Adsorption Research of Polymer on Oil Sands in Qidongyi Block of Xinjiang Conglomerate Reservoir

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1 Applied Mechanics and Materials Online: -7- ISSN: -78, Vols. 8-8, pp 8- doi:.8/ Trans Tech Publications, Switzerland Adsorption Research of Polymer on Oil Sands in Qidongyi Block of Xinjiang Conglomerate Reservoir NIE Xiaobin, GUO Ying,a LOU Qingxiang, LIU Weidong,b SUN Linghui and LI Jiye Experimental detection research institute of Xinjiang Oilfield, Karamay Xinjiang 8, China; Xinjiang Uygur Autonomous Region key laboratory of reservoir, Karamay Xinjiang, 8, China; Institute of Porous flow & Fluid Mechanics, University of Chinese Academy of Sciences,Langfang, Hebei, 7 China; Langfang Branch of PetroChina Research Institute of Petroleum Exploration & Development, Langfang, Hebei, 7,China. Oil Testing and Perforating Company, Daqing Oilfield Company, PetroChina,Daqing, China a guo8y@.com; b lwd9@petrochina.com.cn. Keywords: Conglomerate reservoir; polymer;; static adsorption; dynamic retention. Abstract. In the process of polymer flooding in porous media, polymer was detained due to interactions between surface adsorption and polymer molecules, and this could lead to negative effects on oil displacement. For polymer adsorption in Xinjiang reservoir, HPLC analysis was adopted to study the static and dynamic laws. Results have showed that the adsorption process could be divided into stages: rapid growth, slow growth and stable state. With the loss of polymer molecular weight, equilibrium adsorption quantity reduces gradually. The adsorption amount is different for the same polymer on four types of oil sands. For equilibrium adsorption, the maximum value is argillaceous sandstone, followed by conglomeratic sandstone.the third is argillaceous gravel, and the minimum is sand gravel. For polymer flooding in cores, the dynamic retention amount of seriate is much greater than that of fine particle. These data have provided reference for project design of polymer flooding in reservoir. Introduction During the course of polymer flooding in porous media, polymer solution would be diluted by formation water, and it was stranded due to surface adsorption, mechanical capture, hydrodynamic trap and the interactions between polymer molecules[]. It is certain that this retention could lead to negative effect on oil displacement. For the polymer on surface of core particles, adsorption amount are affected by many factors, which are the types of polymer, molecular weight, degree of hydrolysis, salinity, rock composition, surface properties of particles, environmental temperature and so on. Compared with small molecules for solid-liquid adsorption, macromolecule polymer solution has many traits[]. Nowadays, there are a lot of research on application of polymer flooding in sandstone reservoir. For polymer in sandstone, adsorption is in keeping with the Langmuir isotherm adsorption law. Rarely research has focused on polymer adsorption in reservoir. No comparison study has been published currently about sandstone and glutenite. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID:...7, Pennsylvania State University, University Park, USA-//,::8)

2 Applied Mechanics and Materials Vols Experimental conditions and methods Experimental material These adsorption experments are correlated with four types of polymer, whose molecular weight is million, million, million and million respectively. Xinjiang oilfield has provided the products of polymer. The hydrolyzing degree is %, and the solid content is 9.%. Formation water and injected water were simulated by medicals, and the specific ion content were shown in table. In these experments, oil sand particles could be divided into four types, which are argillaceous sandstone,conglomeratic sandstone, argillaceous gravel and sand gravel. All oil sands and core samples had came from Qidongyi block in Xinjiang oilfield. Table. Salinity of formation water and injected water for Qidongyi Block in Xinjiang oilfield Category - HCO Cl - - SO Ca + Mg + K + and Na + Salinity Injected water(mg/l) Formation water(mg/l) Experimental procedure Static adsorption Firstly, a series of polymer solution were conducted with the known concentration to get criterion concentration curves,, then it is need to determine the relationship of concentration with optical density by high performance liquid chromatography (HPLC) analysis[]. Oil sand particles were mixed with polymer solution which were deployed with different concentration. The weight of oil sand is. gram for each test sample, and solid to liquid ratio is :9. The mixture was put in water-bathing constant temperature vibrator for hours at. []. The mixture was separated by high-speed centrifuge after oscillation to get solid and liquid respectively. Concentration can be got by using HPLC after adsorption of oil sands in polymer solution. According to optical density of test samples, their polymer concentration can be computed by standard curves[]. Adsorption was calculated by fomula (). Γ = ( C C ) G V () C Where,Γ is static adsorption capacity,mg/g;g is quality of oil sands, g; and C are polymer concentration before and after adsorption respectively, mg/l,v is the volume of solution, ml. Dynamic retention After selection of cores, it is also need to get the quality of each core. These cores were put in a vacuum for 8 hours, then they were saturated by formation water. Parameters such as porosity and permeability are available by relevant experimental instruments. Polymer solution was injected into cores after being kept in thermostat for hours at.. Collected at export of displacement device, polymer solution was analysed by HPLC to get the specific cconcentration[]. When the concentration of injected polymer is equal to that of effluent, it is time to stop injecting polymer and to end this experiment. Dynamic retention was computed by equation (). A r t CV f CdV = W V () Where, Ar is the retention capacity of polymer,mg/g; C is the concentratin of injected polymer, mg/l; V f is the volume of injected polymer,ml; C, V are the concentration and volume of polymer

