Numerical simulation of water and sand blowouts when penetrating through shallow water flow formations in deep water drilling

In this study, we applied a two-phase flow model to simulate water and sand blowout processes when penetrating shallow water flow(SWF) formations during deepwater drilling. We define ‘sand' as a pseudo-component with high density and viscosity, which can begin to flow with water when a critical pressure difference is attained. We calculated the water and sand blowout rates and analyzed the influencing factors from them, including overpressure of the SWF formation, as well as its zone size, porosity and permeability, and drilling speed(penetration rate). The obtained data can be used for the quantitative assessment of the potential severity of SWF hazards. The results indicate that overpressure of the SWF formation and its zone size have significant effects on SWF blowout. A 10% increase in the SWF formation overpressure can result in a more than 90% increase in the cumulative water blowout and a 150% increase in the sand blowout when a typical SWF sediment is drilled. Along with the conventional methods of well flow and pressure control, chemical plugging, and the application of multi-layer casing, water and sand blowouts can be effectively reduced by increasing the penetration rate. As such, increasing the penetration rate can be a useful measure for controlling SWF hazards during deepwater drilling.     

Geophysical Signature of the Shallow Water Flow in the Deepwater Basin of the Northern South China Sea

Shallow water flow (SWF), a disastrous geohazard in the continental margin, has threatened deepwater drilling operations. Under overpressure conditions, continual flow delivering unconsolidated sands upward in the shallow layer below the seafloor may cause large and long-lasting uncontrolled flows; these flows may lead to control problems and cause well damage and foundation failure. Eruptions from over-pressured sands may result in seafloor craters, mounds, and cracks. Detailed studies of 2D/3D seismic data from a slope basin of the South China Sea (SCS) indicated the potential presence of SWF. It is commonly characterized by lower elastic impedance, a higher Vp/Vs ratio, and a higher Poisson’s ratio than that for the surrounding sediments. Analysis of geological data indicated the SWF zone originated from a deepwater channel system with gas bearing over-pressured fluid flow and a high sedimentation rate. We proposed a fluid flow model for SWF that clearly identifies its stress and pressure changes. The rupture of previous SWF zones caused the fluid flow that occurred in the Baiyun Sag of the northern SCS.     

Numerical simulation of mechanical compaction of deepwater shallow sediments

To study the compaction law and overpressure evolution in deepwater shallow sediments, a large-strain compaction model that considers material nonlinearity and moving boundary is formulated. The model considers the dependence of permeability and material properties on void ratio. The modified Cam-Clay model is selected as the constitutive relations of the sediments, and the deactivation/reactivation method is used to capture the moving top surface during the deposition process. A one-dimensional model is used to study the compaction law of the shallow sediments. Results show that the settlement of the shallow sediments is large under their own weight during compaction. The void ratio decreases strictly with burial depth and decreases more quickly near the seafloor than in the deeper layers. The generation of abnormal pressure in the shallow flow sands is closely related to the compaction law of shallow sediments. The two main factors that affect the generation of overpressure in the sands are deposition rate and permeability of overlying clay sediments. Overpressure increases with an increase in deposition rate and a decrease in the permeability of the overlying clay sediment. Moreover, an upper limit for the overpressure exists. A two-dimensional model is used to study the differential compaction of the shallow sediments. The pore pressure will still increase due to the inflow of the pore fluid from the neighboring clay sediment even though the deposition process is interrupted.     

实验尺度下钻井液在含水合物地层流动数值模拟

钻井实践表明,钻井液侵入会改变井壁围岩特性,例如岩石强度、孔隙压力等。在非常规的含水合物地层,钻井液侵入还可能诱发地层中水合物分解和再形成,从而对井壁稳定和测井解释产生影响。因此,研究钻井液在含水合物地层中侵入流动特性有非常重要的理论和实际应用价值。基于野外水合物储层的相关数据和室内实验模拟系统,采用数值模拟方法研究了实验尺度下钻井液在含水合物地层中的侵入流动规律及其对储层物性的影响。模拟结果可为后续实验模拟方案设计以及热开采研究提供一定的指导作用。      

Influence of the characteristics of fault gouge on the stability of a borehole wall

How to find more effective way to stabilize the borehole wall in the fault gouge section is the key technical challenge to control the stability of the borehole wall in the Wenchuan fault gouge section during the process of core drilling.Here we try to describe the characters of deep fault gouge in fracture zones from the undisturbed fault gouge samples which are obtained during the core drilling.The XRay Diffraction(XRD),X-Ray Fluorescence(XRF) and Scanning Electron Microscope(SEM) provided the detailed information of the fault gouge's microscopic characteristics on the density,moisture content,expansibility,dispersity,permeability,tensile strength and other main physical-mechanical properties.Based on these systematic experimental studies above and analysis of the fault gouge instability mechanism,a new technical procedure to stabilize the borehole wall is proposed — a low water and a low loss low permeability drilling fluid system that consists of 4% clay + 0.5% CMC-HV + 2% S-1 + 3%sulfonated asphalt + 1% SMC + 0.5% X-1 + 0.5% T type lubricant + barite for core drilling in fault gouge sections.     

