The Mechanism of Radial Separation of Cement Sheath and Casing during Temperature Cycling

1. Introduction Generally, wellbores are in good condition at the early stage of service because such disturbance as formation creep and corrosion failure of the casing has not fully developed. However many casing failures in cyclic steam injection wells indicate that the failures occur mainly in the first three cycles of steam injection, and the most common phenomena are casing collapse and steam leakage outside the casing. Willhite and Dietrich (1967) analyzed the maximum temperatures that t…     

Calculation analysis of sustained casing pressure in gas wells

Sustained casing pressure (SCP) in gas wells brings a serious threat to worker safety and environmental protection. According to geological conditions, wellbore structure and cement data of gas wells in the Sichuan-Chongqing region, China, the position, time, environmental condition and the value of SCP have been analyzed. On this basis, the shape of the pressure bleed-down plot and pressure buildup plot were diagnosed and the mechanism of SCP has been clarified. Based on generalized annular Darcy percolation theory and gas-liquid two-phase fluid dynamics theory, a coupled mathematical model of gas migration in a cemented annulus with a mud column above the cement has been developed. The volume of gas migrated in the annulus and the value of SCP changing with time in a gas well in Sichuan have been calculated by this model. Calculation results coincided well with the actual field data, which provide some reference for the following security evaluation and solution measures of SCP.     

Application of Horizontal Well Technology to Liaohe Oilfield

Horizontal well technology has become one of the main technologies enabling Liaohe Oilfield to realize stable development. By the end of 2006, 296 horizontal wells of various kinds had been completed in Liaohe Oil Field, 273 wells had been put into production, Among uhich 237 were horizontal wells （see Table 1）. So far, the one- million-ton production capacity for horizontal wells has already been established in Liaohe Oilfield, which ranks the third following Tarim and Shengli Oilfields. With its annual completing of 150 horizontal wells,     

Multistring analysis of wellhead movement and uncemented casing strength in offshore oil and gas wells

This paper presents a theoretical method and a finite element method to describe wellhead movement and uncemented casing strength in offshore oil and gas wells.Parameters considered in the theoretical method include operating load during drilling and completion and the temperature field,pressure field and the end effect of pressure during gas production.The finite element method for multistring analysis is developed to simulate random contact between casings.The relevant finite element analysis scheme is also presented according to the actual procedures of drilling,completion and gas production.Finally,field cases are presented and analyzed using the proposed methods.These are four offshore wells in the South China Sea.The calculated wellhead growths during gas production are compared with measured values.The results show that the wellhead subsides during drilling and completion and grows up during gas production.The theoretical and finite element solutions for wellhead growth are in good agreement with measured values and the deviations of calculation are within 10％.The maximum von Mises stress on the uncemented intermediate casing occurs during the running of the oil tube.The maximum von Mises stress on the uncemented production casing,calculated with the theoretical method occurs at removing the blow-out-preventer （BOP） while that calculated with the finite element method occurs at gas production.Finite element solutions for von Mises stress are recommended and the uncemented casings of four wells satisfy strength requirements.     

Analysis of Drilling Troubles in Kazhdumi Formation of Yadavaran Oilfield,Iran

Drilling crews of Sinopec have encountered a series of troubles when drilling a formation called kazhdumi of Yadavaran oilfield, Iran in the last few years. The formation is buried in the depth from 3300 m to 3500 m, mainly including limestone, muddy limestone and some bituminous shale. Many microfissures exist in the formation and the equivalent density of formation pore pressure ranged from 1.19g/cm3 to 1.59g/cm3. Asphalt or heavy oil kicks occurred in drilling three wells in one and a half years, which contaminated the drilling fluid and made well killing difficult due to the kicks and lost circulation in open hole. Gas and hydrogen sulfide(the concentration is up to 40000ppm) were present in the wells, and finally two wells were completely abandoned and one partially lost, which frustrated the drilling engineering seriously. By analyzing the data of the drilled wells, the paper summarized the causes of the troubles, and put forward suggestions and conclusions that can serve as reference and guideline for drilling well in this area in the future.     

