Hard Rock Drilling Problems Explained by Hard Rock Pressure Plots

The first ultradeep hole of the U.S. Continental Scientific Drilling Program (CSDP) is proposed in crystalline rocks of the Southern Appalachian Blue Ridge Mountains. The primary target is a major decollement at a depth of about 10,000 m. Substantial core recovery is needed to meet scientific objectives. Oil industry deep drilling technology entails limited core drilling with little need to drill crystalline rock. Slim-hole diamond core drilling in hard rock has not been carried much beyond 5,000 m. Scientific drilling in exotic environments, such as the deep ocean floor, is leading to the development of down-hole hydraulic motors and hybrid systems, such as a diamond coring bit that is advanced coaxially through an outer roller bit. Elements of an ultradeep core drilling system for hard rock exist within these technical communities but must be brought together in a new system to meet a new challenge. Successful ultradeep scientific drilling probably will depend on sophisticated down-hole motor systems to stabilize and control bit dynamics and the drilling environment.A three-phase drilling plan for the Appalachian hole is described. A sensitivity analysis is applied to the performance parameters reported for the Soviet ultradeep hole on the Kola Peninusla. Bit life, or average meters drilled per bit, is the most important single technical factor in which a significant improvement can be made.Theoretical considerations of the stability of deep vertical holes suggest that there is a critical diameter foe a given rock at a given depth, below which the hole can be inherently stable. Reaming is a viable option if the critical diameter is not exceeded. In theory this favors the Soviet advance open bore hole drilling system in hard rocks. Development of systems to drill within relatively small hole diameters may be the key to ultradeep drilling in hard rock. Geology must playa major role in defining the technology appropriate to each scientific drilling target.KeywordsHard RockCrystalline RockDrill StringCore RecoveryDrilling SystemThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Surge and swab pressures result from pipe movement upward/downward during drill string reciprocation and tripping. surge and swab create costly drilling concerns such well kick, formation breakage, and lost circulation. This study aims to find the optimum pipe tripping speed to avoid surge and swab issues, particularly in lost circulation zones. Also, to determine how drilling factors and well bore geometry affect surge and swab pressures. Mud rheology, mud properties, hole diameters, drill pipe diameter, and bottom hole assembly (BHA) dimensions were also analyzed. Dynamic surge and swab model was employed to simulate two case studies in Rumaila Iraqi oilfield. The findings indicated that the tripping speed is the most effective variable on surge and swab pressures. Annular clearance and BHA design have also a major effect on the surge and swab pressures. For the first case study, it is found that whenever the mud weight is far from the pore pressure and fracture pressure gradients, the 5" drill pipe can be tripped in/out of lost circulation formation (Shuaibba formation) at optimum tripping speed of (80 ft/min) without surge/ swab related problems. The reason is that the generated surge pressures (6110-6300 psi) are below the fracture pressure (7100-7400 psi). The results also showed that tripping 5" drill pipe within a maximum running speed of 80 ft/min in (8.5") open hole section through Tanuma formation till Rumaila formation causes a surge pressures of (4650-5050 psi) which is still below the fracture pressures of formations (4750-5660 psi). the results of the second case study (S-shaped well) revealed that the optimum tripping speed of the drill string in the (12.25") open hole through Dammam and Hartha formations is (90 ft/min). it is also concluded that pulling out of hole (POOH) process must be carried out more carefully than the running process since the mud density is near the pore pressure gradient. The results of this study can be further used to improve the drilling efficiency in Rumaila oil field with decreasing non-productive time (NPT) by employing the appropriate tripping speed and optimal drilling operations.

