A Transient-Pressure-Based Numerical Approach for Interlayer Identification in Sand Reservoirs

Almost all sandstone reservoirs contain interlayers. The identification and characterization of these interlayers iscritical for minimizing the uncertainty associated with oilfield development and improving oil and gas recovery.Identifying interlayers outside wells using identification methods based on logging data and machine learning isdifficult and seismic-based identification techniques are expensive. Herein, a numerical model based on seepageand well-testing theories is introduced to identify interlayers using transient pressure data. The proposed modelrelies on the open-source MATLAB Reservoir Simulation Toolbox. The effects of the interlayer thickness, position,and width on the pressure response are thoroughly investigated. A procedure for inverting interlayer parametersin the reservoir using the bottom-hole pressure is also proposed. This method uses only transient pressuredata during well testing and can effectively identify the interlayer distribution near the wellbore at an extremelylow cost. The reliability of the model is verified using effective oilfield examples.

Lithofacies paleogeography mapping and reservoir prediction in tight sandstone strata: A case study from central Sichuan Basin, China

Sand-rich tight sandstone reservoirs are potential areas for oil and gas exploration. However, the high ratio of sandstone thickness to that of the strata in the formation poses many challenges and uncertainties to traditional lithofacies paleogeography mapping. Therefore, the prediction of reservoir sweet spots has remained problematic in the field of petroleum exploration. This study provides new insight into resolving this problem, based on the analyses of depositional characteristics of a typical modern sand-rich formation in a shallow braided river delta of the central Sichuan Basin, China. The varieties of sand-rich strata in the braided river delta environment include primary braided channels,secondary distributary channels and the distribution of sediments is controlled by the successive superposed strata deposited in paleogeomorphic valleys. The primary distributary channels have stronger hydrodynamic forces with higher proportions of coarse sand deposits than the secondary distributary channels. Therefore, lithofacies paleogeography mapping is controlled by the geomorphology, valley locations, and the migration of channels. We reconstructed the paleogeomorphology and valley systems that existed prior to the deposition of the Xujiahe Formation. Following this, rock-electro identification model for coarse skeletal sand bodies was constructed based on coring data. The results suggest that skeletal sand bodies in primary distributary channels occur mainly in the valleys and low-lying areas,whereas secondary distributary channels and fine deposits generally occur in the highland areas. The thickness distribution of skeletal sand bodies and lithofacies paleogeography map indicate a positive correlation in primary distributary channels and reservoir thickness. A significant correlation exists between different sedimentary facies and petrophysical properties. In addition, the degree of reservoir development in different sedimentary facies indicates that the mapping method reliably predicts the distribution of sweet spots. The application and understanding of the mapping method provide a reference for exploring tight sandstone reservoirs on a regional basis.

Main flow channel index in porous sand reservoirs and its application

Based on well test interpretation,production performance analysis,overburden permeability and porosity test,gas-water core flooding test and high-pressure mercury injection,a quantitative correlation has been built of in-situ effective permeability with routine permeability and water saturation,and the ranges of Main Flow Channel Index(MFCI)are determined for different permeability levels in porous sand gas reservoirs.A new method to evaluate the in-situ effective permeability of porous sand reservoir and a correlation chart of reserves producing degree and main flow channel index are established.The results reveal that the main flow channel index of porous sand gas reservoirs has close correlation with routine matrix permeability and water saturation.The lower the routine matrix permeability and the higher the water saturation,the lower the MFCI is.If the routine matrix permeability is greater than 5.0×10-3,the MFCI is generally greater than 0.5.When the routine matrix permeability is from 1.0×10-3 to 5.0×10-3,the MFCI is mainly between 0.2 and 0.5.When the routine matrix permeability is less than 1.0×10-3,the MFCI is less than 0.2.The evaluation method of in-situ effective permeability can be used to evaluate newly discovered or not tested porous sand gas reservoirs quickly and identify whether there is tight sand gas.The correlation chart of reserves producing degree and main flow channel index can provide basis for recoverable reserves evaluation and well infilling,and provide technical support for formulation of reasonable technical policy of gas reservoir.

