Research and Application of a New Type of Water Flooding Characteristic Curve in Oilfield Development

Transcription

1 Advances in Petroleum Exploration and Development Vol. 11, No. 2, 2016, pp. 1-5 DOI: /8394 ISSN X [Print] ISSN [Online] Research and Application of a New Type of Water Flooding Characteristic Curve in Oilfield Development ZHOU Zhibin [a],* ; WANG Jiexiang [a] [a] School of Petroleum Engineering, China University of Petroleum (East China), Qingdao, China. *Corresponding author. Received 17 April 2016; accepted 1 June 2016 Published online 26 June 2016 Abstract During the exploitation process of an oilfield, the traditional water flooding characteristic curve is not suitable for high water cut period. It often appears downwarping phenomenon in high water cut stage, so the prediction accuracy of water drive development becomes bad. Therefore, the paper has presented a new type of water flooding characteristic curve, which has good adaptability in high water cut stage. Based on the characteristics of oil-water relative permeability and water saturation curve, the new type of water flooding characteristic curve put forward a new method to characterize the flow characteristics, considered the limit of water drive development, and gave a simple method of parameter calculation. The new water flooding characteristic curve can reflect the high water cut reservoir seepage characteristics. The traditional water flooding characteristic curve is a special case of the new water flooding characteristic curve when the recovery percent of reserves is low. The new water flooding characteristic curve can be used to carry out the actual field application. The results showed that the prediction accuracy of the new water flooding characteristic curve was increased by 5.42%, compared with the traditional water flooding characteristic curve. The new water flooding characteristic curve has better adaptability than the traditional water flooding characteristic curve in high water cut stage. Key words: High water-cut stage; Water flooding characteristic curve; Relative permeability; Water saturation; Upwarping phenomenon Zhou, Z. B., & Wang, J. X. (2016). Research and application of a new type of water flooding characteristic curve in oilfield development. Advances in Petroleum Exploration and Development, 11(2), 1-5. Available from: URL: DOI: INTRODUCTION Water flooding characteristic curve is one of the important reservoir engineering methods for the calibration of the recoverable reserves and the prediction of reservoir dynamics by water injection [1]. With the continuous deepening of the research on the water flooding characteristic curve, it is found that in the late stage of water flooding development, the water flooding characteristic curve in semi logarithmic coordinates was no longer a straight line, and the upwarping phenomenon happened. If using the traditional water flooding characteristic curve, the prediction error of recoverable reserves and recovery will be very large by linear extrapolation. Indoor experimental study found that the relationship curve of the ratio of oilwater relative permeability and water saturation in the semi logarithmic coordinate appeared downwarping phenomenon [2-3] in high water cut stage. The traditional method of characterizing percolation property is no longer applicable. Chen Yuanqian [4] deduced the characteristic curve of the type A and B in high water cut stage and pointed out the reasons of the upwarping phenomenon; Yu Bo [5] analyzed the influence of different factors on the dynamic prediction of the upwarping phenomenon; Yang Yong [6] put forward the correction method of water flooding characteristic curve in high water cut stage. On the basis of the above, starting from the characteristics of oil-water relative permeability and water saturation curve, a new method to characterize the seepage feature has been proposed, and a new type of water flooding characteristic 1 Copyright Canadian Research & Development Center of Sciences and Cultures

2 Research and Application of a New Type of Water Flooding Characteristic Curve in Oilfield Development curve has been derived finally in this paper. The new curve can well reflect the high water cut reservoir seepage characteristics, and the conventional water flooding characteristic curve is a special case of the new water flooding characteristic curve, when the recovery percent of reserves is low. 1. CHARACTERIZATION OF SEEPAGE FEATURE EQUATION The theoretical foundation of the water flooding characteristic curve is the seepage characteristic equation and the material balance equation, and the most water flooding characteristic curves are based on the linear relationship [7-8] between the ratio of oil-water relative permeability and water saturation in the semi logarithmic coordinate.. (1) k ro -Relative permeability of oil phase; k rw -Relative permeability of water phase; S w -Water saturation; m, n- Constant. But a lot of water flooding experiment [9-10] (Figure 1) found that the relationship curve of oil-water relative permeability ratio and water saturation in the semi logarithmic coordinates appeared downwarping phenomenon [11-12] in high water cut stage, Formula (1) cannot characterize this phenomenon obviously. Therefore, many researchers [13-14] proposed the seepage characteristic equations of characterization of the downwarping section. Although these equations can better reflect the downwarping phenomenon, these equations only fit the curve in form and ignore the issues of the limit when the water saturation tends to 1. In general, the displacement ratio of the traditional phase permeability experiment is small, which makes the core driving is not sufficient, so that the oil and water characteristics can not be fully reflected. Therefore, it need to carry out the water flooding experiment of high power. Figure 2 is the phase permeability curve of the conventional water flooding and high power water flooding. By curve, we can see that with the increase of water saturation, oil phase relative permeability decreased and water saturation increased. With the displacement ratio increasing, the residual oil saturation became smaller and smaller. When the displacement ratio is large enough, the water saturation can be close to 1 [15-16].. (2) When the water saturation is close to 1, Formula (1) is. (3) Formulas (2) and (3) contradict each other apparently. In view of the above problems, a new seepage characteristic equation is proposed to characterize the relationship between the ratio of oil-water relative permeability and water saturation. k ro ln = a + bsw + c ln(1 Sw ). (4) k rw a, b, c Constant. Using the new seepage characteristic equation, the downwarping section of the laboratory data in block A of Gudong Oilfield was fitted (Figure 1). It can be seen that the new seepage characteristic equation is a good representation of the relationship between the ratio of oilwater relative permeability and water saturation in high water cut stage. Figure 1 Relationship Between the Ratio of Oil-Water Relative Permeability and Water Saturation in High Water Cut Stage Copyright Canadian Research & Development Center of Sciences and Cultures 2