Hard rock drilling technique with abrasive water jet assistance

In deep oil, gas, and geothermal well construction, percussion drilling is sometimes used to improve rate of penetration (ROP) and promote drilling efficiency when breaking hard abrasive rocks (with a uniaxial compressive strength (UCS) > 25 kpsi). Down-the-hole (DTH) differential pressure hydraulic hammers can be used to convert the hydraulic energy of the drilling mud into the percussion energy necessary for rock destruction. The appeal of using DTH hammers for deep hard rock drilling is that this is a highly mature, low-cost, and proven technology. Lacking, however, is a good model to describe mud hammer operation, allowing mud hammer parameters to be tuned for ROP optimization in hard rock environments. In this study, bond graph models are used to investigate the hydraulic and mechanical dynamics of typical DTH hammer stroking cycles. The Colebrook-White equation is used to derive the Darcy-Weisbach friction factor for pressure loss caused by the turbulent flow between hammer chambers. The interactions between the hammer, the bit, and the formation are represented by three mass-spring mechanical systems with various degrees-of-freedoms (DOFs). Rock breaking is modeled using an anisotropic non-linear spring, which can represent the depth of the penetration of the hammer's indenters into the rock. This spring model also allows for seamless integration with the system model. Dynamic percussion drilling behavior is simulated for various rock stiffness values while varying hammer parameters, such as input hydraulic pressure and piston-bit mass ratio. The simulation results provide estimations of both ROP and system energy transfer efficiency (ETE) expected for given hard rock drilling scenarios. The developed model can be used to optimize mud hammer parameters, which in turn will benefit ROP optimization in hard rock environments encountered while drilling deep oil and gas or geothermal wells.

Atypical and innovative tool, holder and mining head designed for roadheaders used to tunnel and gallery drilling in hard rock

Non-dig underground pipeline laying technology is used widely in municipal construction, railway transportation, communications, water conservancy and transportation of petroleum and natural gas fields. Hard rock non-dig construction is a construction field with high technology and construction difficulty in recent years. This paper analyzed the current domestic and international hard rock directional methods and types by used and pointed out its advantages and disadvantages, and put forward a swing driving mode combined with the eccentric bit and DTH to realize Non-dig directional drilling in hard rock. The directional drilling principle is that in directional drilling the eccentric bit lateral force as a fulcrum deflection drilling through the swing mechanism, in order to avoid the drill pipe in curved segment of the cycle characteristics of destruction. On the other hand normal drilling is to use the swing mechanism and the drill pipe coordination with turn slowly to reduce drill speed and the drill pipe damage. The orientation principle is analyzed to solve oriented technology problems and key technologies in hard rock the Non-dig drilling and provides a new method.

At the Utah FORGE test site, they are drilling wells to try to accomplish something others have failed to in 50 years of trying—inject water into hot rock and produce enough steam to power a commercial electric generator. There are many reasons why it is hard, particularly finding a way to use fracturing to create what amounts to a slow-moving, high-volume waterflood that heats the water as it flows from an injection well to a production well. Multiple well pairs per power plant are likely needed, so another problem is finding a way to speed up the drilling, which at the site requires drilling through a mile of granite at temperatures exceeding 400°F. “This approach will take hundreds and hundreds of wells. The challenge is cost, like in an unconventional well,” said Fred Dupriest, professor of engineering practices at Texas A&M University, while delivering a paper at the recent SPE/IADC International Drilling Conference (SPE 208798). The comparison to shale is apt because he was brought in at Utah FORGE to teach drillers how to use the hardware and methods that speeded drilling in unconventionals to accelerate drilling through hard rock. The high cost of slow drilling in hard rock has inspired futuristic ideas such as using plasma energy to disintegrate hard rock. The technology was the basis of a startup, GA Drilling, which was recently bought by Nabors which hopes to commercialize it for hard rock sections. The challenge faced by Dupriest and his partner on the project, Sam Noynaert, an associate professor of engineering practice at Texas A&M, was to demonstrate that faster drilling methods are possible using available technology. The future of geothermal energy depends on efforts like Utah FORGE’s, which are funded by the US Department of Energy (DOE), to overcome the subsurface barriers that have limited geothermal power to less than 1% of the US electric supply. Growth has been limited by the available resources. There are so few places in the US or the world that combine geothermal heating, water, and naturally conductive fractures that make it possible to drill wells that produce superheated steam. On the other hand, it is not hard to find hot, dry rock. If profitable systems can be built to inject the water into hot formations and produce enough very hot water, geothermal power plants could be located near big, urban power markets.