Porosity Calculation of Tight Sand Gas Reservoirs with GA-CM Hybrid Optimization Log Interpretation Method

Tight sand gas reservoirs are our country’s fairly rich unconventional natural gas resources, and their exploration and development is of prime importance. Sulige Gas Field which located in the northern Ordos Basin is tight sand gas reservoirs. It is typically featured by low porosity and low permeability, and the error of porosity calculation by traditional methods is larger. Multicomponent explanation model is built by analyzing the thin slice data, and the objective function is got according to the concept of optimization log interpretation method. This paper puts the Genetic Algorithm and the Complex Algorithm together to form the GA-CM Hybrid Algorithm for searching the optimal solution of the objective function, getting the porosity of tight sandstone gas reservoirs. The deviation got by this method is lesser compared with the core porosity, with a high reliability.

Research on Pore Structure and Fractal Characteristics of Tight Sandstone Reservoir Based on High-Pressure Mercury Injection Method

Pore structure is the key element of tight sandstone reservoir, which restricts the accumulation and flow of oil and gas in the reservoir. At present, reservoir pore structure is the focus and difficulty of unconventional oil and gas exploration and development research. The tight sandstone reservoir in the Chang 4 + 5 member of the Upper Triassic Yanchang Formation is the main reservoir for oil and gas exploration in G area. At present, there is little research on its pore structure and fractal characteristics, which to some extent affects the progress of exploration and development. This paper selects the tight core samples of the Chang 4 + 5 member in the southern edge of the Ordos Basin, and based on the high-pressure mercury intrusion experiment, uses fractal theory to study the pore structure and fractal characteristics of the reservoir in the study area, thus providing theoretical basis for the evaluation and exploration and development of the Chang 4 + 5 tight reservoir in the G area. The research results show that the lithology of the Chang 4 + 5 tight sandstone reservoir in the southern edge of the Ordos Basin is mainly feldspathic sandstone, with the highest feldspar content, followed by quartz, and the clay mineral is mainly chlorite. The reservoir has poor physical properties and strong heterogeneity. There are three main fractal characteristics in Chang 4 + 5 reservoir in G area: the fractal curve of Type I reservoir sample is in two segments, the relatively large pore has certain fractal characteristics, the pore structure is relatively regular, and the heterogeneity is weak;Relatively small pores have no fractal characteristics and pore structure is irregular. The fractal curve of Type II reservoir samples shows a three-segment pattern, and each pore size range has certain fractal characteristics, and it gradually gets better with the increase of pore size. The fractal curve of Type III reservoir samples presents a similar one-segment pattern, and the fractal dimension exceeds the upper limit of 3. It is considered that the full pore size of this type of reservoir does not have fractal characteristics, the pore throat is completely irregular or the surface is rough, and the heterogeneity is very strong.

基于P2PSand模型的水库土石坝坝基地震液化影响分析

为了解决水库土石坝坝基地震液化导致严重坝体变形和边坡失稳等灾害,从而对水库土石坝长效安全运行造成严重威胁的问题,以某水库土石坝为例,利用有限差分软件FLAC3D 7.0及其内置P2PSand模型(practical two-surface plastic sand model),对存在地震液化地基的水库土石坝进行地震动力响应分析。结果表明:地震强度与相对密实度对水库土石坝坝基地震液化趋势影响较大,超孔压比随着地震过程的进行而逐渐增大,增大幅度约为10.46%;随着坝基地震液化程度的提高,坝体变形更明显,并且坝基边坡稳定性劣化。

An Integrated Rock Typing Approach for Unraveling the Reservoir Heterogeneity of Tight Sands in the Whicher Range Field of Perth Basin, Western Australia

