Highly porous carbonaceous nonprecious metal catalysts for the oxygen reduction reaction are prepared by carbonization of low-cost metalloporphyrin-based hyper-crosslinked polymers (MPH-X). With high surface area (2768 m g ), hierarchical porous structure, and high metal loading (9.97 wt %), the obtained hyperporous carbon MPH-Fe/C catalyst exhibits high oxygen reduction reaction (ORR) activity with a half-wave potential (0.816 V) that is comparable to the 0.819 V of commercial Pt/C. Stability tests reveal that MPH-Fe/C also exhibits outstanding long-term durability and methanol tolerance. Our findings may offer an alternative approach to produce nonprecious metal ORR catalysts on a large scale owing to the low-cost MPH-X precursors with diverse metal types.
Separate layer oil production technologies in Daqing Oilfield were developed and improved continually with the course of the oilfield development. The technologies in the medium-low water-cut flowing period were mainly composed of the oil well packers, the Model 625 oil well regulators and the multipurpose eccentric regulating & plugging control system. In the early high water-cut artificial lifting period, 4 types of mechanical water shutoff technologies including integrated, equilibrium, slip and drillable ones were developed and applied. Furthermore, the double fluid chemical water shutoff technology was successfully studied. In the late high water-cut artificial lifting period, the water detection technology by temperature log and the profile testing technology provide accurate guides in determining the high water-cut layers. Adjustable intervals mechanical water shutoff technology and the single fluid chemical water shutoff technology could meet the requirements of subdividing oil production and water shutoff for artificial lifting wells. 1. Introduction Daqing Oilfield is a heterogeneous multi-layer sandstone reservoir, whose exploitation strategy is to inject water to keep the reservoirs' pressure. The major oil reservoirs' physical properties are quite different from the secondary ones. During the water injection process, the water & oil distribution and the rule of their motion are extremely complex, commingled production method could lead the injected water underground easily to be finger advanced. Therefore separate layer oil production technologies that are suitable to Daqing Oilfield's real situation were developed in order to reduce these differences among layers, control rising water-cut, fully exploit each single oil layer, and provide vital technical support for high-efficiency oilfield development. Separate layer oil production technologies in Daqing Oilfield were developed and improved continually with the course of the oilfield development, which were fallen into three successive ones: the medium and low water-cut flowing period; the early high water-cut artificial lifting period and the late high water-cut artificial lifting period. This paper briefly introduces the development of separate layer oil production technologies in terms of each period's characteristics, and also presents the future developing direction of Daqing Oilfield. 2. The medium-low water-cut flowing period This period began from the early days of the oilfield exploitation to the end of the 1970s. At that time, the major exploiting reservoirs in Daqing Oilfield were high permeable layers in the main pays and the medium-high permeable layers in the nonpay zones. The separate layer oil production mainly aimed at controlling the injection into the high permeable layers, increasing the injection into the medium-low permeable layers and regulating the distribution of oil and water among layers and planes by the way of separate layer water injection. Therefore, the production from the medium permeable layers could compensate the production from the high permeable ones. When most layers produced water in oil wells and the high permeable oil reservoirs entered into the high water-cut period, it was necessary to enhance the development for medium-low permeable layers in order to reduce the differences among layers. Meanwhile, separate layer oil production and water shutoff measures were taken for high water-cut intervals. The separate layer oil production technologies in the 1960's, which were mainly composed of the oil well packers and the Model 625 oil well regulators, can divide the reservoirs into 4–5 intervals. Adjusting the size of unfixed nozzles in the Model 625 regulators can control each layer's production. As a result, the wells can produce oil from separate intervals quantitatively. The separate layer oil production technology with the Model 625 oil well regulators can effectively ease the contradiction among layers; exploit each oil layer with proportion rate; control the increasing water-cut rate; enhance the production and increase the recovery ratio. It has been applied at more than 2000 wells on site.
Horizontal well technology is a technological revolution in oil industry, and it is one of the most important methods of thick layer sustainable production and marginal low permeable formation exploitation in Daqing Oilfield. It is commonly believed that fracturing is an effective way to recover oil from thin, low porosity and low permeability sands. However, the existing frac technique in the horizontal wells - the limited entry frac is a kind of commingled frac method that cannot guarantee the fractures' opening and extension uniformly owing to heterogeneity formation. A novel sectional frac technique with dual-retrievable packers by separately stimulating the specific intervals one by one has been developed to recover low permeable reservoirs in the horizontal wells. Sectional frac string chosen includes high pressure, high temperature tools which have been used in several wells application as well as long term tested in a laboratory environment to differential pressures of 7300 psi at 190 °F with functions of stuck-preventing, stuck-releasing and reverse sand flushing. Five intervals treatment can be done in one trip. Up to now, this technique has been applied on 55 horizontal wells in Daqing Oilfield and 281 intervals were fractured in the field. It usually takes one to three days to frac a horizontal well according to the numbers of target reservoirs. The initial oil production after using the sectional frac technique in horizontal wells is 5.7 times higher than that in vertical wells, and 1.04 times higher than that by using the limited entry frac technique in horizontal wells. The current oil production after using the sectional frac technique in horizontal wells is 4.3 times higher than that in vertical wells, and 1.72 times higher than that by using the limited entry frac technique in horizontal wells. Field runs and lab testing have confirmed that sectional frac technique is a viable option in recovering low permeable reservoirs in the horizontal wells. Introduction Daqing oil field is a giant, heterogeneous, multilayer sandstone oilfield. After long-terms of water flooding, 95% of main pay zones have been in production and water cut has exceeded 91%. The development of the oilfield has also aimed at relatively thinner and less permeable layers to maintain stable production. For water-flooding oilfields, the thin and poor reservoirs' development strategy is facing a challenge after oilfields has gone into high water-cut period. Usually, many thinner pay-zones are laminated within the thicker reservoir interval penetrated by the well. Thus, it becomes difficult to optimize the injection strategy for individual zones, even though their flow properties may be different, requiring different injection pressures, different additives, or different polymer concentrations. It is commonly believed that horizontal well has larger contact area in the thinner reservoirs compared with the vertical wells. Moreover, fracturing is an effective method to increase conductivity near the wellbore and improve the horizontal wells' performance. Due to the existed deflecting interval and the horizontal interval with target formations, operation with running frac pipe string and string's force status are far different compared with those in vertical wells. Accordingly, conventional frac technique - the limited entry frac is not suitable for stimulating horizontal wells in the Daqing Oilfield. Large size coiled tubing and coiled tubing with through-tubing packer are less used for horizontal wells in Daqing, which are popular in other places. The average horizontal interval length of horizontal wells is 583.7m in Daqing. There are some difficulties met in the horizontal well frac that are listed as follows: High risk of operation: The actual track of horizontal wellbore is so complicate that it is difficult to run the string smoothly in the well in case of string-stuck accident happened.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.