Determining a formation porosity from neutron logging information
US4816674A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jun 29, 1987 |
| Grant date | Mar 28, 1989 |
| Priority date | — |
| Expiry date | Jun 29, 2007 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01V5/10
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
A method for determining the porosity of a subsurface geological formation traversed by a borehole is provided. The method generally comprises obtaining a means which relates ranges of apparent formation porosity (.phi..sub.a) as determined by a neutron-neutron log, formation fluid salinities, formation total capture cross sections (.SIGMA.), formation matrix and fluid constituents, and true formation porosity (.phi..sub.T) according to a predetermined equation. The predetermined equation relates the apparent porosity to a function of a modified migration length which is obtained in a semi-empirical manner (i.e. physics modifed by data). The modified migration length includes a slowing down length and a diffusion length, but causes at least the diffusion length to be a function of the slowing down length. The means which relates the apparent porosity to salinity, .SIGMA., matrix and fluid constituents, and .phi..sub.T solves a forward problem. Thus, the inverse problem of determining true porosity may be solved by obtaining determinations of salinity, formation matrix and fluid constituents, .SIGMA., and .phi..sub.a, and using the relating means to provide the true porosity. The pr…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.