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.

Development and Applications of the Solid Emulsifier Used to Improve the Performance of Oil-in-water Drilling Fluids

The oil-in-water emulsion drilling fluids, prepared by adding 5～12% (by volume) of mineral oil (or diesel) to water-based muds, have been widely used for stuck-pipe prevention in the Shengli Oilfield. In some cases, the emulsion stability of this kind of mud system is not strong enough to meet the requirements of drilling operations. To overcome this drawback, a solid emulsifier, which is characterized by its very small particle size and special wetting behavior (slightly water-wet), has been developed and successfully applied to improve the emulsion stability and other performances of these drilling fluids. Prior to the development of this technology, an extensive study was conducted to deal with the influence of various kinds of finely divided insoluble solid particles on oil/water emulsification. The substances used include bentonite, organophilic clay, kaolinite, barite, two kinds of calcium carbonate with different particle sizes, two kinds of silica with different wetting behaviors, and a newly developed solid emulsifier. Both the emulsion stability experiments and the drop coalescence experiments are performed to evaluate the contribution of these particles to emulsification. The measured final emulsion volume disappears after 12 hours and the half-life for water and oil drops are used as the measures of emulsion stability. The experimental data show that the type, size, concentration and wettability of the particles, and the presence of some surfactants control the type and stability of emulsions for a given oil/water system, and the fine particles of the solids emulsifier provide the most effective stabilization for water-continuous emulsions compared with other kinds of particles. Meanwhile, it can be observed that these particles also stabilize oil-continuous emulsions effectively in some cases since their wetting behavior is close to neutral. The O/W emulsion mud stabilized by the newly developed solid emulsifier has become one of the major mud systems used in directional and horizontal well drilling in the Shengli Oilfield. In addition to the improvement of emulsion stability, this solid emulsifier has the advantages of improving the lubricity of mud cake and is beneficial to the control of rheological properties and filtration.

Development and applications of solids-free oil-in-water drilling fluids

The increasing application of near balanced drilling technology to low-pressure and depleted fractured reservoirs requires the use of low-density drilling fluids to avoid formation damage. Solidsfree oil-in-water （O/W） emulsion drilling fluid is one type of low-density drilling fluid suitable for depleted fractured reservoirs. In this paper, the solids-free O/W drilling fluid was developed and has been successfully used in the Bozhong 28-1 oil and gas field, by which lost circulation, a severe problem occurred previously when drilling into fractured reservoir beds, was controlled, thereby minimizing formation damage. The O/W emulsion drilling fluid was prepared by adding 20% （by volume） No. 5 mineral oil （with high flash point, as dispersed phase） into seawater （as continuous phase）. Surfactant HTO-1 （as a primary emulsifier） and non-ionic surfactant HTO-2 （as a secondary emulsifier） were added into the drilling fluid system to stabilize the emulsion; and YJD polymer was also added to seawater to improve the viscosity of the continuous phase （seawater）. The drilling fluid was characterized by high flash point, good thermal stability and high stability to crude oil contamination.

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.

A Study of Solid-Free Drilling Fluid for Tight Gas Reservoirs

This project is explaining a laboratory development of a solid free drilling fluid formula that could be potentially used in tight gas reservoirs. The configuration of the weak gel fluid WGL-1, which is resistant to high temperature and high salt, was tested, and concluded that its gelling properties, salt and temperature resistance, and environmental protection were all in line with industry requirements. The final drilling fluid formula was developed as: water + (0.3% ~ 0.5%) NaOH + 5% KCl + 2% WGL-1 + 5% NaCl + (1.0% ~ 2.0%) HBFR Anti-high temperature fluid loss agent + 2% Polyol + (1.5% ~ 2.0%) SDL-1 Lubricant + 0.4% A4O1. The performance of the liquid was tested for temperature resistance, inhibition, gas formation protection effect, plugging performance, and static settlement stability. It was concluded that the temperature resistance performance is satisfied at 150°C, and the cuttings recovery rate is as high as 96.78%. It has good performance in inhibiting water dispersion and swelling of cuttings. The permeability recovery value reaches 88.9%, which meets the requirements of gas formation protection. The SSSI value shows that its settlement stability is good;under high temperature and high pressure, its sealing performance is good. This drilling fluid system has achieved the expected results and laid a foundation for further promoting the development of solid-free drilling fluid systems. The future development direction of solid-free drilling fluids is pointed out, to the improvement of properties to be applied in high temperature environment and have high salt resistance capacity.

