Remaining Oil Distribution Law and Potential Tapping Strategy of Horizontal Well Pattern in Narrow Oil Rim Reservoir with Gas Cap and Edge Water

For thin oil rim reservoir with gas cap and edge water, it is helpful to improve the development effect to find out the distribution law of remaining oil in this kind of reservoirs. For this reason, taking the narrow oil rim reservoir with gas cap and edge water of Oilfield A in Bohai Sea as a case, the main controlling factors, including reservoir structure, fault, gas cap energy, edge water energy and well pattern, affecting the distribution of residual oil in this kind of reservoir were analyzed by using the data of core, logging, paleogeomorphology and production. Then, the distribution law of remaining oil was summarized. Generally, the remaining oil distribution is mainly potato-shaped or strip-shaped in plane. Vertically, it depends on the energy of gas cap and edge water. For the reservoir with big gas gap and weak edge water, the remaining oil mainly lies in the bottom of oil column. And for the reservoir with small gas gap and strong edge water, the remaining oil mainly locates at the top of oil column. Aiming at different distribution modes of remaining oil, the corresponding potential tapping strategies of horizontal wells are put forward: in the late stage of development, for the reservoir with big gas gap and weak edge water, the remaining oil concentrates at the bottom of the oil column, and the position of horizontal well should be placed at the lower 1/3 to the lower 1/5 of the oil column;for the reservoir with small gas cap and strong edge water, the remaining oil locates at the top of the oil column, and the position of horizontal well should be put at the upper 1/5 to the upper 1/3 of the oil column height, vertically. Based on the study on remaining oil of Oilfield A, a potential tapping strategy of well pattern thickening and vertical position optimization of horizontal well was proposed. This strategy guided the efficient implementation of the comprehensive adjustment plan of the oilfield. Moreover, 18 infill development wells were implemented in Oilfield A, and the average production of the infill wells is 2.1 times that of the surrounding old wells. It is estimated that the ultimate recovery factor of the oilfield will reach 33.9%, which is 2.3% higher than that before infilling wells. This study can be used for reference in the development of similar reservoirs.

Adaptability of Development Methods for Offshore Gas Cap Edge Water Reservoirs under Different Permeability Levels

The BZ 34-1 oilfield is a typical gas cap edge water reservoir in the Bohai oilfield. The main characteristics of the oilfield were multi-phase sand body stacking and the sand body was composed of three parts: gas cap, oil reservoir, and edge water. The actual production site results show that the permeability difference of multi-layer sand bodies has a serious impact on the development effect. This article establishes a typical reservoir model numerical model based on the total recovery degree of the reservoir and the recovery degree of each layer, and analyzes the impact of permeability gradient. As the permeability gradient increases, the total recovery degree of all four well patterns decreases, and the total recovery degree gradually decreases. The recovery degree of low permeability layers gradually decreases, and the recovery degree of high permeability layers gradually increases. As the permeability gradient increases, the degree of recovery gradually decreases under different water contents. As the permeability gradient increases, the reduction rate of remaining oil saturation in low permeability layers is slower, while the reduction rate of remaining oil saturation in high permeability layers was faster. By analyzing the impact of permeability gradient on the development effect of oil fields, we could further deepen our understanding of gas cap edge water reservoirs and guide the development of this type of oil field.

Evaluation of reservoir environment by chemical properties of reservoir water‒A case study of Chang 6 reservoir in Ansai oilfield,Ordos Basin,China

The Ordos Basin is the largest continental multi-energy mineral basin in China,which is rich in coal,oil and gas,and uranium resources.The exploitation of mineral resources is closely related to reservoir water.The chemical properties of reservoir water are very important for reservoir evaluation and are significant indicators of the sealing of reservoir oil and gas resources.Therefore,the caprock of the Chang 6 reservoir in the Yanchang Formation was evaluated.The authors tested and analyzed the chemical characteristics of water samples selected from 30 wells in the Chang 6 reservoir of Ansai Oilfield in the Ordos Basin.The results show that the Chang 6 reservoir water in Ansai Oilfield is dominated by calcium-chloride water type with a sodium chloride coefficient of generally less than 0.5.The chloride magnesium coefficients are between 33.7 and 925.5,most of which are greater than 200.The desulfurization coefficients range from 0.21 to 13.4,with an average of 2.227.The carbonate balance coefficients are mainly concentrated below 0.01,with an average of 0.008.The calcium and magnesium coefficients are between 0.08 and 0.003,with an average of 0.01.Combined with the characteristics of the four-corner layout of the reservoir water,the above results show that the graphics are basically consistent.The study indicates that the Chang 6 reservoir in Ansai Oilfield in the Ordos Basin is a favorable block for oil and gas storage with good sealing properties,great preservation conditions of oil and gas,and high pore connectivity.

