The AVO Effect of Formation Pressure on Time-Lapse Seismic Monitoring in Marine Carbon Dioxide Storage

The phase change of CO_(2) has a significant bearing on the siting, injection, and monitoring of storage. The phase state of CO_(2) is closely related to pressure. In the process of seismic exploration, the information of formation pressure can be response in the seismic data. Therefore, it is possible to monitor the formation pressure using time-lapse seismic method. Apart from formation pressure, the information of porosity and CO_(2) saturation can be reflected in the seismic data. Here, based on the actual situation of the work area, a rockphysical model is proposed to address the feasibility of time-lapse seismic monitoring during CO_(2) storage in the anisotropic formation. The model takes into account the formation pressure, variety minerals composition, fracture, fluid inhomogeneous distribution, and anisotropy caused by horizontal layering of rock layers(or oriented alignment of minerals). From the proposed rockphysical model and the well-logging, cores and geological data at the target layer, the variation of P-wave and S-wave velocity with formation pressure after CO_(2) injection is calculated. And so are the effects of porosity and CO_(2) saturation. Finally, from anisotropic exact reflection coefficient equation, the reflection coefficients under different formation pressures are calculated. It is proved that the reflection coefficient varies with pressure. Compared with CO_(2) saturation, the pressure has a greater effect on the reflection coefficient. Through the convolution model, the seismic record is calculated. The seismic record shows the difference with different formation pressure. At present, in the marine CO_(2) sequestration monitoring domain, there is no study involving the effect of formation pressure changes on seismic records in seafloor anisotropic formation. This study can provide a basis for the inversion of reservoir parameters in anisotropic seafloor CO_(2) reservoirs.

Numerical analysis of the effects of downhole dynamic conditions on formation testing while drilling

Formation testing while drilling is an innovative technique that is replacing conventional pressure testing in which the fluid sampling is conducted in a relatively short time following the drilling. At this time, mud invasion has just started, mudcake has not formed entirely and the formation pressure is not stable. Therefore, it is important to study the influence of the downhole dynamic environment on pressure testing and fluid sampling. This paper applies an oil-water two phase finite element model to study the influence of mudcake quality and mud filtrate invasion on supercharge pressure, pretest and sampling in the reservoirs of different permeability. However, the study is only for the cases with water based mud in the wellbore. The results illustrate that the mudcake quality has a significant influence on the supercharge pressure and fluid sampling, while the level of mud filtrate invasion has a strong impact on pressure testing and sampling. In addition, in-situ formation pressure testing is more difficult in low permeability reservoirs as the mud filtrate invasion is deeper and therefore degrades the quality of fluid sampling. Finally, a field example from an oil field on the Alaskan North Slope is presented to validate the numerical studies of the effects of downhole dynamic conditions on formation testing while drilling.

An optimization method of fidelity parameters of formation fluid sampling cylinder while drilling

A design idea of fidelity sampling cylinder while drilling based on surface nitrogen precharging and supplemented by downhole pressurization was proposed, and the working mode and optimization method of sampling parameters were discussed. The nitrogen chamber in the sampling cylinder functions as an energy storage air cushion, which can supplement the pressure loss caused by temperature change in the sampling process to some extent. The downhole pressurization is to press the sample into the sample chamber as soon as possible, and further increase the pressure of sample to make up for the pressure that the nitrogen chamber cannot provide. Through the analysis of working mode of the sampling fidelity cylinder, the non-ideal gas state equation was used to deduce and calculate the optimal values of fidelity parameters such as pre-charged nitrogen pressure, downhole pressurization amount and sampling volume according to whether the bubble point pressure of the sampling fluid was known and on-site emergency sampling situation. Besides, the influences of ground temperature on fidelity parameters were analyzed, and corresponding correction methods were put forward. The research shows that the fidelity sampling cylinder while drilling can effectively improve the fidelity of the sample. When the formation fluid sample reaches the surface, it can basically ensure that the sample does not change in physical phase state and keeps the same chemical components in the underground formation.

