Pore structure differences of the extra-low permeability sandstone reservoirs and the causes of low resistivity oil layers: A case study of Block Yanwumao in the middle of Ordos Basin, NW China

The influence of pore structure difference on rock electrical characteristics of reservoir and oil reservoir was analyzed taking Triassic Chang 6 reservoir in Block Yanwumao in the middle of Ordos Basin as an example. The relationship between the pore structure difference and the low resistivity oil layer was revealed and demonstrated through core observation, lab experiments, geological research, well log interpretation and trial production etc. The results show that there were two kinds of oil layers in Chang 6 oil layer set, normal oil layer and low resistivity oil layer in the region, corresponding to two types of pore structures, pore type mono-medium and micro-fracture-pore type double-medium; the development of micro-fracture changed greatly the micro-pore structure of the reservoir, and the pore structure difference had an important influence on the rock electrical characteristics of the extra-low permeability sandstone reservoir and oil reservoir; the normal oil layers had obvious characteristics of pore-type mono-medium, and were concentrated in Chang 61, Chang 6232 and Chang 62; the low resistivity oil layers had obvious characteristics of micro-fracture-pore type double-medium, which were mainly distributed in Chang 612 and Chang 63. The mud filtrate penetrated deep into the oil layers along the micro-cracks, leading to sharp reduction of resistivity, and thus low resistivity of the oil layer; the low resistivity oil layers had better storage capacity and higher productivity than the normal oil layers.

The new finding of Neogene marine low-resistivity light oil field in the western part of Pearl River Mouth Basin

Based on the new finding of Wenchang L low-resistivity light oil field, the finding process, reservoir characteristics and pool-forming pattern were studied. The oil-rock correlation, neritic reservoir type, hydrocarbon conduct system and dominant migration and accumulation direction,and new techniques were discussed. The results showed that large amount of hydrocarbon generated by shallow lacustrine mudstone and shale of Eocene Wenchang formation could migrate from sag to Qionghai uplift distantly; neritic shoal-bar reservoir have developed in the 1st member of Zhujiang formation, dip-sag faults and regional good marine sandstone layers of the 1st and the 2nd member of Zhujiang formation have constituted hydrocarbon conduct system in Qionghai uplift; the late fault system which were controlled by Dongsha tectonic movement constructed the connection between lower hydrocarbon and upper neritic shoal-bar reservoir. Therefore, the pool-forming pattern with "vertical migration and accumulation, secondary structure-lithology-dominated" was proposed. Finally the enlightenment of explorating new findings was discussed.

Necessity and feasibility of improving the residual resistance factor of polymer flooding in heavy oil reservoirs

The efficiency of water flooding in heavy oil reservoirs would be improved by increasing the viscosity of the displacing phase, but the sweep efficiency is not of significance due to the low mobility of the vicious oil. On the basis of mobility control theory, increasing the residual resistance factor not only reduces the water-oil mobility ratio but also decreases the requirement for viscosity enhancement of the polymer solution. The residual resistance factor caused by hydrophobic associating polymer solution is higher than that caused by polyacrylamide solution in brine containing high concentrations of calcium and magnesium ions. The results of numerical simulations show that the polymer flooding efficiency improved by increasing the residual resistance factor is far better than that by only increasing solution viscosity. The recovery factor of heavy oil reservoirs （70 mPa·s） can be enhanced by hydrophobic associating polymer solution of high residual resistance factor （more than 3） and high effective viscosity （24 mPa·s）. Therefore, increasing the residual resistance factor of the polymer solution not only decreases the requirement for the viscosity of polymer solution injected into heavy oil reservoirs but also is favorable to enhanced oil recovery during polymer flooding.

A novel profile modification HPF-Co gel satisfied with fractured low permeability reservoirs in high temperature and high salinity

