Sources of Information on the Properties of Subsurface Fluids
The USGS Water Supply Paper by Lico, Kharaka, Carothers, and Wright (1982), 'Methods of collection and analysis of geopressured-geothermal and oil field waters,' gives state of the art information on field sampling techniques and procedures of chemical analysis for formation waters. Additional information is given in the book of oil-field brines by Collins (1975) and the short course notes by Kharaka et al. (1985).
Here are a few things to remember if you are contemplating field sampling, particularly of water co-produced with oil or natural gas. Opportunities for downhole sampling in sealed bombs are rare. The next best procedure is to pull the sample right at the well head. The next best is to sample at the separator, i.e., the apparatus in which mixtures of gas, oil, and water are allowed to separate out gravitationally. If you are sampling at the separator, beware of possible comingling of waters from various wells and of the presence of industrial chemicals added to retard plugging or to make things flow or separate more readily. Keep in mind that the fluids moving up an oil or gas well are hot, under high pressure, and flammable. Go with someone, preferably a field engineer, who knows the business. Do not sample without getting permission from the operator.
Fluids change in physical properties as they are brought to the surface. The changes in pressure or temperature may be sufficient to induce degassing of the aqueous fluid and precipitation of mineral phases. Most in-situ conditions are fairly reducing,
Figures & Tables
The topics covered in these notes have been selected to provide the general sedimentary geologist with an introduction to some of the key problems and a conversational familiarity with some of the basic techniques in this important area of sedimentary geology. A number of field examples are drawn from the Louisiana Gulf Coast, buy many of the general principles will be applicable to other areas and problems.