Wei, Chenji (Research Institute of Petroleum Exploration and Development, CNPC) | Zheng, Jie (Research Institute of Petroleum Exploration and Development, CNPC) | Ouyang, Xiaohu (China Petroleum Pipeline Engineering Co., Ltd, CNPC) | Ding, Yutao (China National Oil and Gas Exploration and Development Company Ltd. CNPC) | Ding, Mingming (China National Oil and Gas Exploration and Development Company Ltd. CNPC) | Lin, Shiyao (China National Oil and Gas Exploration and Development Company Ltd. CNPC) | Song, Hongqing (University of Science and Technology Beijing)
Understanding the heterogeneity is critical for a successful water injection in a carbonate reservoir. Thief zone is one of the most obvious forms of heterogeneity, which indicates the thin layer with higher permeability compared to the average reservoir permeability. The existence of thief zone results in earlier water breakthrough and faster water cut increase, which then lead to lower sweep efficiency and smaller recovery factor. Therefore, determining the distribution of thief zone and its impact towards production, and proposing a corresponding development plan are very important.
In this paper, a novel method is established to determine the thief zone distribution based on dynamic surveillance data. A new index is proposed as the relative contribution index to characterize the relative contribution of a certain layer, which is fundamental for thief zone determination. In addition, effect on water flooding development of thief zone's location is studied by experimental and theoretical analysis. The changes of water cut and production rate are analyzed under different conditions such as location of the thief zone, injection rate, and variogram. Finally, optimized development strategy is proposed to deal with the existence of thief zone.
Distribution of thief zone is characterized based on the proposed method, which indicates that thief zone development has intimate relationship with depositional facies and diagenesis. Experimental and theoretical analysis results show that the present model considering stratified water-flood is consistent with the experimental results. The water displacement effect is the best when the thief zone is located in the upper reservoir. This paper also points out the optimal adjustment period for water shutoff and profile control of the reservoir with thief zones. In addition, the greater the injection rate, the faster the water cut increase. Furthermore, the smaller the variogram, the slower the water cut increase, and the later the water breakthrough time.
This study provides a method to characterize thief zone, which can be used as a reference for similar oilfield development. In addition, it provides a quick and reasonable guide in the later adjustment of water flooding development of carbonate reservoirs with thief zones.
Tan, Zhuoying (University of Science and Technology Beijing) | Yue, Pengjun (University of Science and Technology Beijing) | Liu, Wenjing (University of Science and Technology Beijing) | Qi, Kuan (University of Science and Technology Beijing) | Xia, Zhiyuan (University of Science and Technology Beijing) | Ding, Yu (University of Science and Technology Beijing) | Wu, Bin (University of Science and Technology Beijing)
This paper presents a new method to accurately determine the strata while drilling. We developed an original prototype of instrumented drilling system, with it the measurement was performed on a hydraulic servo drilling rig. The drilling parameters (i.e., thrust or weight of drill strings, rotational speed, bit shift, torque as well as vibration of drilling rig) were recorded. According to the harmonious principle, a coding method for identification of sub-penetrating processes is established through the determination of parameter status. A slope coefficient searching identification algorithm is proposed for the penetrating data with the features of multiple pulses, noisy, huge data and nonlinear. Field drilling tests were carried out in three different sites. The results show that the approach well agrees with that of conventional drilling investigation, which provides a new method for in-situ intelligent survey in geological and geotechnical engineering.
In geological and geotechnical engineering investigation, the primary methods to obtain strata structure are drilling and related in-situ test techniques. For example, geophysical detecting techniques (GD), resistivity, magnetics, electromagnetic, seismic wave, seismic CT, gravity, sonic and ultrasonic methods have been extensively applied to the identification of strata interfaces at initial stage of geologic prospecting (1). In terms of technology, borehole penetrating test and coring are the most authentic and reliable for geotechnical investigation and geological survey. Unfortunately, the job of borehole logging, sampling, in-situ testing and indoor physical mechanical parameters testing is overloaded, time-consuming and expensive. According to incomplete survey, in drilling exploration of foundation, the time consuming ratio of net penetrating in the whole drilling is less than 30%, the costs of drilling exploration are generally accounted for 8%-28% of a project cost, this ratio will possibly increase with the increase of investigation depth.
