Digital Drilling Research Articles

Research on an evaluation method for the strength of broken coal mass reinforced by cement slurry based on digital drilling test technology

Fault fracture zones, high stress, extremely soft rock, and other complex conditions of underground engineering cause the surrounding rocks to become friable and fragmented after chamber excavation. It is common to observe phenomena such as bolt body slips, fractures, severe support buckling and breaking, resulting in safety issues. The broken rock mass is often reinforced by cement slurry, and the relative strength increase in the surrounding rock is an important index used to evaluate the reinforcement effect. However, it is currently challenging to quantify the strength of surrounding rock after reinforcement by cement slurry. A digital drilling test technique provides an effective method for quantitative evaluation of the strength of a broken coal mass reinforced by cement slurry. The key is to establish a quantitative relation between the drilling parameters and the strength of the rock mass after reinforcement. Therefore, this study used the 1000-km-deep Zhaolou coal mine in China as an engineering background. Based on a multi-function rock drilling test system developed by the authors, digital drilling tests and uniaxial compression tests of broken coal mass reinforced by cement slurry were performed, and the variation law of drilling parameters with uniaxial compressive strength was analyzed. Additionally, a quantitative relational model between the uniaxial compressive strength and drilling parameters was built by means of an energy analysis method. A method to quantitatively evaluate the reinforcement strength of a broken coal mass based on a digital drilling test technique was developed. A study on the impact laws of different water:cement ratios and coal particle sizes with respect to the strength of broken coal masses after reinforcement was also conducted. The study results provide an effective method for the quantitative evaluation of the reinforcement effect of broken surrounding rocks and optimization of the cement slurry parameter.

Method for Measuring Rock Mass Characteristics and Evaluating the Grouting-Reinforced Effect Based on Digital Drilling

Various types of broken rock masses, such as those in fault-fracture zones and fracture zones, which form as a result of disturbance from tunnelling, are often encountered during underground engineering construction. These rock masses have low self-supporting capacity and poor stability, which can easily cause damage to surrounding rock, such as large deformation features, collapse and falling blocks, etc., posing a threat to construction safety. During a field project, reinforcement by grouting is a primary means for addressing the aforementioned problems. The effective measurement of rock mass characteristics (e.g., rock layer interfaces and the broken area of surrounding rock) provides a basis for the reasonable design of a grouting scheme. The quantitative evaluation of the effect of rock mass grouting is essential for optimizing the grouting scheme. In view of this, in this study, a multi-functional rock mass digital drilling test system and a special polycrystalline diamond compact drill bit for digital testing were developed and were applied to conduct digital drilling tests on intact, broken and grouted rock masses. In addition, a digital drilling test (DDT) technique-based method for measuring rock mass characteristics in real time and rapidly evaluating the grouting effect was proposed. The proposed method is capable of identifying rock layer interfaces, determining the broken area and obtaining the equivalent strength of grouted rock masses. This method is advantageous for obtaining quantitative and rapid test results, which can provide a theoretical basis and technical means for optimizing the grouting parameters and designing support schemes for underground engineering construction.

Relationship model for the drilling parameters from a digital drilling rig versus the rock mechanical parameters and its application

Measuring rock mechanical parameters is an essential step for support design in an underground project. To quickly obtain the surrounding rock mechanical parameters at a construction site in real time using a digital drilling rig, a quantitative relationship between the drilling parameters and rock mechanical parameters should be defined. In this paper, based on the fracture characteristics of rock cutting, a relationship model for the drilling parameters of the digital drilling rig versus the rock mechanical parameters (DP-RMP model) is created. Based on the multi-function rock drilling test system developed by the authors, rock drilling tests for different drilling parameters and theoretical results are compared and analysed to prove the validity and accuracy of the DP-RMP model. Additionally, the influence laws of the cohesion and internal friction angle on the rock cutting drilling torque are investigated. Drilling parameters from the digital drilling rig-based rock mechanical parameter inversion method is proposed; the feasibility of this method is verified by rock drilling test results. The study provides a theoretical basis for quickly obtaining the rock mechanical parameters using drilling parameters on site in real time.