Tight gas sands in Whicher Range Field of Perth Basin show large heterogeneity in reservoir characteristics and production behavior related to depositional and diagenetic features. Diagenetic events (compaction and cementation) have severely affected the pore system. In order to investigate the petrophysical characteristics, reservoir sandstone facies were correlated with core porosity and permeability and their equivalent well log responses to describe hydraulic flow units and electrofacies, respectively. Thus, very tight, tight, and sub-tight sands were differentiated. To reveal the relationship between pore system properties and depositional and diagenetic characteristics in each sand type, reservoir rock types were extracted. The identified reservoir rock types are in fact a reflection of internal reservoir heterogeneity related to pore system properties. All reservoir rock types are characterized by a compacted fabric and cemented framework. But distribution and dominance of diagenetic products in each of them depend on primary depositional composition and texture. The results show that reservoir rock typing based on three aspects of reservoir sandstones (depositional properties, diagenetic features and petrophysical characteristics) is a suitable technique for depiction of reservoir heterogeneity, recognition of reservoir units and identifying factors controlling reservoir quality of tight sandstones. This methodology can be used for the other tight reservoirs.

Fungi Associated with Sand and Plants from Marine Coastlines: Potential Relevance for Human Health

The fungal community associated with beach sand and plants located along marine coasts are an under-studied area of research despite its potential relevance to human health. In this study, we isolated and identified the cultivable mycobiota associated with sand and plants collected along the coast of Gran Canaria (Spain) using culture-dependent and -independent methods. Clinically relevant species belonging to Cryptococcus spp. and related genera such as Naganishia and Papilotrema were isolated and identified from shoreline plants. Moreover, Candida tropicalis was isolated from beach sand, and Aspergillus fumigatus and Aspergillus terreus strains were associated with both types of samples (i.e., plants and beach sand). We conclude that beach sand and shoreline plants are potential reservoirs of fungi of high clinical interest. We recommend including beach sand and plants from the environment when assessing the quality of marine coastal systems. Our results open a framework for studying the natural marine environment and its role in the epidemiology of infectious diseases in order to more accurately manage public health.

The Seismic-Geological Comprehensive Prediction Method of the Low Permeability Calcareous Sandstone Reservoir

Currently in Niu-zhuang sub-sag, the seismic reflection amplitude of the newly discovered turbidite sandstone is stronger in the third Segment. The main reason is that Calcareous components accounts for a large part and physical properties is relatively poor, which results in no corresponding relation between reservoir and seismic attributes, and effective reservoir is difficult to predict and describe. Therefore, using the method of geological statistics, we firstly study the distribution of calcareous matters, secondly study the contribution to seismic reflection amplitude made by Calcareous high impedance component;thirdly analyze its influence on actual seismic reflection amplitude and determine the lithology thickness of Calcareous via replacement forward modeling. At last, we characterize the reservoir using the amplitude of calcareous matters. It proves that the method of seismic-geological comprehensive prediction is reliable. It has good guidance for exploration and development of the calcareous sand lithologic reservoir in similar areas.

Fracture prediction in the tight-oil reservoirs of the Triassic Yanchang Formation in the Ordos Basin,northern China

It is important to predict the fracture distribution in the tight reservoirs of the Ordos Basin because fracturing is very crucial for the reconstruction of the low-permeability reservoirs. Three-dimensional finite element models are used to predict the fracture orientation and distribution of the Triassic Yanchang Formation in the Longdong area, southern Ordos Basin. The numerical modeling is based on the distribution of sand bodies in the Chang 7a and 72 members, and the different forces that have been exerted along each boundary of the basin in the Late Mesozoic and the Cenozoic. The calculated results demonstrate that the fracture orientations in the Late Mesozoic and the Ceno- zoic are NW-EW and NNE-ENE, respectively. In this paper, the two-factor method is applied to analyze the distribution of fracture density. The distribution maps of predicted fracture density in the Chang 71 and 72 members are obtained, indicating that the tectonic movement in the Late Mesozoic has a greater influence on the fracture development than that in the Cenozoic. The average fracture densities in the Chang 71 and 72 members are similar, but there are differences in their distributions. Compared with other geological elements, the lithology and the layer thickness are the primary factors that control the stress distribution in the study area, which further determine the fracture distribution in the stable Ordos Basin. The predicted fracture density and the two-factor method can be utilized to guide future exploration in the tight-sand reservoirs.

