Evaluation of Compaction Reaming Process and Assessment of Associated Reduced Drilling Fluid Usage During Horizontal Directional Drilling

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1 North American Society for Trenchless Technology (NASTT) NASTT s 2015 No-Dig Show Denver, Colorado March 15-19, 2015 TA-T2-01 Evaluation of Compaction Reaming Process and Assessment of Associated Reduced Drilling Fluid Usage During Horizontal Directional Drilling Sarkar Sayem, Trenchless Technology Center, Louisiana Tech University, Ruston, LA Chris Bartlett, Trenchless Technology Center, Louisiana Tech University, Ruston, LA Xuanchen Yan, Trenchless Technology Center, Louisiana Tech University, Ruston, LA Steven Aaron, Trenchless Technology Center, Louisiana Tech University, Ruston, LA Erez Allouche, Trenchless Technology Center, Louisiana Tech University, Ruston, LA Floyd Gunsaulis, Charles Machine Works, Perry, OK ABSTRACT The utilization of adequate amount of drilling fluid is widely recognized as a critical factor in the successful completion of a HDD crossing. At the same time, the overall price tag is influenced by the volume of drilling fluid usage. With contractors under pressure to keep per foot cost as low as possible, the practice of constructing a borehole 1.3 to 1.5 times the diameter of the pipe product of 24 in. or less, should be re-examined. The research work reported in this paper aimed at development and testing a new method that can reduce drilling fluid usage during HDD installations by up to 33%. Five (5) full-scale HDD bores were constructed. Two of the bores followed traditional installation procedures while the remaining three bores utilized a newly developed partial compaction reamer. Data collected during the installations included in-situ soil characteristics, borehole geometry, pulling force, borehole pressure, required thrust and torque, changes in the in-situ soil pressure immediately outside of the bore path, and the characteristics of the drilling fluids and cuttings. The analyzed test data is presented in tabular and graphical formats, and discussed in the context of installation time, risk and cost. A demonstration project in the New Orleans area where this new reaming technology is currently been considered as a means to address the requirements of the USACE is also described. 2. INTRODUCTION Drilling fluid plays an important role in calculating drilling fluid drag effect and skin friction coefficient during directional drilling operation [1]. Drilling fluids also contribute to the overall price tag associated with horizontal directional drilling (HDD) operations. With contractors under pressure to keep per foot cost as low as possible, the practice of constructing a borehole 1.5 times the diameter of NPS24 and lower to ensure an annular void for returning of drilling fluids should be re-examined as the disposal of the cutting returns is becoming increasingly more difficult and costly. This research was aimed at full scale testing of a new cutting head/reamer technology that could reduce drilling fluid use by up to 35%. The construction was initiated with pilot drilling of 4.5 in. borehole with a standard drill bit. The drill bit was advanced through the borehole by rotating and pushing forward assisted by drilling fluid pumped out at a rate of 50 gpm with a drilling fluid pressure capacity up to 1,500 psi. through the nozzle located at the drill bit. The relatively high pressure of flow facilitates the transportation of the cuttings out of the borehole and maintained the borehole Paper TA-T

2 pressure. To ensure the proper drilling fluid mix design, drilling fluids in the mixing tank, and the returns were sampled and tested on a regular basis throughout the installation. The diameter of the pilot hole was then enlarged with a larger diameter reamer, depending on the targeted diameter of the borehole. This step was accomplished in two steps in the new method of compaction reaming process. After attaining the target diameter of the borehole, the product pipe was attached to the drill string and pulled back into the borehole at a constant speed sufficient for the removal of the cuttings out of the borehole. A custom-made load cell developed by Baumert and Allouche (2002) and tested at University of Western Ontario was used to record the pull load and borehole pressure at the location of the pull head [2]. Vibrating earth pressure cells were placed to collect the data of horizontal ground movement due to the compaction process. Data was also collected from the gauge of the rig to cross check the data collected by the load cell. 3. METHODOLOGY This paper presents a full-scale field study which was performed on a newly developed cutting head/reamer technology designed to minimize drilling fluid usage during HDD installation in deformable clay soil (CL) above the ground water level. The objective of the study was to determine the volume of drilling fluid usage, pull force and torque during the product pipe pull back operation, pull load at the product s pull head, borehole pressure at the pull head and ground movements at the immediate vicinity of the bore for each bore. To accomplish the above described research plan, the experimental program outlined in Table 1 was executed. Table 1. Test Matrix (Design of Experiments) Test Series Method Used Fluid Medium 1 2 Using Traditional Reamer 1.30 x pipe diameter Using Partial Compaction Reamer 1.08 x pipe diameter Drilling Fluid 300 Drilling Fluid 300 Drilling Fluid 300 Drilling Fluid 300 Drilling Fluid 300 Length of the Bore Number of Test ft. Total Number of Tests 5 The product pipe was 9 in. DR18 FPVC pipe. Test Series 1 was used to establish the baseline values associated with current construction practices. Test Series 2 was performed using a new method or process of partial compaction. Information about the tentative borehole profile is given in Table 2 and the tentative drilling path in Figure 1. Table 2. Tentative Borehole Information Parameters Value Drilled Length (ft.) 300 Target Depth (ft.) 8 Approach Angle (%) 15 Exit Angle (%) 15 Maximum build angle per 10 ft. rod ( ) Paper TA-T

