CHARACTERISATION OF ROCK FORMATIONS FOR THE IMPROVED CALIBRATION OF NUCLEAR LOGGING TOOLS

Objectif

The primary aim of the project is to develop a range of calibration formations for nuclear logging tools which will serve as a basis to satisfy the requirements of the oil industry into the next century. The requirements are :
(i) the development of test formations which will be needed for Primary Standards to calibrate Wireline and MWD tools;
(ii) the development of a representative range of borehole environments which can be used to check the various corrections made to tool responses.
The key innovation features are (i) the use of nuclear techniques to characterise the test formations combined with (ii) the use of Monte Carlo code MCBEND to predict absolute responses of neutron tools from a knowledge of the absolute neutron source strengths. This will enable the code to be used not only for the calculation of environmental corrections but also for extrapolation to field conditions with the aid of nuclear core analysis.
The characterisation and installation work has been completed for all of the formations. Processing of the characterisation data and verification by comparison with reference tool measurements and computer modelling is also complete.
The basic limestone, standstone and dolomite porosity scales have been completed. These provide limestone formations with porosity 0, 8, 18, 24 pu; sandstone formations with porosity 0, 12, 18 pu; and dolomite formations with porosity 0, 13, 22 pu. All of these formations have a 216 mm diameter borehole. In addition three formations have been provided with a larger 311 mm diameter borehole and four formations have been provided that are saturated with brine solutions. The borehole sizes and the final selection of formations has been agreed with the steering committee. Locating suitable rocks to fulfil the original specification proved to be more difficult than was originally anticipated. Some delays have arisen due to problems in finding suitable rocks or late delivery of machined blocks.
Each formation has been subjected to an extensive programme of core analysis to determine the porosity, density, permeability and chemical/mineral composition. The core data is tested for internal consistency to ensure that no systematic errors have arisen. The petrophysical data and saturation processing data are verified by comparison with the measurements made using a reference gamma-density tool. Similarly the chemical data is verified initially by comparison with the thermal neutron absorption cross-section measured on samples using the NESTOR reactor at Winfrith and then with measurements made using a reference neutron porosity tool. Monte-Carlo predictions of the neutron tool detector responses are made based on models for the formation derived from the core data. Testing of the existing formations in this way has confirmed that the formations are well defined by the characterisation data. For the basic limestone, sandstone and dolomite porosity formations the consistency between the core data and measurements made using the reference tools are within 0.015g/cc and 1.0 pu respectively.
As such the formations meet the specification given in the original proposal document and will be suitable for calibrating and testing neutron porosity tools. They will also provide useful test conditions for checking the calibration of gamma density tools.
The code MCBEND has been further developed specifically with well-logging tool problems in mind. The acceleration modules have been improved to provide importance maps for both neutron porosity and neutron lifetime tools with a minimum amount of information required from the user. The input data format has been examined and in the case of neutron porosity tool a simplified input macro has been developed that will enable first time users to produce input files from some basic tool dimensions. This macro will be useful for training purposes and for setting up simple generic calculations.
Five specific tasks have been completed :
Task 1 : Open Hole Porosity Scale
For porosity calibration in the three classical reservoir rocks, sandstone, limestone and dolomite, ten formations have been installed in tanks saturated with fresh water. Four porosity values have been provide for limestone with three each for sandstone and dolomite. Each formation has a 216 mm borehole.
Task 2 : Environmental Correction Tanks
These comprise two fresh water tanks and two tanks saturated with a high and low salinity fluid. The fresh water tanks contain 2 limestone and 1 sandstone formation with 311 mm diameter boreholes. The other tanks contain 2 limestone formations each of different porosity with a 216 mm diameter borehole.
Task 3 : Evaluating Formation Properties
Each formation has been subjected to an extensive programme of core analysis to determine porosity, density, permeability and chemical/mineral composition.
Task 4 : Testing the Formations
Once the formations were installed andsaturated, they were tested with an agreed suite of logging tools. The results completed the characterisation data set for each tank including comparison with computer predictions of measurements for each tool in each formation.
Task 5 : Computer Program Development
The Monte Carlo code MCBEND used for these calculations was specially adapted for this work with the aim of simplifying the data input/output modules and introducing an automatic procedure for acceleration.
During the fourth year of the project, the test pits were made available to sponsors so that a thorough evaluation can lead to their acceptance as Industry Standards.

Programme(s)

ENG-HYDROCARB 2C - Programme (EEC) of support for technological development in the hydrocarbons sector, 1986-1989

Thème(s)

1.4 - GEOPHYSICS AND PROSPECTING

Appel à propositions

Data not available

Régime de financement

DEM - Demonstration contracts

Coordinateur

AEA Technology

Contribution de l’UE

Aucune donnée

Adresse

Winfrith Technology Centre
DT2 8DH Dorchester
Royaume-Uni

Coût total