Sediment compaction and pore pressure prediction in deepwater basin of the South China Sea: Estimation from ODP and IODP drilling well data

Overpressure in deepwater basins not only causes serious soft sediment deformation, but also significantly affects the safety of drilling operations. Therefore, prediction of overpressure in sediments has become an important task in deepwater oil exploration and development. In this study, we analyze the drilling data from ODP Leg 184 Sites 1144, 1146, and 1148, and IODP Leg 349 Sites U1431, U1432, U1433, and U1435 to study the sediment compaction and controls in the northern South China Sea. Sedimentation rate, sediment content, distribution area, and buried depth are the factors that influence sediment compaction in the deepwater basin of the South China Sea. Among these factors, the sediment content is the most important. The fitted normal compacted coefficients and mudline porosity for an interval of 50 m shows disciplinary variation versus depth. The pore pressure predicted from different fitted results shows varying overpressure situations. The normal compaction trend from Site 1144 reflects the porosity variation trend in stable deposition basins in the northern South China Sea. The predicted pore pressure shows overpressure at Site 1144, which is attributed to compaction disequilibrium. Nevertheless, the mixed lithology column may influence the predicted over-pressure at Site 1148, which is responsible for the confusing result. Above all, we find that sediment compaction should serve as a proxy for pore pressure in the deepwater basin of the South China Sea.     

Numerical analysis of wellbore instability in gas hydrate formation during deep-water drilling

Gas hydrate formation may be encountered during deep-water drilling because of the large amount and wide distribution of gas hydrates under the shallow seabed of the South China Sea. Hydrates are extremely sensitive to temperature and pressure changes, and drilling through gas hydrate formation may cause dissociation of hydrates, accompanied by changes in wellbore temperatures, pore pressures, and stress states, thereby leading to wellbore plastic yield and wellbore instability. Considering the coupling effect of seepage of drilling fluid into gas hydrate formation, heat conduction between drilling fluid and formation, hydrate dissociation, and transformation of the formation framework, this study established a multi-field coupling mathematical model of the wellbore in the hydrate formation. Furthermore, the influences of drilling fluid temperatures, densities, and soaking time on the instability of hydrate formation were calculated and analyzed. Results show that the greater the temperature difference between the drilling fluid and hydrate formation is, the faster the hydrate dissociates, the wider the plastic dissociation range is, and the greater the failure width becomes. When the temperature difference is greater than 7℃, the maximum rate of plastic deformation around the wellbore is more than 10%, which is along the direction of the minimum horizontal in-situ stress and associated with instability and damage on the surrounding rock. The hydrate dissociation is insensitive to the variation of drilling fluid density, thereby implying that the change of the density of drilling fluids has a minimal effect on the hydrate dissociation. Drilling fluids that are absorbed into the hydrate formation result in fast dissociation at the initial stage. As time elapses, the hydrate dissociation slows down, but the risk of wellbore instability is aggravated due to the prolonged submersion in drilling fluids. For the sake of the stability of the wellbore in deep-water drilling through hydrate formation, the drilling fluid with low temperatures should be given priority. The drilling process should be kept under balanced pressures, and the drilling time should be shortened.     

钻孔应变观测影响因素的数值模拟分析

利用有限元数值模拟方法,研究在非均匀地应力作用下,钻孔开挖前后区域应力场的变化特征,并探讨钻孔开挖后岩石、水泥、探头的弹性模量、泊松比及水泥的厚度与膨胀系数的变化对分量应变及面应变观测的影响。研究结果表明：钻孔开挖造成区域应力场扰动的范围大概为1.5倍孔径。在“探头 水泥环 围岩”系统中,各参数的变化对应变观测的影响程度不同,但分量应变对外界载荷的响应趋势基本一致。在均匀地应力作用下,水泥厚度对应变的影响与水泥的弹性模量有关,且随着水泥膨胀系数的增加,面应变存在减小的趋势。     

河南中牟凹陷浅层天然气成藏条件研究

中牟凹陷是一个以早第三纪沉积为主的凹陷,在对以往的钻井资料复查过程中发现,浅层（ ＜ ２０００ｍ）具有良好的气测显示。本文通过对中牟凹陷浅层地质、构造发育特征等的研究,从气源、储盖的角度论证了中牟凹陷特别是中牟凹陷北坡具有良好的勘探前景。     