Solidification and utilization of water-based drill cuttings to prepare ceramsite proppant with low-density and high performance

Water-based drill cuttings(WBDC)and bauxite are used as raw materials to prepare proppants with low density and high performance.The effects of sintering temperature,sintering period,mixture ratios of materials,doping with iron oxide,and acid modification of WBDC on the properties of proppants are discussed.The proppant performance is evaluated according to the national standard SY/T5108-2014.The morphology of the proppant is analyzed using scanning electron microscopy(SEM).The crystal phase structure of the proppant is studied using X-ray diffraction(XRD).Thermal analysis of the proppant sintering process is performed using thermogravimetry(TG).Proppant Z-23 completely satisfied the SY/T5108-2014 standard.This study provides a new perspective for the resource utilization of water-based drill cuttings and preparation of low-density proppants.

The study of formulation and performance of formate drilling and completion fluid system

Formate drilling and completion fluid system is a new type of clean organic salt brine system which has been developed from inorganic salt brine drilling fluid system. It is beneficial to protecte and find hydrocarbon reservoir. Due to the solid free system, the damage of solid phase particles on reservoir, especially low permeability oil and gas layer, can be greatly eliminated, at the same time, drilling fluid and completion fluid have greater compatibility. It will avoid that precipitation which is not compatible with drilling and completion fluid and generates damages on reservoir. And because mud cake of the solid free system is thin and resilient, it is conductive to improve cementing quality greatly. Experiments show that the formate drilling and completion system has good rheological property, strong inhibition ability, good lubricating performance, good compatibility with reservoir rocks and formation water at high temperature.

连山关地区铀矿地质钻探技术优化

由于连山关地区存在着地层复杂、岩石胶结松散、水敏性强等诸多不利因素,钻探施工中存在钻孔漏失、掉块卡钻以及坍塌埋钻等问题,导致钻孔报废,降低了铀矿地质钻探施工的经济效益。为了解决以上问题,以ZK93-1孔钻为对象,针对铀矿地质地层特性以及常用设备、泥浆等存在的不利因素,对钻孔设备进行优化,选用CSD-1800A型全液压动力头钻机、HQ绳索取心钻具,并配备镦粗钻杆的NQ绳索取心钻具,提高了钻进效率及安全性,也降低了劳动强度;选用成膜防塌无固相冲洗液,有效降低钻孔偏斜,保证了岩矿心采取率,降低了施工成本,为类似地质条件地区的钻探工作提供参考依据。

页岩储层钻井液-压裂液复合损害机理及保护对策

为了分析钻井液与压裂液复合作用导致的储层损害,考虑油基钻井液侵蚀页岩矿物诱发的裂缝延伸,建立钻井液动态侵入深度预测方法,评价页岩裂缝面力学性质弱化、裂缝闭合与岩粉堵塞导致的天然/水力裂缝损害,提出钻井液-压裂液复合作用储层损害模式,揭示页岩油气层钻完井损害机理并提出保护对策。研究表明,钻开储层过程中,钻井液通过页岩诱导裂缝和天然裂缝深度侵入储层,侵蚀页岩矿物并导致侵入带页岩力学性质普遍弱化;水力压裂过程中,钻井液-压裂液复合作用进一步弱化页岩力学性质,导致生产过程裂缝更易闭合并发生岩粉脱落,诱发天然/水力裂缝应力敏感损害和固相堵塞损害,造成钻井液-压裂液复合作用带裂缝导流能力大幅降低,制约页岩油气井高产稳产。提出了防塌防漏加速储层段钻进、化学成膜防止页岩裂缝面力学性质弱化、强化页岩裂缝封堵减少钻井液侵入范围、优化压裂液体系保护裂缝导流能力的页岩储层保护对策。

废弃油基钻井液的环境影响特性及其亚微米固相性质研究

采用化学絮凝方法有效清除废液中亚微米固相钻井液,利用气相色谱-质谱联用仪、X射线衍射仪、X射线荧光光谱仪、傅里叶变换红外光谱仪等分析了固控设备处理后的废弃油基钻井液的组分、污染特性、毒性以及废液中亚微米固相的性质。结果表明,废弃油基钻井液的固相、油类含量明显超标,主要有机物为长链烷烃,占总质量的91%,无机物主要有石英石、赤铁矿、硬石膏及斜长石;废液中的镉元素、COD和BOD_(5)的含量超标,不易被生物降解,属于危险废弃物,可根据废液特征选择合适的无害化处理方式;废弃油基钻井液中固相的粒径分布在0.1~100μm,平均为4.5μm。

