Improving the anti-collapse performance of water-based drilling fluids of Xinjiang Oilfield using hydrophobically modified silica nanoparticles with cationic surfactants

Wellbore instability,especially drilling with water-based drilling fluids(WBDFs)in complex shale for-mations,is a critical challenge for oil and gas development.The purpose of this paper is to study the feasibility of using hydrophobically modified silica nanoparticle(HMN)to enhance the comprehensive performance of WBDFs in the Xinjiang Oilfield,especially the anti-collapse performance.The effect of HMN on the overall performance of WBDFs in the Xinjiang Oilfield,including inhibition,plugging,lu-bricity,rheology,and filtration loss,was studied with a series of experiments.The mechanism of HMN action was studied by analyzing the changes of shale surface structure and chemical groups,wettability,and capillary force.The experimental results showed that HMN could improve the performance of WBDFs in the Xinjiang Oilfeld to inhibit the hydration swelling and dispersion of shale.The plugging and lubrication performance of the WBDFs in the Xinjiang Oilfield were also enhanced with HMN based on the experimental results.HMN had less impact on the rheological and filtration performance of the WBDFs in the Xinjiang Oilfield.In addition,HMN significantly prevented the decrease of shale strength.The potential mechanism of HMN was as follows.The chemical composition and structure of the shale surface were altered due to the adsorption of HMN driven by electrostatic attraction.Changes of the shale surface resulted in significant wettability transition.The capillary force of the shale was converted from a driving force of water into the interior to a resistance.In summary,hydrophobic nanoparticles presented afavorable application potential for WBDFs.

The influence of water-based drilling fluid on mechanical property of shale and the wellbore stability

Because of high cost and pollution of oil-based drilling fluid,the water-based drilling fluid is increasingly used now.However,bedding planes and micro-cracks are rich in shale formation.When water-based drilling fluid contacts formation rock,it causes the propagation of crack and invasion of drilling fluid,which decrease shale strength and cause wellbore instability.In this paper,we analyzed influence of water-based drilling fluid on shale strength and failure mode by mechanics experiment.Based on those experimental results,considering the effect of bedding plane and drilling time,we established modeling of wellbore stability for shale formation.The result from this model indicates that in certain azimuth of horizontal well,collapsing pressure increases dramatically due to shale failure along with bedding plane.In drilling operation,those azimuths are supposed to be avoided.This model is applicable for predication of collapsing pressure in shale formation and offers reference for choosing suitable mud weight.

A new environmentally friendly water-based drilling fluids with laponite nanoparticles and polysaccharide/polypeptide derivatives

Considering the increasing environmental pressure,environmentally friendly and high-performance water-based drilling fluids(WBDFs)have been widely studied in recent years to replace the commonly used oil-based drilling fluids(OBDFs).However,few of these drilling fluids are entirely composed of natural materials,which makes it difficult to achieve real environmental protection.Using laponite nanoparticles and various derivatives of natu ral mate rials,including cro sslinked starch,cellulose composite,gelatin ammonium salt,poly-l-arginine,and polyanionic cellulose,a kind of environmentally friendly water-based drilling fluid(EF-WBDF)was built for drilling in environment-sensitive areas.The properties of this EF-WBDF were evaluated by thermal stability tests on rheology,filtration,inhibition,and salt contamination.Besides,biological toxicity,biodegradability,heavy mental content and wheat cultivation tests were conducted to investigate the environmental factor of EF-WBDF.Results showed that EF-WBDF displayed satisfactory thermal resistance up to 150℃,and the rheological properties did not suffer significant fluctuation,showing potential application in high-temperature wells.The optimal rheological model of EF-WBDF was Herschel-Bulkley model.This EF-WBDF performed an eligible filtration of 14.2 mL at 150℃and a differential pressure of 3.5 MPa.This fluid could still maintain colloidal stability after being contaminated by 7.5%NaCl or 0.5%CaC1_(2).Meanwhile,rather low clay swelling degree of 2.44 mm and high shale recovery of more than 95%ensured the inhibitive capability of EF-WBDF.Furthermore,EF-WBDF presented a half maximal effective concentration(EC_(50))of51200 mg/L and a BOD/COD ratio of 47.55%,suggesting that EF-WBDF was non-toxic and easily biodegradable.The wheat cultivated in EF-WBDF could grow healthily,beneficial for reducing the adverse impact on ecological environment.The formed EF-WBDF has a promising future for drilling in environment-sensitive and high-temperature areas.

