Formation damage mechanism and control strategy of the compound function of drilling fluid and fracturing fluid in shale reservoirs

For the analysis of the formation damage caused by the compound function of drilling fluid and fracturing fluid,the prediction method for dynamic invasion depth of drilling fluid is developed considering the fracture extension due to shale minerals erosion by oil-based drilling fluid.With the evaluation for the damage of natural and hydraulic fractures caused by mechanical properties weakening of shale fracture surface,fracture closure and rock powder blocking,the formation damage pattern is proposed with consideration of the compound effect of drilling fluid and fracturing fluid.The formation damage mechanism during drilling and completion process in shale reservoir is revealed,and the protection measures are raised.The drilling fluid can deeply invade into the shale formation through natural and induced fractures,erode shale minerals and weaken the mechanical properties of shale during the drilling process.In the process of hydraulic fracturing,the compound effect of drilling fluid and fracturing fluid further weakens the mechanical properties of shale,results in fracture closure and rock powder shedding,and thus induces stress-sensitive damage and solid blocking damage of natural/hydraulic fractures.The damage can yield significant conductivity decrease of fractures,and restrict the high and stable production of shale oil and gas wells.The measures of anti-collapse and anti-blocking to accelerate the drilling of reservoir section,forming chemical membrane to prevent the weakening of the mechanical properties of shale fracture surface,strengthening the plugging of shale fracture and reducing the invasion range of drilling fluid,optimizing fracturing fluid system to protect fracture conductivity are put forward for reservoir protection.

Drilling Operation and Formation Damage

Transport of particle suspensions in oil reservoirs is an essential phenomenon in many oil industry processes. Solid and liquid particles dispersed in the drilling fluid (mud) are trapped by the rock (porous medium) and permeability decline takes place during drilling fluid invasion into reservoir resulting in formation damage. The formation damage due to mud filtration is explained by erosion of external filter cake. Nevertheless, the stabilization is observed in core floods, which demonstrates internal erosion. A new mathematical model for detachment of particles is based on mechanical equilibrium of a particle positioned on the internal cake or matrix surface in the pore space. In the current work the analytical solution obtained to mud filtration with one particle capture mechanism with damage stabilization. The particle torque equilibrium is determined by the dimensionless ratio between the drag and normal forces acting on the particle. The maximum retention function of the dimensionless ratio closes system of governing equations for colloid transport through porous medium.

家H2分支水平井钻井液技术

家H2井是大港油田第一口分支水平井,位于沈家铺油田官107×1断块,目的层为孔二油组上砂体。该井为三开井,由一个主井眼和两个分支井眼构成,完钻垂深为2211.65m,斜深为2658m,井底水平位移为521m,最大井斜为92.87°;一分支水平段段长为119.12m,最大井斜为92.19°;二分支水平段段长为25m,最大井斜为92°。该井二开井段使用聚合物钻井液,三开井段使用无固相KCl聚合物钻井液,采用无固相超低渗透技术保护油层,满足了筛管完井对油层保护技术的要求。在施工过程中无固相KCl聚合物钻井液性能稳定,携砂冼井能力强,滤失量小,能有效地稳定井壁,保护油气层,大大提高了原油产量。

二连油田巴38断块保护油层钻井液技术

巴38断块储层物性从中孔特低渗到中孔中渗,非均质性强,属于强水敏、强盐敏地层。针对巴38断块储层特征和现场使用的钾铵基聚合物钻井液体系特点,研究出了适用于巴38断块的油层保护剂L-RP-2。该油层保护剂L-RP-2中引入了中-低分子量聚合物,利用聚合物分子链可以将不同形状和不同粒度的惰性颗粒,包括原井浆中的固相颗粒链接起来共同对储层进行有效封堵。室内评价结果表明,油层保护剂L-RP-2对岩心的封堵效率大于85%,封堵深度小于10mm,满足了油层封堵技术的要求。加有油层保护剂L-RP-2的保护油层钻井液体系现场应用40口井,在进行测试的15口井中,12口井共计13层表皮系数均小于零,为完善井,3口井表皮系数小于1,为轻微损害井,可见油层保护剂L-RP-2的应用取得了良好的深护油层效果。

