Field Processing of Natural Gas

Well streams must be sampled and analyzed with great care if the resulting data are to serve as a reliable design basis. Even then, the well-stream composition used in design must be viewed realistically. The likelihood that the actual feed to the processing equipment will be identical to the design basis is remote. Production is usually from a combination of wells that may have differing compositions. The producing pattern (number of wells and flow rate from each) may be different from that originally envisioned. Also, well-stream compositions change as reservoir pressure declines. Equipment must be sufficiently flexible and/or adequately sized to operate well in the face of changing feed composition and flow rate.

In addition to well-stream composition, important design data are wellhead pressure, temperature, and flow rate. These variables change with time in a manner often difficult to predict, but nevertheless important. Decline of reservoir pressure with production is a much-studied, but often difficult phenomenon to forecast. Pressure and flow variation in oil formations depends on the reservoir drive mechanism as well as the possible use of secondary and tertiary recovery techniques. Gas-oil ratio often increases with time. This latter factor is important in predicting associated-gas yield.

Pressure and flow-rate changes will affect selection and design of vessel and pipe sizes and of compressor horsepower, or even the necessity for compression. Design of equipment based solely on initial production conditions only can lead to inadequate sizing and/or omission of vital equipment. Generalizations are difficult; each project must be analyzed with consideration of its peculiar characteristics, including capacities both early and late in the life of the project.