3 Advances in Civil and Industrial Engineering IV of effluent samples separately,ml; V t is the total volume of injected polymer and water,ml; W is the weight of core, g. Experimental results and analysis Static adsorption Four kinds of oil sands were employed in these experiments, and they were argillaceous sandstone, conglomeratic sandstone, argillaceous gravel and sand gravel. Argillaceous sandstone and conglomeratic sandstone contain a certain amount of clay and gravel respectively. Argillaceous gravel and glutenite refer to the having a small quantity of mud and sand separately. The results of polymer static adsorption experiment were showed in figure. With the increase of polymer concentration, the adsorption quantity also enhanced gradually for one unit quality of oil sands. As surface coverage fraction (solute on the surface of the oil sand particles) increasing, the adsorption of particles gradually reached equilibrium status when the polymer concentration is about 7 mg/l. The whole adsorption process can be divided into three stages: Stage I: With the increase of polymer concentration, individual molecule accelerates to the surface of adsorbent, and the number of polymer molecules increases quickly on surface of oil sands. It also shows that the thread size of a single polymer molecule is small in the dilute solution, so the activated adsorption bits occupied by individual molecule are relatively less. Stage II: Adsorption quantity increases slowly. When the adsorption of polymer on the adsorbent has reached a certain degree, a few of adsorption bits exists on the surface. Adsorption volume changes slowly with the increase of polymer concentration, and monolayer adsorption is basically saturated. Stage III: State of dynamic stable equilibrium. Saturated by monolayer adsorption, parts of surface have adsorbed two or more layers of molecules. On the surface of adsorbent, polymer in the solution would act on molecules which had been adsorbed by particles, so polymer may be associated together. When the concentration reaches critical associating point, a structure of dynamic physical crosslinking network was formed by polymer s mutual combination. In the solution, individual polymer molecule was impacted by both of adsorbed molecules and association aggregation. Adsorption of particle surface is in the state of dynamic stable equilibrium. Because of interactions of ions and molecules in the solution, rates of adsorption and desorption are differrent. The adsorption on surface of various particles is different for the same polymer at adsorption equilibrium. For equilibrium adsorption, the maximum value is from argillaceous sandstone, followed by conglomeratic sandstone.the third is argillaceous gravel, and the minimum is sand gravel. Under the condition of same quality of oil sands, larger surface area is beneficial to the adsorption of polymer at active point. Take million molecular weight for example, both the surface area of argillaceous sandstone and the adsorption activity point are the maximum, and the adsorption quantity is. mg/g for argillaceous sandstone. For conglomeratic sandstone, argillaceous and sand gravel, the adsorption are. mg/g,. mg/g, and.8 mg/g respectively.