Super-amphiphobic, strong self-cleaning and high-efficiency water-based drilling fluids

Based on the amphiphobic theory on underground rock surface, a super-amphiphobic agent is developed and evaluated which can form nano-micro papilla structure on rock, filter cake and metal surface, reduce surface free energy, prevent collapse, protect reservoir, lubricate and increase drilling speed. With this super-amphiphobic agent as the core agent, a super-amphiphobic, strong self-cleaning and high-performance water-based drilling fluid system has been developed by combining with other agents based on drilled formation, and compared with high-performance water-based drilling fluid and typical oil based drilling fluid commonly used in oilfields. The results show that the super-amphiphobic, strong self-cleaning and high-performance water-based drilling fluid has better rheology, and high temperature and high pressure filtration similar with that of oil-based drilling fluid, inhibiting and lubricating properties close to oil based drilling fluid. Besides, the super-amphiphobic system is non-toxic, safe and environmentally friendly. Field tests show this newly developed drilling fluid system can prevent wellbore collapse, reservoir damage and pipe-sticking, increase drilling speed and lower drilling cost, meeting the requirement of safe, high efficient, economic and environmentally friendly drilling. Compared with other drilling fluids, this new drilling fluid system can reduce downhole complexities by 82.9%, enhance the drilling speed by about 18.5%, lower drilling fluid cost by 39.3%, and increase the daily oil output by more than 1.5 times in the same block.

Micro/nano structured oleophobic agent improving the wellbore stability of shale gas wells

Through embedding modified nano-silica particles on the surface of polystyrene using the method of Pickering emulsion polymerization,a kind of nano/micro oleophobic agent named OL-1 was developed.The effects of OL-1 on the rock surface properties and its performance in inhibiting the oil phase imbibition into the rock were explored.The performance and mechanisms of OL-1 in improving the wellbore stability of shale gas wells were evaluated and analyzed.OL-1 could absorb on the surface of the shale core to form a membrane with a micro-nano two-stage roughness,making the surface energy of the core decrease to 0.13 mN/m and the contact angle of the white oil on the core surface increase from 16.39°to 153.03°.Compared with the untreated capillary tube,when immersed into 3#white oil,the capillary tube treated by OL-1 had a reversal of capillary pressure from 273.76 Pa to-297.71 Pa,and the oil imbibition height inside the capillary tube decreased from 31 mm above the external liquid level to 33 mm below the external liquid level.The amount of oil invading into the rock core modified by OL-1 decreased by 64.29%compared with the untreated one.The shale core immersed into the oil-based drilling fluids with 1%OL-1 had a porosity reduction rate of only 4.5%.Compared with the core immersed in the drilling fluids without OL-1,the inherent force of the core treated by 1%OL-1 increased by 24.9%,demonstrating that OL-1 could effectively improve the rock mechanical stability by inhibiting oil phase imbibition.

