Objective
Apply to:
- a significant part of the field, the micro-emulsion/polymer process which was successfully tested on a small scale during a previous pilot test subsidized by the EEC.
- test the process on a spacing compatible with that of the field
- test the time behaviour of the product
- optimize the quantity and the quality of injected products
- test the injectivity of important volumes of product
- test the on-line injection methods of the product
- evaluate the economy of the process at industrial scale.
The test aims at raising the ultimate recovery rate in processed areas from 43% to 73%.
1. OIL PRODUCTION
From 14 June to 31 December 1986, 41,563 tons of oil were produced compared to an expected figure of 52,000 tons. The breakthrough of tertiary oil in the production wells was a little more rapid than expected, and today the production exceeds the forecasts by over 3,000 tons.
Among the 9 wells of the panel, 7 showed a production increase of their oil rate. The behaviour of the central well CHU 18 was extremely marked, the production oil rate raised from 11% to a maximum of 52%, and it is now down to 25%. The two North Wells, which serve mainly as a protection against the ingress of the aquifereous layer, completely hydrated at the beginning, produced 1 to 3% of oil.
The average oil rate in the pilot production has progressed by 8 to 22% to come back down to 12% in December 1986.
2. FIGHTING AGAINST HETEROGENEITIES
Preliminary interference tests had evidenced a drain between an injection well CHU 525 and a production well CHU 18. In November 83, when only 12% of the porous volume of chemicals was injected, a breakthrough of sulfonates was observed. This breakthrough provoked the unconsolidation of the sand around the well. Furthermore, the produced sulfonates were in a sodic form, soluble in water, and thus not subjected to the exchange of ions with the matrice. A comparative interference test showed a high viscosification of the medium, which reveals the good quality of the polymer solution in the formation.
3. INJECTABILITY
Injection of the micro-emulsion increased the injectivity index of wells by 30 to 50%. Injectivity occurs at fracturation pressure during polymer injection.
4. CHEMICAL PRODUCTS
Sulfonates and alcohols were detected in all wells, at a level below 1,5% of the injected concentration. After the central well CHU 18 which showed a very rapid increase of production in three months, wells which responded the most rapidly were as expected the East wells where the breakthrough of surfactants occured since January 1984. On thewhole, less than 2% of the injected quantity was produced. It is interesting to note that the sulfonates and the alcohols were not subjected to important chromatographic separation during their progression. The major part of the sulfonates was produced in calcic form, in the production oil.
Polymers were not detected at more than 22% of their initial concentration. The increase of their concentration in the effluents water corresponds with a rapid decrease of the oil production.
5. ECONOMY
The cost of the marginal oil produced by the pilot is estimated at about 40 dollar/bbl, without actualisation,and the breakdown is the following:
3% laboratory and studies
8% utilities and flowlines
28% surface installations
41% chemical products
20% staff cost
Extension of the process would represent approximately 32 dollar/bbl, for this type of field.
1. LABORATORY PREPARATION
- development of a micro-emulsion based on non ionic surfactants + sulfonates. Failure due to the fractioning between species of different surfactants in the progression in porous medium.
- study of ionic exchanges (particularly important due to the presence of calcium carbonates, and to the low salinity of the water) between the matrice, the water and the surfactants.
- optimization, with the aid of industrial products, of the volume and the composition of the injected micro-emulsion
- study of a carbonate preflush.2. NUMERICAL SIMULATIONS
- with the aid of the POMEVOL model (developed by IFP) with evolutive current tubes
- research of the optimum well layout. Definition of a system of 4 inversed five-spots, measuring each 300 m per side, and including a central well completely confined
- definition of influence zones for each injection well
- technical and financial optimization of volumes to be injected.
3. FIELD STUDY AND DRILLING
- interference tests
- drilling of four production wells, completed with gravel pack
- recomposition of the other production wells
- drilling of injection wells, completed with packer and tubings in glass fiber. The porous volume in the pannel is of 224,000 m3, the initial oil saturation of 48,6%
- additional interference tests. Occurence of a drain between two production wells (CHU 525 and CHU 18).
4. SURFACE INSTALLATIONS, PREPARATION OF PRODUCTS
STUDY AND CONSTRUCTION OF UNITS FOR THE:
- water treatment (production water is reinjected)
- storage of chemical products for the micro-emulsion (surfactants + premixed alcohols)
- storage of polymers (polyacrylamides in emulsion)
- mixing of products, with computer assisted control mixing
- dispersal unit in water, polymer solutions
- filtration, injection of a bactericide (formol) and injection in the wells
- sampling, precise measurement of the produced water and oil rates
Preparation at the refinery of the surfactant + alcohol mixture
5. OPERATIONS
Injection of 7860 m3 (3,5% of the porous volume) of micro-emulsion between 14 June and 24 July 1983.
This was followed by the injection of 40% of the porous volume of polyacrylamide solution at 1,700 ppm of active matter from August 1983 to March 1985, then by the injection of a solution of decreasing concentration till December 1986.
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DEM - Demonstration contractsCoordinator
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