3 ZHOU Zhibin; WANG Jiexiang (2016). Advances in Petroleum Exploration and Development, 11(2), 1-5 Figure 2 Relationship Between Oil-Water Relative Permeability and Water Saturation Under Different Displacement Ratio 2. DERIVATION OF A NEW TYPE OF WATER FLOODING CHARACTERISTIC CURVE Without considering the influence of capillary force and gravity, water-oil ratio in water flooding process can be expressed as:. (5) WOR-Water-oil ratio; Q w -Water production, t/d; Q o -Oil production, t/d; μ w -Viscosity of formation water, mpa s; μ o -Viscosity of formation oil, mpa s; Bw -Volume factor of formation water; B o -Volume factor of formation oil; γ w - Relative density of surface water; γ o -Relative density of crude oil. By combining Formula (5) and taking the logarithm, it can be obtained:. (6) After entering extra high water-cut stage, there is the following formula [17] :. (7) -Formation average water saturation. In addition, the following formula can be obtained from the mass balance equation:. (8) S wc -Irreducible water saturation; R-Recovery percent of reserves. According to Formulas (6), (7), (8), the following formula can be obtained: B= b(1-S wc ), C= c. The Formula (10) is the new type of water flooding characteristic curve which reflects the extra high water-cut stage. When the recovery percent of reserves is lower, ln(1-r) 0, the Formula (10) becomes: 1gWOR=A+BR. (11) The Formula (11) is a familiar type of water flooding characteristic curve. It can be seen that the Formula (9) is a special case of the new water flooding characteristic curve. In order to facilitate the field application, this paper presented a new method to calculate the new water flooding characteristic curve. The left and right sides of Formula (10) was done derivation calculus about R. and. (12) show a linear relationship obviously. Then the curve diagram of A and B is drawn. The negative number of straight line slope is the value of parameter C. The linear intercept is the value of the parameter B. Finally, according to the development of dynamic data, it can be calculated to get the value of the parameter A. In order to improve the accuracy, the average value obtained from the multi group data is calculated as the value of A., That is:. (9) lgwor=a+br+c ln(1-r). (10) 3. OILFIELD APPLICATION Taking the block A in Gudong Oilfield as an example, the dynamic prediction of this block is made by using the 3 Copyright Canadian Research & Development Center of Sciences and Cultures

4 Research and Application of a New Type of Water Flooding Characteristic Curve in Oilfield Development new water flooding characteristic curve, and the curve is compared with the traditional water flooding characteristic curve. The block has been developed since At present, the water yield of block A has reached 97.9%. According to the data of development, the Formula (13) is obtained by fitting the traditional water flooding characteristic curve in the straight line segment. The Formula (14) is obtained by fitting the new water flooding characteristic curve in the upwarping segment. Traditional water flooding characteristic curve: 1gWOR= R. (13) New water flooding characteristic curve: 1gWOR= R ln(1-R). (14) Figure 3 Comparison of the Results of Water Flooding Characteristic Curve of Block A in Gudong Oilfield It can be seen from Figure 3 that the new water flooding characteristic curve can describe the dynamic development of water flooding in high water cut stage better. By the year 2015, the cumulative water injection volume of the block A is million tons, and the cumulative oil production volume of the block A is million tons. The recovery percent of reserves is close to Using the traditional water flooding characteristic curve, the cumulative water injection volume of the block is million tons when the recovery percent of reserves is Using the new water flooding characteristic curve, the cumulative water injection volume of the block is million tons when the recovery percent of reserves is The prediction accuracy of the new water flooding characteristic curve reached 99.26%, and the prediction accuracy of the new water flooding characteristic curve reached 93.84%. Compared with the traditional water flooding characteristic curve, the prediction accuracy of the new water flooding characteristic curve was increased by 5.42%. Therefore, the new water flooding characteristic curve has better adaptability than the traditional water flooding characteristic curve in high water cut stage. CONCLUSION (a) According to the characteristic of oil-water relative permeability and water saturation curve, a new method of characterization of seepage characteristics has been presented, which can fully reflect the characteristics of the seepage flow in high water cut stage. (b) Based on the characteristic equation of seepage flow, a new type of water flooding characteristic curve has been derived and the solution method has been given. It is proved that the traditional water flooding characteristic curve is a special case of the new water flooding characteristic curve, when the recovery percent of reserves is low. (c) The upwarping phenomenon can be characterized very well by the new water flooding characteristic curve in high water cut stage. Compared with the traditional water flooding characteristic curve, the prediction accuracy of the new water flooding characteristic curve was increased by 5.42%. The prediction accuracy of the new water flooding characteristic curve in high water cut stage is better. REFERENCES [1] Feng, Q. H., Chen, X. C., & Sun, M. D. (2012). Study of the multiple-profile control system to enhance oil recovery after polymer flooding. Journal of Petroleum Exploration and Production Technology, 2(3), [2] Hu, G. (2013). A new method for calculating volumetric sweep efficiency in a water-flooding oilfield. Petroleum Exploration and Development Online, 40(1), [3] Craig, F. F. (1971). The reservoir engineering aspects of water flooding (pp ). New York: Society of Petroleum Engineers of AIME. [4] Chen, Y. Q., & Tao, Z. Q. (1997). Derivation of water drive curve at high water-cut stage and its analysis of upwarding problem. Fault-Block Oil & Gas Field, 4(3), Copyright Canadian Research & Development Center of Sciences and Cultures 4

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