Theories and practices of carbonate reservoirs development in China

Carbonate reservoirs in China have the characteristics of diversified accumulation pattern, complex structure and varying reservoir conditions. Concerning these characteristics, this article tracks the technical breakthroughs and related practices since the 1950 s, summarizes the developed theory and technologies of carbonate reservoir development, analyzes their adaptability and problems, and proposes their development trend. The following theory and technologies have come into being:(1) carbonate reservoir formation mechanisms and compound flow mechanisms in complex medium;(2) reservoir identification and description technologies based on geophysics and discrete fracture-vuggy modeling method;(3) well testing analysis technology and numerical simulation method of coupling free flow and porous media flow;(4) enhanced oil recovery techniques for nitrogen single well huff and puff, and water flooding development techniques with well pattern design in spatial structure, changed intensity water injection, water plugging and channel blocking as the core;(5) drilling and completion techniques, acid fracturing techniques and its production increasing techniques. To realize the efficient development of carbonate oil and gas reservoirs, researches in four aspects need to be done:(1) complex reservoir description technology with higher accuracy;(2) various enhanced oil recovery techniques;(3) improving the drilling method and acid fracturing method for ultra-deep carbonate reservoir and significantly cutting engineering cost;(4) strengthening the technological integration of information, big data, cloud computation, and artificial intelligence in oilfield development to realize the smart development of oilfield.

Simulation studies on optimizing oil productivity in oil rim reservoirs under gas cap blow down production strategy

Gas cap blow down strategy is normally deployed for Ultra-thin oil rim reservoirs with huge gas caps due to extremely high gas oil ratios from wells in such reservoirs.The current state leads to loss of production from the oil reserves due to high initial reservoir pressure thus,reducing its net present value.Data on important factors essential to the productivity of oil rim reservoirs are used to build a heterogeneous ultra-thin reservoir with a time step of 10,000 days using the Eclipse software and its embedded correlations.The reservoir is subjected to a gas cap blowdown via a gas well,then an oil well is initiated into the model at onset and after time periods of 2000 days,4000 days,6000 days and 8000 days to estimate the oil recovery.It is expected that due to the large nature of the gas cap,pressure decline will be drastic and leading to a low oil recovery,hence the injection of water and gas at different rates at the periods indicated.The results indicate an oil recovery of 4.3%during gas cap blow down and 10.34%at 6000 days.Peak oil recoveries of 12.64%and 10.80%are estimated under 30,000 Mscf/day at 4000 days and 1000 stb/day at 6000 days respectively.This shows an incremental oil recovery of 8.34%and 6.5%over that recorded during gas cap blow down.The results also indicate that the gas production at those periods was not greatly affected with an estimated increment of 257 Bscf recorded during 30,000 Mscf/day at 4000 days.All secondary injection schemes at the respective time steps had positive impact on the overall oil recoveries.It is recommended that extra production and injection wells be drilled,enhanced oil recovery options and injection patterns be considered to further increase oil recovery.

Progress and prospects of EOR technology in deep,massive sandstone reservoirs with a strong bottom-water drive

The Triassic massive sandstone reservoir in the Tahe oilfield has a strong bottom-water drive and is characterized by great burial depth,high temperature and salinity,a thin pay zone,and strong heterogeneity.At present,the water-cut is high in each block within the reservoir;some wells are at an ultrahigh water-cut stage.A lack of effective measures to control water-cut rise and stabilize oil production have necessitated the application of enhanced oil recovery(EOR)technology.This paper investigates the development and technological advances for oil reservoirs with strong edge/bottom-water drive globally,and compares their application to reservoirs with characteristics similar to the Tahe oilfield.Among the technological advances,gas injection from the top and along the direction of structural dip has been used to optimize the flow field in a typical bottom-water drive reservoir.Bottom-water coning is restrained by gas injection-assisted water control.In addition,increasing the lateral driving pressure differential improves the plane sweep efficiency which enhances oil recovery in turn.Gas injection technology in combination with technological measures like channeling prevention and blocking,and water plugging and profile control,can achieve better results in reservoir development.Gas flooding tests in the Tahe oilfield are of great significance to identifying which EOR technology is the most effective and has the potential of large-scale application for improving development of deep reservoirs with a strong bottomwater drive.

