Research and Application of CO₂Flooding Enhanced Oil Recovery in Low Permeability Oilfield

This paper discusses the new progress and field application of CO2 flooding in low permeability reservoirs enhanced oil recovery. The study shows that CO2 flooding can improve the oil recovery rate of low permeability oilfield by more than 10%. The practice shows that the liquid CO2 injection in low permeability reservoir is easier than water injection, and the reservoir generally has better CO2 storage.

Model building for Chang-8 low permeability sandstone reservoir in the Yanchang formation of the Xifeng oil field

In order to build a model for the Chang-8 low permeability sandstone reservoir in the Yanchang formation of the Xifeng oil field,we studied sedimentation and diagenesis of sandstone and analyzed major factors controlling this low permeability reservoir.By doing so,we have made clear that the spatial distribution of reservoir attribute parameters is controlled by the spatial distribution of various kinds of sandstone bodies.By taking advantage of many coring wells and high quality logging data,we used regression analysis for a single well with geological conditions as constraints,to build the interpretation model for logging data and to calculate attribute parameters for a single well,which ensured accuracy of the 1-D vertical model.On this basis,we built a litho-facies model to replace the sedimentary facies model.In addition,we also built a porosity model by using a sequential Gaussian simulation with the lithofacies model as the constraint.In the end,we built a permeability model by using Markov-Bayes simula-tion,with the porosity attribute as the covariate.The results show that the permeability model reflects very well the relative differences between low permeability values,which is of great importance for locating high permeability zones and forecasting zones favorable for exploration and exploitation.

The coupling of dynamics and permeability in the hydrocarbon accumulation period controls the oil-bearing potential of low permeability reservoirs:a case study of the low permeability turbidite reservoirs in the middle part of the third member of Shahejie

The relationships between permeability and dynamics in hydrocarbon accumulation determine oil- bearing potential （the potential oil charge） of low perme- ability reservoirs. The evolution of porosity and permeability of low permeability turbidite reservoirs of the middle part of the third member of the Shahejie Formation in the Dongying Sag has been investigated by detailed core descriptions, thin section analyses, fluid inclusion analyses, carbon and oxygen isotope analyses, mercury injection, porosity and permeability testing, and basin modeling. The cutoff values for the permeability of the reservoirs in the accumulation period were calculated after detailing the accumulation dynamics and reservoir pore structures, then the distribution pattern of the oil-bearing potential of reservoirs controlled by the matching relationship between dynamics and permeability during the accumulation period were summarized. On the basis of the observed diagenetic features and with regard to the paragenetic sequences, the reservoirs can be subdivided into four types of diagenetic facies. The reservoirs experienced two periods of hydro- carbon accumulation. In the early accumulation period, the reservoirs except for diagenetic facies A had middle to high permeability ranging from 10 × 10-3 gm2 to 4207 × 10-3 lain2. In the later accumulation period, the reservoirs except for diagenetic facies C had low permeability ranging from 0.015 × 10-3 gm2 to 62× 10-3 -3m2. In the early accumulation period, the fluid pressure increased by the hydrocarbon generation was 1.4-11.3 MPa with an average value of 5.1 MPa, and a surplus pressure of 1.8-12.6 MPa with an average value of 6.3 MPa. In the later accumulation period, the fluid pressure increased by the hydrocarbon generation process was 0.7-12.7 MPa with an average value of 5.36 MPa and a surplus pressure of 1.3-16.2 MPa with an average value of 6.5 MPa. Even though different types of reservoirs exist, all can form hydrocarbon accumulations in the early accumulation per- iod. Such types of reservoirs can form hydrocarbon accumulation with high accumulation dynamics; however, reservoirs with diagenetic facies A and diagenetic facies B do not develop accumulation conditions with low accumu- lation dynamics in the late accumulation period for very low permeability. At more than 3000 m burial depth, a larger proportion of turbidite reservoirs are oil charged due to the proximity to the source rock, Also at these depths, lenticular sand bodies can accumulate hydrocarbons. At shallower depths, only the reservoirs with oil-source fault development can accumulate hydrocarbons. For flat surfaces, hydrocarbons have always been accumulated in the reservoirs around the oil-source faults and areas near the center of subsags with high accumulation dynamics.

