On the Investigation of Core Analysis of a Exploration Well

Abstract

Edogawa R-I is the exploration well for the northern extension of the newly found Tokyo Gas Field. The core and circulating mud water were examined under the principle of geochemical survey for natural gas field. The subjects of examination are as follows:
(1) Methane in mud water-After driving CH₄ by air from mud water, the mixed gas is dealt with interferometer.
(2) Chlorinity of mud water-After separating mud by centrifugal machine chlorine is titrated.
(3) Chlorinity of intersticial water-Adding distilled water, the core is disintegrated by roller mill, then the chlorinity is measured as well (2). The titration value is exchanged into the concentration for intersticial water, using the specific gravity and water content.
(4) Ammonia in intersticial water-The residual water of (3) is used. The concentration is decided using Nessler's reagent.
(5) Foraminifera-Foraminiferal number and percentage distribution of main species were studied with depth.
(6) Grain size composition-Beaker Method was used for fine grains.
Method (1), which has been widely tried in the Japanese gas fields, could not give conspicuous result in the present case. In general, this method should be criticized at the lower reservoir pressure, when almost no free gas.
Method (2) may roughly indicate the variation of chlorinity of intersticial water with depth. The value, however, is highty controlled by many factors.
The chlorinity and ammonia content of intersticial water of core may be chiefly controlled by permeability of stratum, although these two values may have different meaning regarding the process of gas formation. The chlorinity-depth relation reflects the destruction process of gas deposits caused by clear invading water. Foraminifera may be available for preliminary correlation and important to environmental indicator of deposition.