Pre-Drilling Prediction Techniques on the High-Temperature High-Pressure Hydrocarbon Reservoirs Offshore Hainan Island,China

Decreasing the risks and geohazards associated with drilling engineering in high-temperature high-pressure(HTHP) geologic settings begins with the implementation of pre-drilling prediction techniques(PPTs). To improve the accuracy of geopressure prediction in HTHP hydrocarbon reservoirs offshore Hainan Island, we made a comprehensive summary of current PPTs to identify existing problems and challenges by analyzing the global distribution of HTHP hydrocarbon reservoirs, the research status of PPTs, and the geologic setting and its HTHP formation mechanism. Our research results indicate that the HTHP formation mechanism in the study area is caused by multiple factors, including rapid loading, diapir intrusions, hydrocarbon generation, and the thermal expansion of pore fluids. Due to this multi-factor interaction, a cloud of HTHP hydrocarbon reservoirs has developed in the Ying-Qiong Basin, but only traditional PPTs have been implemented, based on the assumption of conditions that do not conform to the actual geologic environment, e.g., Bellotti's law and Eaton's law. In this paper, we focus on these issues, identify some challenges and solutions, and call for further PPT research to address the drawbacks of previous works and meet the challenges associated with the deepwater technology gap. In this way, we hope to contribute to the improved accuracy of geopressure prediction prior to drilling and provide support for future HTHP drilling offshore Hainan Island.

Managed Pressure Drilling Technology:A Research on the Formation Adaptability

Existing pressure drilling technologies are based on different principles and display distinct characteristics in terms of control pressure and degree of formation adaptability.In the present study,the constant-bottomhole-pressure(CBHP)and controlled-mud-level(CML)dual gradient drilling methods are considered.Models for the equivalent circulating density(ECD)are introduced for both drilling methods,taking into account the control pressure parameters(wellhead back pressure,displacement,mud level,etc.)and the relationship between the equivalent circulating density curve in the wellbore and two different types of pressure profiles in deep-water areas.The findings suggest that the main pressure control parameter for CBHP drilling is the wellhead back pressure,while for CML dual gradient drilling,it is the mud level.Two examples are considered(wells S1 and B2).For S1,CML dual gradient drilling only needs to adjust the ECD curve once to drill down to the target layer without risk.By comparison,CBHP drilling requires multiple adjustments to reach the target well depth avoiding a kick risk.In well B2,the CBHP method can drill down to the desired zone or even deeper after a single adjustment of the ECD curve.In contrast,CML dual-gradient drilling requires multiple adjustments to reach the target well depth(otherwise there is a risk of lost circulation).Therefore,CML dual-gradient drilling should be considered as a better choice for well S1,while CBHP drilling is more suitable for well B2.

Modern Shale Gas Horizontal Drilling： Review of Best Practices for Exploration Phase Planning and Execution

The challenging characteristics of shale formations often require horizontal drilling to economically develop their potential. While every shale gas play is unique, there are several best practices for the proper planning and execution of a horizontal well. In planning a horizontal well, the optimal method and technology for building inclination and extending the lateral section must be determined. Properly specified logging-while-drilling tools are essential to keep the wellbore within the target formation. Planning must also focus on casing design. Doing so will help ensure stability and enable reliable and productive completions. Shales pose a challenge for these elements of well planning due to their thin strata and potentially low mechanical competence when foreign fluids are introduced. Once a plan is developed, executing it is even more important to prove a viable exploration program. Fast, efficient drilling with wellbore control and minimal torque and drag should be the priority. This may be achieved by focusing on fluid hydraulics and rheology and bottom hole assembly. Managed pressure drilling (MPD) will help fast drilling, well control and stability. If MPD can be combined with new generation rotary steerable systems that allow the drill string to maintain rotation, impressive efficiencies are possible. Modern drilling parameter analysis represents the newest opportunity for executing shale gas horizontal wells. A method for ROP analysis to improve operational parameters and equipment selection is also proposed.

Wellsite Evaluation Method of Undercompacted Formation

Staring from the view point of practical application, based on large amount of pressure well - logging data home and abroad, the author demonstrated how to distinguish overpressure Formation using wellsite data through selected methods such as drilling parameters, rock cutting analysis, drilling fluid parameters, and electric welline logs.

Formation Pressure Evaluation Method for Single Well

The paper deals with the methods of formation pressure evaluation for a single well by using the very common accepted parameters, such as drilling exponent , and flowline temperature , etc. which is part of compiling the end well report.

