Abstract

Functionally Graded Material (FGM) has the potential to endure in a deep well and sour environment. Japan National Oil Corporation (JNOC), Japan Research and Development Center for Metals (JRCM) and Sumitomo Electric Industries, Ltd. (SEI) applied FGM to a stabilizer blade and then developed a prototype stabilizer with it. This FGM is composed of Cobalt- composition graded cemented carbide layers and a steel substrate with lower Co compositionin the surface. The graded cemented carbide powders stacked on steel were sinter-bonded by pulse-current resistance heating. We manufactured the desired structure and confirmed the stress relief, high bonding strength, and distribution of functionality of coated layers between the surface (with highwear resistance) and the inside (with high toughness). The new stabilizer, with FGM blades composed of WC-25%Co (thickness of the layer is 1.5mm) and WC-40%Co(thickness of layer is 1.5mm), was tested in the Kashiwazaki Test Field (KTF)well and in the Ministry of International Trade and Industry's (MITI)Sanriku-oki well in Japan. To compare a conventional type of stabilizer whichhas cemented carbide buttons with this new stabilizer, we drilled with both stabilizers for about 270m in the KTF well and for about 980m in the MITI well. The wear resistance of FGM blade was more than 2 times that of the conventional blade in the KTF well and more than 20 times higher in the MITI well. These results suggest that we might expect the new stabilizer to have high performance in deep wells and to achieve at least twice the tool life of conventional stabilizers while drilling.

Introduction

The cemented carbide steel currently in wide use requires a harder and thethicker coated layer to improve durability. However, it is difficult to buildup a hard and thick layer, because the thermal expansion mismatch between the cemented carbide and steel promotes cracks and peeling of the layer. To overcome the thermal stresses and improve the mechanical properties of thecoated layer, it is necessary to distribute the functions of high wear resistance to the surface and high toughness to the inside layers. A new functionally graded material (FGM) was studied by Uchino1 and Ikegaya2–4 as shown in Fig.1. This FGM is composed of Cobalt compositionally graded cemented carbide layers and a steel substrate. Cobalt compositionally graded cemented carbide powders were stacked on a steel substrate by a new sintering process, using high pressure and direct resistance heating by pulse current. We were able to acquire the desired structure and confirm the stress relief, high bonding strength and distribution off unctionality of the cemented carbide layers.

The purpose of this study is to apply this new FGM to drilling and production tools which need to have high wear resistance and high toughness.Therefore, we tried to apply this FGM to a stabilizer blade. The outer diameter of the stabilizer is the same as the hole diameter, so the blade surface should have high wear resistance and toughness.

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