三维钻孔应变的力学模型

讨论了两个问题：（１）三维圆孔问题的力学模型。论证了常用的平面弹性力学圆孔问题的钻孔应变公式并不能满足三维弹性力学平衡方程。为此重新推导出三维空孔问题的解，进而可得到有底空孔、有底耦合封固、有底顶头加力等几种边界条件的钻孔应变解。（２）在边界条件上，实际地球潮汐形变应力与三维圆孔问题力学模型的应力有差异。论证了在目前钻孔应变测量的精度情况下，边界条件的这一差异不影响三维圆孔问题力学模型在应变固体潮中的应用     

Research on drilling parameters of engine-powered auger ice drill

Drilling operations in polar regions and mountainous areas are complicated by nature of the extreme environment. Yet conventional rotary drilling technologies can be used to drill ice for scientific samples and other research. Due to such reasons as power consumption and weight complications,it is hard to apply a conventional rotary drilling rig for glacial exploration. Use of small,relatively lightweight,portable engine-powered drilling systems in which the drill lifting from the borehole is carried by the winch. It is reasonable enough for near-surface shallow ice-drilling down to 50 m. Such systems can be used for near-surface ablation-stakes installation,also temperature measurements at the bottom of active strata layer,revealing of anthropogenic pollution,etc. The specified used in this research is an auger ice drill powered by a gasoline engine. At this stage,it is crucial to choose effective drilling parameters such as weight on bit( WOB) and drill bit rotation rate. Sensors equipped on the rig have measured the main parameters of the drilling process,such as drill speed,WOB,drill rotation speed,torque and temperature. This paper addresses research on drilling parameters of engine powered auger ice drill and supplies some recommendations for optimization of any ice-core drilling process.     

内插管式气举反循环钻进工艺在基岩地热井中的应用

随着地热资源被广泛利用,地热井各种钻井技术新方法不断应用,如何提高地热井施工效率、降低地热井施工成本是地热井项目钻探施工的关键.气举反循环钻进工艺被广泛应用于地热井钻探施工中,然而在基岩浅井和中深井地热项目施工中,使用常规气举反循环钻进工艺存在钻具重量大、结构复杂、双壁密封不严等问题,对钻机提升能力要求较高,中小型钻机...     

Elasticity soltion of rupture model of shallow earthquake

Based on the theory of elastic mechanics, and using the typical rupture model of shallow earthquake, the authors considered the shallow earthquake as a plane mechanical problem, which was constructed the corresponding mechanical model. By the stress components' formulas of the semi-infinite model acted by the finite even shearing force, the main stress is deduced. It is clear that the sector on the right of the center section is squeezed zone, where the maximum principal stress points at the "source of stress", and that on the left is tensile zone, where the minimum principal stress points to the "source of stress".     

青岛台体应变短周期气压系数变化原因探讨

青岛台体应变短周期(小于128 min)气压系数2018-01出现阶变，通过对观测系统、台站周边施工情况、监测环境等逐项现场核实，排除观测系统、周边施工的影响。利用离散小波变换和回归分析发现，钻孔水位的气压系数与体应变气压系数同步阶变，结合台站钻孔施工当天体应变钻孔水位变化、体应变趋势变化、其他相邻台站水位气压系数变化等数据认为，台站钻孔施工是导致体应变气压系数变化的原因，并定性分析其变化机理。     

浅钻孔安装应变仪的试验

钻孔应变仪探头与钻孔用膨胀水泥固封,探头损坏后钻孔不能再使用,这样给监测工作造成了很大的经济损失.如何充分利用台站山洞资源,进行浅钻孔应变仪的安装,是值得研究的课题.在井深1.96m的浅钻孔内安装形应变仪的试验取得了很好的结果,经与徐州地震台山洞内的体应变、振弦仪和伸缩仪同期观测资料的对比,发现仪器安装在山洞里,采用电瓶供电方法,可以大大减少或避免雷害的影响.     

