EARLY TESTING

Practical Field Testing

During the development of the composite resin blades, a practical field test was needed before the centralizers could be used downhole. The critical characteristics to be proven were adhesion and wear resistence. A practical test to evaluate these factors was developed that would simulate the wear and irregular resistance that the centralizer would encounter while running into the well bore.

Agip supplied an analysis of lateral forces for casing programs that could be used as a guide to identify the required loads in order to determine wear resistance. These forces were then transformed into load values per square centimeter which then helped to determine the composite centralizer blade size and the weight that was needed to simulate lateral loads and forces that would be encountered by the centralizers during installation into a well.

Composite centralizer blades in the form of sleigh rudders were applied to heavy steel plates and the weight of the entire test sled was adjusted to give the required load factors. The test sled was attached by cable to a motor vehicle and the test sled was then drawn across various types of road surface that would be similar to what is expected downhole. These preliminary tests offered very promising results. Test parameters and results were recorded confirming the excellent wear resistance of the composite material and equally important there was no sign of blade detachment despite numerous violent impacts while under load.

Fig. 1 - Test sled for preliminary wear test

Deviated Lean Profile Well Test

The trajectory for the first deviated well would not be very demanding with the casing design being vertical from the 16" casing shoe to the KOP set at 2700 meters. A build up section with a dog leg of 1.5° / 30 meters was then applied to 3850 meters with a final build-up of 30° of inclination. At that depth a tangent section was established down to casing point. Because of the expected friction forces and the consequent drag and casing-to-borehole interaction, a substantial centralization program was designed. The casing string was 13 3/8" ST-L P110 72#/ft. Unlike the vertical wells the composite centralizers were used to the surface as follows:

• C1 from 3754 to 3742 meters
• C2 from 3742 to 3474 meters
• C3 from 3474 to 2497 meters
• C4 from 2497 to 100 meters

The shape and size of the composite centralizer blades were applied to the center of each joint in the same shape as the previous wells with a 120° angle between blades. The casing report can be summarized as follows:

• No problems were encountered while RIH and the casing was run freely down to TD.
• Even though caliper analysis showed some areas of hole enlargement (max. of 5 inches) and bore hole ovalization from the KOP to shoe depth, casing ran smoothly.
• The results from the CBL-VDL analysis showed a discrete to good bond response with better results in the deviated section below the KOP. The composite centralizers performed well by keeping the casing string aligned along the hole axis despite hole enlargement. This conclusion is further supported by the fact that the bond response improves with increasing depth which corresponds to the number of centralizers in that section of hole.

Fig. 2 - The Who vs. time for Well C; the smoothness of the running curve clearly demonstrates the effectiveness of the composite centralizers.

Fig. 3 - The CBL log (lower section only) provides an indication that there is good bond response of close to 5mV on a horizontal scale of 0-100 mV.