百虑亨通 思齐致达
SPE有关论文摘译
petrostar

     The evaluation of complex carbonate reservoirs is a challenging task, and a detailed understanding of reservoir heterogeneity is still lacking. In this study, the effect of static rock type and sample size was investigated on special-core-analysis laboratory (SCAL) data derived from capillary pressure and resistivity-index experiments at reservoir temperature and net confining stress. Whole cores were generally found to yield different capillary pressure and saturation exponents that may not be possible to derive from average plug data.

     对复杂碳酸盐储层的评价是一项具有挑战性的任务,并且仍然缺少对储层非均质性的详细了解。在这篇文章中,特殊岩心分析实验室(SCAL)对静态岩石类型和样品尺寸的作用进行了研究,实验室的数据来自关于储层温度和纯封闭应力的毛细管压力实验和电阻率指数实验。整个岩心通常有不同的毛细管压力和饱和指数,从岩心平均数据中不可能得到此类数据。

     Most carbonate reservoirs are characterized by multiple-porosity systems that impart petrophysical heterogeneity to the gross reservoir interval. Reservoir heterogeneity is dependent upon the depositional environments and subsequent events in the history of the reservoir. In previous work, the effect of multiscale measurements (whole cores down to small trims) was studied on porosity/permeability and cementation factor. The whole-core samples were taken from a single well in a carbonate reservoir in Abu Dhabi, where 1.5-in. core plugs were drilled adjacent to the whole cores. Small trims were cut from the plugs for ¬mercury-injection capillary pressure (MICP) determination. The main findings were that whole-core porosity matched log data very well and the plug porosities, when compared with the whole-core data, were systematically higher. The degree of heterogeneity played a major role in comparing whole-core to plug permeability: In the low-¬permeability range (less than 10 md), whole cores could enhance 3D connection pathways and yield higher permeability values, whereas, in the high-permeability range, permeability can be overestimated in plugs through relatively larger porosity channels. The cementation factor was systematically reported to be lower in the measured whole-core samples. X-ray computed-tomography (CT) scanning was essential in explaining most of the variability seen in the measured rock properties at different scales. In another investigation on four different wells in the same reservoir, these earlier observations were confirmed on hundreds of multiscale samples.

     大部分碳酸盐储层都具有标志性的多种孔隙系统,此类系统反映出整个储层段岩石的非均质性。储层的非均质性取决于沉积环境和油藏历史的构造。在以前的工作中,在孔隙度/渗透率和胶结系数方面,对多尺度测量(从全岩心到小的边角)的作用进行了研究。全岩心样品取自Abu Dhabi一口井中的碳酸盐储层,在临近全岩心的地方取了一些1.5英寸的岩心塞,为了测定压汞毛细管压力(MICP),研究人员切除了这些岩心塞上的一些边角。主要的发现是,根据配套的录井数据,得出全岩心的孔隙度非常高,而岩心塞的孔隙度比全岩心高。对比全岩心和岩心塞的渗透性发现,孔隙度起决定作用:在低渗透性(小于10md)时,全岩心能增强3D连通性且能产生更高的渗透率,反之,在高渗透性时,通过相对大的多孔通道后,岩心塞的渗透率可能会被高估。这个胶结系数在测量的全岩心样品中是比较低的,当解释以不同量程测量大多数岩性变化时,X射线断层扫描(CT)是必需的。根据相同储层另外四口不同井的调查发现,这些早期的观察已经通过上百个样品进行证实。

     The paper presents extended investigations from the same well to include ¬porous-plate capillary pressure and ¬resistivity-index measurements on individual whole-core samples and adjacent plugs. The measurements are conducted at reservoir temperature and net confining stress using dead crude oil and a simulated formation-brine-fluid system. The objective is to compare multiscale measurements to assess the effect of heterogeneity on Pc curves, saturation data, and the saturation exponent. Reservoir rock types (RRTs) on the core plugs were identified and discussed in a separate publication, where the effect of these rock types on residual-oil saturation and capillarity was studied thoroughly and found to be mainly dependent on the size range, the relative presence, and the distribution of pore throats. We discuss the effect of sample size from four different selected rock types in the reservoir. The whole-core primary-drainage capillary pressure curve seems to average the variability seen from core plugs. Whole-core resistivity-index measurements were on the lower-end of values from the plug measurements, especially when large variations were recorded from the plug data. For rock types with higher degrees of heterogeneity, whole-core imbibition capillary pressure data were found to deviate from individual-plug Pc curves and found to be a function of the relative presence of intermediate pore throats. These SCAL measurements from whole-core samples and from plugs provide the literature with high-quality multiscale measurements at representative reservoir conditions from different heterogeneous rock types that are rarely acquired. The experiments are the first of their kind in the industry and offer insight on the magnitude of possible variation between the whole-core and plug scales in such complex carbonates. They also confirmed that, with different scales, the influencing parameters stay the same, which in our case are the pore-throat sizes, their relative presence, and their distribution. In the future, we will acquire high-resolution X-ray CT imaging on the different rock-type samples at micro- and nanoscales to evaluate the effect of different pore types on the macroscopic measurements presented here.

