Determination of the Minimum Testing Time for Wireline Formation Testing with the Finite Element Method

1. Introduction The first generation of formation testing tool was introduced more than half a century ago. Since then, three generations of wireline formation tester tools (WFT) have been developed. WFT is an effective method for locating the fluid contact interface (gas/oil/water), verifying the formation pressure, and estimating the fluid density in respective zones. (Michaels, et al., 1995) As a sole tool used in dynamic formation testing, especially in exploration of complex reservoirs…     

复杂地层条件下钻井液优化使用的探讨

中国石化西部新区等地层情况十分复杂,对在钻井中存在的钻井液问题进行了分析,着重从钻井液优化使用方面进行了探讨.认为:提高体系的抑制性,应该尽可能采用电性较高的钻井液,不同电性的处理剂尽量不要混用;为简化钻井现场配浆时间,提高钻井液流变性能及胶体稳定性,应按照钻井液配方,预先在泥浆站采用湿挤压钠化、改性和增效的方法制成方便钻井液复合粉;为在井壁形成高质量泥饼,钻井液体系应具备尽可能高的正电性,体系中固相颗粒应有一定的细度和合理级配,并且钻井过程中,井底应保持一定的过平衡压力,另外,应重视对所选用钻井液泥饼的物理化学性质进行检测和研究.     

Numerical Model of Countercurrent Spontaneous Imbibition in Underbalanced Drilling: Formation Damage Investigation

Abstract

Although mud filtrate invasion is mostly concerned in overbalanced drilling (OBD), it is shown that it also occurs during underbalanced drilling (UBD) operations. UBD is a drilling operation in which the hydrostatic head of a mud column is maintained at a pressure less than that of fluid in the porous medium. Formation damage due to mud invasion in OBD could be eliminated in UBD. However, this benefit of UBD can be missed when pressure suddenly turns to overbalance and/or spontaneous imbibition. During UBD it is difficult to maintain mud pressure less than formation pressure especially for short periods of time for operational reasons such as bit trips, and it will cause major damage due to nonexistence of internal and external mud cake. Also, spontaneous imbibition, which occurs in low-permeable reservoirs, causes drilling fluid invasion. In this case, the hydrostatic head of drilling mud is less than formation pore (oil phase) pressure, but it may be higher than water-phase pressure in the formation because of capillary pressure. This causes the flow of water into the formation, which causes formation damage. The aim of this study is to present a model for spontaneous imbibition of water into the water-wet formation during underbalanced drilling and to investigate the effect of drilling fluid, reservoir rock, reservoir fluid, and drilling operation parameters on the extension of damage in nonfractured formations. The numerical solution of governing equations and sensitivity analysis on different parameters are presented. The results show that in the case of strong capillary pressure, (1) the damage due to spontaneous imbibition is considerable and (2) the most effective criteria are temporary overbalanced and static drilling fluid situations where both increase the extend and amount of drilling filtrate invasion. Also, it was concluded that a low UBD pressure difference causes damage, whereas the very high UBD pressure difference is inefficient.     

应用数值模拟软件探究动滤失影响因素

利用数值模拟软件,模拟地层条件下钻井过程中的钻井液动滤失情况,研究了滤失时间、滤液黏度、压差、内泥饼渗透率、外泥饼渗透率对滤失量的影响。模拟结果表明,当地层渗透率为100 mD,外泥饼渗透率小于0.01 mD时,90%以上的压力被外泥饼消耗,外泥饼是控制滤失量的主要因素;当外泥饼渗透率大于0.1 mD时,外泥饼消耗的压力低于总压差的55%,内泥饼及原始地层的渗透率对钻井液的动滤失也有较大的影响。在模拟条件下,压力很快会传递到地层边界,随着时间的变化,地层中相同位置的地层压力逐渐增加,但增加的幅度很小,滤失速率基本为一定值。从模拟结果可以看出,滤失量与滤失时间、压差成正比,与钻井液滤液黏度成反比,同时,滤失量随着外泥饼渗透率的增加而增加,但2者不呈线性关系。      