3 Figure 1. Drill path Data collected consisted of the site layout, soil characterization, borehole profiles, drilling mud formulations, durations of the pilot bore and pull back operations, and the pull force and torque recorded at the drill rig. The axial pull force applied to the product pipe and borehole pressure at the location of the pull head were also recorded using a custom-built load cell. Changes in soil horizontal pressure at the immediate vicinity of the pilot bore were recorded using vibrating-wires earth pressure cells. 4. TEST SERIES 1. (INSTALLATION WITH TRADITIONAL REAMING METHOD) The pilot bore was drilled using a standard 4.5 in. wide plain duckbill bit, while both the pre-ream and the pull-back operations were conducted using a 12 in. diameter paddle reamer (Figure 2). Figure 2. Pilot bore drilling (left) and product pull (right) The drilling plan called for the construction of a stable borehole in the soil formation. During the pilot boring the drilling rod was pushed at a rate of 4-5 minutes per 10 ft. of rod, and the pump s output was kept between 4.8 and 6 gpm (~ 60% efficiency), while the viscosity of the drilling fluid was 50. During the back reaming operation, the product pipe was pulled at a rate of 9-10 minutes per 10 ft. rod. The pump s output was gpm (~ 70% efficiency), while the viscosity of the drilling fluid was 40. The installation cover was determined to be 8 ft. to 9 ft. in order to minimize the risk of frac-out during the installation. A mud pit (9-ft deep) was excavated to provide access needed for removal of the returns and borehole tools (e. g., reamers, pig, and load cell). A backhoe and a mini excavator were used during the pull-back operation to maintain the minimum bending radius allowed by the pipe product manufacturer during the installation (Figure 3). Paper TA-T

4 Figure 3. Drilling plan at the site Based on test results, the drilling fluid formulation and the reaming advancement rates were adjusted for maximum compatibility with local soil conditions. The pulling load and torque measured at the rig were recorded for the pilot bore, pre-ream, and pipe product pull-back operations for each drill rod (i.e., the average thrust and torque values per each 10-ft length of borehole construction or product installation). 5. TEST SERIES 2. (INSTALLATION USING PARTIAL COMPACTION REAMING METHOD) In this method, the 4.5 in. diameter of pilot hole was enlarged in two different steps, pre-reaming and partial compaction reaming. An additional step of Pigging was introduced to ensure the borehole is free of spoils prior to compaction reaming and product pull back. In case of Borehole #3 and Borehole #4, pilot drilling of 4.5 in. borehole was followed by an 8 in. pre-reaming operation. The drill bit was replaced with an 8 in. diameter paddle reamer (6 in. in case of Borehole #5), and the reamer was pulled back to the rig, enlarging the borehole, while at the same time removing the cuttings from the borehole and eliminating some of the profile deviations created during drilling of the pilot bore. Following the pre-reaming operation, a pig or ball device (Figure 4) of same or somewhat smaller diameter of paddle reamer was attached to the drill string and pushed toward the entry point at a speed of 1 minute per rod. The objective of this step was to clean the borehole by displacing or purging the remaining cuttings out of the borehole. Required torque and thrust for this stage were found to be very low even though no drilling fluid was used. Figure 4. Pigging with Pig or Ball device After the pigging device reached the entry pit, it was replaced by the partial compaction reamer. This reamer has two radius; major diameter of 9.75 in., minor diameter of 5 in.(figure 6). When the reamer was pushed through the borehole with controlled thrust and torque, the 8 in. borehole was gradually enlarged to 9.75 in diameter with the Paper TA-T

