Static models have been used in the last two decades to analyze the hydraulic behavior of gas gathering systems. The driving forces for building these models include the need to increase system awareness and enhance production. Building these systems in any production software and keeping them up to date are processes that require expertise and time; the latter depends on the system complexity. Manual data transfer can delay recognition of problems until changes have adversely impacted production. This paper describes the implementation of a systematic workflow to build the Raton basin gas gathering system model in PIPESIM* and to control and automate the model data transfer and optimization through Microsoft Visual Basic® macros. The results demonstrate how the modeling, combined with an automated interface, became an invaluable tool for updating, optimizing, and simulating scenarios for the gas gathering system.
Pioneer Natural Resources USA Inc. owns and operates a low-pressure natural gas gathering system, in parallel with a produced-water gathering system, in Las Animas County, Colorado, west of the town of Trinidad in the Sangre de Cristo Range of the Rocky Mountains (Figure 1). The system services the Purgatoire coalbed methane field in the Raton basin and comprises about 1,000 miles of pipeline and 2,100 active wells.
Development of Raton basin field began in 1995. The most notable player was Evergreen Resources Inc., which drilled most of the wells and constructed and operated the bulk of the gathering system. Evergreen's growth was facilitated by several acquisitions of smaller well and gathering packages within the field. When Pioneer acquired Evergreen in 2003, there were 1,000 wells producing into the gathering system. Since the acquisition, the system was expanded further (Figure 2), continuing the philosophy of designing, constructing, and operating the gathering in-house.
The gathering system involves four discrete systems: Lorencito/Rita, Long's Canyon, Maxwell, and North of the River, or simply North; the latter is by far the most complicated of the four. Mainline (sales) compression consists of approximately 123,000 site-rated horsepower in nine stations. In addition, there are 10 (185-hp) screw units installed as lateral compressors, and about 300 wellhead boosters. The main line compressor stations follow two basic configurations: Conventional four-stage reciprocating units and stations with a screw or blower first-stage boosting into three-stage reciprocating units. The conventional reciprocating compressors boost from about 6 psig to sales pressures of about 1,100 psig. The "compound" stations hold a suction of 1 to 2 psig. All satellite compression, lateral, and wellhead units run at about 1-psig suction.
The evolution of the Raton basin system has presented many design challenges as a result of extreme mountain terrain and landowner, homeowner, and environmental issues. Responsible environmental stewardship, being a good neighbor to the ranches and subdivisions, and extremely difficult topography have frequently dictated pipeline routes. In fast-developing fields such as Raton basin, almost every step-out play requires a new trunkline sized to carry an unknown amount of production from an unknown number of wells.