Key technologies and practice for gas field storage facility construction of complex geological conditions in China

In view of complex geological characteristics and alternating loading conditions associated with cyclic large amount of gas injection and withdrawal in underground gas storage(UGS) of China, a series of key gas storage construction technologies were established, mainly including UGS site selection and evaluation, key index design, well drilling and completion, surface engineering and operational risk warning and assessment, etc. The effect of field application was discussed and summarized. Firstly, trap dynamic sealing capacity evaluation technology for conversion of UGS from the fault depleted or partially depleted gas reservoirs. A key index design method mainly based on the effective gas storage capacity design for water flooded heterogeneous gas reservoirs was proposed. To effectively guide the engineering construction of UGS, the safe well drilling, high quality cementing and high pressure and large flow surface injection and production engineering optimization suitable for long-term alternate loading condition and ultra-deep and ultra-low temperature formation were developed. The core surface equipment like high pressure gas injection compressor can be manufactured by our own. Last, the full-system operational risk warning and assessment technology for UGS was set up. The above 5 key technologies have been utilized in site selection, development scheme design, engineering construction and annual operations of 6 UGS groups, e.g. the Hutubi UGS in Xinjiang. To date, designed main indexes are highly consistent with actural performance, the 6 UGS groups have the load capacity of over 7.5 billion cubic meters of working gas volume and all the storage facilities have been running efficiently and safely.

New model for standpipe pressure prediction while drilling using Group Method of Data Handling

The continuous evaluation of the measured Stand Pipe Pressure(SPP)against a modeled SPP value in real-time involves the automatic detection of undesirable drilling events such as drill string washouts and mud pump failures.Numerous theoretical and experimental studies have been established to calculate the friction pressure losses using different rheological models and based on an extension of pipe flow correlations to an annular geometry.However,it would not be feasible to employ these models for real-time applications since they are limited to some conditions and intervals of application and require input parameters that might not be available in real-time on each rig.In this study,The Group Method of Data Handling(GMDH)is applied to develop a trustworthy model that can predict the SPP in real-time as a function of mud flow,well depth,RPM and the Fan VG viscometer reading at 600 and 300 rpm.In order to accomplish the modeling task,3351 data points were collected from two wells from Algerian fields.Graphical and statistical assessment criteria disclosed that the model predictions are in excellent agreement with the experimental data with a coefficient of determination of 0.9666 and an average percent relative error less than 2.401%.Furthermore,another dataset(1594 data points)from well-3 was employed to validate the developed correlation for SPP.The obtained results confirmed that the proposed GMDH-SPP model can be applied in real-time to estimate the SPP with high accuracy.Besides,it was found that the proposed GMDH correlation follows the physically expected trends with respect to the employed input parameters.Lastly,the findings of this study can help for the early detection of downhole problems such as drill string washout,pump failure,and bit balling.

各向异性地层中随钻地层测试压力响应数值模拟

在随钻地层测试器测试过程中,钻井液动态侵入和地层各向异性会导致不同的压力响应特征,并直接影响地层压力测试结果的解释精度。为此,基于各向异性多孔介质渗流理论,建立了钻井液侵入条件下横观各向同性地层随钻地层测试压力响应数学模型,采用有限元方法对模型进行求解,通过与经典解析解对比进行了模型验证,并分析了渗透率各向异性、地层产状、抽吸间歇时间、抽吸探头半径对随钻地层测试压力响应的影响规律。结果表明:在抽吸前阶段,地层各向异性和地层产状对钻井液侵入导致的井周增压影响较大;在压力恢复阶段,由于井周地层增压作用的影响,测试压力响应初始值会高于原始地层压力,且压力呈先升高后降低的演化趋势;渗透率各向异性程度越小、地层倾角和倾向越小,抽吸压降阶段的压力响应初始值越大、压降值越大、压力恢复速率越低;抽吸间隔时间和抽吸探头半径对压力响应也有一定影响,抽吸间隔时间越小,测试初始压力越大,探头半径越大,压力恢复速率越快。揭示了渗透率各向异性对随钻地层测试压力响应的影响规律,研究结果可为随钻地层测试结果解释和地层参数反演提供理论依据。