Conformance control and water plugging are a widely used EOR method in mature oilfields.However,majority of conformance control and water plugging agents are unavoidable dehydrated situation in high-temperature and high-salinity low permeability reservoirs.Consequently,a novel conformance control system HPF-Co gel,based on high-temperature stabilizer(CoCl_(2)·H_(2)O,CCH)is developed.The HPF-Co bulk gel has better performances with high temperature(120℃)and high salinity(1×10^(5)mg/L).According to Sydansk coding system,the gel strength of HPF-Co with CCH is increased to code G.The dehydration rate of HPF-Co gel is 32.0%after aging for 150 d at 120℃,showing excellent thermal stability.The rheological properties of HPF gel and HPF-Co gel are also studied.The results show that the storage modulus(G′)of HPF-Co gel is always greater than that of HPF gel.The effect of CCH on the microstructure of the gel is studied.The results show that the HPF-Co gel with CCH has a denser gel network,and the diameter of the three-dimensional network skeleton is 1.5-3.5μm.After 90 d of aging,HPF-Co gel still has a good three-dimensional structure.Infrared spectroscopy results show that CCH forms coordination bonds with N and O atoms in the gel amide group,which can suppress the vibration of cross-linked sites and improve the stability at high temperature.Fractured core plugging test determines the optimized polymer gel injection strategy and injection velocity with HPF-Co bulk gel system,plugging rate exceeding 98%.Moreover,the results of subsequent waterflooding recovery can be improved by 17%.

Temperature-resistant and salt-tolerant mixed surfactant system for EOR in the Tahe Oilfield

A new temperature-resistant and salt-tolerant mixed surfactant system(referred to as the SS system)for enhancing oil recovery at the Tahe Oilfield(Xinjiang,China)was evaluated.Based on the analysis of the crude oil,the formation water and rock components in the Tahe Oilfield,the long-term thermal stability,salt tolerance and the ability to change the wettability,interfacial activity and oil washing efficiency of the mixed surfactant system were studied.The system contains the anionic surfactant SDB and another cationic surfactant SDY.When the total mass concentration of the SS solution is 0.15 wt%,m(SDB)/m(SDY)ratio is 1 to 1,and excellent efficiencies are achieved for oil washing for five kinds of Tahe Oilfield crude oils(more than 60%).In addition,after adding cationic surfactant,the adsorption capacity of the surfactant is further reduced,reaching 0.261 mg/g.The oil displacement experiments indicate that under a temperature of 150°C and a salinity of 24.6×104 mg/L,the SS system enhances the oil recovery by over 10%after water flooding.The SS anionic–cationic surfactant system is first presented in the open literature that can be successfully applied to obtain predictions of Tahe Oilfield carbonate reservoirs with a high temperature and high salinity.

Exploration Technology for Complex Sandstone Reservoirs in the Developed Area of Shengli Oilfield

Jiyang depression, which is the main oil productive area of Shengli oil field, is located at the southeast part of the Bohai Bay Basin and is a terrestrial lacustrine rift subsidence basin formed in the late Mesozoic with fully developed fault system. The main hydrocarbon productive formations of this depression are the terrestrial clastic rocks of the Tertiary, which are of strong lateral variation. The complex fault reservoirs and subtle lithological reservoirs distributed extensively and are becoming the main exploration targets in recent years. The exploration and development practice in these years has formed the exploration technologies, mainly including detailed study and description of low grade faults, delineation of microstructures, facies constrained formation description and prediction and low resistivity oil bearing formation’s identification. These exploration technologies have resulted in remarkable effectiveness on the reserve and oil production increments.

Application of deviation rate in oil and gas reservoir exploration

Three dimensional geophysical models were abstracted and established according to characteristics of oil and gas reservoir.Then direct current fields for different models were simulated with finite element software(finite element program generator) by hole-to-surface resistivity method.Numerical solution was compared with analytical one for the homogeneity earth model.And a new parameter of deviation rate was proposed by analyzing different plot curves.The results show that the relative error of solution for homogeneity earth model may attain to 0.043%.And deviation rate decreases from 18% to 1% and its anomaly range becomes wide gradually when the depth of oil and gas reservoir increases from 200 to 1 500 m.If resistivity ratio of oil and gas reservoir to sur-rounding rock decreases from 100 to 10 for the resistive oil and gas reservoir,the amplitude attenuation of deviation rate nearly reaches 8%.When there exists stratum above oil and gas reservoir,and influence of resistive stratum may be eliminated or weakened and anomaly of oil and gas reservoir can be strengthened.