Development of the theory and technology for low permeability reservoirs in China

The development theories of low-permeability oil and gas reservoirs are refined, the key development technologies are summarized, and the prospect and technical direction of sustainable development are discussed based on the understanding and research on developed low-permeability oil and gas resources in China. The main achievements include:(1) the theories of low-permeability reservoir seepage, dual-medium seepage, relative homogeneity, etc.(2) the well location optimization technology combining favorable area of reservoir with gas-bearing prediction and combining pre-stack with post-stack;(3) oriented perforating multi-fracture, multistage sand adding, multistage temporary plugging, vertical well multilayer, horizontal and other fracturing techniques to improve productivity of single well;(4) the technology of increasing injection and keeping pressure, such as overall decreasing pressure, local pressurization, shaped charge stamping and plugging removal, fine separate injection, mild advanced water injection and so on;(5) enhanced recovery technology of optimization of injection-production well network in horizontal wells. To continue to develop low-permeability reserves economically and effectively, there are three aspects of work to be done well:(1) depending on technical improvement, continue to innovate new technologies and methods, establish a new mode of low quality reservoir development economically, determine the main technical boundaries and form replacement technology reserves of advanced development;(2) adhering to the management system of low cost technology & low cost, set up a complete set of low-cost dual integration innovation system through continuous innovation in technology and management;(3) striving for national preferential policies.

A Case of Multi-Stage Fracturing Horizontal Well Used in BZ Oilfield in Bohai Bay Low-Permeability Oilfield Development

BZ oilfield in Bohai Bay of China was a typical offshore low permeability oilfield, which was restricted by many factors such as environment and economy. In this paper, the development characteristics of BZ oilfield were summarized in depth, and the new development mode of offshore low-permeability oilfield was explored from reservoir prediction, well spacing and fracturing technology. Taking BZ oilfield as an example, a set of technical system for the effective development of offshore low permeability oilfield had been formed through research, which mainly includes reservoir prediction and evaluation of offshore middle and deep low permeability oilfield, optimization of horizontal well pattern, multi-stage fracturing design of horizontal well and other technologies. The results show that improving the resolution of seismic data, strengthening the analysis of seismic reflection characteristics and carrying out the comprehensive study of seismic geology were the keys to solve the reservoir prediction of offshore low-permeability oil fields. Multi-stage fracturing horizontal well pattern is the main pattern of offshore low-permeability oilfield development. The parameters of multi-stage fracturing horizontal well together affect the development effect. Selecting the optimal fractured horizontal well pattern can greatly improve the development effect. The successful combination and application of new technology system was the foundation and core of conquering offshore low-permeability oil fields. On the basis of understanding the geological characteristics of oil reservoirs, it is an effective means of developing offshore low-permeability oil fields by selecting reasonable production methods, well types and well patterns. Using efficient perforation and fracturing technology to successfully control fracture parameters and form optimal injection and production well pattern was the key to improve low permeability offshore oil fields.

Advances in enhanced oil recovery technologies for low permeability reservoirs

Low permeability oil and gas resources are rich and have great potential all over the world, which has gradually become the main goal of oil and gas development. However, after traditional primary and secondary exploitation, there is still a large amount of remaining oil that has not been recovered.Therefore, in recent years, enhanced oil recovery(EOR) technologies for low permeability reservoirs have been greatly developed to further improve crude oil production. This study presents a comprehensive review of EOR technologies in low permeability reservoirs with an emphasis on gas flooding, surfactant flooding, nanofluid flooding and imbibition EOR technologies. In addition, two kinds of gel systems are introduced for conformance control in low permeability reservoirs with channeling problems. Finally,the technical challenges, directions and outlooks of EOR in low permeability reservoirs are addressed.

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.