Numerical Simulation Research on Energy Supplement of Low Permeability Reservoirs with Fractured Horizontal Wells

The fractured horizontal wells are widely used in many large oil fields to enhance oil recovery.Currently most of fractured horizontal wells were developed in elastic recovery.It is urgently needed to supply formation energy because of the fast production and pressure decline.In this paper,a five-spot model of horizontal wells was built based on the Jilin Oilfield geological data from the horizontal wells demonstration area.Compositional simulation were applied to study on the effectiveness of four development methods for three types of low permeability reservoirs with fractured horizontal wells and the impact of the distribution of the fracture was analyzed.Reasonable suggestions were proposed for three types of low permeability reservoirs from two aspects,development mode and fracturing design.This paper will provide some guidance for fractured horizontal well development.     

Calculating single layer production contribution of heavy oil commingled wells by analysis of aromatic parameters in whole-oil GC-MS

Traditional fluid production profile logging is not usually suitable for heavy-viscous crude oil wells.Biodegradation of heavy oil can lead to the loss of n-alkanes,and the use of chromatogram fingerprint techniques in studying the production contributions of single layers in heavy oil commingled wells has limitations.However,aromatic compounds are relatively well preserved.We took the heavy oil commingled wells of small layers NG55 and NG61 in the ninth area of the Gudong oil field as examples.Based on the principle of chromatography,the whole-oil GC-MS was used,and the aromatic parameters which have a strongly linear relationship with the ratio of mixed two end member oils were verified and selected in laboratory.Studies showed that the ratio of （1,4,6-＋ 2,3,6-trimethylnaphthalene） to 1,2,5-trimethylnaphthalene has a strongly linear relationship with the ratio of the mixed two end member oils （R2=0.992）.The oil contributions from single layers NG55 and NG61 in six commingled heavy oil wells were calculated using established charts and this relationship.The calculated results are consistent with the results of long period dynamic monitoring and logging interpretation in the study area and can provide a scientific basis for monitoring production performance and hierarchical management of reservoirs.The study provides a new geochemical method for calculation of the contributions of single layers in heavy oil commingled wells when conventional fluid production profile logging is not suitable.     

Reservoir characterization of the Odovician oil and gas pools in the Tahe Oilfield, Tarim Basin, Northwest China

About 88. 1% of the proven reserves in the Tahe Oilfield in the Tarim Basin of Northwest China are trapped in Ordovician carbonate reservoirs. These reservoirs are formed by unconnected and interconnected networks of karstic porosity forming a heterogeneous and complex reservoir system. Oil, water and gas characteristics vary significantly in different portions of the Ordovician reservoir. There is no uniform oil/water contact in the field, adding to its complexity.An acid fracture treatment is beneficial in 76% of the wells, stimulating nonproductive wells and enhancing production in other wells by fracturing into unconnected reservoirs and enhancing flow pathways with acid. Acid fracture treatments should be a standard procedure for developing this and similar oil fields.     

Terminal Fan and Its Impact on Reservoir Quality of 2+3 Reservoir of Upper Second Member of Shahejie Formation,West Zone of Dongpu Depressio

正Introduction The 2+3 reservoir are two of the important sets of oil and gas reservoir intervals in Pucheng Oilfield.The latest resources assessment result indicated that oil-gas resources is plentiful where total petroleum resources is1298.24×104 tons and that of nature gas is 17.31×108cubic meters.Since they were put into exploration and development,2+3 reservoir in south district of Pucheng Oilfield had been drilled in 109 wells.67 wells have obtained the oil and gas flows.However,exploration of the 2+3 reservoir is complicated and stable oil production is difficult to be maintained in some wells in the discovered oil fields.The most essential reason for this,except for the complex geological structure     

Sequence stratigraphy of the petroliferous Dariyan Formation (Aptian) in Qeshm Island and offshore (southern Iran)