特低渗透砂岩油层钻井液侵入程度及影响

根据地质录井、实验分析、压裂试采等资料，基于动态分析、渗流理论及物质平衡原理，动、静态分析相结合，对特低渗透砂岩油层钻井液（泥浆滤液）侵入程度及其影响的评价方法进行了研究。利用压裂试采曲线特征将特低渗透油层的生产动态划分为初产与稳产2个阶段：1初产阶段主要表现为大量外来流体沿人工及天然裂缝系统的快速返排，产水量及含水率变化迅猛；2稳产阶段主要表现为地层原始流体在饱和度控制下的相对渗流，产水量及含水率变化处于低稳状态。正常油层具孔隙型单孔介质，通常无明显的钻井液侵入，其初产阶段的地层吞吐水量大致相当。低阻油层具微裂缝-孔隙型双孔介质，具有显著的钻井液侵入特征，其初产阶段的地层吞吐水量差异大致等于钻井液的侵入体积。利用地层初始吞吐液量差异确定了特低渗透砂岩油层的钻井液侵入程度，并以地层吞吐液量、钻井液侵入深度、结合压裂曲线特征，量化判断油层属性。建立了油层电阻率与钻井液侵入深度关系图版，定量评价了钻井液侵入的影响，分析了低阻油层成因。结果表明，钻井液侵入深度越大，则油层电阻率越小，低阻油层是钻井液超深侵入的结果；由于双孔介质及其微裂缝的发育，低阻油层的钻井液侵入深度通常超过了感应系列的径向探测半径，因此导致了"低阻"的发生。     

微电极曲线负异常在低渗透油藏储层评价中的新认识

微电极曲线的负差异现象在低渗透油藏中非常普遍。从微电极测量原理入手,对微电极曲线的负差异现象进行了解释,认为原因是储层的渗透性差,泥浆的侵入非常弱,没有形成泥饼造成的;并结合压裂后试油资料,将微电极负差异现象应用于低渗透油藏储层判别中,取得了良好的效果。     

Axially symmetric compositional simulation of formation tester measurements

This paper describes the development, testing, and successful application of a new compositional code for the numerical simulation of oil-based mud invasion and formation tester measurements that involve arbitrary miscibility between oil-based mud and native oil. The simulator assumes axially symmetric variations of petrophysical properties as well as axially symmetric flow-rate sources and boundary conditions. However, there are no restricting assumptions to the degree of miscibility between the fluids involved in the simulations. We solve the time–space evolution of component concentration with a time-marching implicit pressure explicit concentration (IMPEC) scheme. This method of solution considers the complete equations of state and implements flash calculations to describe the thermo-dynamical evolution of the various compositional phases due to space–time variations of pressure and concentration.Simulations described in this paper consider the process of oil-based mud–filtrate invasion into reservoirs containing mixtures of connate water and oil. Subsequently, we simulate formation tester measurements by enforcing fluid withdrawal through the dual-packer section of the tester. Measurements consist of fluid pressure, fractional flow rates, fluid density, and fluid viscosity. Examples of application include homogenous and multi-layer formations as well as a capillary transition zone. Comparison of simulation results against those obtained with a commercial code confirms the efficiency, accuracy, and reliability of our method of solution.Sensitivity analysis indicate that time evolution of fractional flow rates, fluid density, and fluid viscosity measured with the formation tester remain influenced by the petrophysical properties of the formation, volume of mud–filtrate invasion, and by saturation-dependent rock–fluid properties (relative permeability and capillary pressure). The simulations described in this paper provide suitable guidelines for the acquisition of clean samples of in-situ formation fluids in the presence of invasion and heterogeneous conditions of petrophysical and rock–fluid properties.     

