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Elastomer is the core component of progressing cavity pump (PCP) which influences the running life of PCP considerably. Conventional elastomer performance tests only show basic mechanical and physical properties mainly simulate the static mechanic performance of elastomer. Numerical simulation indicates that dynamic performance is much more valuable in evaluating PCP's running life, while elastomer's dynamic test has not common criteria in the industry, especially for dynamic fatigue property test. This paper presents a novel simulated experimental design which could effectively evaluate dynamic fatigue properties of PCP elastomer.
Based on the operating conditions of PCP lifting system, a special experiment system has been designed and tested. It consists of power transmission system, friction pair system, and temperature control system. After implementing a series of contrasted tests, a special structure of elastomer sample and testing process were designed which showed best performance in accelerating dynamic fatigue process of elastomer as well as to simplify simulated test principle.
In order to verify the evaluation result of this fatigue testing system, three candidate elastomer formula (sample A, B, C) were evaluated. Experiments showed that dynamic fatigue properties of sample C were better than A and B. The fatigue properties of sample A was the worst. Statistics indicated that average running life of elastomer A was about 550 days, while running life of Elastomer B was 590 days and Elastomer C was 670 days. The application results had the same principle with experimental results. Experiments indicated that this simulated experimental system could describe the dynamic fatigue performance directly and clearly.
This paper presented a new experimental design which could evaluate the dynamic fatigue properties of PCP elasomer based on simulating PCP's operating conditions in practice. This experimental system has been applied to guide the design of elastomer formula and showed good results. This experimental system and testing process are of great significance in evaluating PCP elastomer's performance and developing high performance PCP elastomer in various operating conditions.
Li, Jing (China University of Petroleum) | Li, Xiangfang (China University of Petroleum) | Wang, Rui (China University of Petroleum) | Zhang, Kai (University of Calgary) | Wu, Keliu (University of Calgary) | Shi, Juntai (China University Of Petroleum) | Xia, Jun (China University Of Petroleum) | Xin, Yinan (China University Of Petroleum) | Liu, Dunqing (China University Of Petroleum) | Miao, Yanan (China University Of Petroleum) | Jiang, Mingjie (China University Of Petroleum) | Ge, Zimo (China University Of Petroleum)
Characteristics of sorption and distribution of water in shale porosity are topics of great interest for evaluation of unconventional reservoirs. Also, the study of surface force interactions between bound water and pore surface at the nanoscale is significant for understanding the fate of residual treatment water in shale systems. In this work, thickness and stability of water film were investigated by water sorption isotherm on clay and shale samples. Meanwhile, a new approach based on surface forces (disjoining pressure), which result in the instability of adsorbed film transition into condensed bulk liquid, was developed to describe molecule/pore-wall interactions. Our experimental results directly demonstrated the evidence of capillary condensation in hydrophilic clay minerals, however, water would not entirely fill in shale nonopores even in high moist condition. This remarkable finding may be caused by the inaccessibility of water molecules into micropores of organic matter. In addition, water distribution characteristics significantly vary in different sized pores. As the pore size decreases, the scale of surface interaction increases, directly leading to a higher water saturation and a lower critical relative humidity for condensation. Therefore, under a moist condition with certain relative humidity (e.g. RH=0.98), the water distributed in different sized pores mainly as: (i) capillary water in the smaller pores (e.g. <6nm), and (ii) water film in the larger pores (e.g. >6nm). These inorganic porosities blocked by water may be unavailable for gas transport or adsorption capacity in actual shale system with initial water saturation.
Shale gas is a typical unconventional gas resource which is derived from the organic matter within the mudrock and kerogen through biogenic and/or thermogenic processes  The recoverable reserves of shale gas in the United States are estimated to be 24.4×1012m3 , and the gas production from a particular shale reservoir will depend on its storage potential and transport properties [3~5]. Moreover, the initial water saturation or moisture within shale porosity under actual condition will be a significant factor that influence the evaluation of gas deliverability. Present studies showed that the methane adsorption capacity of shale samples in moist conditions would reduce about 40%~90% compared with dry conditions [6~7]. Meanwhile, the presence of pre-adsorbed water would obviously decrease the apparent permeability (or diffusion coefficient) and increase the stress sensitivity of shale matrix [8~10]. Therefore, Understanding how water is stored and distributed in shale system is essential information required for shale-reservoir gas in place estimation and gas production prediction.
Chen, Wenyi (State Key Laboratory of Petroleum Resources and Prospecting, CUPB) | Chen, Mian (State Key Laboratory of Petroleum Resources and Prospecting, CUPB) | Jin, Yan (State Key Laboratory of Petroleum Resources and Prospecting, CUPB) | Lu, Yunhu (State Key Laboratory of Petroleum Resources and Prospecting, CUPB) | Zhu, Jinzhi (Taim Oil Field Branch-CNPC) | Wang, Xiaoliang (Taim Oil Field Branch-CNPC) | Liu, Ming (China University Of Petroleum)
As to the strong sensitivity of shale to drilling fluids, drilling in shale gas wells is still challenging today. People have long hoped to improve the anti-sloughing ability of drilling fluids mainly by designing the proper density, sealing ability and inhibition ability. However there has not been a quantitative criterion to evaluate these parameters or to define "proper". This could lead to high cost of excessive additives, or wellbore instability due to the scarcity of additives.