After sea level rises during the Early Cretaceous,upper parts of the Khami Group sediments(Fahliyan.Gadvan.and Dariyan Formations) deposited over Jurassic sediments.The Lower Cretaceous(Aptian) Dariyan Formation(equivalent to the Shu'aiba Formation and Hawar Member of the Arabian Plate) carbonates,which have hydrocarbon reservoir potential,form the uppermost portion of the Khami Group that unconformably overlays the Gadvan Formation and was unconformably covered by the Kazhdumi Formation and Burgan sandstones.Detailed paleontological.sedimentological.and well log analysis were performed on seven wells from Qeshm Island and offshore in order to analyze the sequence stratigraphy of this interval and correlate with other studies of the Dariyan Formation in this region.According to this study,the Dariyan Formation contains 14 carbonate lithofacies,which deposited on a ramp system that deepened in both directions(NE—wells 5,6 and SW—wells 1,2).Sequence stratigraphy led to recognition of 5 Aptian third-order sequences toward the Bab Basin(SW—well 1) and 4 Aptian third-order sequences toward Qeshm Island(NE—wells 5and 6) so these areas show higher gamma on the gamma ray logs and probably have higher source rock potential.Other wells(wells 2-4 and 7) mainly deposited in shallower ramp systems and contain 3 Aptian third-order sequences.On the other hand,rudstone and boundslone lilhofacies of studied wells have higher reservoir potential and were deposited during Apt 3 and Apt 4 sequences of the Arabian Plate.The Dariyan Formation in Qeshm Island(well 6) and adjacent well(well 5) was deposited in an intrashelf basin that should be classified as a new intrashelf basin in future Aptian paleogeographic maps.We interpret that salt-related differential subsidence,crustal warping.and reactivation of basement faults of the Arabian Plate boundary were responsible for the creation of the intrashelf basin in the Qeshm area.     

高含水后期套损井综合治理配套技术

大庆油田杏北开发区自1972年出现套损以来至2004年底已发现套损井2473口,套损形势十分严峻。套管损坏不仅造成油田的注采失衡,而且对套损井采取增产增注措施都会产生不同程度的限制,降低了套损井区剩余油的挖掘潜力。近几年通过不断加强套损井治理工作,套损井区的注采关系逐步得到改善。在套损井大修方面,研究应用了通径70mm以上套损井整形扩径技术,开展了段铣扩径技术和膨胀管加固技术攻关,不仅提高了套损井大修的修复率,而且提高了修井质量;在套损井利用方面,研究并应用了套损井分层注水工艺技术和细分堵水技术,开展了套损井分层压裂改造技术攻关．为通径100mm以上套损井细分注水、增产增注等措施提供了技术保证,充分发挥了套损井在油田高含水后期的生产潜力。     

小套管二次固井工艺技术

随着油田开发时间的延长，各种因素导致的油水井套管损坏日益严重，直接影响了油田的开发和经济效益。利用小套管二次固井工艺，在因套管损坏而报废的油水井上，采取封堵、打通道措施，全井或部分悬挂小套管后，采取延时固井法封固环空，二次射孔投产，达到恢复油水井生产的目的。在平方王、林凡家2个油田实施了12井(次)，成功地恢复了10口注水井，为套管损坏井的治理探索出了一条新途径，成为老油田挖潜增效的一个重要手段。     

含水泥环的变形套管修复过程实验

油气田现场经常凭经验确定旋压整形器修复变形套管所需的修复力和扭矩,而不合理的整形力或扭矩容易造成变形套管和周围水泥环的二次损伤及卡钻事故。为此,在YAW-200压力试验机上分别制作了无水泥环(水泥环完全损伤)、水泥环部分损伤和水泥环未损伤等3种类型的P110SS变形套管,并采用?126 mm和?133 mm的2种旋压整形器对3种变形套管进行整形测试,得到了变形套管整形所需的整形力和修复扭矩、变形套管回弹量的测试数据。实验结果表明:(1)修复过程中整形力与扭矩整形时间的关系密切——弹性变形阶段,随修复时间增加环向应变呈线性增加,整形力和扭矩早期呈缓慢增加后期保持不变,塑性变形阶段套管开始屈服,随修复时间增加环向应变呈非线性增加,整形力和扭矩急剧降低,直到整形工具通过变形套管,直到整形力和扭矩降低到最低为止;(2)修复后的回弹量不可避免且较大(2.90~3.04 mm),表明水泥环的损伤程度对变形套管的修复具有较大影响;(3)水泥环未损伤的变形套管修复所需机械载荷大于水泥环部分损伤变形套管所需机械载荷,带水泥环变形套管修复所需机械载荷大于无水泥环变形套管所需的机械载荷。     

