About This Item
- Full TextFull Text(subscription required)
- Pay-Per-View PurchasePay-Per-View
Purchase Options Explain
Share This Item
The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
Volume:
Issue:
First Page:
Last Page:
Title: Migration
of Fluids in Miocene Mudstone, Nagaoka Plain, Japan
Author(s):
Abstract:
The main hydrocarbon reservoirs in Nagaoka Plain, Japan, are volcanic and pyroclastic rocks of the Nanatanian-Nishiyaman Stages (Neogene). The migration
of hydrocarbons seems to have occurred from adjacent sedimentary source beds to the volcanic reservoirs, facilitated by differential compaction. Therefore, it is possible to determine the directions of the compaction currents by using horizontal porosity distributions of covered mudstone bodies. The differential compaction maps of the mudstone source beds overlying the reservoirs may indicate the directions of hydrocarbon
migration
, and may suggest the location of hydrocarbon accumulations in Nagaoka Plain.
As fluid is expelled from pores of the mudstone, compaction occurs and porosity decreases. However, if fluid expulsion is inhibited because of low permeability, mudstone compaction may not be great and a high porosity-high fluid pressure situation will result. With such a low-permeability mudstone acting as a barrier to fluid expulsion, compaction currents could move downward in the level below the low-permeability zone and upward above that zone.
The volumes of the compaction currents are estimated from the vertical porosity distributions and the porosity differences before and after compaction. The resultant figures are discussed in connection with the possible hydrocarbon accumulations.
There are some abnormal pressures in the reservoirs of the Fujikawa, Kumoide, and Mitsuke gas and oil fields in the plain, whereas normal hydrostatic pressures are observed in the reservoirs of such fields as Katagai, Nishi-Nagaoka, and Higashi-Sanjo. This suggests the presence of permeability barriers in the volcanic reservoir rocks.
The depths of the volcanic reservoirs and the thicknesses of the sealing mudstone beds are greater at Fujikawa, Kumoide, and Mitsuke, where abnormal pressures are found, than at Katagai, Nishi-Nagaoka, and Higashi-Sanjo, where reservoir pressures are hydrostatic. Therefore abnormal pressures in this district may be ascribed to the thick mudstone seals and overburden pressures.
Pay-Per-View Purchase Options
The article is available through a document delivery service. Explain these Purchase Options.
Watermarked PDF Document: $14 | |
Open PDF Document: $24 |
AAPG Member?
Please login with your Member username and password.
Members of AAPG receive access to the full AAPG Bulletin Archives as part of their membership. For more information, contact the AAPG Membership Department at [email protected].