In geological drilling, the borehole depth generally reaches thousands of meters. At present, the maximum depth has reached over 4500 m in metal mining; for nearly 1/3 underground metal mines, the mined depth has exceeded 1000 m in China; in coal mines, the numbers of well over 1000 m in depth have made a substantial growth in recent 10 years; the constructed depth of tunnel has rose up to near 3000 m. In earth science drilling, this figure has exceeded 10 000 m, and among the earth science boreholes, there are dozens of boreholes over 4000 m in depth worldwide. Obviously, with the growth of drilling depth, the complexity of geological conditions will increase, processing time will greatly grow in non-drilling such as sampling, lifting and lowering of drill strings and in-situ testing. For example, the depth of core drilling in the earth drilling-CCSD-1 reached 5158 m, totally spent 16.6189 million Chinese Yuan, core length of 4400 m with a cored rate 85.30%, for nearly 4 years. On the other hand, the geophysical approaches have good prospect for application in field investigation, but can be easily interfered with external factors and the interpretation accuracy is not very high when a single method is applied. Due to uncertainty, multiplicity of interpretation, it needs a combination of various methods to recognize formations. Besides, it is hard to give all the required basic data for geotechnical and geological engineering, and is difficult for rock mass classification.
Zhang, Shihuai (University of Science and Technology Beijing) | Wu, Shunchuan (University of Science and Technology Beijing / Kunming University of Science and Technology) | Zhang, Guang (University of Science and Technology Beijing)
The objective of this paper is to investigate the three-dimensional strength characteristics of a porous sandstone, which is referred to as Zigong sandstone, under true triaxial stress states (σ1 ≥ σ2 ≥ σ3) by means of a Mogi-type true triaxial testing apparatus. Three series of tests (σ3 = 0, 20, and 60 MPa) are conducted. Within each series, σ2 is varied from σ2=σ3 to σ2=σ1 from test to test. For each test, σ1 is raised monotonically to failure while σ2 and σ3 are kept constant and the post-peak behavior is also captured. Deformability and strength are investigated in term of the effect of σ2. It is found that, for a constant σ3, the onset of dilatancy generally increases with the increase of σ2. Regarding peak strength, the variation of σ1 at failure versus σ2 exhibits a typical ascending-then-descending trend. A versatile deviatoric function is used to replace the one of Hoek-Brown strength criterion, which is referred to as the modified Hoek-Brown strength criterion and is further adopted to depict the strength characteristics in the three-dimensional principal stress space. Results show that the effect of σ2 on rock strength is actually a combined effect of mean stress and Lode angle.
Sandstone is one of the main formations in the earth’s crust. Many human activities, such as hydrocarbon production, CO2 sequestration, and waste disposal, are intimately related to the failure of host sandstones. Understanding and charactering the mechanical responses of sandstone under different stress conditions is essential to the design and construction of many underground projects.
In the past several decades, efforts have been taken to investigate the failure mechanisms of porous sandstones based on laboratory tests. Extensive conventional triaxial tests have been conducted on cylindrical specimens of different sandstones (Wong T et al., 2012), revealing that mechanical responses of sandstones, such as failure modes, strength, deformability, and porosity evolution, are heavily dependent on the first two stress invariants related to the mean stress and the differential principal stress (Wong T et al., 1997; Grueschow E et al., 2005; Baud P et al., 2006), respectively. The effect of the third stress invariant, however, is rarely known except for the limited comparison between conventional triaxial compression (CTC: σ1 > σ2 = σ3) and conventional triaxial extension (CTE: σ1 = σ2 >σ3) (Murrell S, 1963; Mogi K, 1967). Moreover, in situ stress measurements at depths indicate a state of stress in the earth’s crust that is totally non-uniform (σ1 ≠ σ2 ≠σ3) (Haimson BC, 1978; Brace WF et al., 1980; Vernik L et al., 1992). It is important to consider general states of stress to fully understand failure characteristics of sandstone.