Upper bound analytic mechanics model for rock cutting and its application in field testing

The rock cohesion c and internal friction angle φ are essential parameters (combined as the c-φ parameter) used to characterise rock strength. Accurate measurement of these parameters is necessary for surrounding rock stability analysis and supporting scheme design in underground engineering. The currently used indoor test procedure is time-consuming and difficult to quantitatively evaluate the mechanical properties of fragmented rocks because these rocks cannot be effectively cored. Most field test methods can measure rock tensile or compressive strength parameters; however, it is difficult to determine the c-φ parameter. “Digital drilling rig” test technology provides a new way to solve the aforementioned problem. The key to implement this technology is to create a quantitative relation between the drilling parameters and the rock c-φ parameter. In this study, based on the characteristics of the rock cutting failure, an upper bound analytic mechanics model is developed for rock cutting. In this model, the ultimate rock cutting force is derived and the relation between the drilling parameters and the c-φ parameter is obtained. A comparative analysis of indoor tests and theoretical calculations shows that the average difference between the drilling parameters from the digital drilling test versus parameters from the theoretical calculation for the limestone tests is 9.33%; for the sandstone tests, the average difference is 5.85%. This validates the rock cutting mechanical model and the formula for the relation between the drilling parameters and the c-φ parameter. Based on these results, a digital drilling measurement method for the surrounding rock c-φ parameter in the field is proposed. The feasibility and effectiveness of the proposed method is verified via indoor testing. This method is convenient to implement in the field and can effectively measure the c-φ parameter of both intact and relatively fragmented rock mass in the field.

Research on 3D Dredged Soil Visualization Analysis of Qinhuangdao Harbor Project

In order to rapidly, accurately and vividly provide plenty of underwater soil analysis information for design and construction in dredging engineering, this paper took Qinhuangdao harbor project as an example, introducing a three-dimensional underwater soil modeling method and establishing the 3D unified soil solid model of Qinhuangdao harbor. The model has a small amount of data storage, high precision and is easy to operate graphical computing. Based on the model, and with 3D visualization technology, a series of soil visual analysis were conducted, including virtual digital drilling, arbitrary cutting analysis and water depth elevation analysis. Moreover, the model could quickly output scene graph, 2D cross-section and isoline map. Practical engineering applications indicate that 3D dredged soil visualization helps engineers to understand the space distribution of underwater soil. The proposed method can provide a convenient support tool for dredging engineering soil analysis.

Case Study: Drillstring Failure Analysis and New Deep-Well Guidelines Lead to Success

Summary Three drillstring fatigue failures occurred while drilling two deep wells below 16,500 ft true-vertical depth (TVD) in the US midcontinent region. All the failures occurred across 2°/100 ft- to 3°/100 ft-dogleg severity (DLS) intervals from 6,000 to 8,000 ft. The well conditions (i.e., pipe condition and directional plan) were not significantly different from other deep wells in the area, which had not failed. A deep-well drillstring failure study was conducted, which included a review of drillstring-inspection reports, daily drilling reports, digital data, technical literature, and engineering analysis for the two wells. A cumulative fatigue analysis (CFA) modeling technique taking into account specific well conditions [i.e., wellbore geometry, rotary speed, rate of penetration (ROP), hook load, and drillstring configuration] was applied. The model indicated that drillstring failures would occur across shallow doglegs mainly because of high hang-down loads combined with slow ROP. The results of the study led to the development of new deep-well design criteria and implementation of new drilling guidelines. The new guidelines included the use of look-ahead CFA modeling when approaching drillstring endurance limits to minimize drillpipe-fatigue failures. Look-ahead CFA modeling and the new drilling guidelines were used on two subsequent deep wells in the area, leading to successful drilling to total depth (TD) of 18,000 ft TVD without failure. One of the wells had a 1.4°/100-ft DLS (calculated based on 100-ft survey spacing) at 1,500 ft, and drillpipe shuffling was required to prevent drillstring failure in the deep-hole section. The drillstring-fatigue failure prevention guidelines apply to deep wells drilled worldwide. Introduction BP America, Inc. experienced three high-load cyclic fatigue tube failures while drilling in the US midcontinent region's deep Anadarko basin. All of the failures occurred within a four-month period on two wells drilled by different rigs. The three fatigue failures occurred in the highest shallow dogleg interval of the wells, and all three failures were in the inclination-angle dropping section of the well. In Well A, poor mud properties caused the hole to pack off, leading to a heat-related tensile failure of a crossover in the bottomhole assembly (BHA). An unsuccessful fishing job for the remaining BHA led to a sidetrack. The sidetrack around the fish created shallow doglegs and led to the two drillpipe-fatigue failures in Well A. Shallow directional walk problems combined with a small directional target created shallow doglegs in Well B. The well scope was also changed at TD to drill 375 ft deeper. Mud circulation was lost, and the drillstring was rotated without circulation while building mud volume. Well B subsequently experienced a fatigue failure while pulling out of the hole at TD of 16,628 ft. After these failures occurred, a comprehensive study was performed to understand why these two wells experienced drillpipe failures while other area wells with similar conditions did not experience a failure. The study included a review of drillpipe-inspection reports, daily drilling reports, digital drilling recorder data, and engineering analysis.