钻井液侵入机理特征及影响因素研究

通过钻井液动态侵入的3种过程分析钻井液侵入储层的机理及影响因素，根据达西定律，描述了泥浆侵入的基本特征。实例说明，钻井液动态侵入造成油气层低阻，使测井响应趋于复杂化。     

欠平衡钻井NW无固相充气钻井液的研究

为了有效配合欠平衡钻井开发低压低渗透气藏，最大限度地保护气层．研制了NW无固相充气钻井液。该钻井液的特点是可避免钻井液中的固相颗粒堵塞储层孔隙，抑制性强，减少滤液进入储层，即削弱水锁损害，保护储层岩石孔隙的连通性；小阳离子具有优先吸附形成一层阳离子保护膜的特点，其分子结构中的憎水基团．起到阻止水分子侵入的作用，进而削弱由低压低渗储层天然渗吸效应产生的水锁损害；司时钻井液滤失量小，仅约为10mL，而且钻井液具有强抑制性，可以减小钻井液对油层岩石渗透率的影响，达到保护储层、增加采收率的目的。该钻井液可满足充气工艺要求。此外，该钻井液密度连续可调，能有效降低液柱压力．形成泡沫群体结构，具有群体封堵、疏水屏蔽及特有的流变特性等良好特性，防止低压地层漏失，保护气层；配方简单，维护使用方便，能够很好地满足欠平衡钻井工程的需要。     

考虑交接面附加阻力的复合油藏试井模型

油井在钻井和完井过程中泥浆的侵入造成近井污染导致渗透率下降；相反由于增产措施近井地带渗透性得到改善致使渗透率升高，这样就可以形成径向渗透性甚至流体特性差异的多区复合油藏。为此，通过引入表皮系数的方法，建立了考虑流体在交接面流动存在附加阻力的复合油藏试井模型，并且应用积分变换方法对该模型进行求解，得到了无因次井底压力解及其特征曲线。计算表明流动对井底压力特征存在一定影响，主要表现在过渡区。     

Modeling of fluid filtration and near-wellbore damage along a horizontal well

A method was developed to simulate drilling fluid invasion of a two-phase system (water-based mud in an oil-bearing formation) and to subsequently evaluate the damage along a horizontal well. The proposed model includes fluid invasion, filter cake buildup, and relative permeability components. Filter cake and mud filtration models were developed based on a mass balance equation of cake deposition and erosion and Darcy's equation. A convection–dispersion equation was solved numerically to characterize filtrate invasion. Exposure time, permeability anisotropy, and various formation properties are considered as factors causing non-uniform fluid invasion in horizontal wells. The results of the simulation provide the distribution of fluid filtrate and indicate the maximum invasion depths and the degree of fluid invasion around the wellbore. Coupling these results with relative permeability curves allows the assessment of the distribution of effective permeabilities. The effective permeability distribution and the depth of invasion are the keys to estimating the damage caused by fluid invasion. Damage radius and skin factor predicted by the model are in agreement with published results. Overall, this method provides improvement of fluid filtrate characterization and estimation of damage along a horizontal well.     

页岩气井钻井液井眼强化技术

页岩气地层有着易表面水化剥落掉块、微裂缝发育、脆性好而裂缝易压裂等理化特性,目前,页岩气开发中常用的油基和合成基钻井液体系,起到了很好的防塌防卡效果。但随着开发的深入和地层特性的变化,如钻遇破碎带、裂缝异常发育的地层,采用油基体系仍然会出现大量掉块和严重井塌。为了解决易破碎性地层又垮又漏的复杂情况,需要及时有效地强化已形成的井眼。在钻井液中引入井眼强化剂YH11和BT100,室内实验对加入2种处理剂的钻井液进行了评价,研究出了一套适用于页岩气钻井液的井眼强化技术。该钻井液密度可调范围大,现场可控制在低密度范围1.14~1.50 g·cm-3,该体系抑制能力强,在防漏方面实现了低密度钻进,并且该钻井液体系具有良好的成膜封堵效果,解决了井壁稳定和承压能力低的矛盾,减少了井下复杂情况,确保了井下安全,进一步促进了机械钻速的提高。室内实验和现场应用都表明,井眼强化剂能及时胶结破碎性地带和封堵微裂缝而使井壁变得更致密,大大降低井壁的孔隙度和渗透性,有效阻止液柱压力向井壁孔隙的传递和阻止滤液的深度侵入,减少井壁支撑力的损失,获得防塌和防漏的双重效果。      

