American Petroleum Institute

Sampling Petroleum Reservoir Fluids - Second Edition
 N RP 44

Annotation

Proper management of production from a natural gas or petroleum reservoir can maximize the recovery of the hydrocarbon fluids (gas and oil) originally in the reservoir. Developing proper management strategies requires accurate knowledge of the characteristics of the reservoir fluid. Practices are recommended herein for obtaining samples of the reservoir fluid, from which the pertinent properties can be determined by subsequent laboratory tests.

The objective of reservoir fluid sampling is to collect a sample that is representative of the fluid present in the reservoir at the time of sampling. If the sampling procedure is incorrect or if samples are collected from an improperly "conditioned" well, the resulting samples may not be representative of the reservoir fluid. A non-representative sample may not exhibit the same properties as the reservoir fluid. The use of fluid property data obtained from non-representative samples, however accurate the laboratory test methods, may result in errors in reservoir management. Poor planning can also result in incomplete data being taken during the sampling program. Incomplete data can make it difficult or impossible for laboratory personnel to perform and interpret tests that provide accurate and meaningful fluid property information.

Reservoir fluids found in gas and oil fields around the world vary greatly in composition. In some fields, the fluid is in the gaseous state and in others it is in the liquid state; frequently, gas and liquid coexist in a given reservoir. The rocks which contain these reservoir fluids also vary considerably in composition, and in physical and flow properties. In certain cases, this can serve to complicate the sampling procedure. Other factors, such as producing area, height of the column of hydrocarbon fluid, fracturing or faulting, and water production also serve to distinguish one reservoir from another. The combination of all these factors affects the choice of sampling methods and preparations for sampling.