薄层砂岩边底水油藏空气辅助内源微生物驱油技术

针对边底水油藏“双高阶段”零散分布剩余油如何有效动用、低成本高效微生物驱油体系如何研发、微生物驱效果评价及配套技术攻关等难题,建立微生物驱筛选图版并评价了油藏微生物驱的适应性;利用微生物分子生态学技术全面解析了油藏微生物群落结构,筛选了乳化效果好的采油功能菌株H3;通过对主要营养成分碳源、氮源、磷源的筛选,开展单因素实验和正交实验,确定了可实现原油乳化分散和抑制硫酸盐还原菌生长的复合粉激活体系;研究了底水油层“船底形”剩余油富集特征,形成了“微生物乳化+空气提效+稠化剂封堵”提高采收率驱油模式,明确了提高采收率幅度与注入菌体浓度、注入孔隙体积倍数正相关。将研究成果应用于准噶尔盆地陆梁油田薄层砂岩边底水油藏,实施“4注20采”微生物驱提高采收率矿场先导试验,注入微生物激活剂0.13倍孔隙体积,2017至2023年阶段增油5.6×104 t,采收率提高4.0个百分点,增油效果好的井主要分布在总菌浓度高、石油地质储量大、构造高部位、油层厚度大、底水薄、采出程度较高的区域。研究成果对丰富微生物驱提高采收率技术序列具有借鉴作用。

气顶边水油藏油气协同开发下流体界面运移特征

气顶边水油藏的开发,存在明显的油气水互侵现象,导致产量快速递减,开发难度增大。为了防止生产井过早停产,需明确流体界面运移特征,制定油气协同开发生产制度。通过油藏数值模拟方法,建立了月东油田气顶边水油藏实际模型与机理模型,根据气顶与边水作用能量强弱,将油气协同开发区域划分为边水控制区、气顶控制区和气顶边水联合控制区三类进行研究,综合评估气窜、水淹、油侵风险,明确油气、油水界面运移特征并形成运移速度图版。结果表明:随着开发的进行,气顶膨胀导致油气界面从油藏顶部向油井方向运移,边水侵入导致油水界面从油藏底部向油井与气井方向运移,油井存在气窜与水淹的风险,气井存在水淹与油侵的风险,剩余油主要分布在气顶下部和井间高部位,确定月东油田气顶边水油藏合理采气速度为6%~8%。基于实际与理论研究形成的成果认识为气顶边水油藏油气协同高效开发提供理论指导。

气顶边水油藏衰竭开发剩余油分布及挖潜研究

H油田为气顶边水油藏,以天然能量开发为主。目前该油田采出程度较大,剩余油分布零散且研究手段有限,油田挖潜难度大。为了认清该油田油水运移及剩余油分布规律,论证现阶段转变开发方式的可行性,基于二维物理模拟实验开展研究。结果表明:H油田衰竭开发后期剩余油主要分布在气顶高部位渗透率较低的储层中,转屏障注水和布调整井对采收率的提高均有一定的作用,但仍然不能弥补由于渗透率差异导致的剩余油分布特征。考虑到H油田气顶边水窄油环的特殊性,布调整井仍然面临成本高以及气窜和水窜的风险,对目标油田实施屏障注水井,措施实施后累增油4.8×10^(4)m^(3),井组提高采收率4.9%。

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。

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.

边底水发育低渗透高含水油藏剩余油精准挖潜技术

以靖边DW区延9油藏为例,采用物质平衡法计算剩余油储量,明确了剩余油类型和分布规律,找出了针对不同类型剩余油的精准挖潜技术,并选择典型井组进行了现场实施,结果表明:研究区单井平均剩余地质储量2.45×10^(4) t,剩余油潜力较好;剩余油的成因可分为单一层内剩余油、双层系层间剩余油和复杂多层系层间层内剩余油;根据剩余油类型精准挖潜的重点不同,通过完善注采对应、精准补孔等措施可改变液流方向,达到精准挖掘剩余油的目的。现场试验结果表明,剩余油精准挖潜措施能够显著提高超低渗透油藏水驱开发后的采收率,措施后日产油量平均增幅达到215%,含水率平均降低幅度达到11.5%,达到了良好的降水增油效果,可在同类油藏中进一步推广应用。

气顶边水油藏中后期开发调整三维物理模拟研究

气顶边水油藏天然能量开发中后期气窜、水锥加剧,地层压力加速下降,产量递减加快,生产形势急剧变差。为探索其后期开发调整方向,以海上气顶边水油藏为例,根据相似理论,设计了气顶边水油藏大型三维物理模型,研究了继续天然能量开发、转屏障注水和转老井侧钻等3种开发调整方式的生产特征及其挖潜效果。试验结果表明,天然能量开发以气顶能量为主,受高渗层气窜影响,水平井上部的中、低渗透率储层为后续挖潜的方向;屏障注水开发可以抑制高渗层气顶气窜,对低渗层增产和稳产效果明显;老井侧钻开发对中等渗透率储层占比大的油藏更为有效。现场优选了1口老井,实施了高部位侧钻,取得了良好的现场试验效果。研究结果可以为提升多种提高采收率方式的调整效果提供理论指导。