奥连特盆地隐蔽油藏高效滚动勘探开发方法技术及应用——以厄瓜多尔14和17区块为例

厄瓜多尔14和17区块位于奥连特盆地前渊带,主要含油层系为Napo组的M1,U和T段。现已开发油田进入高含水阶段,资源接替面临挑战。通过基于趋势面驱动的叠后地震数据连片一致性处理、时-频衰减高精度合成记录标定和解释及各向异性变速成图,精细刻画了低幅度构造,发现了一批低幅度构造油藏。采用分频迭代去噪拾取薄层弱反射系数,以其重构的叠后宽频有效信号为约束,采用相控波形非线性反演,定量预测了埋深3 000 m的2~5 m厚潮汐水道砂岩,发现了多个M1超薄层岩性油藏。依据区域水动力条件、低幅度构造油藏油-水界面趋势及油藏能量特征,发现了LU水动力油藏并滚动扩边。通过观察大量岩心薄片,发现海绿石在石英砂岩储层中呈胶结物和颗粒两种赋存状态,建立了海绿石双组构测井解释体积模型,评价并识别了UT低电阻率油藏。基于热带雨林地表和隐蔽油藏特点,按照“整体部署、分批实施、跟踪评价、及时调整”的策略,实现滚动勘探、评价和快速建产,探井和评价井成功率大于90%。

海上低阻油藏注水开发影响因素分析

低阻油藏储层的研究一直是国内外油田开发人员亟待解决的难题之一。本文结合岩心、薄片、扫描电镜、物性及黏土矿物分析化验数据,H油田Ⅳ油组储层成岩作用可见压实作用、胶结作用和溶解作用。胶结物泥质、高岭石、菱铁矿和黄铁矿是影响该段储层物性的主要因素,主要的建设性成岩作用为溶解作用,溶解作用对改善储层的储集性能更为有利,产生的次生孔隙及裂缝一定程度上改善了本井的孔隙结构。Ⅳ油组储层分析样品含油饱和度随着地层深度增加呈现递增趋势;而含水饱和度随着地层深度增加呈现递减趋势;含油饱和度平均为7.5%;而含水饱和度平均为84%。Ⅳ油组深度2094.35~2129.39 m划分为中成岩A期,2130.00~2136.42 m划分为中成岩B期。研究成果为低阻H油田储层的高效开发提供了依据。

绥靖油田延长组长2储层流体识别方法

绥靖油田延长组属于低孔、低渗复杂致密砂岩储层,低孔低渗致密砂岩储层常常会出现低阻油层,低阻油层的成因机理研究随着非常规油气田的勘探开发而备受关注,本论文针对研究区长2段电阻率明显偏低的现象,从孔隙结构、构造圈闭幅度等方面展开研究,对目标地层低阻油层成因进行探讨。本轮研究在深入分析长2段低阻油层成因的基础上,根据绥靖油田延长组长2储层的物性特征,将孔隙度和束缚水饱和度的关系拟合曲线,得出了束缚水饱和度计算公式,采用束缚水饱和度与含水饱和度重叠法,对研究区长2段储层进行流体性质识别。在此基础上,还建立了双孔隙度重叠法,可以有效、快速对延长组长2段储层进行流体性质识别。

底水油藏开发中超高清随钻油藏描绘技术分析

底水油藏开发过程中地质导向效率主要受到储层非均质性、油水分布的复杂性以及构造预测的不确定性的影响。因此,需要准确的定量刻画井眼附近的储层特征,才能有效的控制轨迹贴顶钻进和抑制底水锥进。由此,引入了超高清随选油藏描绘仪(PeriScope Edge)工具提供的超高清随钻油藏描绘技术,通过反演井眼周围一定范围内的储层特征,来指导地质导向施工。综合分析验证了PeriScope Edge技术在底水油藏精细开发中的有效性。

LH2500抗盐聚合物对注聚后期开发效果影响研究

为了改善普通聚合物驱(聚丙烯酰胺)在注聚后期含水回升速度快、剖面反转严重、中低渗透层剩余油富集等问题,在X油田A块6#站开展普通聚合物注聚后期更换LH2500抗盐聚合物现场试验。本文依据注聚后期更换LH2500抗盐聚合物后动态指标变化特征,开展该聚合物受效规律及效果评价方法研究。研究表明,由于其分子结构及理化性能特点,LH2500抗盐聚合物具有注聚后期注入能力强、含水升幅小、聚合物用量小、对中低渗透层有效动用等优势,其中注入速度达0.2 PV/a,采收率提升12%以上。该技术经济效益显著,推广应用前景广阔。