Fluid-solid coupling model for studying wellbore instability in drilling of gas hydrate bearing sediments

As the oil or gas exploration and development activities in deep and ultra- deep waters become more and more, encountering gas hydrate bearing sediments （HBS） is almost inevitable. The variation in temperature and pressure can destabilize gas hydrate in nearby formation around the borehole, which may reduce the strength of the formation and result in wellbore instability. A non-isothermal, transient, two-phase, and fluid-solid coupling mathematical model is proposed to simulate the complex stability performance of a wellbore drilled in HBS. In the model, the phase transition of hydrate dissociation, the heat exchange between drilling fluid and formation, the change of mechanical and petrophysical properties, the gas-water two-phase seepage, and its interaction with rock deformation are considered. A finite element simulator is developed, and the impact of drilling mud on wellbore instability in HBS is simulated. Results indicate that the re- duction in pressure and the increase in temperature of the drilling fluid can accelerate hydrate decomposition and lead to mechanical properties getting worse tremendously. The cohesion decreases by 25% when the hydrate totally dissociates in HBS. This easily causes the wellbore instability accordingly. In the first two hours after the formation is drilled, the regions of hydrate dissociation and wellbore instability extend quickly. Then, with the soaking time of drilling fluid increasing, the regions enlarge little. Choosing the low temperature drilling fluid and increasing the drilling mud pressure appropriately can benefit the wellbore stability of HBS. The established model turns out to be an efficient tool in numerical studies of the hydrate dissociation behavior and wellbore stability of HBS.

Novel Water-Based Drilling and Completion Fluid Technology to Improve Wellbore Quality During Drilling and Protect Unconventional Reservoirs

The efficient exploration and development of unconventional oil and gas are critical for increasing the self-sufficiency of oil and gas supplies in China.However,such operations continue to face serious problems(e.g.,borehole collapse,loss,and high friction),and associated formation damage can severely impact well completion rates,increase costs,and reduce efficiencies.Water-based drilling fluids possess certain advantages over oil-based drilling fluids(OBDFs)and may offer lasting solutions to resolve the aforementioned issues.However,a significant breakthrough with this material has not yet been made,and major technical problems continue to hinder the economic and large-scale development of unconventional oil and gas.Here,the international frontier external method,which only improves drilling fluid inhibition and lubricity,is expanded into an internal-external technique that improves the overall wellbore quality during drilling.Bionic technologies are introduced into the chemical material synthesis process to imitate the activity of life.A novel drilling and completion fluid technique was developed to improve wellbore quality during drilling and safeguard formation integrity.Macroscopic and microscopic analyses indicated that in terms of wellbore stability,lubricity,and formation protection,this approach could outperform methods that use typical OBDFs.The proposed method also achieves a classification upgrade from environmentally protective drilling fluid to an ecologically friendly drilling fluid.The developed technology was verified in more than 1000 unconventional oil and gas wells in China,and the results indicate significant alleviation of the formation damage attributed to borehole collapse,loss,and high friction.It has been recognized as an effective core technology for exploiting unconventional oil and gas resources.This study introduces a novel research direction for formation protection technology and demonstrates that observations and learning from the natural world can provide an inexhaustible source of ideas and inspire the creation of original materials,technologies,and theories for petroleum engineering.

Fabrication of a Hydrophobic Hierarchical Surface on Shale Using Modified Nano-SiO_(2)for Strengthening the Wellbore Wall in Drilling Engineering

Wellbore stability is essential for safe and efficient drilling during oil and gas exploration and development.This paper introduces a hydrophobic nano-silica(HNS)for use in strengthening the wellbore wall when using a water-based drilling fluid(WBF).The wellbore-strengthening performance was studied using the linear swelling test,hot-rolling recovery test,and compressive strength test.The mechanism of strengthening the wellbore wall was studied by means of experiments on the zeta potential,particle size,contact angle,and surface tension,and with the use of a scanning electron microscope(SEM).The surface free energy changes of the shale before and after HNS treatment were also calculated using the contact angle method.The experimental results showed that HNS exhibited a good performance in inhibiting shale swelling and dispersion.Compared with the use of water,the use of HNS resulted in a 20%smaller linear swelling height of the bentonite pellets and an 11.53 times higher recovery of water-sensitive shale—a performance that exceeds those of the commonly used shale inhibitors KCl and polyamines.More importantly,the addition of HNS was effective in preventing a decrease in shale strength.According to the mechanism study,the good wellbore-strengthening performance of HNS can be attributed to three aspects.First,the positively charged HNS balances parts of the negative charges of clay by means of electrostatic adsorption,thus inhibiting osmotic hydration.Second,HNS fabricates a lotus-leaf-like surface with a micro-nano hierarchical structure on shale after adsorption,which significantly increases the water contact angle of the shale surface and considerably reduces the surface free energy,thereby inhibiting surface hydration.Third,the decrease in capillary action and the effective plugging of the shale pores reduce the invasion of water and promote wellbore stability.The approach described herein may provide an avenue for inhibiting both the surface hydration and the osmotic hydration of shale.