莱州湾南岸XZK2钻孔晚更新世以来的沉积环境探讨

通过钻孔岩性特征、沉积构造及沉积物粒度、磁化率与测井曲线对莱州湾南岸XZK2钻孔上部晚更新世以来的松散沉积物进行了沉积相划分,结合14C同位素年龄测定,划分了深海氧同位素阶段,表明该地区沉积物磁化率与砂含量曲线具有明显的正相关关系,结合已有研究,证明该地区晚更新世以来古环境经历了三次冷暖交替,而莱州湾西南海岸所发现的相当于沧州海侵、献县海侵和黄骅海侵的三次海侵事件,钻孔上仅见全新世黄骅海侵,沧州海侵、献县海侵相应层位为滨海沉积。     

基于多孔介质弹性理论的碳酸盐岩地层超压预测

碳酸盐岩地层超压预测目前仍然是国内外研究的难点问题。碎屑岩超压预测方法均是建立在明显的超压测井、地震宏观响应规律基础上的经验关系,这些经验性方法不适用于因岩性致密使得超压地球物理响应微弱的碳酸盐岩地层。通过碳酸盐岩样品超压岩石物理模拟实验,分析了在应力-孔隙压力共同作用下岩石中声波速度、弹性参数的变化规律;基于多孔介质弹性理论和广义胡克定律推导并建立了表征孔隙压力与岩石弹性参数定量关系的理论模型,即多孔介质弹性理论的超压预测量化模型。以川东北地区典型碳酸盐岩超压钻井为例,开展了碳酸盐岩地层超压预测应用研究:针对碳酸盐岩地层选择油气水测井综合解释模型获取岩石物性参数;利用Voigt-Reuss-Hill平均模量模型计算岩石基质体积模量,利用Wood模型和Patchy模型计算孔隙流体体积模量,利用BISQ模型计算岩石骨架体积模量,然后通过多孔介质弹性理论量化模型预测超压。预测结果显示预测压力与钻杆实测压力(DST)吻合较好,与泥浆密度换算压力和随钻监测压力变化趋势相近,表明这种基于多孔介质弹性理论的超压预测量化模型是一种解决碳酸盐岩地层超压预测的新途径。     

Research and development on foam breaking and recycling technology in air-foam drilling

In recent years, air-foam combining the advantages of both liquid and air drilling has been utilized as a drilling medium. Air-foam drilling has proved its efficiency in numerous situations where serious problems were encountered, such as in fractured formations and depleted or high permeable zones. However, the major disadvantage of air-foam drilling system is that the foam can only be used once, so that an extremely large pit is required to contain the foam to allow sufficient room for cuttings and for the foam to dissipate. Moreover, it needs enormous volume prepared, consuming abundance of water and ingredient additives, which results in the high cost of foam drilling. The recycling foam fluid by using foam breaking technology is the only effective method to solve these problems associated with the known foam drilling. Various types of equipment and technique have been employed to suppress foam formation in biological and process equipment in foam drilling. The study described various methods of foam breaking technology, and the trend of the foam breaking technology for foam drilling is discussed.     

济南千佛山断裂与文化桥断裂导水透水性研究

针对已有资料,推断出济南市区段千佛山断裂与文化桥断裂的构造形成过程,通过整理千佛山断裂与文化桥断裂周围分布的大量钻孔数据,从地层岩性特点,重点研究市区内千佛山断裂与文化桥断裂的导水性与透水性。研究表明,地垒处东南高、西北低的地势特点,对四大泉群的形成具有重要作用。千佛山断裂在市区内从南郊宾馆至明湖北路4km范围内具有透水性,明湖北路以北断裂EW向隔水不连通。文化桥断裂在市区内经十路至明湖北路之间3.7km范围内为EW向透水断裂;在经十路以南部分,断裂处南北向导水受阻,这是由于浅层强风化闪长岩钙华沉积所致。位于四大泉群正西方向的千佛山断裂,东西两侧透水性好,垂直方向上导水畅通,但由于上部沉积较厚粘土隔水层,因而没有出现泉水喷涌。     

含CaCl2水基聚合物钻井液沿井周地层渗透规律研究

利用微生物诱导碳酸钙沉积（MICP）技术来提高油气井固井二界面胶结质量近年来受到了越来越多的重视。当前,针对3 000 m以浅油气井已实现了含成矿微生物的固井水泥浆技术。为了使固井水泥浆滤液中的成矿微生物在二界面处高效发挥MICP作用以提高二界面胶结质量,还需在钻井过程中利用钻井液携带CaCl₂的渗透向井周地层中预先注入一定量的钙源。因此,有必要研究含CaCl₂钻井液在井周地层的渗透规律,从而合理控制CaCl₂的注入量和钻井成本。基于此,以当前常用的环保水基聚合物钻井液为基本载体,综合考虑钻井液渗透时在井壁处泥饼动态形成机理、井周地层物性参数变化规律以及含CaCl₂水基聚合物钻井液流变性等因素,利用理论计算与模拟实验相结合的方法,建立了含CaCl₂水基聚合物钻井液滤液沿井周地层渗透量及渗透距离的定量预测模型。该预测模型的计算结果与模拟实验测试结果吻合程度较高,证实该预测模型具有较好的可靠性,有助于为钻井生产企业合理优化钻井液和固井水泥浆施工工艺提供理论支持。