BIT BALANCING

BIT BALANCING

Another development that is becoming more important is bit balancing. This concept considers the forces acting on the bit to create designs in which no single come or cutting system is overstressed. This increases cutting efficiency and extends bit service life. Two type of balancing method are: force balancing and load balancing.

Force Balancing: of the three forces acting on bit- axial force, lateral forces and bending moment- it has long been recognized that balancing the lateral force is very important for preventing whirl. In fact, previous concepts of PDC bit force balance, due to the belief that once lateral force, was balanced, foe bit bending moment was balance also.

However, further study revealed that balancing moment contributes not  only to bit lateral motion or whirl, but also to till motion, which significantly affects directwial  control, Even a perfectly force-balanced bit may exhibit tilt motion if due axial forces is equally as important as balancing lateral force.

A PDC bit that as balanced, both in terms of lateral force and bending moment, is a “global force-balanced” but. Designing such bit involves adjusting the cutting structure to reduce the imbalance numbers. For instance, newer series are force-balanced according to a specific set of design criteria that consider the summation of cutter forces to a global, lateral and axial bit imbalance, resulting in a global force-balanced design.

Load Balancing: a bit which the dulling force acting on individual cutter is balanced and is evenly distributed across the entire cutter is said to be” Load balanced”. This technician is meant to prevent cutter wear and excessive point loading that can break or damage cutters.

Roller come bits are load balance in two ways-by volume and by force, Volume balancing almost equalizes rock removal among all the comes, while force balancing ensure that all comes are subjected to nearly the same loads, including weight-on-come, bending moment are force-nonbearing.

For PDC bits load balancing which was employed originally on rather come bits only, is now being used to improve the PDC bit performance. The concept of load balancing is based on the fact that the amount of formation removed by each individual cutter differs and as a realist the forces acting on each cutter also differ from blade to blade. Therefore the force force acting on each blade differs, it is necessary to control these load distribute :- (Australian, 1992).

Equally distributing the force minimizes the change in work, or force, among zones of the cutting structure. Thus designing a “tongue and drag balanced” PDC  bit involves analyzing the distribution of work and force acting on a cutting structure, with the goal of controlling the force distribution, these bits are able to reduce impact damage and uneven wear while promoting in proved ROP.

ADVANCES IN CUTTING STRUCTURES

  No matter the design, size or shape of a roller come bit, its basic purpose is still to grind rock as it turns, hence the term “rock” bit. However, today’s roller come bits utilize technical advancements that enable higher rate of penetration, lower mechanical wear and lengthier service left in tough formations.

One important improvement in roller come bits is the structure or “teeth” during the manufacturing process. As the inter face point with the formation, a bits cutting structure must both with stand and perform under the tremendous forces required to grind rock and produce a borehole. This point of contact is subjected to extreme pressure, heat and resistance as the bit rotates. New manifesting techniques are enabling this cutting suture to become more efficient and wear-resistance.

Additional improvement in bit cutting structure is the recognition of the unusval loads and dynamics that occurs when bits are nun on directional or steerable assemblies.  Where a steerable assembly is rotated, the bits are subject to off-center rotation, as well as high side loading. These conditions can reduce beading life, and damage the bits gauge areas.

REMEDY TO BOREHOLE DRILL-BIT PROBLEM  

  The drill pipe and bit may become jammed when the drilling field is not allowed to thoroughly dean the borehole prior to stopping to add another joint of drilling pipe or the fluid is too thin to lift gravel from the bottom of the borehole. Therefore, if the dull bit starts to catch when dulling stop further drilling and allow the drilling fluid to circulate and remove accumulated cutting from the borehole. Then continue to drill at a lower rate. If it continues to catch, thicken the drill field. If the drill bit and pipe become jammed, stop drilling and circulate drilling field until it is freed. If circulation is blocked, try to winch the bit and pipe out of the borehole. Stop the engine and use a pipe wrench to reverse rotation (no more than I fern of the rod may unscrew).

Rapidly hit the drill pipe with a hammer to try and jolt the bit free. If these actions are not successful, use lengths of drill pipe without a bit attached to “jet out” the cuttings. Attach the pipe or tubing directly to discharge hose from the mud pump. Thicken the drilling fluid to ensure that cuttings holding the bit can be removed.

Then place tension of the stuch pipe with drill rig winch. Once slowly push the fitting pipe/tubing down the borehole beside the jammed drill pipe until the bit is reached. When fluid starts to circulate out of the stuck pipe or it loosens, pull the stuck drill pipe and resume circulation of the thickened drill fluid back down the drill water freely circulates out of the borehole slowly lower the drill pipe and bit and resume drilling (Australian, 1992)