差压步进钻头提高破岩速度原理及现场试验

井底岩石承受较大的原地应力作用,且随着井深增加原地应力呈增大趋势。原地应力的存在增加了岩石的压实程度,导致岩石坚硬、可钻性差、研磨性强等问题,成为破岩工具切削效率低、使用寿命短和钻井速度慢的最主要原因之一。针对此背景,提出释放井底部分原地应力弱化地层抗钻特性提高破岩速度的理念,研发一种可释放井底部分原地应力弱化地层抗钻特性且能够集中钻压强化攻击能力的差压步进钻头,该钻头充分利用钻井过程中的井底钻压波动,实现扩眼钻头与领眼钻头钻压动态分配及钻进过程交替进行的目标,通过弱化地层、强化攻击及转化振动三重效果提高破岩速度。为验证差压步进钻头的应力释放效应,建立三维流固耦合的阶梯井底应力场模型,并在江苏油区某区块砾石层井段开展3口井的实钻试验。结果表明:阶梯井底能够使阶梯处岩石更易破碎;小直径领眼钻头应力释放效果较好;随着地层深度的增加,差压步进钻头应力释放效果更加显著,应力释放比约为60.2%;差压步进钻头提速效果显著,砾石层钻速较牙轮钻头提升可达161.89%,最高提速318.11%。

C/S架构的新型控压钻井计算模拟与控制软件

由于油气勘探开发中井下高温高压和复杂压力系统导致钻井过程面临的风险日益增大,因此迫切需要一款集工况数据模拟计算与井下复杂监测控制相结合的软件系统,助力实现安全高效钻井。为此,运用先进的控压钻井技术,实时监测井底压力、钻井液循环出入口流量差和密度等关键参数的变化,分析井下工况的变化,实现在钻井过程中井筒压力的快速、准确控制,有效降低钻井过程的安全隐患,及早发现并快速控制井下复杂情况,为形成预测、预控和快速处置的井筒安全提供支持。设计的控压钻井计算模拟与控制软件旨在从录井、PWD(Pressure While Drilling)、MWD(Measure While Drilling)、控压等设备获取钻井相关信息,建立水力学模型计算井筒压力、流量等参数。通过采用客户端/服务端网络架构,实现了多个客户端同时连接一个服务端,达到客户端数据同步的效果,经现场验证既可满足单机使用,又可方便网络连接,实现后方集中分析处理与远程操控。结果表明,该软件能准确地模拟计算各种钻井参数,保证安全高效钻井。实现了控压钻井由现场工程师处理模式转变为后方基于数据平台的模式,奠定了1个平台对N个现场控压钻井装备之间的互联互通基础,有力推动了控压钻井的智能化发展。

钻爆法施工隧道风流场及CO运移规律研究

为探究压入式通风下隧道钻爆法施工产生的CO运移情况,以卡拉水电站绕坝交通洞工程为依托,根据计算流体力学理论,通过Fluent软件建立隧道CO组分运输模型,并使用现场监测数据对模型准确性进行验证。结果表明,压入式通风产生远离风筒一侧的回流区提供了CO运移的主要动力,风流卷吸纠缠的涡流区对CO运移具有较强的阻碍作用;对比直立呼吸带高度1.5 m和坐立呼吸带高度0.3 m两者的CO浓度变化情况,发现高度越低,CO浓度越低,CO浓度降低速率越慢。可见建立的CO运移模型能够准确地反映CO扩散运移规律,可以为实际工程的通风设计提供参考。

裂缝性地层油基钻井液用堵漏材料的研究进展

油基钻井液漏失后不仅经济损失较大,而且影响钻采进度,甚至会对环境造成一定污染。油基钻井液相较于水基钻井液更易发生漏失,现场应用中因缺乏专用于油基钻井液的堵漏材料常造成封堵效果不佳。针对裂缝性地层因承压能力不足易发生钻井液漏失的问题,从地层承压能力强化机理出发,阐述了地层承压能力对于控制钻井液漏失的重要性以及堵漏材料在提高承压能力中所起到的关键作用。对油基钻井液用堵漏材料包括桥接、吸油膨胀聚合物、聚合物凝胶、复合、树脂基以及无机胶凝等堵漏材料的特点、堵漏机理以及适用条件等方面进行了综述,并对不同类型堵漏材料的优缺点进行了一定总结。指出了现有地层承压能力强化机理与堵漏材料所存在的不足,并对其未来的研究方向进行了展望。