川中地区金秋气田侏罗系沙一段有利含气区预测

针对金秋气田沙溪庙组一段(沙一段)河道砂体普遍致密化、物性差且非均质性强的问题,通过正演模拟优选多种叠前属性,运用三维透视和人工智能反演开展砂体边界、储层和含气性预测,优选致密气开发有利区。结果表明:沙一段Ⅲ、Ⅳ砂组河道最发育,河道集中在西部近物源区,向东宽度明显变窄,Ⅱ砂组和Ⅴ砂组次之,Ⅰ砂组河道数量最少。沙一段储层受分流河道控制明显,Ⅲ砂组和Ⅳ砂组储层厚度普遍大于8 m,呈连片状集中分布在西部JQ8井区,或呈条带状局限分布于东部JQ5H井区,Ⅱ砂组和Ⅴ砂组储层厚度为6~8 m,分别位于西部JQ8井区河道交汇处和东部JQ5H井区分流河道内部。通过人工智能有监督的学习,预测各砂组有利含气区,Ⅲ和Ⅳ砂组含气饱和度高,气藏集中分布在JQ8、JQ5H井区河道交汇处,Ⅱ砂组气藏呈窄条状分布在JQ8和JQ5H井区河道发育区,Ⅴ砂组则局限分布在QL7和JH5井区分流河道内。Ⅲ、Ⅳ砂组河道和储层厚度大,含气饱和度高,是致密气开发重点目的层。研究成果可以为川中地区金秋气田沙一段致密气高效开发提供地质依据。

塔里木盆地库车山前超深气井砂垢堵塞成因及靶向解除技术

塔里盆地库车山前超深气田是西气东输主力气源地,具有超高温、超高压、高矿化度、储层裂缝非均质性强等特征,气井生产过程中砂垢堵塞问题突出,据统计最高影响气田产能达800×104 m^(3)/d。为实现超深气井高效解堵,通过气水两相结垢热力学预测模型、裂缝性储层岩石力学实验、井筒内气液固流动模拟等研究,揭示了超深气井砂垢复合堵塞成因,并形成了靶向解堵复产关键技术。研究结果表明:①“高温流动压降结垢、裂缝面破裂出砂”是超深气井出砂结垢的内在机理;②结垢固化松散砂桥形成复合堵塞是气井堵塞减产的主要原因,其中靶向除垢是解堵复产的关键所在;③靶向除垢解堵区域为井筒变径处和井周5 m内基质—裂缝系统,气井堵塞率30%~60%为最佳解堵时机;④非酸性除垢解堵液相比常用的酸性解堵液,在同级别溶垢能力的基础上,腐蚀速率降至0.49 g/(m^(2)·h),可同时满足低腐蚀和高效除垢的技术要求。结论认为,形成的超深气井靶向除垢解堵技术在塔里木盆地库车山前超深气田规模应用159井次,有效率达93.3%,累计增产天然气75.08×10^(8)m^(3),已成为西气东输主力气井快速解堵复产的“冬保良方”,可为国内外同类气田解堵复产提供技术借鉴。

