Apple, which occupies the first position in the world with regard to its yield, is an important economic crop in China. Pruning of apple trees is still dominated by manual pruning, resulting in high labor costs and low efficiency. Additionally, there are some limitations with pruning machines. Thus, research regarding the mechanical properties of apple branches is the basis for the designing proper pruning machine. This paper aims to study the effect of the feed rate, cutting line speed, branch diameter, and moisture content on the cutting force. Results revealed that cutting force depended on the feed rate, cutting line speed, and branch diameter. Furthermore, both the cutting line speed and the branch diameter had a significant effect on the cutting force (p < 0.01), while the feed rate had a small effect on the cutting force (p > 0.05). However, the moisture content had no effect on the cutting force, with a difference of cutting force between samples with moisture content of 15% and 50% less than 5%. Based on the experiments performed, an equation relating the feed rate, the cutting line speed, the branch diameter was derived to calculate the cutting force. By verification test, it established that regression equation was valid with error less than 4%. This study explored the mechanical properties of apple branch, and obtained the optimal cutting parameters, which can provide a reference for the design of the pruning machine.

AbstractLost circulation is a frequently encountered problem during workover operations of a low-pressure reservoir. Many lost circulation materials (LCM) have been used to solve the problem, but various disadvantages still exist, for example, oil-soluble materials are easy to get stuck in the pipe string as the temperature drops and gel time and gel strength of the cross-linking gel systems are difficult to control in the occasion of inadequate stirring. A self-breaking supramolecular plugging system used to control lost circulation of workover operations is developed, and it can encounter the aforementioned disadvantages of the traditional LCM. The system forms a space grid structure by non-covalent bonds between the molecules without adding a cross-linking agent. Sand beds plugged with the supramolecular plugging system had a pressure bearing capacity of 4.5 MPa. The self-breaking rate of the supramolecular system was 100% after 7 days at a temperature of 120°C. The core permeability recovery of the self-breaking liquid was 91.9%, indicated that the plugging system is compatible of the reservoir. The supramolecular plugging system has been used in four wells in the Jidong oilfield of East China. Field practice showed that the supramolecular LCM can effectively control lost circulation at different rates during workover operations. The increase in the daily fluid after operations indicated that the slurry has not damaged the reservoir.

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The fault roots of Liuzan north block in Jidong oilfield of China have been long-term explored by solution gas drive. Recently, oil production declined rapidly because of shortage of formation energy and needing high water injection pressure. Carbon dioxide injection pressure is found to be generally low, and CO 2 has good solubility in crude oil to supply formation energy and achieve high oil recovery efficiency. In this work, a pilot program of CO 2 EOR technology was carried out. The slim tube test results showed that the minimal miscible pressure of Liuzan north block was 28.28 MPa. The injection parameters were optimized by numerical simulation method: the injection method was continuous, the slug size was 0.2 HCPV and the EOR efficiency was 7.23%. After two months of gas injection field test, the formation pressure of two gas injectors just increased by 14.02 MPa and 2.98 MPa, respectively, indicating that carbon dioxide could supply the formation energy effectively. 16 months after gas injection, the CO 2 injection amount was 14640 t, and the oil increment was 16424 t. The present work demonstrates the potential applicability of CO 2 flooding technology from high water injection reservoirs.

During the workover treatment process, poorly compatible workover fluids infiltrating into reservoir could cause serious formation damage. To tackle the aformentioned issues, in this work, low-damage workover fluid was systematically studied. By investigating reservoir damage mechanisms, chemical property study, compatibility evaluation test and core flow test, we obtain three kinds of workover fluids suitable for different blocks in Nanpu oilfield. Attractively, JRYL workover fluid which contains antiswelling agents can effectively prevent water sensitivity, and the permeability recovery values of JRYL workover fluid to NP1-5 and PG2 core are 95.3% and 86.9%, respectively. JRYD workover fluid which contains antiswelling agents and anti-waterblocking agent can prevent both water sensitivity and water blocking damage, and the permeability recovery value of JRYD workover fluid to NP403X1 core is 89.4%. JRYJ workover fluid suitable for high pressure formation can prevent water sensitivity and water blocking damage, and the permeability recovery value of the JRYJ workover fluid to NP403X1 core is 95.1%. The actual field application in Nanpu oilfield indicates that these workover fluids can not only reduce the oil well recovery time after workover treatment, but also increase production recovery rate. These results display great potential to efficiently develop low permeability reservoirs.