页岩气调查井复杂地层有机硅聚合物钻井液体系的研制与应用

页岩气调查井通常地质条件复杂,钻探难度大。在对页岩气调查川沐地2井井壁稳定性分析的基础上,优选了有机硅聚合物钻井液体系,并通过正交试验,明确了有机硅改性聚合物、多级配超细碳酸钙、乳化石蜡和硅氟聚合物等主要处理剂的最优加量,形成了基本配方,在室内实验评价中该体系展现了良好的抗钻屑污染能力、抗钙侵能力、抑制性和封堵性。现场应用表明,川沐地2井在采用有机硅聚合物钻井液体系后,井内复杂情况得到明显改善,有效保障了井内安全,并顺利钻进至设计井深,实现了地质目标,钻进效率相比同区域同类型钻井大幅提高。研究成果可为页岩气调查井复杂地层钻探钻井液的选择与应用提供借鉴。

国内外盐膏层钻井液技术分析

盐膏层作为一个世界性技术难题,国内外油田在油气勘探开发的钻井过程中均不同程度钻遇了盐膏层,且许多深部盐膏层井因井眼稳定原因被迫提前完钻,或因盐膏层的蠕变发生套管挤毁而报废,浪费了大量的人力、物力和材料,严重影响着盐下油气资源的勘探开发。从盐膏层特性出发,从钻井液角度全面总结分析了盐膏层作业工程中出现的技术难题,并对国内外盐膏层钻井液技术和现场应用案例进行了介绍,同时对深水盐膏层钻井液技术后期的解决方式提出了技术思路。

纳米材料提高水基钻井液页岩稳定性研究进展

维持井壁稳定一直是油气钻探过程中的技术难题。由于页岩微纳米孔缝与层理发育、水敏性高,井壁失稳问题在页岩层尤为突出。提高钻井液的性能是减少井壁失稳的重要途径。纳米材料因其独特的尺度和性质,可作为水基钻井液添加剂以提高页岩的稳定性。通过对国内外技术的跟踪与分析,阐述纳米材料提高页岩稳定性的评价方法、纳米材料类型及其作用机制。开展纳米材料在非均质地层的基础理论研究,开发在高温高压及高盐环境下稳定有效的新型纳米材料,建立纳米材料提高页岩稳定性的微观评价方法,是纳米材料的重要发展方向。

渝西区块龙马溪组强封堵油基钻井液技术研究

渝西区块龙马溪组在水平段钻进过程中因井壁失稳而导致的卡钻、憋顶驱、测井困难等复杂情况频发,研究发现,造成此现象的主要原因是该区块龙马溪组地层微纳米孔、缝发育和钻井液封堵性能不足。因此,在强化现场钻井液封堵性能的基础上优选了钻井液主要处理剂,构建了适用于该区块龙马溪组强封堵油基钻井液体系,室内测试结果表明,经过220 nm和450 nm微孔滤膜时未发生滤失,且综合性能均优于普通钻井液。现场应用表明,龙马溪组水平段钻进过程中未出现井壁失稳问题,与同平台采用常规封堵技术的已钻井相比,平均机械钻速提高8.81 m/h,水平段钻井周期缩短2.79 d,铂金靶体钻遇率100%,创渝西区块深层页岩气井5项钻井指标纪录,强封堵油基钻井液技术能满足该区块钻井工程需要。