Li, Dapeng (Safetech Research Institute) | Zhang, Lei (University of Science and Technology Beijing) | Wang, Xiuyun (Safetech Research Institute) | Yang, Zhiwen (Safetech Research Institute) | Yue, Xiaoqi (University of Science and Technology Beijing) | Lu, Minxu (University of Science and Technology Beijing)
Recently, there are several cracking and severe localized corrosion failures of API 5CT Grade C110 tubing in high-density formate completion fluid at high temperature, where the temperature up to 180 °C, with the possibility of CO2 mixed, and mechanical damage on the tubing surface. In this paper, the corrosion performance of C110 tubing is investigated in high-density formate completion fluid at 180 °C with different combinations of CO2 mixed and mechanical damage, and the initiation and growth of cracking and localized corrosion are studied by scanning electron microscopy (SEM),, X-ray diffraction (XRD) and stereo microscope, considering the formate decomposition at high temperature, aiming to clarify the corrosion mechanism of C110 tubing in high-density formate completion fluid at high temperature.
The unique physic-chemical properties of high relative gravity, high temperature stability and low corrosivity make formate brines the ideal fluids1-3. However, recently there are several severe cracking and severe localized corrosion failures of API 5CT Grade C110 tubing in high-density formate completion at high temperature, where the temperature up to 180 °C, with the possibility of CO2 mixed, and mechanical damage on the tubing surface. How could this happen? The formate brines could decompose in high temperature, especially up to 160 °C and the decomposition might lead to severe corrosion and cracking4-7. Also it is possibly that the leakage of corrosive gas in the tubing brought about the decrease of pH and the susceptibility of corrosion and stress corrosion cracking8-12. Moreover, the mechanical damage brings about the stress concentration and the damage of corrosion product, which result in the failures more likely happen in the damage region13-17.
Did the formate brines thermal degradation and cause the failure or the leakage of CO2 result in the severe cracking and severe localized corrosion of C110 tubing? And did the mechanical damage accelerate the corrosion degree?
Wang, Min (Texas A&M University) | Wei, Chenji (Research Institute of Petroleum Exploration & Development, PetroChina) | Song, Hongqing (University of Science and Technology Beijing) | Efendiev, Yalchin (Texas A&M University) | Wang, Yuhe (Texas A&M University)
In this paper, we couple Discrete Fracture Network (DFM) and multi-continuum model with Generalized Multiscale Finite Element Method (GMsFEM) for simulating flow in fractured and vuggy reservoir. Various scales of fractures are treated hierarchically. Fractures that have global effect are modeled by continua while the local ones are embedded as discrete fracture network based on the geologic observation. For independent vugs, a continuum is used to represent their effects with specific configuration that there's no intra-flow of this continua. GMsFEM enables us to systematically develop an approximation space that contains prominent sub-grid scale heterogeneous background information based on the multi-continuum and DFM model. Conforming unstructured mesh is used to surrender the application of random discrete fracture networks. This paper targets on the improvement of the flow simulation performance in complex high-contrast domain by extending the ability of multiscale method to modeling arbitrary discrete fracture network. This advancement by GMsFEM is motivated by the limited capability of Multiscale Finite Element Method (MsFEM) on modeling discrete fractures when multiple fracture networks present in same coarse block. Multiple numerical results are shown to validate the efficiency of our coupled method.