Instrumented borehole drilling for interface identification in intricate weathered granite ground engineering

The successful application in drilling for HK simple weathered granite foundation has revealed its further use in instrumented drilling system as a ground investigation tool in the detection of other lithology formations, geohazards, underground water, and boundary of orebody. To expand the further use and test the accuracy in identification of formation, an R-20 rotary-hydraulic drill rig was instrumented with a digital drilling process monitoring system (DPM) for drilling in an intricate decomposed granite site. In this test ground, the boreholes revealed that the weathered granite alternately changes between moderate and strong. The qualitative and quantitative analysis of the penetrating parameters, indicates the effective thrust force, rotary speed, flushing pressure, penetrating rate, and displacement of the bit fluctuate at ground interfaces. It shows that the parameters get a good response with the change of rock strength at the interfaces, which can reveal the change of the intricate granite formation. Besides, a variable-slope method has been established, for identification of dominative and subsidiary interfaces in the granite site. The result from a t-test shows that the confidence of the instrumented drilling system in identification of the geotechnical interfaces is up to 99%.

Enhanced NURBS modeling and visualization for large 3D geoengineering applications: An example from the Jinping first-level hydropower engineering project, China

Large engineering projects with complex underlying geologic structures require 3D geological integration and analysis. Presented is an example of a large hydroelectric dam, highlighting the need for 3D visualization and modeling as a requirement for the engineering design and construction process. Due to the complex nature of these projects, geological analysis using 3D modeling is commonly necessary. In this paper we present an integrated 3D geological modeling methodology for the analysis of large amounts of exploration data, and subsequent geological interpretation based on the non-uniform rational B-spline (NURBS) technique, the triangulated irregular network (TIN) algorithm and boundary representation. The procedural details and application of the proposed approach are demonstrated with reference to an actual hydropower engineering project. The new approach offered a good scheme to solve the inconsistencies among storage, accuracy and operational speed of the model. A 3D model was developed and validated using testing data from the engineering project. Visual analysis of the 3D model helps engineers to comprehend the complexity of geological structures, and enables arbitrary cutting, rock-mass quality classification, and digital drilling.

Positioning of screw holes group based on digital camera and digital control drilling

Positioning of screw holes is an important production procedure for steel construction connecting with bolts. In this paper, a new production method is presented, in which the digital camera is used for taking pictures of screw holes and other techniques are advanced. This paper also indicates that the pixels of CCD chip in photogrammetry should be chosen as all geometric units in an image, such as interior elements and all kinds of distortions. The measure can also simplify the camera calibration for determining the size of non-square pixel.

Data Gathering System for Drilling Optimization Work

A digital computer-controlled drilling data processing system has been developed which has the capability of monitoring drilling operations and storing information on magnetic tape. This data processing system is combined with a management information system which provides timely management-oriented reports on a spud-to-spud basis providing cost and time accounting for the entire operation while drilling and while off bottom. Capability includes casualty prevention routines which monitor drilling parameters and provide alarms for prevention of blowouts, twist-offs, and stuck pipe.