Drilling Rate Of Penetration Research Articles

Casing Wear: The Effect of Contact Pressure

Summary One of the major factors affecting casing wear is the magnitude of the loading between the drillstring and the casing. This paper describes a new test machine and experimental procedure used to study the effect of contact loads on casing wear. The results of extensive testing show that contact pressure instead of contact load is the appropriate parameter controlling the wear rate of the casing. An experimental relationship is found between contact pressure and casing wear rate for nonhard-faced tool joints in a laboratory prepared drilling mud. Knowing this, a computer program is devised to model accumulated casing wear during drilling. A hypothetical example is given estimating the additional feet that can safely be drilled past a dogleg without catastrophic wear. The paper also shows the relative effects of tool joint size and drilling penetration rate on casing wear. Additional factors penetration rate on casing wear. Additional factors such as the addition of steel wear protectors in the center of the drillpipe also are explored. Conclusions are drawn as to the limitations of simple casing wear guidelines based on maximum allowable contact load. It also is concluded that the addition of steel wear protectors does not increase casing wear. Introduction It is well known that casing wear can result in significant losses if allowed to progress to failure. As holes are drilled to greater depths, the length of time available for wear increases. The longer drillstrings used have greater tension and therefore larger forces between the tool joints and the casing. Also, highly deviated directional wells increase the contact loads resulting in increased casing wear. Obviously, it is important to understand casing wear more completely for today's drilling. One approach to controlling casing wear to acceptable values was suggested by Lubinski. A study of wells drilled before 1960 showed that when the tool-joint-to-casing loads were below 2,000 lbf (8.9 kN), the holes were trouble-free. This led to the concept of controlling the maximum side load to minimize casing wear. More recently, Bradley presented a means of estimating casing wear based on presented a means of estimating casing wear based on an experimentally determined wear rate. The wear rate was approximated as varying linearly with contact force. Whether these or other methods of estimating casing wear are used, it is clear that the magnitude of the contact load is a very important parameter. It is the objective of this paper to investigate the effect of loading more fully. Once this is done, other parameters such as the tool joint diameter, drilling parameters such as the tool joint diameter, drilling rate, and the addition of steel wear protectors can be analyzed. Background Casing wear is a complex process involving many variables: temperature, mud type, percent abrasives in the mud, tool joint hardfacing, revolutions per minute (second), tool joint diameter, contact load, and many others. In the face of such complexity, it easily is understood why so little is known about casing wear. Even so, several fine papers have been written on the subject. Some of these are listed in the references. Many papers are concerned with the effect of tool joint hardfacing on casing wear. Two of the papers looked at the drilling mud type effect. Only Bradley's work has studied the variation of casing wear with contact load. JPT P. 2382

A Study on the Effect of Hydraulics on the Penetration Rate of Rotary Drilling

The equations for the penetration rate reported by many researcher are applicable only under the condition of the adequate hydraulic action, i.e. clean bottom hole condition. But field drilling practices are in many case under the incomplete hydraulic condition. It is quite important to understand quantitatively the effects of hydraulics on the rock bit performance. The effects of hydraulics have been investigated from two standpoints: one is the maximum penetration rate attained under the adequate hydraulic action, other is the behavior of the penetration rate under the condition of the incomplete hydraulics. By drilling experiments by 11/4 in. two-cone microbits, three basic equations have been derived to describe the penetration trate in any hydraulic condition. (1) The equation for a performance line. This was proposed by Bingham (1964-65). This is applicable under the complete hydraulic action. (2) The equation for a branch-off-point penetration rate. When bit weight is increased with hydaulics maintained at the same level, the penetration rate branches off at a specific point on the performance line corresponding to the hydraulics level. Then, the penetration rate at the branch-off point is able to he used as a measure of the hydraulics effect. The relationship between them is affected by the properties of rock. When that relationship is obtained, it could be used to estimate the branch-off-point penetration rate for any level of hydraulics. (3) The equation for a relative penetration rate. The relative penetration rate and the relative bit weight are defined as follows:the relative penetration rate=R/R0R=penetration rate under the incomplete hydraulic conditionR0=penetration rate calculated by the equation for the performance line at the same bit weight and rotary speed, the relative bit weight=(W-Wc)/(Wb-Wc)W=bit weightWb=bit weight at the branch-off pointWc=performance-line intercept. By using these quantities the relationship between the penetration rate and the bit weight is described by a single equation, i.e. the equation for the relative peneeration rate which is not affected by rotary speed, hydraulics and properties of rock. The characteristics of the bit design and wearing, if any, are only factors that affect the form of the equation. A tentative equation for the relative penetration rate has been obtained by rearranging the Thompsom's field data (1953). That is This equation would be applicable for analyzing and estimating the performance of any soft-type three-cone rock bit under the condition of the incomplete hydraulics.