Wang, Zhu (University of Science and Technology Beijing) | Tang, Xian (University of Science and Technology Beijing) | Xue, Junpeng (University of Science and Technology Beijing) | Zhang, Lei (University of Science and Technology Beijing) | Li, Ting (University of Science and Technology Beijing) | Lu, Minxu (University of Science and Technology Beijing)
ABSTRACTWith increasing concerns of air pollution, the emission of sulfur from industries in the form of SOx has been closely monitored and regulated by many countries. Technological and industrial efforts have been taken in the past several decades and many clean-up methods have been developed. However, corrosion, especially pitting and stress corrosion cracking, has been reported previously under the condition with both SO2 and Cl- / F- contamination in the solvent. In this paper, pitting risk of stainless steels under wet SO2 environments with Cl- and F- in high temperature and high pressure conditions was investigated. Cyclic polarization measurements were used to illustrate the corrosion and passive behavior of the stainless steels under the tail gas conditions. Electrochemical behavior of stainless steels in SO2-saturated solutions with various concentrations of Cl- and F- was also studied.INTRODUCTIONWith increasing concerns of air pollution, the emission of sulfur from industries in the forms of SOx has been closely monitored and regulated by many countries. The reduction of sulfur dioxide (SO2) emission from the flue gases of fossil fuel-fired power plants has become one of the most urgent environmental issues for the sustainable society 1-5. Meanwhile, once dissolved in the solution, SO2 can be corrosive to materials. The researchers found that the effect of SO2 would be more moderate in comparison with those of contaminants such as HCl, HNO3, and SO3, which would exert a significant effect on the aqueous phase pH even in small concentrations 6. SO2, which has a high solubility in H2O, results in the formation of H2SO3 and consequently lowers the pH (~2) of the aqueous phase 6.In SO2 saturated solutions, carbon steels may suffer high corrosion rates. Therefore, corrosion Resistant Alloys (CRAs) are widely used in SO2 conditions to meet the requirement for materials. However, the CRAs may also suffer corrosion, especially pitting and stress corrosion cracking in Cl- / F- condition 7-11. This paper focused on the effect of F- and Cl- on the corrosion behavior of stainless steels. Different concentrations of F- and Cl- were selected to investigate their effect. Additionally, the materials selection of stainless steels under low and high Cl/F containing conditions was also studied.
Du, Yanxia (University of Science and Technology Beijing) | Tang, Dezhi (Beijing Safetech Pipeline Co., Ltd) | Lu, Minxu (University of Science and Technology Beijing) | Chen, Shaosong (Beijing Safetech Pipeline Co., Ltd)
ABSTRACTThe research status of AC corrosion risk assessment criteria for cathodic protected carbon steel was introduced initially. Then AC interference experiments were carried out to study the effects of AC interference on cathodic protection (CP) parameters and corrosion behavior. The changes of CP potential and current density under AC interference and AC corrosion rates in different conditions were obtained. Based on the experiment results, the determination of effective CP potential under AC interference was analyzed and the corrosion rates in three different corrosive media under the same level of CP and AC interference were compared. Besides, the reason for the instant shift of CP potential when AC interference is applied was discussed. The results could provide reference for the determination of CP parameters in the presence of AC interference and the improvement of existing AC corrosion risk assessment criteria for cathodic protected carbon steel.INTRODUCTIONWith the development of oil, electricity and transportation industry, more and more oil and gas pipelines were buried in parallel with high voltage alternating current (AC) transmission lines and electrified railway, which lead to increasingly serious AC interference. In the recent twenty years, AC corrosion problem has caused wide attention in the international corrosion field.1-14 Although cathodic protection (CP) has been widely used to protect buried pipelines from corrosion, the occurrence of AC corrosion brought out challenge to the industry accepted CP criteria.After the 1980s, a series of AC corrosion cases have been reported. For example, in 1986, a corrosion failure on a high-pressure gas pipeline in Germany was attributed to AC corrosion. 1 In this case, field investigations showed corrosion rate was very high, although CP current density was 1.5~2 A/m2 and on-potential reached -1.8~-2.0 V (referenced to copper-copper sulfate reference electrode, abbreviated as CSE). In 2002, an AC corrosion failure occurred on a buried pipeline at the location of Highway 66 crossing the USA. 7 At this location, the piping was well protected with the off-potential of -1.230 V (CSE) on the pipe and -1.056 V (CSE) on the coupon, but the coupon AC density was found to be 144.13 A/m2. In 2003, an AC corrosion failure occurred on a buried pipeline with CP potential of -1.2 V (CSE) and AC current density of 130 A/m2. 8 These cases indicated AC corrosion could occur when protection criteria were met, which means the industry accepted CP criteria are not suitable to decrease the corrosion rate to negligible level under AC interference.
