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Park, J.S. (Research Institute Of Technology) | Ryu, D.W. (Korea Institute Of Geoscience & Mineral Resources) | Ryu, C.H. (Korea Institute Of Geoscience & Mineral Resources) | Lee, C.I. (Seoul National University)
Abstract Microseismicity can be triggered by various dynamic processes related to a hydraulic fracturing treatment. These processes alter the in-situ stress field inside and around the stimulated reservoir volume, due to both creation of new fractures and fluid leakoff into the surrounding rock matrix. The analysis of spatiotemporal dynamics of fluid-induced seismicity can reveal important characteristics of the hydraulic fracturing process. With the knowledge of treatment data, it can be used in conjunction with the reservoir geomechanical theories in hydraulic fracture growth to investigate the fracture geometry and fluid-rock interactions. By applying these theories to a real microseismic dataset, two types of triggering front expansion patterns are evident. With the presence of a dominant hydraulic fracture, the radius of the triggering front expands linearly with time. Moreover, the microseismic event cloud forms a planar shape with low opening angles (failed by shear), indicating fracture slippages around the major hydraulic fracture. On the other hand, in the case of a complex fracture network with the absence of any major hyfraulic fracture, the triggering front grows non-linearly with time. This scenario can be treated as equivalent to a diffusion model and the microseismic events exhibit a higher fracture of tensile components (either opening or closing) and an equidimensional event cloud. In this study, two stages were analyzed and the derived fracture widths and fluid-loss coeffcients fall into a realistic range of general observations in the context of these two theories.
Ye, Qinyou (Jilin Oilfield Company, Petrochina) | Wang, Feng (Jilin Oilfield Company, Petrochina) | Wang, Yucai (Jilin Oilfield Company, Petrochina) | Zhu, Yongzhi (Jilin Oilfield Company, Petrochina) | Xu, Jianguo (Jilin Oilfield Company, Petrochina) | Li, Xingke (Jilin Oilfield Company, Petrochina) | Yang, Gao (RIPED, Petrochina)
Abstract Pulley-free directly-connected hydraulic pumping unit lift technology, developed based on the characteristics of Jilin Oilfield, can be applied to produce cost-effectively the difficult-to-produce reserves, and to improve the low fluid production and reduce the high energy consumption of developed oilfields. Featuring low cost, low energy consumption and high efficiency with one unit serving several wells, this technology can meet the lift demand of different flow rate at different well depth. The hydraulic pumping system consists of three discrete units, namely main frame, hydraulic station and electric cabinet. The piston and sucker rod of the main frame are connected directly. When the system works, the pump of the hydraulic station provides power for the hydraulic cylinder of the main frame, which drives directly the reciprocating movements of the sucker rod to lift fluid via the reciprocating movements of the piston. The centerline of the main frame coincides with that of the casing, and so there is no unbalance loading. Substituting for the polish rod, the piston rod of the pumping unit connects directly with the sucker rod. The elimination of pulley, wire rope, rope hanger and packing box minimizes the wear parts of the system. Besides, when the system is in service, the main frame can be disassembled like tubing, having no impact on workover. The electric cabinet acquires signals via the displacement sensor and pressure sensor on the main frame and processes them, with such information as indicator diagram, stroke and stroke times displayed on the touch screen. The ground equipment in this technology has light weight, which is about 15% of a beam pumping unit of the same model. With this technology, long stroke, low stroke times, big pump size lift, reduced rod-casing wear, prolonged maintenance free period and improved operation efficiency can be realized. Compared with existing pumping units, its investment in equipment is less. The cost of a twin well system can be reduced by more than 30%, and the energy conservation at the same fluid production rate is above 25%. By December 2016, 24 wells of different depth in Jilin Oilfield had been subjected to pilot test successively. The "one driving one" hydraulic pumping units applied to two wells had operated stably for more than 700 days free of trouble, and the pumping efficiency had been improved by 35% compared with other types. The successful application of this system has verified its overall stability and its adaptability to the extremely cold environment in the northeast China. The "one driving two" hydraulic pumping units had been applied to 22 wells, and the test results show that both the process flow and the system are stable.
Explanations for how fracturing works are often based more on the imaginations of experts than observations of the damage caused by hydraulic pressure. A rare study that spent the tens of millions of dollars required to get a direct look at horizontal wells drilled in South Texas (URTEC 2670034) described its findings as "very different from the simple view of the stimulated reservoir volume commonly modeled or predicted with current fracture models." The paper added: "The absence of proppant on most of the hydraulic fractures indicates that proppant emplacement is quite different from idealized transport model predictions." And, "The apparent side-by-side propagation of closely spaced, near parallel hydraulic fractures also differs from the output of currently accepted fracture models and may call into question the role of stress shadowing in hydraulic fracture propagation." When the paper was delivered at the Unconventional Resources Technology Conference (URTEC) last August, it generated a lot of buzz among experts starved for direct observations.
Lv, Yanjun (China University of Petroleum-Beijing) | Zhang, Guangqing (China University of Petroleum-Beijing) | Zhao, Zhenfeng (Oil & Gas Technology Research Institute) | Wang, Yue (State Key Laboratory of Petroleum Resources and Engineering)
ABSTRACT: Hydraulic pulse fracturing technology, which is applied to the reservoir rocks by instantaneous pulse pressure, can form fractures not perpendicular to the direction of minimum stress in the tight rocks. It is of great significance for the production development of low permeability reservoir and repeat treatment of old oilfield. In this paper, the influence of hydraulic pulse on hydraulic fracture is studied by a large scale of true triaxial physical simulation test. Test conditions of four experiments focus on the influence of peak pressure and pulse times on hydraulic fractures, respectively. The experiment is divided into two stages, conventional hydraulic fracturing and hydraulic pulse fracturing. Experimental results show: Hydraulic pulse fracturing can form fractures in different directions, especially not perpendicular to the direction of minimum stress. A single hydraulic pulse can form many small cracks, and repeated pulses can make cracks extend fully and eventually develop into a network of complex fractures. In hydraulic pulse fracturing with a higher peak pressure, there are fewer hydraulic fractures being formed, but the size of them are larger than fractures of conventional hydraulic fracturing.
In the 1850s, people began to study how to create artificial fractures in the reservoir to improve the efficiency of oil and gas production. The methods of forming artificial fractures can be classified into three types: hydraulic fracturing, gas fracturing and explosion fracturing (Ma and Zhang, 2002, King, 2010, Gandossi, 2013, Zhou 2017).
Gas fracturing and explosion fracturing can form a network of complex fractures. Their influence reach only a small area because of limited energy. And they may cause formation damage, casing failure, and unpredictable fracturing effect (Liu and Ma, 1991, Han and Yang, 1992, Pu, 2015). Hydraulic fracturing has predictable results and causes less damage to the formation and casing. However, hydraulic fracturing often only forms a single fracture, the direction of which is controlled by ground stress. Sometimes, the stimulation of hydraulic fracturing may be difficult to reach the target expected and with a huge cost (Wang, 1987, Zhang, 2013, Fan, 2014).