Effects of vugs on resistivity of vuggy carbonate reservoirs

The pore structure characteristic parameters of vuggy carbonate reservoirs were extracted,and matrix resistivity of vuggy reservoir was calculated by the percolation network simulation.A segmented cross-scale resistivity calculation method was established,in which the finite element method was used to simulate the resistivity of vuggy reservoirs.The mathematical models of vug porosity and water saturation with rock resistivity in vuggy carbonate reservoir were established,and the relationships between them were obtained.Experimental results verified the reliability of the simulation results.The method presented provides new technical means and research method for the resistivity log interpretation of vuggy carbonate reservoirs.The matrix porosity,vug porosity and matrix pore water saturation are the key factors determining the resistivity of reservoir rocks.

Automatic fracture–vug identification and extraction from electric imaging logging data based on path morphology

We present a path morphology method to separate total rock pore space into matrix, fractures and vugs and derive their pore structure spectrum. Thus, we can achieve fine pore evaluation in fracture–vug reservoirs based on electric imaging logging data. We automatically identify and extract fracture–vug information from the electric imaging images by adopting a path morphological operator that remains flexible enough to fit rectilinear and slightly curved structures because they are independent of the structuring element shape. The Otsu method was used to extract fracture–vug information from the background noise caused by the matrix. To accommodate the differences in scale and form of the different target regions,including fracture and vug path, operators with different lengths were selected for their recognition and extraction at the corresponding scale. Polynomial and elliptic functions are used to fit the extracted fractures and vugs, respectively, and the fracture–vug parameters are deduced from the fitted edge. Finally, test examples of numerical simulation data and several measured well data have been provided for the verification of the effectiveness and adaptability of the path morphology method in the application of electric imaging logging data processing. This also provides algorithm support for the fine evaluation of fracture–vug reservoirs.

A review of pressure transient analysis in reservoirs with natural fractures,vugs and/or caves

A review of the pressure transient analysis of flow in reservoirs having natural fractures,vugs and/or caves is presented to provide an insight into how much knowledge has been acquired about this phenomenon and to highlight the gaps still open for further research.A comparison-based approach is adopted which involved the review of works by several authors and identifying the limiting assumptions,model restrictions and applicability.Pressure transient analysis provides information to aid the identification of important features of reservoirs.It also provides an explanation to complex reservoir pressuredependent variations which have led to improved understanding and optimization of the reservoir dynamics.Pressure transient analysis techniques,however,have limitations as not all its models find application in naturally fractured and vuggy reservoirs as the flow dynamics differ considerably.Pollard’s model presented in 1953 provided the foundation for existing pressure transient analysis in these types of reservoirs,and since then,several authors have modified this basic model and come up with more accurate models to characterize the dynamic pressure behavior in reservoirs with natural fractures,vugs and/or caves,with most having inherent limitations.This paper summarizes what has been done,what knowledge is considered established and the gaps left to be researched on.

Production prediction for fracture-vug carbonate reservoirs using electric imaging logging data

Considering the fluid flow non-darcy characteristics in fracture-vug carbonate reservoirs, a new multi-scale conduit flow model production prediction method for fracture-vug carbonate reservoirs was presented using image segmentation technique of electric imaging logging data. Firstly, based on Hagen-Poiseuille's law of incompressible fluid flow and the different cross-sectional areas in single fractures and vugs in carbonate reservoirs, a multi-scale conduit flow model for fracture-vug carbonate reservoir was established, and a multi-scale conduit radial fluid flow equation was deduced. Then, conduit flow production index was introduced. The conduit flow production index was calculated using fracture-vug area extracted from the result of electrical image segmentation. Finally, production prediction of fracture-vug carbonate reservoir was realized by using electric imaging logging data. The method has been applied to Ordovician fracture-vug carbonate reservoirs in the Tabei area, and the predicted results are in good agreement with the oil testing data.

Experiments on the influences of well pattern on water flooding characteristics of dissolution vug-cave reservoir

