Influence of wear on rock contact area of V-shaped cutter PDC bit

Abstract:

With the increasing demand for deep-sea and deep-earth drilling， the downhole drilling tools using traditional PDC bits are severely worn out and cannot fully meet the drilling requirements of deep wells in hard formations. Therefore， special-shaped cutter PDC bit， especially V-shaped cutter PDC bit， has become the focus of research. There are fewer studies on the effect of wear on the contact area of V-shaped cutter PDC bit. The contact area affects contact pressure of cutter， which in turn affects the depth of penetration into the rock and drilling efficiency， so it is of great significance to study the change rule of contact area of V-shaped cutter. In order to calculate the contact area of V-shaped cutter with the rock during wear， the expressions for contact area as a function of the wear height and the geometric parameters of V-shaped cutter， such as chord length and tangent angle， were derived using the method of planar oblique intersection of the cylindrical surface on which the cutter is located， and the effects of the geometric parameters of V-shaped cutter and wear height on contact area and contact pressure were analyzed. The results show that the cylindrical cutter and V-shaped cutter have the same contact area in the early stage of wear， when the cutter is worn to a certain stage， the contact area of the V-shaped cutters is smaller than that of the cylindrical cutter. The smaller the chord length and tangent angle are， the smaller the contact area is. Under the same load and the wear height of the cutters， the contact pressure between the V-shaped cutter and rock is larger than that of the cylindrical cutter， so the V-shaped cutter has the ability to penetrate deeper into the rock. For wellsite applications， the driller can measure and record the wear height and the corresponding ROP of a batch of bits of the same type after lifting. The statistical relationship between the wear height and ROP can be obtained for this type of bit， and then the contact area can be estimated from the wear height. This method makes it easy to adjust the weight on bit in time to maintain a high ROP， or to optimize the V-shaped cutter geometry parameters during design， which also helps to improve drilling efficiency.