of the Lower Cretaceous succession. At relatively shallow structural levels in the hangingwalls of these faults, a series of open, low-amplitude, fault-parallel anticlines are developed. These anticlines, which are asymmetric and verge towards the footwalls of the adjacent faults, are interpreted to have formed in response to mild inversion of the Egersund Basin. The amplitude of and apparent shortening associated with the anticlines vary along strike, and these variations mimic the along-strike variations in throw observed on the adjacent fault segments. We suggest that this relationship can be explained by along-strike changes in the propensity of the normal faults to reactivate during shortening; wider damage zones and lower angles of internal friction, coupled with higher pore fluids pressures at the fault centre, mean that reactivation is easier at this location than at the fault tips or in the undeformed country rock. Seismic-stratigraphic analysis of growth strata indicate that the folds initiated in the latest Turonian-to-earliest Coniacian (c. 88.6 Ma) and Santonian (c. 82.6 Ma); the control on this c. 6 Myr diachroneity in the initiation of fold growth is not clear, but it may be related to strain partitioning during the early stages of shortening. Anticline growth ceased in the Maastrichtian and the inversion event is therefore interpreted to have lasted at least c. 20 Myr. This study indicates that 3D seismic reflection data is a key tool to investigate the role that normal fault segmentation can play in controlling the structural style and timing of inversion in sedimentary basins. Furthermore, our results highlight the impact that this structural style variability may have on the development of structural and stratigraphic hydrocarbon traps in weakly-inverted rifts.