5 advancement of the reamer. A minimal amount of drilling fluid was supplied through the fluid port located at the reamer face for lubrication during this process. For data collection, a load cell was attached to the compaction reamer using a swivel connection. The pipe product attached to an internal pull head, was then connected to the load cell (i.e., the diameter of the pull-head was equal to the OD of the product pipe) (Figure 6). The use of an internal pull-head ensured lower friction with the borehole wall while maximizing the available annular space. The pull-back process was found to be faster as no additional time was needed to allow the cuttings to flow out of the borehole. Figure 5. Partial Compaction Reamer Figure 6. Partial compaction reaming and product pull assembly A lubrication system was introduced to lubricate the product pipe during compaction reaming and product pull back operation (Figure 7). This system consisted of a perforated pipe which was fed via a 200 L barrel filled with drilling fluid. The gravity driven flow of drilling fluid from the barrel through the perforated pipe supplies the required drilling fluid for pipe lubrication. This system was placed at the entry pit of product pipe to ensure that the pipe entering the borehole is lubricated as there was not enough cuttings flow to lubricate the product pipe at the pullback stage. Paper TA-T

6 Figure 7. Product Pipe lubrication system 6. DATA ANALYSIS The pull-back force and mud pressure, were compared to the horizontal distance travelled (Figure 7), which revealed similar trends suggested that mud-pressure form an internal component in the pull-back force as proposed by Baumert, Allouche and Moore (2004) [2]. Figure 8. Pull back force (lbf) and mud pressure during product pull operation (Load cell measurement at pull head) In this research, the HDD method was used to construct boreholes with diameter equal to either 1.33 (traditional method) or 1.08 (partial compaction method) times the pipe outside diameter. From Figure 8 it can be seen that in the traditional method (Bores #1 and #2), the maximum thrust force ranged between 10,000 and 13,000 lbf, whereas the corresponding range in partial compaction method (Bore #4 and Bore #5) was 8,000 to 10,000 lbf (BH #3 is excluded from consideration due to the presence of a horizontal curve in the bore path). Considering the variability associated with deviations in the path of the borehole (and thus friction force between the pipe product and the borehole wall), the results implies that using the partial compaction method does not increase the required pull load during product installation. Paper TA-T

7 Figure 9. Required thrust (lbf) at rig during product pull operation (rig gauge) Similarly Figure 10 shows that the torque force developed during the traditional installation method (BH #1 and BH #2) was 2.5 to 3.2 times higher than that of partial compaction method (BH #3, BH #4, and BH #5), on average. Increase in compaction level (1.75 in. to 3.75 in.) resulted in 23% increase in torque and similar thrust force recorded during the 1.75 in. compaction. Summarizing on thrust force and torque (Figure 8 & Figure 10), it can be conclude that enlarging the hole by compaction (1.08 times) is as efficient as enlarging it by a factor of Moreover 114% increase in compaction level is attainable by increasing 23% torque without any significant increase in thrust force, given that the soil cover is enough to prevent any frac-out and crack along the borehole alignment. Figure 10. Torque (lb-ft.) during the product pull operation (at rig gauge) Utilizing the compaction reamer, enlarging the hole 1.08 times the pipe OD rather than 1.33, the pulling force at the pull head was comparable to that measured using the traditional method (Figure 11). The reason of comparatively less pulling force to the pull-head can be explained by focusing on the inside borehole condition. During the compaction method, though the borehole was smaller than that of the traditional method, it was comparatively cleaner due to cuttings and spoils removal with the borehole pigging operation. Moreover, the compaction force squeezed the borehole wall toward outside which added the extra advantage of preventing further collapsing of materials from the borehole wall into the bore path. This practice also leaves a smaller void around the installed pipe which will reduce the risk of future surface settlement immediate above the bore path. Paper TA-T

8 Figure 11. Thrust (lbf) at the pull-head during product pull (load cell) The added level of cleanness associated with the partial compaction seems to also result in a similar level of mud pressure during the product pipe pull-back installation. Figure 12 shows that the mud pressure during the compaction reaming method (BH #4) was similar to that recorded during BH #1 and BH #2, and didn t cross the critical pressure for frac-out. Increasing the compaction level from 1.75 to 3.75, resulted in increased downhole drilling fluid pressure (from an average downhole drilling fluid pressure of 21 psi to 37 psi), as well as two fracout occurrence. Though the fluid release happened in the case of BH #5, in both cases the maximum mud pressure never crossed that value of traditional method. So the compaction method in our case enabled a frac-out free HDD installation as long as the compaction level is in within a pre-determined level. According to present case, it can be recommended that any compaction level of greater than 1.2 times but less than 1.6 times the initial borehole diameter may yield a frac-out free installation. Figure 12. Mud pressure (psi.) during product pull Earth pressure cells (EPCs) were deployed to observe any change in the horizontal soil pressure due to the partial compaction reaming process. During the first two bore of compaction (1.75 in. compaction level) the readings recorded by the EPCs is shown in Figure 12. No meaningful change in stress level was recorded due to the approach and passing of the partial compaction reamer across the position of the EPCs. Paper TA-T