Based on the similarity criterion, volcanic rock samples were taken from outcrops to make experimental models. Water flooding experiments of five-spot well pattern, nine-spot well pattern, five-spot to nine-spot well pattern, the relationship between relative well and fracture positions, and injection rate in dissolution vug-cave reservoirs with/without fractures were carried out to analyze variation regularities of development indexes, find out development characteristics of water flooding with different well patterns and sort out the optimal water flooding development mode. For dissolution vug-cave reservoirs without fractures, five-spot well pattern waterflooding has very small sweeping area, serious water channeling and low oil recovery. When the well pattern was adjusted from five-spot to nine-spot well pattern, oil recovery could be largely improved, but the corner well far from the injector is little affected. In dissolution vug-cave reservoirs with fractures, when the injector and producer are not connected by fractures, the fractures could effectively connect the poorly linked vugs to improve the development effect of water flooding. Whether there are fractures or not in dissolution vug-cave reservoirs, the development effect of nine-spot well-pattern is much better than that of five-spot well pattern and five-spot to nine-spot well pattern, this is more evident when there are fractures, and the edge well has better development indexes than corner well. At the high-water cut stage of water flooding with nine-spot well pattern, the oil recovery can be further improved with staggered line-drive pattern by converting the corner well into injection well. It is helpful to increase the oil production of corner well of nine-spot well pattern by increasing the injection rate, and improve ultimate oil recovery, but the water-free production period would be greatly shortened and water-free recovery would decrease.

四川盆地中部地区震旦系大型碳酸盐岩气藏开发技术新进展

四川盆地中部地区(以下简称川中地区)震旦系灯影组气藏为大型古老深层岩溶风化壳型碳酸盐岩气藏,气藏整体表现为低孔隙度低渗透率,储集空间小尺度缝洞发育,储层非均质性强特征,气藏开发面临储层表征难、井位部署和效益开发难度大等系列挑战。为此,以川中地区安岳气田灯影组气藏为对象,通过地质工程一体技术化攻关,深化了对储层发育特征和成因机理的认识,提出了气藏开发新模式,创建形成了气藏高效开发的关键技术。研究结果表明:①灯影组储层主要为岩溶成因储层,具有“叠合岩溶差异控储”的发育特征;②岩溶储层非均质性强,“溶蚀相成因控储”可精细刻画储层的非均质性;③灯影组气藏宜采用“单井指标叠加论证气藏规模”的开发新模式;④创新形成了“双界面”岩溶古地貌恢复及定量刻画方法,并指导平面选区,其中Ⅰ+Ⅱ类井比例由评价期的40%提高到方案建设期的100%;⑤创建了小尺度缝洞识别、刻画及表征技术,并指导钻井轨迹设计,测试百万立方米气井比例由开发评价期的41.6%提高到建产期的60%;⑥配套完善了分段酸压工艺技术,高效动用了优质储层,并解放了低品位储层,储层渗透率由改造前的0.62 mD提高到酸压改造后的6.77 mD。结论认为,“十四五”期间,在上述开发技术的支持下,安岳气田由台缘带灯四段高效开发转向长期稳产和台内地区多层系效益开发,蓬莱含气区由单井高产转向区块高产和气藏规模建产,将强力支撑中国石油西南油气田公司“十四五”末天然气上产500×10^(8)m^(3)。

基于“扩缝串洞”理念的超深层小缝洞群碳酸盐岩储层改造数值模拟

随着四川盆地和塔里木盆地碳酸盐岩油气藏勘探开发逐渐迈向超深层领域,受地质条件影响,储层由大型缝洞向以厘米—毫米级小缝洞群转变,以往针对大型缝洞储层改造的酸压技术系列难以适应小缝洞群储层。为充分释放超深层小缝洞群碳酸盐岩储层的天然气产能潜力,基于小缝洞群碳酸盐岩储层特征,构建了多尺度离散缝洞方法,建立了考虑岩石变形、裂缝延伸、酸液流动反应、温度变化的热流固化多场耦合数值模型,最后提出了以多级转向扩面积、精准控黏串缝洞、定点生酸扩缝长为核心的“扩缝串洞”缝控改造理念,并对小缝洞群碳酸盐岩储层“扩缝串洞”缝控改造方式进行了优化分析。研究结果表明:①多级交替注入形成的黏性指进现象可以促进缝控改造面积的增加和裂缝非均匀刻蚀,从而提高改造后的产能,且缝控改造效果最佳;②酸液注入黏度比增加,缝控改造无因次产能指数呈现先增大后减小的规律,当黏度比超过30,缝控改造无因次产能指数开始迅速减小,缝控改造中酸液交替黏度比需控制在25~35区间;③酸液用量越大,缝控改造面积及改造后无因次产能指数越大,但对于一定地层参数和单井控制面积的缝控改造存在极限酸液用量,超过该酸液用量后缝控面积趋于极限值,而无因次产能指数仍随酸液用量的增加而稳定增大。结论认为,提高缝控改造面积和激活动用小缝洞群是小缝洞群碳酸盐岩储层提产的关键,该认识为超深层小缝洞群碳酸盐岩气藏的高效开发提供了理论指导。