不同支撑剂组合方式下页岩导流能力实验评价

为了深入了解多粒径支撑剂组合条件下页岩储层导流能力的大小,依据达西定律,采用API支撑剂实验装置,评价分析不同支撑剂质量比例、粒径、铺砂浓度、类型、流体类型、岩性等对导流能力的影响。实验结果表明:随着闭合压力增加,各种支撑剂组合方式下的导流能力都有很大程度下降;相同条件下,铺砂浓度与导流能力呈正相关关系,覆膜砂的导流能力高于石英砂,清水条件下的导流能力高于破胶液,硬度高的页岩储层导流能力高于硬度低的页岩储层;70/140目陶粒+40/70目覆膜砂+30/50目覆膜砂支撑剂组合,在质量比为1∶6∶3时导流能力最优;在高闭合压力下,70/140目陶粒+40/70目覆膜砂+30/50目覆膜砂组合的导流能力,略高于70/140目陶粒+30/50目覆膜砂+20/40目覆膜砂支撑剂组合。可见,对于较软地层采用覆膜砂组合支撑剂,更有利于长期保持较高的导流能力;压裂液选用时更要注重压裂液配方的低伤害性,以提高导流能力。

Oil／Gas Accumulation Characteristics and Exploration Methods of the Deltaic Lithologic Reservoirs in Northern Shaanxi Area

There are large deltaic systems in the Triassic Yanchang Formation in the northern Shaanxi area of the Ordos Basin, and developed two sets of good source-reservoir-caprock assemblages and many sets of oil-bearing beds. Exploration experience demonstrates that the formation and distribution of the reservoir were controlled by the generative depression of the Yanchang Formation, and deltaic reservoir sand body is the material basis for large-scale oilfields. In addition, secondary laumontite in a low permeable area was dissolved and then a high permeable area was formed. The updip lithologic variety of reservoir sand bodies is favorable to the formation of subtle lithologic traps, and the deltaic reservoirs are characterized by large multi-beds of oil-generation and abundant hydrocarbon resources. In this paper, the petroleum geologic settings of the studied area are analyzed, and the accumulation characteristics and exploration methods of lithologic reservoirs are summarized. It is of theoretical significance for the study of the exploration theories of lithologic reservoirs, and also expedites the exploration steps of deltaic reservoirs in the northern Shaanxi area.

走航式电阻率法探测平原水库库底砂体效果分析及应用

平原水库库底沉积层中的砂体会对水库运行以及穿过库底地下空间工程建设的安全造成不可忽视的影响,一种快速且准确识别库底砂体空间位置的探测手段可为破解以上问题提供技术支持。本文以位于黄河流域的济南鹊山水库为研究区,基于数值模拟与原位探测结果,分析评价了走航式电阻率法识别平原水库库底砂体的最优装置参数和能力,并将所得结论在原位探测中应用、验证。研究结果表明,选用通用走航探测航速(航速2.5 m/s)对平原水库(水深6 m)进行探测时,走航式电阻率法对埋深浅(埋深<30 m)、厚度大(厚度>6 m)的砂体有较好的理论分辨能力。对于薄层深埋砂体(厚度<2 m,埋深>10 m)则难以识别;砂体探测顶、底界位置与实际顶、底界位置间的偏移距离与砂体顶界埋深、砂体长度呈正相关关系。砂体厚度增大会提高不同顶界埋深条件下砂体界面偏移距离差异,偏移距离正相关于深埋砂体厚度,负相关于浅埋砂体厚度;建立了修正原位探测结果并识别砂体的方法。基于原位探测结果所识别的砂体形态并不精确,其厚度普遍厚于实际砂体厚度约0~3 m。厚度小于3 m的薄砂体则难以被该方法识别。