地层测试评价仪在渤海油田的应用

电缆地层测试是求取储层流体性质、进行储层评价最为直接的方法之一[1]。地层测试评价仪(FET)是国产新一代地层测试评价仪器,不仅可以精确测量地层压力并根据压力剖面确定地层流体类型和油气水界面,而且在目的层取样时可以抽排污染流体、实时检测地层流体特性,对确定地层流体性质和分析流体成分起到了重要作用,同时它也可以计算地层渗透率,进行储层产能预测。通过在渤海油田的成功应用,简单介绍FET的基本工作原理和主要用途,重点论述其优越性和局限性,以及在渤海油田成功应用的典型实例,这对FET在其它油田的推广应用具有参考意义。     

临兴区块致密砂岩气储层损害机理及钻井液优化

致密砂岩气储层钻井过程中,钻井液入侵将造成严重的储层伤害难题。通过岩心分析技术、岩心流动实验等系统分析了临兴区块致密砂岩气储层主要损害机理,统计并分析了现场钻井液存在的技术难题,并优化出具有良好性能的致密砂岩气储层保护钻井液。研究结果表明,临兴区块致密砂岩气储层岩石具有中-粗砂状结构,胶结致密,孔喉细小,含敏感性黏土矿物,储层潜在严重的水锁伤害与中等偏强的水敏性及应力敏感性损害（临界压力为7.0 MPa）,潜在中等偏弱的速敏性（临界流速为0.75 mL/min）、盐敏性（临界矿化度为7500 mg/L）、碱敏性（临界pH值为10.0）及土酸敏感性损害;临兴区块主要存在储层损害、钻井液漏失、井眼垮塌、摩阻扭矩大与井眼清洁等钻井液技术难题。优化出的钻井液封堵性能良好,滤液表面张力低（23.3 mN·m-1）,能减少固相侵入,削弱水锁效应,提高岩石渗透率恢复值至91.3%,具有良好的储层保护性能。现场应用结果表明,该储层保护钻井液完全满足复杂井段或水平井段钻进的钻井液技术要求。      

随钻防漏堵漏技术的研究与应用进展

井漏是钻井作业中长期存在并且尚未得到有效解决的技术难题。文章介绍了目前国内外随钻防漏堵漏技术的研究与应用现状及常规处理井漏的方法,针对渗透性漏失及裂缝性漏失地层特点,首次提出了基于物理法随钻防漏堵漏技术。该技术通过特殊的井下侧向水力工具,利用旋转射流的水力能量作用在井壁上形成渗透率接近于零的滤饼,即所谓“人造井壁”。井壁不仅渗透率极低,而且具有很高的强度和稳定性,能够承受一定的压差作用。在井眼内可以有效的阻止钻井液漏入地层,从而达到随钻防漏堵漏目的。     

钻井液固相和滤液侵入储层深度的预测模型

对于中高渗透砂岩,导致储层损害的主要因素是钻井液固相和滤液的侵入。为了确定钻井液固相和滤液侵入深度,根据质量守恒方程和径向摩阻公式,在考虑内泥饼的情况下,建立了钻井液固相和滤液动态侵入储层的深度模型。并将室内API滤失实验和动态岩心污染实验的结果应用到该模型中。预测结果表明,随着岩心渗透率的增加,钻井液固相侵入深度也逐渐增加,利用理想充填暂堵技术能减小钻井液固相的侵入深度。影响钻井液滤液侵入深度的主要因素有压差、滤液黏度、外泥饼渗透率、外泥饼厚度、内泥饼渗透率以及储层渗透率变化。     