Geologic characteristics, controlling factors and hydrocarbon accumulation mechanisms of China’s Large Gas Provinces of low porosity and permeability

Based on the analysis of the geological characteristics and controlling factors, we analyzed the formation mechanism of different types of gas reservoirs. The main characteristics of gas provinces with low porosity and permeability are mainly as follows: large area, low abundance, small gas pools and large gas provinces; widely distributed excellent hydrocarbon source rocks with closely contacted source-reservoir-cap association; development mainly in large continental depressions or in paralic shallow-river delta systems; many kinds of traps coexisting in large areas, dominantly para-layered lithologic, digenetic and capillary pressure traps; double fluid flow mechanisms of Darcy flow and non-Darcy flow; complicated gas and water relations; and having the resource distribution of highly productive "sweet spots", banding concentration, and macroscopically large areas integrated. The main controlling factors of large sandstone gas provinces with low porosity and permeability are stable dynamic backgrounds and gentle structural frameworks which control the extensive distribution of alternate (interbedded) sandstones and mudstones; weak hydropower of large gentle lake basins controlling the formation of discontinuous, low porosity and permeability reservoirs in shallow-water deltas; regionally differential diagenesis and no homogeneous digenetic facies controlling the development of favorable reservoirs and digenetic traps; and weak and dispersive reservoir-forming dynamic forces leading to the widely distributed small traps with low abundance. Low porosity and permeability gas provinces with different trap types have different formation mechanisms which include fluid diversion pressure difference interactive mechanism of lithologic-trap gas accumulations, separated differential collection mechanism of digenetic-trap gas accumulations, and the Non-Darcy flow mechanism of capillary-pressure gas accumulations.

长岭断陷龙凤山气田营城组储层非均质性研究

龙凤山气田是目前中石化在东北地区勘探开发的首个深盆致密砂岩近饱和高含油凝析气储集系统,主力含气层位营城组储层在空间上表现出了较强的非均质性特征,气层在纵向上、平面上分布规律复杂将制约后续的地质研究工作(于翠玲,2007)。通过对岩心描述和测井资料进行分析,对比地质储量和实际测试生产情况,从层内、层间和平面3个方面分析储层的宏观非均质性。

海上低渗透油田油井低效原因分析及解堵措施

为了找出海上X油田油井低产低效的原因,并进一步提高海上低渗透油田的开发效率,在分析了目标油田基本概况以及开发现状的基础上,通过室内实验对目标油田油井损害原因进行的分析,并研制了一套新型复合解堵体系。结果表明:水锁伤害、入井流体伤害、有机质沉积伤害以及注入水和地层水不配伍导致的结垢伤害是造成海上X油田油井低效的主要原因。新型复合解堵体系主要由有机解堵液、无机解堵液和顶替液组成,有机解堵液对有机垢的溶解效果较好,无机解堵液对现场无机堵塞物的溶蚀能力较强,并且缓蚀性能较好。复合解堵体系对污染后的岩心具有良好的解堵效果,解堵后岩心的渗透率恢复值均能达到97%以上。现场应用结果表明,A1井采取复合解堵体系施工后解堵效果显著,日增油达到了60 m^(3)以上,措施有效期较长,施工效果较好。

高效疏水性纳米颗粒合成及其在低渗透油田驱油特性

为提高低渗透油田的驱油效率,通过化学还原法合成了高效疏水性银纳米颗粒(SHAg),并系统评估了其在油田模拟水中的稳定性、分散性以及岩心驱替实验中的驱油性能。研究发现,通过控制三甲基氯硅烷(TMCS)的质量分数,可以有效调节SHAg的疏水性,当TMCS质量分数为0.5%时,SHAg的接触角达到112.4°,表现出优异的疏水性。此外,SHAg在模拟油田水中展现出良好的稳定性和分散性,特别是在5%的NaCl质量分数下,其平均粒径仅为83.6 nm。岩心驱替实验结果表明,含有400 mg·L^(-1)SHAg的驱替液的驱油效率高达59.7%,显著高于纯水驱的基础驱油效率。这一研究不仅揭示了疏水性纳米颗粒在提高低渗透油田驱油效率中的潜力,而且为实际油田应用提供了重要的理论依据和技术支持。

