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Yongjun, Lu (Langfang Branch of Research of Petroleum E&D. CNPC) | Yandong, Chen (Langfang Branch of Research of Petroleum E&D. CNPC) | Zhongyang, Zhao (Langfang Branch of Research of Petroleum E&D. CNPC) | Zhenduo, Wang (Langfang Branch of Research of Petroleum E&D. CNPC)
This paper was prepared for presentation at the 1999 SPE International Symposium on Oilfield Chemistry held in Houston, Texas, 16-19 February 1999.
Wenjun, Wang (China University of Petroleum and Petrochina Daqing Oilfield Co. Ltd.) | Lin, Wang (Petrochina Daqing Oilfield Co. Ltd) | Xingfu, Zhang (Petrochina Daqing Oilfield Co. Ltd) | Sun, Qingyou (Petrochina Daqing Oilfield Co. Ltd) | Tang, Pengfei (Petrochina Daqing Oilfield Co. Ltd) | Haitao, Wang (Petrochina Daqing Oilfield Co. Ltd) | Zhongsheng, Wu (Petrochina Daqing Oilfield Co. Ltd) | Qingtiao, Zhang (Petrochina Daqing Oilfield Co. Ltd)
Abstract For shallow burying, the temperature is less than 30°C and low pressure in Putaohua formations in Chaoyanggou area in Daqing oilfield. Eight horizontal wells have been drilled in the area and need hydraulic fracturing to improve the oil production. Two challenges have to be faced. One is how to rapidly completely breaking for gel at the low temperature and improve the flow-back ratio of fracturing fluid after the fracturing, to reduce the formation damage. It is difficult to gel breaking quickly with conventional breaker in the conventional hydraulic fluid system under the super low temperature. Another one is how to improve the production of fracturing in the horizontal wells. According to the characteristic of the horizontal wells in the low temperature, low pressure reservoir, some new technologies have been used in the 8 wells fracturing jobs, such as a new type low temperature breaker, a new type of cleanup, mechanical isolation staged fracturing. In this paper, we provide details about these new hydraulic fracturing techniques applied in the horizontal wells. The Application in eight wells just as the following aspects: According to the study in the lab, a new type of fracturing fluid system has been used to suit the low temperature. At 30°C, after 4h later, the fracturing fluid was broken, and the viscosity of fracturing fluid is 3.5mPa.s. Mechanical isolation and staged fracturing with two packers is used in the horizontal wells with high efficient treatment about 4 to 6 stages per day to improve the oil production. Base on above all, we get the good result of oil production on the 8 horizontal wells, about 5.2 times higher than that on vertical fracturing wells at the same area. In this paper, we provide details about these new hydraulic fracturing techniques applied in the horizontal wells. These new technologies of fracturing provide an effective method for the horizontal wells in low temperature reservoirs in Daqing oil field.
Yang, Jiang (RIPED-Langfang, PetroChina) | Cui, Weixiang (RIPED-Langfang, PetroChina) | Duan, Yaoyao (RIPED-Langfang, PetroChina) | Yang, Zhanwei (RIPED-Langfang, PetroChina) | Qiu, Xiaohui (RIPED-Langfang, PetroChina) | Guan, Baoshan (RIPED-Langfang, PetroChina) | Lu, Yongjun (RIPED-Langfang, PetroChina) | Zhai, Wen (RIPED-Langfang, PetroChina) | Liu, Ping (RIPED-Langfang, PetroChina) | Ding, Yunhong (RIPED-Langfang, PetroChina) | Bai, Jianwen (Changing oilfield company, PetroChina)
Abstract A new fracturing fluid based on supramolecular complex of associative polymer and wormlike micelle was developed and applied in a gas well in China. The crosslink complex gel was based on weak physical attractive force such as van der waals, hydrogen bonding and electrostatic interaction between associative polymer and wormlike micelle. The fluid contained much less surfactant than that of conventional viscoelastic surfactant. The associative polymer is used at less than 0.25% by weight. The gel is reversible, and has 50% lower formation damage than that of conventional guar. The mixture of the two fluids synergistically enhances the viscosity ten times more than individually combined. The viscosity of fluid can maintain at the test temperature and suspend proppant up under static condition. The dynamic proppant transport test in flow tube also showed good proppant suspension ability. The fluid was simple to prepare with less additives, and formed gel instantly upon mixing in the field. The gel can be completely broken with no residue by an internal breaker. Field application of the new fracturing fluid in a gas well of Sulige basin in China showed the enhancement of gas production over 100%. The fracture height is also well controlled. The fluid also has 20% lower friction pressure than that of guar fluid. Hence, the supramolecular complex gel provides a new fracturing fluid system with less formation damage for fracturing operation.