4 Applied Mechanics and Materials Vols. 8-8 (a) (b) (c) (d) Fig. Static adsorption of polymer on oil sands (a, b, c, d are the polymer of molecule weight million, million, million and million respectively, these abbreviations of,, and are argillaceous sandstone, conglomeratic sandstone, argillaceous gravel and sand gravel separately) These curves of adsorption isotherm presented "L" type. The polymer adsorption is in keeping with the Langmuir isotherm law. Under the same polymer concentration, due to the extension of molecular chains, small molecular weight of polymer has more freedom. It is easy to contact with adsorption activity bits for smaller molecule. At the same time, smaller molecular weight polymer is more likely to deviate from the sands surface for less chance of association and more freedom, so the adsorption for small molecule is much more than that of high molecule. Dynamic retention When polymer flows in porous media of reservoir, hydrodynamic trapping and mechanical capture would occur on the rock surface due to its pore structure and permeability heterogeneity[7]. It is generally considered that four mechanisms have caused the polymer retention, and they are surface absorption, mechanical capture, capture of fluid dynamics and interactions between polymer molecules[8]. Dynamic retention experiments have simulated the retention phenomenon when polymer flows through the reservoir. These cores can be divided into two categories, fine particle and seriate. These experiments involved gravel particles whose diameter is between and mm. The fine particle s diameter is in uniform distribution of to mm, while the seriate particle diameter is in uneven distribution between and mm.

5 Advances in Civil and Industrial Engineering IV Core numbers Table. Dynamic retention capacity of polymer in different cores Category Molecule Water Concentration Retention weight permeability(md) (mg/l) capacity(mg/g) (million) Fine particle.. Fine particle.. Fine particle..7 Seriate..7 For core numbers of,,and, dynamic retention of fine particle were. mg/g,. mg/g and.7 mg/g separately. The difference of quantity is very small in polymer dynamic retention. The dynamic retention for core number is.7 mg/g, which is significantly greater than that of fine particle in table. In seriate cores, more adsorption activity points, pore throat structure and particle surface are beneficial to the adsorption retention. In the process of core flowing, polymer solution does not go along with the wall of hole. It is difficult to spread to areas with small permeability for polymer solution in the cores, so value of dynamic retention is much smaller than that of static adsorption. Conclusions.The static adsorption process could be divided into stages: rapid growth, slow growth and stable state. Due to differences from composition of sand particle, surface areas and adsorption activity points, the maximum value of equilibrium adsorption is from argillaceous sandstone, followed by conglomeratic sandstone. Argillaceous gravel is less than conglomeratic sandstone, and the minimum is from sand gravel..multilayer adsorption and intermolecular association would occurred on the surface of oil sands. Polymer adsorption for million molecular weight is the largest, followed by million molecular weight. The third is million molecular weight, and the minimal adsorption is million molecular weight. Determining the allocation of pore throats, particle size distribution has a significant impact on polymer retention. The dynamic retention for seriate is significantly greater than that of fine particle. Acknowledgements The authors wish to thank the experimental detection research institute of Xinjiang Oilfield, Xinjiang Uygur Autonomous Region key laboratory of reservoir, and Langfang Branch of PetroChina Research Institute of Petroleum Exploration & Development, under which the present work was possible. Reference [] Chengzhi Yang. The chemical flooding enhancing oil recovery. Beijing: Petroleum industry press (999), p.7-7. [] Shiyu Ma. Polymer and practical method of reservoir engineering. Beijing: Petroleum industry press (99), p.-. [] Yefei Wang, Dingyong Zhang, Xiaoming Le. Journal of the University of Petroleum, Vol. (), p.9-.

6 Applied Mechanics and Materials Vols. 8-8 [] Zhongqiang Tian, Chunyan Sui, Guozhuang Wang. Oilfield Chemistry, Vol.9 (), p.9-7,. [] Daoshan Li, Jirui Hou, Ruijuan Xu. Oilfield chemistry, Vol. (), p.8-. [] Jinbang HU, Xuejun Li, Chenglin Han. Oilfield Chemistry, Vol. 8(99), p.-. [7] Puhua Yang, Chengzhi Yang. Chemical flooding enhancing oil recovery. Beijing: Petroleum industry press, (998). [8] Rui Weng. Oil and gas recovery technology, Vol. (998), p.-.

7 Advances in Civil and Industrial Engineering IV.8/ Adsorption Research of Polymer on Oil Sands in Qidongyi Block of Xinjiang Conglomerate Reservoir.8/

Study on the change of porosity and permeability of sandstone reservoir after water flooding

IOSR Journal of Engineering (IOSRJEN) ISSN (e): 2250-3021, ISSN (p): 2278-8719 Vol. 06, Issue 02 (February. 2016), V2 PP 35-40 www.iosrjen.org Study on the change of porosity and permeability of sandstone