Advanced Materials Research Vol. 868

Abstract: Desorption of Coalbed Methane is one of the key controls to CBM recovery ratio and production capacity. This paper discusses the impact of engineered measures on CBM overall desorption and production capacity with CBM model of Eclipse numerical simulation software. The simulation results show that: with the extension of hydraulic fracture half-length, overall desorption of coal reservoir increased and CBM production capacity improved, daily gas production, maximum gas production and stable yield time increased correspondingly; in different deployment of spacing and well network, the smaller spacing is beneficial to the overall desorption of coal reservoir, but its production can not keep stability because of the serious decline in the late stage of development, while the larger spacing shows in the opposite way.

Abstract: Improving the productivity of CBM wells is one of the most emergency issues in the development of CBM. Preliminary characteristics of water discharge can indicate the productivity to some extent. Based on the data of 49 CBM wells in Fanzhuang Block, Qinshui basin, this paper makes research on the relations between the Preliminary characteristics of water discharge and CBM well production by theory of reservoir engineering. According to the index and quantity of water discharge, the CBM wells were divided into five types. Contrast this block, develop the I-type wells preferentially, reduce the fracture strength for the II-type wells, improve the fracturing technology for the IV-type wells, and shouldnt take the III & V-type wells into consideration generally.

Abstract: Flow mechanism in tight reservoir is different from that in normal reservoir because of the nanoscale and micro-scale holes in the reservoir. Beskok-Karniadakis model can describe gas diffusion and flow. In this paper, Beskok-Karniadakis model was applied and optimized in consideration of the tight gas productivity influenced by both Knudsen diffusion and desorption. Furthermore, tight gass productivity of fractured vertical wells was obtained with the method of permeability resistance. In combination of examples and theory, the influence of diffusion coefficient, half-length of fractures and fracture conductivity on well gas productivity was analyzed. The results show that free gas has a close connection with total productivity. Diffusion coefficients are not the same in different reservoir, and this can also influence the productivity. For fracture conductivity, the productivity goes up with the fracture conductivity increases. A method to provide guidance of effective productivity is gotten with optimizing the conductivity.

Abstract: By the methods of in-house experiment and theory analysis, the fracture initiation, stretch and interconnected mechanism of natural fracture is studied in the fracturing process of main fracture and branch fracture extending. The results have shown that, the hydraulic fracture in fractured formation is composed of a few main fractures in large size and many s secondary fractures in small size. The main fracture has the extending trend with the maximum crustal stress direction. The direction of sub fracture is network along the maximum crustal stress. The higher the degree of natural fractures, the difference between maximum and minimum crustal stress smaller. And the natural fracture is easier to form larger fracture. Fracture orientation and fracture width are determined by different combinations of natural fractures and the relative orientation with the maximum crustal stress.

Abstract: The properties of mixed waterwater from a certain river (RW) and Chang-6 layer output water (C-6W) -- in Shanbei Oil Production is studied in this paper, including ion content, analysis of scale, scale type and calcium loss rate, etc. It shows that the salinity of C-6W is more than 80000 mg/L, while RWs salinity is about 1200 mg/L; Under 30 °C, the calcium loss rate and amount of scale buildup of C-6W and RW when their volume ratio were 4:6 reached to 9.5% and 36mg/L; while reservoir calcium the loss rate and scale buildup amount reached to 0.59% and 21.5 mg/L when the volume ratio of C-6W and Mixed Water came to 3:7, which satisfies the reinjection water quality standard; and a low core damage rate (<20%) could be found when the reinjection volume is 1 ~ 15 PV.

Abstract: Through studying on the application principle of existing metal lenticular gasket, the structure design was finished, and design methods and calculating models of lenticular gasket larger than 6inch diameter were attained. Seal mechanism of the lenticular gasket and contact mechanics of the flange joint was analyzed by using finite element method. Stress state, contact width and contact deformation parameters of the lenticular gasket on working was obtained. Based on the analyzing results, leakage forecast model of metal lenticular gasket was presented. In the influencing factors of actual working state, such as inner pressure, outer pressure, medium viscosity, and surface roughness and so on, surface roughness is important, so surface machining precision of an in-use large-diameter lenticular gasket should be improved as far as possible. The conclusions will lay foundation for the future engineering application of large-diameter lenticular gasket.

Abstract: The phenomenon of hydrate freeze-plugging is very widespread in Jilin oilfield M gas field exploitation. Freeze-plugging tends to occur in winter, mainly including ground pipeline, wellhead and wellbore freeze-plugging, etc, which affects the normal production of gas well, also has restricted the gas reservoir development and will cause huge economic losses. In order to prevent the freeze-plugging occurred in gas well, methyl alcohol is used to inject into single well at the rate of 600 to 3080 L/day. The field condition shows that the result of injecting methanol is not obvious, besides, the toxicity of methanol and its high cost already cannot satisfy the oilfield actual demand. Therefore, we need to research and develop new hydrate inhibitors with low cost and high efficiency to solve the problem of freeze-plugging.