Zhang, Lei (University of Science and Technology Beijing) | Shen, Hongjie (University of Science and Technology Beijing) | Xing, Yunying (Safetech Research Institute) | Cao, Wenhai (University of Science and Technology Beijing) | Fang, Yichen (University of Science and Technology Beijing) | Lu, Minxu (University of Science and Technology Beijing)
ABSTRACTWith the wider application of pipeline steels higher than API X80 grade, the hydrogen embrittlement risk induced by the hydrogen evolution effect under cathodic protection has been recognized. Since the increased strengthening of pipeline steel might significantly increase the hydrogen cracking sensitivity, a greater understanding on the different criteria of cathodic protection potential or current density compared with those of traditional pipeline steels are required. This paper focuses on the hydrogen embrittlement behaviors of API X70, X80 and X90 high strength pipeline steel under cathodic protection in soil simulation conditions. The uptake and diffusion of hydrogen in the steels under different cathodic protection levels were analyzed by hydrogen permeation test and hydrogen content measurement. Slow strain rate testing (SSRT) under cathodic conditions as well as mechanical performance degradation testing after long term immersion were used to determine the hydrogen embrittlement (HE) susceptibilities of the three kinds of steel. The results showed the changes of hydrogen diffusion rate, hydrogen accumulation limit and hydrogen embrittlement with the increased steel strength under different soil and cathodic protection conditions.INTRODUCTIONWith growing need in energy supply, petroleum industry has paid extensive attention to increase the transport capacity and the safety of pipeline. There has been a noteworthy trend toward increasing the relevant mechanical properties of pipeline steels, particularly as the application of high-strength steel pipeline is cost effective, given the increased pressure of the transmitted oil or gas and the decreased wall thickness of the pipeline [1-4]. However, it is well known that the hydrogen embrittlement (HE) susceptibility of high-strength steel increases with increasing the strength level, cathodic protection at too negative potentials also can enhance the risks of hydrogen embrittlement [5- 8].In addition to the strength grade of steel, the HE sensitivity of high-strength pipeline steel is also closely related to microstructure, service environment, and current density. As the grade ascends from traditional X60, X70 to X80, X90 and the newest X100, X120, the metallographic structure of pipeline steel change from polygonal ferrite-pearlite to acicular ferrite and bainite . And the susceptibility to hydrogen embrittlement increases in the order of polygonal ferrite, acicular ferrite, bainite . By cathodic protection, corrosion can be effectively controlled. However, cathodic charging is one of the reasons that lead to the hydrogen embrittlement of high strength steel. On the one hand, the amount of absorbed hydrogen in steels is affected by the the pH of the service environment [11-13]. On the other hand, it is also greatly affected by the cathodic protection parameters, such as current density, overpotential and charging time[7-16]. The studies of Yan and Weng indicated that the hydrogen in steels increased as current density (i) rose . Devanathan and Stachurski believed that the surface coverage with atomic hydrogen was a constant at higher overpotential, as indicated by the fixed hydrogen permeation into the steel . After charging hydrogen for a long sufficient time, the amount of absorbed hydrogen would be proportional to the applied current density [16,17]. But these researches did not systematically clarify the relationship between hydrogen embrittlement sensitivity and hydrogen diffusion and hydrogen content, and the effect of steel strength, service environment and cathodic protection parameters on it.