Permeability analysis of fractured vuggy porous media based on homogenization theory

Based on the characteristics of fractured vuggy porous media,a novel mathematical model was proposed to model fluid flow in such media on fine scale,i.e.,the discrete fracture-vug network model.The new model consists of three systems:porous rock system,fracture system,and vug system.The fractures and vugs are embedded in porous rock,and the isolated vugs could be connected via the discrete fracture network.The flow in porous rock and fractures follows Darcy's law,and the vugs system is free fluid region.Using a two-scale homogenization limit theory,we obtained a macroscopic Darcy's law governing the media on coarse scale.The theoretical formula of the equivalent permeability of the fractured vuggy porous media was derived.The model and method of this paper were verified by some numerical examples.At the end the permeability of some fractured vuggy porous media with typical fracture-vug structures was analyzed.

塔河油田碳酸盐岩缝洞型油藏井网优化

碳酸盐岩缝洞型油藏具有储集体规模差异大、空间离散性强,井间缝洞连通结构复杂、流体流动模式多样等特征。缝洞控制程度低,储量动用不均衡,生产效果差异大,常规砂岩油藏规则和不规则井网部署方式均不适用,需要建立一种匹配油藏特点的井网构建与优化方法。将物理模拟实验和理论分析相结合,采用“立体化”、“系统化”的井网构建思路,丰富空间结构井网的理论内涵,深化重力驱替理论在空间结构井网构建中的根本性认识。建立以缝洞结构、连通关系、储量动用、能量状况和注采结构为主线的井网设计方法和六步法井网构建流程。总之,流体密度差是重力置换的主导因素,缝洞连通结构的位势差是纵向驱替的重要驱动力,主次通道的驱替速度差是垂向平衡的关键,是缝洞型油藏空间结构井网提高采收率的增效机制。

塔河油田海西运动早期岩溶水系统划分及特征

塔里木盆地塔河油田中—下奥陶统海西运动早期地表及地下岩溶形态多样,地下岩溶缝洞系统中油气资源丰富。根据高精度地震资料及钻井资料,统一地下及地表水系统,构建了塔河油田中—下奥陶统海西运动早期岩溶水系统。研究结果表明:塔河油田中—下奥陶统在海西运动早期发育4个岩溶台地,总体呈东高西低阶梯分布,岩溶水差异化排泄和溶蚀作用造成各岩溶台地发育峡谷、伏流、深切曲流、宽谷等不同水文地貌形态;岩溶水系统的边界主要为地表分水岭、排泄基准面、地层岩性组合、断裂和弱溶蚀带;塔河油田岩溶水系统划分为4个相对独立的二级岩溶水系统,分别为高原峡谷水系统、伏流峡谷水系统、深切曲流水系统和宽谷水系统;岩溶水系统层级结构的划分为深化塔河油田岩溶缝洞系统和岩溶缝洞单元认识提供地质依据。

顺北地区碳酸盐岩断控缝洞体油气产能定量化估算技术

走滑断裂带及其控制的缝洞体是顺北地区奥陶系新的勘探领域,探索断控缝洞体储层单井产量多属性量化预测技术,为顺北地区断裂带井位部署与井轨迹优选提供科学依据和技术支撑。断控缝洞体储层中,断裂是油气运移通道,其纵向延伸和宽度是断裂的通源性,主干断裂与次级断裂平面交汇结构表征断裂的汇聚性,通源性和汇聚性表征成藏断裂特征。断控缝洞体中缝洞是储集空间的主体,断控缝洞体储层规模和断裂裂缝分布密度表征缝洞特征。断控缝洞体储层的单井产量既与断裂特征有关,更与缝洞特征有关。因此,量化的断裂特征和缝洞特征是单井产量量化预测的基础。地震数据及其多种属性的断层精细解释,量化后得到断裂特征值。结构张量属性圈定断控缝洞体储层范围,异常体振幅属性表征缝洞的分布及其体量,最大似然概率属性表征断裂裂缝分布密度,3种属性融合得到缝洞特征值。最后将量化的断裂特征值和缝洞特征值融合为断控缝洞体特征值,与实测钻井的年产液量进行统计分析,得到年产液量与断控缝洞体特征值的统计关系式,实现断控缝洞体储层单井产量的量化预测。

