On the Core Analysis of Natural Gas Exploration Well, Chiba R-1

Abstract

Recently in Japan the methane gas, of which geological occurence is free from petroleum, has been utilized. Except some cases, the gas is dissolved into formational water according to hydro-static pressure-temperature relation. The writer describes the result of the core analysis of exploration well for natural gas of this kind in this paper. The formational water dissolving natural gas under the reducing condition may be teken the place or degenerate by the invasion or diffusion of meteoric water along the permeable sediments, and consequently the gas potentiality may decline. The chemical analysis of the interstitial water of core may indicate the influence of the meteoric water and detect the vertical distribution of gas potentiality. In practice, this method is a application of usual methodology of “geochemical survey by underground water” to the interstitial water of muddy core. Chlorine may be a factor of chemical environment atf deposition and slso the measure of the destructive process by meteoric fresh water. Its concentration well shows the vertical change of the destructive process together with the values of long normal curve of electric logging. Ammonium and bicarbonate may be tne measure of potentiality as the products of the same phase of formation _??_ destruction equilibrium of gas. Furthermore, ammonium may be a measure of the destructive process by metheoric water as well as chlorine. The presence of nitrite and nitrate shows decidedly the characteristics of meteoric water of oxidative status. The consumption of potassium permanganate reaches the first peak at the contact zone of connate and meteoric water, where the intersticial water is dark brown-colored by humic matter, and again becomes larger downwards, where the interstitial water is colorless. The similar phenomenon is known horizontally within the Mobara gas field. But the absolute value is far higher in the core analysis. This may be caoused by the condition (especially pH) at the extraction of interstitial water. By the micropaleontological study of core, the gas bearing formations may be the Plio-Pleistocene sediment of lower neritic deposition. In the vicinity of the Mobara gas field, these formations are invaded by meteoric water, having no gas potentiality.