The Interwell Pressure Matching Analysis of Different Topologies in the Gathering and Transporting System

Interwell pressure matching (IWPM) refers to the mutual effects of flow parameters between wells under a certain topology. In a low pressure gathering and transporting (G&T) system, the wellhead pressures drop at different rates, leading to discordance. If the wellhead pressure cannot reach the system pressure, the gas would flow backward, which impedes normal production. Currently this issue has increasing attention from engineers; however, they only describe this issue qualitatively. In structure design of a G&T system, only the economy of different topologies, such as star topology (ST), concatenated topology (CT) and main line access topology (MLAT), have been considered; different topologies’ influence on interwell matching has been ignored. The author first defined the IWPM, further divided the concept into node pressure matching (NPM), structure pressure matching (SPM) and type pressure matching (TPM). NPM refers to the influence of one node’s parameter change on other nodes; SPM reflects the influence of one node on the whole network; TPM shows the matching difference of different topologies. Secondly, quantitative evaluating functions and evaluating method are developed. The evaluating method is that given changing rules of wellhead parameters, using a steady-state network program to simulate the system condition in a production period, then calculate the values of the evaluating functions. Last is a case study of a low pressure CBM system. The wellhead pressure can be low as 0.2MPa. The wellhead parameters rely on the extraction system. With this evaluation method, the author systematically analyzed NPM, SPM and TPM of 11 structures under 3 pipe topologies, and each structure connects 2–4 wells. The results show that, as far as NPM is concerned: in ST, the interference of one well would not influence others; in CT, the interference of a node would only affect adjoining nodes; in MLAT, any interference would affect all the wells. Because of the symmetry of ST, the interference of each well would influence the structure to the same degree (value of 1.74); yet the other two topologies have different influencing degrees caused by interference of different nodes. The SPM value range of the other two topologies are 6–16 and 15–45. Among all three topologies, the TPM value of star is 1.74, main line access 11.74, concatenation 32.56. With different topologies the anti-interference capabilities are different. ST is prior to MLAT, which precedes CT. This technique for the first time offers a tool to analyze IWPM and provides supports for the development and design of G&T system.