精细控压钻井技术及装备研究进展

精细控压钻井技术可使复杂地层普遍存在的井涌、漏失、坍塌、卡钻等井下复杂,特别是“溢漏同存”的窄密度窗口钻井难题得到有效解决,并提高复杂地层钻井成功率,实现安全、高效、快速钻井作业。实践证明,精细控压钻井技术越来越多地体现出常规钻井技术无法比拟的技术优势。文章介绍了精细控压钻井技术及装备的发展过程,重点介绍了笔者研究团队研发的控压钻井工况模拟装置及评价方法、精细控压钻井成套装备、集“钻、录、测”于一体的控压钻井方法以及欠平衡精细控压钻井工艺技术等核心技术,分析了精细控压钻井技术现场应用效果与适用性,提出了下步发展方向。精细控压钻井技术作为一项先进钻井技术,将是未来闭环钻井技术发展的重要基础。

钻井机械能效地层压力监测新方法在南海莺琼盆地的应用

南海莺琼盆地超压成因复杂,传统的地层压力监测方法现场应用局限性较大。基于此采用基于钻井机械能效的地层压力监测新方法通过破岩效率分析实时反演地层压力。结果表明:MSE数据对加载和卸载型超压均有较好的响应特征,且随钻定量监测结果与实测数据吻合度较高;该区域超压起于莺歌海组二段,黄流组超压显著,存在地层压力“台阶”现象。新方法的经验参数选取方便,可直接通过随钻参数对地层压力进行实时监测,相对于传统的Dc指数等方法,定量计入了扭矩的影响,并联合测井数据进行综合评价,监测结果更为可靠。

覆岩承压含水层疏水应力场演化规律电荷监测研究

【目的】针对我国内蒙古、陕西、山东和甘肃等深部煤炭开采矿区面临水文地质条件复杂,导致顶板疏水量大,覆岩承压含水层疏水诱发的冲击地压灾害日益凸显的问题,开展了覆岩承压含水层疏水过程中煤层应力场演化规律研究。【方法】通过实验室分级加载条件下的煤体电荷感应试验与煤矿现场顶板疏水前后的电荷参数监测相结合的方法,系统研究了不同应力水平下煤体感应电荷的变化特征,以及顶板疏水过程中应力场的动态转移规律。【结果和结论】实验室研究表明,随着加载应力的逐级增大,煤样感应电荷量呈现非线性增长趋势,有效反映了煤体所受的应力水平。现场监测则揭示了顶板疏水过程中,富水区内电荷量均值和变异系数减小,而富水区外一定范围内电荷量先增后减,出现峰值点,表明应力从富水区边缘向外动态转移,并存在转移范围阈值;此外,基于富水区外各测点电荷量峰值的出现时间,得出了不同疏水量下的应力转移特征,即缓慢转移–快速转移–缓慢转移三个阶段。最后,通过大直径钻孔卸压试验,验证了该技术在降低顶板疏水条件下应力集中、防治冲击地压方面的有效性。研究成果可为顶板富水矿井冲击地压的预测与防治提供了理论依据和技术支持。

基于气测录井的高温高压地层压力随钻监测技术

基于气测录井地层压力监测基本原理,给出高温高压地层钻井液静态当量泥浆密度(ESD)和钻井液循环当量泥浆密度(ECD)的计算方法,并在此基础上对高温高压井地层压力进行随钻监测。研究发现,当井底压差增大时气测值呈指数式降低,且当井底压力处于过平衡状态时气测值不会降至0,而是保持一个较低的数值水平。据此分析泥浆循环气与循环压差以及单根气与静压差的相关关系,建立井底压差与气测值的相关方程,进而对地层压力作出定性和定量评价。

基于钻井机械比能的地层压力监测方法在探井工程的应用

高风险探井为降低复杂情况处理难度以及减少损失,通常采用常规钻具实现安全完钻后进行测井取资料。根据dc指数PreVue地层压力监测缺少随钻测井数据参考印证,难以满足实钻指导需求。为此提出采用基于钻井机械比能的地层压力监测方法,分析预测地层压力变化趋势,进行异常高压风险预警,指导钻井工程有效采取防范措施。该监测方法在北部湾探井应用成功钻前预测外的异常高压,对安全高效钻井提供更充分保障。