海陆过渡相页岩储层液岩作用机理及钻井液体系构建

我国海陆过渡相页岩地质储量大、资源丰度高,开发前景广阔。但钻井过程中井壁极易发生掉块、坍塌,导致井壁失稳影响钻井安全。本文通过钻井岩心观察、电镜和CT扫描、X射线衍射分析等相关实验,得到储层岩样矿物组分及微观结构等特征,结果表明:页岩气储层全岩主要含石英和黏土矿物,地层黏土矿物含量高达45.7%,且黏土矿物中不含蒙脱石,高岭石含量为35%,伊/蒙混层含量为26%;岩样表面纳微米孔隙和微裂缝发育,裂缝宽度在微米级并连通多条窄裂缝;通过岩液作用后晶层间距、表面张力、线性膨胀率和裂缝扩展变化分析,海陆过渡相页岩仅发生表面水化,揭示了海陆过渡相页岩气储层岩液作用机理。优选了水基钻井液抑制剂、封堵剂与润滑剂,构建了一套海陆过渡相页岩气储层的高性能水基钻井液体系,并对其展开了室内评价。钻井液常规性能、抑制性、封堵性、润滑性评价实验结果表明,该钻井液体系抗温100℃,高温高压失水6 mL,泥页岩膨胀率为1.03%,钻井液润滑系数整体小于0.15,体系30 min的API滤失量较基浆降低40%,可对地层微裂缝实现有效封堵,且生物毒性EC50值为37260 mg/L,属于无毒级别,能够满足海陆过渡相页岩气钻井作业施工对钻井液性能的要求并进行了现场应用,封堵防塌效果良好,可有效解决海陆过渡相泥页岩井壁失稳的技术难题。

吐哈油田胜北区块地层特性及钻井液技术对策

吐哈油田胜北区块钻井过程中遇到井壁失稳引起的下钻遇阻、划眼、卡钻等井下复杂情况,制约了钻井提速提效。以胜北508H为代表井,对不同层位岩屑样品的矿物组成及理化性能进行了测定,进而分析了上部地层和下部地层的主要特性和井壁失稳机理。研究表明,地层中普遍存在泥岩,泥岩中粘土矿物含量较高且其组成主要以伊蒙混层和伊利石为主,同时也含有蒙脱石,这些是导致井下发生复杂情况的地层因素。针对上部地层泥岩易水化分散造浆、缩径,提出了采取聚合物强化包被性能以及复合盐强化抑制性能的钻井液技术措施,优化后钻井液的滚动回收率高达88.40%,膨胀率为1.17%。针对下部地层泥岩易剥落掉块、坍塌,提出了通过微-纳米全尺寸封堵并结合复合盐的活度控制及聚胺强化抑制性能的钻井液技术措施,优化后钻井液的平衡压力时间大幅延长,达160 h。钻井液活度低于0.76,钻井液72 h浸泡泥岩岩心的强度降幅减小。优化后的钻井液在胜北区块SH5s21-2和SH5s13-2两口井应用中取得了良好的效果,钻井过程中未发生复杂事故,实现了维持井壁稳定、提高钻井时效的目的。

破碎地层护壁防塌剂研制及性能评价

针对顺北奥陶系碳酸盐岩地层揭开后坍塌掉块严重,遇阻卡钻频发的难题,以二甲基二烯丙基氯化铵、N,N-二甲基丙烯酰胺及自制含甲氧基硅烷基团的有机硅单体为原料,合成了可与碳酸盐岩地层发生键合反应的抗高温有机硅护壁防塌剂SMHB-1。通过红外光谱、核磁共振氢谱及热重等表征了产物的分子结构及稳定性,并评价了其搭接抗剪切强度、降滤失性能及封堵性能等进行了研究。结果表明,1.5%SMHB-1溶液处理过的碳酸盐岩岩心片的搭接抗剪强度可达到0.2 MPa, 160℃老化16 h后1%SMHB-1可使4%土浆滤失量降低60.7%,SMHB-1可降低体系渗透率降约61.68%,并且与现场钻井液的配伍性能好。以SMHB-1为核心的水基护壁防塌钻井液体系在顺北X井奥陶系地层进行应用,奥陶系井壁稳定性好,没有掉块产生,扭矩平稳,起下钻顺利,无阻卡,试验井段平均井径扩大率8.6%~11.4%。

