China is abundant in coalbed methane (CBM) resource. The unconventional natural gas reserves has reached 36.81*1012 m3. The Qinshui Basin in Shanxi Province is the largest gas field among CBM gas fields in China which are commercially exploited since the year 2003. In order to solve some typical problems in CBM production, this article considered the geographical characteristics of the fields, introduced and analyzed the low pressure gathering and transporting process and facilities, as well as the important techniques. Respectively, this article introduced the surface gathering and transporting procedure, analyzed the characteristics and topological structure; it also proposed the optimization scheme of combining steel pipes with PE pipes in processing system. The gathering and transporting processes of remote areas should be flexible and able to solve the problems during gas recovery from both largely exploited CBM blocks and remote blocks with low production. Thus a more reasonable system design should be proposed. To carry out the scheme, it first defined the topological structure of the system with graph theory, then established the economic model of the combined scheme. The article calculated the critical length of pipeline between two methods and defined the concept of “remote” well area. With the analysis of the actual conditions in a certain block in Qinshui Shanxi, the conclusion shows that: the scheme of laying pipelines can make more profit, which is consistent with the actual field situation., At the same time, we chose a phased optimization method, which divided the optimization of entire system into several sub-problems, including well group division, nodes connection relationship, determination of plant’s optimal position, and optimization of pipe diameter. Then we established optimization model that takes the investment costs of each stage as objective functions. The example shows that compared with the artificial design result, the total length of pipeline was reduced by 4.576 km, pipeline investment by 7.35×104 US$, with the respective rates of returns of 19.57% and 4.89%. The number of valve sets in the system fell from 16 to 11 (31%). By analyzing the investment and construction scale of the existing pipe network and optimal pipe network we have proved that the method has an ideal optimization effect. These techniques and schemes can give reasonable instructions in CBM surface gathering system design, powerfully promoting the development of the Chinese CBM industry.
Optimization design of multi-gathering mode for the surface system in coalbed methane field