高性能测试完井液的评价与应用

测试完井液性能稳定是高温超深气井安全测试的关键因素。库1井直井段在完井测试期间, 2次测试井下封隔器均被埋死,造成非常严重的井下事故。根据库1井侧钻完井试油及井身特殊要求,通过室内研究,测试完井液采用无固相甲酸盐完井液+甲酸盐钻井液稠垫液+高密度聚磺钻井液体系的高性能复合型完井测试液,该体系抗温达167℃以上、悬浮能力强、对油层无污染。使用高密度的完井液现场测试25d静止后, RD安全阀开启和解封均很顺利,有效解决了复杂深井高温、高压及长时间测试环境下的井眼稳定性和长时间静止下的测试稳定性,为以后高温高压井的完井安全测试提供了一个范例。     

基于随钻和电缆测井电阻率的钻井液侵入校正方法——以阿曼DLL油田高孔低渗碳酸盐岩油藏为例

基于阿曼DLL油田高孔低渗碳酸盐岩油藏的随钻测井(LWD)和电缆测井资料,综合研究了从钻开储集层到完井测井时间内钻井液侵入对高孔低渗碳酸盐岩储集层电阻率的影响。结果表明,钻井液侵入对储集层电阻率的影响程度与储集层的孔隙度、钻井液柱与地层压力差、含水饱和度、钻井液矿化度以及侵入时间相关,其与孔隙度增加呈指数增大关系,与钻井液柱和地层压力差呈对数增大关系,与含水饱和度以及侵入时间呈幂指数增大关系。根据DLL油田LWD测井资料和MDT压力资料,得出储集层电阻率受钻井液侵入影响的校正方程。由校正后电阻率计算的含油饱和度比电阻率校正前计算的含油饱和度增加了6.3%~20.0%,平均增加10.2%。图9表4参16     

海上低渗储层自降解暂堵液研究与应用

针对南海西部涠洲RRX油田低渗储层修井漏失造成水敏、水锁伤害的问题,通过单因素实验分析及药剂协同复配,研发了一套自降解暂堵液体系。室内实验结果表明,该体系流变性能优异,滤失量低,无需替入破胶液,6 d自降解率超过50%;气-液表面张力低于20 mN/m,防膨率超过95%,岩心模拟实验渗透率平均恢复值为90%。在现场应用过程中,零漏失,零污染,可解决低渗储层修井过程中的储层保护难题。      

KCl-有机盐聚合物钻井液在川西双鱼石区块的应用

川西地区双鱼石区块目的层埋藏深,完钻井深在7 000 m以深,上部φ444.5 mm、φ333.4 mm井眼主要采用“空气钻”提速,空气钻井转钻井液如何保证井壁稳定至关重要,在“高效PDC+螺杆”提速方式下优质的钻井液性能也尤其重要。为此,KCl-有机盐聚合物钻井液在KCl、有机盐的共同作用下抑制能力强,能够抑制岩石组分水化分散、膨胀,封堵防塌剂可以快速形成致密泥饼,减少滤液侵入井壁地层,防止“空气钻”后干燥井壁“吸水”引起的井塌;抑制钻屑水化分散,钻井液流变性能稳定、波动小、易调控、现场维护处理简单;钻井液强抑制性、低黏度和切力可提高钻头水马力,减少钻屑在钻头上的吸附,防止钻头泥包现象,减少钻井液中微米、亚微米粒子,有助于提高机械钻速。双探8井等现场应用表明,KCl-有机盐聚合物钻井液确保了“空气钻”井段井壁稳定,顺利钻过沙溪庙组下部（沙一段）、凉高山组、自流井组及须家河组易垮塌地层,井眼畅通、井壁稳定、井径规则、电测顺利、井下安全、钻速较高,满足工程、地质录井需要。