9 Figure 13. Earth pressure recorded by EPCs at 24 in. and 30 in. from final bore wall The reading recorded by the EPCs during Borehole #5, when the compaction level was 3.75 in., are shown in Figure 14. The EPC located at 23 in. recorded a spike of 1.7 psi (4.2 psi to 5.9 psi) and the EPC at 29 in. from the borehole wall experienced a spike of 0.9 psi (4.2 psi to 5.1 psi) during the passing of the compaction reamer. This level of increase in horizontal earth pressure is considered to be minor and should not adversely affect existing utilities within 30 in. of the newly installed pipe. Figure 14. Earth pressure recorded for 3.75 in. compaction level Figure 15 presents the volume of drilling fluids that were utilized during the pre-ream and pull-back phases for each of the five boreholes. It can be seen that the utilization of the compaction reamer resulted in approximately 32% reduction in the volume of drilling fluid used. The increase in compaction level from 1.75 in. to 3.75 in was expected to further reduce the usage of drilling fluid (total reduction ~40%),) according to the calculation based on Baroid Technology Inc. formula. But the adverse ground condition along the bore path #5, (a buried iron pipe and other artifacts from previous research projects) required an amount of drilling fluid greater than anticipated to clean the bore during the pre-reaming stage. Paper TA-T

10 Figure 15. Comparison of drilling fluid usage (gals) (excluding the pilot bore operation) In terms of productivity, deployment of the partial compaction method somewhat increased the total installation time due to the additional activities (pre-ream and pigging operations) (Figure 16). These activities were found to represent an average increase of minutes per linear foot of borehole length (87 minutes, 116 minutes, and 91 minutes for Bores #3, #4, and #5, respectively), which can be considered acceptable in view of the benefits associated with this installation procedure 7. CONCLUSION Figure 16. Comparison of time (minutes) duration (based on real installation time) An analysis of small non engineered commercial horizontal directional drilling (HDD) installations was presented by Baumert et al.2003, where an important observation made was that a clean borehole was not achieved in the majority of these installations [3]. In partial compaction reaming method, the additional stage of pigging which pushes out the solid cuttings settled at the bottom of the borehole, ensures a clean annular space before compaction and product pull stage. The advancement of the compaction reamer left the borehole with a thin layer of drilling fluid (from drilling fluid used in lubrication of reamer) on the walls of the bore. These two steps will help the contractors to attain clean borehole conditions. From this point of view, the compaction method will allow the contractor to predict the pulling force more accurately which is important for proper rig sizing which in turn saves cost in mobilizing and operation of the machine (Baik et al. 2003) [4]. Paper TA-T

11 This study evaluated the performance of the compaction reamer only for two different compaction levels (1.75 in. and 3.75 in). Based on these two cases, it can be concluded that the thrust and torque, downhole mud pressure, and horizontal stresses near the borehole wall is closely depended on the compaction level and the initial borehole diameter to be enlarged. Future study could be performed, for further understanding of the behavior of this partial compaction reamer, with boreholes of larger diameter, and different compaction levels of 1in., 2 in, and 3 in. 8. REFERENCES [1] Michael E. Baumert, Erez N. Allouche, and Ian D. Moore. (2005), Drilling fluid considerations in design of engineered horizontal directional drilling installations. International Journal of Geomechanics, December 1, 2005, Vol. 5, No.4. [2] Michael E Baumert, Erez N Allouche, Ian D. Moore.(2004), Experimental Investigation of Pull Loads and Borehole Pressures during Horizontal Directional Drilling Installations. Canadian Geotechnical Journal, 2004, 41(4): , /t [3] Baumert, M. E., and Allouche, E. N. (2002). Methods for estimating pipe pullback loads for horizontal directional drilling (HDD) crossings. J. Infrastruct. Syst., 8(1), [4] Baik, H., Dulcy, M. A., and Gokhale, S. (2003), A decision support system for horizontal directional drilling. Tunn, Undergr. Space Technol., 18(1), Paper TA-T