中国海上低渗油气田开发历程、关键技术及攻关方向

中国海上低渗透油气资源丰富、分布广泛,但受海洋特殊作业环境、技术和经济性等限制,经济有效开采难度大,攻克技术瓶颈、推进规模化开发意义重大。历经多年实践,充分吸收陆上油田开发经验,立足少井高产,围绕“四个匹配”攻关形成了具有海上特色的低渗有效开发技术路径,提出三项开发策略“压裂投产、能量补充、降本增效”和5项关键技术内容,即储层综合评价、有效能量补充、地质工程一体化、压裂工艺工具与经济评价,成功突破了20 mD以上低渗透油藏开发瓶颈,并逐渐下探至5 mD近特低渗油藏有效开发,有力地推进了海上低渗油田开发进程。未来将进一步探索深层-超深层油气领域关键技术,研发大型压裂作业技术装备,打造海上低渗“CO_(2)驱油+封存”联合工程。

海上低渗砂岩储层酸压可行性及酸液体系研究

采用常规基质酸化作业无法对海上低渗砂岩储层实施整体改造,并且由于部分储层渗透率较低,酸液无法顺利进入地层。因此,以涠洲X低渗砂岩油藏为研究对象,开展了适合海上低渗砂岩储层的酸化压裂可行性分析研究,并优选了相应的酸液体系,评价了酸液体系的综合性能。结果表明:目标油田储层段含有一定量的碳酸盐岩矿物,储层的脆性较好,并且储层段水平主应力差异系数在0.114~0.130之间,具备酸化压裂施工的物质基础,压裂施工可使储层形成复杂的裂缝网络。采用有机酸HCW-1、有机酸盐HCF和高温缓蚀剂HSJL-3为主要处理剂,构建了一套适合海上低渗砂岩储层酸压施工的酸液体系,该酸液体系具有较低的表面张力和腐蚀速率,同时具有较强的铁离子稳定能力和防膨能力。另外,储层段天然岩心采用酸压工作液酸蚀作用后裂缝导流能力大幅度提高,并且岩心表面完整,未出现微粒脱落的现象。研究结果认为目标海上低渗砂岩储层具备酸压施工的条件,可以采取酸压施工对其进行增产改造。

低渗透油田压裂技术研究分析

石油在我国社会经济发展中具有举足轻重的地位。与此同时,随着社会经济的迅速发展,人们对能源的需求量越来越大。随着各类科技的发展,越来越多的新技术被用于开发和利用,所以,对油气田的开发与利用就显得尤为重要。尤其是在对许多油田进行了深入的研究后,发现许多油区属于低渗透油区,而对这些油区所使用的压裂技术效果显著。文章对以低渗透油藏为中心的压裂工艺进行了论述与分析,并就其进展作了较为详尽的介绍,希望能够提供相关参考。

海上低渗油田CO_(2)驱降混剂的研发与评价

针对海上低渗J油田注CO_(2)难以实现混相驱的问题,通过室内合成柠檬酸异丁酯,采用高温高压界面张力仪和细管实验仪开展了不同降混剂的界面性能及浓度优选评价实验,筛选出适合目标油田的降混剂。实验结果表明:J油田地层压力低于CO_(2)驱油最小混相压力,无法达到混相。室内合成的柠檬酸异丁酯相比乙二醇、石油醚具有更高的安全性,能有效降低最小混相压力至17.5 MPa,可以实现混相,最佳质量分数为0.6%。

海上低渗油田注入伴生气驱油最小混相压力实验

为分析L油田注入伴生气驱油能否实现混相驱,开展了最小混相压力测定实验。采用长细管实验法分别测定了海上低渗L油田W31、W32和W51油组含CO_(2)伴生气驱油的最小混相压力,并通过气相色谱仪分析了长细管末端见气前后产出油气组分变化规律。结果表明:气驱前期(0~0.5PV),注入气未运移至长细管末端,产出流体为原油,不同压力下驱油效率和气油比的变化规律相近;随压力增大,注入气与原油两相相态从非混相到近混相再到混相,气液界面逐渐消失,驱油效率不断增大;在地层压力下,L油田W31和W32油组注入伴生气无法实现混相驱,W51油组注入伴生气可以实现混相驱;伴生气驱油过程中主要萃取原油中的轻烃组分,同时伴生气中CO_(2)和C^(5+)会溶解于原油。