Characterization and prevention of formation damage for fractured carbonate reservoir formations with low permeability

Stress sensitivity and water blocking in fractured carbonate reservoir formations with low permeability were determined as the main potential damage mechanisms during drilling and completion operations in the ancient buried hill Ordovician reservoirs in the Tarim Basin. Geological structure, lithology, porosity, permeability and mineral components all affect the potential for formation damage. The experimental results showed that the permeability loss was 83.8%-98.6% caused by stress sensitivity, and was 27.9%-48.1% caused by water blocking. Based on the experimental results, several main conclusions concerning stress sensitivity can be drawn as follows： the lower the core permeability and the smaller the core fracture width, the higher the stress sensitivity. Also, stress sensitivity results in lag effect for both permeability recovery and fracture closure. Aimed at the mechanisms of formation damage, a modified low-damage mixed metal hydroxide （MMH） drilling fluid system was developed, which was mainly composed of low-fluorescence shale control agent, filtration control agent, lowfluorescence lubricant and surfactant. The results of experimental evaluation and field test showed that the newly-developed drilling fluid and engineering techniques provided could dramatically increase the return permeability （over 85%） of core samples. This drilling fluid had such advantages as good rheological and lubricating properties, high temperature stability, and low filtration rate （API filtration less than 5 ml after aging at 120 ℃ for 4 hours）. Therefore, fractured carbonate formations with low permeability could be protected effectively when drilling with the newly-developed drilling fluid. Meanwhile, field test showed that both penetration rate and bore stability were improved and the soaking time of the drilling fluid with formation was sharply shortened, indicating that the modified MMH drilling fluid could meet the requirements of drilling engineering and geology.

微膨胀水泥浆在涠洲11-1N区块固井中的应用

涠洲11-1N区块油水层相距较近,隔层薄,固井时要完全封住水层、油层和油水层之间的隔层。采用以非渗透降失水剂为主、膨胀剂为辅组成的微膨胀水泥浆体系固井,该水泥浆气侵阻力大,能有效防止水泥石孔隙窜槽,同时能有效消除因水泥凝固后体积收缩造成的微环空间隙,增强水泥石的强度,提高水泥环与套管和井壁两个界面的胶结质量。现场应用表明,微膨胀水泥浆适用于井底静止温度低于120℃的固井作业,凝固后具有气侵阻力大和微膨胀特性,能有效封隔油气水层;清洗液+稠隔离液+清洗液+紊流清扫水泥浆组成的前置液能有效提高钻井液顶替效率,取得了固井质量SBT电测结果优良的效果。

二氧化氯解堵技术

针对老油田长期开采后,多数油水井均出现产量和注水量下降的现象,利用二氧化氯解堵技术解除压裂液、钻井液滤液中有机高分子堵塞、去除铁垢、杀死细菌达到解堵的目的。对二氧化氯的物理性能、解堵原理研究表明,二氧化氯是一种强氧化剂,可以有效解除油井的细菌、铁硫化物及聚合物的腐蚀及堵塞。二氧化氯解堵技术主要适用地层存在垢堵、乳化堵、压裂液损害、聚合物堵塞、细菌、FeS堵塞等有机无机复合堵塞;地层能量较高,物性较好;堵塞原因复杂,常规措施无效。现场应用表明,二氧化氯能有效地控制油田污水中的细菌,其他水质指标则受影响较小;二氧化氯能氧化分解铁硫化物,使油井恢复生产,并对原油性质影响小。介绍了二氧化氯解堵工艺,同时提出了二氧化氯解堵技术存在的问题。

