New drill pipe reduces body wear during shale drilling
Existing shale well designs and drilling operations, especially in the Bakken play, have led to an unprecedented increase in wear of the drill pipe body. The center of the pipe body has been observed to shine while drilling horizontal wells. This wear suggests that there exists continuous, downhole contact between the pipe body and the abrasive formation, as well as the casing. As a result, the drill pipe body wears out faster than the tool joints, reducing the life of the drill pipe, as well as the drilling efficiency, and increasing the overall cost of operations. Hence, to analyze the existing pipe body contact and to develop a comprehensive understanding of the downhole conditions, a joint effort was undertaken to model the underlying drilling scenario in a conventional shale well design, and to provide a possible solution to reduce wear.
DRILL PIPE BODY WEAR ANALYSIS
The drilling activity of a typical horizontal well in the Bakken has been analyzed using field drilling parameters to perform a step-by-step investigation of drill pipe body wear. The build and lateral sections of the well are expected to have most of the wellbore and pipe body contact. Therefore, all the joints of the drill pipe in these locations of potential wear have been examined, using advanced drillstring modeling techniques. The drilling program has been monitored closely from the kick-off point at about 9,500 ft for the well under consideration, as it builds the 8¾-in. hole section and completes the lateral portion until the target casing depth of 11,900 ft is reached, followed by a 6-in. horizontal section to approximately 20,000 ft. This model helps in calculating the clearance of the center of the pipe body from the wellbore for each joint of pipe, and further estimates the tube side force, if there is any contact. The underlying side force acting on the pipe body would be directly proportional to the downhole pipe body wear for the given drilling parameters. A method to reduce the side force and also decrease the number of contact points, will help to mitigate the wear. Figure 1 shows an example of one of the modeling steps using DecisionSpace well engineering software.
NEW DRILL PIPE, TOOL JOINT DESIGN
The increase in downhole pipe body wear has led to the development of a new and proprietary 4¼-in. drill pipe with 4⅞-in. × 5¼-in. dual-diameter tool joints. The performance of this new drill pipe has been compared with conventional 4-in. and 4½-in. drill pipes that are typically used to drill the 8¾-in. hole section, using the above-mentioned modeling approach. A comprehensive analysis of the progress of the drilling activity from the kick-off point of 9,500 ft, to the drilling of the target casing depth of 11,900 ft, suggests a significant reduction in the side forces experienced by the pipe body, due to wellbore contact.
Analyzing the portion of the drillstring above the kick-off point suggests that there is no contact nor side force at the center of the pipe body for any size of drill pipe considered for analysis. However, as activity progresses to drill the build section, almost all the joints (98%) of the 4-in. drill pipe experience downhole contact between the center of the pipe body and the wellbore, between the depths of 9,400 ft and 11,000 ft. For the new 4¼-in. drill pipe, the number of joints in this section with pipe body contact reduces to about 90%; while for the 4½-in. drill pipe, only 70% of the joints experience wellbore and pipe body contact. Further analyzing the drilling of the lateral section suggests that about 46% of the currently used 4-in. drill pipes would experience pipe body and wellbore contact, while this percentage decreases to about 20% of the joints for the new 4¼-in. drill pipes and about 18% for the 4½-in. pipes.
This comprehensive analysis for all joints of the drill pipe clearly suggests a reduction in the number of drill pipes that would experience pipe body and wellbore contact, if the drilling program uses the new 4¼-in. pipe instead of the commonly used 4-in. pipe to drill the 8¾-in. hole section. In addition, a large decrease in the side force acting on the pipe body has also been estimated for the 4¼-in. pipe, when compared with conventional 4-in. pipe. As the drilling activity progresses, the underlying side force, due to wellbore contact with the pipe body, suggests an average reduction of about 20% to 30%, or roughly 100 lb, in the tube side force by using the new 4¼-in. drill pipe.
In some of the pipe joints along the drillstring, a reduction in side force of more than 50% also was observed, which would have a significant influence on mitigating downhole pipe body wear. Figure 2 presents the percentage reduction in side force by using 4¼-in. pipe over 4-in. pipe for one of the drilling steps, when the drill bit has reached the target casing depth. These trends are expected to continue, as the 6-in. section is drilled. This modeling approach has been developed with the objective of improving the performance of the pipe tubes, reducing the cost of operations, and enhancing the overall drilling program.
The prime challenge in existing shale drilling operations is to drill the entire planned horizontal well using the same-sized drill pipe to improve logistics and reduce costs. The operators find it difficult to use conventional 4-in. drill pipe to drill the 8¾-in. hole section, due to the high pump pressure, high rate of drill pipe body wear, and reduction in the operating life of the tube. The 4½-in. drill pipe often cannot be used to further drill the 6-in. lateral section after the casing depth, as a result of high ECDs and low fishing clearances.
Based on this detailed analysis, the new 4¼-in. drill pipe seems to provide a good fit for operator’s purposes by helping to reduce the wear on the pipe body while drilling the intermediate 8¾-in. hole section, as well as providing adequate annular clearance between the pipe and the wellbore to keep the ECDs in check. Successful implementation of the 4¼-in pipe in shale drilling programs and field operations will enable us to drill the entire horizontal well with the same-sized pipe, and provide solutions to some of the logistical and financial constraints in ongoing operations.
An advanced torque and drag, as well as hydraulics analysis using DecisionSpace Well Engineering, also could be performed in combination with analyzing the pipe body wear, due to wellbore contact, to improve the existing drillstring designs for shale drilling programs. Implementation of this modeling approach would help operators to select the most appropriate combination of 4-in. drill pipes and new 4¼-in. drill pipes, to be used in locations with high pipe body wear along the drillstring, for drilling the various planned stages of the well. This advanced drillstring analysis would help to substantially reduce drill pipe tube failures observed in field operations, as well as significantly enhance the overall performance of shale drilling programs.
This article is based on SPE paper 171005, presented at the 2014 SPE Eastern Regional Meeting in Charleston, W. Va., Oct. 21-23, 2014.
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