     这篇文章发布了来自同一口井的进一步地调查,包含了全岩心样品和临近岩心塞的孔板毛细管压力测量值和电阻率指数测量值。这些储层温度和纯封闭应力的测量,使用了脱气原油和模拟地层盐水流体体系。试验目的是通过比较多尺度测量,以评价非均质性对Pc曲线、饱和度和饱和度指数的影响。在一篇独立的出版物中,对岩心塞的储藏岩石类型(RRTs)进行了鉴定和讨论。这篇出版物在岩石类型对于残余油饱和度和毛细管现象的影响上进行了充分的研究,发现其主要取决于孔喉的尺寸范围、相对存在和分布情况。我们讨论了储层中所选择的四个不同岩石类型样品尺寸的影响效果,从岩心塞看,全岩心的毛细管排驱压力曲线变化均衡。全岩心的电阻率系数测量处于岩心塞测量值的低端,尤其是当岩心塞数据的记录发生巨大变化时。对于高度非均质岩石类型来说,我们发现,全岩心毛细管吸入压力数据偏离了个别岩心塞Pc曲线,成为中间孔隙喉道相对存在的一个函数。SCAL测量方法提供了不同类型非均质性油藏岩心和柱塞样品的试验方法。这些实验都是首次进行的,并洞察了复杂的碳酸盐层中,全岩心和岩心塞之间可能的变化量级。他们也证实了在不同尺度中,造成影响的参数是一致的,在我们的案例中,这些参数是孔隙吼道尺寸它们的相对存在和分布。将来,我们会获得不同岩石类型样品微米和纳米级别的高分辨率X射线CT影像,来评估宏观测量的不同孔隙类型的作用。

     A fit-for-purpose conventional and ¬special-core-analysis program was carried out on a carbonate core from the Middle East. The objective of the program was to measure macroscopic rock properties on various scales in order to identify the effect of heterogeneity on different volume measurements.

     研究人员通过某种合适的常规及特殊岩心分析程序,对中东的一个碳酸盐岩心进行了分析,这个程序的目的是测量不同尺度的宏观岩性,以确定在不同体积下非均匀性的作用。

     SCAL data from porous-plate capillary pressure and resistivity-index measurements are presented from four main RRTs in the reservoir. The measurements are acquired on 4-in.-diameter whole cores and 1.5-in.-diameter plugs. Helium porosity of the selected samples ranges from approximately 15 to 30%, and the permeability varies from approximately 5 to 1,000 md. One whole-core sample is selected to represent one rock type, including available core plugs from each rock type. Core plugs were cut adjacent to the whole cores as closely as possible. A clear trend is seen for porosity with rock type. Whole-core porosity is systematically lower than plug porosity, with one violation to this trend in RRT 4A depending on heterogeneity. Permeability presents less-¬systematic variation with rock types and between whole cores and plugs. This is because of complex carbonate heterogeneity. It is interesting that the higher plug-permeability range yields lower whole-core permeability (see RRT 1A and RRT 3A). For the lower-range plug permeability (i.e., RRT 4A and RRT 3B), higher whole-core permeability values are obtained.