Formation and Prevention of Hurricanes,Typhoons and Cyclones

Hurricanes,typhoons and cyclones are the most destructive weather systems.In order to mitigate the disasters caused by these storms,it is necessary to clarify the cause and activity rule of these storms.However,the formation of hurricanes,typhoons and cyclones as well as the cause of their path and strength changes still remains the major unsolved problems in today’s world.Fortunately,the author has recently studied the formation and activity of polar vortices,therefore can reveal the formation and current driving warm core structure of hurricanes,typhoons and cyclones,which plays an important guiding role in preventing major disasters caused by them.The author finds that all hurricanes,typhoons and cyclones are formed by polar vortices pulled by the moon.In order to prevent hurricanes from raging along the east coast of the United States or cyclones from setting wildfires in western United States,the potentially dangerous vortex genesises near Baffin Island and those over northeastern Siberia should be monitored and weakened in the month before they prevail;in order to prevent typhoons from ravaging the Northwest Pacific or South China Sea,the potentially dangerous vortex genesises over northeastern Siberia should be monitored and weakened in the month before they prevail;in order to prevent cyclones from raging over the South Indian Ocean or the Bay of Bengal,the potentially dangerous vortex genesises in Antarctic should be monitored and weakened in the month before they prevail;in order to avoid abnormal cold in late winter or early spring in the Northern Hemisphere,the potentially dangerous Arctic cold vortex genesises near Baffin Island and those over northeastern Siberia should be monitored and weakened in the month before they prevail.

Evaluation and prevention of formation damage in offshore sandstone reservoirs in China

Reduction in water injectivity would be harmful to the waterflood development of offshore sandstone oil reservoirs. In this paper the magnitude of formation damage during water injection was evaluated by analyzing the performance of water injection in the Bohai offshore oilfield, China. Two parameters, permeability reduction and rate of wellhead pressure rise, were proposed to evaluate the formation damage around injection wells. The pressure performance curve could be divided into three stages with different characteristics. Analysis of field data shows that formation damage caused by water injection was severe in some wells in the Bohai offshore oilfield, China. In the laboratory, the content of clay minerals in reservoir rock was analyzed and sensitivity tests （including sensitivity to water, ftow rate, alkali, salt and acid） were also conducted. Experimental results show that the reservoir had a strong to medium sensitivity to water （i.e. clay swelling） and a strong to medium sensitivity to flow rate, which may cause formation damage. For formation damage prevention, three injection schemes of clay stabilizer （CS） were studied, i.e. continuous injection of low concentration CS （CI）, slug injection of high concentration CS （SI）, and slug injection of high concentration CS followed by continuous injection of low concentration CS （SI-CI）. Core flooding experiments show that SI-CI is an effective scheme to prevent formation damage and is recommended for the sandstone oil reservoirs in the Bohai offshore oilfield during water injection.

双保仿油基改性MEG的研究与应用

MEG是近年来利用半透膜机理优选出的一种优质处理剂,有良好的润滑性、热稳定性和页岩抑制性,无荧光、易生物降解。但MEG本身为液体,加量偏高(10%-30%)。通过大量的文献调研和试验,成功地将MEG液体制成固体,不仅保持了MEG原液体的基本性能,又增加了MEG抑制能力的成分。由性能评价得知,改性MEG单剂具有良好的页岩抑制性及润滑性,经150℃老化后MEG钻井液流变性能、滤失性能、pH值变化不明显,随着改性MEG加量的增加,钻井液性能持续得到改善,综合考虑经济效益,改性MEG加量定为7%。现场应用表明,MEG钻井液具有较强的悬浮性和携带岩屑的能力及良好的护壁作用,抗膏岩污染能力强,流变性易于调节;使用MEG钻井液钻进的井机械钻速比同类井提高15%;并具有良好的保护油气层的作用,郑607-平6井试油日产油量为52t,是邻井的3倍。

用于预防和解除有机垢的修井液添加剂

原油沥青质沉积形成的有机垢是造成油气层损害的主要原因之一,并且某些损害是永久性和不可逆的,因此有必要对原油中沥青质的沉积采取有效的预防和解除措施。使用所建立的评价方法,筛选出了能有效预防有机垢损害的修井液添加剂正电聚醇,以及用于解除有机垢损害的修井液添加剂L-01。正电聚醇分子链上的多个羟基具有较强的正电性和比沥青质更强的吸附能力,因此能够优先吸附在岩石表面上,形成保护层,从而起到很好的预防沥青质沉积的作用。L-01中的甲苯对沥青质具有很好的溶解能力,并且其中的石油磺酸(或盐酸)还对无机垢具有一定的溶解和解堵能力。在适宜的加量下,正电聚醇的抑制率可达到100%,而L-01的相对溶解度可达到80%以上。