基于全直径岩心二维核磁共振测量的低阻油层评价方法

河套盆地临河组砂岩储层中油层类型多样,低阻油层普遍存在,油层识别难度大。本文通过室内柱塞样岩心离心状态、饱和状态测量核磁T谱,结合测井资料及油水分析,明确河套盆地临河组砂岩低阻油层主要成因;根据移动式全直径岩心核磁共振Ti一T,现场测量数据,分析不同流体组分T1-T,图谱特征,明确典型油层、低阻油层、水层孔隙流体组分分布特征规律,确定二维核磁TI-T,图谱中油水信号的分布特征;同时,根据低阻油信号在二维核磁Ti-T,图谱中的分布特征建立含油饱和度计算模型,实现低阻油层含油性定量评价;形成了基于全直径岩心二维核磁共振测量的低阻油层评价方法,该方法在河套盆地规模化应用,效果显著。

Low resistivity oil(gas)-bearing reservoir conductive model——Dual water clay matrix conductive model in the north area of Tarim Basin, Xinjiang, China

Shaly sands reservoir is one of the most distributive types of the oil(gas)-bearing reservoirs discovered in China, and low resistivity oil(gas)-bearing reservoirs are mostly shaly sands reservoirs. Therefore, shaly sands reservoir conductive model is the key to evaluate low resistivity oil(gas)-bearing reservoirs using logging information. Some defects were found when we studied the clay distribution type conductive model, dual-water conductive model, conductive rock matrix model, etc. Some models could not distinguish the conductive path and nature of microporosity water and clay water and some models did not consider the clay distribution type and the mount of clay volume. So, we utilize the merits,overcome the defects of the above models, and put forward a new shaly sands conductive model-dual water clay matrix conductive model (DWCMCM) in which dual water is the free water and the microporosity water in shaly sands and the clay matrix(wet clay) is the clay grain containing water. DWCMCM is presented here, the advantages of which can tell the nature and conductive path from different water (microporosity water and freewater), in consid-eration of the clay distribution type and the mount of clay volume in shaly sands. So, the results of logging interpretation in the oil(gas)-bearing reservoirs in the north of Tarim Basin area, China with DWCMCM are better than those interpreted by the above models.

Permeability Estimation of Shale Oil Reservoir with Laboratory-derived Data: A Case Study of the Chang 7 Member in Ordos Basin

The shale oil reservoir within the Yanchang Formations of Ordos Basin harbors substantial oil and gas resources and has recently emerged as the primary focus of unconventional oil and gas exploration and development.Due to its complex pore and throat structure,pronounced heterogeneity,and tight reservoir characteristics,the techniques for conventional oil and gas exploration and production face challenges in comprehensive implementation,also indicating that as a vital parameter for evaluating the physical properties of a reservoir,permeability cannot be effectively estimated.This study selects 21 tight sandstone samples from the Q area within the shale oil formations of Ordos Basin.We systematically conduct the experiments to measure porosity,permeability,ultrasonic wave velocities,and resistivity at varying confining pressures.Results reveal that these measurements exhibit nonlinear changes in response to effective pressure.By using these experimental data and effective medium model,empirical relationships between P-and S-wave velocities,permeability and resistivity and effective pressure are established at logging and seismic scales.Furthermore,relationships between P-wave impedance and permeability,and resistivity and permeability are determined.A comparison between the predicted permeability and logging data demonstrates that the impedance–permeability relationship yields better results in contrast to those of resistivity–permeability relationship.These relationships are further applied to the seismic interpretation of shale oil reservoir in the target layer,enabling the permeability profile predictions based on inverse P-wave impedance.The predicted results are evaluated with actual production data,revealing a better agreement between predicted results and logging data and productivity.

页岩油储层水平井随钻电磁波电阻率测井资料校正方法

页岩油储层具有非均质强、各向异性显著等特征,造成水平井随钻电磁波电阻率测井响应复杂,资料定性解释和定量评价极为困难。为此,本文研发了一种适用于页岩油储层水平井随钻电磁波电阻率测井资料的校正方法。首先,考虑储层电性特征和泥浆类型,构建页岩油储层水平井电测井解释模型;研究相位差和幅度比曲线随井眼尺寸的变化,进而建立复杂仪器响应到均匀介质点源响应的映射关系,以消除钻铤及井眼等影响;在此基础上,针对页岩油储层,建立了基于解析算法的随钻电磁波电阻率测井资料逐点实时各向异性校正方法;最后,借助成像资料提供的界面和倾角信息,采用一维层状介质模型和梯度反演算法,逐层提取地层水平和垂向电阻率。结果表明:经井眼校正,随钻电磁波电阻率测井资料的处理可简化至一维,为资料快速处理奠定了基础;水平井随钻电磁波电阻率测井各向异性校正方法,可准确提取页岩油储层的水平和垂向电阻率信息,为该类油藏测井解释和定量评价提供准确的电性参数。