基于3DMine软件三维实体建模及资源量估算应用探讨——以瓮福磷矿区谷龙磷矿勘探为例

以3DMine矿业工程软件为基础,以贵州省瓮福磷矿区谷龙磷矿为研究对象,探索在地质勘查过程中钻孔数据库建立、三维实体建模等。利用钻孔数据库、实体模型进行可视化三维空间分析、综合图件绘制,以及资源量估算等。通过软件应用和实践,为其他类似矿山地质勘查的信息化、数字化、三维可视化和空间分析提供借鉴。

三维粗糙裂缝网络钻井液漏失流固耦合模型研究

针对现有三维裂缝性地层钻井液漏失模型未考虑粗糙裂缝网络对钻井液漏速影响的情况,建立了三维椭圆裂缝粗糙表面形貌方程,采用分形维数、高度幅值和粗糙峰叠加数量3个参数表征粗糙裂缝;建立了三维裂缝性地层钻井液漏失流固耦合力学模型,修正了粗糙裂缝中流体流动的立方定律,研究了漏失过程中储层压力和裂缝开度的变化规律。实例计算表明,分形维数和高度幅值与钻井液漏失量呈正相关关系;粗糙峰叠加数量与裂缝的平均开度、钻井液漏失量呈负相关关系,裂缝的最大开度与钻井液漏失量有显著的正相关关系。选择堵漏材料粒径时需要充分考虑裂缝表面粗糙度的影响,堵漏材料应重点在开度较大处架桥。研究成果为进一步认识钻井液在裂缝性地层的漏失规律和裂缝开度反演提供了理论基础。

超支化高分子水基钻井液仿生润滑机理

随着定向钻井技术的发展,水基钻井液润滑性逐渐成为确保定向井钻进的关键指标,设计新型钻井液润滑材料已成为油田化学领域的研究热点和重点。为探究超支化高分子水基钻井液仿生润滑机理,首先采用发散法合成了第1.5代超支化聚丙烯酸乙二胺基丙烯酸十八酯G1.5 P(EDA—MA—OA),然后进行了合成产物结构、微观形貌与热稳定性检测及其强化水基钻井液润滑性能评价,最后系统分析了超支化高分子与膨润土粒子的吸附行为。研究结果表明:①G1.5 P是粒径分布在几十纳米的分散性粒子,具有良好的热稳定性,热解温度集中在214℃;②以G1.5 P为润滑添加剂,构建的水基钻井液润滑系数为0.068,具有良好降摩减磨性;③G1.5 P呈“分子刷”状吸附于亲水材料表面,不仅改变了表面润湿性,而且还可促进膨润土粒子聚结形成致密、韧性的泥饼;④基于超支化高分子强化水基钻井液润滑的构效关系,提出了一种水基钻井液边界—固体润滑新模型,即超支化高分子促进在钻具与井壁摩擦副间形成低剪切强度泥饼,以泥饼结构内摩擦代替钻具刚性外摩擦,实现钻井液降摩减磨功能。结论认为,该认识完善了水基钻井液润滑添加剂的设计思路,为新型高性能润滑处理剂设计及超滑水基钻井液的开发提供了理论与技术支撑。

基于温敏聚合物/纳米复合材料的抗200℃高温无固相水基钻井液研究

针对传统无固相钻井液抗温性能较差的难题,以纳米复合材料N-AMPA为主剂,构建了具有优良抗温性能的无固相钻井液体系。评价结果表明,在25~180℃,1%N-AMPA水溶液的黏度增加率达43%,表现出优良的高温增黏性能;1%N-AMPA水溶液经200℃/16 h老化后,黏度保持率达67.6%,其抗温增黏效果明显优于增黏剂HE300。以N-AMPA为主剂构建的无固相钻井液体系,抗温能力达200℃,热滚16 h后的表观黏度保持率达67.0%、API中压滤失量为7 mL,耐温能力较强;抗氯化钠、氯化钙和劣土污染能力分别达20%、0.8%和10%,污染后于200℃热滚16 h, API中压滤失量始终低于9.5 mL,具有较好的抗污染性能;泥页岩膨胀率约3%,抑制防塌性能好;岩心渗透率恢复率达90%,储层保护效果好。