四川盆地天府气田中侏罗统沙溪庙组砂岩储层致密化机理及其与油气充注的耦合关系

近年来,四川盆地中侏罗统沙溪庙组致密砂岩气勘探开发取得持续突破,展示出了良好的天然气勘探开发前景,但是砂岩储层致密导致“甜点区”分布复杂,特别是对储层致密化机理及其与油气充注的耦合关系认识不清,严重制约了沙溪庙组致密砂岩气藏的规模效益开发。为此,以四川盆地天府气田沙溪庙组一段(以下简称沙一段)致密砂岩储层为研究对象,综合岩心物性测试、薄片鉴定、扫描电镜、地球化学测试等多种资料,系统表征了致密砂岩储层的物质组成、储集物性、成岩作用等特征,并探讨了储层致密化机理,最后结合油气成藏期次,明确了储层致密化过程与油气充注耦合关系。研究结果表明:(1)沙一段储层以岩屑长石砂岩为主,发育少量长石岩屑砂岩,储层孔隙度为0.82%~17.48%,平均孔隙度为10.09%,渗透率为0.0001~632.4200 mD,平均渗透率为5.4200 mD,储层储集空间以原生孔隙为主,局部发育长石溶孔和浊沸石胶结物溶孔;(2)沙一段压实作用以弱—中等为主,绿泥石包壳广泛发育,浊沸石呈基底式、孔隙式和颗粒交代状等多种形式胶结,方解石呈基底式和孔隙式胶结,溶蚀作用以长石溶蚀和浊沸石溶蚀为主;(3)沙一段发育3种类型的致密储层,第一种致密储层是在压实作用基础上早期强胶结作用下形成的;第二种致密储层是在压实作用基础上晚期胶结作用下形成的;第三种储层现今并未致密,但是早期的压实胶结作用导致储层曾经致密,后期溶蚀作用改善储层物性。结论认为:(1)该区沙一段储层具有一期成藏特征,发生在距今88~68 Ma,第一种和第三种致密储层不能发生有效的油气充注,第二种致密储层可以发生有效的油气充注;(2)该区储层致密化过程与油气充注的耦合关系控制了天府气田简阳区块的天然气相对富集程度。

多层砂岩油藏油井层间干扰机理解析及讨论

多层砂岩油藏开发过程中普遍存在层间干扰现象,众多学者从不同角度开展了层间干扰机理、规律及应对策略研究,但层间干扰机理的认识程度多数停留在层间干扰系数宏观规律统计及对矿场应用的经验指导层面,有必要开展深入的定量化解析及讨论。本文首先从矿场油井层间干扰测试资料分析入手,确定了层间干扰研究的突破点,然后采用油藏数值模拟方法模拟了考虑启动压力梯度影响的油井产能测试过程,厘清了油井层间干扰规律,并综合诸多因素分析揭示了多层砂岩油藏层间干扰机理;最后深化了储层纵向非均质性认识,并探讨了油藏非均质性表征研究思路,为提高多层砂岩油藏油井产能预测精度、制定更加精细的开发对策提供理论、技术指导。

Rock Physics Models and Seismic Inversion in Reservoir Characterization, “MUN” Onshore Niger Delta Field

Rock Physics Modelling and Seismic Inversion were carried out in an Onshore Niger Delta Field for the purpose of characterizing a hydrocarbon reservoir. The aim of the study was to integrate rock physics models and seismic inversion to improve the characterization of a selected reservoir using well-log and 3D seismic data sets. Seven reservoir sands were delineated using suite of logs from three wells. In this study, the sand 4 reservoir was selected for analysis. The result of petrophysical evaluation shows that the sand 4 reservoir is relatively thick (62 ft) with low water saturation (0.33), shale volume (0.11) and high porosity (0.32). These results indicate reservoir of good quality and producibility. Cross-plot of property pairs (acoustic impedance (Ip) vs. lambda-rho (λρ) and mu-rho (μρ) vs. lambda-rho (λρ) color-coded with reservoir properties reveals three distinct probable zones: hydrocarbon sand, brine sand and shale. Results show that low Ip, λρ and μρ associated with hydrocarbon charged sands correspond to low Sw and Vsh and high &#216. The integration of rock physics models and inverted rock attributes effectively delineated and improved understanding of already producing reservoirs, as well as other hydrocarbon charged sands of low Sw, Vsh, and high?&#216 to the east of existing well locations, which indicate possible by-passed hydrocarbon pays. The results of this work can assist in forecasting hydrocarbon prospectivity and lessen chances of drilling dry holes in MUN onshore Niger delta field.