西湖凹陷上部杂色泥岩井壁失稳研究和钻井液优化

东海西湖凹陷部分区块在Φ311.15 mm井段钻遇龙井组、花港组杂色泥岩地层时,频繁发生起下钻阻卡、倒划眼困难等复杂情况,严重影响井下安全和作业时效。室内采用X射线衍射、扫描电镜、压汞法、抗压强度测试等方法对地层岩性组构特征、力学特性以及其他物理化学性能进行试验,研究井壁岩石失稳机理,表明杂色泥岩本身极具失稳特性。模拟现场条件,试验研究现场油基钻井液封堵和井壁稳定能力、钻井液润湿性能对岩屑井壁黏附和润滑性的影响,发现影响杂色泥岩起下钻遇阻的主控因素是钻井液胶结封堵稳定井壁能力和钻井液润湿性能不够。针对地层特性和钻井液性能不足,制定油基钻井液稳定井壁优化对策,强化钻井液封堵固壁性,提高地层承压能力;优选钻井液乳化剂,提高体系高温稳定性和润湿性。优化后的油基钻井液体系能够有效封堵泥岩微纳米孔缝,提高井壁稳定性,提高泥饼润滑性,可降低起下钻阻卡风险。现场应用表明,钻井过程中井壁稳定,起下钻、下套管等均顺利,与邻井相比起下钻效率提升96%~353%,取得了良好的应用效果,有效解决了西湖凹陷上部杂色泥岩地层井壁失稳问题。

万米深井SDCK1井上部超大尺寸井眼钻井液技术

部署在四川盆地西北部的超深井SDCK1井上部为ϕ812.8 mm超大尺寸井眼,钻井过程中面临岩屑运移困难、井壁稳定要求高等技术难题。为此,进行了钻井液流型参数调配,以辅助携砂;引入有机盐、无机盐复配的双盐抑制剂,嵌入黏土晶层间隙,降低钻井液活度,并协同包被剂对泥页岩进行强抑制;优选多粒径封堵剂,形成了高抑制强封堵的聚合物钻井液体系。室内评价结果表明,该钻井液体系流变性良好,动塑比大于0.60,泥页岩一次回收率为99.54%,二次回收率为97.23%;API滤失量小于3.0 mL,具有较好的抑制封堵效果。现场应用表明,高抑制强封堵的聚合物钻井液体系能够抑制剑门关组、蓬莱镇组的泥页岩坍塌,无井下故障和复杂情况发生,为SDCK1井顺利施工提供了技术支撑。研究结果为其他超大尺寸井眼钻井施工提供了技术借鉴。

苏北陆相页岩油高性能水基钻井液技术

为解决常规油基钻井液在苏北页岩油工区钻井施工中面临的井壁失稳、环境污染等技术问题,在研究井壁失稳机理的基础上,提出了“外防水侵、内控膨胀”的井壁稳定控制方法,制定了“封堵为主+强化抑制+润湿反转+合理密度”的技术措施,研发了可变形微纳米聚合物封堵剂、页岩润湿反转剂和原油乳化分散降黏剂等关键助剂,构建了高性能水基钻井液体系SM-ShaleMud-II。该钻井液体系高温高压滤失量小于6.0 mL,极压润滑系数小于0.12,可有效降低储层泥页岩力学性能的弱化程度。苏北页岩油区块的10口井应用了该钻井液体系,钻井过程中井壁稳定,套管下入顺利,取得了良好的应用效果。高性能水基钻井液体系SM-ShaleMud-II的成功研制,为非常规页岩油气低成本绿色开发提供了一种有效的技术手段。