Side Cutting Characteristics Of Rock Bits And Stabilizers While Drilling
Authors: Millheim Keith K. , Warren Tommy M. 
Published: December 2007

The trajectory of a drill bit is controlled by the complex interaction of the bit, bottom-hole assembly, penetration rate, and formation properties. This holds penetration rate, and formation properties. This holds true for all wells, whether they are "directional" wells or "straight holes".

Extensive research indicates that the trajectory of a bit can be understood and predicted if the following information is known:the side forces and vector directions at the bit and stabilizers,the penetration rate,the rotary speed,the side penetration rate,the rotary speed,the side cutting characteristics of the bit and stabilizers, andthe amount of hole enlargement due to hydraulic and/or chemical action.

All of these parameters can be measured or calculated while drilling a well except items (4) and (5).

This paper describes a full-scale, automated drilling apparatus that measures the side cutting characteristics of a bit or stabilizer in the laboratory. The drilling machine is equipped with servo-controllers to maintain constant penetration rate and side force during a test. The rotary speed and bit hydraulics are also maintained at a constant level. All data is recorded in digital form on magnetic tape to facilitate computer processing.

The test results cited in this paper were obtained with a 9-7/8 inch (25.08 cm) series 1-1-1 bit and with full-scale 9-7/8 inch (25.08 cm) stabilizers. The tests were conducted in Bedford Limestone and Carthage Marble. The results of the tests support the theory that both the bit and stabilizers cut sideways under conditions typically experienced in the field. The rate of displacement is a function of penetration rate, side force, rotary speed, and rock type.

This paper outlines the trajectory mechanism model and details the evolution of this model as well as the resulting side force testing program. A description of the drilling apparatus, testing procedure, and test results are presented.

Introduction

Drilling costs are a significant portion of any petroleum fuel development scheme. The economic petroleum fuel development scheme. The economic success of many of the new oil recovery processes is closely linked to drilling costs. Some of the projects require special high-angle directionally drilled wells while others require wells drilled to very closely spaced small targets. The success of many of these projects depends on the technology and economics of projects depends on the technology and economics of drilling these wells.

Offshore drilling costs are spiraling. Already some fields that could have been economically developed one or two years ago are now marginal. Higher oil and gas prices offset some increase in costs but there are immense savings to be achieved by significantly reducing drilling costs.

The goal of every company engaged in drilling is to optimize the drilling program so that each well is drilled as cheaply as possible. In many areas this is achieved. In others, it is not. The success of any optimization program relies heavily on the men that are directly responsible for the actual drilling. This is especially true for wells that have a controlled trajectory.

The major consideration while drilling a directional well has traditionally been to hit a particular target. Management has accepted the longer drilling times and higher costs as a necessary sacrifice in order to hit the target.

The person in charge of the directional operation controls the drilling of the inclined portion of the well. The major tool he uses to optimize the well is his experience and ability to relate causes and effects as the well is being drilled. In view of the complex mechanisms that are involved in trajectory control, he does an admirable job.

Post-analysis of directional wells drilled in North America, the North Sea, Iran, Trinidad, and Holland indicate that many unnecessary changes are made while drilling a typical directional well. All these extra operations of changing the bottom-hole assembly, rotary speed, and/or weight-on-bit have the effect of increasing the overall drilling time.