     来自孔板毛细管压力的SCAL数据和电阻率指数测量,反映了四种主要的储层岩石类型(RRT),这些测量来自4英寸直径全岩心和1.5英寸直径的岩心塞。这些选择出来的样品的氦透气度范围从大约15%到30%,渗透率变化范围从大约5md到1000md。研究人员选择某个全岩心样品以代表一种岩石类型,包括来自每种岩石类型的有效岩心塞,岩心塞尽可能从靠近整个岩心的地方切割。这样我们能看出岩石类型孔隙度有一个清晰的趋势。而全岩心孔隙度系统地低于岩心塞的孔隙度,由于岩心非均质性,在RRT 4A中,这个趋势发生了偏离。渗透性显示全岩心和岩心塞的岩石类型没有系统性的变化,这是由复杂的碳酸盐层非均质性造成的。较高的岩心塞渗透率范围却产生了较低的全岩心渗透率,这种情况很有趣(见RRT 1A和RRT 3A)。对于渗透率较低的岩心塞(如RRT4A和RRT 3B),我们得到了较高的全岩心渗透率值。

     High-pressure MICP experiments were performed on end trims from each core plug to assist in rock typing. For the whole-core samples, top and bottom trims were cut from the same whole core to evaluate heterogeneity better and to have improved interpretations for any possible variation between whole-core and plug data. X-ray CT scanning and thin-section photomicrographs were also used in identifying variations in the internal structures and in rock typing.

     我们对每个岩心塞上末端边角进行了高压MICP实验,以帮助确定岩石类型。针对这些全岩心样品,我们从同一个全岩心样品切割下顶部和末端边角来更好地评价它们的非均匀性,并对全岩心和岩心塞数据的可能变化进行更好的解释。我们也使用了X射线CT扫描和薄片显微照片,以识别内部结构的变化来对岩石进行定型。

     Primary-drainage and imbibition experiments were performed on whole-core samples and plugs. All samples were thoroughly cleaned by flow-through techniques, using repeated cycles of several hot solvents to render the rocks ¬water-wet (presumed wettability condition before oil entered the reservoir). The samples were saturated with 100% simulated formation water that is assumed to be representative of the reservoir-water composition. The capillary pressure and resistivity-index tests were conducted by the porous-plate method at net overburden stress and reservoir temperature by use of dead crude oil and simulated formation brine. During primary drainage, crude oil entered the rock samples at reservoir temperature. In this regard, aging would start as the oil penetrates the pore space. Several equilibrium capillary pressure steps were used in each saturation cycle, where the equilibrium criteria were no changes in saturation and resistivity at each step for at least 9 days (total duration at each Pc step was a minimum of 20 days). At the initial water saturation (Swi) at the highest drainage, Pc aging continued for 1 month before the imbibition experiments were commenced.

     我们针对这些全岩心和岩心塞样品进行了原始排驱和吸入实验,所有的样品通过注入替出法进行了彻底的清洁,研究人员使用几种热溶剂,进行重复循环以润湿岩石(假定油进入储层前是可润湿的)。这些样品被可以代表储层水的100%仿造地层水所浸透。他们在纯上覆岩应力和储层温度下使用残余原油和模拟地层盐水通过孔板法进行了毛细管压力和电阻率指数实验。在排驱期间,原油在储层温度下进入岩石样品,就这点而言,当原油穿透孔隙空间时,老化就会开始。每个饱和周期都采取了一些措施来平衡毛细管压力,饱和度和电阻率的平衡标准没有发生改变,每个试验步骤至少持续9天(每个Pc总共持续至少20天)。最初含水饱和度(Swi)最高,在吸入实验开始前,Pc老化会持续一个月。

     For RRT 1A, although the porosity/permeability crossplot shows variations between whole-core and plug data, the MICP curves obtained from plug trims and whole-core trims agree reasonably for the selected samples in this rock type. One may notice, however, slight variation between the whole-core MICP curves and the plug MICP data. This would be expected in such a heterogeneous carbonate reservoir. The porous-plate whole-core Pc curve agrees well with the corresponding MICP curves taken from the top and bottom of the whole-core sample. Similar observations can be derived for RRT 4A and RRT 3B. These observations may indicate that these rock types are less heterogeneous and apparently yield more or less similar macroscopic saturation measurements. Therefore, the heterogeneity effect in such rock types may have only minor effect on the multiscale macroscopic measurements.