北京市地面沉降发展及对城市建设的影响

地面沉降是北京市平原区主要地质灾害之一,最早在1935年发现于西单至东单一带,到目前为止已经形成了多个地面沉降中心,到2005年底,累计沉降量大于50mm的沉降区达4114km2,大于1OOmm的沉降区达2815km2。地面沉降已经对城市基础设施造成一定程度的损坏,并且已经对奥运场馆．规划新城,CBD等重要区域构成潜在威胁,所以必须及时制定完善的防治措施来降低地面沉降的危害。

Laboratory Evaluation Procedures of Formation Damage Induced by Completion Fluids in Horizontal Wells

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吉林大情字井地区油气层损害机理

按标准实验程序和方法,系统研究了吉林油田大情字井地区钻井液损害油气层的机理及影响因素。结果表明,对渗透率在1×10-3μm2左右的岩心,水锁损害为14.05%-23.01%;水敏、钻井液滤液与储层不配伍和大分子吸附造成的损害为13.73%-18.84%;固相损害为2.36%-4.80%。对渗透率在20×10-3-30×10-3μm2之间的岩心,水锁损害为7.48%-12.20%;水敏、钻井液滤液与储层不配伍和大分子吸附造成的损害为6.47%-9.17%;固相损害为0.57%-4.55%,因此该地区主要的损害方式为液相损害。钻井液滤失量,特别是高温高压滤失量,对储层渗透率影响很大,随着钻井液压差的增大,岩心的渗透率恢复值下降了4%-7%,因此在钻井过程中特别应控制进入油气层的钻井液滤液量和性质,并且应尽可能降低钻井液密度。

Stabilizing silica nanoparticles in high saline water by using polyvinylpyrrolidone for reduction of asphaltene precipitation damage under dynamic condition

In this study, the performance of stable nanofluid containing SiO2 nanoparticles dispersed and stabilized in high salinity brine for asphaltene inhibition in dynamic condition is evaluated. In the first stage of this work, the stability of silica nanoparticles in different range of water salinity(0–100000 mg·L-1) is investigated. Next, stable nanofluid containing highest salinity is selected as asphaltene inhibitor agent to inject into the damaged core sample. The estimated values of oil recovery for base case, after damage process and after inhibition of asphaltene precipitation using nanofluid are 51.6%, 36.1% and 46.7%, respectively. The results showed the reduction in core damage after using nanofluid. In addition, the relative permeability curves are plotted for the base case, after damage process and also after inhibition of asphaltene precipitation using nanofluid. Comparison of relative permeability curves shows, relative permeability of oil phase decreased after damage process as compared with the base case. But after using nanofluid the oil relative permeability curve has shifted to the right and effective permeability of oil phase has been improved.

Tight sandstone reservoir sensitivity and damage mechanism analysis: A case study from Ordos Basin, China and implications for reservoir damage prevention

Analysis of reservoir sensitivity to velocity,water,salt,acid,alkali and stress is critical for reservoir protection.To study the tight sandstone reservoir sensitivity at different formation depths(effective stress)and formation water conditions(pH,salinity,and fluid velocity),a series of dynamic core flow tests under different pH,salinity,acid,and effective stress conditions were performed on samples from tight sandstone reservoirs of the Upper Triassic Yanchang 8(T_(3)y^(8))Member and conventional reservoirs of the Middle-Lower Jurassic Yan'an 9(J_(1-2)y^(9))Member in the Ordos Basin.The results indicate that,compared with the conventional reservoirs,the tight sandstone reservoirs are more sensitive to velocity and stress,less sensitive to water,alkali and salinity,and respond better to acid fracturing.In addition,the critical conditions(salinity,velocity,pH,and stress)for pumping drilling,completion,and fracturing fluids into tight sandstone reservoirs were investigated.A combination of scanning electron microscopy coupled with energy-dispersive spectrometry(SEM-EDS),cathodoluminescence(CL),casting thin section(CTS)and nuclear magnetic resonance(NMR)images,high-pressure mercury injection capillary pressure(MICP)measurements as well as X-ray fluorescence spectral(XRF)analyses were employed to analyze the damage mechanisms of the conventional reservoirs(J_(1-2)y^(9))and tight sandstone reservoirs(T_(3)y^(8))caused by fluid invasion.The results suggest that reservoir sensitivity is primarily conditioned by the composition of detrital components and interstitial fillings,petrophysical properties,pore-throat structure,and diagenetic facies.All these factors control the sensitivity types and extent of the reser-voirs.Our results indicate that the poorer the reservoir physical properties,the stronger the reservoir heterogeneity and sensitivity,implying that tight sandstone reservoirs are more susceptible to changes in fluids than conventional reservoirs.This study offers insights into the reservoir damage types and helps to improve the design and implementation of protection measures for tight sandstone reservoir exploration.