液压扩径整形技术在套管变形井杜813-42-63中的应用

针对常规套管整形技术在套管变形井应用中存在的技术缺欠,研究并应用了液压扩径整形技术.该技术利用小修设备及高效液压整形工具对油水井套管变形部位进行液压整形,达到缩短修井周期、提高修井效率、最大限度恢复套管通径以及提高套管变形井产能的目的,为套管变形井的修复提供了强有力的技术支持,并在曙光油田杜813-42-63井得到成功应用.现场应用结果表明,该技术施工简便,使用安全,整形效果显著,在套损井治理工作中具有较好的推广应用前景.     

套损井压裂管柱的研制

针对大庆油田套损井压裂情况,强调套损井压裂的必要性。套损井压裂技术的关键内容是套损井压裂管柱,其技术难点是过套损点封隔器胶筒承压低、肩部凸出和残余变形过大,以及喷砂器通径过小等。介绍了过套损点压裂管柱的结构原理及其主要工具,侧重介绍解决的技术难题,说明套损井压裂管柱的实用性。     

可膨胀管修复套损井技术研究与应用

随着油田开发进入中、后期,套损井越来越多。目前采用的几种常规套管补贴技术已无法满足长井段修复的要求,针对施工工艺复杂、工序多、修复后井眼内径变化较大的问题,提出膨胀管套管补贴技术。介绍了膨胀管补贴原理及在W11-261井上进行套管补贴的应用情况。应用结果证明,该膨胀管补贴技术克服了以往套管补贴技术存在的不足,具有施工工艺简单、套管修复后能产生永久性密封且井眼尺寸变化小等特点,具有广阔的推广应用前景。     

大庆地区深部取套修井技术的应用

大庆油田已进入开发的中后期,随着投产时间的延长和作业次数的增加,井况变差,作业井和待大修井逐年增多,尤其由于高压注水、地质和工程技术等因素造成的套损井逐渐增多。目前,大庆约有6000多口套管损坏井,占投产油水井总数的17.22%,对油田可持续发展影响巨大。根据深部取套修井技术在大庆地区的应用情况,介绍了深部取套修井工艺、深部取换套方法、修井施工中出现的问题及解决办法,对发展深部取套工艺提出几点建议,为国内各油田深部取套修井提供参考。     

采油井侧斜修井地质设计方法

由于侧斜修井技术在套损井上的应用，使因深部油层井段套损严重而难以修复的套损井恢复了生产，不但改善了套损井区的注采关系，还降低了投入成本。为此，在目前侧斜井工艺技术发展的基础上，根据侧斜修井技术原理、工艺特点和适用范围，以充分挖掘单砂层剩余油潜力为目的，从井网、井区、井点等不同角度研究了采油井侧斜修井及侧斜方位的合理确定方法，指出侧斜方位的确定应在确保侧斜井与原井或周围邻井不相碰的同时力求较高的目的层钻遇率，应满足挖掘剩余油潜力的方位钻井设计要求。按该方法设计投产16口油井，目的层钻遇率达到100％，为有效实施套损采油井的侧斜修井措施提供了依据。     

用磁记忆检测技术预测井下套管故障

复杂断块油气田的套损井，有近70％是由于地质因素和工程因素造成的。这些因素使套管受到非均匀载荷的作用产生塑性变形。套管承受力而失去平衡，该失衡点为应力集中区，易造成套管弯曲、变形或错断。研究发现．铁磁部件在应力集中部位将发生自然磁化，这种磁化具有不可逆性。这一现象称为磁记忆现象。利用铁磁材料的磁记忆性，研制井下在役套管检测系统。这一检测系统可以快速、准确地检测在役套管的应力集中区所产生的磁记忆信号，从而可快速、准确地判断套管的应力集中区状况。     

纯化油田高压注水井套管损坏原因及防治措施

针对纯化油田实施高压注水以来,注水井套管损伤日益增多的现象,通过现场调研,找出该油田套管损害的主要原因,并从物理和化学两方面提出了防治措施,即在管柱上加设套管保护封隔器和环空保护液,对已发生套损的井应用套管补贴、换套管、注水泥等方法进行治理,矿场已取得较好效果。