Method for determining calcareous interbed and formation porosity by neutron lifetime and compensated neutron combination logging

Abstract

The invention relates to a method for determining a calcareous interbed and formation porosity by neutron lifetime and compensated neutron combination logging, which comprises the following steps: adopting mudstone counting rate to respectively standardize the counting rate of a compensated neutron logging far detector and the capturing counting rate of a neutron lifetime logging far detector; defining DSFC divided by TMFC as the index curve CAI of the calcareous interbed, wherein the obvious peak of the CAI curve indicates the calcareous interbed; and utilizing the ratio of the counting rateof the compensated neutron logging far detector and the capturing counting rate of the neutron lifetime logging far detector to be linearly fit with the total porosity determined by neutron-density logging, obtaining the total porosity Phi t of a gas zone, and obtaining the effective porosity Phi of the gas zone after shale correction. The invention provides the method for determining the calcareous interbed and the formation porosity by neutron lifetime and compensated neutron combination logging, and the method improves the interpretation coincidence rate and the reserves calculation accuracy of a superficial layer gas zone of a testing block.

Description

Technical field: [0001] The invention relates to a well logging method in the field of oil field logging, in particular to a new method for determining calcareous interlayer and formation porosity through combined logging of neutron lifetime and compensated neutron. Background technique: [0002] In blocks with active natural gas in oilfields, blowouts and kicks often occur during drilling, and it is urgent to evaluate shallow natural gas reserves in this block. However, there is very little logging information of shallow open-hole wells in old wells, and many wells only have 2.5-meter gradient logging and spontaneous potential logging, which cannot be used to evaluate shallow gas layers. Studies have shown that adding neutron compensation and neutron lifetime logging in cased holes can identify shallow gas layers well. However, due to the common shallow calcareous cementation in this area, the calcareous interlayers and gas-bearing reservoirs have the same response charact...

AI Technical Summary

Problems solved by technology

[0004] In order to solve the problem that it is impossible to distinguish between gas layers and tight calcium layers and to determine the porosity of gas layers when there are only cased hole compensated neutron and neutron lifetime logging data, the present invention provides a combination of neutron lifetime and compensated neutron A method for determining the porosity of calcareous interlayers and formations by well logging, which improves the coincidence rate of interpretation of shallow gas layers in the test block and the accuracy of reserve calculation

Images