Wang, Bei (University of Science and Technology Beijing) | Zhang, Lei (University of Science and Technology Beijing) | Chen, Guang (University of Science and Technology Beijing) | Li, Qingping (CNOOC Research Institute) | Chang, Wei (CNOOC Research Institute) | Yao, Haiyuan (CNOOC Research Institute) | Liu, Yingkun (Safetech Research Institute) | Zhang, Yunan (Safetech Research Institute)
ABSTRACTCorrosion is always recognized as one of the biggest flow assurance challenges of natural gas fields. During the pipeline design and maintenance, it is not enough to only use the equations of the limitation for the maximum erosional velocity from API RP 14E to deal with the balance of pipeline diameter, flow rate and the corrosion inhibitor film stability and effectiveness. In order to get more information of the relationship between flow and inhibitor for wet subsea pipeline, a HTHP-RC and a wet gas flow loop were employed to simulate typical flow conditions of subsea gas pipeline in this paper, as well as the research of corrosion behaviors before and after inhibitor injection. The stability of inhibitor film on the pipeline steel's surface under high gas velocities under the CO2 wet gas corrosion environment was evaluated. The influence of pipeline operating parameters such as gas velocity, wall shear stress, CO2 pressure, total pressure, and inhibitor dosage, was investigated during the HTHP-RC tests and flow loop tests. The results give the recommendation of the gas velocity and the inhibitor limits of the subsea wet gas pipeline.INTRODUCTIONWith the development of deep water offshore gas fields in recent years, long distance subsea gas pipelines have been built up and flow assurance becomes more and more important. The need to maintain gas production at reducing reservoir pressure had already resulted in much higher gas velocities in the field.However, higher gas velocity leads to higher wall shear stress. Generated wall shear stress in some high flow velocity systems can reach 300 Pa. Gopal et.al indicated that shear stress can reach 80-160 Pa in slug flow. In addition, values as high as 3000 Pa have been recorded in some laboratories.1-3A high wall shear stress can be detrimental to the corrosion inhibitor adsorption on the internal surface of a pipeline, which will increase the corrosion and erosion risk especially for wet gas transportation. For some inhibitors, the inhibitor film on the steel surface can be destroyed by the fluid when the wall shear stress is higher than a critical value.4 Some authors claim that above a certain critical fluid velocity, corrosion inhibition would no longer be possible,5 but some indicate that the inhibitor can still protect steel by increasing the concentration even at a high flow velocity.6 But anyway, it is necessary to determine the critical erosion velocity and the concentration that corrosion inhibitor can filmed on the surface stable under the condition with high flow velocity during the pipeline design and maintenance.
Qin, Runzhi (University of Science and Technology Beijing) | Du, Yanxia (University of Science and Technology Beijing) | Peng, Guozheng (University of Science and Technology Beijing) | Lu, Minxu (University of Science and Technology Beijing) | Jiang, Zitao (Safetech Research Institute)
ABSTRACTHigh Voltage Direct Current systems are developing fast in China. But the electrodes working in monopolar modes may introduce DC interferences on buried metallic pipelines nearby, and increase the risk of corrosion and hydrogen embrittlement. Focusing on a real case of HVDC interference, this paper aimed to study the field test, the numerical simulation calculation, and the design of mitigation. Firstly, field tests found that a natural gas pipeline system was interfered by a HVDC electrode in Guangdong province. The pipe-to-soil potentials along the pipe had deviations up to 300V, posing severe threats to safety operation of the pipeline system. Then, the numerical simulation technique was used to model the electrode and pipeline system based on field parameters. The interference level was computed and the results showed good agreements with the measured values, which indicated the validity of the model. Finally, for the purpose of interference elimination, the effectiveness of various mitigation methods was computed and discussed, including insulating joints, sacrificed anodes drainage system, zinc ribbon drainage system, impressed current drainage system, etc. Based on the results above, the integrated mitigation of this interference case was designed.BACKGROUNDHigh Voltage Direct Current (HVDC) systems are developing fast in China because of its economic and technical advantages. As a part of national strategy, dozens of systems are running in operation, and more has been planned. HVDC has 2 operation modes: bipolar mode and monopolar mode1~4. As shown in figure 1, when working at monopolar mode, the electrode of HVDC system discharges large amount of current into earth. A portion of current can be captured and collected by the pipeline nearby, then discharged elsewhere faraway. Thus the interference is introduced into the pipeline, bring risk to personnel safety, equipment damage and corrosion5~9.In this case, the transmission system is Niucong HVDC system built by China Southern Power Group. It sends power from Jinsha river of Yunnan province, to Conghua city of Guangdong province. The electrode is located in Conghua city. The shape of the electrode is double-rings, and the rated current is 3232A. The soil nearby is farmland, with low resistivity in the surface and high resistivity underneath.