The Early Development of Knowledge About Connate Water
Authors: Torrey Paul D. 
Published: December 2007

Introduction

Although it has been known for more than 40 years that water is present in varying amounts in oilfield reservoir rocks, information as to how the presence of interstitial water was first determined and then confirmed has been inadequately disseminated. The commemorative article by Whorton, read with much interest and appreciation, did nob discuss in detail the development of methods for determining the physical properties and the content of oil and gas physical properties and the content of oil and gas reservoir rocks. Because these methods were developed principally in Pennsylvania at a time when much principally in Pennsylvania at a time when much of the industry paid little attention to the technology of oil and gas production, there is a disconnected and incomplete record in the literature about them, and about how the results of laboratory work were first applied to the recovery of oil. These comments are intended to review pertinent information from published literature in chronological order, and to published literature in chronological order, and to amplify it with certain facts based on Bradford field operations that are not well known.

Early Published Works

The term "connate", in the literal sense, was originally applied by Lane to water held in the pore spaces of sedimentary rocks at the time of deposition. He did not distinguish between fresh water and water of marine origin. In later years the term became more restricted to fossil sea water, which has been present in porous rocks since the time of original entrapment and very likely has undergone changes in chemical composition and in the concentration of the mineral salts dissolved in it during the course of geologic time. The restricted definition of "connate" was accepted by Johnson in an early discussion of the relation between water in sedimentary rocks and the migration of gas and oil into both commercial and sparsely concentrated accumulations. Johnson assumed complete segregation between water and gaseous and liquid hydrocarbons, although he states that water likely is held in minute pores and oil in larger pores by reason of capillary action, and that this is pores by reason of capillary action, and that this is owing to the higher viscosity of liquid hydrocarbons, and to the fact that the walls of the pore spaces are originally water-wet. This discussion is one of the earliest to suggest that immobile water is held in the pore spaces of reservoir rocks along with oil. pore spaces of reservoir rocks along with oil. Washburn gave a formula for determining the recovery of oil by a volumetric equation, and Carll recognized that oil in Pennsylvania fields usually occurs in the fine pore spaces of sandstone. In 1917, two years after the publication of the Johnson and Washburn papers. Lewis presented what was probably, up to that time, the best exposition of the various factors controlling the performance of oil reservoirs. This contribution stimulated studies of the physical characteristics of oil reservoir rocks, particularly the series by Melcher that described a method for determining porosity. Nevertheless, none of these papers considered the contents of the oil reservoir papers considered the contents of the oil reservoir rocks that were tested. In his study of what was probably the first complete core of an oil reservoir probably the first complete core of an oil reservoir rock, Melcher listed the porosity of the various lithologic units of the Bradford sand. In 1926, Fettke described the results of analyses of five cores of the Second Venango sand. The porosity of the sand is listed in tabular and in graphic porosity of the sand is listed in tabular and in graphic forms; and these are believed to be the first graphic porosity profiles of an oil sand ever published. Of porosity profiles of an oil sand ever published. Of greater importance, Fettke described his distillation method for determining oil and water saturations of nine core samples. He recognized that the oil saturation values he reported were minimum figures and that a certain amount of oil escapes while a core is being cut, brought to surface, and transferred to a sealed container. The oil lost is replaced in part, according to Fettke, by the water used as the coring fluid. Although all the Fettke core samples contained as much water as oil, or more, it is not certain that at that time he appreciated the fact that part of the water was indigenous to the oil reservoir rock.

Discovery of Interstitial Water In Oil Reservoirs

The first commercial core laboratory was established by me in Bradford, Pa., in 1928; and the first core tested was of the Bradford Third sand from Borden No. 46. Soluble mineral salts were extracted from fresh samples of the core, leading me to suspect that water similar to that found at low structural position in the Bradford field was present in the sand. However, it was not possible to determine how much of the water was indigenous to the sand and how much had resulted from the replacement of oil by water during coring operation, as had been suggested by Fettke. The answer to this question was obtained, somewhat accidentally a short time later. Soon after the core from Borden No. 46 was analyzed, a test well was drilled near Custer City, Pa. Higher than average oil saturation was Pa. Higher than average oil saturation was encountered in the lower part of the Bradford sand. This resulted from an unsuspected flood, the existence of which was not known when the test well location was selected. Toward the end of the cutting of the first core, oil began to enter the hole so fast that it was not necessary to add water for the cutting of the second section of sand. The lower 2.5 ft of the Bradford Sand was cut with oil in a hole free of water. Two samples from this section were analyzed, and results indicated a water content of approximately 20 percent PV. This well produced about 10 BOPD, and percent PV. This well produced about 10 BOPD, and after being shot with nitroglycerine it produced no water.

JPT

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