The Contrast in Initial and Present Application of the Term, "Connate Water"

Abstract

For several years it has been noted that the use of the adjective "connate" as applied to buried waters has become increasingly confusing. Recently published articles and discussions on core analyses have made no progress toward clarification of the terminology of pore water. Rather, it would appear that the situation has deteriorated to the extent that very few engineers have a clear idea concerning the conditions implied by "connate" in description of the water of oil formations. The existing varied usage is best illustrated by the opinions received from a number of engineers. These men are all reservoir or petroleum engineers, excepting one who is a mechanical engineering graduate serving as field area engineer. The following definitions of "connate" water were obtained orally, no time being allowed for reference or discussion.Irreducible minimum water, by any method of obtaining restored state.Interstitial water in the formation, with oil, before wells are drilled.Interstitial water in pores of formation. normally immovable.Interstitial water - will not move.Irreducible water of saturation, sometimes producible.Interstitial water in formation, not necessarily with oil.Water in formations which is immobile.Original water in place.Water which fills finer pores, with oil and above oil-water contact.The per cent of water saturation in an oil reservoir which exists before wells are drilled.Water remaining in the rocks after partial displacement by oil or gas.Water existing in formations before wells are drilled. Some is mobile, some is not. The absence of agreement in the above definitions is remarkable. Let us now examine briefly the original conception of the term "connate water" and the vicissitudes to which it has been subjected in the last two decades of its 50-year history. The word "connate" is of Latin origin and antedated considerably its application to subsurface waters. The initial use of "connate water," occurring in 1906 and being firmly established in succeeding publications prior to 1930, caused it to appear in dictionaries long before engineers became aware of core analyses and their interpretation. Webster's New International Dictionary still carries the unchanged definition: "Connate water. Geol. Sea water held in the interstices of sedimentary deposits and sealed in by the deposition of overlying beds."