水平井+CO_(2)吞吐改善中低渗稠油油藏开发效果机制解析——以大港油田刘官庄埕隆1601区块为例

大港油田刘官庄埕隆1601区块特稠油油藏由于受原油粘度大、渗透率低、油层厚度薄、出砂及地面环境复杂等苛刻条件的制约,多年来常规的开采技术无法实现动用,为此开展了“水平井+CO_(2)吞吐”技术研究及矿场试验。利用室内实验及数值模拟手段,开展增油机制研究及注采参数优化,结果表明CO_(2)与稠油在非混相状态下混溶后,稠油粘度由16800 mPa·s下降至69 mPa·s,降粘率达99.6%,原油启动压力梯度由19.1 MPa/m降低至0.2 MPa/m,储层绝对渗透率提高了约41.86%,有效提高了稠油的流动性能;优化后的合理注采参数为:单位水平段注入强度3.5~5.5 t/m,单位水平段注入速度0.5~0.6 t/(m·d),闷井时间为25~35 d,单位水平段产液强度为0.075~0.125 m3/(m·d),采用“抽油机+液力反馈泵+电加热杆”及水力喷射泵两种注采一体化工艺。矿场“水平井+CO_(2)吞吐”技术试验证实,单井单轮次增油1000~2000 t,最高增油达4000 t以上,换油率2.0~4.5 t/t,技术和经济效果显著,证实了该技术的可靠实用性,为中低渗稠油油藏的有效开发提供了很好的借鉴。

低渗透油藏注水开发中存在的问题及解决措施

我国第二个百年计划已拉开序幕,在新时期的发展与建设背景下我国对石油资源的需求呈现出了阶梯式的增长趋势,相应的油田的开发规模也在不断扩大。低渗透油藏注水开发技术能够增强油田的产能,对石油行业的进步具有重要的积极影响。为实现充分发挥低渗透油藏注水开发技术价值、助力油田产能升级的目标,需对低渗透油藏注水开发过程中存在的问题进行挖掘与合理化分析,并结合实际情况设计合理的优化、解决措施。

低渗透油田聚合物纳米微球驱油化学特性与评价

以丙烯酰胺为单体,基于反相微乳液聚合方式制备了粒径为60 nm左右的聚合物纳米微球,微球形状规则、热稳定性良好、可分离固形物有效质量分数大于20%,且具备良好的耐盐性及溶胀性能。通过室内调驱实验,优选了聚合物纳米微球体系注入量0.4 PV、注入质量浓度1 200 mg·L^(-1)、注入速率0.3 mL·min^(-1)为最佳注入参数。测试结果显示,注入微球数量相同时,综合考虑低渗透油田实际生产工期、成本及效益,中等浓度中等段塞、间隙的注入工艺效果较优。

油田空气泡沫驱化学分析及提高采收率研究

低渗透油藏的开发主要依赖于储层的自然驱动力和人工注水驱动,但这些驱动方式对于低渗透油藏的开采效率不高,导致采收率较低。空气泡沫驱是一种利用空气和表面活性剂制备的泡沫流体进行驱替的提高采收率技术,具有成本低、效果好、环境友好等优点。基于此,通过长岩心驱替装置进行了空气泡沫段塞驱实验,并与水驱和注空气采油驱替实验进行对比分析。结果表明:泡沫段塞为0.1 PV时,采出程度最高,优于0.2 PV、0.3 PV和0.4 PV的情况,表明0.1 PV泡沫段塞最合理;在泡沫驱阶段,当注入速度由0.1 mL·min^(-1)减至0.05 mL·min^(-1)后,总体采收率和段塞驱阶段的采收率提高幅度都有所提升,表明注入速度与采收率成负相关性;非均质性是低渗透油藏开发效率的主要制约因素,空气泡沫驱能有效实现油藏的封堵调剖。水驱后采用空气泡沫驱能够增加油藏的最终采收率。实验结果可为同类型低渗透油田提高采收率提供借鉴。