The development of wear resistant materials for drill-bit inserts are of primary importance for efficient percussive drilling in hard abrasive rock. To speed up the development of enhanced wear resistance materials, the laboratory tests are fundamental to evaluate the material performance before proceeding to the in-field drilling test which is labor-intensive and costly in time and resources.The current work aims to perform a comparative study of the wear resistances of drill-bit inserts intended for rotary-percussive drilling. Three laboratory testing methods were adapted to evaluate the abrasive sliding wear and abrasive impact wear which are the main wear components in rotary-percussive drilling. The standard abrasion value (AV) test and the standard LCPC (Laboratoire Central des Ponts et Chaussées) test which were originally developed to study the rock abrasivity, are adapted to study, respectively, the abrasive sliding wear and abrasive impact wear of drill-bit inserts. The disintegrator abrasive impact wear test was adapted to study the effect of impact velocity on impact abrasive wear. The testing setups were modified to enable testing drill-bit inserts as specimens. The drill-bit insert materials were selected to represent various cemented carbide microstructures including five WC-Co grades which differ by the volume fraction of Co and the grain size of WC, and one diamond enhanced insert. All drill-bit inserts were tested in dry condition against Kuru grey granite which is a homogenous rock and well suited as a reference in connection with hard rock testing. The wear measurements were evaluated with respect to the effects of drill-bit insert material and microstructure.The abrasive sliding wear test and abrasive impact wear tests exhibit similar behavior related to the effects of average grain size of WC and volume fraction of Co on the wear measurements for the investigated WC-Co inserts. In all performed tests, the weight losses of WC-Co inserts increased with the volume fraction of Co and average grain size of WC. The abrasive impact wear tests performed on diamond enhanced insert showed a significant improvement of the impact wear resistance by adding diamond particles. Though the removal of the composite matrix between diamond particles was observed, the diamonds particles were providing an additional protection for the composite matrix which explain the lower mass losses of diamond enhanced insert compared to WC-Co inserts. However, an initial stage of decohesion at the diamond/WC-metallic binder interface were observed indicating possibilities of diamond removal at more higher impact energy.

The United States Department of Energy is involved in a variety of scientific and engineering feasibility studies requiring extensive drilling in hard crystalline rock. In many cases well depths extend from 6000 to 20,000 feet in high-temperature, granitic formations. Examples of such projects are the Hot Dry Rock well system at Fenton Hill, New Mexico and the planned exploratory magma well near Mammoth Lakes, California. In addition to these programs, there is also continuing interest in supporting programs to reduce drilling costs associated with the production of geothermal energy from underground sources such as the Geysers area near San Francisco, California. The overall progression in these efforts is to drill deeper holes in higher temperature, harder formations. In conjunction with this trend is a desire to improve the capability to recover geological information. Spot coring and continuous coring are important elements in this effort. It is the purpose of this report to examine the current methods used to obtain core from deep wells and to suggest projects which will improve existing capabilities. 28 refs., 8 figs., 2 tabs.

Rapid horizontal directional well drilling in hard or fractured formations requires efficient drilling technology. The penetration rate of conventional hard rock drilling technology in horizontal directional well excavations is relatively low, resulting in multiple overgrinding of drill cuttings in bottom boreholes. Conventional drilling techniques with reamer or diamond drill bit face difficulties due to the long construction periods, low penetration rates, and high engineering costs in the directional well drilling of hard rock. To improve the impact energy and penetration rate of directional well drilling in hard formations, a new drilling system with a percussive and rotary drilling technology has been proposed, and a hydro-hammer with a jet actuator has also been theoretically designed on the basis of the impulse hydro-turbine pressure model. In addition, the performance parameters of the hydro-hammer with a jet actuator have been numerically and experimentally analyzed, and the influence of impact stroke and pumped flow rate on the motion velocity and impact energy of the hydro-hammer has been obtained. Moreover, the designed hydro-hammer with a jet actuator has been applied to hard rock drilling in a trenchless drilling program. The motion velocity of the hydro-hammer ranges from 1.2 m/s to 3.19 m/s with diverse flow rates and impact strokes, and the motion frequency ranges from 10 Hz to 22 Hz. Moreover, the maximum impact energy of the hydro-hammer is 407 J, and the pumped flow rate is 2.3 m3/min. Thus, the average penetration rate of the optimized hydro-hammer improves by over 30% compared to conventional directional drilling in hard rock formations.