对标产能的碳酸盐岩储集层测井分类评价——以塔里木盆地托甫台地区一间房组为例

孔隙类型多样是塔里木盆地托甫台地区中奥陶统一间房组碳酸盐岩储集层非均质性强的主要原因,储集层有效性难以评价。在岩心和薄片观察的基础上,依据成像测井资料,将碳酸盐岩孔洞分为溶蚀孔和洞穴;裂缝分为构造缝、溶蚀缝和压溶缝。根据孔洞和裂缝的组合形式,将研究区一间房组碳酸盐岩储集层划分为裂缝型、裂缝-孔洞型和孔洞型。综合导电效率、裂缝孔隙度和深侧向电阻率变化幅度,建立了储集层类型的定量划分标准,孔洞型储集层导电效率小于0.008,裂缝孔隙度小于0.13%;裂缝-孔洞型储集层导电效率为0.008~0.024,裂缝孔隙度为0.13%~0.60%;裂缝型储集层导电效率大于0.024,裂缝孔隙度大于0.60%。依据累计有效孔隙厚度、平均有效孔隙度以及产能,建立了裂缝-孔洞型储集层和孔洞型储集层分类判别图版。托甫台地区一间房组裂缝-孔洞型储集层和孔洞型储集层均主要为Ⅱ类储集层,测试日产液量分别超过55 t和50 t。

缝洞型油藏一井多靶分段压裂开发效果数值模拟

为了研究缝洞型油藏一井多靶分段压裂开发效果,基于离散缝洞模型,建立了考虑基质—裂缝渗流和溶洞自由流耦合的缝洞型油藏油水两相流动模型及数值模拟方法,分析了天然裂缝发育程度、底水及压裂簇数对开发效果的影响。结果表明:在无底水条件下,天然裂缝发育程度仅影响采油速度,对累计产油量影响很小;在有底水条件下,底水沿天然裂缝上升会驱替溶洞中原油,产油量会随天然裂缝密度增大而升高;溶洞尺寸和压裂裂缝对缝洞型油藏产能具有显著影响;当天然裂缝发育程度较高时,每段一簇和多簇压裂裂缝开发效果差异明显减小,即采用一簇压裂裂缝便可控制整个缝洞甜点区域。

应力对超深层碳酸盐岩气藏孔喉结构的影响

超深层碳酸盐岩气藏埋藏深,应力状态复杂,非均质性极强,应力变化前后孔喉结构的变化规律尚不明确。选取高石梯-磨溪区块台内灯四气藏储层岩心,通过CT扫描得到应力实验和压裂实验前后不同类型储层的孔喉尺寸分布、缝洞占比和连通性等,研究应力和压裂对超深层碳酸盐岩储层孔喉结构的影响规律。结果表明:在受压恢复后,孔洞型和缝洞型岩心的孔隙和喉道个数均大幅度下降且主要集中在半径在1 mm以下的微孔、中孔和0.04mm以下的微喉,孔隙平均半径、喉道平均半径和喉道平均长度均大幅度增加,缝洞比例大幅度增加,孔隙和喉道总体积趋于减小;孔洞型岩心连通孔喉体积占比大幅下降,而缝洞型岩心由于裂缝发育,其连通孔喉体积占比维持原有水平。压裂后,孔洞型岩心孔隙个数大幅度下降,减少的孔隙半径主要集中在0.5 mm以下的微孔和中孔,孔隙平均半径大幅度上升,增加的孔隙半径主要集中在0.5~0.8 mm,孔隙体积总体呈上升趋势,喉道个数、喉道平均半径、喉道平均长度和喉道总体积均趋于增加,缝洞比例大幅度增加,连通孔喉体积大幅度提高。实验表明超深层碳酸盐岩储层受压恢复后,渗流能力不降反而大幅度提升,压裂主要通过提高孔喉空间中裂缝占比来改善孔喉连通性。

滨里海盆地东缘石炭系盐下碳酸盐岩油气藏成藏规律与勘探技术

根据地震、钻井及薄片等资料,采用地震波阻抗储层反演技术,对滨里海盆地东缘石炭系盐下碳酸盐岩储层特征、油气成藏规律进行了研究,并指出了下一步风险勘探方向。研究结果表明:①滨里海盆地东缘石炭系盐下碳酸盐岩储层可分为灰岩类、云岩类、云灰岩/灰云岩类、硅化硅质岩类等,储层孔隙度为4%~12%,渗透率通常小于1 mD,属于低—中孔、低渗孔洞-孔隙型储层。②研究区阿克若尔构造带主要发育岩性油气藏,无统一油水界面,油层呈薄层状分散分布,对比性和连续性均较差,优质储层多为高频三级层序旋回中上部的高生长率滩体及不整合面附近的岩溶储层。③采用基于层位-测井约束的初始模型的地震波阻抗储层反演技术预测碳酸盐岩薄储层,可更清晰地呈现KT-Ⅰ和KT-Ⅱ油层组储层的纵、横向展布特征。研究区有利储层主要发育在KT-Ⅱ油层组顶部的G1和G4小层。