In this paper, some essential parameters of drilling fluids, which are mud density, sealing ability and inhibition ability, were quantitatively developed based on rock mechanics theories and laboratory survey. The time-dependent fluid-solid-chemistry coupling model for wellbore stability was established to analyze the near-wellbore stress distribution. A dynamic core flow apparatus was used to investigate the shale-fluid interaction and fluid pressure transmission under the simulated HTHP downhole conditions. Shale mechanical parameters were studied under HTHP conditions by applying a true triaxial compression cell.
In the paper, the influences of mud sealing and inhibition ability on wellbore stability were studied. The research results show that the sealing ability and inhibition ability of drilling fluids do play an important role in enhancing wellbore stability. The volume of drilling fluids invading into shale was defined as the "sealing coefficient" to quantify the sealing ability of drilling fluids. The mechanical strength of shale exposed to the drilling fluids for some time was defined as the "inhibition coefficient" to quantify the inhibition ability of drilling fluids. The quantitative cross plot among mud density, sealing coefficient and inhibition coefficient was obtained from fluid-solid-chemistry model according to the field required stability duration and the borehole enlargement ratio. Practically, the combinations of mud additives could be applied to fit the quantitative diagram regarding the cost and convenience.
The field application results indicated that it is reliable to quantitatively design drilling fluids based on the fluid-solid-chemistry coupling theory. A new idea and way of designing drilling fluids and maintaining shale wellbore stability was introduced.
Dongfeng, Zhao (China University of Petroleum, Beijing) | Xinwei, Liao (China University of Petroleum, Beijing) | Yin, Dandan (China University of Petroleum, Beijing) | Li, Zhen (China University Of Petroleum) | Gai, Jian (China University of Petroleum, Beijing) | Huan, Wang (China University of Petroleum, Beijing)
Most oil reservoirs in Changqing Oilfield area are low permeability. After several ten years of production, the effect of water flooding becomes worse and worse as the reservoir enters middle development stages. CO2 flooding is an important method for oil fields in the future to enhance recovery factor. In this paper, based on the data of 253 mature oil reservoirs, a set of potential evaluation method for CO2 flooding were builded to assess the potential of CO2 EOR in Changqing Oilfield.
A numerical model was established to study the effect of the related factors to CO2 miscible flooding and immiscible flooding. These factors are reservoir properties (thickness, Angle, temperature, pressure, depth), rock physical property (porosity, permeability, saturation, permeability differential, fracture development degree and permeability) and fluid properties (viscosity, density). Technical and economic benefits is assessed, to determine screening criteria and index for CO2 miscible flooding, their relative importance, and the index weights. Using comprehensive fuzzy evaluation method, this paper sets up a comprehensive evaluation method of CO2 miscible flooding and immiscible flooding, Which suit for the different blocks of Changqing Oilfield. Comprehensive evaluation value of reservoir was calculated , according to the evaluation method.
With evaluation value of 0.53 as a boundary, CO2 flooding potential assessment of Changqing Oilfield has been done. Among 253 reserviors, 213 reservoirs are suitable for CO2 flooding EOR, which accouts for 84% of the total number of reservoirs within the block. The geological reserves which is suitable for CO2 flooding could be 25.05×108t, equaling to 80% of the total reserves of Changqing Oilfield. Therefore, CO2 flooding has a good application prospect in Changqing Oilfield, and it would bring huge economic benefits to Changqing Oilfield.
Zhang, Cheng (Research Institute of Production Engineering of Zhongyuan oilfield) | Zhang, Qingsheng (Puguang Branch, Zhongyuan oil field) | Chen, Weiguo (Puguang Branch, Zhongyuan oil field) | Liu, Dexu (Puguang Branch, Zhongyuan oil field) | Ou, Tiongxiong (Puguang Branch, Zhongyuan oil field) | Huang, Xuesong (Research Institute of Production Engineering, Zhongyuan oil field) | Chen, Can (Research Institute of Production Engineering of Zhongyuan Oil field) | Chen, Changfeng (China University Of Petroleum)
In this work, the corrosion behavior and mechanical degradation of two types of pipe steel, Inconoy 825 and L360, after two years of high sour environments service in Puguang gas-field were studied. Results demonstrated that a fearful elemental sulfur layer deposited on the inner wall of pipeline, pitting corrosion and hydrogen-induced cracking was observed in L360 pipe. In comparison, no pitting corrosion and hydrogen-induced cracking was found in Inconoy 825 steel pipe due to its excellent resistance to corrosion. Furthermore, mechanical properties (yield strength, impact strength, elongation, hardness, fracture toughness) and stress corrosion cracking were investigated. Results showed that the yield strength decreased obviously and the percentage of elongation increased in Inconoy 825 steel but little change in L360. The analysis a change of the mentioned mechanical characteristics together with the results of the diffusion and tapping of hydrogen of them indicated that the properties degradation of Inconoy 825 pipeline steel after long term service was associated with essential role of hydrogen in these processes.
The consequences of sudden failures and severe corrosion of metallic material in the high sour gas-field, which associated with their exposure to H2S/CO2 containing gas, led to the preparation of evaluation tests of pipeline. However, passing evaluation tests cannot guarantee the safety in actual work condition unless the field experience had been at least two years. As the first attempt to exploit high sour gas-field in China, it is anticipated that this work of Puguang provides valuable data and an essential insight into the corrosion and degradation of pipeline steel services in high-sour environmental.
Hou, J.R. (China University Of Petroleum) | Liu, Z.C. (Sinopec Exploration And Production Research Institute) | Dong, M.Z. (University of Regina) | Yue, X.A. (China University Of Petroleum) | Yang, J.Z. (Dalian University Of Technology)