Drilling jar

The drill string is defined here as a drill pipe with tool joints and drill collars. The drill stem consists of the drill string and other components of the drilling assembly that includes the kelly, subs, stabilizers, reamers as well as shock absorbers, and junk baskets or drilling jars used in certain drilling conditions. The drill stem (1) transmits power by rotary motion from the surface to a rock bit, (2) conveys drilling fluid to the rock bit, (3) produces the weight on bit for efficient rock destruction by the bit, and (4) provides control of borehole direction. 

Downhole drilling tools are the components of the lower part of a drill string used in normal drilling operations such as the drill bits, drill collars, stabilizers, shock absorbers, hole openers, underreamers, drilling jars as well as a variety of drill stem subs. 

Types of Jars. There are two general classes of Jars fishing Jars and drilling Jars. 

Types of Drilling Jars. There are two types commonly used commercial drilling jars, combination of hydraulic (upward) and mechanical (downward) motion, and purely mechanical action. The examples of both types follow. 

Hew -H/ffer Christensen Jar. (See Figure 4-173 [57A].) This is a mechanical drilling jar with firing racks system applied. Its jar force is constant regardless of torque applied. 

Figure 4-172. Christensen s mason drilling jar. (Courtesy Hughes Christensen.)...

Ajar is a device for providing an impact load to the fish when the fish cannot be retrieved by normal string and derrick forces. There are purely mechanical jars and hydraulic Jars (see the section titled Drilling Bits and Downhole Tools for details on drilling Jars). In a fishing operation the Jar is usually placed... 

Drilling jars, stabilizers and, usually, core barrels are also made from AISI 4140 or 4145H steel and sometimes AISI 4340 or 4340H steel is also used. Tbe steel is heat treated to the hardness level of 285 to 341 Bhn. 

Drilling. Common drill rigs available for monitor-well installation include cable tool, air rotary, mud rotary, reverse rotary, and hollow-stem auger. The cable tool rig repeatedly lifts and drops a drill bit, drill stem, drilling jars, and rope socket. The drill bit crushes hard rock or loosens unconsolidated material and mixes the loosened particles with water to form a slurry or sludge. The sludge is removed at intervals by a sand pump or a bailer. 

An extended Bayesian updating approach to support product selection based on performance testing - A drilling jar case... 

Establishing and assessing a set of suitable criteria is considered the main activity of this selection problem. These criteria comprise the minimum equipment requirements relevant for the drilling jar selection, e.g. availability, manufacturer service agreements, documentation of earlier performance and specification of drilling jar sizes and material properties compatible to other assembly equipment planned used in the drilling operations. Based on these criteria the set of alternatives is reduced, and in many cases these criteria are decisive for the decision-making. 

To summarize the decision-making for drilling jar selection as typically performed in the industry today, one or several of the following activities are carried out ... 

Analyse jar performance using available software, e.g. larPro to compare available drilling jars with respect to ontpnt performance and the prob-abihty of exceeding the relevant stick forces. See Fig. 1. 

Perform cost assessments and select the drilling jar that has the optimal cost-efficient ratio. Often analysis software is nsed to compute the costs. 

The following sections in this paper are structured as follows. Section 2 describes the basic ideas and principles of the Bayesian updating approach and explains how this approach can be used for the drilling jar selection case. In Section 3 we present the main features of the extended analysis, emphasising the assessment of the uncertainty factors that extends beyond the probabilistic analysis. In Section 4 we outline how the total uncertainty picture can be presented for the jar case. Section 5 provides some conclusions. 

The overall purpose of the suggested approach is to establish an adequate procedure for determining which of the available products that will perform best in real offshore situations, i.e. which drilling jar that will use least time for freeing stuck-pipe. The main quantity of interest is the stuck-pipe downtime. 

Another imcertainty factor is the number of drilling jar failures. The performance testing is not specifically designed to test the rehabUity of the jar. T3rpicaUy the jar is re-tested if a failure occurs during testing. Therefore there is considerable uncertainty related to the actual number of drilling jar failures. 

The change in the expected downtime 0 by using a data selection criterion based on 6 /2" hydraulic drilling jars in the North Sea area. 

Table 1 presents the qualitative assessment and classification of the four uncertainty factors identified for the drilling jar selection problem. 

Combining the uncertainty and sensitivity assessments we conclude that factor 4 is the only one to have high importance. This may indicate a need for a further look into this factor, i.e. the durability testing of drilling jars and studies on the extent of specific non-jarring activities. 

From a crude criterion of 6 diameter size, we end up with two drilling jars (Jar A and B say) to consider for the selection. 

The chan in the e7q>ected downtime by excluding specific tests from the test data The chan in the e7q>ected downtime by using a data selection criterion based on 6 hydraulic drilling jars in the North Sea area The change in e7q>ected downtime 0 by using data that reflect also non-jarring activities... 

The authors are grateful to an anonymous drilling jar manufacturer who has accepted the use of the performance testing data. 

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