钻井液离心机预防绳索取心钻杆内壁结垢研究

针对钻杆内壁结垢严重制约绳索取心安全、优质、高效实施的技术难题,开展了金刚石绳索取心钻进钻杆内壁的结垢机理与影响因素综合研究,结果表明:当钻具结构与钻井液性能一定的情况下,钻井液中的固相含量与颗粒大小是影响钻杆内壁结垢的主要因素。金刚石岩心钻进所产生的岩屑粒径在5~100μm之间,总体偏细,难以依靠自然沉降清除。为此,研制了TGLW系列小型离心机,现场试验表明:该离心机可使钻井液中固相颗粒的峰值从5~80μm降到3~10μm,固相粒度中值从11.189μm降到3.513μm,固相清除率达90%以上,控制钻井液固相含量在0.5%以下,既维护了钻井液性能、又预防了绳索取心钻杆内壁结垢。

高含水钻井固废超细颗粒过滤分离实验研究

针对钻井固废处理的难点在于其含有大量10μm以下的超细颗粒难以分离问题,结合振动筛分和深层过滤处理方法,从减少整体固相含量和分离超细颗粒出发,开发了一种能有效去除高含水钻井固废中超细颗粒的新型处理方法。结果表明,在优选工艺参数下,高含水钻井固废经过振动筛分处理后,10μm以上的较大颗粒被去除,固相含量从30.42%降低至9.55%。筛下液再经过深层过滤处理,92.77%的超细颗粒被去除。研究结果表明,新型处理方法对高含水钻井固废超细颗粒有良好的去除效果,有利于实现高含水钻井固废回收利用要求。

陕西榆林废弃钻井液固液分离技术研究

采用稀硫酸作为破胶剂,通过室内抽滤实验对各种常用絮凝剂进行了优选,优化了废弃钻井液固液分离配方,即采用酸化破胶后加入3.09 g/L硫酸铝和3.09 g/L硫酸铁,能够将废弃钻井液进行脱稳分离。经陕西榆林现场应用表明,废弃钻井液应用此技术脱稳后,一次压滤成功,滤饼中平均含水量为31.79%。与前期固液分离效果相比,滤饼平均含水量降低了17.90%,废弃钻井液处理成本降低了10.21%。

滚动负压筛在国内油气钻井中的试验与应用

传统钻井振动筛在常压下依靠振动产生5~6g的抛掷力将钻屑从钻井液中筛分出来,钻屑含液率高,固废量大。滚动负压筛是一种基于带式真空过滤原理与微振动复合作用的钻井液固液分离装置,其钻井液的透筛主要依靠真空作用,钻屑含液率低,钻井液回收率高,固废产生量少。2014年以来,国内陆续引进部分滚动负压筛,在海洋钻井固废减量和陆地钻井钻屑减量中进行了试验和小范围的应用,但相关的试验和应用报道较少。对滚动负压筛在国内陆地钻井中进行了应用和对比试验,试验结果表明,滚动负压筛排出钻屑的体积含液率可降低到35%以下,油基泥浆时,每米进尺泥浆消耗量和固废实际产生量比传统振动筛可分别降低32.25%和51.63%,分离出的钻井液含砂量和有害固相降低,提升了钻井液的性能。滚动负压筛的应用具有较好的经济效益和环保效益,但一次性设备投入成本较高,可能影响其大面积的推广应用。

废弃水基钻井液固液分离产水回用技术

以废弃水基钻井液为对象,采用“破胶—压滤—沉淀”工艺进行处理,将处理产水回用于钻井液配制。实验结果表明:适宜的破胶剂为质量分数20%的聚合氯化铝(GW-CFA)溶液,加入量36 mL/L;适宜的离子沉淀剂为三巯基-三嗪三钠盐(TMT-15)(固),加入量7.5 g/L。现场试验结果表明,选用石灰与GW-CFA复合破胶剂(GW-CFA溶液(质量分数20%)加入量15mL/L,石灰加入量5.0g/L)对废弃钻井液进行破胶,压滤产水时间可缩短至10'10'',产水率为61%。废弃水基钻井液经“破胶—压滤—沉淀”工艺处理后,产水回用于钻井液配制是完全可行的,所配制钻井液的各项性能均能满足现场需要。

水基钻井液储层保护技术研究进展

钻井液储层保护性能对后续油气资源产能的影响至关重要。文章综述了储层伤害的主要类型以及储层保护钻井液的关键功能,钻井液对储层的主要伤害分为固相污染、聚合物的吸附堵塞、储层黏土易发生水化膨胀,并可能因钻井液中的成分而分散或运移,以及钻井液滤液与地层水配伍性伤害。储层保护钻井液大致分为强封堵低滤失钻井液、强抑制低伤害水基钻井液、低固相/无固相聚合物钻井液体系以及在无固相聚合物钻井液体系上发展的可生物降解的无固相钻井液,在现场应用中取得了较好的储层保护效果,为现场储层保护提供了技术支持。