边底水超稠油油藏改性石墨烯封堵技术的研究与应用

以0.5%石墨烯体系为研究对象,通过优选悬浮剂,形成改性石墨烯颗粒封堵汽窜技术。通过物模实验评价了改性石墨烯的封堵性,分析了封堵机理。实验结果表明:石墨烯颗粒堵剂随温度升高膨胀率增加,300℃膨胀率达10~25倍;悬浮液使用质量分数0.15%时,改性石墨烯封堵体系析水率小于5%,不同渗透率下封堵率大于97%。现场应用井注汽压力1.5~2.4 MPa,蒸汽吞吐有效期延长30~50 d,累积增油1066 t。

辽河油区稠油油藏边底水控制技术研究

针对辽河油区边底水稠油油藏储量丰富,分布广泛的特点,通过对边底水稠油油藏水侵规律的分析研究,总结出针对不同油藏控制边底水的有效技术。开发过程中,在利用边底水能量的同时,延长了油井的见水时间,取得了较好的开发效果。

断块油藏气顶-边水双向驱油藏筛选标准

为提高断块油藏采收率,提出气顶-边水双向驱的开发方式,即利用注入N2挖潜阁楼油,利用边缘注水挖潜低部位剩余油的双向驱替方式,以此提高波及体积和采油速度。新方法提高采收率的主控因素有待明确,相应的油藏筛选标准尚未建立。运用数值模拟方法,建立了断块油藏双向驱的理论模型,研究了不同因素对双向驱开发效果的敏感性及相应的油藏筛选标准。研究表明:对于含油条带较窄(低于100 m),气顶宽度低于50 m的油藏不推荐进行双向驱;低渗透油藏采用双向驱时应降低注气速度,保持注采平衡;在油层厚度不大于10 m,地层原油黏度小于75 m Pa·s,没有较厚夹层的条件下,双向驱开发能取得较好的效果。采用该筛选标准选取实际区块,预测双向驱比水驱提高采收率14.21个百分点。研究成果对断块油藏高含水期剩余油有效动用和高效波及有重要意义。

气顶边水油藏剩余油分布模式及挖潜对策

针对国外某气顶边水油藏地质特征和开发状况,开展了剩余油分布规律研究,分析了影响剩余油分布的主控因素,即隔夹层、气顶、构造高点、井网和井型。在此基础上,总结出剩余油的分布模式,纵向分布模式为屋脊油、屋檐油、屋顶油和屋内油4种,平面分布模式为朵状和火山锥状剩余油2种。针对不同模式剩余油提出了相应的挖潜对策:屋脊油可以在顶部钻水平井挖潜,屋檐油宜采用水平井底部挖潜,屋顶油建议采用过路井补孔,屋内油采用水平井或直井加密挖潜;开发朵状剩余油应进一步完善井网,采用水平井挖潜底部剩余油,而火山锥状剩余油宜采用局部直井加密开发。

不同类型油藏水平井开发适应性分析

水平井技术是一种高效的提高油气采收率的方法,目前在所发现的各类油藏中均有应用水平井的报道。从我国近年完钻水平井的情况来看,水平井主要应用于稠油油藏、边底水油藏、低渗透油藏以及高含水油藏挖潜之中。通过对我国主要油田以上4种不同油藏类型中水平井生产特征的统计,分析总结出水平井开采技术存在的问题以及对各类油藏的适应性,为我国水平井技术的进一步应用提供参考。

高浅南区边水断块油藏类型及剩余油特征

复杂小断块油藏的剩余油在开发后期极为复杂,不仅受多个因素的控制,同时,某一种因素单独控制的剩余油非常分散且数量有限。针对高浅南区小断块油藏边水发育的特点,考虑剩余油的主控因素、断块油藏的形状、天然能量的充足程度以及能量供体等将边水断块油藏划分为3类:开启型边水断块油藏、半封闭型边水断块油藏以及封闭型边水断块油藏。并研究了每种油藏类型的剩余油分布特征和挖潜潜力。发现:开启型边水断块油藏采出程度最高、剩余油少而分散;封闭型边水断块油藏采出程度最低、剩余油多而连片;半封闭型边水断块油藏介于两者之间。在以上研究的基础上,根据每种油藏类型的特点提出了下一步挖潜的技术对策。

油藏数值模拟法预测剩余油分布及调整挖潜措施——以临南油田夏32块油藏为例

以临南油田夏32块油藏为例,叙述了边水活跃油藏中高含水期油田调整模式。在精细油藏描述的基础上,利用油藏数值模拟技术研究剩余油分布规律是较为直观的好方法。通过对开发动态进行历史拟合,分析了剩余油的分布特征及其控制因素,针对不同的剩余油分布形式,提出控水稳油的挖潜调整措施。