细粒沉积岩典型低阻油层成因及甜点分布

细粒沉积岩已成为非常规油气勘探的重要目标,普遍发育了低电阻率油气层。利用测井、录井、地震和薄片电镜测试等资料,结合相控储层参数分布技术,揭示了细粒沉积岩典型低阻油层成因机制,并提出了3类基于低阻成因的甜点分布规律。研究表明:①低阻油层成因主要包括大比表面积、高含量伊/蒙混层矿物、发达的微孔隙网络及其内部束缚水、高矿化度水以及高含量导电矿物等5个方面。②识别出了3类细粒沉积岩低阻类型,包括高泥质含量致密型低阻油层(致密低阻型)、高含量导电矿物型低阻油层(导电矿物低阻型)和疏松砂岩强连通水网型低阻油层(强连通水网导电低阻型),并在此基础上进行了成因分析。③明确了低阻隐蔽油层的甜点分布特征。致密型低阻油层甜点主要发育在电阻率相对较高的储层中,导电矿物型低阻油层甜点主要发育在白云质粉砂岩基质溶蚀段与白云质泥/页岩裂缝发育段,而强连通水网导电型低阻油层甜点主要发育在具有双模态孔隙结构的极细粒岩性中。研究结果对于指导下一步细粒沉积岩储层油气勘探意义重大。

低渗致密储层微纳米孔喉分布及其对渗流的影响

低渗-致密储层微观孔喉分布有较大差异,导致其渗流特征亦有明显不同。将室内实验与油藏工程计算相结合,定量研究了低渗-致密储层微纳米孔喉分布特征及其对渗流的影响。结果表明:1)孔喉半径小于1μm的孔喉体积占总孔喉体积的主体;2)岩心渗流特征曲线呈非线性渗流规律,渗透率降低,启动压力梯度显著增大,附加渗流阻力占总渗流阻力的比例也增大,研究物性范围内,附加渗流阻力占比均大于50%,渗透率为0.4 mD时,附加渗流阻力占比可达84.8%;3)微纳米孔喉的存在使得油井泄油半径降低,渗透率为0.4 mD时,极限泄油半径仅28.5 m,制约了井间及压裂水平井段间原油的动用。该研究成果可为认识低渗-致密油藏流体渗流规律和制定合理开发方案提供指导。

稠油油藏耐高温洗油剂体系的研制及性能

基于分子模拟技术设计并合成了一种以C_(12)^(+)蒽为疏水基团、磺酸钠为亲水基团的全新结构的表面活性剂,对合成的反应条件进行优化。将合成的表面活性剂与降黏剂及助剂复配增效制得耐高温洗油剂复配体系,考察了洗油剂复配体系的耐高温性、表面张力、洗油率等,并对洗油剂复配体系的性能进行评价。实验结果表明,以三氯化铝为催化剂、硝基苯为溶剂,在反应温度70℃、反应时间8 h的条件下,表面活性剂产率可达92%。在油藏条件下1.00%(w)的洗油剂复配体系的洗油率达72%,沉降脱水率达83%;针对不同黏度的原油,0.30%(w)的复配体系降黏率均可达99%,具有优异的降黏性能和洗油性能。

随钻核磁共振测井在南海文昌油田低阻油层流体识别中的应用

随钻核磁共振测井在南海文昌油田低阻油层的开发中以安全高效的测井方式提供了孔隙度、渗透率等参数,且在定性识别轻质油层方面发挥了关键作用。为了进一步提升随钻核磁共振测井在文昌油田低阻油层流体识别中的使用价值,从孔隙结构和流体性质2个影响因素出发,提出了T2谱含油特征指标法并引入纯水谱重构法开展流体定量识别。其中T2谱含油特征指标法以消除孔隙结构的影响为基础,利用轻质油和水的横向弛豫时间差异提取轻质油真实的拖尾现象达到定量识别流体的目的;水谱重构法则采用球管模型和正态分布模型分别构建束缚水谱和可动水谱,并将两者之和作为纯水谱,通过与实测核磁T2谱的对比提取流体性质信息,达到识别流体性质的目的,2种方法在文昌油田低阻油层的流体识别中均取得了良好的应用效果,可在低阻油层、水淹层等储层流体的定量识别中发挥显著作用。