Coiled tubing (CT) drilling offers more efficient drilling operations compared to normal drilling practises resulting in lower operational costs and drilling time in oil and gas operations. This technology is recommended to be used for mineral exploration drilling in hard rock. This requires drilling micro-boreholes at very high speed with small size cuttings. A large volume of such small size cuttings can influence the rheological properties of the drilling fluids significantly.The aim of this study is to understand the effect of small size inert cuttings on the rheological properties of drilling fluids and its consequences on pressure drop changes in the annulus space. Experimental tests were performed on cuttings collected from a mining site, and the results indicated that the fluid rheology is sensitive to the cuttings size. This conclusion suggests that careful measurement of rheological properties of the mud is necessary when it is designed for drilling hard rocks.

Drilling in crystalline rock to very great depth (10 to 15 km) requires drilling techniques which depart considerably from standard rotary drilling. Weaknesses of rotary drilling in hard rock include: cutting efficiency of rotary rock bits, tendency to deviate from the vertical, tendency to create axial vibration, speed of downhole motors, and increased wear on drill string due to the lack of a filter cake.

Axial-torsional coupled percussive drilling (ATCPD) is a practical technique for creating volumetric breaking patterns and increasing rate of penetration (ROP) of hard rocks. Our paper focus on numerical investigations on ATCPD process. We employed a continuous-discrete coupling method based on cohesive elements to characterize the rock failure subjected to different percussion (axial, torsional and coupled percussion). Based on this model, the penetration-cutting process of the single cutter at different percussion modes was simulated, respectively. The corresponding cracks characteristics, penetration/cutting force and torque were analyzed. Rock scratch experiments were further conducted on granites to validate the model. The results show that the complex cracks propagation zone and the larger tensile cracks around the cutter are developed subjected to coupled percussion, resulting in larger failure elements number and cracks volume. That is, more significant macro damage is thought to form in coupled percussion, thereby increasing the penetration and cutting force of single cutter. It is worth noting that the coupled percussion mode can also generate stable fluctuation torque, which improves the ROP enhancement performance. Our results are expected to provide some guidance for efficient drilling in hard rocks. INTRODUCTION Increasing oil, gas, and heat reserves in deep formations will be critical in addressing the worldwide energy supply (Santos et al., 2000; Moore and Simmons, 2013; Hu et al., 2013). The construction of wells to exploit deeper energy in more challenging environments requires large investments, which are mainly related to the involved drilling operations (Abdo and Haneef, 2013; Diaz et al., 2017). For example, the reliance on drilling costs is especially high in the development of enhanced geothermal system (EGS), primarily because this method of obtaining geothermal energy necessitates the challenge of drilling deep holes in hard crystalline basement rocks, such as granites (Song et al., 2018; Anderson and Rezaie, 2019). These limiting factors pose a major challenge to our traditional drilling technologies (e.g. rotary drilling), whose poor performance in hard rocks, in terms of wearing of the drill bits and low penetration rates (Diaz et al., 2017; Rossi et al., 2020). As a result, the development of drilling techniques to increase the ROP enhancement effect in deep reservoir hard rocks has attracted more and more interest in the engineering field.

The drilling and demolition by low-duration, high-voltage electric pulses is based on the fact that, for very short times, the breakdown inside the solid dielectric occurs faster than the surface flashover benveen the electrodes. It was shown that most solid dielectrics could be broken down in insulating liquids, such as transformer oil, diesel fuel, and even in water. This study includes experimental and theoretical results on the drilling of rocks in insulating liquids, including transformer oil and diesel fuel.

Improving the process of blast-hole drilling in hard rock and permafrost : ONOTSKII, MI RUMIANTSEV, RA SHEINBAUM, VS In Russian. TRANSP. STROITEL. N11, NOV. 1975, P3–6