ABSTRACT The success of hydraulic fracturing as a production stimulation technique is controlled to a large degree by the depth of penetration of the fracture system. The loss of fluid to the formation adjacent the fracture governs the fracture extent and depends upon three flow mechanisms which are controlled by the viscosity and the permeability of the formation to the fracturing fluid, its wall-building properties, or the combined effects of viscosity and compressibility of the reservoir fluid. The effects of these flow mechanisms can be evaluated in terms of a fracturing-fluid coefficient, the fundamental concepts of which are developed in the paper. The coefficient can be used in calculating the areal extent of fracturing. The fracturing-fluid coefficient affords a direct measure of the fluid's effectiveness, because the area of hydraulically created fractures is increased as the coefficient is decreased. The fifteenfold variation noted in this coefficient for the commercially available fracturing fluids tested resulted in a sixfold difference in the calculated areal extent of the fracture system. INTRODUCTION A review of hydraulic-fracturing technology over the last few years reveals a marked trend towards larger volume, higher injection-rate fracturing jobs. This trend is reaching a limit primarily because of pressure limitations and friction losses encountered in tubular goods installed in wells. In an effort to use the best fracturing fluids available it appears advisable to analyze carefully those factors which control or determine the fracture extension that can be produced with various types of fracturing fluids. This paper presents a discussion of the effect of fracture penetration on well productivity, develops a formula for calculating the extent of fracturing, and presents a method of determining the optimum fluid characteristics for maximum fracture extension for various types of fracturing fluids. With the methods presented it is possible to arrive at the best treatment, both from a productivity and an economic standpoint. Such calculations are important in that fracturing services are available from 30 companies, each offering a variety of fluids. Variations in both cost and physical characteristics of these materials affect the economics of the operation and the effectiveness of the treating procedure. EFFECT OF FRACTURE AREAL EXTENT ON WELL PRODUCTIVITY Analytical and electrical model studies have shown the influence of fracture penetration on both the flush and stabilized production that may be obtained from a given reservoir with a given fracture system. Such studies have shown that a fracturing treatment is influenced not only by the flow capacity of a hydraulically created fracture but also, to a large degree, by the areal extent of the fracture. The benefits derived from fracturing may be classified as flush production and post-flush production. Flush Production The effect of fracture penetration on the flush production immediately following a fracturing treatment has been illustrated by analytical calculations. Typical results of these calculations are presented in Fig. 1, which-is a plot of producing rate vs. time on a logarithmic scale for the conditions shown. Fig. 1-Effect of Fracture Radius on Production Rate (After Bearden, Wilsey AlME TP 3788)
Abstract This paper evaluates polymer fluid cleanup in general and more specifically why Cotton Valley fracture treatments recover less than one half of the injected polymer. The inefficient cleanup is expected to explain why post-fracture well testing often indicates a smaller fracture length and conductivity than anticipated. Numerical simulations were performed on a typical fracture treatment using a compositional reservoir model and considered a range of yield values for the rheology of the fluid remaining after leakoff. The yield value range was based on that provided by an independent laboratory. Simulation results compare favorably to actual field production and well tests. The yield value for the polymer residue was introduced into the simulator by newly derived flow relations based on the Herschel-Bulkley yield power-law model. The paper presents these relations and the method for inclusion into a compositional reservoir model. Simulations indicate that the fracture only cleans up to a length governed by the yield stress of the fluid and multiphase effects. Without a yield value, the complete length would eventually clean-up if nominal values of dimensionless conductivity are provided. This study represents the first attempt to investigate the effect of yield stress in fracture fluid cleanup. The results suggest that yield stress and relative permeability effects are the dominant mechanisms controlling the cleanup of the fracture and that the cleanup length is determined before gas breakthrough. A curve is presented which relates effective fracture length to polymer yield stress. This type of relation, developed for specific reservoir conditions, can be used to adjust the predicted fracture length and permit more accurate project evaluations without the need for detailed simulation of every fracture treatment. Introduction Fracture fluid cleanup is one of the most important aspects of a fracturing treatment. For many years the relationship between load recovery and post-fracture productivity has been known but only recently have the various mechanisms affecting cleanup been characterized. Research to date has identified five major contributing mechanisms to fracture cleanup and proppant pack permeability. These mechanisms are (1) the effects of time and temperature on proppants, (2) gel residue and its damage to the proppant pack, (3) viscous fingering through the proppant pack, (4) the effects of unbroken fluid on proppant pack permeability, (5) non-Darcy and multiphase fluid flow effects, and (6) capillary pressure (water block) effects. Pope. et al studied guar removal after hydraulic fracturing in the Codell formation of Colorado. This report shows that load recovery is not the key driver in fracture fluid cleanup. They suggest that a better gauge of cleanup would be to measure the amount of polymer recovered, because polymer recovery and load recovery are not always proportional. Willberg, et al performed a similar analysis of cleanup in the Cotton Valley formation of East Texas. They reach similar conclusions as Pope, however their work better characterizes the entire flowback period. They found that in formations which produce significant formation water, that formation water production begins almost immediately upon flowback and that this occurs before gas breakthrough. In addition, they noted that the flowback polymer concentration is generally less than or equal to the average pump-in polymer concentration. Also, they found that only about 35% of the total guar pumped is recovered, with the majority being returned in the initial flowback period, and that the flowback rate does not effect the amount of polymer recovery when formation water is also produced. In another study, Pope, et al studied the viscous fingering of fluids through the proppant pack. They observed that the permeability reduction in the proppant pack caused by viscous fingering can be attributed to a reduction in the effective porosity of the pack. P. 517^