Evaluation of formation damages during filter cake deposition and removal process:The effect of primary damage on secondary damage

The properties of oil and gas formation could be significantly damaged during drilling and completion operations as a result of mud invasion,fluid incompatibility and interaction with rock minerals.This paper presents a systematic method for evaluating formation damage during filter cake deposition(primary damage)and removal process(secondary damage).The role of primary damage in the evolution of secondary damage was also investigated.The interaction of the filter cake solvent(chelating agent solution)with the rock samples was implemented through core flooding experiment.Nuclear Magnetic Resonance(NMR)was used to evaluate the properties of the rock sample,pre and post filter cake deposition and removal processes.The results show that secondary damaged is a strong function of the location and the intensity of the primary damage.The rock type and its pore structure also play important roles in both primary and secondary damage.The extent of secondary damage depends on the amount of barium sulphate deposited during primary damage.The chelating agent used to dissolve the barites in sandstones,deposited the barite in the small pores while it enlarges the bigger pores.In contrast,the chelating agent in the carbonate samples had multiple barite deposition points.

过冷水动态冰晶制取的实验研究

本文提供了一种过冷水动态制取冰晶的实验装置,着重介绍了系统的设计过程以及各部分的技术要求。为保证系统稳定运行,本实验装置采取了一系列措施,包括冰晶消除、过冷解除以及防冻结策略等。实验采用自来水、纯水、6%的乙二醇溶液作为试样,在不同的冷却速率、速度以及壁面条件下进行了对比实验,并给出了定性分析。

腰英台地区钻井完井液保护油气层效果评价

腰英台区块地处松辽盆地南部长岭凹陷东北部,储层属低孔特低渗油气藏,具有中等偏弱速敏、弱水敏、中等偏强酸敏等特点,水锁损害程度属中等偏弱。为了保护油气层,减小储层伤害,选用了两种钻井完井液体系:两性离子聚合物钻井液体系和聚合物腐钾聚合物钻井液体系。实验表明:两种聚合物体系的各种处理剂与地层水的配伍性好,储层岩心的动态渗透率恢复值在80%以上。现场测试也表明,这两种钻井完井液体系对腰英台区块复杂油气层保护效果较好。

A new laboratory method for evaluating formation damage in fractured carbonate reservoirs

Natural carbonate core samples with artificial fractures are often used to evaluate the damage of fractured carbonate formations in the laboratory. It is shown that the most frequent error for evaluation results directly from the random width characterized by the artificial fractures. To solve this problem, a series of simulated fractured core samples made of stainless steel with a given width of fracture were prepared. The relative error for the width of artificial fracture decreased to 1%. The width of natural and artificial fractures in carbonate reservoirs can be estimated by image log data. A series of tests for formation damage were conducted by using the stainless steel simulated core samples flushed with different drilling fluids, such as the sulfonate/polymer drill-in fluid and the solids-flee drill-in fluid with or without ideal packing bridging materials. Based on the experimental results using this kind of simulated cores, a novel approach to the damage control of fractured carbonate reservoirs was presented. The effective temporary plugging ring on the end face of the simulated core sample can be observed clearly. The experimental results also show that the stainless steel simulated cores made it possible to visualize the solids and filtrate invasion.