     在RRT 1A,尽管孔隙度/渗透率图表显示了全岩心和岩心塞的变化,对于从这种岩石类型中选择的样品来说,岩心塞和全岩心边角的压汞毛细管压力(MICP)曲线一致。但是,我们需要注意到全岩心压汞毛细管压力(MICP)曲线和岩心塞数据的轻微变化,预计在非均质碳酸盐储层中将会看到这种现象。这些孔板全岩心Pc曲线非常一致,同时这些一致的压汞毛细管压力(MICP)曲线来自全岩心样品的顶部和底部,对于RRT 4A和RRT 3B,我们会看到相似的情况。这些情况显示这些岩石类型的非均质性较低,并且很明显与宏观饱和度测量多少有些相似。因此,此岩石类型的非均匀性可能会对多尺度宏观测量有较小的影响。

     For RRT 3A, however, there appears to be significant Pc variation within the plugs in the same rock type and within the whole-core sample itself. The whole-core top and bottom MICP curves are very different, indicating different rock properties along the whole-core length. This is rather confirmed by the X-ray CT slices from the whole-core sample depicted in Fig. 1. The top X-ray slice shows a darker gray, which indicates higher porosity and larger pores. This is indeed in line with the top MICP curve giving lower Swi than the MICP curve corresponding to the bottom section of the whole core. The porous-plate Pc curve from the whole core seems to average the rock-¬property variation seen in the plugs and within the whole-core sample itself. This can be viewed as an upscaled Pc curve from the various core plugs in this rock type, but directly measured on the whole-core sample. In this case, the whole-core measurement seems to be essential in capturing the heterogeneity in this rock type.

     在RRT 3A中,相同岩石类型的岩心塞和全岩心本身的Pc变化好像比较大。全岩心顶部和底部的压汞毛细管压力(MICP)曲线有很大不同,这表明在全岩心长度上有不同的岩石属性,这已经被全岩心样品的X射线CT薄片证实,如图1。顶部薄片X射线显示是深灰色,显示孔隙度较高,并且孔隙较大。这和顶部压汞毛细管压力(MICP)曲线一致,得出比全岩心底部压汞毛细管压力(MICP)曲线低的水饱和度(Swi)。从全岩心的多孔板Pc曲线看,似乎岩心塞的岩性变化和全岩心样品本身比较平均。这可以看做是来自这种岩石类型中不同岩心塞的升级版Pc曲线,而不是全岩心样品测量曲线。这种情况下,在获得这种岩石类型的非均质性方面,全岩心测量是很有必要的。

     Whole-core capillary pressure curves and resistivity data from RRT 4A and RRT 3B seem to be averaging the slight variability seen in the corresponding plug data. The pore-throat-size-¬distribution curves from these two rock types show that they are less--heterogeneous rocks; nevertheless, the whole-core saturation-exponent values are measured to be at the lower range of the corresponding plug data. This observation is detected on all the involved rock types, a consideration of great importance for proper saturation determinations from resistivity logs.

     RRT 4AHE RRT 3B的这些全岩心毛细管压力曲线和电阻率数据,似乎和相应的岩心塞数据稍微有些不同。这两种岩石类型的孔喉大小分布曲线表明,它们是均质性岩石,不过,全岩心饱和指数是在相应岩心塞数据的一个较低范围内测量的。在所有相关的岩石类型上都观察到了这种现象,通过电阻率测井得出的正确饱和度也很重要。

     All the plugs from RRT 3B gave similar imbibition behavior, which ties very well with the initially established static rock typing from petrophysical properties and geological descriptions. The whole-core sample shows behavior similar to that indicated by the plug imbibition curves, with small variation (higher entry pressure) that can be explained from the whole-core primary-drainage entry Pc curve being slightly higher than the plug curves. Another reason for the variation could be the very long time it takes for the whole-core sample to saturate, which could have resulted in nonequilibrium intermediate-saturation points during the imbibition process. Certainly, full equilibrium was attained at the lowest negative Pc, which gave ¬residual-oil saturation (Sor) similar to that in the plug data.

     RRT 3B中所有的岩心塞中都表现出相似的吸入特性,这和最初通过岩石物理属性和地质描述所确定的静态岩石分类联系的非常紧密。全岩心样品实验显示出与从岩心塞吸入实验曲线相类似的特性,反应相似变化较小(进入压力较高),这种现象可以通过全岩心驱排Pc曲线解释,而这个曲线稍微高于岩心塞曲线。发生变化的另外一个原因可能是全岩心样品浸透所花的时间比较长,这在吸入实验过程中,会导致中间饱和点不平衡。当然,在Pc曲线最低时,可以获得完全平衡,这和岩心塞中残余油饱和度相似。