缝洞型油藏试井模型及其在顺北油田的应用

塔里木盆地顺北油田为缝洞型油藏,裂缝、大尺度溶洞并存,流动机理复杂,常规试井模型无法进行解释。在分析地层渗流、溶洞流体波动、井筒管流耦合的流体流动特征基础上,建立了钻遇溶洞、未钻遇溶洞2种缝洞型油藏试井模型。研究结果表明:缝洞型油井的井底压力响应曲线上可识别出井储、过渡、溶洞1、地层裂缝、溶洞2等流动阶段,而顺北地区油井多洞参与流动的特征较多,主要表现为有明显双洞特征和无明显双洞特征2种曲线类型;通过模型参数反演能够得到溶洞体积、溶洞距离、缝洞体积等参数。对顺北油田1口油井进行分析表明,新模型与实测曲线拟合精度高,拟合率达85%以上,计算的地层参数能够满足工程精度,且符合油藏地质特征。研究成果可用于缝洞型油藏试井资料解释。

基于上覆地层频率约束的匹配追踪强反射层分离方法

基于匹配追踪强反射分离方法在实际应用中取得了较好的效果,但关键参数的选择仍存在一些问题,相关研究较少。本文针对匹配追踪强反射分离方法中频率参数的优选问题,开展了详细的研究工作,并形成技术流程。首先,从地震波传播和衰减的角度,分析了地震波频率的空间变化特征,提出频率约束匹配追踪算法的思路;然后,设计相应的地质模型,开展频率优选测试研究,采用上覆地层频率约束匹配追踪算法进行强反射分离,测试结果验证了方法的准确性和有效性;最后,针对塔里木盆地碳酸盐岩缝洞型储层,开展上覆地层频率约束匹配追踪强反射分离技术的应用。应用成果表明,基于上覆层频率约束的匹配强反射分离技术能更合理、有效地分离强反射同相轴,下伏小尺度缝洞体特征更加明显,应用效果显著。研究促进了匹配追踪强反射分离技术的进一步优化,提高了资料的适应能力和实际应用效果,为后续进一步推广应用奠定了更好的基础。

超深断控缝洞型储层迭代反演方法——以富满油田为例

塔里木盆地塔河南岸富满油田超深层奥陶系灰岩地层缝洞型油藏现如今是油田产能建设的核心靶区。研究区储层是受走滑断裂作用控制地层破裂形成的大量溶蚀孔洞,非均质性强。而常规波阻抗反演的低频模型是由层位、断裂和测井数据建立起来的,不能表征储层的断控非均质性。为此,提出以“断裂破碎带相”为约束的迭代反演方法来预测储层,其技术流程是先对原始地震数据进行解释性处理,得到能反映储层断裂破碎带特征的属性体,将其与常规波阻抗反演得到的优质储层空间轮廓数据和初始低频模型进行比例融合,生成新的非均质性低频模型,进而开展多轮次迭代反演。反演结果可真实地刻画非均质储层断裂破碎带特征,10口井的预测吻合率可达92.86%。应用表明,该方法改善了储层预测效果,提高了断控储层的预测精度,有效地支撑了研究区的工作。

微电阻率成像测井缝洞有效性分析新技术在灯影组的应用

四川盆地高石梯-磨溪地区震旦系灯影组碳酸盐岩储层溶蚀缝洞发育、非均质性强、测试产量变化大、控制因素复杂,常规测井在碳酸盐岩复杂溶蚀缝洞定量分析及有效性评价上具有很大的局限性。为了更好地进行储层评价,采用微电阻率成像测井缝洞有效性分析新技术对溶蚀缝洞进行有效性半定量-定量评价,可计算得到面孔率、孔洞面积及连通性指数等关键参数。该技术的优势在于可基于岩心刻度,通过人机互动的方式来约束门槛值的选取,从而去除电成像图像上泥质、黄铁矿、诱导缝及井壁崩落等信息的影响,只提取有效缝洞的信息。通过现场应用得出,缝洞有效性分析新技术能够较为准确地评价井筒附近溶蚀缝洞的有效性,高石梯-磨溪地区优质储层缝洞有效性分析结果与岩心特征吻合度较高。此外,还尝试将有效性参数与单井无阻流量作为输入,利用神经网络学习,进行无阻流量与缝洞有效性参数及储层厚度关系的探讨分析,形成了初步预测无阻流量级别的方法。